1 GCC(1) GNU GCC(1) 2 NAME 3 gcc - GNU project C and C++ compiler 4 SYNOPSIS 5 gcc [-c|-S|-E] [-std=standard] 6 [-g] [-pg] [-Olevel] 7 [-Wwarn...] [-Wpedantic] 8 [-Idir...] [-Ldir...] 9 [-Dmacro[=defn]...] [-Umacro] 10 [-foption...] [-mmachine-option...] 11 [-o outfile] [@file] infile... 12 Only the most useful options are listed here; see below for the remainder. g++ accepts mostly the same options as gcc. 13 DESCRIPTION 14 When you invoke GCC, it normally does preprocessing, compilation, assembly and linking. The "overall options" allow you to stop this process at an intermediate stage. For example, the -c 15 option says not to run the linker. Then the output consists of object files output by the assembler. 16 Other options are passed on to one stage of processing. Some options control the preprocessor and others the compiler itself. Yet other options control the assembler and linker; most of these 17 are not documented here, since you rarely need to use any of them. 18 Most of the command-line options that you can use with GCC are useful for C programs; when an option is only useful with another language (usually C++), the explanation says so explicitly. If 19 the description for a particular option does not mention a source language, you can use that option with all supported languages. 20 The gcc program accepts options and file names as operands. Many options have multi-letter names; therefore multiple single-letter options may not be grouped: -dv is very different from -d -v. 21 You can mix options and other arguments. For the most part, the order you use doesn't matter. Order does matter when you use several options of the same kind; for example, if you specify -L 22 more than once, the directories are searched in the order specified. Also, the placement of the -l option is significant. 23 Many options have long names starting with -f or with -W---for example, -fmove-loop-invariants, -Wformat and so on. Most of these have both positive and negative forms; the negative form of 24 -ffoo is -fno-foo. This manual documents only one of these two forms, whichever one is not the default. 25 OPTIONS 26 Option Summary 27 Here is a summary of all the options, grouped by type. Explanations are in the following sections. 28 Overall Options 29 -c -S -E -o file -no-canonical-prefixes -pipe -pass-exit-codes -x language -v -### --help[=class[,...]] --target-help --version -wrapper @file -fplugin=file -fplugin-arg-name=arg 30 -fdump-ada-spec[-slim] -fada-spec-parent=unit -fdump-go-spec=file 31 C Language Options 32 -ansi -std=standard -fgnu89-inline -aux-info filename -fallow-parameterless-variadic-functions -fno-asm -fno-builtin -fno-builtin-function -fhosted -ffreestanding -fopenacc -fopenmp 33 -fopenmp-simd -fms-extensions -fplan9-extensions -trigraphs -traditional -traditional-cpp -fallow-single-precision -fcond-mismatch -flax-vector-conversions -fsigned-bitfields -fsigned-char 34 -funsigned-bitfields -funsigned-char 35 C++ Language Options 36 -fabi-version=n -fno-access-control -fcheck-new -fconstexpr-depth=n -ffriend-injection -fno-elide-constructors -fno-enforce-eh-specs -ffor-scope -fno-for-scope -fno-gnu-keywords 37 -fno-implicit-templates -fno-implicit-inline-templates -fno-implement-inlines -fms-extensions -fno-nonansi-builtins -fnothrow-opt -fno-operator-names -fno-optional-diags -fpermissive 38 -fno-pretty-templates -frepo -fno-rtti -fsized-deallocation -fstats -ftemplate-backtrace-limit=n -ftemplate-depth=n -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ 39 -fvisibility-inlines-hidden -fvtable-verify=[std|preinit|none] -fvtv-counts -fvtv-debug -fvisibility-ms-compat -fext-numeric-literals -Wabi=n -Wabi-tag -Wconversion-null 40 -Wctor-dtor-privacy -Wdelete-non-virtual-dtor -Wliteral-suffix -Wnarrowing -Wnoexcept -Wnon-virtual-dtor -Wreorder -Weffc++ -Wstrict-null-sentinel -Wno-non-template-friend 41 -Wold-style-cast -Woverloaded-virtual -Wno-pmf-conversions -Wsign-promo 42 Objective-C and Objective-C++ Language Options 43 -fconstant-string-class=class-name -fgnu-runtime -fnext-runtime -fno-nil-receivers -fobjc-abi-version=n -fobjc-call-cxx-cdtors -fobjc-direct-dispatch -fobjc-exceptions -fobjc-gc 44 -fobjc-nilcheck -fobjc-std=objc1 -fno-local-ivars -fivar-visibility=[public|protected|private|package] -freplace-objc-classes -fzero-link -gen-decls -Wassign-intercept -Wno-protocol 45 -Wselector -Wstrict-selector-match -Wundeclared-selector 46 Language Independent Options 47 -fmessage-length=n -fdiagnostics-show-location=[once|every-line] -fdiagnostics-color=[auto|never|always] -fno-diagnostics-show-option -fno-diagnostics-show-caret 48 Warning Options 49 -fsyntax-only -fmax-errors=n -Wpedantic -pedantic-errors -w -Wextra -Wall -Waddress -Waggregate-return -Waggressive-loop-optimizations -Warray-bounds -Warray-bounds=n -Wbool-compare 50 -Wno-attributes -Wno-builtin-macro-redefined -Wc90-c99-compat -Wc99-c11-compat -Wc++-compat -Wc++11-compat -Wc++14-compat -Wcast-align -Wcast-qual -Wchar-subscripts -Wclobbered -Wcomment 51 -Wconditionally-supported -Wconversion -Wcoverage-mismatch -Wdate-time -Wdelete-incomplete -Wno-cpp -Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init -Wdisabled-optimization 52 -Wno-discarded-qualifiers -Wno-discarded-array-qualifiers -Wno-div-by-zero -Wdouble-promotion -Wempty-body -Wenum-compare -Wno-endif-labels -Werror -Werror=* -Wfatal-errors -Wfloat-equal 53 -Wformat -Wformat=2 -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral -Wformat-security -Wformat-signedness -Wformat-y2k -Wframe-larger-than=len -Wno-free-nonheap-object 54 -Wjump-misses-init -Wignored-qualifiers -Wincompatible-pointer-types -Wimplicit -Wimplicit-function-declaration -Wimplicit-int -Winit-self -Winline -Wno-int-conversion 55 -Wno-int-to-pointer-cast -Wno-invalid-offsetof -Winvalid-pch -Wlarger-than=len -Wunsafe-loop-optimizations -Wlogical-op -Wlogical-not-parentheses -Wlong-long -Wmain -Wmaybe-uninitialized 56 -Wmemset-transposed-args -Wmissing-braces -Wmissing-field-initializers -Wmissing-include-dirs -Wno-multichar -Wnonnull -Wnormalized=[none|id|nfc|nfkc] 57 -Wodr -Wno-overflow -Wopenmp-simd -Woverlength-strings -Wpacked -Wpacked-bitfield-compat -Wpadded -Wparentheses -Wpedantic-ms-format -Wno-pedantic-ms-format -Wpointer-arith 58 -Wno-pointer-to-int-cast -Wredundant-decls -Wno-return-local-addr -Wreturn-type -Wsequence-point -Wshadow -Wno-shadow-ivar -Wshift-count-negative -Wshift-count-overflow -Wsign-compare 59 -Wsign-conversion -Wfloat-conversion -Wsizeof-pointer-memaccess -Wsizeof-array-argument -Wstack-protector -Wstack-usage=len -Wstrict-aliasing -Wstrict-aliasing=n -Wstrict-overflow 60 -Wstrict-overflow=n -Wsuggest-attribute=[pure|const|noreturn|format] -Wsuggest-final-types -Wsuggest-final-methods -Wsuggest-override -Wmissing-format-attribute -Wswitch -Wswitch-default 61 -Wswitch-enum -Wswitch-bool -Wsync-nand -Wsystem-headers -Wtrampolines -Wtrigraphs -Wtype-limits -Wundef -Wuninitialized -Wunknown-pragmas -Wno-pragmas -Wunsuffixed-float-constants 62 -Wunused -Wunused-function -Wunused-label -Wunused-local-typedefs -Wunused-parameter -Wno-unused-result -Wunused-value -Wunused-variable -Wunused-but-set-parameter 63 -Wunused-but-set-variable -Wuseless-cast -Wvariadic-macros -Wvector-operation-performance -Wvla -Wvolatile-register-var -Wwrite-strings -Wzero-as-null-pointer-constant 64 C and Objective-C-only Warning Options 65 -Wbad-function-cast -Wmissing-declarations -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs -Wold-style-declaration -Wold-style-definition -Wstrict-prototypes 66 -Wtraditional -Wtraditional-conversion -Wdeclaration-after-statement -Wpointer-sign 67 Debugging Options 68 -dletters -dumpspecs -dumpmachine -dumpversion -fsanitize=style -fsanitize-recover -fsanitize-recover=style -fasan-shadow-offset=number -fsanitize-undefined-trap-on-error 69 -fcheck-pointer-bounds -fchkp-check-incomplete-type -fchkp-first-field-has-own-bounds -fchkp-narrow-bounds -fchkp-narrow-to-innermost-array -fchkp-optimize -fchkp-use-fast-string-functions 70 -fchkp-use-nochk-string-functions -fchkp-use-static-bounds -fchkp-use-static-const-bounds -fchkp-treat-zero-dynamic-size-as-infinite -fchkp-check-read -fchkp-check-read -fchkp-check-write 71 -fchkp-store-bounds -fchkp-instrument-calls -fchkp-instrument-marked-only -fchkp-use-wrappers -fdbg-cnt-list -fdbg-cnt=counter-value-list -fdisable-ipa-pass_name -fdisable-rtl-pass_name 72 -fdisable-rtl-pass-name=range-list -fdisable-tree-pass_name -fdisable-tree-pass-name=range-list -fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links -fdump-translation-unit[-n] 73 -fdump-class-hierarchy[-n] -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline -fdump-passes -fdump-statistics -fdump-tree-all -fdump-tree-original[-n] -fdump-tree-optimized[-n] 74 -fdump-tree-cfg -fdump-tree-alias -fdump-tree-ch -fdump-tree-ssa[-n] -fdump-tree-pre[-n] -fdump-tree-ccp[-n] -fdump-tree-dce[-n] -fdump-tree-gimple[-raw] -fdump-tree-dom[-n] 75 -fdump-tree-dse[-n] -fdump-tree-phiprop[-n] -fdump-tree-phiopt[-n] -fdump-tree-forwprop[-n] -fdump-tree-copyrename[-n] -fdump-tree-nrv -fdump-tree-vect -fdump-tree-sink -fdump-tree-sra[-n] 76 -fdump-tree-forwprop[-n] -fdump-tree-fre[-n] -fdump-tree-vtable-verify -fdump-tree-vrp[-n] -fdump-tree-storeccp[-n] -fdump-final-insns=file -fcompare-debug[=opts] -fcompare-debug-second 77 -feliminate-dwarf2-dups -fno-eliminate-unused-debug-types -feliminate-unused-debug-symbols -femit-class-debug-always -fenable-kind-pass -fenable-kind-pass=range-list -fdebug-types-section 78 -fmem-report-wpa -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs -fopt-info -fopt-info-options[=file] -frandom-seed=number -fsched-verbose=n -fsel-sched-verbose 79 -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose -fstack-usage -ftest-coverage -ftime-report -fvar-tracking -fvar-tracking-assignments -fvar-tracking-assignments-toggle -g -glevel 80 -gtoggle -gcoff -gdwarf-version -ggdb -grecord-gcc-switches -gno-record-gcc-switches -gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf -gvms -gxcoff -gxcoff+ -gz[=type] 81 -fno-merge-debug-strings -fno-dwarf2-cfi-asm -fdebug-prefix-map=old=new -femit-struct-debug-baseonly -femit-struct-debug-reduced -femit-struct-debug-detailed[=spec-list] -p -pg 82 -print-file-name=library -print-libgcc-file-name -print-multi-directory -print-multi-lib -print-multi-os-directory -print-prog-name=program -print-search-dirs -Q -print-sysroot 83 -print-sysroot-headers-suffix -save-temps -save-temps=cwd -save-temps=obj -time[=file] 84 Optimization Options 85 -faggressive-loop-optimizations -falign-functions[=n] -falign-jumps[=n] -falign-labels[=n] -falign-loops[=n] -fassociative-math -fauto-profile -fauto-profile[=path] -fauto-inc-dec 86 -fbranch-probabilities -fbranch-target-load-optimize -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves -fcheck-data-deps -fcombine-stack-adjustments -fconserve-stack 87 -fcompare-elim -fcprop-registers -fcrossjumping -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range -fdata-sections -fdce -fdelayed-branch -fdelete-null-pointer-checks 88 -fdevirtualize -fdevirtualize-speculatively -fdevirtualize-at-ltrans -fdse -fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects -ffast-math -ffinite-math-only -ffloat-store 89 -fexcess-precision=style -fforward-propagate -ffp-contract=style -ffunction-sections -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity -fgcse-sm -fhoist-adjacent-loads 90 -fif-conversion -fif-conversion2 -findirect-inlining -finline-functions -finline-functions-called-once -finline-limit=n -finline-small-functions -fipa-cp -fipa-cp-clone -fipa-cp-alignment 91 -fipa-pta -fipa-profile -fipa-pure-const -fipa-reference -fipa-icf -fira-algorithm=algorithm -fira-region=region -fira-hoist-pressure -fira-loop-pressure -fno-ira-share-save-slots 92 -fno-ira-share-spill-slots -fira-verbose=n -fisolate-erroneous-paths-dereference -fisolate-erroneous-paths-attribute -fivopts -fkeep-inline-functions -fkeep-static-consts 93 -flive-range-shrinkage -floop-block -floop-interchange -floop-strip-mine -floop-unroll-and-jam -floop-nest-optimize -floop-parallelize-all -flra-remat -flto -flto-compression-level 94 -flto-partition=alg -flto-report -flto-report-wpa -fmerge-all-constants -fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves -fmove-loop-invariants -fno-branch-count-reg 95 -fno-defer-pop -fno-function-cse -fno-guess-branch-probability -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 -fno-sched-interblock -fno-sched-spec -fno-signed-zeros 96 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss -fomit-frame-pointer -foptimize-sibling-calls -fpartial-inlining -fpeel-loops -fpredictive-commoning 97 -fprefetch-loop-arrays -fprofile-report -fprofile-correction -fprofile-dir=path -fprofile-generate -fprofile-generate=path -fprofile-use -fprofile-use=path -fprofile-values 98 -fprofile-reorder-functions -freciprocal-math -free -frename-registers -freorder-blocks -freorder-blocks-and-partition -freorder-functions -frerun-cse-after-loop 99 -freschedule-modulo-scheduled-loops -frounding-math -fsched2-use-superblocks -fsched-pressure -fsched-spec-load -fsched-spec-load-dangerous -fsched-stalled-insns-dep[=n] 100 -fsched-stalled-insns[=n] -fsched-group-heuristic -fsched-critical-path-heuristic -fsched-spec-insn-heuristic -fsched-rank-heuristic -fsched-last-insn-heuristic -fsched-dep-count-heuristic 101 -fschedule-fusion -fschedule-insns -fschedule-insns2 -fsection-anchors -fselective-scheduling -fselective-scheduling2 -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops 102 -fsemantic-interposition -fshrink-wrap -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller -fsplit-wide-types -fssa-phiopt -fstack-protector -fstack-protector-all 103 -fstack-protector-strong -fstack-protector-explicit -fstdarg-opt -fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer -ftree-bit-ccp -ftree-builtin-call-dce -ftree-ccp -ftree-ch 104 -ftree-coalesce-inline-vars -ftree-coalesce-vars -ftree-copy-prop -ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre -ftree-loop-if-convert 105 -ftree-loop-if-convert-stores -ftree-loop-im -ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize 106 -ftree-loop-vectorize -ftree-parallelize-loops=n -ftree-pre -ftree-partial-pre -ftree-pta -ftree-reassoc -ftree-sink -ftree-slsr -ftree-sra -ftree-switch-conversion -ftree-tail-merge 107 -ftree-ter -ftree-vectorize -ftree-vrp -funit-at-a-time -funroll-all-loops -funroll-loops -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops -fipa-ra 108 -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb -fwhole-program -fwpa -fuse-linker-plugin --param name=value -O -O0 -O1 -O2 -O3 -Os -Ofast -Og 109 Preprocessor Options 110 -Aquestion=answer -A-question[=answer] -C -dD -dI -dM -dN -Dmacro[=defn] -E -H -idirafter dir -include file -imacros file -iprefix file -iwithprefix dir -iwithprefixbefore dir 111 -isystem dir -imultilib dir -isysroot dir -M -MM -MF -MG -MP -MQ -MT -nostdinc -P -fdebug-cpp -ftrack-macro-expansion -fworking-directory -remap -trigraphs -undef -Umacro 112 -Wp,option -Xpreprocessor option -no-integrated-cpp 113 Assembler Option 114 -Wa,option -Xassembler option 115 Linker Options 116 object-file-name -fuse-ld=linker -llibrary -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic -s -static -static-libgcc -static-libstdc++ -static-libasan -static-libtsan 117 -static-liblsan -static-libubsan -static-libmpx -static-libmpxwrappers -shared -shared-libgcc -symbolic -T script -Wl,option -Xlinker option -u symbol -z keyword 118 Directory Options 119 -Bprefix -Idir -iplugindir=dir -iquotedir -Ldir -specs=file -I- --sysroot=dir --no-sysroot-suffix 120 Machine Dependent Options 121 AArch64 Options -mabi=name -mbig-endian -mlittle-endian -mgeneral-regs-only -mcmodel=tiny -mcmodel=small -mcmodel=large -mstrict-align -momit-leaf-frame-pointer 122 -mno-omit-leaf-frame-pointer -mtls-dialect=desc -mtls-dialect=traditional -mfix-cortex-a53-835769 -mno-fix-cortex-a53-835769 -mfix-cortex-a53-843419 -mno-fix-cortex-a53-843419 -march=name 123 -mcpu=name -mtune=name 124 Adapteva Epiphany Options -mhalf-reg-file -mprefer-short-insn-regs -mbranch-cost=num -mcmove -mnops=num -msoft-cmpsf -msplit-lohi -mpost-inc -mpost-modify -mstack-offset=num -mround-nearest 125 -mlong-calls -mshort-calls -msmall16 -mfp-mode=mode -mvect-double -max-vect-align=num -msplit-vecmove-early -m1reg-reg 126 ARC Options -mbarrel-shifter -mcpu=cpu -mA6 -mARC600 -mA7 -mARC700 -mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr -mea -mno-mpy -mmul32x16 -mmul64 -mnorm -mspfp -mspfp-compact -mspfp-fast 127 -msimd -msoft-float -mswap -mcrc -mdsp-packa -mdvbf -mlock -mmac-d16 -mmac-24 -mrtsc -mswape -mtelephony -mxy -misize -mannotate-align -marclinux -marclinux_prof -mepilogue-cfi -mlong-calls 128 -mmedium-calls -msdata -mucb-mcount -mvolatile-cache -malign-call -mauto-modify-reg -mbbit-peephole -mno-brcc -mcase-vector-pcrel -mcompact-casesi -mno-cond-exec -mearly-cbranchsi 129 -mexpand-adddi -mindexed-loads -mlra -mlra-priority-none -mlra-priority-compact mlra-priority-noncompact -mno-millicode -mmixed-code -mq-class -mRcq -mRcw -msize-level=level -mtune=cpu 130 -mmultcost=num -munalign-prob-threshold=probability 131 ARM Options -mapcs-frame -mno-apcs-frame -mabi=name -mapcs-stack-check -mno-apcs-stack-check -mapcs-float -mno-apcs-float -mapcs-reentrant -mno-apcs-reentrant -msched-prolog 132 -mno-sched-prolog -mlittle-endian -mbig-endian -mfloat-abi=name -mfp16-format=name -mthumb-interwork -mno-thumb-interwork -mcpu=name -march=name -mfpu=name -mtune=name -mprint-tune-info 133 -mstructure-size-boundary=n -mabort-on-noreturn -mlong-calls -mno-long-calls -msingle-pic-base -mno-single-pic-base -mpic-register=reg -mnop-fun-dllimport -mpoke-function-name -mthumb 134 -marm -mtpcs-frame -mtpcs-leaf-frame -mcaller-super-interworking -mcallee-super-interworking -mtp=name -mtls-dialect=dialect -mword-relocations -mfix-cortex-m3-ldrd -munaligned-access 135 -mneon-for-64bits -mslow-flash-data -masm-syntax-unified -mrestrict-it 136 AVR Options -mmcu=mcu -maccumulate-args -mbranch-cost=cost -mcall-prologues -mint8 -mn_flash=size -mno-interrupts -mrelax -mrmw -mstrict-X -mtiny-stack -nodevicelib -Waddr-space-convert 137 Blackfin Options -mcpu=cpu[-sirevision] -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly -mlow-64k 138 -mno-low64k -mstack-check-l1 -mid-shared-library -mno-id-shared-library -mshared-library-id=n -mleaf-id-shared-library -mno-leaf-id-shared-library -msep-data -mno-sep-data -mlong-calls 139 -mno-long-calls -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram -micplb 140 C6X Options -mbig-endian -mlittle-endian -march=cpu -msim -msdata=sdata-type 141 CRIS Options -mcpu=cpu -march=cpu -mtune=cpu -mmax-stack-frame=n -melinux-stacksize=n -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects -mstack-align -mdata-align 142 -mconst-align -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt -melf -maout -melinux -mlinux -sim -sim2 -mmul-bug-workaround -mno-mul-bug-workaround 143 CR16 Options -mmac -mcr16cplus -mcr16c -msim -mint32 -mbit-ops -mdata-model=model 144 Darwin Options -all_load -allowable_client -arch -arch_errors_fatal -arch_only -bind_at_load -bundle -bundle_loader -client_name -compatibility_version -current_version -dead_strip 145 -dependency-file -dylib_file -dylinker_install_name -dynamic -dynamiclib -exported_symbols_list -filelist -flat_namespace -force_cpusubtype_ALL -force_flat_namespace 146 -headerpad_max_install_names -iframework -image_base -init -install_name -keep_private_externs -multi_module -multiply_defined -multiply_defined_unused -noall_load 147 -no_dead_strip_inits_and_terms -nofixprebinding -nomultidefs -noprebind -noseglinkedit -pagezero_size -prebind -prebind_all_twolevel_modules -private_bundle -read_only_relocs 148 -sectalign -sectobjectsymbols -whyload -seg1addr -sectcreate -sectobjectsymbols -sectorder -segaddr -segs_read_only_addr -segs_read_write_addr -seg_addr_table -seg_addr_table_filename 149 -seglinkedit -segprot -segs_read_only_addr -segs_read_write_addr -single_module -static -sub_library -sub_umbrella -twolevel_namespace -umbrella -undefined -unexported_symbols_list 150 -weak_reference_mismatches -whatsloaded -F -gused -gfull -mmacosx-version-min=version -mkernel -mone-byte-bool 151 DEC Alpha Options -mno-fp-regs -msoft-float -mieee -mieee-with-inexact -mieee-conformant -mfp-trap-mode=mode -mfp-rounding-mode=mode -mtrap-precision=mode -mbuild-constants -mcpu=cpu- 152 type -mtune=cpu-type -mbwx -mmax -mfix -mcix -mfloat-vax -mfloat-ieee -mexplicit-relocs -msmall-data -mlarge-data -msmall-text -mlarge-text -mmemory-latency=time 153 FR30 Options -msmall-model -mno-lsim 154 FRV Options -mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 -mhard-float -msoft-float -malloc-cc -mfixed-cc -mdword -mno-dword -mdouble -mno-double -mmedia -mno-media -mmuladd -mno-muladd 155 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic -mlinked-fp -mlong-calls -malign-labels -mlibrary-pic -macc-4 -macc-8 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move 156 -moptimize-membar -mno-optimize-membar -mscc -mno-scc -mcond-exec -mno-cond-exec -mvliw-branch -mno-vliw-branch -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec 157 -mno-nested-cond-exec -mtomcat-stats -mTLS -mtls -mcpu=cpu 158 GNU/Linux Options -mglibc -muclibc -mbionic -mandroid -tno-android-cc -tno-android-ld 159 H8/300 Options -mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300 160 HPPA Options -march=architecture-type -mdisable-fpregs -mdisable-indexing -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld -mfixed-range=register-range -mjump-in-delay -mlinker-opt 161 -mlong-calls -mlong-load-store -mno-disable-fpregs -mno-disable-indexing -mno-fast-indirect-calls -mno-gas -mno-jump-in-delay -mno-long-load-store -mno-portable-runtime -mno-soft-float 162 -mno-space-regs -msoft-float -mpa-risc-1-0 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime -mschedule=cpu-type -mspace-regs -msio -mwsio -munix=unix-std -nolibdld -static -threads 163 IA-64 Options -mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic -mvolatile-asm-stop -mregister-names -msdata -mno-sdata -mconstant-gp -mauto-pic -mfused-madd 164 -minline-float-divide-min-latency -minline-float-divide-max-throughput -mno-inline-float-divide -minline-int-divide-min-latency -minline-int-divide-max-throughput -mno-inline-int-divide 165 -minline-sqrt-min-latency -minline-sqrt-max-throughput -mno-inline-sqrt -mdwarf2-asm -mearly-stop-bits -mfixed-range=register-range -mtls-size=tls-size -mtune=cpu-type -milp32 -mlp64 166 -msched-br-data-spec -msched-ar-data-spec -msched-control-spec -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec -msched-spec-ldc -msched-spec-control-ldc 167 -msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns -msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path -msel-sched-dont-check-control-spec 168 -msched-fp-mem-deps-zero-cost -msched-max-memory-insns-hard-limit -msched-max-memory-insns=max-insns 169 LM32 Options -mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled -msign-extend-enabled -muser-enabled 170 M32R/D Options -m32r2 -m32rx -m32r -mdebug -malign-loops -mno-align-loops -missue-rate=number -mbranch-cost=number -mmodel=code-size-model-type -msdata=sdata-type -mno-flush-func 171 -mflush-func=name -mno-flush-trap -mflush-trap=number -G num 172 M32C Options -mcpu=cpu -msim -memregs=number 173 M680x0 Options -march=arch -mcpu=cpu -mtune=tune -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 -mcfv4e -mbitfield 174 -mno-bitfield -mc68000 -mc68020 -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort -mno-short -mhard-float -m68881 -msoft-float -mpcrel -malign-int -mstrict-align -msep-data 175 -mno-sep-data -mshared-library-id=n -mid-shared-library -mno-id-shared-library -mxgot -mno-xgot 176 MCore Options -mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields -m4byte-functions -mno-4byte-functions 177 -mcallgraph-data -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment 178 MeP Options -mabsdiff -mall-opts -maverage -mbased=n -mbitops -mc=n -mclip -mconfig=name -mcop -mcop32 -mcop64 -mivc2 -mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax -mmult 179 -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf -mtiny=n 180 MicroBlaze Options -msoft-float -mhard-float -msmall-divides -mcpu=cpu -mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift -mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss 181 -mxl-multiply-high -mxl-float-convert -mxl-float-sqrt -mbig-endian -mlittle-endian -mxl-reorder -mxl-mode-app-model 182 MIPS Options -EL -EB -march=arch -mtune=arch -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips32r3 -mips32r5 -mips32r6 -mips64 -mips64r2 -mips64r3 -mips64r5 -mips64r6 183 -mips16 -mno-mips16 -mflip-mips16 -minterlink-compressed -mno-interlink-compressed -minterlink-mips16 -mno-interlink-mips16 -mabi=abi -mabicalls -mno-abicalls -mshared -mno-shared 184 -mplt -mno-plt -mxgot -mno-xgot -mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float -msoft-float -mno-float -msingle-float -mdouble-float -modd-spreg -mno-odd-spreg -mabs=mode 185 -mnan=encoding -mdsp -mno-dsp -mdspr2 -mno-dspr2 -mmcu -mmno-mcu -meva -mno-eva -mvirt -mno-virt -mxpa -mno-xpa -mmicromips -mno-micromips -mfpu=fpu-type -msmartmips -mno-smartmips 186 -mpaired-single -mno-paired-single -mdmx -mno-mdmx -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc -mlong64 -mlong32 -msym32 -mno-sym32 -Gnum -mlocal-sdata -mno-local-sdata 187 -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt -membedded-data -mno-embedded-data -muninit-const-in-rodata -mno-uninit-const-in-rodata -mcode-readable=setting -msplit-addresses 188 -mno-split-addresses -mexplicit-relocs -mno-explicit-relocs -mcheck-zero-division -mno-check-zero-division -mdivide-traps -mdivide-breaks -mmemcpy -mno-memcpy -mlong-calls 189 -mno-long-calls -mmad -mno-mad -mimadd -mno-imadd -mfused-madd -mno-fused-madd -nocpp -mfix-24k -mno-fix-24k -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 -mfix-r10000 190 -mno-fix-r10000 -mfix-rm7000 -mno-fix-rm7000 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 -mflush-func=func -mno-flush-func -mbranch-cost=num 191 -mbranch-likely -mno-branch-likely -mfp-exceptions -mno-fp-exceptions -mvr4130-align -mno-vr4130-align -msynci -mno-synci -mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address 192 MMIX Options -mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols -melf -mbranch-predict -mno-branch-predict 193 -mbase-addresses -mno-base-addresses -msingle-exit -mno-single-exit 194 MN10300 Options -mmult-bug -mno-mult-bug -mno-am33 -mam33 -mam33-2 -mam34 -mtune=cpu-type -mreturn-pointer-on-d0 -mno-crt0 -mrelax -mliw -msetlb 195 Moxie Options -meb -mel -mmul.x -mno-crt0 196 MSP430 Options -msim -masm-hex -mmcu= -mcpu= -mlarge -msmall -mrelax -mhwmult= -minrt 197 NDS32 Options -mbig-endian -mlittle-endian -mreduced-regs -mfull-regs -mcmov -mno-cmov -mperf-ext -mno-perf-ext -mv3push -mno-v3push -m16bit -mno-16bit -misr-vector-size=num 198 -mcache-block-size=num -march=arch -mcmodel=code-model -mctor-dtor -mrelax 199 Nios II Options -G num -mgpopt=option -mgpopt -mno-gpopt -mel -meb -mno-bypass-cache -mbypass-cache -mno-cache-volatile -mcache-volatile -mno-fast-sw-div -mfast-sw-div -mhw-mul -mno-hw-mul 200 -mhw-mulx -mno-hw-mulx -mno-hw-div -mhw-div -mcustom-insn=N -mno-custom-insn -mcustom-fpu-cfg=name -mhal -msmallc -msys-crt0=name -msys-lib=name 201 Nvidia PTX Options -m32 -m64 -mmainkernel 202 PDP-11 Options -mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 -mbcopy -mbcopy-builtin -mint32 -mno-int16 -mint16 -mno-int32 -mfloat32 -mno-float64 -mfloat64 -mno-float32 203 -mabshi -mno-abshi -mbranch-expensive -mbranch-cheap -munix-asm -mdec-asm 204 picoChip Options -mae=ae_type -mvliw-lookahead=N -msymbol-as-address -mno-inefficient-warnings 205 PowerPC Options See RS/6000 and PowerPC Options. 206 RL78 Options -msim -mmul=none -mmul=g13 -mmul=rl78 -m64bit-doubles -m32bit-doubles 207 RS/6000 and PowerPC Options -mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model -mpowerpc64 -maltivec -mno-altivec -mpowerpc-gpopt -mno-powerpc-gpopt -mpowerpc-gfxopt -mno-powerpc-gfxopt 208 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd -mfprnd -mno-fprnd -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp -mfull-toc -mminimal-toc 209 -mno-fp-in-toc -mno-sum-in-toc -m64 -m32 -mxl-compat -mno-xl-compat -mpe -malign-power -malign-natural -msoft-float -mhard-float -mmultiple -mno-multiple -msingle-float 210 -mdouble-float -msimple-fpu -mstring -mno-string -mupdate -mno-update -mavoid-indexed-addresses -mno-avoid-indexed-addresses -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align 211 -mstrict-align -mno-strict-align -mrelocatable -mno-relocatable -mrelocatable-lib -mno-relocatable-lib -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian -mdynamic-no-pic 212 -maltivec -mswdiv -msingle-pic-base -mprioritize-restricted-insns=priority -msched-costly-dep=dependence_type -minsert-sched-nops=scheme -mcall-sysv -mcall-netbsd -maix-struct-return 213 -msvr4-struct-return -mabi=abi-type -msecure-plt -mbss-plt -mblock-move-inline-limit=num -misel -mno-isel -misel=yes -misel=no -mspe -mno-spe -mspe=yes -mspe=no -mpaired 214 -mgen-cell-microcode -mwarn-cell-microcode -mvrsave -mno-vrsave -mmulhw -mno-mulhw -mdlmzb -mno-dlmzb -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double -mprototype 215 -mno-prototype -msim -mmvme -mads -myellowknife -memb -msdata -msdata=opt -mvxworks -G num -pthread -mrecip -mrecip=opt -mno-recip -mrecip-precision -mno-recip-precision 216 -mveclibabi=type -mfriz -mno-friz -mpointers-to-nested-functions -mno-pointers-to-nested-functions -msave-toc-indirect -mno-save-toc-indirect -mpower8-fusion -mno-mpower8-fusion 217 -mpower8-vector -mno-power8-vector -mcrypto -mno-crypto -mdirect-move -mno-direct-move -mquad-memory -mno-quad-memory -mquad-memory-atomic -mno-quad-memory-atomic -mcompat-align-parm 218 -mno-compat-align-parm -mupper-regs-df -mno-upper-regs-df -mupper-regs-sf -mno-upper-regs-sf -mupper-regs -mno-upper-regs 219 RX Options -m64bit-doubles -m32bit-doubles -fpu -nofpu -mcpu= -mbig-endian-data -mlittle-endian-data -msmall-data -msim -mno-sim -mas100-syntax -mno-as100-syntax -mrelax 220 -mmax-constant-size= -mint-register= -mpid -mno-warn-multiple-fast-interrupts -msave-acc-in-interrupts 221 S/390 and zSeries Options -mtune=cpu-type -march=cpu-type -mhard-float -msoft-float -mhard-dfp -mno-hard-dfp -mlong-double-64 -mlong-double-128 -mbackchain -mno-backchain -mpacked-stack 222 -mno-packed-stack -msmall-exec -mno-small-exec -mmvcle -mno-mvcle -m64 -m31 -mdebug -mno-debug -mesa -mzarch -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd -mwarn-framesize 223 -mwarn-dynamicstack -mstack-size -mstack-guard -mhotpatch=halfwords,halfwords 224 Score Options -meb -mel -mnhwloop -muls -mmac -mscore5 -mscore5u -mscore7 -mscore7d 225 SH Options -m1 -m2 -m2e -m2a-nofpu -m2a-single-only -m2a-single -m2a -m3 -m3e -m4-nofpu -m4-single-only -m4-single -m4 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al -m5-64media 226 -m5-64media-nofpu -m5-32media -m5-32media-nofpu -m5-compact -m5-compact-nofpu -mb -ml -mdalign -mrelax -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave -mieee -mno-ieee 227 -mbitops -misize -minline-ic_invalidate -mpadstruct -mspace -mprefergot -musermode -multcost=number -mdiv=strategy -mdivsi3_libfunc=name -mfixed-range=register-range -mindexed-addressing 228 -mgettrcost=number -mpt-fixed -maccumulate-outgoing-args -minvalid-symbols -matomic-model=atomic-model -mbranch-cost=num -mzdcbranch -mno-zdcbranch -mcbranch-force-delay-slot -mfused-madd 229 -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra -mpretend-cmove -mtas 230 Solaris 2 Options -mclear-hwcap -mno-clear-hwcap -mimpure-text -mno-impure-text -pthreads -pthread 231 SPARC Options -mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model -mmemory-model=mem-model -m32 -m64 -mapp-regs -mno-app-regs -mfaster-structs -mno-faster-structs -mflat -mno-flat -mfpu 232 -mno-fpu -mhard-float -msoft-float -mhard-quad-float -msoft-quad-float -mstack-bias -mno-stack-bias -munaligned-doubles -mno-unaligned-doubles -muser-mode -mno-user-mode -mv8plus 233 -mno-v8plus -mvis -mno-vis -mvis2 -mno-vis2 -mvis3 -mno-vis3 -mcbcond -mno-cbcond -mfmaf -mno-fmaf -mpopc -mno-popc -mfix-at697f -mfix-ut699 234 SPU Options -mwarn-reloc -merror-reloc -msafe-dma -munsafe-dma -mbranch-hints -msmall-mem -mlarge-mem -mstdmain -mfixed-range=register-range -mea32 -mea64 -maddress-space-conversion 235 -mno-address-space-conversion -mcache-size=cache-size -matomic-updates -mno-atomic-updates 236 System V Options -Qy -Qn -YP,paths -Ym,dir 237 TILE-Gx Options -mcpu=CPU -m32 -m64 -mbig-endian -mlittle-endian -mcmodel=code-model 238 TILEPro Options -mcpu=cpu -m32 239 V850 Options -mlong-calls -mno-long-calls -mep -mno-ep -mprolog-function -mno-prolog-function -mspace -mtda=n -msda=n -mzda=n -mapp-regs -mno-app-regs -mdisable-callt 240 -mno-disable-callt -mv850e2v3 -mv850e2 -mv850e1 -mv850es -mv850e -mv850 -mv850e3v5 -mloop -mrelax -mlong-jumps -msoft-float -mhard-float -mgcc-abi -mrh850-abi -mbig-switch 241 VAX Options -mg -mgnu -munix 242 Visium Options -mdebug -msim -mfpu -mno-fpu -mhard-float -msoft-float -mcpu=cpu-type -mtune=cpu-type -msv-mode -muser-mode 243 VMS Options -mvms-return-codes -mdebug-main=prefix -mmalloc64 -mpointer-size=size 244 VxWorks Options -mrtp -non-static -Bstatic -Bdynamic -Xbind-lazy -Xbind-now 245 x86 Options -mtune=cpu-type -march=cpu-type -mtune-ctrl=feature-list -mdump-tune-features -mno-default -mfpmath=unit -masm=dialect -mno-fancy-math-387 -mno-fp-ret-in-387 -msoft-float 246 -mno-wide-multiply -mrtd -malign-double -mpreferred-stack-boundary=num -mincoming-stack-boundary=num -mcld -mcx16 -msahf -mmovbe -mcrc32 -mrecip -mrecip=opt -mvzeroupper -mprefer-avx128 247 -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx -mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -msha -maes -mpclmul -mfsgsbase -mrdrnd -mf16c -mfma -mprefetchwt1 248 -mclflushopt -mxsavec -mxsaves -msse4a -m3dnow -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -mlzcnt -mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mlwp -mmpx -mmwaitx -mthreads -mno-align-stringops 249 -minline-all-stringops -minline-stringops-dynamically -mstringop-strategy=alg -mmemcpy-strategy=strategy -mmemset-strategy=strategy -mpush-args -maccumulate-outgoing-args 250 -m128bit-long-double -m96bit-long-double -mlong-double-64 -mlong-double-80 -mlong-double-128 -mregparm=num -msseregparm -mveclibabi=type -mvect8-ret-in-mem -mpc32 -mpc64 -mpc80 251 -mstackrealign -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs -mcmodel=code-model -mabi=name -maddress-mode=mode -m32 -m64 -mx32 -m16 -mlarge-data-threshold=num -msse2avx 252 -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv -mavx256-split-unaligned-load -mavx256-split-unaligned-store -malign-data=type -mstack-protector-guard=guard 253 x86 Windows Options -mconsole -mcygwin -mno-cygwin -mdll -mnop-fun-dllimport -mthread -municode -mwin32 -mwindows -fno-set-stack-executable 254 Xstormy16 Options -msim 255 Xtensa Options -mconst16 -mno-const16 -mfused-madd -mno-fused-madd -mforce-no-pic -mserialize-volatile -mno-serialize-volatile -mtext-section-literals -mno-text-section-literals 256 -mtarget-align -mno-target-align -mlongcalls -mno-longcalls 257 zSeries Options See S/390 and zSeries Options. 258 Code Generation Options 259 -fcall-saved-reg -fcall-used-reg -ffixed-reg -fexceptions -fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables -fasynchronous-unwind-tables -fno-gnu-unique 260 -finhibit-size-directive -finstrument-functions -finstrument-functions-exclude-function-list=sym,sym,... -finstrument-functions-exclude-file-list=file,file,... -fno-common -fno-ident 261 -fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-jump-tables -frecord-gcc-switches -freg-struct-return -fshort-enums -fshort-double -fshort-wchar -fverbose-asm -fpack-struct[=n] 262 -fstack-check -fstack-limit-register=reg -fstack-limit-symbol=sym -fno-stack-limit -fsplit-stack -fleading-underscore -ftls-model=model -fstack-reuse=reuse_level -ftrapv -fwrapv 263 -fbounds-check -fvisibility=[default|internal|hidden|protected] -fstrict-volatile-bitfields -fsync-libcalls 264 Options Controlling the Kind of Output 265 Compilation can involve up to four stages: preprocessing, compilation proper, assembly and linking, always in that order. GCC is capable of preprocessing and compiling several files either into 266 several assembler input files, or into one assembler input file; then each assembler input file produces an object file, and linking combines all the object files (those newly compiled, and 267 those specified as input) into an executable file. 268 For any given input file, the file name suffix determines what kind of compilation is done: 269 file.c 270 C source code that must be preprocessed. 271 file.i 272 C source code that should not be preprocessed. 273 file.ii 274 C++ source code that should not be preprocessed. 275 file.m 276 Objective-C source code. Note that you must link with the libobjc library to make an Objective-C program work. 277 file.mi 278 Objective-C source code that should not be preprocessed. 279 file.mm 280 file.M 281 Objective-C++ source code. Note that you must link with the libobjc library to make an Objective-C++ program work. Note that .M refers to a literal capital M. 282 file.mii 283 Objective-C++ source code that should not be preprocessed. 284 file.h 285 C, C++, Objective-C or Objective-C++ header file to be turned into a precompiled header (default), or C, C++ header file to be turned into an Ada spec (via the -fdump-ada-spec switch). 286 file.cc 287 file.cp 288 file.cxx 289 file.cpp 290 file.CPP 291 file.c++ 292 file.C 293 C++ source code that must be preprocessed. Note that in .cxx, the last two letters must both be literally x. Likewise, .C refers to a literal capital C. 294 file.mm 295 file.M 296 Objective-C++ source code that must be preprocessed. 297 file.mii 298 Objective-C++ source code that should not be preprocessed. 299 file.hh 300 file.H 301 file.hp 302 file.hxx 303 file.hpp 304 file.HPP 305 file.h++ 306 file.tcc 307 C++ header file to be turned into a precompiled header or Ada spec. 308 file.f 309 file.for 310 file.ftn 311 Fixed form Fortran source code that should not be preprocessed. 312 file.F 313 file.FOR 314 file.fpp 315 file.FPP 316 file.FTN 317 Fixed form Fortran source code that must be preprocessed (with the traditional preprocessor). 318 file.f90 319 file.f95 320 file.f03 321 file.f08 322 Free form Fortran source code that should not be preprocessed. 323 file.F90 324 file.F95 325 file.F03 326 file.F08 327 Free form Fortran source code that must be preprocessed (with the traditional preprocessor). 328 file.go 329 Go source code. 330 file.ads 331 Ada source code file that contains a library unit declaration (a declaration of a package, subprogram, or generic, or a generic instantiation), or a library unit renaming declaration (a 332 package, generic, or subprogram renaming declaration). Such files are also called specs. 333 file.adb 334 Ada source code file containing a library unit body (a subprogram or package body). Such files are also called bodies. 335 file.s 336 Assembler code. 337 file.S 338 file.sx 339 Assembler code that must be preprocessed. 340 other 341 An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way. 342 You can specify the input language explicitly with the -x option: 343 -x language 344 Specify explicitly the language for the following input files (rather than letting the compiler choose a default based on the file name suffix). This option applies to all following input 345 files until the next -x option. Possible values for language are: 346 c c-header cpp-output 347 c++ c++-header c++-cpp-output 348 objective-c objective-c-header objective-c-cpp-output 349 objective-c++ objective-c++-header objective-c++-cpp-output 350 assembler assembler-with-cpp 351 ada 352 f77 f77-cpp-input f95 f95-cpp-input 353 go 354 java 355 -x none 356 Turn off any specification of a language, so that subsequent files are handled according to their file name suffixes (as they are if -x has not been used at all). 357 -pass-exit-codes 358 Normally the gcc program exits with the code of 1 if any phase of the compiler returns a non-success return code. If you specify -pass-exit-codes, the gcc program instead returns with the 359 numerically highest error produced by any phase returning an error indication. The C, C++, and Fortran front ends return 4 if an internal compiler error is encountered. 360 If you only want some of the stages of compilation, you can use -x (or filename suffixes) to tell gcc where to start, and one of the options -c, -S, or -E to say where gcc is to stop. Note that 361 some combinations (for example, -x cpp-output -E) instruct gcc to do nothing at all. 362 -c Compile or assemble the source files, but do not link. The linking stage simply is not done. The ultimate output is in the form of an object file for each source file. 363 By default, the object file name for a source file is made by replacing the suffix .c, .i, .s, etc., with .o. 364 Unrecognized input files, not requiring compilation or assembly, are ignored. 365 -S Stop after the stage of compilation proper; do not assemble. The output is in the form of an assembler code file for each non-assembler input file specified. 366 By default, the assembler file name for a source file is made by replacing the suffix .c, .i, etc., with .s. 367 Input files that don't require compilation are ignored. 368 -E Stop after the preprocessing stage; do not run the compiler proper. The output is in the form of preprocessed source code, which is sent to the standard output. 369 Input files that don't require preprocessing are ignored. 370 -o file 371 Place output in file file. This applies to whatever sort of output is being produced, whether it be an executable file, an object file, an assembler file or preprocessed C code. 372 If -o is not specified, the default is to put an executable file in a.out, the object file for source.suffix in source.o, its assembler file in source.s, a precompiled header file in 373 source.suffix.gch, and all preprocessed C source on standard output. 374 -v Print (on standard error output) the commands executed to run the stages of compilation. Also print the version number of the compiler driver program and of the preprocessor and the 375 compiler proper. 376 -### 377 Like -v except the commands are not executed and arguments are quoted unless they contain only alphanumeric characters or "./-_". This is useful for shell scripts to capture the driver- 378 generated command lines. 379 -pipe 380 Use pipes rather than temporary files for communication between the various stages of compilation. This fails to work on some systems where the assembler is unable to read from a pipe; but 381 the GNU assembler has no trouble. 382 --help 383 Print (on the standard output) a description of the command-line options understood by gcc. If the -v option is also specified then --help is also passed on to the various processes invoked 384 by gcc, so that they can display the command-line options they accept. If the -Wextra option has also been specified (prior to the --help option), then command-line options that have no 385 documentation associated with them are also displayed. 386 --target-help 387 Print (on the standard output) a description of target-specific command-line options for each tool. For some targets extra target-specific information may also be printed. 388 --help={class|[^]qualifier}[,...] 389 Print (on the standard output) a description of the command-line options understood by the compiler that fit into all specified classes and qualifiers. These are the supported classes: 390 optimizers 391 Display all of the optimization options supported by the compiler. 392 warnings 393 Display all of the options controlling warning messages produced by the compiler. 394 target 395 Display target-specific options. Unlike the --target-help option however, target-specific options of the linker and assembler are not displayed. This is because those tools do not 396 currently support the extended --help= syntax. 397 params 398 Display the values recognized by the --param option. 399 language 400 Display the options supported for language, where language is the name of one of the languages supported in this version of GCC. 401 common 402 Display the options that are common to all languages. 403 These are the supported qualifiers: 404 undocumented 405 Display only those options that are undocumented. 406 joined 407 Display options taking an argument that appears after an equal sign in the same continuous piece of text, such as: --help=target. 408 separate 409 Display options taking an argument that appears as a separate word following the original option, such as: -o output-file. 410 Thus for example to display all the undocumented target-specific switches supported by the compiler, use: 411 --help=target,undocumented 412 The sense of a qualifier can be inverted by prefixing it with the ^ character, so for example to display all binary warning options (i.e., ones that are either on or off and that do not take 413 an argument) that have a description, use: 414 --help=warnings,^joined,^undocumented 415 The argument to --help= should not consist solely of inverted qualifiers. 416 Combining several classes is possible, although this usually restricts the output so much that there is nothing to display. One case where it does work, however, is when one of the classes 417 is target. For example, to display all the target-specific optimization options, use: 418 --help=target,optimizers 419 The --help= option can be repeated on the command line. Each successive use displays its requested class of options, skipping those that have already been displayed. 420 If the -Q option appears on the command line before the --help= option, then the descriptive text displayed by --help= is changed. Instead of describing the displayed options, an indication 421 is given as to whether the option is enabled, disabled or set to a specific value (assuming that the compiler knows this at the point where the --help= option is used). 422 Here is a truncated example from the ARM port of gcc: 423 % gcc -Q -mabi=2 --help=target -c 424 The following options are target specific: 425 -mabi= 2 426 -mabort-on-noreturn [disabled] 427 -mapcs [disabled] 428 The output is sensitive to the effects of previous command-line options, so for example it is possible to find out which optimizations are enabled at -O2 by using: 429 -Q -O2 --help=optimizers 430 Alternatively you can discover which binary optimizations are enabled by -O3 by using: 431 gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts 432 gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts 433 diff /tmp/O2-opts /tmp/O3-opts | grep enabled 434 -no-canonical-prefixes 435 Do not expand any symbolic links, resolve references to /../ or /./, or make the path absolute when generating a relative prefix. 436 --version 437 Display the version number and copyrights of the invoked GCC. 438 -wrapper 439 Invoke all subcommands under a wrapper program. The name of the wrapper program and its parameters are passed as a comma separated list. 440 gcc -c t.c -wrapper gdb,--args 441 This invokes all subprograms of gcc under gdb --args, thus the invocation of cc1 is gdb --args cc1 .... 442 -fplugin=name.so 443 Load the plugin code in file name.so, assumed to be a shared object to be dlopen'd by the compiler. The base name of the shared object file is used to identify the plugin for the purposes 444 of argument parsing (See -fplugin-arg-name-key=value below). Each plugin should define the callback functions specified in the Plugins API. 445 -fplugin-arg-name-key=value 446 Define an argument called key with a value of value for the plugin called name. 447 -fdump-ada-spec[-slim] 448 For C and C++ source and include files, generate corresponding Ada specs. 449 -fada-spec-parent=unit 450 In conjunction with -fdump-ada-spec[-slim] above, generate Ada specs as child units of parent unit. 451 -fdump-go-spec=file 452 For input files in any language, generate corresponding Go declarations in file. This generates Go "const", "type", "var", and "func" declarations which may be a useful way to start writing 453 a Go interface to code written in some other language. 454 @file 455 Read command-line options from file. The options read are inserted in place of the original @file option. If file does not exist, or cannot be read, then the option will be treated 456 literally, and not removed. 457 Options in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character 458 (including a backslash) may be included by prefixing the character to be included with a backslash. The file may itself contain additional @file options; any such options will be processed 459 recursively. 460 Compiling C++ Programs 461 C++ source files conventionally use one of the suffixes .C, .cc, .cpp, .CPP, .c++, .cp, or .cxx; C++ header files often use .hh, .hpp, .H, or (for shared template code) .tcc; and preprocessed 462 C++ files use the suffix .ii. GCC recognizes files with these names and compiles them as C++ programs even if you call the compiler the same way as for compiling C programs (usually with the 463 name gcc). 464 However, the use of gcc does not add the C++ library. g++ is a program that calls GCC and automatically specifies linking against the C++ library. It treats .c, .h and .i files as C++ source 465 files instead of C source files unless -x is used. This program is also useful when precompiling a C header file with a .h extension for use in C++ compilations. On many systems, g++ is also 466 installed with the name c++. 467 When you compile C++ programs, you may specify many of the same command-line options that you use for compiling programs in any language; or command-line options meaningful for C and related 468 languages; or options that are meaningful only for C++ programs. 469 Options Controlling C Dialect 470 The following options control the dialect of C (or languages derived from C, such as C++, Objective-C and Objective-C++) that the compiler accepts: 471 -ansi 472 In C mode, this is equivalent to -std=c90. In C++ mode, it is equivalent to -std=c++98. 473 This turns off certain features of GCC that are incompatible with ISO C90 (when compiling C code), or of standard C++ (when compiling C++ code), such as the "asm" and "typeof" keywords, and 474 predefined macros such as "unix" and "vax" that identify the type of system you are using. It also enables the undesirable and rarely used ISO trigraph feature. For the C compiler, it 475 disables recognition of C++ style // comments as well as the "inline" keyword. 476 The alternate keywords "__asm__", "__extension__", "__inline__" and "__typeof__" continue to work despite -ansi. You would not want to use them in an ISO C program, of course, but it is 477 useful to put them in header files that might be included in compilations done with -ansi. Alternate predefined macros such as "__unix__" and "__vax__" are also available, with or without 478 -ansi. 479 The -ansi option does not cause non-ISO programs to be rejected gratuitously. For that, -Wpedantic is required in addition to -ansi. 480 The macro "__STRICT_ANSI__" is predefined when the -ansi option is used. Some header files may notice this macro and refrain from declaring certain functions or defining certain macros that 481 the ISO standard doesn't call for; this is to avoid interfering with any programs that might use these names for other things. 482 Functions that are normally built in but do not have semantics defined by ISO C (such as "alloca" and "ffs") are not built-in functions when -ansi is used. 483 -std= 484 Determine the language standard. This option is currently only supported when compiling C or C++. 485 The compiler can accept several base standards, such as c90 or c++98, and GNU dialects of those standards, such as gnu90 or gnu++98. When a base standard is specified, the compiler accepts 486 all programs following that standard plus those using GNU extensions that do not contradict it. For example, -std=c90 turns off certain features of GCC that are incompatible with ISO C90, 487 such as the "asm" and "typeof" keywords, but not other GNU extensions that do not have a meaning in ISO C90, such as omitting the middle term of a "?:" expression. On the other hand, when a 488 GNU dialect of a standard is specified, all features supported by the compiler are enabled, even when those features change the meaning of the base standard. As a result, some strict- 489 conforming programs may be rejected. The particular standard is used by -Wpedantic to identify which features are GNU extensions given that version of the standard. For example -std=gnu90 490 -Wpedantic warns about C++ style // comments, while -std=gnu99 -Wpedantic does not. 491 A value for this option must be provided; possible values are 492 c90 493 c89 494 iso9899:1990 495 Support all ISO C90 programs (certain GNU extensions that conflict with ISO C90 are disabled). Same as -ansi for C code. 496 iso9899:199409 497 ISO C90 as modified in amendment 1. 498 c99 499 c9x 500 iso9899:1999 501 iso9899:199x 502 ISO C99. This standard is substantially completely supported, modulo bugs and floating-point issues (mainly but not entirely relating to optional C99 features from Annexes F and G). 503 See for more information. The names c9x and iso9899:199x are deprecated. 504 c11 505 c1x 506 iso9899:2011 507 ISO C11, the 2011 revision of the ISO C standard. This standard is substantially completely supported, modulo bugs, floating-point issues (mainly but not entirely relating to optional 508 C11 features from Annexes F and G) and the optional Annexes K (Bounds-checking interfaces) and L (Analyzability). The name c1x is deprecated. 509 gnu90 510 gnu89 511 GNU dialect of ISO C90 (including some C99 features). 512 gnu99 513 gnu9x 514 GNU dialect of ISO C99. The name gnu9x is deprecated. 515 gnu11 516 gnu1x 517 GNU dialect of ISO C11. This is the default for C code. The name gnu1x is deprecated. 518 c++98 519 c++03 520 The 1998 ISO C++ standard plus the 2003 technical corrigendum and some additional defect reports. Same as -ansi for C++ code. 521 gnu++98 522 gnu++03 523 GNU dialect of -std=c++98. This is the default for C++ code. 524 c++11 525 c++0x 526 The 2011 ISO C++ standard plus amendments. The name c++0x is deprecated. 527 gnu++11 528 gnu++0x 529 GNU dialect of -std=c++11. The name gnu++0x is deprecated. 530 c++14 531 c++1y 532 The 2014 ISO C++ standard plus amendments. The name c++1y is deprecated. 533 gnu++14 534 gnu++1y 535 GNU dialect of -std=c++14. The name gnu++1y is deprecated. 536 c++1z 537 The next revision of the ISO C++ standard, tentatively planned for 2017. Support is highly experimental, and will almost certainly change in incompatible ways in future releases. 538 gnu++1z 539 GNU dialect of -std=c++1z. Support is highly experimental, and will almost certainly change in incompatible ways in future releases. 540 -fgnu89-inline 541 The option -fgnu89-inline tells GCC to use the traditional GNU semantics for "inline" functions when in C99 mode. 542 Using this option is roughly equivalent to adding the "gnu_inline" function attribute to all inline functions. 543 The option -fno-gnu89-inline explicitly tells GCC to use the C99 semantics for "inline" when in C99 or gnu99 mode (i.e., it specifies the default behavior). This option is not supported in 544 -std=c90 or -std=gnu90 mode. 545 The preprocessor macros "__GNUC_GNU_INLINE__" and "__GNUC_STDC_INLINE__" may be used to check which semantics are in effect for "inline" functions. 546 -aux-info filename 547 Output to the given filename prototyped declarations for all functions declared and/or defined in a translation unit, including those in header files. This option is silently ignored in any 548 language other than C. 549 Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped (I, N for new 550 or O for old, respectively, in the first character after the line number and the colon), and whether it came from a declaration or a definition (C or F, respectively, in the following 551 character). In the case of function definitions, a K&R-style list of arguments followed by their declarations is also provided, inside comments, after the declaration. 552 -fallow-parameterless-variadic-functions 553 Accept variadic functions without named parameters. 554 Although it is possible to define such a function, this is not very useful as it is not possible to read the arguments. This is only supported for C as this construct is allowed by C++. 555 -fno-asm 556 Do not recognize "asm", "inline" or "typeof" as a keyword, so that code can use these words as identifiers. You can use the keywords "__asm__", "__inline__" and "__typeof__" instead. -ansi 557 implies -fno-asm. 558 In C++, this switch only affects the "typeof" keyword, since "asm" and "inline" are standard keywords. You may want to use the -fno-gnu-keywords flag instead, which has the same effect. In 559 C99 mode (-std=c99 or -std=gnu99), this switch only affects the "asm" and "typeof" keywords, since "inline" is a standard keyword in ISO C99. 560 -fno-builtin 561 -fno-builtin-function 562 Don't recognize built-in functions that do not begin with __builtin_ as prefix. 563 GCC normally generates special code to handle certain built-in functions more efficiently; for instance, calls to "alloca" may become single instructions which adjust the stack directly, and 564 calls to "memcpy" may become inline copy loops. The resulting code is often both smaller and faster, but since the function calls no longer appear as such, you cannot set a breakpoint on 565 those calls, nor can you change the behavior of the functions by linking with a different library. In addition, when a function is recognized as a built-in function, GCC may use information 566 about that function to warn about problems with calls to that function, or to generate more efficient code, even if the resulting code still contains calls to that function. For example, 567 warnings are given with -Wformat for bad calls to "printf" when "printf" is built in and "strlen" is known not to modify global memory. 568 With the -fno-builtin-function option only the built-in function function is disabled. function must not begin with __builtin_. If a function is named that is not built-in in this version 569 of GCC, this option is ignored. There is no corresponding -fbuiltin-function option; if you wish to enable built-in functions selectively when using -fno-builtin or -ffreestanding, you may 570 define macros such as: 571 #define abs(n) __builtin_abs ((n)) 572 #define strcpy(d, s) __builtin_strcpy ((d), (s)) 573 -fhosted 574 Assert that compilation targets a hosted environment. This implies -fbuiltin. A hosted environment is one in which the entire standard library is available, and in which "main" has a 575 return type of "int". Examples are nearly everything except a kernel. This is equivalent to -fno-freestanding. 576 -ffreestanding 577 Assert that compilation targets a freestanding environment. This implies -fno-builtin. A freestanding environment is one in which the standard library may not exist, and program startup 578 may not necessarily be at "main". The most obvious example is an OS kernel. This is equivalent to -fno-hosted. 579 -fopenacc 580 Enable handling of OpenACC directives "#pragma acc" in C/C++ and "!$acc" in Fortran. When -fopenacc is specified, the compiler generates accelerated code according to the OpenACC 581 Application Programming Interface v2.0 . This option implies -pthread, and thus is only supported on targets that have support for -pthread. 582 Note that this is an experimental feature, incomplete, and subject to change in future versions of GCC. See for more information. 583 -fopenmp 584 Enable handling of OpenMP directives "#pragma omp" in C/C++ and "!$omp" in Fortran. When -fopenmp is specified, the compiler generates parallel code according to the OpenMP Application 585 Program Interface v4.0 . This option implies -pthread, and thus is only supported on targets that have support for -pthread. -fopenmp implies -fopenmp-simd. 586 -fopenmp-simd 587 Enable handling of OpenMP's SIMD directives with "#pragma omp" in C/C++ and "!$omp" in Fortran. Other OpenMP directives are ignored. 588 -fcilkplus 589 Enable the usage of Cilk Plus language extension features for C/C++. When the option -fcilkplus is specified, enable the usage of the Cilk Plus Language extension features for C/C++. The 590 present implementation follows ABI version 1.2. This is an experimental feature that is only partially complete, and whose interface may change in future versions of GCC as the official 591 specification changes. Currently, all features but "_Cilk_for" have been implemented. 592 -fgnu-tm 593 When the option -fgnu-tm is specified, the compiler generates code for the Linux variant of Intel's current Transactional Memory ABI specification document (Revision 1.1, May 6 2009). This 594 is an experimental feature whose interface may change in future versions of GCC, as the official specification changes. Please note that not all architectures are supported for this 595 feature. 596 For more information on GCC's support for transactional memory, 597 Note that the transactional memory feature is not supported with non-call exceptions (-fnon-call-exceptions). 598 -fms-extensions 599 Accept some non-standard constructs used in Microsoft header files. 600 In C++ code, this allows member names in structures to be similar to previous types declarations. 601 typedef int UOW; 602 struct ABC { 603 UOW UOW; 604 }; 605 Some cases of unnamed fields in structures and unions are only accepted with this option. 606 Note that this option is off for all targets but x86 targets using ms-abi. 607 -fplan9-extensions 608 Accept some non-standard constructs used in Plan 9 code. 609 This enables -fms-extensions, permits passing pointers to structures with anonymous fields to functions that expect pointers to elements of the type of the field, and permits referring to 610 anonymous fields declared using a typedef. This is only supported for C, not C++. 611 -trigraphs 612 Support ISO C trigraphs. The -ansi option (and -std options for strict ISO C conformance) implies -trigraphs. 613 -traditional 614 -traditional-cpp 615 Formerly, these options caused GCC to attempt to emulate a pre-standard C compiler. They are now only supported with the -E switch. The preprocessor continues to support a pre-standard 616 mode. See the GNU CPP manual for details. 617 -fcond-mismatch 618 Allow conditional expressions with mismatched types in the second and third arguments. The value of such an expression is void. This option is not supported for C++. 619 -flax-vector-conversions 620 Allow implicit conversions between vectors with differing numbers of elements and/or incompatible element types. This option should not be used for new code. 621 -funsigned-char 622 Let the type "char" be unsigned, like "unsigned char". 623 Each kind of machine has a default for what "char" should be. It is either like "unsigned char" by default or like "signed char" by default. 624 Ideally, a portable program should always use "signed char" or "unsigned char" when it depends on the signedness of an object. But many programs have been written to use plain "char" and 625 expect it to be signed, or expect it to be unsigned, depending on the machines they were written for. This option, and its inverse, let you make such a program work with the opposite 626 default. 627 The type "char" is always a distinct type from each of "signed char" or "unsigned char", even though its behavior is always just like one of those two. 628 -fsigned-char 629 Let the type "char" be signed, like "signed char". 630 Note that this is equivalent to -fno-unsigned-char, which is the negative form of -funsigned-char. Likewise, the option -fno-signed-char is equivalent to -funsigned-char. 631 -fsigned-bitfields 632 -funsigned-bitfields 633 -fno-signed-bitfields 634 -fno-unsigned-bitfields 635 These options control whether a bit-field is signed or unsigned, when the declaration does not use either "signed" or "unsigned". By default, such a bit-field is signed, because this is 636 consistent: the basic integer types such as "int" are signed types. 637 Options Controlling C++ Dialect 638 This section describes the command-line options that are only meaningful for C++ programs. You can also use most of the GNU compiler options regardless of what language your program is in. For 639 example, you might compile a file firstClass.C like this: 640 g++ -g -frepo -O -c firstClass.C 641 In this example, only -frepo is an option meant only for C++ programs; you can use the other options with any language supported by GCC. 642 Here is a list of options that are only for compiling C++ programs: 643 -fabi-version=n 644 Use version n of the C++ ABI. The default is version 0. 645 Version 0 refers to the version conforming most closely to the C++ ABI specification. Therefore, the ABI obtained using version 0 will change in different versions of G++ as ABI bugs are 646 fixed. 647 Version 1 is the version of the C++ ABI that first appeared in G++ 3.2. 648 Version 2 is the version of the C++ ABI that first appeared in G++ 3.4, and was the default through G++ 4.9. 649 Version 3 corrects an error in mangling a constant address as a template argument. 650 Version 4, which first appeared in G++ 4.5, implements a standard mangling for vector types. 651 Version 5, which first appeared in G++ 4.6, corrects the mangling of attribute const/volatile on function pointer types, decltype of a plain decl, and use of a function parameter in the 652 declaration of another parameter. 653 Version 6, which first appeared in G++ 4.7, corrects the promotion behavior of C++11 scoped enums and the mangling of template argument packs, const/static_cast, prefix ++ and --, and a 654 class scope function used as a template argument. 655 Version 7, which first appeared in G++ 4.8, that treats nullptr_t as a builtin type and corrects the mangling of lambdas in default argument scope. 656 Version 8, which first appeared in G++ 4.9, corrects the substitution behavior of function types with function-cv-qualifiers. 657 See also -Wabi. 658 -fabi-compat-version=n 659 On targets that support strong aliases, G++ works around mangling changes by creating an alias with the correct mangled name when defining a symbol with an incorrect mangled name. This 660 switch specifies which ABI version to use for the alias. 661 With -fabi-version=0 (the default), this defaults to 2. If another ABI version is explicitly selected, this defaults to 0. 662 The compatibility version is also set by -Wabi=n. 663 -fno-access-control 664 Turn off all access checking. This switch is mainly useful for working around bugs in the access control code. 665 -fcheck-new 666 Check that the pointer returned by "operator new" is non-null before attempting to modify the storage allocated. This check is normally unnecessary because the C++ standard specifies that 667 "operator new" only returns 0 if it is declared "throw()", in which case the compiler always checks the return value even without this option. In all other cases, when "operator new" has a 668 non-empty exception specification, memory exhaustion is signalled by throwing "std::bad_alloc". See also new (nothrow). 669 -fconstexpr-depth=n 670 Set the maximum nested evaluation depth for C++11 constexpr functions to n. A limit is needed to detect endless recursion during constant expression evaluation. The minimum specified by 671 the standard is 512. 672 -fdeduce-init-list 673 Enable deduction of a template type parameter as "std::initializer_list" from a brace-enclosed initializer list, i.e. 674 template auto forward(T t) -> decltype (realfn (t)) 675 { 676 return realfn (t); 677 } 678 void f() 679 { 680 forward({1,2}); // call forward> 681 } 682 This deduction was implemented as a possible extension to the originally proposed semantics for the C++11 standard, but was not part of the final standard, so it is disabled by default. 683 This option is deprecated, and may be removed in a future version of G++. 684 -ffriend-injection 685 Inject friend functions into the enclosing namespace, so that they are visible outside the scope of the class in which they are declared. Friend functions were documented to work this way 686 in the old Annotated C++ Reference Manual. However, in ISO C++ a friend function that is not declared in an enclosing scope can only be found using argument dependent lookup. GCC defaults 687 to the standard behavior. 688 This option is for compatibility, and may be removed in a future release of G++. 689 -fno-elide-constructors 690 The C++ standard allows an implementation to omit creating a temporary that is only used to initialize another object of the same type. Specifying this option disables that optimization, 691 and forces G++ to call the copy constructor in all cases. 692 -fno-enforce-eh-specs 693 Don't generate code to check for violation of exception specifications at run time. This option violates the C++ standard, but may be useful for reducing code size in production builds, 694 much like defining "NDEBUG". This does not give user code permission to throw exceptions in violation of the exception specifications; the compiler still optimizes based on the 695 specifications, so throwing an unexpected exception results in undefined behavior at run time. 696 -fextern-tls-init 697 -fno-extern-tls-init 698 The C++11 and OpenMP standards allow "thread_local" and "threadprivate" variables to have dynamic (runtime) initialization. To support this, any use of such a variable goes through a 699 wrapper function that performs any necessary initialization. When the use and definition of the variable are in the same translation unit, this overhead can be optimized away, but when the 700 use is in a different translation unit there is significant overhead even if the variable doesn't actually need dynamic initialization. If the programmer can be sure that no use of the 701 variable in a non-defining TU needs to trigger dynamic initialization (either because the variable is statically initialized, or a use of the variable in the defining TU will be executed 702 before any uses in another TU), they can avoid this overhead with the -fno-extern-tls-init option. 703 On targets that support symbol aliases, the default is -fextern-tls-init. On targets that do not support symbol aliases, the default is -fno-extern-tls-init. 704 -ffor-scope 705 -fno-for-scope 706 If -ffor-scope is specified, the scope of variables declared in a for-init-statement is limited to the "for" loop itself, as specified by the C++ standard. If -fno-for-scope is specified, 707 the scope of variables declared in a for-init-statement extends to the end of the enclosing scope, as was the case in old versions of G++, and other (traditional) implementations of C++. 708 If neither flag is given, the default is to follow the standard, but to allow and give a warning for old-style code that would otherwise be invalid, or have different behavior. 709 -fno-gnu-keywords 710 Do not recognize "typeof" as a keyword, so that code can use this word as an identifier. You can use the keyword "__typeof__" instead. -ansi implies -fno-gnu-keywords. 711 -fno-implicit-templates 712 Never emit code for non-inline templates that are instantiated implicitly (i.e. by use); only emit code for explicit instantiations. 713 -fno-implicit-inline-templates 714 Don't emit code for implicit instantiations of inline templates, either. The default is to handle inlines differently so that compiles with and without optimization need the same set of 715 explicit instantiations. 716 -fno-implement-inlines 717 To save space, do not emit out-of-line copies of inline functions controlled by "#pragma implementation". This causes linker errors if these functions are not inlined everywhere they are 718 called. 719 -fms-extensions 720 Disable Wpedantic warnings about constructs used in MFC, such as implicit int and getting a pointer to member function via non-standard syntax. 721 -fno-nonansi-builtins 722 Disable built-in declarations of functions that are not mandated by ANSI/ISO C. These include "ffs", "alloca", "_exit", "index", "bzero", "conjf", and other related functions. 723 -fnothrow-opt 724 Treat a "throw()" exception specification as if it were a "noexcept" specification to reduce or eliminate the text size overhead relative to a function with no exception specification. If 725 the function has local variables of types with non-trivial destructors, the exception specification actually makes the function smaller because the EH cleanups for those variables can be 726 optimized away. The semantic effect is that an exception thrown out of a function with such an exception specification results in a call to "terminate" rather than "unexpected". 727 -fno-operator-names 728 Do not treat the operator name keywords "and", "bitand", "bitor", "compl", "not", "or" and "xor" as synonyms as keywords. 729 -fno-optional-diags 730 Disable diagnostics that the standard says a compiler does not need to issue. Currently, the only such diagnostic issued by G++ is the one for a name having multiple meanings within a 731 class. 732 -fpermissive 733 Downgrade some diagnostics about nonconformant code from errors to warnings. Thus, using -fpermissive allows some nonconforming code to compile. 734 -fno-pretty-templates 735 When an error message refers to a specialization of a function template, the compiler normally prints the signature of the template followed by the template arguments and any typedefs or 736 typenames in the signature (e.g. "void f(T) [with T = int]" rather than "void f(int)") so that it's clear which template is involved. When an error message refers to a specialization of a 737 class template, the compiler omits any template arguments that match the default template arguments for that template. If either of these behaviors make it harder to understand the error 738 message rather than easier, you can use -fno-pretty-templates to disable them. 739 -frepo 740 Enable automatic template instantiation at link time. This option also implies -fno-implicit-templates. 741 -fno-rtti 742 Disable generation of information about every class with virtual functions for use by the C++ run-time type identification features ("dynamic_cast" and "typeid"). If you don't use those 743 parts of the language, you can save some space by using this flag. Note that exception handling uses the same information, but G++ generates it as needed. The "dynamic_cast" operator can 744 still be used for casts that do not require run-time type information, i.e. casts to "void *" or to unambiguous base classes. 745 -fsized-deallocation 746 Enable the built-in global declarations 747 void operator delete (void *, std::size_t) noexcept; 748 void operator delete[] (void *, std::size_t) noexcept; 749 as introduced in C++14. This is useful for user-defined replacement deallocation functions that, for example, use the size of the object to make deallocation faster. Enabled by default 750 under -std=c++14 and above. The flag -Wsized-deallocation warns about places that might want to add a definition. 751 -fstats 752 Emit statistics about front-end processing at the end of the compilation. This information is generally only useful to the G++ development team. 753 -fstrict-enums 754 Allow the compiler to optimize using the assumption that a value of enumerated type can only be one of the values of the enumeration (as defined in the C++ standard; basically, a value that 755 can be represented in the minimum number of bits needed to represent all the enumerators). This assumption may not be valid if the program uses a cast to convert an arbitrary integer value 756 to the enumerated type. 757 -ftemplate-backtrace-limit=n 758 Set the maximum number of template instantiation notes for a single warning or error to n. The default value is 10. 759 -ftemplate-depth=n 760 Set the maximum instantiation depth for template classes to n. A limit on the template instantiation depth is needed to detect endless recursions during template class instantiation. 761 ANSI/ISO C++ conforming programs must not rely on a maximum depth greater than 17 (changed to 1024 in C++11). The default value is 900, as the compiler can run out of stack space before 762 hitting 1024 in some situations. 763 -fno-threadsafe-statics 764 Do not emit the extra code to use the routines specified in the C++ ABI for thread-safe initialization of local statics. You can use this option to reduce code size slightly in code that 765 doesn't need to be thread-safe. 766 -fuse-cxa-atexit 767 Register destructors for objects with static storage duration with the "__cxa_atexit" function rather than the "atexit" function. This option is required for fully standards-compliant 768 handling of static destructors, but only works if your C library supports "__cxa_atexit". 769 -fno-use-cxa-get-exception-ptr 770 Don't use the "__cxa_get_exception_ptr" runtime routine. This causes "std::uncaught_exception" to be incorrect, but is necessary if the runtime routine is not available. 771 -fvisibility-inlines-hidden 772 This switch declares that the user does not attempt to compare pointers to inline functions or methods where the addresses of the two functions are taken in different shared objects. 773 The effect of this is that GCC may, effectively, mark inline methods with "__attribute__ ((visibility ("hidden")))" so that they do not appear in the export table of a DSO and do not require 774 a PLT indirection when used within the DSO. Enabling this option can have a dramatic effect on load and link times of a DSO as it massively reduces the size of the dynamic export table when 775 the library makes heavy use of templates. 776 The behavior of this switch is not quite the same as marking the methods as hidden directly, because it does not affect static variables local to the function or cause the compiler to deduce 777 that the function is defined in only one shared object. 778 You may mark a method as having a visibility explicitly to negate the effect of the switch for that method. For example, if you do want to compare pointers to a particular inline method, 779 you might mark it as having default visibility. Marking the enclosing class with explicit visibility has no effect. 780 Explicitly instantiated inline methods are unaffected by this option as their linkage might otherwise cross a shared library boundary. 781 -fvisibility-ms-compat 782 This flag attempts to use visibility settings to make GCC's C++ linkage model compatible with that of Microsoft Visual Studio. 783 The flag makes these changes to GCC's linkage model: 784 1. It sets the default visibility to "hidden", like -fvisibility=hidden. 785 2. Types, but not their members, are not hidden by default. 786 3. The One Definition Rule is relaxed for types without explicit visibility specifications that are defined in more than one shared object: those declarations are permitted if they are 787 permitted when this option is not used. 788 In new code it is better to use -fvisibility=hidden and export those classes that are intended to be externally visible. Unfortunately it is possible for code to rely, perhaps accidentally, 789 on the Visual Studio behavior. 790 Among the consequences of these changes are that static data members of the same type with the same name but defined in different shared objects are different, so changing one does not 791 change the other; and that pointers to function members defined in different shared objects may not compare equal. When this flag is given, it is a violation of the ODR to define types with 792 the same name differently. 793 -fvtable-verify=[std|preinit|none] 794 Turn on (or off, if using -fvtable-verify=none) the security feature that verifies at run time, for every virtual call, that the vtable pointer through which the call is made is valid for 795 the type of the object, and has not been corrupted or overwritten. If an invalid vtable pointer is detected at run time, an error is reported and execution of the program is immediately 796 halted. 797 This option causes run-time data structures to be built at program startup, which are used for verifying the vtable pointers. The options std and preinit control the timing of when these 798 data structures are built. In both cases the data structures are built before execution reaches "main". Using -fvtable-verify=std causes the data structures to be built after shared 799 libraries have been loaded and initialized. -fvtable-verify=preinit causes them to be built before shared libraries have been loaded and initialized. 800 If this option appears multiple times in the command line with different values specified, none takes highest priority over both std and preinit; preinit takes priority over std. 801 -fvtv-debug 802 When used in conjunction with -fvtable-verify=std or -fvtable-verify=preinit, causes debug versions of the runtime functions for the vtable verification feature to be called. This flag also 803 causes the compiler to log information about which vtable pointers it finds for each class. This information is written to a file named vtv_set_ptr_data.log in the directory named by the 804 environment variable VTV_LOGS_DIR if that is defined or the current working directory otherwise. 805 Note: This feature appends data to the log file. If you want a fresh log file, be sure to delete any existing one. 806 -fvtv-counts 807 This is a debugging flag. When used in conjunction with -fvtable-verify=std or -fvtable-verify=preinit, this causes the compiler to keep track of the total number of virtual calls it 808 encounters and the number of verifications it inserts. It also counts the number of calls to certain run-time library functions that it inserts and logs this information for each 809 compilation unit. The compiler writes this information to a file named vtv_count_data.log in the directory named by the environment variable VTV_LOGS_DIR if that is defined or the current 810 working directory otherwise. It also counts the size of the vtable pointer sets for each class, and writes this information to vtv_class_set_sizes.log in the same directory. 811 Note: This feature appends data to the log files. To get fresh log files, be sure to delete any existing ones. 812 -fno-weak 813 Do not use weak symbol support, even if it is provided by the linker. By default, G++ uses weak symbols if they are available. This option exists only for testing, and should not be used 814 by end-users; it results in inferior code and has no benefits. This option may be removed in a future release of G++. 815 -nostdinc++ 816 Do not search for header files in the standard directories specific to C++, but do still search the other standard directories. (This option is used when building the C++ library.) 817 In addition, these optimization, warning, and code generation options have meanings only for C++ programs: 818 -Wabi (C, Objective-C, C++ and Objective-C++ only) 819 When an explicit -fabi-version=n option is used, causes G++ to warn when it generates code that is probably not compatible with the vendor-neutral C++ ABI. Since G++ now defaults to 820 -fabi-version=0, -Wabi has no effect unless either an older ABI version is selected (with -fabi-version=n) or an older compatibility version is selected (with -Wabi=n or 821 -fabi-compat-version=n). 822 Although an effort has been made to warn about all such cases, there are probably some cases that are not warned about, even though G++ is generating incompatible code. There may also be 823 cases where warnings are emitted even though the code that is generated is compatible. 824 You should rewrite your code to avoid these warnings if you are concerned about the fact that code generated by G++ may not be binary compatible with code generated by other compilers. 825 -Wabi can also be used with an explicit version number to warn about compatibility with a particular -fabi-version level, e.g. -Wabi=2 to warn about changes relative to -fabi-version=2. 826 Specifying a version number also sets -fabi-compat-version=n. 827 The known incompatibilities in -fabi-version=2 (which was the default from GCC 3.4 to 4.9) include: 828 * A template with a non-type template parameter of reference type was mangled incorrectly: 829 extern int N; 830 template struct S {}; 831 void n (S) {2} 832 This was fixed in -fabi-version=3. 833 * SIMD vector types declared using "__attribute ((vector_size))" were mangled in a non-standard way that does not allow for overloading of functions taking vectors of different sizes. 834 The mangling was changed in -fabi-version=4. 835 * "__attribute ((const))" and "noreturn" were mangled as type qualifiers, and "decltype" of a plain declaration was folded away. 836 These mangling issues were fixed in -fabi-version=5. 837 * Scoped enumerators passed as arguments to a variadic function are promoted like unscoped enumerators, causing "va_arg" to complain. On most targets this does not actually affect the 838 parameter passing ABI, as there is no way to pass an argument smaller than "int". 839 Also, the ABI changed the mangling of template argument packs, "const_cast", "static_cast", prefix increment/decrement, and a class scope function used as a template argument. 840 These issues were corrected in -fabi-version=6. 841 * Lambdas in default argument scope were mangled incorrectly, and the ABI changed the mangling of "nullptr_t". 842 These issues were corrected in -fabi-version=7. 843 * When mangling a function type with function-cv-qualifiers, the un-qualified function type was incorrectly treated as a substitution candidate. 844 This was fixed in -fabi-version=8. 845 It also warns about psABI-related changes. The known psABI changes at this point include: 846 * For SysV/x86-64, unions with "long double" members are passed in memory as specified in psABI. For example: 847 union U { 848 long double ld; 849 int i; 850 }; 851 "union U" is always passed in memory. 852 -Wabi-tag (C++ and Objective-C++ only) 853 Warn when a type with an ABI tag is used in a context that does not have that ABI tag. See C++ Attributes for more information about ABI tags. 854 -Wctor-dtor-privacy (C++ and Objective-C++ only) 855 Warn when a class seems unusable because all the constructors or destructors in that class are private, and it has neither friends nor public static member functions. Also warn if there are 856 no non-private methods, and there's at least one private member function that isn't a constructor or destructor. 857 -Wdelete-non-virtual-dtor (C++ and Objective-C++ only) 858 Warn when "delete" is used to destroy an instance of a class that has virtual functions and non-virtual destructor. It is unsafe to delete an instance of a derived class through a pointer to 859 a base class if the base class does not have a virtual destructor. This warning is enabled by -Wall. 860 -Wliteral-suffix (C++ and Objective-C++ only) 861 Warn when a string or character literal is followed by a ud-suffix which does not begin with an underscore. As a conforming extension, GCC treats such suffixes as separate preprocessing 862 tokens in order to maintain backwards compatibility with code that uses formatting macros from "". For example: 863 #define __STDC_FORMAT_MACROS 864 #include 865 #include 866 int main() { 867 int64_t i64 = 123; 868 printf("My int64: %"PRId64"\n", i64); 869 } 870 In this case, "PRId64" is treated as a separate preprocessing token. 871 This warning is enabled by default. 872 -Wnarrowing (C++ and Objective-C++ only) 873 Warn when a narrowing conversion prohibited by C++11 occurs within { }, e.g. 874 int i = { 2.2 }; // error: narrowing from double to int 875 This flag is included in -Wall and -Wc++11-compat. 876 With -std=c++11, -Wno-narrowing suppresses the diagnostic required by the standard. Note that this does not affect the meaning of well-formed code; narrowing conversions are still 877 considered ill-formed in SFINAE context. 878 -Wnoexcept (C++ and Objective-C++ only) 879 Warn when a noexcept-expression evaluates to false because of a call to a function that does not have a non-throwing exception specification (i.e. "throw()" or "noexcept") but is known by 880 the compiler to never throw an exception. 881 -Wnon-virtual-dtor (C++ and Objective-C++ only) 882 Warn when a class has virtual functions and an accessible non-virtual destructor itself or in an accessible polymorphic base class, in which case it is possible but unsafe to delete an 883 instance of a derived class through a pointer to the class itself or base class. This warning is automatically enabled if -Weffc++ is specified. 884 -Wreorder (C++ and Objective-C++ only) 885 Warn when the order of member initializers given in the code does not match the order in which they must be executed. For instance: 886 struct A { 887 int i; 888 int j; 889 A(): j (0), i (1) { } 890 }; 891 The compiler rearranges the member initializers for "i" and "j" to match the declaration order of the members, emitting a warning to that effect. This warning is enabled by -Wall. 892 -fext-numeric-literals (C++ and Objective-C++ only) 893 Accept imaginary, fixed-point, or machine-defined literal number suffixes as GNU extensions. When this option is turned off these suffixes are treated as C++11 user-defined literal numeric 894 suffixes. This is on by default for all pre-C++11 dialects and all GNU dialects: -std=c++98, -std=gnu++98, -std=gnu++11, -std=gnu++14. This option is off by default for ISO C++11 onwards 895 (-std=c++11, ...). 896 The following -W... options are not affected by -Wall. 897 -Weffc++ (C++ and Objective-C++ only) 898 Warn about violations of the following style guidelines from Scott Meyers' Effective C++ series of books: 899 * Define a copy constructor and an assignment operator for classes with dynamically-allocated memory. 900 * Prefer initialization to assignment in constructors. 901 * Have "operator=" return a reference to *this. 902 * Don't try to return a reference when you must return an object. 903 * Distinguish between prefix and postfix forms of increment and decrement operators. 904 * Never overload "&&", "||", or ",". 905 This option also enables -Wnon-virtual-dtor, which is also one of the effective C++ recommendations. However, the check is extended to warn about the lack of virtual destructor in 906 accessible non-polymorphic bases classes too. 907 When selecting this option, be aware that the standard library headers do not obey all of these guidelines; use grep -v to filter out those warnings. 908 -Wstrict-null-sentinel (C++ and Objective-C++ only) 909 Warn about the use of an uncasted "NULL" as sentinel. When compiling only with GCC this is a valid sentinel, as "NULL" is defined to "__null". Although it is a null pointer constant rather 910 than a null pointer, it is guaranteed to be of the same size as a pointer. But this use is not portable across different compilers. 911 -Wno-non-template-friend (C++ and Objective-C++ only) 912 Disable warnings when non-templatized friend functions are declared within a template. Since the advent of explicit template specification support in G++, if the name of the friend is an 913 unqualified-id (i.e., friend foo(int)), the C++ language specification demands that the friend declare or define an ordinary, nontemplate function. (Section 14.5.3). Before G++ implemented 914 explicit specification, unqualified-ids could be interpreted as a particular specialization of a templatized function. Because this non-conforming behavior is no longer the default behavior 915 for G++, -Wnon-template-friend allows the compiler to check existing code for potential trouble spots and is on by default. This new compiler behavior can be turned off with 916 -Wno-non-template-friend, which keeps the conformant compiler code but disables the helpful warning. 917 -Wold-style-cast (C++ and Objective-C++ only) 918 Warn if an old-style (C-style) cast to a non-void type is used within a C++ program. The new-style casts ("dynamic_cast", "static_cast", "reinterpret_cast", and "const_cast") are less 919 vulnerable to unintended effects and much easier to search for. 920 -Woverloaded-virtual (C++ and Objective-C++ only) 921 Warn when a function declaration hides virtual functions from a base class. For example, in: 922 struct A { 923 virtual void f(); 924 }; 925 struct B: public A { 926 void f(int); 927 }; 928 the "A" class version of "f" is hidden in "B", and code like: 929 B* b; 930 b->f(); 931 fails to compile. 932 -Wno-pmf-conversions (C++ and Objective-C++ only) 933 Disable the diagnostic for converting a bound pointer to member function to a plain pointer. 934 -Wsign-promo (C++ and Objective-C++ only) 935 Warn when overload resolution chooses a promotion from unsigned or enumerated type to a signed type, over a conversion to an unsigned type of the same size. Previous versions of G++ tried 936 to preserve unsignedness, but the standard mandates the current behavior. 937 Options Controlling Objective-C and Objective-C++ Dialects 938 (NOTE: This manual does not describe the Objective-C and Objective-C++ languages themselves. 939 This section describes the command-line options that are only meaningful for Objective-C and Objective-C++ programs. You can also use most of the language-independent GNU compiler options. For 940 example, you might compile a file some_class.m like this: 941 gcc -g -fgnu-runtime -O -c some_class.m 942 In this example, -fgnu-runtime is an option meant only for Objective-C and Objective-C++ programs; you can use the other options with any language supported by GCC. 943 Note that since Objective-C is an extension of the C language, Objective-C compilations may also use options specific to the C front-end (e.g., -Wtraditional). Similarly, Objective-C++ 944 compilations may use C++-specific options (e.g., -Wabi). 945 Here is a list of options that are only for compiling Objective-C and Objective-C++ programs: 946 -fconstant-string-class=class-name 947 Use class-name as the name of the class to instantiate for each literal string specified with the syntax "@"..."". The default class name is "NXConstantString" if the GNU runtime is being 948 used, and "NSConstantString" if the NeXT runtime is being used (see below). The -fconstant-cfstrings option, if also present, overrides the -fconstant-string-class setting and cause 949 "@"..."" literals to be laid out as constant CoreFoundation strings. 950 -fgnu-runtime 951 Generate object code compatible with the standard GNU Objective-C runtime. This is the default for most types of systems. 952 -fnext-runtime 953 Generate output compatible with the NeXT runtime. This is the default for NeXT-based systems, including Darwin and Mac OS X. The macro "__NEXT_RUNTIME__" is predefined if (and only if) 954 this option is used. 955 -fno-nil-receivers 956 Assume that all Objective-C message dispatches ("[receiver message:arg]") in this translation unit ensure that the receiver is not "nil". This allows for more efficient entry points in the 957 runtime to be used. This option is only available in conjunction with the NeXT runtime and ABI version 0 or 1. 958 -fobjc-abi-version=n 959 Use version n of the Objective-C ABI for the selected runtime. This option is currently supported only for the NeXT runtime. In that case, Version 0 is the traditional (32-bit) ABI without 960 support for properties and other Objective-C 2.0 additions. Version 1 is the traditional (32-bit) ABI with support for properties and other Objective-C 2.0 additions. Version 2 is the 961 modern (64-bit) ABI. If nothing is specified, the default is Version 0 on 32-bit target machines, and Version 2 on 64-bit target machines. 962 -fobjc-call-cxx-cdtors 963 For each Objective-C class, check if any of its instance variables is a C++ object with a non-trivial default constructor. If so, synthesize a special "- (id) .cxx_construct" instance 964 method which runs non-trivial default constructors on any such instance variables, in order, and then return "self". Similarly, check if any instance variable is a C++ object with a non- 965 trivial destructor, and if so, synthesize a special "- (void) .cxx_destruct" method which runs all such default destructors, in reverse order. 966 The "- (id) .cxx_construct" and "- (void) .cxx_destruct" methods thusly generated only operate on instance variables declared in the current Objective-C class, and not those inherited from 967 superclasses. It is the responsibility of the Objective-C runtime to invoke all such methods in an object's inheritance hierarchy. The "- (id) .cxx_construct" methods are invoked by the 968 runtime immediately after a new object instance is allocated; the "- (void) .cxx_destruct" methods are invoked immediately before the runtime deallocates an object instance. 969 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has support for invoking the "- (id) .cxx_construct" and "- (void) .cxx_destruct" methods. 970 -fobjc-direct-dispatch 971 Allow fast jumps to the message dispatcher. On Darwin this is accomplished via the comm page. 972 -fobjc-exceptions 973 Enable syntactic support for structured exception handling in Objective-C, similar to what is offered by C++ and Java. This option is required to use the Objective-C keywords @try, @throw, 974 @catch, @finally and @synchronized. This option is available with both the GNU runtime and the NeXT runtime (but not available in conjunction with the NeXT runtime on Mac OS X 10.2 and 975 earlier). 976 -fobjc-gc 977 Enable garbage collection (GC) in Objective-C and Objective-C++ programs. This option is only available with the NeXT runtime; the GNU runtime has a different garbage collection 978 implementation that does not require special compiler flags. 979 -fobjc-nilcheck 980 For the NeXT runtime with version 2 of the ABI, check for a nil receiver in method invocations before doing the actual method call. This is the default and can be disabled using 981 -fno-objc-nilcheck. Class methods and super calls are never checked for nil in this way no matter what this flag is set to. Currently this flag does nothing when the GNU runtime, or an 982 older version of the NeXT runtime ABI, is used. 983 -fobjc-std=objc1 984 Conform to the language syntax of Objective-C 1.0, the language recognized by GCC 4.0. This only affects the Objective-C additions to the C/C++ language; it does not affect conformance to 985 C/C++ standards, which is controlled by the separate C/C++ dialect option flags. When this option is used with the Objective-C or Objective-C++ compiler, any Objective-C syntax that is not 986 recognized by GCC 4.0 is rejected. This is useful if you need to make sure that your Objective-C code can be compiled with older versions of GCC. 987 -freplace-objc-classes 988 Emit a special marker instructing ld(1) not to statically link in the resulting object file, and allow dyld(1) to load it in at run time instead. This is used in conjunction with the Fix- 989 and-Continue debugging mode, where the object file in question may be recompiled and dynamically reloaded in the course of program execution, without the need to restart the program itself. 990 Currently, Fix-and-Continue functionality is only available in conjunction with the NeXT runtime on Mac OS X 10.3 and later. 991 -fzero-link 992 When compiling for the NeXT runtime, the compiler ordinarily replaces calls to "objc_getClass("...")" (when the name of the class is known at compile time) with static class references that 993 get initialized at load time, which improves run-time performance. Specifying the -fzero-link flag suppresses this behavior and causes calls to "objc_getClass("...")" to be retained. This 994 is useful in Zero-Link debugging mode, since it allows for individual class implementations to be modified during program execution. The GNU runtime currently always retains calls to 995 "objc_get_class("...")" regardless of command-line options. 996 -fno-local-ivars 997 By default instance variables in Objective-C can be accessed as if they were local variables from within the methods of the class they're declared in. This can lead to shadowing between 998 instance variables and other variables declared either locally inside a class method or globally with the same name. Specifying the -fno-local-ivars flag disables this behavior thus 999 avoiding variable shadowing issues. 1000 -fivar-visibility=[public|protected|private|package] 1001 Set the default instance variable visibility to the specified option so that instance variables declared outside the scope of any access modifier directives default to the specified 1002 visibility. 1003 -gen-decls 1004 Dump interface declarations for all classes seen in the source file to a file named sourcename.decl. 1005 -Wassign-intercept (Objective-C and Objective-C++ only) 1006 Warn whenever an Objective-C assignment is being intercepted by the garbage collector. 1007 -Wno-protocol (Objective-C and Objective-C++ only) 1008 If a class is declared to implement a protocol, a warning is issued for every method in the protocol that is not implemented by the class. The default behavior is to issue a warning for 1009 every method not explicitly implemented in the class, even if a method implementation is inherited from the superclass. If you use the -Wno-protocol option, then methods inherited from the 1010 superclass are considered to be implemented, and no warning is issued for them. 1011 -Wselector (Objective-C and Objective-C++ only) 1012 Warn if multiple methods of different types for the same selector are found during compilation. The check is performed on the list of methods in the final stage of compilation. 1013 Additionally, a check is performed for each selector appearing in a "@selector(...)" expression, and a corresponding method for that selector has been found during compilation. Because 1014 these checks scan the method table only at the end of compilation, these warnings are not produced if the final stage of compilation is not reached, for example because an error is found 1015 during compilation, or because the -fsyntax-only option is being used. 1016 -Wstrict-selector-match (Objective-C and Objective-C++ only) 1017 Warn if multiple methods with differing argument and/or return types are found for a given selector when attempting to send a message using this selector to a receiver of type "id" or 1018 "Class". When this flag is off (which is the default behavior), the compiler omits such warnings if any differences found are confined to types that share the same size and alignment. 1019 -Wundeclared-selector (Objective-C and Objective-C++ only) 1020 Warn if a "@selector(...)" expression referring to an undeclared selector is found. A selector is considered undeclared if no method with that name has been declared before the 1021 "@selector(...)" expression, either explicitly in an @interface or @protocol declaration, or implicitly in an @implementation section. This option always performs its checks as soon as a 1022 "@selector(...)" expression is found, while -Wselector only performs its checks in the final stage of compilation. This also enforces the coding style convention that methods and selectors 1023 must be declared before being used. 1024 -print-objc-runtime-info 1025 Generate C header describing the largest structure that is passed by value, if any. 1026 Options to Control Diagnostic Messages Formatting 1027 Traditionally, diagnostic messages have been formatted irrespective of the output device's aspect (e.g. its width, ...). You can use the options described below to control the formatting 1028 algorithm for diagnostic messages, e.g. how many characters per line, how often source location information should be reported. Note that some language front ends may not honor these options. 1029 -fmessage-length=n 1030 Try to format error messages so that they fit on lines of about n characters. If n is zero, then no line-wrapping is done; each error message appears on a single line. This is the default 1031 for all front ends. 1032 -fdiagnostics-show-location=once 1033 Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit source location information once; that is, in case the message is too long to fit on a single 1034 physical line and has to be wrapped, the source location won't be emitted (as prefix) again, over and over, in subsequent continuation lines. This is the default behavior. 1035 -fdiagnostics-show-location=every-line 1036 Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit the same source location information (as prefix) for physical lines that result from the process of 1037 breaking a message which is too long to fit on a single line. 1038 -fdiagnostics-color[=WHEN] 1039 -fno-diagnostics-color 1040 Use color in diagnostics. WHEN is never, always, or auto. The default depends on how the compiler has been configured, it can be any of the above WHEN options or also never if GCC_COLORS 1041 environment variable isn't present in the environment, and auto otherwise. auto means to use color only when the standard error is a terminal. The forms -fdiagnostics-color and 1042 -fno-diagnostics-color are aliases for -fdiagnostics-color=always and -fdiagnostics-color=never, respectively. 1043 The colors are defined by the environment variable GCC_COLORS. Its value is a colon-separated list of capabilities and Select Graphic Rendition (SGR) substrings. SGR commands are 1044 interpreted by the terminal or terminal emulator. (See the section in the documentation of your text terminal for permitted values and their meanings as character attributes.) These 1045 substring values are integers in decimal representation and can be concatenated with semicolons. Common values to concatenate include 1 for bold, 4 for underline, 5 for blink, 7 for 1046 inverse, 39 for default foreground color, 30 to 37 for foreground colors, 90 to 97 for 16-color mode foreground colors, 38;5;0 to 38;5;255 for 88-color and 256-color modes foreground colors, 1047 49 for default background color, 40 to 47 for background colors, 100 to 107 for 16-color mode background colors, and 48;5;0 to 48;5;255 for 88-color and 256-color modes background colors. 1048 The default GCC_COLORS is 1049 error=01;31:warning=01;35:note=01;36:caret=01;32:locus=01:quote=01 1050 where 01;31 is bold red, 01;35 is bold magenta, 01;36 is bold cyan, 01;32 is bold green and 01 is bold. Setting GCC_COLORS to the empty string disables colors. Supported capabilities are as 1051 follows. 1052 "error=" 1053 SGR substring for error: markers. 1054 "warning=" 1055 SGR substring for warning: markers. 1056 "note=" 1057 SGR substring for note: markers. 1058 "caret=" 1059 SGR substring for caret line. 1060 "locus=" 1061 SGR substring for location information, file:line or file:line:column etc. 1062 "quote=" 1063 SGR substring for information printed within quotes. 1064 -fno-diagnostics-show-option 1065 By default, each diagnostic emitted includes text indicating the command-line option that directly controls the diagnostic (if such an option is known to the diagnostic machinery). 1066 Specifying the -fno-diagnostics-show-option flag suppresses that behavior. 1067 -fno-diagnostics-show-caret 1068 By default, each diagnostic emitted includes the original source line and a caret '^' indicating the column. This option suppresses this information. The source line is truncated to n 1069 characters, if the -fmessage-length=n option is given. When the output is done to the terminal, the width is limited to the width given by the COLUMNS environment variable or, if not set, 1070 to the terminal width. 1071 Options to Request or Suppress Warnings 1072 Warnings are diagnostic messages that report constructions that are not inherently erroneous but that are risky or suggest there may have been an error. 1073 The following language-independent options do not enable specific warnings but control the kinds of diagnostics produced by GCC. 1074 -fsyntax-only 1075 Check the code for syntax errors, but don't do anything beyond that. 1076 -fmax-errors=n 1077 Limits the maximum number of error messages to n, at which point GCC bails out rather than attempting to continue processing the source code. If n is 0 (the default), there is no limit on 1078 the number of error messages produced. If -Wfatal-errors is also specified, then -Wfatal-errors takes precedence over this option. 1079 -w Inhibit all warning messages. 1080 -Werror 1081 Make all warnings into errors. 1082 -Werror= 1083 Make the specified warning into an error. The specifier for a warning is appended; for example -Werror=switch turns the warnings controlled by -Wswitch into errors. This switch takes a 1084 negative form, to be used to negate -Werror for specific warnings; for example -Wno-error=switch makes -Wswitch warnings not be errors, even when -Werror is in effect. 1085 The warning message for each controllable warning includes the option that controls the warning. That option can then be used with -Werror= and -Wno-error= as described above. (Printing of 1086 the option in the warning message can be disabled using the -fno-diagnostics-show-option flag.) 1087 Note that specifying -Werror=foo automatically implies -Wfoo. However, -Wno-error=foo does not imply anything. 1088 -Wfatal-errors 1089 This option causes the compiler to abort compilation on the first error occurred rather than trying to keep going and printing further error messages. 1090 You can request many specific warnings with options beginning with -W, for example -Wimplicit to request warnings on implicit declarations. Each of these specific warning options also has a 1091 negative form beginning -Wno- to turn off warnings; for example, -Wno-implicit. This manual lists only one of the two forms, whichever is not the default. For further language-specific options 1092 also refer to C++ Dialect Options and Objective-C and Objective-C++ Dialect Options. 1093 Some options, such as -Wall and -Wextra, turn on other options, such as -Wunused, which may turn on further options, such as -Wunused-value. The combined effect of positive and negative forms is 1094 that more specific options have priority over less specific ones, independently of their position in the command-line. For options of the same specificity, the last one takes effect. Options 1095 enabled or disabled via pragmas take effect as if they appeared at the end of the command-line. 1096 When an unrecognized warning option is requested (e.g., -Wunknown-warning), GCC emits a diagnostic stating that the option is not recognized. However, if the -Wno- form is used, the behavior is 1097 slightly different: no diagnostic is produced for -Wno-unknown-warning unless other diagnostics are being produced. This allows the use of new -Wno- options with old compilers, but if something 1098 goes wrong, the compiler warns that an unrecognized option is present. 1099 -Wpedantic 1100 -pedantic 1101 Issue all the warnings demanded by strict ISO C and ISO C++; reject all programs that use forbidden extensions, and some other programs that do not follow ISO C and ISO C++. For ISO C, 1102 follows the version of the ISO C standard specified by any -std option used. 1103 Valid ISO C and ISO C++ programs should compile properly with or without this option (though a rare few require -ansi or a -std option specifying the required version of ISO C). However, 1104 without this option, certain GNU extensions and traditional C and C++ features are supported as well. With this option, they are rejected. 1105 -Wpedantic does not cause warning messages for use of the alternate keywords whose names begin and end with __. Pedantic warnings are also disabled in the expression that follows 1106 "__extension__". However, only system header files should use these escape routes; application programs should avoid them. 1107 Some users try to use -Wpedantic to check programs for strict ISO C conformance. They soon find that it does not do quite what they want: it finds some non-ISO practices, but not all---only 1108 those for which ISO C requires a diagnostic, and some others for which diagnostics have been added. 1109 A feature to report any failure to conform to ISO C might be useful in some instances, but would require considerable additional work and would be quite different from -Wpedantic. We don't 1110 have plans to support such a feature in the near future. 1111 Where the standard specified with -std represents a GNU extended dialect of C, such as gnu90 or gnu99, there is a corresponding base standard, the version of ISO C on which the GNU extended 1112 dialect is based. Warnings from -Wpedantic are given where they are required by the base standard. (It does not make sense for such warnings to be given only for features not in the 1113 specified GNU C dialect, since by definition the GNU dialects of C include all features the compiler supports with the given option, and there would be nothing to warn about.) 1114 -pedantic-errors 1115 Give an error whenever the base standard (see -Wpedantic) requires a diagnostic, in some cases where there is undefined behavior at compile-time and in some other cases that do not prevent 1116 compilation of programs that are valid according to the standard. This is not equivalent to -Werror=pedantic, since there are errors enabled by this option and not enabled by the latter and 1117 vice versa. 1118 -Wall 1119 This enables all the warnings about constructions that some users consider questionable, and that are easy to avoid (or modify to prevent the warning), even in conjunction with macros. This 1120 also enables some language-specific warnings described in C++ Dialect Options and Objective-C and Objective-C++ Dialect Options. 1121 -Wall turns on the following warning flags: 1122 -Waddress -Warray-bounds=1 (only with -O2) -Wc++11-compat -Wc++14-compat -Wchar-subscripts -Wenum-compare (in C/ObjC; this is on by default in C++) -Wimplicit-int (C and Objective-C only) 1123 -Wimplicit-function-declaration (C and Objective-C only) -Wcomment -Wformat -Wmain (only for C/ObjC and unless -ffreestanding) -Wmaybe-uninitialized -Wmissing-braces (only for C/ObjC) 1124 -Wnonnull -Wopenmp-simd -Wparentheses -Wpointer-sign -Wreorder -Wreturn-type -Wsequence-point -Wsign-compare (only in C++) -Wstrict-aliasing -Wstrict-overflow=1 -Wswitch -Wtrigraphs 1125 -Wuninitialized -Wunknown-pragmas -Wunused-function -Wunused-label -Wunused-value -Wunused-variable -Wvolatile-register-var 1126 Note that some warning flags are not implied by -Wall. Some of them warn about constructions that users generally do not consider questionable, but which occasionally you might wish to 1127 check for; others warn about constructions that are necessary or hard to avoid in some cases, and there is no simple way to modify the code to suppress the warning. Some of them are enabled 1128 by -Wextra but many of them must be enabled individually. 1129 -Wextra 1130 This enables some extra warning flags that are not enabled by -Wall. (This option used to be called -W. The older name is still supported, but the newer name is more descriptive.) 1131 -Wclobbered -Wempty-body -Wignored-qualifiers -Wmissing-field-initializers -Wmissing-parameter-type (C only) -Wold-style-declaration (C only) -Woverride-init -Wsign-compare -Wtype-limits 1132 -Wuninitialized -Wunused-parameter (only with -Wunused or -Wall) -Wunused-but-set-parameter (only with -Wunused or -Wall) 1133 The option -Wextra also prints warning messages for the following cases: 1134 * A pointer is compared against integer zero with "<", "<=", ">", or ">=". 1135 * (C++ only) An enumerator and a non-enumerator both appear in a conditional expression. 1136 * (C++ only) Ambiguous virtual bases. 1137 * (C++ only) Subscripting an array that has been declared "register". 1138 * (C++ only) Taking the address of a variable that has been declared "register". 1139 * (C++ only) A base class is not initialized in a derived class's copy constructor. 1140 -Wchar-subscripts 1141 Warn if an array subscript has type "char". This is a common cause of error, as programmers often forget that this type is signed on some machines. This warning is enabled by -Wall. 1142 -Wcomment 1143 Warn whenever a comment-start sequence /* appears in a /* comment, or whenever a Backslash-Newline appears in a // comment. This warning is enabled by -Wall. 1144 -Wno-coverage-mismatch 1145 Warn if feedback profiles do not match when using the -fprofile-use option. If a source file is changed between compiling with -fprofile-gen and with -fprofile-use, the files with the 1146 profile feedback can fail to match the source file and GCC cannot use the profile feedback information. By default, this warning is enabled and is treated as an error. 1147 -Wno-coverage-mismatch can be used to disable the warning or -Wno-error=coverage-mismatch can be used to disable the error. Disabling the error for this warning can result in poorly 1148 optimized code and is useful only in the case of very minor changes such as bug fixes to an existing code-base. Completely disabling the warning is not recommended. 1149 -Wno-cpp 1150 (C, Objective-C, C++, Objective-C++ and Fortran only) 1151 Suppress warning messages emitted by "#warning" directives. 1152 -Wdouble-promotion (C, C++, Objective-C and Objective-C++ only) 1153 Give a warning when a value of type "float" is implicitly promoted to "double". CPUs with a 32-bit "single-precision" floating-point unit implement "float" in hardware, but emulate "double" 1154 in software. On such a machine, doing computations using "double" values is much more expensive because of the overhead required for software emulation. 1155 It is easy to accidentally do computations with "double" because floating-point literals are implicitly of type "double". For example, in: 1156 float area(float radius) 1157 { 1158 return 3.14159 * radius * radius; 1159 } 1160 the compiler performs the entire computation with "double" because the floating-point literal is a "double". 1161 -Wformat 1162 -Wformat=n 1163 Check calls to "printf" and "scanf", etc., to make sure that the arguments supplied have types appropriate to the format string specified, and that the conversions specified in the format 1164 string make sense. This includes standard functions, and others specified by format attributes, in the "printf", "scanf", "strftime" and "strfmon" (an X/Open extension, not in the C 1165 standard) families (or other target-specific families). Which functions are checked without format attributes having been specified depends on the standard version selected, and such checks 1166 of functions without the attribute specified are disabled by -ffreestanding or -fno-builtin. 1167 The formats are checked against the format features supported by GNU libc version 2.2. These include all ISO C90 and C99 features, as well as features from the Single Unix Specification and 1168 some BSD and GNU extensions. Other library implementations may not support all these features; GCC does not support warning about features that go beyond a particular library's limitations. 1169 However, if -Wpedantic is used with -Wformat, warnings are given about format features not in the selected standard version (but not for "strfmon" formats, since those are not in any version 1170 of the C standard). 1171 -Wformat=1 1172 -Wformat 1173 Option -Wformat is equivalent to -Wformat=1, and -Wno-format is equivalent to -Wformat=0. Since -Wformat also checks for null format arguments for several functions, -Wformat also 1174 implies -Wnonnull. Some aspects of this level of format checking can be disabled by the options: -Wno-format-contains-nul, -Wno-format-extra-args, and -Wno-format-zero-length. -Wformat 1175 is enabled by -Wall. 1176 -Wno-format-contains-nul 1177 If -Wformat is specified, do not warn about format strings that contain NUL bytes. 1178 -Wno-format-extra-args 1179 If -Wformat is specified, do not warn about excess arguments to a "printf" or "scanf" format function. The C standard specifies that such arguments are ignored. 1180 Where the unused arguments lie between used arguments that are specified with $ operand number specifications, normally warnings are still given, since the implementation could not know 1181 what type to pass to "va_arg" to skip the unused arguments. However, in the case of "scanf" formats, this option suppresses the warning if the unused arguments are all pointers, since 1182 the Single Unix Specification says that such unused arguments are allowed. 1183 -Wno-format-zero-length 1184 If -Wformat is specified, do not warn about zero-length formats. The C standard specifies that zero-length formats are allowed. 1185 -Wformat=2 1186 Enable -Wformat plus additional format checks. Currently equivalent to -Wformat -Wformat-nonliteral -Wformat-security -Wformat-y2k. 1187 -Wformat-nonliteral 1188 If -Wformat is specified, also warn if the format string is not a string literal and so cannot be checked, unless the format function takes its format arguments as a "va_list". 1189 -Wformat-security 1190 If -Wformat is specified, also warn about uses of format functions that represent possible security problems. At present, this warns about calls to "printf" and "scanf" functions where 1191 the format string is not a string literal and there are no format arguments, as in "printf (foo);". This may be a security hole if the format string came from untrusted input and 1192 contains %n. (This is currently a subset of what -Wformat-nonliteral warns about, but in future warnings may be added to -Wformat-security that are not included in -Wformat-nonliteral.) 1193 -Wformat-signedness 1194 If -Wformat is specified, also warn if the format string requires an unsigned argument and the argument is signed and vice versa. 1195 -Wformat-y2k 1196 If -Wformat is specified, also warn about "strftime" formats that may yield only a two-digit year. 1197 -Wnonnull 1198 Warn about passing a null pointer for arguments marked as requiring a non-null value by the "nonnull" function attribute. 1199 -Wnonnull is included in -Wall and -Wformat. It can be disabled with the -Wno-nonnull option. 1200 -Winit-self (C, C++, Objective-C and Objective-C++ only) 1201 Warn about uninitialized variables that are initialized with themselves. Note this option can only be used with the -Wuninitialized option. 1202 For example, GCC warns about "i" being uninitialized in the following snippet only when -Winit-self has been specified: 1203 int f() 1204 { 1205 int i = i; 1206 return i; 1207 } 1208 This warning is enabled by -Wall in C++. 1209 -Wimplicit-int (C and Objective-C only) 1210 Warn when a declaration does not specify a type. This warning is enabled by -Wall. 1211 -Wimplicit-function-declaration (C and Objective-C only) 1212 Give a warning whenever a function is used before being declared. In C99 mode (-std=c99 or -std=gnu99), this warning is enabled by default and it is made into an error by -pedantic-errors. 1213 This warning is also enabled by -Wall. 1214 -Wimplicit (C and Objective-C only) 1215 Same as -Wimplicit-int and -Wimplicit-function-declaration. This warning is enabled by -Wall. 1216 -Wignored-qualifiers (C and C++ only) 1217 Warn if the return type of a function has a type qualifier such as "const". For ISO C such a type qualifier has no effect, since the value returned by a function is not an lvalue. For C++, 1218 the warning is only emitted for scalar types or "void". ISO C prohibits qualified "void" return types on function definitions, so such return types always receive a warning even without 1219 this option. 1220 This warning is also enabled by -Wextra. 1221 -Wmain 1222 Warn if the type of "main" is suspicious. "main" should be a function with external linkage, returning int, taking either zero arguments, two, or three arguments of appropriate types. This 1223 warning is enabled by default in C++ and is enabled by either -Wall or -Wpedantic. 1224 -Wmissing-braces 1225 Warn if an aggregate or union initializer is not fully bracketed. In the following example, the initializer for "a" is not fully bracketed, but that for "b" is fully bracketed. This 1226 warning is enabled by -Wall in C. 1227 int a[2][2] = { 0, 1, 2, 3 }; 1228 int b[2][2] = { { 0, 1 }, { 2, 3 } }; 1229 This warning is enabled by -Wall. 1230 -Wmissing-include-dirs (C, C++, Objective-C and Objective-C++ only) 1231 Warn if a user-supplied include directory does not exist. 1232 -Wparentheses 1233 Warn if parentheses are omitted in certain contexts, such as when there is an assignment in a context where a truth value is expected, or when operators are nested whose precedence people 1234 often get confused about. 1235 Also warn if a comparison like "x<=y<=z" appears; this is equivalent to "(x<=y ? 1 : 0) <= z", which is a different interpretation from that of ordinary mathematical notation. 1236 Also warn about constructions where there may be confusion to which "if" statement an "else" branch belongs. Here is an example of such a case: 1237 { 1238 if (a) 1239 if (b) 1240 foo (); 1241 else 1242 bar (); 1243 } 1244 In C/C++, every "else" branch belongs to the innermost possible "if" statement, which in this example is "if (b)". This is often not what the programmer expected, as illustrated in the 1245 above example by indentation the programmer chose. When there is the potential for this confusion, GCC issues a warning when this flag is specified. To eliminate the warning, add explicit 1246 braces around the innermost "if" statement so there is no way the "else" can belong to the enclosing "if". The resulting code looks like this: 1247 { 1248 if (a) 1249 { 1250 if (b) 1251 foo (); 1252 else 1253 bar (); 1254 } 1255 } 1256 Also warn for dangerous uses of the GNU extension to "?:" with omitted middle operand. When the condition in the "?": operator is a boolean expression, the omitted value is always 1. Often 1257 programmers expect it to be a value computed inside the conditional expression instead. 1258 This warning is enabled by -Wall. 1259 -Wsequence-point 1260 Warn about code that may have undefined semantics because of violations of sequence point rules in the C and C++ standards. 1261 The C and C++ standards define the order in which expressions in a C/C++ program are evaluated in terms of sequence points, which represent a partial ordering between the execution of parts 1262 of the program: those executed before the sequence point, and those executed after it. These occur after the evaluation of a full expression (one which is not part of a larger expression), 1263 after the evaluation of the first operand of a "&&", "||", "? :" or "," (comma) operator, before a function is called (but after the evaluation of its arguments and the expression denoting 1264 the called function), and in certain other places. Other than as expressed by the sequence point rules, the order of evaluation of subexpressions of an expression is not specified. All 1265 these rules describe only a partial order rather than a total order, since, for example, if two functions are called within one expression with no sequence point between them, the order in 1266 which the functions are called is not specified. However, the standards committee have ruled that function calls do not overlap. 1267 It is not specified when between sequence points modifications to the values of objects take effect. Programs whose behavior depends on this have undefined behavior; the C and C++ standards 1268 specify that "Between the previous and next sequence point an object shall have its stored value modified at most once by the evaluation of an expression. Furthermore, the prior value shall 1269 be read only to determine the value to be stored.". If a program breaks these rules, the results on any particular implementation are entirely unpredictable. 1270 Examples of code with undefined behavior are "a = a++;", "a[n] = b[n++]" and "a[i++] = i;". Some more complicated cases are not diagnosed by this option, and it may give an occasional false 1271 positive result, but in general it has been found fairly effective at detecting this sort of problem in programs. 1272 The standard is worded confusingly, therefore there is some debate over the precise meaning of the sequence point rules in subtle cases. Links to discussions of the problem, including 1273 proposed formal definitions, may be found on the GCC readings page, at . 1274 This warning is enabled by -Wall for C and C++. 1275 -Wno-return-local-addr 1276 Do not warn about returning a pointer (or in C++, a reference) to a variable that goes out of scope after the function returns. 1277 -Wreturn-type 1278 Warn whenever a function is defined with a return type that defaults to "int". Also warn about any "return" statement with no return value in a function whose return type is not "void" 1279 (falling off the end of the function body is considered returning without a value), and about a "return" statement with an expression in a function whose return type is "void". 1280 For C++, a function without return type always produces a diagnostic message, even when -Wno-return-type is specified. The only exceptions are "main" and functions defined in system 1281 headers. 1282 This warning is enabled by -Wall. 1283 -Wshift-count-negative 1284 Warn if shift count is negative. This warning is enabled by default. 1285 -Wshift-count-overflow 1286 Warn if shift count >= width of type. This warning is enabled by default. 1287 -Wswitch 1288 Warn whenever a "switch" statement has an index of enumerated type and lacks a "case" for one or more of the named codes of that enumeration. (The presence of a "default" label prevents 1289 this warning.) "case" labels outside the enumeration range also provoke warnings when this option is used (even if there is a "default" label). This warning is enabled by -Wall. 1290 -Wswitch-default 1291 Warn whenever a "switch" statement does not have a "default" case. 1292 -Wswitch-enum 1293 Warn whenever a "switch" statement has an index of enumerated type and lacks a "case" for one or more of the named codes of that enumeration. "case" labels outside the enumeration range 1294 also provoke warnings when this option is used. The only difference between -Wswitch and this option is that this option gives a warning about an omitted enumeration code even if there is a 1295 "default" label. 1296 -Wswitch-bool 1297 Warn whenever a "switch" statement has an index of boolean type. It is possible to suppress this warning by casting the controlling expression to a type other than "bool". For example: 1298 switch ((int) (a == 4)) 1299 { 1300 ... 1301 } 1302 This warning is enabled by default for C and C++ programs. 1303 -Wsync-nand (C and C++ only) 1304 Warn when "__sync_fetch_and_nand" and "__sync_nand_and_fetch" built-in functions are used. These functions changed semantics in GCC 4.4. 1305 -Wtrigraphs 1306 Warn if any trigraphs are encountered that might change the meaning of the program (trigraphs within comments are not warned about). This warning is enabled by -Wall. 1307 -Wunused-but-set-parameter 1308 Warn whenever a function parameter is assigned to, but otherwise unused (aside from its declaration). 1309 To suppress this warning use the "unused" attribute. 1310 This warning is also enabled by -Wunused together with -Wextra. 1311 -Wunused-but-set-variable 1312 Warn whenever a local variable is assigned to, but otherwise unused (aside from its declaration). This warning is enabled by -Wall. 1313 To suppress this warning use the "unused" attribute. 1314 This warning is also enabled by -Wunused, which is enabled by -Wall. 1315 -Wunused-function 1316 Warn whenever a static function is declared but not defined or a non-inline static function is unused. This warning is enabled by -Wall. 1317 -Wunused-label 1318 Warn whenever a label is declared but not used. This warning is enabled by -Wall. 1319 To suppress this warning use the "unused" attribute. 1320 -Wunused-local-typedefs (C, Objective-C, C++ and Objective-C++ only) 1321 Warn when a typedef locally defined in a function is not used. This warning is enabled by -Wall. 1322 -Wunused-parameter 1323 Warn whenever a function parameter is unused aside from its declaration. 1324 To suppress this warning use the "unused" attribute. 1325 -Wno-unused-result 1326 Do not warn if a caller of a function marked with attribute "warn_unused_result" does not use its return value. The default is -Wunused-result. 1327 -Wunused-variable 1328 Warn whenever a local variable or non-constant static variable is unused aside from its declaration. This warning is enabled by -Wall. 1329 To suppress this warning use the "unused" attribute. 1330 -Wunused-value 1331 Warn whenever a statement computes a result that is explicitly not used. To suppress this warning cast the unused expression to "void". This includes an expression-statement or the left-hand 1332 side of a comma expression that contains no side effects. For example, an expression such as "x[i,j]" causes a warning, while "x[(void)i,j]" does not. 1333 This warning is enabled by -Wall. 1334 -Wunused 1335 All the above -Wunused options combined. 1336 In order to get a warning about an unused function parameter, you must either specify -Wextra -Wunused (note that -Wall implies -Wunused), or separately specify -Wunused-parameter. 1337 -Wuninitialized 1338 Warn if an automatic variable is used without first being initialized or if a variable may be clobbered by a "setjmp" call. In C++, warn if a non-static reference or non-static "const" 1339 member appears in a class without constructors. 1340 If you want to warn about code that uses the uninitialized value of the variable in its own initializer, use the -Winit-self option. 1341 These warnings occur for individual uninitialized or clobbered elements of structure, union or array variables as well as for variables that are uninitialized or clobbered as a whole. They 1342 do not occur for variables or elements declared "volatile". Because these warnings depend on optimization, the exact variables or elements for which there are warnings depends on the 1343 precise optimization options and version of GCC used. 1344 Note that there may be no warning about a variable that is used only to compute a value that itself is never used, because such computations may be deleted by data flow analysis before the 1345 warnings are printed. 1346 -Wmaybe-uninitialized 1347 For an automatic variable, if there exists a path from the function entry to a use of the variable that is initialized, but there exist some other paths for which the variable is not 1348 initialized, the compiler emits a warning if it cannot prove the uninitialized paths are not executed at run time. These warnings are made optional because GCC is not smart enough to see all 1349 the reasons why the code might be correct in spite of appearing to have an error. Here is one example of how this can happen: 1350 { 1351 int x; 1352 switch (y) 1353 { 1354 case 1: x = 1; 1355 break; 1356 case 2: x = 4; 1357 break; 1358 case 3: x = 5; 1359 } 1360 foo (x); 1361 } 1362 If the value of "y" is always 1, 2 or 3, then "x" is always initialized, but GCC doesn't know this. To suppress the warning, you need to provide a default case with assert(0) or similar 1363 code. 1364 This option also warns when a non-volatile automatic variable might be changed by a call to "longjmp". These warnings as well are possible only in optimizing compilation. 1365 The compiler sees only the calls to "setjmp". It cannot know where "longjmp" will be called; in fact, a signal handler could call it at any point in the code. As a result, you may get a 1366 warning even when there is in fact no problem because "longjmp" cannot in fact be called at the place that would cause a problem. 1367 Some spurious warnings can be avoided if you declare all the functions you use that never return as "noreturn". 1368 This warning is enabled by -Wall or -Wextra. 1369 -Wunknown-pragmas 1370 Warn when a "#pragma" directive is encountered that is not understood by GCC. If this command-line option is used, warnings are even issued for unknown pragmas in system header files. This 1371 is not the case if the warnings are only enabled by the -Wall command-line option. 1372 -Wno-pragmas 1373 Do not warn about misuses of pragmas, such as incorrect parameters, invalid syntax, or conflicts between pragmas. See also -Wunknown-pragmas. 1374 -Wstrict-aliasing 1375 This option is only active when -fstrict-aliasing is active. It warns about code that might break the strict aliasing rules that the compiler is using for optimization. The warning does 1376 not catch all cases, but does attempt to catch the more common pitfalls. It is included in -Wall. It is equivalent to -Wstrict-aliasing=3 1377 -Wstrict-aliasing=n 1378 This option is only active when -fstrict-aliasing is active. It warns about code that might break the strict aliasing rules that the compiler is using for optimization. Higher levels 1379 correspond to higher accuracy (fewer false positives). Higher levels also correspond to more effort, similar to the way -O works. -Wstrict-aliasing is equivalent to -Wstrict-aliasing=3. 1380 Level 1: Most aggressive, quick, least accurate. Possibly useful when higher levels do not warn but -fstrict-aliasing still breaks the code, as it has very few false negatives. However, it 1381 has many false positives. Warns for all pointer conversions between possibly incompatible types, even if never dereferenced. Runs in the front end only. 1382 Level 2: Aggressive, quick, not too precise. May still have many false positives (not as many as level 1 though), and few false negatives (but possibly more than level 1). Unlike level 1, 1383 it only warns when an address is taken. Warns about incomplete types. Runs in the front end only. 1384 Level 3 (default for -Wstrict-aliasing): Should have very few false positives and few false negatives. Slightly slower than levels 1 or 2 when optimization is enabled. Takes care of the 1385 common pun+dereference pattern in the front end: "*(int*)&some_float". If optimization is enabled, it also runs in the back end, where it deals with multiple statement cases using flow- 1386 sensitive points-to information. Only warns when the converted pointer is dereferenced. Does not warn about incomplete types. 1387 -Wstrict-overflow 1388 -Wstrict-overflow=n 1389 This option is only active when -fstrict-overflow is active. It warns about cases where the compiler optimizes based on the assumption that signed overflow does not occur. Note that it 1390 does not warn about all cases where the code might overflow: it only warns about cases where the compiler implements some optimization. Thus this warning depends on the optimization level. 1391 An optimization that assumes that signed overflow does not occur is perfectly safe if the values of the variables involved are such that overflow never does, in fact, occur. Therefore this 1392 warning can easily give a false positive: a warning about code that is not actually a problem. To help focus on important issues, several warning levels are defined. No warnings are issued 1393 for the use of undefined signed overflow when estimating how many iterations a loop requires, in particular when determining whether a loop will be executed at all. 1394 -Wstrict-overflow=1 1395 Warn about cases that are both questionable and easy to avoid. For example, with -fstrict-overflow, the compiler simplifies "x + 1 > x" to 1. This level of -Wstrict-overflow is 1396 enabled by -Wall; higher levels are not, and must be explicitly requested. 1397 -Wstrict-overflow=2 1398 Also warn about other cases where a comparison is simplified to a constant. For example: "abs (x) >= 0". This can only be simplified when -fstrict-overflow is in effect, because "abs 1399 (INT_MIN)" overflows to "INT_MIN", which is less than zero. -Wstrict-overflow (with no level) is the same as -Wstrict-overflow=2. 1400 -Wstrict-overflow=3 1401 Also warn about other cases where a comparison is simplified. For example: "x + 1 > 1" is simplified to "x > 0". 1402 -Wstrict-overflow=4 1403 Also warn about other simplifications not covered by the above cases. For example: "(x * 10) / 5" is simplified to "x * 2". 1404 -Wstrict-overflow=5 1405 Also warn about cases where the compiler reduces the magnitude of a constant involved in a comparison. For example: "x + 2 > y" is simplified to "x + 1 >= y". This is reported only at 1406 the highest warning level because this simplification applies to many comparisons, so this warning level gives a very large number of false positives. 1407 -Wsuggest-attribute=[pure|const|noreturn|format] 1408 Warn for cases where adding an attribute may be beneficial. The attributes currently supported are listed below. 1409 -Wsuggest-attribute=pure 1410 -Wsuggest-attribute=const 1411 -Wsuggest-attribute=noreturn 1412 Warn about functions that might be candidates for attributes "pure", "const" or "noreturn". The compiler only warns for functions visible in other compilation units or (in the case of 1413 "pure" and "const") if it cannot prove that the function returns normally. A function returns normally if it doesn't contain an infinite loop or return abnormally by throwing, calling 1414 "abort" or trapping. This analysis requires option -fipa-pure-const, which is enabled by default at -O and higher. Higher optimization levels improve the accuracy of the analysis. 1415 -Wsuggest-attribute=format 1416 -Wmissing-format-attribute 1417 Warn about function pointers that might be candidates for "format" attributes. Note these are only possible candidates, not absolute ones. GCC guesses that function pointers with 1418 "format" attributes that are used in assignment, initialization, parameter passing or return statements should have a corresponding "format" attribute in the resulting type. I.e. the 1419 left-hand side of the assignment or initialization, the type of the parameter variable, or the return type of the containing function respectively should also have a "format" attribute 1420 to avoid the warning. 1421 GCC also warns about function definitions that might be candidates for "format" attributes. Again, these are only possible candidates. GCC guesses that "format" attributes might be 1422 appropriate for any function that calls a function like "vprintf" or "vscanf", but this might not always be the case, and some functions for which "format" attributes are appropriate may 1423 not be detected. 1424 -Wsuggest-final-types 1425 Warn about types with virtual methods where code quality would be improved if the type were declared with the C++11 "final" specifier, or, if possible, declared in an anonymous namespace. 1426 This allows GCC to more aggressively devirtualize the polymorphic calls. This warning is more effective with link time optimization, where the information about the class hierarchy graph is 1427 more complete. 1428 -Wsuggest-final-methods 1429 Warn about virtual methods where code quality would be improved if the method were declared with the C++11 "final" specifier, or, if possible, its type were declared in an anonymous 1430 namespace or with the "final" specifier. This warning is more effective with link time optimization, where the information about the class hierarchy graph is more complete. It is 1431 recommended to first consider suggestions of -Wsuggest-final-types and then rebuild with new annotations. 1432 -Wsuggest-override 1433 Warn about overriding virtual functions that are not marked with the override keyword. 1434 -Warray-bounds 1435 -Warray-bounds=n 1436 This option is only active when -ftree-vrp is active (default for -O2 and above). It warns about subscripts to arrays that are always out of bounds. This warning is enabled by -Wall. 1437 -Warray-bounds=1 1438 This is the warning level of -Warray-bounds and is enabled by -Wall; higher levels are not, and must be explicitly requested. 1439 -Warray-bounds=2 1440 This warning level also warns about out of bounds access for arrays at the end of a struct and for arrays accessed through pointers. This warning level may give a larger number of false 1441 positives and is deactivated by default. 1442 -Wbool-compare 1443 Warn about boolean expression compared with an integer value different from "true"/"false". For instance, the following comparison is always false: 1444 int n = 5; 1445 ... 1446 if ((n > 1) == 2) { ... } 1447 This warning is enabled by -Wall. 1448 -Wno-discarded-qualifiers (C and Objective-C only) 1449 Do not warn if type qualifiers on pointers are being discarded. Typically, the compiler warns if a "const char *" variable is passed to a function that takes a "char *" parameter. This 1450 option can be used to suppress such a warning. 1451 -Wno-discarded-array-qualifiers (C and Objective-C only) 1452 Do not warn if type qualifiers on arrays which are pointer targets are being discarded. Typically, the compiler warns if a "const int (*)[]" variable is passed to a function that takes a 1453 "int (*)[]" parameter. This option can be used to suppress such a warning. 1454 -Wno-incompatible-pointer-types (C and Objective-C only) 1455 Do not warn when there is a conversion between pointers that have incompatible types. This warning is for cases not covered by -Wno-pointer-sign, which warns for pointer argument passing or 1456 assignment with different signedness. 1457 -Wno-int-conversion (C and Objective-C only) 1458 Do not warn about incompatible integer to pointer and pointer to integer conversions. This warning is about implicit conversions; for explicit conversions the warnings 1459 -Wno-int-to-pointer-cast and -Wno-pointer-to-int-cast may be used. 1460 -Wno-div-by-zero 1461 Do not warn about compile-time integer division by zero. Floating-point division by zero is not warned about, as it can be a legitimate way of obtaining infinities and NaNs. 1462 -Wsystem-headers 1463 Print warning messages for constructs found in system header files. Warnings from system headers are normally suppressed, on the assumption that they usually do not indicate real problems 1464 and would only make the compiler output harder to read. Using this command-line option tells GCC to emit warnings from system headers as if they occurred in user code. However, note that 1465 using -Wall in conjunction with this option does not warn about unknown pragmas in system headers---for that, -Wunknown-pragmas must also be used. 1466 -Wtrampolines 1467 Warn about trampolines generated for pointers to nested functions. A trampoline is a small piece of data or code that is created at run time on the stack when the address of a nested 1468 function is taken, and is used to call the nested function indirectly. For some targets, it is made up of data only and thus requires no special treatment. But, for most targets, it is 1469 made up of code and thus requires the stack to be made executable in order for the program to work properly. 1470 -Wfloat-equal 1471 Warn if floating-point values are used in equality comparisons. 1472 The idea behind this is that sometimes it is convenient (for the programmer) to consider floating-point values as approximations to infinitely precise real numbers. If you are doing this, 1473 then you need to compute (by analyzing the code, or in some other way) the maximum or likely maximum error that the computation introduces, and allow for it when performing comparisons (and 1474 when producing output, but that's a different problem). In particular, instead of testing for equality, you should check to see whether the two values have ranges that overlap; and this is 1475 done with the relational operators, so equality comparisons are probably mistaken. 1476 -Wtraditional (C and Objective-C only) 1477 Warn about certain constructs that behave differently in traditional and ISO C. Also warn about ISO C constructs that have no traditional C equivalent, and/or problematic constructs that 1478 should be avoided. 1479 * Macro parameters that appear within string literals in the macro body. In traditional C macro replacement takes place within string literals, but in ISO C it does not. 1480 * In traditional C, some preprocessor directives did not exist. Traditional preprocessors only considered a line to be a directive if the # appeared in column 1 on the line. Therefore 1481 -Wtraditional warns about directives that traditional C understands but ignores because the # does not appear as the first character on the line. It also suggests you hide directives 1482 like "#pragma" not understood by traditional C by indenting them. Some traditional implementations do not recognize "#elif", so this option suggests avoiding it altogether. 1483 * A function-like macro that appears without arguments. 1484 * The unary plus operator. 1485 * The U integer constant suffix, or the F or L floating-point constant suffixes. (Traditional C does support the L suffix on integer constants.) Note, these suffixes appear in macros 1486 defined in the system headers of most modern systems, e.g. the _MIN/_MAX macros in "". Use of these macros in user code might normally lead to spurious warnings, however GCC's 1487 integrated preprocessor has enough context to avoid warning in these cases. 1488 * A function declared external in one block and then used after the end of the block. 1489 * A "switch" statement has an operand of type "long". 1490 * A non-"static" function declaration follows a "static" one. This construct is not accepted by some traditional C compilers. 1491 * The ISO type of an integer constant has a different width or signedness from its traditional type. This warning is only issued if the base of the constant is ten. I.e. hexadecimal or 1492 octal values, which typically represent bit patterns, are not warned about. 1493 * Usage of ISO string concatenation is detected. 1494 * Initialization of automatic aggregates. 1495 * Identifier conflicts with labels. Traditional C lacks a separate namespace for labels. 1496 * Initialization of unions. If the initializer is zero, the warning is omitted. This is done under the assumption that the zero initializer in user code appears conditioned on e.g. 1497 "__STDC__" to avoid missing initializer warnings and relies on default initialization to zero in the traditional C case. 1498 * Conversions by prototypes between fixed/floating-point values and vice versa. The absence of these prototypes when compiling with traditional C causes serious problems. This is a 1499 subset of the possible conversion warnings; for the full set use -Wtraditional-conversion. 1500 * Use of ISO C style function definitions. This warning intentionally is not issued for prototype declarations or variadic functions because these ISO C features appear in your code when 1501 using libiberty's traditional C compatibility macros, "PARAMS" and "VPARAMS". This warning is also bypassed for nested functions because that feature is already a GCC extension and thus 1502 not relevant to traditional C compatibility. 1503 -Wtraditional-conversion (C and Objective-C only) 1504 Warn if a prototype causes a type conversion that is different from what would happen to the same argument in the absence of a prototype. This includes conversions of fixed point to 1505 floating and vice versa, and conversions changing the width or signedness of a fixed-point argument except when the same as the default promotion. 1506 -Wdeclaration-after-statement (C and Objective-C only) 1507 Warn when a declaration is found after a statement in a block. This construct, known from C++, was introduced with ISO C99 and is by default allowed in GCC. It is not supported by ISO C90. 1508 -Wundef 1509 Warn if an undefined identifier is evaluated in an "#if" directive. 1510 -Wno-endif-labels 1511 Do not warn whenever an "#else" or an "#endif" are followed by text. 1512 -Wshadow 1513 Warn whenever a local variable or type declaration shadows another variable, parameter, type, class member (in C++), or instance variable (in Objective-C) or whenever a built-in function is 1514 shadowed. Note that in C++, the compiler warns if a local variable shadows an explicit typedef, but not if it shadows a struct/class/enum. 1515 -Wno-shadow-ivar (Objective-C only) 1516 Do not warn whenever a local variable shadows an instance variable in an Objective-C method. 1517 -Wlarger-than=len 1518 Warn whenever an object of larger than len bytes is defined. 1519 -Wframe-larger-than=len 1520 Warn if the size of a function frame is larger than len bytes. The computation done to determine the stack frame size is approximate and not conservative. The actual requirements may be 1521 somewhat greater than len even if you do not get a warning. In addition, any space allocated via "alloca", variable-length arrays, or related constructs is not included by the compiler when 1522 determining whether or not to issue a warning. 1523 -Wno-free-nonheap-object 1524 Do not warn when attempting to free an object that was not allocated on the heap. 1525 -Wstack-usage=len 1526 Warn if the stack usage of a function might be larger than len bytes. The computation done to determine the stack usage is conservative. Any space allocated via "alloca", variable-length 1527 arrays, or related constructs is included by the compiler when determining whether or not to issue a warning. 1528 The message is in keeping with the output of -fstack-usage. 1529 * If the stack usage is fully static but exceeds the specified amount, it's: 1530 warning: stack usage is 1120 bytes 1531 * If the stack usage is (partly) dynamic but bounded, it's: 1532 warning: stack usage might be 1648 bytes 1533 * If the stack usage is (partly) dynamic and not bounded, it's: 1534 warning: stack usage might be unbounded 1535 -Wunsafe-loop-optimizations 1536 Warn if the loop cannot be optimized because the compiler cannot assume anything on the bounds of the loop indices. With -funsafe-loop-optimizations warn if the compiler makes such 1537 assumptions. 1538 -Wno-pedantic-ms-format (MinGW targets only) 1539 When used in combination with -Wformat and -pedantic without GNU extensions, this option disables the warnings about non-ISO "printf" / "scanf" format width specifiers "I32", "I64", and "I" 1540 used on Windows targets, which depend on the MS runtime. 1541 -Wpointer-arith 1542 Warn about anything that depends on the "size of" a function type or of "void". GNU C assigns these types a size of 1, for convenience in calculations with "void *" pointers and pointers to 1543 functions. In C++, warn also when an arithmetic operation involves "NULL". This warning is also enabled by -Wpedantic. 1544 -Wtype-limits 1545 Warn if a comparison is always true or always false due to the limited range of the data type, but do not warn for constant expressions. For example, warn if an unsigned variable is 1546 compared against zero with "<" or ">=". This warning is also enabled by -Wextra. 1547 -Wbad-function-cast (C and Objective-C only) 1548 Warn when a function call is cast to a non-matching type. For example, warn if a call to a function returning an integer type is cast to a pointer type. 1549 -Wc90-c99-compat (C and Objective-C only) 1550 Warn about features not present in ISO C90, but present in ISO C99. For instance, warn about use of variable length arrays, "long long" type, "bool" type, compound literals, designated 1551 initializers, and so on. This option is independent of the standards mode. Warnings are disabled in the expression that follows "__extension__". 1552 -Wc99-c11-compat (C and Objective-C only) 1553 Warn about features not present in ISO C99, but present in ISO C11. For instance, warn about use of anonymous structures and unions, "_Atomic" type qualifier, "_Thread_local" storage-class 1554 specifier, "_Alignas" specifier, "Alignof" operator, "_Generic" keyword, and so on. This option is independent of the standards mode. Warnings are disabled in the expression that follows 1555 "__extension__". 1556 -Wc++-compat (C and Objective-C only) 1557 Warn about ISO C constructs that are outside of the common subset of ISO C and ISO C++, e.g. request for implicit conversion from "void *" to a pointer to non-"void" type. 1558 -Wc++11-compat (C++ and Objective-C++ only) 1559 Warn about C++ constructs whose meaning differs between ISO C++ 1998 and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are keywords in ISO C++ 2011. This warning turns on -Wnarrowing 1560 and is enabled by -Wall. 1561 -Wc++14-compat (C++ and Objective-C++ only) 1562 Warn about C++ constructs whose meaning differs between ISO C++ 2011 and ISO C++ 2014. This warning is enabled by -Wall. 1563 -Wcast-qual 1564 Warn whenever a pointer is cast so as to remove a type qualifier from the target type. For example, warn if a "const char *" is cast to an ordinary "char *". 1565 Also warn when making a cast that introduces a type qualifier in an unsafe way. For example, casting "char **" to "const char **" is unsafe, as in this example: 1566 /* p is char ** value. */ 1567 const char **q = (const char **) p; 1568 /* Assignment of readonly string to const char * is OK. */ 1569 *q = "string"; 1570 /* Now char** pointer points to read-only memory. */ 1571 **p = 'b'; 1572 -Wcast-align 1573 Warn whenever a pointer is cast such that the required alignment of the target is increased. For example, warn if a "char *" is cast to an "int *" on machines where integers can only be 1574 accessed at two- or four-byte boundaries. 1575 -Wwrite-strings 1576 When compiling C, give string constants the type "const char[length]" so that copying the address of one into a non-"const" "char *" pointer produces a warning. These warnings help you find 1577 at compile time code that can try to write into a string constant, but only if you have been very careful about using "const" in declarations and prototypes. Otherwise, it is just a 1578 nuisance. This is why we did not make -Wall request these warnings. 1579 When compiling C++, warn about the deprecated conversion from string literals to "char *". This warning is enabled by default for C++ programs. 1580 -Wclobbered 1581 Warn for variables that might be changed by "longjmp" or "vfork". This warning is also enabled by -Wextra. 1582 -Wconditionally-supported (C++ and Objective-C++ only) 1583 Warn for conditionally-supported (C++11 [intro.defs]) constructs. 1584 -Wconversion 1585 Warn for implicit conversions that may alter a value. This includes conversions between real and integer, like "abs (x)" when "x" is "double"; conversions between signed and unsigned, like 1586 "unsigned ui = -1"; and conversions to smaller types, like "sqrtf (M_PI)". Do not warn for explicit casts like "abs ((int) x)" and "ui = (unsigned) -1", or if the value is not changed by the 1587 conversion like in "abs (2.0)". Warnings about conversions between signed and unsigned integers can be disabled by using -Wno-sign-conversion. 1588 For C++, also warn for confusing overload resolution for user-defined conversions; and conversions that never use a type conversion operator: conversions to "void", the same type, a base 1589 class or a reference to them. Warnings about conversions between signed and unsigned integers are disabled by default in C++ unless -Wsign-conversion is explicitly enabled. 1590 -Wno-conversion-null (C++ and Objective-C++ only) 1591 Do not warn for conversions between "NULL" and non-pointer types. -Wconversion-null is enabled by default. 1592 -Wzero-as-null-pointer-constant (C++ and Objective-C++ only) 1593 Warn when a literal '0' is used as null pointer constant. This can be useful to facilitate the conversion to "nullptr" in C++11. 1594 -Wdate-time 1595 Warn when macros "__TIME__", "__DATE__" or "__TIMESTAMP__" are encountered as they might prevent bit-wise-identical reproducible compilations. 1596 -Wdelete-incomplete (C++ and Objective-C++ only) 1597 Warn when deleting a pointer to incomplete type, which may cause undefined behavior at runtime. This warning is enabled by default. 1598 -Wuseless-cast (C++ and Objective-C++ only) 1599 Warn when an expression is casted to its own type. 1600 -Wempty-body 1601 Warn if an empty body occurs in an "if", "else" or "do while" statement. This warning is also enabled by -Wextra. 1602 -Wenum-compare 1603 Warn about a comparison between values of different enumerated types. In C++ enumeral mismatches in conditional expressions are also diagnosed and the warning is enabled by default. In C 1604 this warning is enabled by -Wall. 1605 -Wjump-misses-init (C, Objective-C only) 1606 Warn if a "goto" statement or a "switch" statement jumps forward across the initialization of a variable, or jumps backward to a label after the variable has been initialized. This only 1607 warns about variables that are initialized when they are declared. This warning is only supported for C and Objective-C; in C++ this sort of branch is an error in any case. 1608 -Wjump-misses-init is included in -Wc++-compat. It can be disabled with the -Wno-jump-misses-init option. 1609 -Wsign-compare 1610 Warn when a comparison between signed and unsigned values could produce an incorrect result when the signed value is converted to unsigned. This warning is also enabled by -Wextra; to get 1611 the other warnings of -Wextra without this warning, use -Wextra -Wno-sign-compare. 1612 -Wsign-conversion 1613 Warn for implicit conversions that may change the sign of an integer value, like assigning a signed integer expression to an unsigned integer variable. An explicit cast silences the warning. 1614 In C, this option is enabled also by -Wconversion. 1615 -Wfloat-conversion 1616 Warn for implicit conversions that reduce the precision of a real value. This includes conversions from real to integer, and from higher precision real to lower precision real values. This 1617 option is also enabled by -Wconversion. 1618 -Wsized-deallocation (C++ and Objective-C++ only) 1619 Warn about a definition of an unsized deallocation function 1620 void operator delete (void *) noexcept; 1621 void operator delete[] (void *) noexcept; 1622 without a definition of the corresponding sized deallocation function 1623 void operator delete (void *, std::size_t) noexcept; 1624 void operator delete[] (void *, std::size_t) noexcept; 1625 or vice versa. Enabled by -Wextra along with -fsized-deallocation. 1626 -Wsizeof-pointer-memaccess 1627 Warn for suspicious length parameters to certain string and memory built-in functions if the argument uses "sizeof". This warning warns e.g. about "memset (ptr, 0, sizeof (ptr));" if "ptr" 1628 is not an array, but a pointer, and suggests a possible fix, or about "memcpy (&foo, ptr, sizeof (&foo));". This warning is enabled by -Wall. 1629 -Wsizeof-array-argument 1630 Warn when the "sizeof" operator is applied to a parameter that is declared as an array in a function definition. This warning is enabled by default for C and C++ programs. 1631 -Wmemset-transposed-args 1632 Warn for suspicious calls to the "memset" built-in function, if the second argument is not zero and the third argument is zero. This warns e.g.@ about "memset (buf, sizeof buf, 0)" where 1633 most probably "memset (buf, 0, sizeof buf)" was meant instead. The diagnostics is only emitted if the third argument is literal zero. If it is some expression that is folded to zero, a 1634 cast of zero to some type, etc., it is far less likely that the user has mistakenly exchanged the arguments and no warning is emitted. This warning is enabled by -Wall. 1635 -Waddress 1636 Warn about suspicious uses of memory addresses. These include using the address of a function in a conditional expression, such as "void func(void); if (func)", and comparisons against the 1637 memory address of a string literal, such as "if (x == "abc")". Such uses typically indicate a programmer error: the address of a function always evaluates to true, so their use in a 1638 conditional usually indicate that the programmer forgot the parentheses in a function call; and comparisons against string literals result in unspecified behavior and are not portable in C, 1639 so they usually indicate that the programmer intended to use "strcmp". This warning is enabled by -Wall. 1640 -Wlogical-op 1641 Warn about suspicious uses of logical operators in expressions. This includes using logical operators in contexts where a bit-wise operator is likely to be expected. 1642 -Wlogical-not-parentheses 1643 Warn about logical not used on the left hand side operand of a comparison. This option does not warn if the RHS operand is of a boolean type. Its purpose is to detect suspicious code like 1644 the following: 1645 int a; 1646 ... 1647 if (!a > 1) { ... } 1648 It is possible to suppress the warning by wrapping the LHS into parentheses: 1649 if ((!a) > 1) { ... } 1650 This warning is enabled by -Wall. 1651 -Waggregate-return 1652 Warn if any functions that return structures or unions are defined or called. (In languages where you can return an array, this also elicits a warning.) 1653 -Wno-aggressive-loop-optimizations 1654 Warn if in a loop with constant number of iterations the compiler detects undefined behavior in some statement during one or more of the iterations. 1655 -Wno-attributes 1656 Do not warn if an unexpected "__attribute__" is used, such as unrecognized attributes, function attributes applied to variables, etc. This does not stop errors for incorrect use of 1657 supported attributes. 1658 -Wno-builtin-macro-redefined 1659 Do not warn if certain built-in macros are redefined. This suppresses warnings for redefinition of "__TIMESTAMP__", "__TIME__", "__DATE__", "__FILE__", and "__BASE_FILE__". 1660 -Wstrict-prototypes (C and Objective-C only) 1661 Warn if a function is declared or defined without specifying the argument types. (An old-style function definition is permitted without a warning if preceded by a declaration that specifies 1662 the argument types.) 1663 -Wold-style-declaration (C and Objective-C only) 1664 Warn for obsolescent usages, according to the C Standard, in a declaration. For example, warn if storage-class specifiers like "static" are not the first things in a declaration. This 1665 warning is also enabled by -Wextra. 1666 -Wold-style-definition (C and Objective-C only) 1667 Warn if an old-style function definition is used. A warning is given even if there is a previous prototype. 1668 -Wmissing-parameter-type (C and Objective-C only) 1669 A function parameter is declared without a type specifier in K&R-style functions: 1670 void foo(bar) { } 1671 This warning is also enabled by -Wextra. 1672 -Wmissing-prototypes (C and Objective-C only) 1673 Warn if a global function is defined without a previous prototype declaration. This warning is issued even if the definition itself provides a prototype. Use this option to detect global 1674 functions that do not have a matching prototype declaration in a header file. This option is not valid for C++ because all function declarations provide prototypes and a non-matching 1675 declaration declares an overload rather than conflict with an earlier declaration. Use -Wmissing-declarations to detect missing declarations in C++. 1676 -Wmissing-declarations 1677 Warn if a global function is defined without a previous declaration. Do so even if the definition itself provides a prototype. Use this option to detect global functions that are not 1678 declared in header files. In C, no warnings are issued for functions with previous non-prototype declarations; use -Wmissing-prototypes to detect missing prototypes. In C++, no warnings 1679 are issued for function templates, or for inline functions, or for functions in anonymous namespaces. 1680 -Wmissing-field-initializers 1681 Warn if a structure's initializer has some fields missing. For example, the following code causes such a warning, because "x.h" is implicitly zero: 1682 struct s { int f, g, h; }; 1683 struct s x = { 3, 4 }; 1684 This option does not warn about designated initializers, so the following modification does not trigger a warning: 1685 struct s { int f, g, h; }; 1686 struct s x = { .f = 3, .g = 4 }; 1687 In C++ this option does not warn either about the empty { } initializer, for example: 1688 struct s { int f, g, h; }; 1689 s x = { }; 1690 This warning is included in -Wextra. To get other -Wextra warnings without this one, use -Wextra -Wno-missing-field-initializers. 1691 -Wno-multichar 1692 Do not warn if a multicharacter constant ('FOOF') is used. Usually they indicate a typo in the user's code, as they have implementation-defined values, and should not be used in portable 1693 code. 1694 -Wnormalized[=] 1695 In ISO C and ISO C++, two identifiers are different if they are different sequences of characters. However, sometimes when characters outside the basic ASCII character set are used, you can 1696 have two different character sequences that look the same. To avoid confusion, the ISO 10646 standard sets out some normalization rules which when applied ensure that two sequences that 1697 look the same are turned into the same sequence. GCC can warn you if you are using identifiers that have not been normalized; this option controls that warning. 1698 There are four levels of warning supported by GCC. The default is -Wnormalized=nfc, which warns about any identifier that is not in the ISO 10646 "C" normalized form, NFC. NFC is the 1699 recommended form for most uses. It is equivalent to -Wnormalized. 1700 Unfortunately, there are some characters allowed in identifiers by ISO C and ISO C++ that, when turned into NFC, are not allowed in identifiers. That is, there's no way to use these symbols 1701 in portable ISO C or C++ and have all your identifiers in NFC. -Wnormalized=id suppresses the warning for these characters. It is hoped that future versions of the standards involved will 1702 correct this, which is why this option is not the default. 1703 You can switch the warning off for all characters by writing -Wnormalized=none or -Wno-normalized. You should only do this if you are using some other normalization scheme (like "D"), 1704 because otherwise you can easily create bugs that are literally impossible to see. 1705 Some characters in ISO 10646 have distinct meanings but look identical in some fonts or display methodologies, especially once formatting has been applied. For instance "\u207F", 1706 "SUPERSCRIPT LATIN SMALL LETTER N", displays just like a regular "n" that has been placed in a superscript. ISO 10646 defines the NFKC normalization scheme to convert all these into a 1707 standard form as well, and GCC warns if your code is not in NFKC if you use -Wnormalized=nfkc. This warning is comparable to warning about every identifier that contains the letter O 1708 because it might be confused with the digit 0, and so is not the default, but may be useful as a local coding convention if the programming environment cannot be fixed to display these 1709 characters distinctly. 1710 -Wno-deprecated 1711 Do not warn about usage of deprecated features. 1712 -Wno-deprecated-declarations 1713 Do not warn about uses of functions, variables, and types marked as deprecated by using the "deprecated" attribute. 1714 -Wno-overflow 1715 Do not warn about compile-time overflow in constant expressions. 1716 -Wno-odr 1717 Warn about One Definition Rule violations during link-time optimization. Requires -flto-odr-type-merging to be enabled. Enabled by default. 1718 -Wopenmp-simd 1719 Warn if the vectorizer cost model overrides the OpenMP or the Cilk Plus simd directive set by user. The -fsimd-cost-model=unlimited option can be used to relax the cost model. 1720 -Woverride-init (C and Objective-C only) 1721 Warn if an initialized field without side effects is overridden when using designated initializers. 1722 This warning is included in -Wextra. To get other -Wextra warnings without this one, use -Wextra -Wno-override-init. 1723 -Wpacked 1724 Warn if a structure is given the packed attribute, but the packed attribute has no effect on the layout or size of the structure. Such structures may be mis-aligned for little benefit. For 1725 instance, in this code, the variable "f.x" in "struct bar" is misaligned even though "struct bar" does not itself have the packed attribute: 1726 struct foo { 1727 int x; 1728 char a, b, c, d; 1729 } __attribute__((packed)); 1730 struct bar { 1731 char z; 1732 struct foo f; 1733 }; 1734 -Wpacked-bitfield-compat 1735 The 4.1, 4.2 and 4.3 series of GCC ignore the "packed" attribute on bit-fields of type "char". This has been fixed in GCC 4.4 but the change can lead to differences in the structure layout. 1736 GCC informs you when the offset of such a field has changed in GCC 4.4. For example there is no longer a 4-bit padding between field "a" and "b" in this structure: 1737 struct foo 1738 { 1739 char a:4; 1740 char b:8; 1741 } __attribute__ ((packed)); 1742 This warning is enabled by default. Use -Wno-packed-bitfield-compat to disable this warning. 1743 -Wpadded 1744 Warn if padding is included in a structure, either to align an element of the structure or to align the whole structure. Sometimes when this happens it is possible to rearrange the fields 1745 of the structure to reduce the padding and so make the structure smaller. 1746 -Wredundant-decls 1747 Warn if anything is declared more than once in the same scope, even in cases where multiple declaration is valid and changes nothing. 1748 -Wnested-externs (C and Objective-C only) 1749 Warn if an "extern" declaration is encountered within a function. 1750 -Wno-inherited-variadic-ctor 1751 Suppress warnings about use of C++11 inheriting constructors when the base class inherited from has a C variadic constructor; the warning is on by default because the ellipsis is not 1752 inherited. 1753 -Winline 1754 Warn if a function that is declared as inline cannot be inlined. Even with this option, the compiler does not warn about failures to inline functions declared in system headers. 1755 The compiler uses a variety of heuristics to determine whether or not to inline a function. For example, the compiler takes into account the size of the function being inlined and the 1756 amount of inlining that has already been done in the current function. Therefore, seemingly insignificant changes in the source program can cause the warnings produced by -Winline to appear 1757 or disappear. 1758 -Wno-invalid-offsetof (C++ and Objective-C++ only) 1759 Suppress warnings from applying the "offsetof" macro to a non-POD type. According to the 2014 ISO C++ standard, applying "offsetof" to a non-standard-layout type is undefined. In existing 1760 C++ implementations, however, "offsetof" typically gives meaningful results. This flag is for users who are aware that they are writing nonportable code and who have deliberately chosen to 1761 ignore the warning about it. 1762 The restrictions on "offsetof" may be relaxed in a future version of the C++ standard. 1763 -Wno-int-to-pointer-cast 1764 Suppress warnings from casts to pointer type of an integer of a different size. In C++, casting to a pointer type of smaller size is an error. Wint-to-pointer-cast is enabled by default. 1765 -Wno-pointer-to-int-cast (C and Objective-C only) 1766 Suppress warnings from casts from a pointer to an integer type of a different size. 1767 -Winvalid-pch 1768 Warn if a precompiled header is found in the search path but can't be used. 1769 -Wlong-long 1770 Warn if "long long" type is used. This is enabled by either -Wpedantic or -Wtraditional in ISO C90 and C++98 modes. To inhibit the warning messages, use -Wno-long-long. 1771 -Wvariadic-macros 1772 Warn if variadic macros are used in ISO C90 mode, or if the GNU alternate syntax is used in ISO C99 mode. This is enabled by either -Wpedantic or -Wtraditional. To inhibit the warning 1773 messages, use -Wno-variadic-macros. 1774 -Wvarargs 1775 Warn upon questionable usage of the macros used to handle variable arguments like "va_start". This is default. To inhibit the warning messages, use -Wno-varargs. 1776 -Wvector-operation-performance 1777 Warn if vector operation is not implemented via SIMD capabilities of the architecture. Mainly useful for the performance tuning. Vector operation can be implemented "piecewise", which 1778 means that the scalar operation is performed on every vector element; "in parallel", which means that the vector operation is implemented using scalars of wider type, which normally is more 1779 performance efficient; and "as a single scalar", which means that vector fits into a scalar type. 1780 -Wno-virtual-move-assign 1781 Suppress warnings about inheriting from a virtual base with a non-trivial C++11 move assignment operator. This is dangerous because if the virtual base is reachable along more than one 1782 path, it is moved multiple times, which can mean both objects end up in the moved-from state. If the move assignment operator is written to avoid moving from a moved-from object, this 1783 warning can be disabled. 1784 -Wvla 1785 Warn if variable length array is used in the code. -Wno-vla prevents the -Wpedantic warning of the variable length array. 1786 -Wvolatile-register-var 1787 Warn if a register variable is declared volatile. The volatile modifier does not inhibit all optimizations that may eliminate reads and/or writes to register variables. This warning is 1788 enabled by -Wall. 1789 -Wdisabled-optimization 1790 Warn if a requested optimization pass is disabled. This warning does not generally indicate that there is anything wrong with your code; it merely indicates that GCC's optimizers are unable 1791 to handle the code effectively. Often, the problem is that your code is too big or too complex; GCC refuses to optimize programs when the optimization itself is likely to take inordinate 1792 amounts of time. 1793 -Wpointer-sign (C and Objective-C only) 1794 Warn for pointer argument passing or assignment with different signedness. This option is only supported for C and Objective-C. It is implied by -Wall and by -Wpedantic, which can be 1795 disabled with -Wno-pointer-sign. 1796 -Wstack-protector 1797 This option is only active when -fstack-protector is active. It warns about functions that are not protected against stack smashing. 1798 -Woverlength-strings 1799 Warn about string constants that are longer than the "minimum maximum" length specified in the C standard. Modern compilers generally allow string constants that are much longer than the 1800 standard's minimum limit, but very portable programs should avoid using longer strings. 1801 The limit applies after string constant concatenation, and does not count the trailing NUL. In C90, the limit was 509 characters; in C99, it was raised to 4095. C++98 does not specify a 1802 normative minimum maximum, so we do not diagnose overlength strings in C++. 1803 This option is implied by -Wpedantic, and can be disabled with -Wno-overlength-strings. 1804 -Wunsuffixed-float-constants (C and Objective-C only) 1805 Issue a warning for any floating constant that does not have a suffix. When used together with -Wsystem-headers it warns about such constants in system header files. This can be useful 1806 when preparing code to use with the "FLOAT_CONST_DECIMAL64" pragma from the decimal floating-point extension to C99. 1807 -Wno-designated-init (C and Objective-C only) 1808 Suppress warnings when a positional initializer is used to initialize a structure that has been marked with the "designated_init" attribute. 1809 Options for Debugging Your Program or GCC 1810 GCC has various special options that are used for debugging either your program or GCC: 1811 -g Produce debugging information in the operating system's native format (stabs, COFF, XCOFF, or DWARF 2). GDB can work with this debugging information. 1812 On most systems that use stabs format, -g enables use of extra debugging information that only GDB can use; this extra information makes debugging work better in GDB but probably makes other 1813 debuggers crash or refuse to read the program. If you want to control for certain whether to generate the extra information, use -gstabs+, -gstabs, -gxcoff+, -gxcoff, or -gvms (see below). 1814 GCC allows you to use -g with -O. The shortcuts taken by optimized code may occasionally produce surprising results: some variables you declared may not exist at all; flow of control may 1815 briefly move where you did not expect it; some statements may not be executed because they compute constant results or their values are already at hand; some statements may execute in 1816 different places because they have been moved out of loops. 1817 Nevertheless it proves possible to debug optimized output. This makes it reasonable to use the optimizer for programs that might have bugs. 1818 The following options are useful when GCC is generated with the capability for more than one debugging format. 1819 -gsplit-dwarf 1820 Separate as much dwarf debugging information as possible into a separate output file with the extension .dwo. This option allows the build system to avoid linking files with debug 1821 information. To be useful, this option requires a debugger capable of reading .dwo files. 1822 -ggdb 1823 Produce debugging information for use by GDB. This means to use the most expressive format available (DWARF 2, stabs, or the native format if neither of those are supported), including GDB 1824 extensions if at all possible. 1825 -gpubnames 1826 Generate dwarf .debug_pubnames and .debug_pubtypes sections. 1827 -ggnu-pubnames 1828 Generate .debug_pubnames and .debug_pubtypes sections in a format suitable for conversion into a GDB index. This option is only useful with a linker that can produce GDB index version 7. 1829 -gstabs 1830 Produce debugging information in stabs format (if that is supported), without GDB extensions. This is the format used by DBX on most BSD systems. On MIPS, Alpha and System V Release 4 1831 systems this option produces stabs debugging output that is not understood by DBX or SDB. On System V Release 4 systems this option requires the GNU assembler. 1832 -feliminate-unused-debug-symbols 1833 Produce debugging information in stabs format (if that is supported), for only symbols that are actually used. 1834 -femit-class-debug-always 1835 Instead of emitting debugging information for a C++ class in only one object file, emit it in all object files using the class. This option should be used only with debuggers that are 1836 unable to handle the way GCC normally emits debugging information for classes because using this option increases the size of debugging information by as much as a factor of two. 1837 -fdebug-types-section 1838 When using DWARF Version 4 or higher, type DIEs can be put into their own ".debug_types" section instead of making them part of the ".debug_info" section. It is more efficient to put them 1839 in a separate comdat sections since the linker can then remove duplicates. But not all DWARF consumers support ".debug_types" sections yet and on some objects ".debug_types" produces larger 1840 instead of smaller debugging information. 1841 -gstabs+ 1842 Produce debugging information in stabs format (if that is supported), using GNU extensions understood only by the GNU debugger (GDB). The use of these extensions is likely to make other 1843 debuggers crash or refuse to read the program. 1844 -gcoff 1845 Produce debugging information in COFF format (if that is supported). This is the format used by SDB on most System V systems prior to System V Release 4. 1846 -gxcoff 1847 Produce debugging information in XCOFF format (if that is supported). This is the format used by the DBX debugger on IBM RS/6000 systems. 1848 -gxcoff+ 1849 Produce debugging information in XCOFF format (if that is supported), using GNU extensions understood only by the GNU debugger (GDB). The use of these extensions is likely to make other 1850 debuggers crash or refuse to read the program, and may cause assemblers other than the GNU assembler (GAS) to fail with an error. 1851 -gdwarf-version 1852 Produce debugging information in DWARF format (if that is supported). The value of version may be either 2, 3, 4 or 5; the default version for most targets is 4. DWARF Version 5 is only 1853 experimental. 1854 Note that with DWARF Version 2, some ports require and always use some non-conflicting DWARF 3 extensions in the unwind tables. 1855 Version 4 may require GDB 7.0 and -fvar-tracking-assignments for maximum benefit. 1856 -grecord-gcc-switches 1857 This switch causes the command-line options used to invoke the compiler that may affect code generation to be appended to the DW_AT_producer attribute in DWARF debugging information. The 1858 options are concatenated with spaces separating them from each other and from the compiler version. See also -frecord-gcc-switches for another way of storing compiler options into the 1859 object file. This is the default. 1860 -gno-record-gcc-switches 1861 Disallow appending command-line options to the DW_AT_producer attribute in DWARF debugging information. 1862 -gstrict-dwarf 1863 Disallow using extensions of later DWARF standard version than selected with -gdwarf-version. On most targets using non-conflicting DWARF extensions from later standard versions is allowed. 1864 -gno-strict-dwarf 1865 Allow using extensions of later DWARF standard version than selected with -gdwarf-version. 1866 -gz[=type] 1867 Produce compressed debug sections in DWARF format, if that is supported. If type is not given, the default type depends on the capabilities of the assembler and linker used. type may be 1868 one of none (don't compress debug sections), zlib (use zlib compression in ELF gABI format), or zlib-gnu (use zlib compression in traditional GNU format). If the linker doesn't support 1869 writing compressed debug sections, the option is rejected. Otherwise, if the assembler does not support them, -gz is silently ignored when producing object files. 1870 -gvms 1871 Produce debugging information in Alpha/VMS debug format (if that is supported). This is the format used by DEBUG on Alpha/VMS systems. 1872 -glevel 1873 -ggdblevel 1874 -gstabslevel 1875 -gcofflevel 1876 -gxcofflevel 1877 -gvmslevel 1878 Request debugging information and also use level to specify how much information. The default level is 2. 1879 Level 0 produces no debug information at all. Thus, -g0 negates -g. 1880 Level 1 produces minimal information, enough for making backtraces in parts of the program that you don't plan to debug. This includes descriptions of functions and external variables, and 1881 line number tables, but no information about local variables. 1882 Level 3 includes extra information, such as all the macro definitions present in the program. Some debuggers support macro expansion when you use -g3. 1883 -gdwarf-2 does not accept a concatenated debug level, because GCC used to support an option -gdwarf that meant to generate debug information in version 1 of the DWARF format (which is very 1884 different from version 2), and it would have been too confusing. That debug format is long obsolete, but the option cannot be changed now. Instead use an additional -glevel option to 1885 change the debug level for DWARF. 1886 -gtoggle 1887 Turn off generation of debug info, if leaving out this option generates it, or turn it on at level 2 otherwise. The position of this argument in the command line does not matter; it takes 1888 effect after all other options are processed, and it does so only once, no matter how many times it is given. This is mainly intended to be used with -fcompare-debug. 1889 -fsanitize=address 1890 Enable AddressSanitizer, a fast memory error detector. Memory access instructions are instrumented to detect out-of-bounds and use-after-free bugs. See 1891 for more details. The run-time behavior can be influenced using the ASAN_OPTIONS environment variable; see 1892 for a list of supported options. 1893 -fsanitize=kernel-address 1894 Enable AddressSanitizer for Linux kernel. See for more details. 1895 -fsanitize=thread 1896 Enable ThreadSanitizer, a fast data race detector. Memory access instructions are instrumented to detect data race bugs. See for more details. 1897 The run-time behavior can be influenced using the TSAN_OPTIONS environment variable; see for a list of supported options. 1898 -fsanitize=leak 1899 Enable LeakSanitizer, a memory leak detector. This option only matters for linking of executables and if neither -fsanitize=address nor -fsanitize=thread is used. In that case the 1900 executable is linked against a library that overrides "malloc" and other allocator functions. See for more details. The 1901 run-time behavior can be influenced using the LSAN_OPTIONS environment variable. 1902 -fsanitize=undefined 1903 Enable UndefinedBehaviorSanitizer, a fast undefined behavior detector. Various computations are instrumented to detect undefined behavior at runtime. Current suboptions are: 1904 -fsanitize=shift 1905 This option enables checking that the result of a shift operation is not undefined. Note that what exactly is considered undefined differs slightly between C and C++, as well as between 1906 ISO C90 and C99, etc. 1907 -fsanitize=integer-divide-by-zero 1908 Detect integer division by zero as well as "INT_MIN / -1" division. 1909 -fsanitize=unreachable 1910 With this option, the compiler turns the "__builtin_unreachable" call into a diagnostics message call instead. When reaching the "__builtin_unreachable" call, the behavior is undefined. 1911 -fsanitize=vla-bound 1912 This option instructs the compiler to check that the size of a variable length array is positive. 1913 -fsanitize=null 1914 This option enables pointer checking. Particularly, the application built with this option turned on will issue an error message when it tries to dereference a NULL pointer, or if a 1915 reference (possibly an rvalue reference) is bound to a NULL pointer, or if a method is invoked on an object pointed by a NULL pointer. 1916 -fsanitize=return 1917 This option enables return statement checking. Programs built with this option turned on will issue an error message when the end of a non-void function is reached without actually 1918 returning a value. This option works in C++ only. 1919 -fsanitize=signed-integer-overflow 1920 This option enables signed integer overflow checking. We check that the result of "+", "*", and both unary and binary "-" does not overflow in the signed arithmetics. Note, integer 1921 promotion rules must be taken into account. That is, the following is not an overflow: 1922 signed char a = SCHAR_MAX; 1923 a++; 1924 -fsanitize=bounds 1925 This option enables instrumentation of array bounds. Various out of bounds accesses are detected. Flexible array members, flexible array member-like arrays, and initializers of 1926 variables with static storage are not instrumented. 1927 -fsanitize=alignment 1928 This option enables checking of alignment of pointers when they are dereferenced, or when a reference is bound to insufficiently aligned target, or when a method or constructor is 1929 invoked on insufficiently aligned object. 1930 -fsanitize=object-size 1931 This option enables instrumentation of memory references using the "__builtin_object_size" function. Various out of bounds pointer accesses are detected. 1932 -fsanitize=float-divide-by-zero 1933 Detect floating-point division by zero. Unlike other similar options, -fsanitize=float-divide-by-zero is not enabled by -fsanitize=undefined, since floating-point division by zero can 1934 be a legitimate way of obtaining infinities and NaNs. 1935 -fsanitize=float-cast-overflow 1936 This option enables floating-point type to integer conversion checking. We check that the result of the conversion does not overflow. Unlike other similar options, 1937 -fsanitize=float-cast-overflow is not enabled by -fsanitize=undefined. This option does not work well with "FE_INVALID" exceptions enabled. 1938 -fsanitize=nonnull-attribute 1939 This option enables instrumentation of calls, checking whether null values are not passed to arguments marked as requiring a non-null value by the "nonnull" function attribute. 1940 -fsanitize=returns-nonnull-attribute 1941 This option enables instrumentation of return statements in functions marked with "returns_nonnull" function attribute, to detect returning of null values from such functions. 1942 -fsanitize=bool 1943 This option enables instrumentation of loads from bool. If a value other than 0/1 is loaded, a run-time error is issued. 1944 -fsanitize=enum 1945 This option enables instrumentation of loads from an enum type. If a value outside the range of values for the enum type is loaded, a run-time error is issued. 1946 -fsanitize=vptr 1947 This option enables instrumentation of C++ member function calls, member accesses and some conversions between pointers to base and derived classes, to verify the referenced object has 1948 the correct dynamic type. 1949 While -ftrapv causes traps for signed overflows to be emitted, -fsanitize=undefined gives a diagnostic message. This currently works only for the C family of languages. 1950 -fno-sanitize=all 1951 This option disables all previously enabled sanitizers. -fsanitize=all is not allowed, as some sanitizers cannot be used together. 1952 -fasan-shadow-offset=number 1953 This option forces GCC to use custom shadow offset in AddressSanitizer checks. It is useful for experimenting with different shadow memory layouts in Kernel AddressSanitizer. 1954 -fsanitize-recover[=opts] 1955 -fsanitize-recover= controls error recovery mode for sanitizers mentioned in comma-separated list of opts. Enabling this option for a sanitizer component causes it to attempt to continue 1956 running the program as if no error happened. This means multiple runtime errors can be reported in a single program run, and the exit code of the program may indicate success even when 1957 errors have been reported. The -fno-sanitize-recover= option can be used to alter this behavior: only the first detected error is reported and program then exits with a non-zero exit code. 1958 Currently this feature only works for -fsanitize=undefined (and its suboptions except for -fsanitize=unreachable and -fsanitize=return), -fsanitize=float-cast-overflow, 1959 -fsanitize=float-divide-by-zero and -fsanitize=kernel-address. For these sanitizers error recovery is turned on by default. -fsanitize-recover=all and -fno-sanitize-recover=all is also 1960 accepted, the former enables recovery for all sanitizers that support it, the latter disables recovery for all sanitizers that support it. 1961 Syntax without explicit opts parameter is deprecated. It is equivalent to 1962 -fsanitize-recover=undefined,float-cast-overflow,float-divide-by-zero 1963 Similarly -fno-sanitize-recover is equivalent to 1964 -fno-sanitize-recover=undefined,float-cast-overflow,float-divide-by-zero 1965 -fsanitize-undefined-trap-on-error 1966 The -fsanitize-undefined-trap-on-error option instructs the compiler to report undefined behavior using "__builtin_trap" rather than a "libubsan" library routine. The advantage of this is 1967 that the "libubsan" library is not needed and is not linked in, so this is usable even in freestanding environments. 1968 -fcheck-pointer-bounds 1969 Enable Pointer Bounds Checker instrumentation. Each memory reference is instrumented with checks of the pointer used for memory access against bounds associated with that pointer. 1970 Currently there is only an implementation for Intel MPX available, thus x86 target and -mmpx are required to enable this feature. MPX-based instrumentation requires a runtime library to 1971 enable MPX in hardware and handle bounds violation signals. By default when -fcheck-pointer-bounds and -mmpx options are used to link a program, the GCC driver links against the libmpx 1972 runtime library and libmpxwrappers library. It also passes '-z bndplt' to a linker in case it supports this option (which is checked on libmpx configuration). Note that old versions of 1973 linker may ignore option. Gold linker doesn't support '-z bndplt' option. With no '-z bndplt' support in linker all calls to dynamic libraries lose passed bounds reducing overall 1974 protection level. It's highly recommended to use linker with '-z bndplt' support. In case such linker is not available it is adviced to always use -static-libmpxwrappers for better 1975 protection level or use -static to completely avoid external calls to dynamic libraries. MPX-based instrumentation may be used for debugging and also may be included in production code to 1976 increase program security. Depending on usage, you may have different requirements for the runtime library. The current version of the MPX runtime library is more oriented for use as a 1977 debugging tool. MPX runtime library usage implies -lpthread. See also -static-libmpx. The runtime library behavior can be influenced using various CHKP_RT_* environment variables. See 1978 for more details. 1979 Generated instrumentation may be controlled by various -fchkp-* options and by the "bnd_variable_size" structure field attribute and "bnd_legacy", and "bnd_instrument" function attributes. 1980 GCC also provides a number of built-in functions for controlling the Pointer Bounds Checker. 1981 -fchkp-check-incomplete-type 1982 Generate pointer bounds checks for variables with incomplete type. Enabled by default. 1983 -fchkp-narrow-bounds 1984 Controls bounds used by Pointer Bounds Checker for pointers to object fields. If narrowing is enabled then field bounds are used. Otherwise object bounds are used. See also 1985 -fchkp-narrow-to-innermost-array and -fchkp-first-field-has-own-bounds. Enabled by default. 1986 -fchkp-first-field-has-own-bounds 1987 Forces Pointer Bounds Checker to use narrowed bounds for the address of the first field in the structure. By default a pointer to the first field has the same bounds as a pointer to the 1988 whole structure. 1989 -fchkp-narrow-to-innermost-array 1990 Forces Pointer Bounds Checker to use bounds of the innermost arrays in case of nested static array access. By default this option is disabled and bounds of the outermost array are used. 1991 -fchkp-optimize 1992 Enables Pointer Bounds Checker optimizations. Enabled by default at optimization levels -O, -O2, -O3. 1993 -fchkp-use-fast-string-functions 1994 Enables use of *_nobnd versions of string functions (not copying bounds) by Pointer Bounds Checker. Disabled by default. 1995 -fchkp-use-nochk-string-functions 1996 Enables use of *_nochk versions of string functions (not checking bounds) by Pointer Bounds Checker. Disabled by default. 1997 -fchkp-use-static-bounds 1998 Allow Pointer Bounds Checker to generate static bounds holding bounds of static variables. Enabled by default. 1999 -fchkp-use-static-const-bounds 2000 Use statically-initialized bounds for constant bounds instead of generating them each time they are required. By default enabled when -fchkp-use-static-bounds is enabled. 2001 -fchkp-treat-zero-dynamic-size-as-infinite 2002 With this option, objects with incomplete type whose dynamically-obtained size is zero are treated as having infinite size instead by Pointer Bounds Checker. This option may be helpful if a 2003 program is linked with a library missing size information for some symbols. Disabled by default. 2004 -fchkp-check-read 2005 Instructs Pointer Bounds Checker to generate checks for all read accesses to memory. Enabled by default. 2006 -fchkp-check-write 2007 Instructs Pointer Bounds Checker to generate checks for all write accesses to memory. Enabled by default. 2008 -fchkp-store-bounds 2009 Instructs Pointer Bounds Checker to generate bounds stores for pointer writes. Enabled by default. 2010 -fchkp-instrument-calls 2011 Instructs Pointer Bounds Checker to pass pointer bounds to calls. Enabled by default. 2012 -fchkp-instrument-marked-only 2013 Instructs Pointer Bounds Checker to instrument only functions marked with the "bnd_instrument" attribute. Disabled by default. 2014 -fchkp-use-wrappers 2015 Allows Pointer Bounds Checker to replace calls to built-in functions with calls to wrapper functions. When -fchkp-use-wrappers is used to link a program, the GCC driver automatically links 2016 against libmpxwrappers. See also -static-libmpxwrappers. Enabled by default. 2017 -fdump-final-insns[=file] 2018 Dump the final internal representation (RTL) to file. If the optional argument is omitted (or if file is "."), the name of the dump file is determined by appending ".gkd" to the compilation 2019 output file name. 2020 -fcompare-debug[=opts] 2021 If no error occurs during compilation, run the compiler a second time, adding opts and -fcompare-debug-second to the arguments passed to the second compilation. Dump the final internal 2022 representation in both compilations, and print an error if they differ. 2023 If the equal sign is omitted, the default -gtoggle is used. 2024 The environment variable GCC_COMPARE_DEBUG, if defined, non-empty and nonzero, implicitly enables -fcompare-debug. If GCC_COMPARE_DEBUG is defined to a string starting with a dash, then it 2025 is used for opts, otherwise the default -gtoggle is used. 2026 -fcompare-debug=, with the equal sign but without opts, is equivalent to -fno-compare-debug, which disables the dumping of the final representation and the second compilation, preventing 2027 even GCC_COMPARE_DEBUG from taking effect. 2028 To verify full coverage during -fcompare-debug testing, set GCC_COMPARE_DEBUG to say -fcompare-debug-not-overridden, which GCC rejects as an invalid option in any actual compilation (rather 2029 than preprocessing, assembly or linking). To get just a warning, setting GCC_COMPARE_DEBUG to -w%n-fcompare-debug not overridden will do. 2030 -fcompare-debug-second 2031 This option is implicitly passed to the compiler for the second compilation requested by -fcompare-debug, along with options to silence warnings, and omitting other options that would cause 2032 side-effect compiler outputs to files or to the standard output. Dump files and preserved temporary files are renamed so as to contain the ".gk" additional extension during the second 2033 compilation, to avoid overwriting those generated by the first. 2034 When this option is passed to the compiler driver, it causes the first compilation to be skipped, which makes it useful for little other than debugging the compiler proper. 2035 -feliminate-dwarf2-dups 2036 Compress DWARF 2 debugging information by eliminating duplicated information about each symbol. This option only makes sense when generating DWARF 2 debugging information with -gdwarf-2. 2037 -femit-struct-debug-baseonly 2038 Emit debug information for struct-like types only when the base name of the compilation source file matches the base name of file in which the struct is defined. 2039 This option substantially reduces the size of debugging information, but at significant potential loss in type information to the debugger. See -femit-struct-debug-reduced for a less 2040 aggressive option. See -femit-struct-debug-detailed for more detailed control. 2041 This option works only with DWARF 2. 2042 -femit-struct-debug-reduced 2043 Emit debug information for struct-like types only when the base name of the compilation source file matches the base name of file in which the type is defined, unless the struct is a 2044 template or defined in a system header. 2045 This option significantly reduces the size of debugging information, with some potential loss in type information to the debugger. See -femit-struct-debug-baseonly for a more aggressive 2046 option. See -femit-struct-debug-detailed for more detailed control. 2047 This option works only with DWARF 2. 2048 -femit-struct-debug-detailed[=spec-list] 2049 Specify the struct-like types for which the compiler generates debug information. The intent is to reduce duplicate struct debug information between different object files within the same 2050 program. 2051 This option is a detailed version of -femit-struct-debug-reduced and -femit-struct-debug-baseonly, which serves for most needs. 2052 A specification has the syntax[dir:|ind:][ord:|gen:](any|sys|base|none) 2053 The optional first word limits the specification to structs that are used directly (dir:) or used indirectly (ind:). A struct type is used directly when it is the type of a variable, 2054 member. Indirect uses arise through pointers to structs. That is, when use of an incomplete struct is valid, the use is indirect. An example is struct one direct; struct two * indirect;. 2055 The optional second word limits the specification to ordinary structs (ord:) or generic structs (gen:). Generic structs are a bit complicated to explain. For C++, these are non-explicit 2056 specializations of template classes, or non-template classes within the above. Other programming languages have generics, but -femit-struct-debug-detailed does not yet implement them. 2057 The third word specifies the source files for those structs for which the compiler should emit debug information. The values none and any have the normal meaning. The value base means that 2058 the base of name of the file in which the type declaration appears must match the base of the name of the main compilation file. In practice, this means that when compiling foo.c, debug 2059 information is generated for types declared in that file and foo.h, but not other header files. The value sys means those types satisfying base or declared in system or compiler headers. 2060 You may need to experiment to determine the best settings for your application. 2061 The default is -femit-struct-debug-detailed=all. 2062 This option works only with DWARF 2. 2063 -fno-merge-debug-strings 2064 Direct the linker to not merge together strings in the debugging information that are identical in different object files. Merging is not supported by all assemblers or linkers. Merging 2065 decreases the size of the debug information in the output file at the cost of increasing link processing time. Merging is enabled by default. 2066 -fdebug-prefix-map=old=new 2067 When compiling files in directory old, record debugging information describing them as in new instead. 2068 -fno-dwarf2-cfi-asm 2069 Emit DWARF 2 unwind info as compiler generated ".eh_frame" section instead of using GAS ".cfi_*" directives. 2070 -p Generate extra code to write profile information suitable for the analysis program prof. You must use this option when compiling the source files you want data about, and you must also use 2071 it when linking. 2072 -pg Generate extra code to write profile information suitable for the analysis program gprof. You must use this option when compiling the source files you want data about, and you must also use 2073 it when linking. 2074 -Q Makes the compiler print out each function name as it is compiled, and print some statistics about each pass when it finishes. 2075 -ftime-report 2076 Makes the compiler print some statistics about the time consumed by each pass when it finishes. 2077 -fmem-report 2078 Makes the compiler print some statistics about permanent memory allocation when it finishes. 2079 -fmem-report-wpa 2080 Makes the compiler print some statistics about permanent memory allocation for the WPA phase only. 2081 -fpre-ipa-mem-report 2082 -fpost-ipa-mem-report 2083 Makes the compiler print some statistics about permanent memory allocation before or after interprocedural optimization. 2084 -fprofile-report 2085 Makes the compiler print some statistics about consistency of the (estimated) profile and effect of individual passes. 2086 -fstack-usage 2087 Makes the compiler output stack usage information for the program, on a per-function basis. The filename for the dump is made by appending .su to the auxname. auxname is generated from the 2088 name of the output file, if explicitly specified and it is not an executable, otherwise it is the basename of the source file. An entry is made up of three fields: 2089 * The name of the function. 2090 * A number of bytes. 2091 * One or more qualifiers: "static", "dynamic", "bounded". 2092 The qualifier "static" means that the function manipulates the stack statically: a fixed number of bytes are allocated for the frame on function entry and released on function exit; no stack 2093 adjustments are otherwise made in the function. The second field is this fixed number of bytes. 2094 The qualifier "dynamic" means that the function manipulates the stack dynamically: in addition to the static allocation described above, stack adjustments are made in the body of the 2095 function, for example to push/pop arguments around function calls. If the qualifier "bounded" is also present, the amount of these adjustments is bounded at compile time and the second 2096 field is an upper bound of the total amount of stack used by the function. If it is not present, the amount of these adjustments is not bounded at compile time and the second field only 2097 represents the bounded part. 2098 -fprofile-arcs 2099 Add code so that program flow arcs are instrumented. During execution the program records how many times each branch and call is executed and how many times it is taken or returns. When 2100 the compiled program exits it saves this data to a file called auxname.gcda for each source file. The data may be used for profile-directed optimizations (-fbranch-probabilities), or for 2101 test coverage analysis (-ftest-coverage). Each object file's auxname is generated from the name of the output file, if explicitly specified and it is not the final executable, otherwise it 2102 is the basename of the source file. In both cases any suffix is removed (e.g. foo.gcda for input file dir/foo.c, or dir/foo.gcda for output file specified as -o dir/foo.o). 2103 --coverage 2104 This option is used to compile and link code instrumented for coverage analysis. The option is a synonym for -fprofile-arcs -ftest-coverage (when compiling) and -lgcov (when linking). See 2105 the documentation for those options for more details. 2106 * Compile the source files with -fprofile-arcs plus optimization and code generation options. For test coverage analysis, use the additional -ftest-coverage option. You do not need to 2107 profile every source file in a program. 2108 * Link your object files with -lgcov or -fprofile-arcs (the latter implies the former). 2109 * Run the program on a representative workload to generate the arc profile information. This may be repeated any number of times. You can run concurrent instances of your program, and 2110 provided that the file system supports locking, the data files will be correctly updated. Also "fork" calls are detected and correctly handled (double counting will not happen). 2111 * For profile-directed optimizations, compile the source files again with the same optimization and code generation options plus -fbranch-probabilities. 2112 * For test coverage analysis, use gcov to produce human readable information from the .gcno and .gcda files. Refer to the gcov documentation for further information. 2113 With -fprofile-arcs, for each function of your program GCC creates a program flow graph, then finds a spanning tree for the graph. Only arcs that are not on the spanning tree have to be 2114 instrumented: the compiler adds code to count the number of times that these arcs are executed. When an arc is the only exit or only entrance to a block, the instrumentation code can be 2115 added to the block; otherwise, a new basic block must be created to hold the instrumentation code. 2116 -ftest-coverage 2117 Produce a notes file that the gcov code-coverage utility can use to show program coverage. Each source file's note file is called auxname.gcno. Refer to the -fprofile-arcs option above for 2118 a description of auxname and instructions on how to generate test coverage data. Coverage data matches the source files more closely if you do not optimize. 2119 -fdbg-cnt-list 2120 Print the name and the counter upper bound for all debug counters. 2121 -fdbg-cnt=counter-value-list 2122 Set the internal debug counter upper bound. counter-value-list is a comma-separated list of name:value pairs which sets the upper bound of each debug counter name to value. All debug 2123 counters have the initial upper bound of "UINT_MAX"; thus "dbg_cnt" returns true always unless the upper bound is set by this option. For example, with -fdbg-cnt=dce:10,tail_call:0, 2124 "dbg_cnt(dce)" returns true only for first 10 invocations. 2125 -fenable-kind-pass 2126 -fdisable-kind-pass=range-list 2127 This is a set of options that are used to explicitly disable/enable optimization passes. These options are intended for use for debugging GCC. Compiler users should use regular options for 2128 enabling/disabling passes instead. 2129 -fdisable-ipa-pass 2130 Disable IPA pass pass. pass is the pass name. If the same pass is statically invoked in the compiler multiple times, the pass name should be appended with a sequential number starting 2131 from 1. 2132 -fdisable-rtl-pass 2133 -fdisable-rtl-pass=range-list 2134 Disable RTL pass pass. pass is the pass name. If the same pass is statically invoked in the compiler multiple times, the pass name should be appended with a sequential number starting 2135 from 1. range-list is a comma-separated list of function ranges or assembler names. Each range is a number pair separated by a colon. The range is inclusive in both ends. If the 2136 range is trivial, the number pair can be simplified as a single number. If the function's call graph node's uid falls within one of the specified ranges, the pass is disabled for that 2137 function. The uid is shown in the function header of a dump file, and the pass names can be dumped by using option -fdump-passes. 2138 -fdisable-tree-pass 2139 -fdisable-tree-pass=range-list 2140 Disable tree pass pass. See -fdisable-rtl for the description of option arguments. 2141 -fenable-ipa-pass 2142 Enable IPA pass pass. pass is the pass name. If the same pass is statically invoked in the compiler multiple times, the pass name should be appended with a sequential number starting 2143 from 1. 2144 -fenable-rtl-pass 2145 -fenable-rtl-pass=range-list 2146 Enable RTL pass pass. See -fdisable-rtl for option argument description and examples. 2147 -fenable-tree-pass 2148 -fenable-tree-pass=range-list 2149 Enable tree pass pass. See -fdisable-rtl for the description of option arguments. 2150 Here are some examples showing uses of these options. 2151 # disable ccp1 for all functions 2152 -fdisable-tree-ccp1 2153 # disable complete unroll for function whose cgraph node uid is 1 2154 -fenable-tree-cunroll=1 2155 # disable gcse2 for functions at the following ranges [1,1], 2156 # [300,400], and [400,1000] 2157 # disable gcse2 for functions foo and foo2 2158 -fdisable-rtl-gcse2=foo,foo2 2159 # disable early inlining 2160 -fdisable-tree-einline 2161 # disable ipa inlining 2162 -fdisable-ipa-inline 2163 # enable tree full unroll 2164 -fenable-tree-unroll 2165 -dletters 2166 -fdump-rtl-pass 2167 -fdump-rtl-pass=filename 2168 Says to make debugging dumps during compilation at times specified by letters. This is used for debugging the RTL-based passes of the compiler. The file names for most of the dumps are 2169 made by appending a pass number and a word to the dumpname, and the files are created in the directory of the output file. In case of =filename option, the dump is output on the given file 2170 instead of the pass numbered dump files. Note that the pass number is computed statically as passes get registered into the pass manager. Thus the numbering is not related to the dynamic 2171 order of execution of passes. In particular, a pass installed by a plugin could have a number over 200 even if it executed quite early. dumpname is generated from the name of the output 2172 file, if explicitly specified and it is not an executable, otherwise it is the basename of the source file. These switches may have different effects when -E is used for preprocessing. 2173 Debug dumps can be enabled with a -fdump-rtl switch or some -d option letters. Here are the possible letters for use in pass and letters, and their meanings: 2174 -fdump-rtl-alignments 2175 Dump after branch alignments have been computed. 2176 -fdump-rtl-asmcons 2177 Dump after fixing rtl statements that have unsatisfied in/out constraints. 2178 -fdump-rtl-auto_inc_dec 2179 Dump after auto-inc-dec discovery. This pass is only run on architectures that have auto inc or auto dec instructions. 2180 -fdump-rtl-barriers 2181 Dump after cleaning up the barrier instructions. 2182 -fdump-rtl-bbpart 2183 Dump after partitioning hot and cold basic blocks. 2184 -fdump-rtl-bbro 2185 Dump after block reordering. 2186 -fdump-rtl-btl1 2187 -fdump-rtl-btl2 2188 -fdump-rtl-btl1 and -fdump-rtl-btl2 enable dumping after the two branch target load optimization passes. 2189 -fdump-rtl-bypass 2190 Dump after jump bypassing and control flow optimizations. 2191 -fdump-rtl-combine 2192 Dump after the RTL instruction combination pass. 2193 -fdump-rtl-compgotos 2194 Dump after duplicating the computed gotos. 2195 -fdump-rtl-ce1 2196 -fdump-rtl-ce2 2197 -fdump-rtl-ce3 2198 -fdump-rtl-ce1, -fdump-rtl-ce2, and -fdump-rtl-ce3 enable dumping after the three if conversion passes. 2199 -fdump-rtl-cprop_hardreg 2200 Dump after hard register copy propagation. 2201 -fdump-rtl-csa 2202 Dump after combining stack adjustments. 2203 -fdump-rtl-cse1 2204 -fdump-rtl-cse2 2205 -fdump-rtl-cse1 and -fdump-rtl-cse2 enable dumping after the two common subexpression elimination passes. 2206 -fdump-rtl-dce 2207 Dump after the standalone dead code elimination passes. 2208 -fdump-rtl-dbr 2209 Dump after delayed branch scheduling. 2210 -fdump-rtl-dce1 2211 -fdump-rtl-dce2 2212 -fdump-rtl-dce1 and -fdump-rtl-dce2 enable dumping after the two dead store elimination passes. 2213 -fdump-rtl-eh 2214 Dump after finalization of EH handling code. 2215 -fdump-rtl-eh_ranges 2216 Dump after conversion of EH handling range regions. 2217 -fdump-rtl-expand 2218 Dump after RTL generation. 2219 -fdump-rtl-fwprop1 2220 -fdump-rtl-fwprop2 2221 -fdump-rtl-fwprop1 and -fdump-rtl-fwprop2 enable dumping after the two forward propagation passes. 2222 -fdump-rtl-gcse1 2223 -fdump-rtl-gcse2 2224 -fdump-rtl-gcse1 and -fdump-rtl-gcse2 enable dumping after global common subexpression elimination. 2225 -fdump-rtl-init-regs 2226 Dump after the initialization of the registers. 2227 -fdump-rtl-initvals 2228 Dump after the computation of the initial value sets. 2229 -fdump-rtl-into_cfglayout 2230 Dump after converting to cfglayout mode. 2231 -fdump-rtl-ira 2232 Dump after iterated register allocation. 2233 -fdump-rtl-jump 2234 Dump after the second jump optimization. 2235 -fdump-rtl-loop2 2236 -fdump-rtl-loop2 enables dumping after the rtl loop optimization passes. 2237 -fdump-rtl-mach 2238 Dump after performing the machine dependent reorganization pass, if that pass exists. 2239 -fdump-rtl-mode_sw 2240 Dump after removing redundant mode switches. 2241 -fdump-rtl-rnreg 2242 Dump after register renumbering. 2243 -fdump-rtl-outof_cfglayout 2244 Dump after converting from cfglayout mode. 2245 -fdump-rtl-peephole2 2246 Dump after the peephole pass. 2247 -fdump-rtl-postreload 2248 Dump after post-reload optimizations. 2249 -fdump-rtl-pro_and_epilogue 2250 Dump after generating the function prologues and epilogues. 2251 -fdump-rtl-sched1 2252 -fdump-rtl-sched2 2253 -fdump-rtl-sched1 and -fdump-rtl-sched2 enable dumping after the basic block scheduling passes. 2254 -fdump-rtl-ree 2255 Dump after sign/zero extension elimination. 2256 -fdump-rtl-seqabstr 2257 Dump after common sequence discovery. 2258 -fdump-rtl-shorten 2259 Dump after shortening branches. 2260 -fdump-rtl-sibling 2261 Dump after sibling call optimizations. 2262 -fdump-rtl-split1 2263 -fdump-rtl-split2 2264 -fdump-rtl-split3 2265 -fdump-rtl-split4 2266 -fdump-rtl-split5 2267 These options enable dumping after five rounds of instruction splitting. 2268 -fdump-rtl-sms 2269 Dump after modulo scheduling. This pass is only run on some architectures. 2270 -fdump-rtl-stack 2271 Dump after conversion from GCC's "flat register file" registers to the x87's stack-like registers. This pass is only run on x86 variants. 2272 -fdump-rtl-subreg1 2273 -fdump-rtl-subreg2 2274 -fdump-rtl-subreg1 and -fdump-rtl-subreg2 enable dumping after the two subreg expansion passes. 2275 -fdump-rtl-unshare 2276 Dump after all rtl has been unshared. 2277 -fdump-rtl-vartrack 2278 Dump after variable tracking. 2279 -fdump-rtl-vregs 2280 Dump after converting virtual registers to hard registers. 2281 -fdump-rtl-web 2282 Dump after live range splitting. 2283 -fdump-rtl-regclass 2284 -fdump-rtl-subregs_of_mode_init 2285 -fdump-rtl-subregs_of_mode_finish 2286 -fdump-rtl-dfinit 2287 -fdump-rtl-dfinish 2288 These dumps are defined but always produce empty files. 2289 -da 2290 -fdump-rtl-all 2291 Produce all the dumps listed above. 2292 -dA Annotate the assembler output with miscellaneous debugging information. 2293 -dD Dump all macro definitions, at the end of preprocessing, in addition to normal output. 2294 -dH Produce a core dump whenever an error occurs. 2295 -dp Annotate the assembler output with a comment indicating which pattern and alternative is used. The length of each instruction is also printed. 2296 -dP Dump the RTL in the assembler output as a comment before each instruction. Also turns on -dp annotation. 2297 -dx Just generate RTL for a function instead of compiling it. Usually used with -fdump-rtl-expand. 2298 -fdump-noaddr 2299 When doing debugging dumps, suppress address output. This makes it more feasible to use diff on debugging dumps for compiler invocations with different compiler binaries and/or different 2300 text / bss / data / heap / stack / dso start locations. 2301 -freport-bug 2302 Collect and dump debug information into temporary file if ICE in C/C++ compiler occured. 2303 -fdump-unnumbered 2304 When doing debugging dumps, suppress instruction numbers and address output. This makes it more feasible to use diff on debugging dumps for compiler invocations with different options, in 2305 particular with and without -g. 2306 -fdump-unnumbered-links 2307 When doing debugging dumps (see -d option above), suppress instruction numbers for the links to the previous and next instructions in a sequence. 2308 -fdump-translation-unit (C++ only) 2309 -fdump-translation-unit-options (C++ only) 2310 Dump a representation of the tree structure for the entire translation unit to a file. The file name is made by appending .tu to the source file name, and the file is created in the same 2311 directory as the output file. If the -options form is used, options controls the details of the dump as described for the -fdump-tree options. 2312 -fdump-class-hierarchy (C++ only) 2313 -fdump-class-hierarchy-options (C++ only) 2314 Dump a representation of each class's hierarchy and virtual function table layout to a file. The file name is made by appending .class to the source file name, and the file is created in 2315 the same directory as the output file. If the -options form is used, options controls the details of the dump as described for the -fdump-tree options. 2316 -fdump-ipa-switch 2317 Control the dumping at various stages of inter-procedural analysis language tree to a file. The file name is generated by appending a switch specific suffix to the source file name, and the 2318 file is created in the same directory as the output file. The following dumps are possible: 2319 all Enables all inter-procedural analysis dumps. 2320 cgraph 2321 Dumps information about call-graph optimization, unused function removal, and inlining decisions. 2322 inline 2323 Dump after function inlining. 2324 -fdump-passes 2325 Dump the list of optimization passes that are turned on and off by the current command-line options. 2326 -fdump-statistics-option 2327 Enable and control dumping of pass statistics in a separate file. The file name is generated by appending a suffix ending in .statistics to the source file name, and the file is created in 2328 the same directory as the output file. If the -option form is used, -stats causes counters to be summed over the whole compilation unit while -details dumps every event as the passes 2329 generate them. The default with no option is to sum counters for each function compiled. 2330 -fdump-tree-switch 2331 -fdump-tree-switch-options 2332 -fdump-tree-switch-options=filename 2333 Control the dumping at various stages of processing the intermediate language tree to a file. The file name is generated by appending a switch-specific suffix to the source file name, and 2334 the file is created in the same directory as the output file. In case of =filename option, the dump is output on the given file instead of the auto named dump files. If the -options form is 2335 used, options is a list of - separated options which control the details of the dump. Not all options are applicable to all dumps; those that are not meaningful are ignored. The following 2336 options are available 2337 address 2338 Print the address of each node. Usually this is not meaningful as it changes according to the environment and source file. Its primary use is for tying up a dump file with a debug 2339 environment. 2340 asmname 2341 If "DECL_ASSEMBLER_NAME" has been set for a given decl, use that in the dump instead of "DECL_NAME". Its primary use is ease of use working backward from mangled names in the assembly 2342 file. 2343 slim 2344 When dumping front-end intermediate representations, inhibit dumping of members of a scope or body of a function merely because that scope has been reached. Only dump such items when 2345 they are directly reachable by some other path. 2346 When dumping pretty-printed trees, this option inhibits dumping the bodies of control structures. 2347 When dumping RTL, print the RTL in slim (condensed) form instead of the default LISP-like representation. 2348 raw Print a raw representation of the tree. By default, trees are pretty-printed into a C-like representation. 2349 details 2350 Enable more detailed dumps (not honored by every dump option). Also include information from the optimization passes. 2351 stats 2352 Enable dumping various statistics about the pass (not honored by every dump option). 2353 blocks 2354 Enable showing basic block boundaries (disabled in raw dumps). 2355 graph 2356 For each of the other indicated dump files (-fdump-rtl-pass), dump a representation of the control flow graph suitable for viewing with GraphViz to file.passid.pass.dot. Each function 2357 in the file is pretty-printed as a subgraph, so that GraphViz can render them all in a single plot. 2358 This option currently only works for RTL dumps, and the RTL is always dumped in slim form. 2359 vops 2360 Enable showing virtual operands for every statement. 2361 lineno 2362 Enable showing line numbers for statements. 2363 uid Enable showing the unique ID ("DECL_UID") for each variable. 2364 verbose 2365 Enable showing the tree dump for each statement. 2366 eh Enable showing the EH region number holding each statement. 2367 scev 2368 Enable showing scalar evolution analysis details. 2369 optimized 2370 Enable showing optimization information (only available in certain passes). 2371 missed 2372 Enable showing missed optimization information (only available in certain passes). 2373 note 2374 Enable other detailed optimization information (only available in certain passes). 2375 =filename 2376 Instead of an auto named dump file, output into the given file name. The file names stdout and stderr are treated specially and are considered already open standard streams. For example, 2377 gcc -O2 -ftree-vectorize -fdump-tree-vect-blocks=foo.dump 2378 -fdump-tree-pre=stderr file.c 2379 outputs vectorizer dump into foo.dump, while the PRE dump is output on to stderr. If two conflicting dump filenames are given for the same pass, then the latter option overrides the 2380 earlier one. 2381 all Turn on all options, except raw, slim, verbose and lineno. 2382 optall 2383 Turn on all optimization options, i.e., optimized, missed, and note. 2384 The following tree dumps are possible: 2385 original 2386 Dump before any tree based optimization, to file.original. 2387 optimized 2388 Dump after all tree based optimization, to file.optimized. 2389 gimple 2390 Dump each function before and after the gimplification pass to a file. The file name is made by appending .gimple to the source file name. 2391 cfg Dump the control flow graph of each function to a file. The file name is made by appending .cfg to the source file name. 2392 ch Dump each function after copying loop headers. The file name is made by appending .ch to the source file name. 2393 ssa Dump SSA related information to a file. The file name is made by appending .ssa to the source file name. 2394 alias 2395 Dump aliasing information for each function. The file name is made by appending .alias to the source file name. 2396 ccp Dump each function after CCP. The file name is made by appending .ccp to the source file name. 2397 storeccp 2398 Dump each function after STORE-CCP. The file name is made by appending .storeccp to the source file name. 2399 pre Dump trees after partial redundancy elimination. The file name is made by appending .pre to the source file name. 2400 fre Dump trees after full redundancy elimination. The file name is made by appending .fre to the source file name. 2401 copyprop 2402 Dump trees after copy propagation. The file name is made by appending .copyprop to the source file name. 2403 store_copyprop 2404 Dump trees after store copy-propagation. The file name is made by appending .store_copyprop to the source file name. 2405 dce Dump each function after dead code elimination. The file name is made by appending .dce to the source file name. 2406 sra Dump each function after performing scalar replacement of aggregates. The file name is made by appending .sra to the source file name. 2407 sink 2408 Dump each function after performing code sinking. The file name is made by appending .sink to the source file name. 2409 dom Dump each function after applying dominator tree optimizations. The file name is made by appending .dom to the source file name. 2410 dse Dump each function after applying dead store elimination. The file name is made by appending .dse to the source file name. 2411 phiopt 2412 Dump each function after optimizing PHI nodes into straightline code. The file name is made by appending .phiopt to the source file name. 2413 forwprop 2414 Dump each function after forward propagating single use variables. The file name is made by appending .forwprop to the source file name. 2415 copyrename 2416 Dump each function after applying the copy rename optimization. The file name is made by appending .copyrename to the source file name. 2417 nrv Dump each function after applying the named return value optimization on generic trees. The file name is made by appending .nrv to the source file name. 2418 vect 2419 Dump each function after applying vectorization of loops. The file name is made by appending .vect to the source file name. 2420 slp Dump each function after applying vectorization of basic blocks. The file name is made by appending .slp to the source file name. 2421 vrp Dump each function after Value Range Propagation (VRP). The file name is made by appending .vrp to the source file name. 2422 all Enable all the available tree dumps with the flags provided in this option. 2423 -fopt-info 2424 -fopt-info-options 2425 -fopt-info-options=filename 2426 Controls optimization dumps from various optimization passes. If the -options form is used, options is a list of - separated option keywords to select the dump details and optimizations. 2427 The options can be divided into two groups: options describing the verbosity of the dump, and options describing which optimizations should be included. The options from both the groups can 2428 be freely mixed as they are non-overlapping. However, in case of any conflicts, the later options override the earlier options on the command line. 2429 The following options control the dump verbosity: 2430 optimized 2431 Print information when an optimization is successfully applied. It is up to a pass to decide which information is relevant. For example, the vectorizer passes print the source location 2432 of loops which are successfully vectorized. 2433 missed 2434 Print information about missed optimizations. Individual passes control which information to include in the output. 2435 note 2436 Print verbose information about optimizations, such as certain transformations, more detailed messages about decisions etc. 2437 all Print detailed optimization information. This includes optimized, missed, and note. 2438 One or more of the following option keywords can be used to describe a group of optimizations: 2439 ipa Enable dumps from all interprocedural optimizations. 2440 loop 2441 Enable dumps from all loop optimizations. 2442 inline 2443 Enable dumps from all inlining optimizations. 2444 vec Enable dumps from all vectorization optimizations. 2445 optall 2446 Enable dumps from all optimizations. This is a superset of the optimization groups listed above. 2447 If options is omitted, it defaults to optimized-optall, which means to dump all info about successful optimizations from all the passes. 2448 If the filename is provided, then the dumps from all the applicable optimizations are concatenated into the filename. Otherwise the dump is output onto stderr. Though multiple -fopt-info 2449 options are accepted, only one of them can include a filename. If other filenames are provided then all but the first such option are ignored. 2450 Note that the output filename is overwritten in case of multiple translation units. If a combined output from multiple translation units is desired, stderr should be used instead. 2451 In the following example, the optimization info is output to stderr: 2452 gcc -O3 -fopt-info 2453 This example: 2454 gcc -O3 -fopt-info-missed=missed.all 2455 outputs missed optimization report from all the passes into missed.all, and this one: 2456 gcc -O2 -ftree-vectorize -fopt-info-vec-missed 2457 prints information about missed optimization opportunities from vectorization passes on stderr. Note that -fopt-info-vec-missed is equivalent to -fopt-info-missed-vec. 2458 As another example, 2459 gcc -O3 -fopt-info-inline-optimized-missed=inline.txt 2460 outputs information about missed optimizations as well as optimized locations from all the inlining passes into inline.txt. 2461 Finally, consider: 2462 gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt 2463 Here the two output filenames vec.miss and loop.opt are in conflict since only one output file is allowed. In this case, only the first option takes effect and the subsequent options are 2464 ignored. Thus only vec.miss is produced which contains dumps from the vectorizer about missed opportunities. 2465 -frandom-seed=number 2466 This option provides a seed that GCC uses in place of random numbers in generating certain symbol names that have to be different in every compiled file. It is also used to place unique 2467 stamps in coverage data files and the object files that produce them. You can use the -frandom-seed option to produce reproducibly identical object files. 2468 The number should be different for every file you compile. 2469 -fsched-verbose=n 2470 On targets that use instruction scheduling, this option controls the amount of debugging output the scheduler prints. This information is written to standard error, unless -fdump-rtl-sched1 2471 or -fdump-rtl-sched2 is specified, in which case it is output to the usual dump listing file, .sched1 or .sched2 respectively. However for n greater than nine, the output is always printed 2472 to standard error. 2473 For n greater than zero, -fsched-verbose outputs the same information as -fdump-rtl-sched1 and -fdump-rtl-sched2. For n greater than one, it also output basic block probabilities, detailed 2474 ready list information and unit/insn info. For n greater than two, it includes RTL at abort point, control-flow and regions info. And for n over four, -fsched-verbose also includes 2475 dependence info. 2476 -save-temps 2477 -save-temps=cwd 2478 Store the usual "temporary" intermediate files permanently; place them in the current directory and name them based on the source file. Thus, compiling foo.c with -c -save-temps produces 2479 files foo.i and foo.s, as well as foo.o. This creates a preprocessed foo.i output file even though the compiler now normally uses an integrated preprocessor. 2480 When used in combination with the -x command-line option, -save-temps is sensible enough to avoid over writing an input source file with the same extension as an intermediate file. The 2481 corresponding intermediate file may be obtained by renaming the source file before using -save-temps. 2482 If you invoke GCC in parallel, compiling several different source files that share a common base name in different subdirectories or the same source file compiled for multiple output 2483 destinations, it is likely that the different parallel compilers will interfere with each other, and overwrite the temporary files. For instance: 2484 gcc -save-temps -o outdir1/foo.o indir1/foo.c& 2485 gcc -save-temps -o outdir2/foo.o indir2/foo.c& 2486 may result in foo.i and foo.o being written to simultaneously by both compilers. 2487 -save-temps=obj 2488 Store the usual "temporary" intermediate files permanently. If the -o option is used, the temporary files are based on the object file. If the -o option is not used, the -save-temps=obj 2489 switch behaves like -save-temps. 2490 For example: 2491 gcc -save-temps=obj -c foo.c 2492 gcc -save-temps=obj -c bar.c -o dir/xbar.o 2493 gcc -save-temps=obj foobar.c -o dir2/yfoobar 2494 creates foo.i, foo.s, dir/xbar.i, dir/xbar.s, dir2/yfoobar.i, dir2/yfoobar.s, and dir2/yfoobar.o. 2495 -time[=file] 2496 Report the CPU time taken by each subprocess in the compilation sequence. For C source files, this is the compiler proper and assembler (plus the linker if linking is done). 2497 Without the specification of an output file, the output looks like this: 2498 # cc1 0.12 0.01 2499 # as 0.00 0.01 2500 The first number on each line is the "user time", that is time spent executing the program itself. The second number is "system time", time spent executing operating system routines on 2501 behalf of the program. Both numbers are in seconds. 2502 With the specification of an output file, the output is appended to the named file, and it looks like this: 2503 0.12 0.01 cc1 2504 0.00 0.01 as 2505 The "user time" and the "system time" are moved before the program name, and the options passed to the program are displayed, so that one can later tell what file was being compiled, and 2506 with which options. 2507 -fvar-tracking 2508 Run variable tracking pass. It computes where variables are stored at each position in code. Better debugging information is then generated (if the debugging information format supports 2509 this information). 2510 It is enabled by default when compiling with optimization (-Os, -O, -O2, ...), debugging information (-g) and the debug info format supports it. 2511 -fvar-tracking-assignments 2512 Annotate assignments to user variables early in the compilation and attempt to carry the annotations over throughout the compilation all the way to the end, in an attempt to improve debug 2513 information while optimizing. Use of -gdwarf-4 is recommended along with it. 2514 It can be enabled even if var-tracking is disabled, in which case annotations are created and maintained, but discarded at the end. By default, this flag is enabled together with 2515 -fvar-tracking, except when selective scheduling is enabled. 2516 -fvar-tracking-assignments-toggle 2517 Toggle -fvar-tracking-assignments, in the same way that -gtoggle toggles -g. 2518 -print-file-name=library 2519 Print the full absolute name of the library file library that would be used when linking---and don't do anything else. With this option, GCC does not compile or link anything; it just 2520 prints the file name. 2521 -print-multi-directory 2522 Print the directory name corresponding to the multilib selected by any other switches present in the command line. This directory is supposed to exist in GCC_EXEC_PREFIX. 2523 -print-multi-lib 2524 Print the mapping from multilib directory names to compiler switches that enable them. The directory name is separated from the switches by ;, and each switch starts with an @ instead of 2525 the -, without spaces between multiple switches. This is supposed to ease shell processing. 2526 -print-multi-os-directory 2527 Print the path to OS libraries for the selected multilib, relative to some lib subdirectory. If OS libraries are present in the lib subdirectory and no multilibs are used, this is usually 2528 just ., if OS libraries are present in libsuffix sibling directories this prints e.g. ../lib64, ../lib or ../lib32, or if OS libraries are present in lib/subdir subdirectories it prints e.g. 2529 amd64, sparcv9 or ev6. 2530 -print-multiarch 2531 Print the path to OS libraries for the selected multiarch, relative to some lib subdirectory. 2532 -print-prog-name=program 2533 Like -print-file-name, but searches for a program such as cpp. 2534 -print-libgcc-file-name 2535 Same as -print-file-name=libgcc.a. 2536 This is useful when you use -nostdlib or -nodefaultlibs but you do want to link with libgcc.a. You can do: 2537 gcc -nostdlib ... `gcc -print-libgcc-file-name` 2538 -print-search-dirs 2539 Print the name of the configured installation directory and a list of program and library directories gcc searches---and don't do anything else. 2540 This is useful when gcc prints the error message installation problem, cannot exec cpp0: No such file or directory. To resolve this you either need to put cpp0 and the other compiler 2541 components where gcc expects to find them, or you can set the environment variable GCC_EXEC_PREFIX to the directory where you installed them. Don't forget the trailing /. 2542 -print-sysroot 2543 Print the target sysroot directory that is used during compilation. This is the target sysroot specified either at configure time or using the --sysroot option, possibly with an extra 2544 suffix that depends on compilation options. If no target sysroot is specified, the option prints nothing. 2545 -print-sysroot-headers-suffix 2546 Print the suffix added to the target sysroot when searching for headers, or give an error if the compiler is not configured with such a suffix---and don't do anything else. 2547 -dumpmachine 2548 Print the compiler's target machine (for example, i686-pc-linux-gnu)---and don't do anything else. 2549 -dumpversion 2550 Print the compiler version (for example, 3.0)---and don't do anything else. 2551 -dumpspecs 2552 Print the compiler's built-in specs---and don't do anything else. (This is used when GCC itself is being built.) 2553 -fno-eliminate-unused-debug-types 2554 Normally, when producing DWARF 2 output, GCC avoids producing debug symbol output for types that are nowhere used in the source file being compiled. Sometimes it is useful to have GCC emit 2555 debugging information for all types declared in a compilation unit, regardless of whether or not they are actually used in that compilation unit, for example if, in the debugger, you want to 2556 cast a value to a type that is not actually used in your program (but is declared). More often, however, this results in a significant amount of wasted space. 2557 Options That Control Optimization 2558 These options control various sorts of optimizations. 2559 Without any optimization option, the compiler's goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program 2560 with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the function and get exactly the results you expect 2561 from the source code. 2562 Turning on optimization flags makes the compiler attempt to improve the performance and/or code size at the expense of compilation time and possibly the ability to debug the program. 2563 The compiler performs optimization based on the knowledge it has of the program. Compiling multiple files at once to a single output file mode allows the compiler to use information gained from 2564 all of the files when compiling each of them. 2565 Not all optimizations are controlled directly by a flag. Only optimizations that have a flag are listed in this section. 2566 Most optimizations are only enabled if an -O level is set on the command line. Otherwise they are disabled, even if individual optimization flags are specified. 2567 Depending on the target and how GCC was configured, a slightly different set of optimizations may be enabled at each -O level than those listed here. You can invoke GCC with -Q 2568 --help=optimizers to find out the exact set of optimizations that are enabled at each level. 2569 -O 2570 -O1 Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large function. 2571 With -O, the compiler tries to reduce code size and execution time, without performing any optimizations that take a great deal of compilation time. 2572 -O turns on the following optimization flags: 2573 -fauto-inc-dec -fbranch-count-reg -fcombine-stack-adjustments -fcompare-elim -fcprop-registers -fdce -fdefer-pop -fdelayed-branch -fdse -fforward-propagate -fguess-branch-probability 2574 -fif-conversion2 -fif-conversion -finline-functions-called-once -fipa-pure-const -fipa-profile -fipa-reference -fmerge-constants -fmove-loop-invariants -fshrink-wrap -fsplit-wide-types 2575 -ftree-bit-ccp -ftree-ccp -fssa-phiopt -ftree-ch -ftree-copy-prop -ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre -ftree-phiprop -ftree-sink 2576 -ftree-slsr -ftree-sra -ftree-pta -ftree-ter -funit-at-a-time 2577 -O also turns on -fomit-frame-pointer on machines where doing so does not interfere with debugging. 2578 -O2 Optimize even more. GCC performs nearly all supported optimizations that do not involve a space-speed tradeoff. As compared to -O, this option increases both compilation time and the 2579 performance of the generated code. 2580 -O2 turns on all optimization flags specified by -O. It also turns on the following optimization flags: -fthread-jumps -falign-functions -falign-jumps -falign-loops -falign-labels 2581 -fcaller-saves -fcrossjumping -fcse-follow-jumps -fcse-skip-blocks -fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively -fexpensive-optimizations -fgcse -fgcse-lm 2582 -fhoist-adjacent-loads -finline-small-functions -findirect-inlining -fipa-cp -fipa-cp-alignment -fipa-sra -fipa-icf -fisolate-erroneous-paths-dereference -flra-remat -foptimize-sibling-calls 2583 -foptimize-strlen -fpartial-inlining -fpeephole2 -freorder-blocks -freorder-blocks-and-partition -freorder-functions -frerun-cse-after-loop -fsched-interblock -fsched-spec -fschedule-insns 2584 -fschedule-insns2 -fstrict-aliasing -fstrict-overflow -ftree-builtin-call-dce -ftree-switch-conversion -ftree-tail-merge -ftree-pre -ftree-vrp -fipa-ra 2585 Please note the warning under -fgcse about invoking -O2 on programs that use computed gotos. 2586 -O3 Optimize yet more. -O3 turns on all optimizations specified by -O2 and also turns on the -finline-functions, -funswitch-loops, -fpredictive-commoning, -fgcse-after-reload, 2587 -ftree-loop-vectorize, -ftree-loop-distribute-patterns, -ftree-slp-vectorize, -fvect-cost-model, -ftree-partial-pre and -fipa-cp-clone options. 2588 -O0 Reduce compilation time and make debugging produce the expected results. This is the default. 2589 -Os Optimize for size. -Os enables all -O2 optimizations that do not typically increase code size. It also performs further optimizations designed to reduce code size. 2590 -Os disables the following optimization flags: -falign-functions -falign-jumps -falign-loops -falign-labels -freorder-blocks -freorder-blocks-and-partition -fprefetch-loop-arrays 2591 -Ofast 2592 Disregard strict standards compliance. -Ofast enables all -O3 optimizations. It also enables optimizations that are not valid for all standard-compliant programs. It turns on -ffast-math 2593 and the Fortran-specific -fno-protect-parens and -fstack-arrays. 2594 -Og Optimize debugging experience. -Og enables optimizations that do not interfere with debugging. It should be the optimization level of choice for the standard edit-compile-debug cycle, 2595 offering a reasonable level of optimization while maintaining fast compilation and a good debugging experience. 2596 If you use multiple -O options, with or without level numbers, the last such option is the one that is effective. 2597 Options of the form -fflag specify machine-independent flags. Most flags have both positive and negative forms; the negative form of -ffoo is -fno-foo. In the table below, only one of the 2598 forms is listed---the one you typically use. You can figure out the other form by either removing no- or adding it. 2599 The following options control specific optimizations. They are either activated by -O options or are related to ones that are. You can use the following flags in the rare cases when "fine- 2600 tuning" of optimizations to be performed is desired. 2601 -fno-defer-pop 2602 Always pop the arguments to each function call as soon as that function returns. For machines that must pop arguments after a function call, the compiler normally lets arguments accumulate 2603 on the stack for several function calls and pops them all at once. 2604 Disabled at levels -O, -O2, -O3, -Os. 2605 -fforward-propagate 2606 Perform a forward propagation pass on RTL. The pass tries to combine two instructions and checks if the result can be simplified. If loop unrolling is active, two passes are performed and 2607 the second is scheduled after loop unrolling. 2608 This option is enabled by default at optimization levels -O, -O2, -O3, -Os. 2609 -ffp-contract=style 2610 -ffp-contract=off disables floating-point expression contraction. -ffp-contract=fast enables floating-point expression contraction such as forming of fused multiply-add operations if the 2611 target has native support for them. -ffp-contract=on enables floating-point expression contraction if allowed by the language standard. This is currently not implemented and treated equal 2612 to -ffp-contract=off. 2613 The default is -ffp-contract=fast. 2614 -fomit-frame-pointer 2615 Don't keep the frame pointer in a register for functions that don't need one. This avoids the instructions to save, set up and restore frame pointers; it also makes an extra register 2616 available in many functions. It also makes debugging impossible on some machines. 2617 On some machines, such as the VAX, this flag has no effect, because the standard calling sequence automatically handles the frame pointer and nothing is saved by pretending it doesn't exist. 2618 The machine-description macro "FRAME_POINTER_REQUIRED" controls whether a target machine supports this flag. 2619 The default setting (when not optimizing for size) for 32-bit GNU/Linux x86 and 32-bit Darwin x86 targets is -fomit-frame-pointer. You can configure GCC with the --enable-frame-pointer 2620 configure option to change the default. 2621 Enabled at levels -O, -O2, -O3, -Os. 2622 -foptimize-sibling-calls 2623 Optimize sibling and tail recursive calls. 2624 Enabled at levels -O2, -O3, -Os. 2625 -foptimize-strlen 2626 Optimize various standard C string functions (e.g. "strlen", "strchr" or "strcpy") and their "_FORTIFY_SOURCE" counterparts into faster alternatives. 2627 Enabled at levels -O2, -O3. 2628 -fno-inline 2629 Do not expand any functions inline apart from those marked with the "always_inline" attribute. This is the default when not optimizing. 2630 Single functions can be exempted from inlining by marking them with the "noinline" attribute. 2631 -finline-small-functions 2632 Integrate functions into their callers when their body is smaller than expected function call code (so overall size of program gets smaller). The compiler heuristically decides which 2633 functions are simple enough to be worth integrating in this way. This inlining applies to all functions, even those not declared inline. 2634 Enabled at level -O2. 2635 -findirect-inlining 2636 Inline also indirect calls that are discovered to be known at compile time thanks to previous inlining. This option has any effect only when inlining itself is turned on by the 2637 -finline-functions or -finline-small-functions options. 2638 Enabled at level -O2. 2639 -finline-functions 2640 Consider all functions for inlining, even if they are not declared inline. The compiler heuristically decides which functions are worth integrating in this way. 2641 If all calls to a given function are integrated, and the function is declared "static", then the function is normally not output as assembler code in its own right. 2642 Enabled at level -O3. 2643 -finline-functions-called-once 2644 Consider all "static" functions called once for inlining into their caller even if they are not marked "inline". If a call to a given function is integrated, then the function is not output 2645 as assembler code in its own right. 2646 Enabled at levels -O1, -O2, -O3 and -Os. 2647 -fearly-inlining 2648 Inline functions marked by "always_inline" and functions whose body seems smaller than the function call overhead early before doing -fprofile-generate instrumentation and real inlining 2649 pass. Doing so makes profiling significantly cheaper and usually inlining faster on programs having large chains of nested wrapper functions. 2650 Enabled by default. 2651 -fipa-sra 2652 Perform interprocedural scalar replacement of aggregates, removal of unused parameters and replacement of parameters passed by reference by parameters passed by value. 2653 Enabled at levels -O2, -O3 and -Os. 2654 -finline-limit=n 2655 By default, GCC limits the size of functions that can be inlined. This flag allows coarse control of this limit. n is the size of functions that can be inlined in number of pseudo 2656 instructions. 2657 Inlining is actually controlled by a number of parameters, which may be specified individually by using --param name=value. The -finline-limit=n option sets some of these parameters as 2658 follows: 2659 max-inline-insns-single 2660 is set to n/2. 2661 max-inline-insns-auto 2662 is set to n/2. 2663 See below for a documentation of the individual parameters controlling inlining and for the defaults of these parameters. 2664 Note: there may be no value to -finline-limit that results in default behavior. 2665 Note: pseudo instruction represents, in this particular context, an abstract measurement of function's size. In no way does it represent a count of assembly instructions and as such its 2666 exact meaning might change from one release to an another. 2667 -fno-keep-inline-dllexport 2668 This is a more fine-grained version of -fkeep-inline-functions, which applies only to functions that are declared using the "dllexport" attribute or declspec 2669 -fkeep-inline-functions 2670 In C, emit "static" functions that are declared "inline" into the object file, even if the function has been inlined into all of its callers. This switch does not affect functions using the 2671 "extern inline" extension in GNU C90. In C++, emit any and all inline functions into the object file. 2672 -fkeep-static-consts 2673 Emit variables declared "static const" when optimization isn't turned on, even if the variables aren't referenced. 2674 GCC enables this option by default. If you want to force the compiler to check if a variable is referenced, regardless of whether or not optimization is turned on, use the 2675 -fno-keep-static-consts option. 2676 -fmerge-constants 2677 Attempt to merge identical constants (string constants and floating-point constants) across compilation units. 2678 This option is the default for optimized compilation if the assembler and linker support it. Use -fno-merge-constants to inhibit this behavior. 2679 Enabled at levels -O, -O2, -O3, -Os. 2680 -fmerge-all-constants 2681 Attempt to merge identical constants and identical variables. 2682 This option implies -fmerge-constants. In addition to -fmerge-constants this considers e.g. even constant initialized arrays or initialized constant variables with integral or floating- 2683 point types. Languages like C or C++ require each variable, including multiple instances of the same variable in recursive calls, to have distinct locations, so using this option results in 2684 non-conforming behavior. 2685 -fmodulo-sched 2686 Perform swing modulo scheduling immediately before the first scheduling pass. This pass looks at innermost loops and reorders their instructions by overlapping different iterations. 2687 -fmodulo-sched-allow-regmoves 2688 Perform more aggressive SMS-based modulo scheduling with register moves allowed. By setting this flag certain anti-dependences edges are deleted, which triggers the generation of reg-moves 2689 based on the life-range analysis. This option is effective only with -fmodulo-sched enabled. 2690 -fno-branch-count-reg 2691 Do not use "decrement and branch" instructions on a count register, but instead generate a sequence of instructions that decrement a register, compare it against zero, then branch based upon 2692 the result. This option is only meaningful on architectures that support such instructions, which include x86, PowerPC, IA-64 and S/390. 2693 Enabled by default at -O1 and higher. 2694 The default is -fbranch-count-reg. 2695 -fno-function-cse 2696 Do not put function addresses in registers; make each instruction that calls a constant function contain the function's address explicitly. 2697 This option results in less efficient code, but some strange hacks that alter the assembler output may be confused by the optimizations performed when this option is not used. 2698 The default is -ffunction-cse 2699 -fno-zero-initialized-in-bss 2700 If the target supports a BSS section, GCC by default puts variables that are initialized to zero into BSS. This can save space in the resulting code. 2701 This option turns off this behavior because some programs explicitly rely on variables going to the data section---e.g., so that the resulting executable can find the beginning of that 2702 section and/or make assumptions based on that. 2703 The default is -fzero-initialized-in-bss. 2704 -fthread-jumps 2705 Perform optimizations that check to see if a jump branches to a location where another comparison subsumed by the first is found. If so, the first branch is redirected to either the 2706 destination of the second branch or a point immediately following it, depending on whether the condition is known to be true or false. 2707 Enabled at levels -O2, -O3, -Os. 2708 -fsplit-wide-types 2709 When using a type that occupies multiple registers, such as "long long" on a 32-bit system, split the registers apart and allocate them independently. This normally generates better code 2710 for those types, but may make debugging more difficult. 2711 Enabled at levels -O, -O2, -O3, -Os. 2712 -fcse-follow-jumps 2713 In common subexpression elimination (CSE), scan through jump instructions when the target of the jump is not reached by any other path. For example, when CSE encounters an "if" statement 2714 with an "else" clause, CSE follows the jump when the condition tested is false. 2715 Enabled at levels -O2, -O3, -Os. 2716 -fcse-skip-blocks 2717 This is similar to -fcse-follow-jumps, but causes CSE to follow jumps that conditionally skip over blocks. When CSE encounters a simple "if" statement with no else clause, -fcse-skip-blocks 2718 causes CSE to follow the jump around the body of the "if". 2719 Enabled at levels -O2, -O3, -Os. 2720 -frerun-cse-after-loop 2721 Re-run common subexpression elimination after loop optimizations are performed. 2722 Enabled at levels -O2, -O3, -Os. 2723 -fgcse 2724 Perform a global common subexpression elimination pass. This pass also performs global constant and copy propagation. 2725 Note: When compiling a program using computed gotos, a GCC extension, you may get better run-time performance if you disable the global common subexpression elimination pass by adding 2726 -fno-gcse to the command line. 2727 Enabled at levels -O2, -O3, -Os. 2728 -fgcse-lm 2729 When -fgcse-lm is enabled, global common subexpression elimination attempts to move loads that are only killed by stores into themselves. This allows a loop containing a load/store sequence 2730 to be changed to a load outside the loop, and a copy/store within the loop. 2731 Enabled by default when -fgcse is enabled. 2732 -fgcse-sm 2733 When -fgcse-sm is enabled, a store motion pass is run after global common subexpression elimination. This pass attempts to move stores out of loops. When used in conjunction with 2734 -fgcse-lm, loops containing a load/store sequence can be changed to a load before the loop and a store after the loop. 2735 Not enabled at any optimization level. 2736 -fgcse-las 2737 When -fgcse-las is enabled, the global common subexpression elimination pass eliminates redundant loads that come after stores to the same memory location (both partial and full 2738 redundancies). 2739 Not enabled at any optimization level. 2740 -fgcse-after-reload 2741 When -fgcse-after-reload is enabled, a redundant load elimination pass is performed after reload. The purpose of this pass is to clean up redundant spilling. 2742 -faggressive-loop-optimizations 2743 This option tells the loop optimizer to use language constraints to derive bounds for the number of iterations of a loop. This assumes that loop code does not invoke undefined behavior by 2744 for example causing signed integer overflows or out-of-bound array accesses. The bounds for the number of iterations of a loop are used to guide loop unrolling and peeling and loop exit 2745 test optimizations. This option is enabled by default. 2746 -funsafe-loop-optimizations 2747 This option tells the loop optimizer to assume that loop indices do not overflow, and that loops with nontrivial exit condition are not infinite. This enables a wider range of loop 2748 optimizations even if the loop optimizer itself cannot prove that these assumptions are valid. If you use -Wunsafe-loop-optimizations, the compiler warns you if it finds this kind of loop. 2749 -fcrossjumping 2750 Perform cross-jumping transformation. This transformation unifies equivalent code and saves code size. The resulting code may or may not perform better than without cross-jumping. 2751 Enabled at levels -O2, -O3, -Os. 2752 -fauto-inc-dec 2753 Combine increments or decrements of addresses with memory accesses. This pass is always skipped on architectures that do not have instructions to support this. Enabled by default at -O and 2754 higher on architectures that support this. 2755 -fdce 2756 Perform dead code elimination (DCE) on RTL. Enabled by default at -O and higher. 2757 -fdse 2758 Perform dead store elimination (DSE) on RTL. Enabled by default at -O and higher. 2759 -fif-conversion 2760 Attempt to transform conditional jumps into branch-less equivalents. This includes use of conditional moves, min, max, set flags and abs instructions, and some tricks doable by standard 2761 arithmetics. The use of conditional execution on chips where it is available is controlled by -fif-conversion2. 2762 Enabled at levels -O, -O2, -O3, -Os. 2763 -fif-conversion2 2764 Use conditional execution (where available) to transform conditional jumps into branch-less equivalents. 2765 Enabled at levels -O, -O2, -O3, -Os. 2766 -fdeclone-ctor-dtor 2767 The C++ ABI requires multiple entry points for constructors and destructors: one for a base subobject, one for a complete object, and one for a virtual destructor that calls operator delete 2768 afterwards. For a hierarchy with virtual bases, the base and complete variants are clones, which means two copies of the function. With this option, the base and complete variants are 2769 changed to be thunks that call a common implementation. 2770 Enabled by -Os. 2771 -fdelete-null-pointer-checks 2772 Assume that programs cannot safely dereference null pointers, and that no code or data element resides there. This enables simple constant folding optimizations at all optimization levels. 2773 In addition, other optimization passes in GCC use this flag to control global dataflow analyses that eliminate useless checks for null pointers; these assume that if a pointer is checked 2774 after it has already been dereferenced, it cannot be null. 2775 Note however that in some environments this assumption is not true. Use -fno-delete-null-pointer-checks to disable this optimization for programs that depend on that behavior. 2776 Some targets, especially embedded ones, disable this option at all levels. Otherwise it is enabled at all levels: -O0, -O1, -O2, -O3, -Os. Passes that use the information are enabled 2777 independently at different optimization levels. 2778 -fdevirtualize 2779 Attempt to convert calls to virtual functions to direct calls. This is done both within a procedure and interprocedurally as part of indirect inlining (-findirect-inlining) and 2780 interprocedural constant propagation (-fipa-cp). Enabled at levels -O2, -O3, -Os. 2781 -fdevirtualize-speculatively 2782 Attempt to convert calls to virtual functions to speculative direct calls. Based on the analysis of the type inheritance graph, determine for a given call the set of likely targets. If the 2783 set is small, preferably of size 1, change the call into a conditional deciding between direct and indirect calls. The speculative calls enable more optimizations, such as inlining. When 2784 they seem useless after further optimization, they are converted back into original form. 2785 -fdevirtualize-at-ltrans 2786 Stream extra information needed for aggressive devirtualization when running the link-time optimizer in local transformation mode. This option enables more devirtualization but 2787 significantly increases the size of streamed data. For this reason it is disabled by default. 2788 -fexpensive-optimizations 2789 Perform a number of minor optimizations that are relatively expensive. 2790 Enabled at levels -O2, -O3, -Os. 2791 -free 2792 Attempt to remove redundant extension instructions. This is especially helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit registers after writing to their lower 2793 32-bit half. 2794 Enabled for Alpha, AArch64 and x86 at levels -O2, -O3, -Os. 2795 -fno-lifetime-dse 2796 In C++ the value of an object is only affected by changes within its lifetime: when the constructor begins, the object has an indeterminate value, and any changes during the lifetime of the 2797 object are dead when the object is destroyed. Normally dead store elimination will take advantage of this; if your code relies on the value of the object storage persisting beyond the 2798 lifetime of the object, you can use this flag to disable this optimization. 2799 -flive-range-shrinkage 2800 Attempt to decrease register pressure through register live range shrinkage. This is helpful for fast processors with small or moderate size register sets. 2801 -fira-algorithm=algorithm 2802 Use the specified coloring algorithm for the integrated register allocator. The algorithm argument can be priority, which specifies Chow's priority coloring, or CB, which specifies Chaitin- 2803 Briggs coloring. Chaitin-Briggs coloring is not implemented for all architectures, but for those targets that do support it, it is the default because it generates better code. 2804 -fira-region=region 2805 Use specified regions for the integrated register allocator. The region argument should be one of the following: 2806 all Use all loops as register allocation regions. This can give the best results for machines with a small and/or irregular register set. 2807 mixed 2808 Use all loops except for loops with small register pressure as the regions. This value usually gives the best results in most cases and for most architectures, and is enabled by default 2809 when compiling with optimization for speed (-O, -O2, ...). 2810 one Use all functions as a single region. This typically results in the smallest code size, and is enabled by default for -Os or -O0. 2811 -fira-hoist-pressure 2812 Use IRA to evaluate register pressure in the code hoisting pass for decisions to hoist expressions. This option usually results in smaller code, but it can slow the compiler down. 2813 This option is enabled at level -Os for all targets. 2814 -fira-loop-pressure 2815 Use IRA to evaluate register pressure in loops for decisions to move loop invariants. This option usually results in generation of faster and smaller code on machines with large register 2816 files (>= 32 registers), but it can slow the compiler down. 2817 This option is enabled at level -O3 for some targets. 2818 -fno-ira-share-save-slots 2819 Disable sharing of stack slots used for saving call-used hard registers living through a call. Each hard register gets a separate stack slot, and as a result function stack frames are 2820 larger. 2821 -fno-ira-share-spill-slots 2822 Disable sharing of stack slots allocated for pseudo-registers. Each pseudo-register that does not get a hard register gets a separate stack slot, and as a result function stack frames are 2823 larger. 2824 -fira-verbose=n 2825 Control the verbosity of the dump file for the integrated register allocator. The default value is 5. If the value n is greater or equal to 10, the dump output is sent to stderr using the 2826 same format as n minus 10. 2827 -flra-remat 2828 Enable CFG-sensitive rematerialization in LRA. Instead of loading values of spilled pseudos, LRA tries to rematerialize (recalculate) values if it is profitable. 2829 Enabled at levels -O2, -O3, -Os. 2830 -fdelayed-branch 2831 If supported for the target machine, attempt to reorder instructions to exploit instruction slots available after delayed branch instructions. 2832 Enabled at levels -O, -O2, -O3, -Os. 2833 -fschedule-insns 2834 If supported for the target machine, attempt to reorder instructions to eliminate execution stalls due to required data being unavailable. This helps machines that have slow floating point 2835 or memory load instructions by allowing other instructions to be issued until the result of the load or floating-point instruction is required. 2836 Enabled at levels -O2, -O3. 2837 -fschedule-insns2 2838 Similar to -fschedule-insns, but requests an additional pass of instruction scheduling after register allocation has been done. This is especially useful on machines with a relatively small 2839 number of registers and where memory load instructions take more than one cycle. 2840 Enabled at levels -O2, -O3, -Os. 2841 -fno-sched-interblock 2842 Don't schedule instructions across basic blocks. This is normally enabled by default when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher. 2843 -fno-sched-spec 2844 Don't allow speculative motion of non-load instructions. This is normally enabled by default when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher. 2845 -fsched-pressure 2846 Enable register pressure sensitive insn scheduling before register allocation. This only makes sense when scheduling before register allocation is enabled, i.e. with -fschedule-insns or at 2847 -O2 or higher. Usage of this option can improve the generated code and decrease its size by preventing register pressure increase above the number of available hard registers and subsequent 2848 spills in register allocation. 2849 -fsched-spec-load 2850 Allow speculative motion of some load instructions. This only makes sense when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher. 2851 -fsched-spec-load-dangerous 2852 Allow speculative motion of more load instructions. This only makes sense when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher. 2853 -fsched-stalled-insns 2854 -fsched-stalled-insns=n 2855 Define how many insns (if any) can be moved prematurely from the queue of stalled insns into the ready list during the second scheduling pass. -fno-sched-stalled-insns means that no insns 2856 are moved prematurely, -fsched-stalled-insns=0 means there is no limit on how many queued insns can be moved prematurely. -fsched-stalled-insns without a value is equivalent to 2857 -fsched-stalled-insns=1. 2858 -fsched-stalled-insns-dep 2859 -fsched-stalled-insns-dep=n 2860 Define how many insn groups (cycles) are examined for a dependency on a stalled insn that is a candidate for premature removal from the queue of stalled insns. This has an effect only 2861 during the second scheduling pass, and only if -fsched-stalled-insns is used. -fno-sched-stalled-insns-dep is equivalent to -fsched-stalled-insns-dep=0. -fsched-stalled-insns-dep without a 2862 value is equivalent to -fsched-stalled-insns-dep=1. 2863 -fsched2-use-superblocks 2864 When scheduling after register allocation, use superblock scheduling. This allows motion across basic block boundaries, resulting in faster schedules. This option is experimental, as not 2865 all machine descriptions used by GCC model the CPU closely enough to avoid unreliable results from the algorithm. 2866 This only makes sense when scheduling after register allocation, i.e. with -fschedule-insns2 or at -O2 or higher. 2867 -fsched-group-heuristic 2868 Enable the group heuristic in the scheduler. This heuristic favors the instruction that belongs to a schedule group. This is enabled by default when scheduling is enabled, i.e. with 2869 -fschedule-insns or -fschedule-insns2 or at -O2 or higher. 2870 -fsched-critical-path-heuristic 2871 Enable the critical-path heuristic in the scheduler. This heuristic favors instructions on the critical path. This is enabled by default when scheduling is enabled, i.e. with 2872 -fschedule-insns or -fschedule-insns2 or at -O2 or higher. 2873 -fsched-spec-insn-heuristic 2874 Enable the speculative instruction heuristic in the scheduler. This heuristic favors speculative instructions with greater dependency weakness. This is enabled by default when scheduling 2875 is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. 2876 -fsched-rank-heuristic 2877 Enable the rank heuristic in the scheduler. This heuristic favors the instruction belonging to a basic block with greater size or frequency. This is enabled by default when scheduling is 2878 enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. 2879 -fsched-last-insn-heuristic 2880 Enable the last-instruction heuristic in the scheduler. This heuristic favors the instruction that is less dependent on the last instruction scheduled. This is enabled by default when 2881 scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. 2882 -fsched-dep-count-heuristic 2883 Enable the dependent-count heuristic in the scheduler. This heuristic favors the instruction that has more instructions depending on it. This is enabled by default when scheduling is 2884 enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher. 2885 -freschedule-modulo-scheduled-loops 2886 Modulo scheduling is performed before traditional scheduling. If a loop is modulo scheduled, later scheduling passes may change its schedule. Use this option to control that behavior. 2887 -fselective-scheduling 2888 Schedule instructions using selective scheduling algorithm. Selective scheduling runs instead of the first scheduler pass. 2889 -fselective-scheduling2 2890 Schedule instructions using selective scheduling algorithm. Selective scheduling runs instead of the second scheduler pass. 2891 -fsel-sched-pipelining 2892 Enable software pipelining of innermost loops during selective scheduling. This option has no effect unless one of -fselective-scheduling or -fselective-scheduling2 is turned on. 2893 -fsel-sched-pipelining-outer-loops 2894 When pipelining loops during selective scheduling, also pipeline outer loops. This option has no effect unless -fsel-sched-pipelining is turned on. 2895 -fsemantic-interposition 2896 Some object formats, like ELF, allow interposing of symbols by the dynamic linker. This means that for symbols exported from the DSO, the compiler cannot perform interprocedural 2897 propagation, inlining and other optimizations in anticipation that the function or variable in question may change. While this feature is useful, for example, to rewrite memory allocation 2898 functions by a debugging implementation, it is expensive in the terms of code quality. With -fno-semantic-interposition the compiler assumes that if interposition happens for functions the 2899 overwriting function will have precisely the same semantics (and side effects). Similarly if interposition happens for variables, the constructor of the variable will be the same. The flag 2900 has no effect for functions explicitly declared inline (where it is never allowed for interposition to change semantics) and for symbols explicitly declared weak. 2901 -fshrink-wrap 2902 Emit function prologues only before parts of the function that need it, rather than at the top of the function. This flag is enabled by default at -O and higher. 2903 -fcaller-saves 2904 Enable allocation of values to registers that are clobbered by function calls, by emitting extra instructions to save and restore the registers around such calls. Such allocation is done 2905 only when it seems to result in better code. 2906 This option is always enabled by default on certain machines, usually those which have no call-preserved registers to use instead. 2907 Enabled at levels -O2, -O3, -Os. 2908 -fcombine-stack-adjustments 2909 Tracks stack adjustments (pushes and pops) and stack memory references and then tries to find ways to combine them. 2910 Enabled by default at -O1 and higher. 2911 -fipa-ra 2912 Use caller save registers for allocation if those registers are not used by any called function. In that case it is not necessary to save and restore them around calls. This is only 2913 possible if called functions are part of same compilation unit as current function and they are compiled before it. 2914 Enabled at levels -O2, -O3, -Os. 2915 -fconserve-stack 2916 Attempt to minimize stack usage. The compiler attempts to use less stack space, even if that makes the program slower. This option implies setting the large-stack-frame parameter to 100 2917 and the large-stack-frame-growth parameter to 400. 2918 -ftree-reassoc 2919 Perform reassociation on trees. This flag is enabled by default at -O and higher. 2920 -ftree-pre 2921 Perform partial redundancy elimination (PRE) on trees. This flag is enabled by default at -O2 and -O3. 2922 -ftree-partial-pre 2923 Make partial redundancy elimination (PRE) more aggressive. This flag is enabled by default at -O3. 2924 -ftree-forwprop 2925 Perform forward propagation on trees. This flag is enabled by default at -O and higher. 2926 -ftree-fre 2927 Perform full redundancy elimination (FRE) on trees. The difference between FRE and PRE is that FRE only considers expressions that are computed on all paths leading to the redundant 2928 computation. This analysis is faster than PRE, though it exposes fewer redundancies. This flag is enabled by default at -O and higher. 2929 -ftree-phiprop 2930 Perform hoisting of loads from conditional pointers on trees. This pass is enabled by default at -O and higher. 2931 -fhoist-adjacent-loads 2932 Speculatively hoist loads from both branches of an if-then-else if the loads are from adjacent locations in the same structure and the target architecture has a conditional move instruction. 2933 This flag is enabled by default at -O2 and higher. 2934 -ftree-copy-prop 2935 Perform copy propagation on trees. This pass eliminates unnecessary copy operations. This flag is enabled by default at -O and higher. 2936 -fipa-pure-const 2937 Discover which functions are pure or constant. Enabled by default at -O and higher. 2938 -fipa-reference 2939 Discover which static variables do not escape the compilation unit. Enabled by default at -O and higher. 2940 -fipa-pta 2941 Perform interprocedural pointer analysis and interprocedural modification and reference analysis. This option can cause excessive memory and compile-time usage on large compilation units. 2942 It is not enabled by default at any optimization level. 2943 -fipa-profile 2944 Perform interprocedural profile propagation. The functions called only from cold functions are marked as cold. Also functions executed once (such as "cold", "noreturn", static constructors 2945 or destructors) are identified. Cold functions and loop less parts of functions executed once are then optimized for size. Enabled by default at -O and higher. 2946 -fipa-cp 2947 Perform interprocedural constant propagation. This optimization analyzes the program to determine when values passed to functions are constants and then optimizes accordingly. This 2948 optimization can substantially increase performance if the application has constants passed to functions. This flag is enabled by default at -O2, -Os and -O3. 2949 -fipa-cp-clone 2950 Perform function cloning to make interprocedural constant propagation stronger. When enabled, interprocedural constant propagation performs function cloning when externally visible function 2951 can be called with constant arguments. Because this optimization can create multiple copies of functions, it may significantly increase code size (see --param ipcp-unit-growth=value). This 2952 flag is enabled by default at -O3. 2953 -fipa-cp-alignment 2954 When enabled, this optimization propagates alignment of function parameters to support better vectorization and string operations. 2955 This flag is enabled by default at -O2 and -Os. It requires that -fipa-cp is enabled. 2956 -fipa-icf 2957 Perform Identical Code Folding for functions and read-only variables. The optimization reduces code size and may disturb unwind stacks by replacing a function by equivalent one with a 2958 different name. The optimization works more effectively with link time optimization enabled. 2959 Nevertheless the behavior is similar to Gold Linker ICF optimization, GCC ICF works on different levels and thus the optimizations are not same - there are equivalences that are found only 2960 by GCC and equivalences found only by Gold. 2961 This flag is enabled by default at -O2 and -Os. 2962 -fisolate-erroneous-paths-dereference 2963 Detect paths that trigger erroneous or undefined behavior due to dereferencing a null pointer. Isolate those paths from the main control flow and turn the statement with erroneous or 2964 undefined behavior into a trap. This flag is enabled by default at -O2 and higher. 2965 -fisolate-erroneous-paths-attribute 2966 Detect paths that trigger erroneous or undefined behavior due a null value being used in a way forbidden by a "returns_nonnull" or "nonnull" attribute. Isolate those paths from the main 2967 control flow and turn the statement with erroneous or undefined behavior into a trap. This is not currently enabled, but may be enabled by -O2 in the future. 2968 -ftree-sink 2969 Perform forward store motion on trees. This flag is enabled by default at -O and higher. 2970 -ftree-bit-ccp 2971 Perform sparse conditional bit constant propagation on trees and propagate pointer alignment information. This pass only operates on local scalar variables and is enabled by default at -O 2972 and higher. It requires that -ftree-ccp is enabled. 2973 -ftree-ccp 2974 Perform sparse conditional constant propagation (CCP) on trees. This pass only operates on local scalar variables and is enabled by default at -O and higher. 2975 -fssa-phiopt 2976 Perform pattern matching on SSA PHI nodes to optimize conditional code. This pass is enabled by default at -O and higher. 2977 -ftree-switch-conversion 2978 Perform conversion of simple initializations in a switch to initializations from a scalar array. This flag is enabled by default at -O2 and higher. 2979 -ftree-tail-merge 2980 Look for identical code sequences. When found, replace one with a jump to the other. This optimization is known as tail merging or cross jumping. This flag is enabled by default at -O2 2981 and higher. The compilation time in this pass can be limited using max-tail-merge-comparisons parameter and max-tail-merge-iterations parameter. 2982 -ftree-dce 2983 Perform dead code elimination (DCE) on trees. This flag is enabled by default at -O and higher. 2984 -ftree-builtin-call-dce 2985 Perform conditional dead code elimination (DCE) for calls to built-in functions that may set "errno" but are otherwise side-effect free. This flag is enabled by default at -O2 and higher if 2986 -Os is not also specified. 2987 -ftree-dominator-opts 2988 Perform a variety of simple scalar cleanups (constant/copy propagation, redundancy elimination, range propagation and expression simplification) based on a dominator tree traversal. This 2989 also performs jump threading (to reduce jumps to jumps). This flag is enabled by default at -O and higher. 2990 -ftree-dse 2991 Perform dead store elimination (DSE) on trees. A dead store is a store into a memory location that is later overwritten by another store without any intervening loads. In this case the 2992 earlier store can be deleted. This flag is enabled by default at -O and higher. 2993 -ftree-ch 2994 Perform loop header copying on trees. This is beneficial since it increases effectiveness of code motion optimizations. It also saves one jump. This flag is enabled by default at -O and 2995 higher. It is not enabled for -Os, since it usually increases code size. 2996 -ftree-loop-optimize 2997 Perform loop optimizations on trees. This flag is enabled by default at -O and higher. 2998 -ftree-loop-linear 2999 Perform loop interchange transformations on tree. Same as -floop-interchange. To use this code transformation, GCC has to be configured with --with-isl to enable the Graphite loop 3000 transformation infrastructure. 3001 -floop-interchange 3002 Perform loop interchange transformations on loops. Interchanging two nested loops switches the inner and outer loops. For example, given a loop like: 3003 DO J = 1, M 3004 DO I = 1, N 3005 A(J, I) = A(J, I) * C 3006 ENDDO 3007 ENDDO 3008 loop interchange transforms the loop as if it were written: 3009 DO I = 1, N 3010 DO J = 1, M 3011 A(J, I) = A(J, I) * C 3012 ENDDO 3013 ENDDO 3014 which can be beneficial when "N" is larger than the caches, because in Fortran, the elements of an array are stored in memory contiguously by column, and the original loop iterates over 3015 rows, potentially creating at each access a cache miss. This optimization applies to all the languages supported by GCC and is not limited to Fortran. To use this code transformation, GCC 3016 has to be configured with --with-isl to enable the Graphite loop transformation infrastructure. 3017 -floop-strip-mine 3018 Perform loop strip mining transformations on loops. Strip mining splits a loop into two nested loops. The outer loop has strides equal to the strip size and the inner loop has strides of 3019 the original loop within a strip. The strip length can be changed using the loop-block-tile-size parameter. For example, given a loop like: 3020 DO I = 1, N 3021 A(I) = A(I) + C 3022 ENDDO 3023 loop strip mining transforms the loop as if it were written: 3024 DO II = 1, N, 51 3025 DO I = II, min (II + 50, N) 3026 A(I) = A(I) + C 3027 ENDDO 3028 ENDDO 3029 This optimization applies to all the languages supported by GCC and is not limited to Fortran. To use this code transformation, GCC has to be configured with --with-isl to enable the 3030 Graphite loop transformation infrastructure. 3031 -floop-block 3032 Perform loop blocking transformations on loops. Blocking strip mines each loop in the loop nest such that the memory accesses of the element loops fit inside caches. The strip length can 3033 be changed using the loop-block-tile-size parameter. For example, given a loop like: 3034 DO I = 1, N 3035 DO J = 1, M 3036 A(J, I) = B(I) + C(J) 3037 ENDDO 3038 ENDDO 3039 loop blocking transforms the loop as if it were written: 3040 DO II = 1, N, 51 3041 DO JJ = 1, M, 51 3042 DO I = II, min (II + 50, N) 3043 DO J = JJ, min (JJ + 50, M) 3044 A(J, I) = B(I) + C(J) 3045 ENDDO 3046 ENDDO 3047 ENDDO 3048 ENDDO 3049 which can be beneficial when "M" is larger than the caches, because the innermost loop iterates over a smaller amount of data which can be kept in the caches. This optimization applies to 3050 all the languages supported by GCC and is not limited to Fortran. To use this code transformation, GCC has to be configured with --with-isl to enable the Graphite loop transformation 3051 infrastructure. 3052 -fgraphite-identity 3053 Enable the identity transformation for graphite. For every SCoP we generate the polyhedral representation and transform it back to gimple. Using -fgraphite-identity we can check the costs 3054 or benefits of the GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations are also performed by the code generator ISL, like index splitting and dead code elimination in 3055 loops. 3056 -floop-nest-optimize 3057 Enable the ISL based loop nest optimizer. This is a generic loop nest optimizer based on the Pluto optimization algorithms. It calculates a loop structure optimized for data-locality and 3058 parallelism. This option is experimental. 3059 -floop-unroll-and-jam 3060 Enable unroll and jam for the ISL based loop nest optimizer. The unroll factor can be changed using the loop-unroll-jam-size parameter. The unrolled dimension (counting from the most inner 3061 one) can be changed using the loop-unroll-jam-depth parameter. . 3062 -floop-parallelize-all 3063 Use the Graphite data dependence analysis to identify loops that can be parallelized. Parallelize all the loops that can be analyzed to not contain loop carried dependences without checking 3064 that it is profitable to parallelize the loops. 3065 -fcheck-data-deps 3066 Compare the results of several data dependence analyzers. This option is used for debugging the data dependence analyzers. 3067 -ftree-loop-if-convert 3068 Attempt to transform conditional jumps in the innermost loops to branch-less equivalents. The intent is to remove control-flow from the innermost loops in order to improve the ability of 3069 the vectorization pass to handle these loops. This is enabled by default if vectorization is enabled. 3070 -ftree-loop-if-convert-stores 3071 Attempt to also if-convert conditional jumps containing memory writes. This transformation can be unsafe for multi-threaded programs as it transforms conditional memory writes into 3072 unconditional memory writes. For example, 3073 for (i = 0; i < N; i++) 3074 if (cond) 3075 A[i] = expr; 3076 is transformed to 3077 for (i = 0; i < N; i++) 3078 A[i] = cond ? expr : A[i]; 3079 potentially producing data races. 3080 -ftree-loop-distribution 3081 Perform loop distribution. This flag can improve cache performance on big loop bodies and allow further loop optimizations, like parallelization or vectorization, to take place. For 3082 example, the loop 3083 DO I = 1, N 3084 A(I) = B(I) + C 3085 D(I) = E(I) * F 3086 ENDDO 3087 is transformed to 3088 DO I = 1, N 3089 A(I) = B(I) + C 3090 ENDDO 3091 DO I = 1, N 3092 D(I) = E(I) * F 3093 ENDDO 3094 -ftree-loop-distribute-patterns 3095 Perform loop distribution of patterns that can be code generated with calls to a library. This flag is enabled by default at -O3. 3096 This pass distributes the initialization loops and generates a call to memset zero. For example, the loop 3097 DO I = 1, N 3098 A(I) = 0 3099 B(I) = A(I) + I 3100 ENDDO 3101 is transformed to 3102 DO I = 1, N 3103 A(I) = 0 3104 ENDDO 3105 DO I = 1, N 3106 B(I) = A(I) + I 3107 ENDDO 3108 and the initialization loop is transformed into a call to memset zero. 3109 -ftree-loop-im 3110 Perform loop invariant motion on trees. This pass moves only invariants that are hard to handle at RTL level (function calls, operations that expand to nontrivial sequences of insns). With 3111 -funswitch-loops it also moves operands of conditions that are invariant out of the loop, so that we can use just trivial invariantness analysis in loop unswitching. The pass also includes 3112 store motion. 3113 -ftree-loop-ivcanon 3114 Create a canonical counter for number of iterations in loops for which determining number of iterations requires complicated analysis. Later optimizations then may determine the number 3115 easily. Useful especially in connection with unrolling. 3116 -fivopts 3117 Perform induction variable optimizations (strength reduction, induction variable merging and induction variable elimination) on trees. 3118 -ftree-parallelize-loops=n 3119 Parallelize loops, i.e., split their iteration space to run in n threads. This is only possible for loops whose iterations are independent and can be arbitrarily reordered. The 3120 optimization is only profitable on multiprocessor machines, for loops that are CPU-intensive, rather than constrained e.g. by memory bandwidth. This option implies -pthread, and thus is 3121 only supported on targets that have support for -pthread. 3122 -ftree-pta 3123 Perform function-local points-to analysis on trees. This flag is enabled by default at -O and higher. 3124 -ftree-sra 3125 Perform scalar replacement of aggregates. This pass replaces structure references with scalars to prevent committing structures to memory too early. This flag is enabled by default at -O 3126 and higher. 3127 -ftree-copyrename 3128 Perform copy renaming on trees. This pass attempts to rename compiler temporaries to other variables at copy locations, usually resulting in variable names which more closely resemble the 3129 original variables. This flag is enabled by default at -O and higher. 3130 -ftree-coalesce-inlined-vars 3131 Tell the copyrename pass (see -ftree-copyrename) to attempt to combine small user-defined variables too, but only if they are inlined from other functions. It is a more limited form of 3132 -ftree-coalesce-vars. This may harm debug information of such inlined variables, but it keeps variables of the inlined-into function apart from each other, such that they are more likely to 3133 contain the expected values in a debugging session. 3134 -ftree-coalesce-vars 3135 Tell the copyrename pass (see -ftree-copyrename) to attempt to combine small user-defined variables too, instead of just compiler temporaries. This may severely limit the ability to debug 3136 an optimized program compiled with -fno-var-tracking-assignments. In the negated form, this flag prevents SSA coalescing of user variables, including inlined ones. This option is enabled 3137 by default. 3138 -ftree-ter 3139 Perform temporary expression replacement during the SSA->normal phase. Single use/single def temporaries are replaced at their use location with their defining expression. This results in 3140 non-GIMPLE code, but gives the expanders much more complex trees to work on resulting in better RTL generation. This is enabled by default at -O and higher. 3141 -ftree-slsr 3142 Perform straight-line strength reduction on trees. This recognizes related expressions involving multiplications and replaces them by less expensive calculations when possible. This is 3143 enabled by default at -O and higher. 3144 -ftree-vectorize 3145 Perform vectorization on trees. This flag enables -ftree-loop-vectorize and -ftree-slp-vectorize if not explicitly specified. 3146 -ftree-loop-vectorize 3147 Perform loop vectorization on trees. This flag is enabled by default at -O3 and when -ftree-vectorize is enabled. 3148 -ftree-slp-vectorize 3149 Perform basic block vectorization on trees. This flag is enabled by default at -O3 and when -ftree-vectorize is enabled. 3150 -fvect-cost-model=model 3151 Alter the cost model used for vectorization. The model argument should be one of unlimited, dynamic or cheap. With the unlimited model the vectorized code-path is assumed to be profitable 3152 while with the dynamic model a runtime check guards the vectorized code-path to enable it only for iteration counts that will likely execute faster than when executing the original scalar 3153 loop. The cheap model disables vectorization of loops where doing so would be cost prohibitive for example due to required runtime checks for data dependence or alignment but otherwise is 3154 equal to the dynamic model. The default cost model depends on other optimization flags and is either dynamic or cheap. 3155 -fsimd-cost-model=model 3156 Alter the cost model used for vectorization of loops marked with the OpenMP or Cilk Plus simd directive. The model argument should be one of unlimited, dynamic, cheap. All values of model 3157 have the same meaning as described in -fvect-cost-model and by default a cost model defined with -fvect-cost-model is used. 3158 -ftree-vrp 3159 Perform Value Range Propagation on trees. This is similar to the constant propagation pass, but instead of values, ranges of values are propagated. This allows the optimizers to remove 3160 unnecessary range checks like array bound checks and null pointer checks. This is enabled by default at -O2 and higher. Null pointer check elimination is only done if 3161 -fdelete-null-pointer-checks is enabled. 3162 -fsplit-ivs-in-unroller 3163 Enables expression of values of induction variables in later iterations of the unrolled loop using the value in the first iteration. This breaks long dependency chains, thus improving 3164 efficiency of the scheduling passes. 3165 A combination of -fweb and CSE is often sufficient to obtain the same effect. However, that is not reliable in cases where the loop body is more complicated than a single basic block. It 3166 also does not work at all on some architectures due to restrictions in the CSE pass. 3167 This optimization is enabled by default. 3168 -fvariable-expansion-in-unroller 3169 With this option, the compiler creates multiple copies of some local variables when unrolling a loop, which can result in superior code. 3170 -fpartial-inlining 3171 Inline parts of functions. This option has any effect only when inlining itself is turned on by the -finline-functions or -finline-small-functions options. 3172 Enabled at level -O2. 3173 -fpredictive-commoning 3174 Perform predictive commoning optimization, i.e., reusing computations (especially memory loads and stores) performed in previous iterations of loops. 3175 This option is enabled at level -O3. 3176 -fprefetch-loop-arrays 3177 If supported by the target machine, generate instructions to prefetch memory to improve the performance of loops that access large arrays. 3178 This option may generate better or worse code; results are highly dependent on the structure of loops within the source code. 3179 Disabled at level -Os. 3180 -fno-peephole 3181 -fno-peephole2 3182 Disable any machine-specific peephole optimizations. The difference between -fno-peephole and -fno-peephole2 is in how they are implemented in the compiler; some targets use one, some use 3183 the other, a few use both. 3184 -fpeephole is enabled by default. -fpeephole2 enabled at levels -O2, -O3, -Os. 3185 -fno-guess-branch-probability 3186 Do not guess branch probabilities using heuristics. 3187 GCC uses heuristics to guess branch probabilities if they are not provided by profiling feedback (-fprofile-arcs). These heuristics are based on the control flow graph. If some branch 3188 probabilities are specified by "__builtin_expect", then the heuristics are used to guess branch probabilities for the rest of the control flow graph, taking the "__builtin_expect" info into 3189 account. The interactions between the heuristics and "__builtin_expect" can be complex, and in some cases, it may be useful to disable the heuristics so that the effects of 3190 "__builtin_expect" are easier to understand. 3191 The default is -fguess-branch-probability at levels -O, -O2, -O3, -Os. 3192 -freorder-blocks 3193 Reorder basic blocks in the compiled function in order to reduce number of taken branches and improve code locality. 3194 Enabled at levels -O2, -O3. 3195 -freorder-blocks-and-partition 3196 In addition to reordering basic blocks in the compiled function, in order to reduce number of taken branches, partitions hot and cold basic blocks into separate sections of the assembly and 3197 .o files, to improve paging and cache locality performance. 3198 This optimization is automatically turned off in the presence of exception handling, for linkonce sections, for functions with a user-defined section attribute and on any architecture that 3199 does not support named sections. 3200 Enabled for x86 at levels -O2, -O3. 3201 -freorder-functions 3202 Reorder functions in the object file in order to improve code locality. This is implemented by using special subsections ".text.hot" for most frequently executed functions and 3203 ".text.unlikely" for unlikely executed functions. Reordering is done by the linker so object file format must support named sections and linker must place them in a reasonable way. 3204 Also profile feedback must be available to make this option effective. See -fprofile-arcs for details. 3205 Enabled at levels -O2, -O3, -Os. 3206 -fstrict-aliasing 3207 Allow the compiler to assume the strictest aliasing rules applicable to the language being compiled. For C (and C++), this activates optimizations based on the type of expressions. In 3208 particular, an object of one type is assumed never to reside at the same address as an object of a different type, unless the types are almost the same. For example, an "unsigned int" can 3209 alias an "int", but not a "void*" or a "double". A character type may alias any other type. 3210 Pay special attention to code like this: 3211 union a_union { 3212 int i; 3213 double d; 3214 }; 3215 int f() { 3216 union a_union t; 3217 t.d = 3.0; 3218 return t.i; 3219 } 3220 The practice of reading from a different union member than the one most recently written to (called "type-punning") is common. Even with -fstrict-aliasing, type-punning is allowed, provided 3221 the memory is accessed through the union type. So, the code above works as expected. However, this code might not: 3222 int f() { 3223 union a_union t; 3224 int* ip; 3225 t.d = 3.0; 3226 ip = &t.i; 3227 return *ip; 3228 } 3229 Similarly, access by taking the address, casting the resulting pointer and dereferencing the result has undefined behavior, even if the cast uses a union type, e.g.: 3230 int f() { 3231 double d = 3.0; 3232 return ((union a_union *) &d)->i; 3233 } 3234 The -fstrict-aliasing option is enabled at levels -O2, -O3, -Os. 3235 -fstrict-overflow 3236 Allow the compiler to assume strict signed overflow rules, depending on the language being compiled. For C (and C++) this means that overflow when doing arithmetic with signed numbers is 3237 undefined, which means that the compiler may assume that it does not happen. This permits various optimizations. For example, the compiler assumes that an expression like "i + 10 > i" is 3238 always true for signed "i". This assumption is only valid if signed overflow is undefined, as the expression is false if "i + 10" overflows when using twos complement arithmetic. When this 3239 option is in effect any attempt to determine whether an operation on signed numbers overflows must be written carefully to not actually involve overflow. 3240 This option also allows the compiler to assume strict pointer semantics: given a pointer to an object, if adding an offset to that pointer does not produce a pointer to the same object, the 3241 addition is undefined. This permits the compiler to conclude that "p + u > p" is always true for a pointer "p" and unsigned integer "u". This assumption is only valid because pointer 3242 wraparound is undefined, as the expression is false if "p + u" overflows using twos complement arithmetic. 3243 See also the -fwrapv option. Using -fwrapv means that integer signed overflow is fully defined: it wraps. When -fwrapv is used, there is no difference between -fstrict-overflow and 3244 -fno-strict-overflow for integers. With -fwrapv certain types of overflow are permitted. For example, if the compiler gets an overflow when doing arithmetic on constants, the overflowed 3245 value can still be used with -fwrapv, but not otherwise. 3246 The -fstrict-overflow option is enabled at levels -O2, -O3, -Os. 3247 -falign-functions 3248 -falign-functions=n 3249 Align the start of functions to the next power-of-two greater than n, skipping up to n bytes. For instance, -falign-functions=32 aligns functions to the next 32-byte boundary, but 3250 -falign-functions=24 aligns to the next 32-byte boundary only if this can be done by skipping 23 bytes or less. 3251 -fno-align-functions and -falign-functions=1 are equivalent and mean that functions are not aligned. 3252 Some assemblers only support this flag when n is a power of two; in that case, it is rounded up. 3253 If n is not specified or is zero, use a machine-dependent default. 3254 Enabled at levels -O2, -O3. 3255 -falign-labels 3256 -falign-labels=n 3257 Align all branch targets to a power-of-two boundary, skipping up to n bytes like -falign-functions. This option can easily make code slower, because it must insert dummy operations for when 3258 the branch target is reached in the usual flow of the code. 3259 -fno-align-labels and -falign-labels=1 are equivalent and mean that labels are not aligned. 3260 If -falign-loops or -falign-jumps are applicable and are greater than this value, then their values are used instead. 3261 If n is not specified or is zero, use a machine-dependent default which is very likely to be 1, meaning no alignment. 3262 Enabled at levels -O2, -O3. 3263 -falign-loops 3264 -falign-loops=n 3265 Align loops to a power-of-two boundary, skipping up to n bytes like -falign-functions. If the loops are executed many times, this makes up for any execution of the dummy operations. 3266 -fno-align-loops and -falign-loops=1 are equivalent and mean that loops are not aligned. 3267 If n is not specified or is zero, use a machine-dependent default. 3268 Enabled at levels -O2, -O3. 3269 -falign-jumps 3270 -falign-jumps=n 3271 Align branch targets to a power-of-two boundary, for branch targets where the targets can only be reached by jumping, skipping up to n bytes like -falign-functions. In this case, no dummy 3272 operations need be executed. 3273 -fno-align-jumps and -falign-jumps=1 are equivalent and mean that loops are not aligned. 3274 If n is not specified or is zero, use a machine-dependent default. 3275 Enabled at levels -O2, -O3. 3276 -funit-at-a-time 3277 This option is left for compatibility reasons. -funit-at-a-time has no effect, while -fno-unit-at-a-time implies -fno-toplevel-reorder and -fno-section-anchors. 3278 Enabled by default. 3279 -fno-toplevel-reorder 3280 Do not reorder top-level functions, variables, and "asm" statements. Output them in the same order that they appear in the input file. When this option is used, unreferenced static 3281 variables are not removed. This option is intended to support existing code that relies on a particular ordering. For new code, it is better to use attributes when possible. 3282 Enabled at level -O0. When disabled explicitly, it also implies -fno-section-anchors, which is otherwise enabled at -O0 on some targets. 3283 -fweb 3284 Constructs webs as commonly used for register allocation purposes and assign each web individual pseudo register. This allows the register allocation pass to operate on pseudos directly, 3285 but also strengthens several other optimization passes, such as CSE, loop optimizer and trivial dead code remover. It can, however, make debugging impossible, since variables no longer stay 3286 in a "home register". 3287 Enabled by default with -funroll-loops. 3288 -fwhole-program 3289 Assume that the current compilation unit represents the whole program being compiled. All public functions and variables with the exception of "main" and those merged by attribute 3290 "externally_visible" become static functions and in effect are optimized more aggressively by interprocedural optimizers. 3291 This option should not be used in combination with -flto. Instead relying on a linker plugin should provide safer and more precise information. 3292 -flto[=n] 3293 This option runs the standard link-time optimizer. When invoked with source code, it generates GIMPLE (one of GCC's internal representations) and writes it to special ELF sections in the 3294 object file. When the object files are linked together, all the function bodies are read from these ELF sections and instantiated as if they had been part of the same translation unit. 3295 To use the link-time optimizer, -flto and optimization options should be specified at compile time and during the final link. For example: 3296 gcc -c -O2 -flto foo.c 3297 gcc -c -O2 -flto bar.c 3298 gcc -o myprog -flto -O2 foo.o bar.o 3299 The first two invocations to GCC save a bytecode representation of GIMPLE into special ELF sections inside foo.o and bar.o. The final invocation reads the GIMPLE bytecode from foo.o and 3300 bar.o, merges the two files into a single internal image, and compiles the result as usual. Since both foo.o and bar.o are merged into a single image, this causes all the interprocedural 3301 analyses and optimizations in GCC to work across the two files as if they were a single one. This means, for example, that the inliner is able to inline functions in bar.o into functions in 3302 foo.o and vice-versa. 3303 Another (simpler) way to enable link-time optimization is: 3304 gcc -o myprog -flto -O2 foo.c bar.c 3305 The above generates bytecode for foo.c and bar.c, merges them together into a single GIMPLE representation and optimizes them as usual to produce myprog. 3306 The only important thing to keep in mind is that to enable link-time optimizations you need to use the GCC driver to perform the link-step. GCC then automatically performs link-time 3307 optimization if any of the objects involved were compiled with the -flto command-line option. You generally should specify the optimization options to be used for link-time optimization 3308 though GCC tries to be clever at guessing an optimization level to use from the options used at compile-time if you fail to specify one at link-time. You can always override the automatic 3309 decision to do link-time optimization at link-time by passing -fno-lto to the link command. 3310 To make whole program optimization effective, it is necessary to make certain whole program assumptions. The compiler needs to know what functions and variables can be accessed by libraries 3311 and runtime outside of the link-time optimized unit. When supported by the linker, the linker plugin (see -fuse-linker-plugin) passes information to the compiler about used and externally 3312 visible symbols. When the linker plugin is not available, -fwhole-program should be used to allow the compiler to make these assumptions, which leads to more aggressive optimization 3313 decisions. 3314 When -fuse-linker-plugin is not enabled then, when a file is compiled with -flto, the generated object file is larger than a regular object file because it contains GIMPLE bytecodes and the 3315 usual final code (see -ffat-lto-objects. This means that object files with LTO information can be linked as normal object files; if -fno-lto is passed to the linker, no interprocedural 3316 optimizations are applied. Note that when -fno-fat-lto-objects is enabled the compile-stage is faster but you cannot perform a regular, non-LTO link on them. 3317 Additionally, the optimization flags used to compile individual files are not necessarily related to those used at link time. For instance, 3318 gcc -c -O0 -ffat-lto-objects -flto foo.c 3319 gcc -c -O0 -ffat-lto-objects -flto bar.c 3320 gcc -o myprog -O3 foo.o bar.o 3321 This produces individual object files with unoptimized assembler code, but the resulting binary myprog is optimized at -O3. If, instead, the final binary is generated with -fno-lto, then 3322 myprog is not optimized. 3323 When producing the final binary, GCC only applies link-time optimizations to those files that contain bytecode. Therefore, you can mix and match object files and libraries with GIMPLE 3324 bytecodes and final object code. GCC automatically selects which files to optimize in LTO mode and which files to link without further processing. 3325 There are some code generation flags preserved by GCC when generating bytecodes, as they need to be used during the final link stage. Generally options specified at link-time override those 3326 specified at compile-time. 3327 If you do not specify an optimization level option -O at link-time then GCC computes one based on the optimization levels used when compiling the object files. The highest optimization 3328 level wins here. 3329 Currently, the following options and their setting are take from the first object file that explicitely specified it: -fPIC, -fpic, -fpie, -fcommon, -fexceptions, -fnon-call-exceptions, 3330 -fgnu-tm and all the -m target flags. 3331 Certain ABI changing flags are required to match in all compilation-units and trying to override this at link-time with a conflicting value is ignored. This includes options such as 3332 -freg-struct-return and -fpcc-struct-return. 3333 Other options such as -ffp-contract, -fno-strict-overflow, -fwrapv, -fno-trapv or -fno-strict-aliasing are passed through to the link stage and merged conservatively for conflicting 3334 translation units. Specifically -fno-strict-overflow, -fwrapv and -fno-trapv take precedence and for example -ffp-contract=off takes precedence over -ffp-contract=fast. You can override 3335 them at linke-time. 3336 It is recommended that you compile all the files participating in the same link with the same options and also specify those options at link time. 3337 If LTO encounters objects with C linkage declared with incompatible types in separate translation units to be linked together (undefined behavior according to ISO C99 6.2.7), a non-fatal 3338 diagnostic may be issued. The behavior is still undefined at run time. Similar diagnostics may be raised for other languages. 3339 Another feature of LTO is that it is possible to apply interprocedural optimizations on files written in different languages: 3340 gcc -c -flto foo.c 3341 g++ -c -flto bar.cc 3342 gfortran -c -flto baz.f90 3343 g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran 3344 Notice that the final link is done with g++ to get the C++ runtime libraries and -lgfortran is added to get the Fortran runtime libraries. In general, when mixing languages in LTO mode, you 3345 should use the same link command options as when mixing languages in a regular (non-LTO) compilation. 3346 If object files containing GIMPLE bytecode are stored in a library archive, say libfoo.a, it is possible to extract and use them in an LTO link if you are using a linker with plugin support. 3347 To create static libraries suitable for LTO, use gcc-ar and gcc-ranlib instead of ar and ranlib; to show the symbols of object files with GIMPLE bytecode, use gcc-nm. Those commands require 3348 that ar, ranlib and nm have been compiled with plugin support. At link time, use the the flag -fuse-linker-plugin to ensure that the library participates in the LTO optimization process: 3349 gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo 3350 With the linker plugin enabled, the linker extracts the needed GIMPLE files from libfoo.a and passes them on to the running GCC to make them part of the aggregated GIMPLE image to be 3351 optimized. 3352 If you are not using a linker with plugin support and/or do not enable the linker plugin, then the objects inside libfoo.a are extracted and linked as usual, but they do not participate in 3353 the LTO optimization process. In order to make a static library suitable for both LTO optimization and usual linkage, compile its object files with -flto -ffat-lto-objects. 3354 Link-time optimizations do not require the presence of the whole program to operate. If the program does not require any symbols to be exported, it is possible to combine -flto and 3355 -fwhole-program to allow the interprocedural optimizers to use more aggressive assumptions which may lead to improved optimization opportunities. Use of -fwhole-program is not needed when 3356 linker plugin is active (see -fuse-linker-plugin). 3357 The current implementation of LTO makes no attempt to generate bytecode that is portable between different types of hosts. The bytecode files are versioned and there is a strict version 3358 check, so bytecode files generated in one version of GCC do not work with an older or newer version of GCC. 3359 Link-time optimization does not work well with generation of debugging information. Combining -flto with -g is currently experimental and expected to produce unexpected results. 3360 If you specify the optional n, the optimization and code generation done at link time is executed in parallel using n parallel jobs by utilizing an installed make program. The environment 3361 variable MAKE may be used to override the program used. The default value for n is 1. 3362 You can also specify -flto=jobserver to use GNU make's job server mode to determine the number of parallel jobs. This is useful when the Makefile calling GCC is already executing in 3363 parallel. You must prepend a + to the command recipe in the parent Makefile for this to work. This option likely only works if MAKE is GNU make. 3364 -flto-partition=alg 3365 Specify the partitioning algorithm used by the link-time optimizer. The value is either 1to1 to specify a partitioning mirroring the original source files or balanced to specify 3366 partitioning into equally sized chunks (whenever possible) or max to create new partition for every symbol where possible. Specifying none as an algorithm disables partitioning and 3367 streaming completely. The default value is balanced. While 1to1 can be used as an workaround for various code ordering issues, the max partitioning is intended for internal testing only. 3368 The value one specifies that exactly one partition should be used while the value none bypasses partitioning and executes the link-time optimization step directly from the WPA phase. 3369 -flto-odr-type-merging 3370 Enable streaming of mangled types names of C++ types and their unification at linktime. This increases size of LTO object files, but enable diagnostics about One Definition Rule violations. 3371 -flto-compression-level=n 3372 This option specifies the level of compression used for intermediate language written to LTO object files, and is only meaningful in conjunction with LTO mode (-flto). Valid values are 0 3373 (no compression) to 9 (maximum compression). Values outside this range are clamped to either 0 or 9. If the option is not given, a default balanced compression setting is used. 3374 -flto-report 3375 Prints a report with internal details on the workings of the link-time optimizer. The contents of this report vary from version to version. It is meant to be useful to GCC developers when 3376 processing object files in LTO mode (via -flto). 3377 Disabled by default. 3378 -flto-report-wpa 3379 Like -flto-report, but only print for the WPA phase of Link Time Optimization. 3380 -fuse-linker-plugin 3381 Enables the use of a linker plugin during link-time optimization. This option relies on plugin support in the linker, which is available in gold or in GNU ld 2.21 or newer. 3382 This option enables the extraction of object files with GIMPLE bytecode out of library archives. This improves the quality of optimization by exposing more code to the link-time optimizer. 3383 This information specifies what symbols can be accessed externally (by non-LTO object or during dynamic linking). Resulting code quality improvements on binaries (and shared libraries that 3384 use hidden visibility) are similar to -fwhole-program. See -flto for a description of the effect of this flag and how to use it. 3385 This option is enabled by default when LTO support in GCC is enabled and GCC was configured for use with a linker supporting plugins (GNU ld 2.21 or newer or gold). 3386 -ffat-lto-objects 3387 Fat LTO objects are object files that contain both the intermediate language and the object code. This makes them usable for both LTO linking and normal linking. This option is effective 3388 only when compiling with -flto and is ignored at link time. 3389 -fno-fat-lto-objects improves compilation time over plain LTO, but requires the complete toolchain to be aware of LTO. It requires a linker with linker plugin support for basic 3390 functionality. Additionally, nm, ar and ranlib need to support linker plugins to allow a full-featured build environment (capable of building static libraries etc). GCC provides the gcc- 3391 ar, gcc-nm, gcc-ranlib wrappers to pass the right options to these tools. With non fat LTO makefiles need to be modified to use them. 3392 The default is -fno-fat-lto-objects on targets with linker plugin support. 3393 -fcompare-elim 3394 After register allocation and post-register allocation instruction splitting, identify arithmetic instructions that compute processor flags similar to a comparison operation based on that 3395 arithmetic. If possible, eliminate the explicit comparison operation. 3396 This pass only applies to certain targets that cannot explicitly represent the comparison operation before register allocation is complete. 3397 Enabled at levels -O, -O2, -O3, -Os. 3398 -fcprop-registers 3399 After register allocation and post-register allocation instruction splitting, perform a copy-propagation pass to try to reduce scheduling dependencies and occasionally eliminate the copy. 3400 Enabled at levels -O, -O2, -O3, -Os. 3401 -fprofile-correction 3402 Profiles collected using an instrumented binary for multi-threaded programs may be inconsistent due to missed counter updates. When this option is specified, GCC uses heuristics to correct 3403 or smooth out such inconsistencies. By default, GCC emits an error message when an inconsistent profile is detected. 3404 -fprofile-dir=path 3405 Set the directory to search for the profile data files in to path. This option affects only the profile data generated by -fprofile-generate, -ftest-coverage, -fprofile-arcs and used by 3406 -fprofile-use and -fbranch-probabilities and its related options. Both absolute and relative paths can be used. By default, GCC uses the current directory as path, thus the profile data 3407 file appears in the same directory as the object file. 3408 -fprofile-generate 3409 -fprofile-generate=path 3410 Enable options usually used for instrumenting application to produce profile useful for later recompilation with profile feedback based optimization. You must use -fprofile-generate both 3411 when compiling and when linking your program. 3412 The following options are enabled: -fprofile-arcs, -fprofile-values, -fvpt. 3413 If path is specified, GCC looks at the path to find the profile feedback data files. See -fprofile-dir. 3414 -fprofile-use 3415 -fprofile-use=path 3416 Enable profile feedback-directed optimizations, and the following optimizations which are generally profitable only with profile feedback available: -fbranch-probabilities, -fvpt, 3417 -funroll-loops, -fpeel-loops, -ftracer, -ftree-vectorize, and ftree-loop-distribute-patterns. 3418 By default, GCC emits an error message if the feedback profiles do not match the source code. This error can be turned into a warning by using -Wcoverage-mismatch. Note this may result in 3419 poorly optimized code. 3420 If path is specified, GCC looks at the path to find the profile feedback data files. See -fprofile-dir. 3421 -fauto-profile 3422 -fauto-profile=path 3423 Enable sampling-based feedback-directed optimizations, and the following optimizations which are generally profitable only with profile feedback available: -fbranch-probabilities, -fvpt, 3424 -funroll-loops, -fpeel-loops, -ftracer, -ftree-vectorize, -finline-functions, -fipa-cp, -fipa-cp-clone, -fpredictive-commoning, -funswitch-loops, -fgcse-after-reload, and 3425 -ftree-loop-distribute-patterns. 3426 path is the name of a file containing AutoFDO profile information. If omitted, it defaults to fbdata.afdo in the current directory. 3427 Producing an AutoFDO profile data file requires running your program with the perf utility on a supported GNU/Linux target system. For more information, see . 3428 E.g. 3429 perf record -e br_inst_retired:near_taken -b -o perf.data \ 3430 -- your_program 3431 Then use the create_gcov tool to convert the raw profile data to a format that can be used by GCC. You must also supply the unstripped binary for your program to this tool. See 3432 . 3433 E.g. 3434 create_gcov --binary=your_program.unstripped --profile=perf.data \ 3435 --gcov=profile.afdo 3436 The following options control compiler behavior regarding floating-point arithmetic. These options trade off between speed and correctness. All must be specifically enabled. 3437 -ffloat-store 3438 Do not store floating-point variables in registers, and inhibit other options that might change whether a floating-point value is taken from a register or memory. 3439 This option prevents undesirable excess precision on machines such as the 68000 where the floating registers (of the 68881) keep more precision than a "double" is supposed to have. 3440 Similarly for the x86 architecture. For most programs, the excess precision does only good, but a few programs rely on the precise definition of IEEE floating point. Use -ffloat-store for 3441 such programs, after modifying them to store all pertinent intermediate computations into variables. 3442 -fexcess-precision=style 3443 This option allows further control over excess precision on machines where floating-point registers have more precision than the IEEE "float" and "double" types and the processor does not 3444 support operations rounding to those types. By default, -fexcess-precision=fast is in effect; this means that operations are carried out in the precision of the registers and that it is 3445 unpredictable when rounding to the types specified in the source code takes place. When compiling C, if -fexcess-precision=standard is specified then excess precision follows the rules 3446 specified in ISO C99; in particular, both casts and assignments cause values to be rounded to their semantic types (whereas -ffloat-store only affects assignments). This option is enabled 3447 by default for C if a strict conformance option such as -std=c99 is used. 3448 -fexcess-precision=standard is not implemented for languages other than C, and has no effect if -funsafe-math-optimizations or -ffast-math is specified. On the x86, it also has no effect if 3449 -mfpmath=sse or -mfpmath=sse+387 is specified; in the former case, IEEE semantics apply without excess precision, and in the latter, rounding is unpredictable. 3450 -ffast-math 3451 Sets the options -fno-math-errno, -funsafe-math-optimizations, -ffinite-math-only, -fno-rounding-math, -fno-signaling-nans and -fcx-limited-range. 3452 This option causes the preprocessor macro "__FAST_MATH__" to be defined. 3453 This option is not turned on by any -O option besides -Ofast since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications 3454 for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. 3455 -fno-math-errno 3456 Do not set "errno" after calling math functions that are executed with a single instruction, e.g., "sqrt". A program that relies on IEEE exceptions for math error handling may want to use 3457 this flag for speed while maintaining IEEE arithmetic compatibility. 3458 This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math 3459 functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. 3460 The default is -fmath-errno. 3461 On Darwin systems, the math library never sets "errno". There is therefore no reason for the compiler to consider the possibility that it might, and -fno-math-errno is the default. 3462 -funsafe-math-optimizations 3463 Allow optimizations for floating-point arithmetic that (a) assume that arguments and results are valid and (b) may violate IEEE or ANSI standards. When used at link-time, it may include 3464 libraries or startup files that change the default FPU control word or other similar optimizations. 3465 This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math 3466 functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. Enables -fno-signed-zeros, -fno-trapping-math, -fassociative-math and 3467 -freciprocal-math. 3468 The default is -fno-unsafe-math-optimizations. 3469 -fassociative-math 3470 Allow re-association of operands in series of floating-point operations. This violates the ISO C and C++ language standard by possibly changing computation result. NOTE: re-ordering may 3471 change the sign of zero as well as ignore NaNs and inhibit or create underflow or overflow (and thus cannot be used on code that relies on rounding behavior like "(x + 2**52) - 2**52". May 3472 also reorder floating-point comparisons and thus may not be used when ordered comparisons are required. This option requires that both -fno-signed-zeros and -fno-trapping-math be in effect. 3473 Moreover, it doesn't make much sense with -frounding-math. For Fortran the option is automatically enabled when both -fno-signed-zeros and -fno-trapping-math are in effect. 3474 The default is -fno-associative-math. 3475 -freciprocal-math 3476 Allow the reciprocal of a value to be used instead of dividing by the value if this enables optimizations. For example "x / y" can be replaced with "x * (1/y)", which is useful if "(1/y)" 3477 is subject to common subexpression elimination. Note that this loses precision and increases the number of flops operating on the value. 3478 The default is -fno-reciprocal-math. 3479 -ffinite-math-only 3480 Allow optimizations for floating-point arithmetic that assume that arguments and results are not NaNs or +-Infs. 3481 This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math 3482 functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. 3483 The default is -fno-finite-math-only. 3484 -fno-signed-zeros 3485 Allow optimizations for floating-point arithmetic that ignore the signedness of zero. IEEE arithmetic specifies the behavior of distinct +0.0 and -0.0 values, which then prohibits 3486 simplification of expressions such as x+0.0 or 0.0*x (even with -ffinite-math-only). This option implies that the sign of a zero result isn't significant. 3487 The default is -fsigned-zeros. 3488 -fno-trapping-math 3489 Compile code assuming that floating-point operations cannot generate user-visible traps. These traps include division by zero, overflow, underflow, inexact result and invalid operation. 3490 This option requires that -fno-signaling-nans be in effect. Setting this option may allow faster code if one relies on "non-stop" IEEE arithmetic, for example. 3491 This option should never be turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for 3492 math functions. 3493 The default is -ftrapping-math. 3494 -frounding-math 3495 Disable transformations and optimizations that assume default floating-point rounding behavior. This is round-to-zero for all floating point to integer conversions, and round-to-nearest for 3496 all other arithmetic truncations. This option should be specified for programs that change the FP rounding mode dynamically, or that may be executed with a non-default rounding mode. This 3497 option disables constant folding of floating-point expressions at compile time (which may be affected by rounding mode) and arithmetic transformations that are unsafe in the presence of 3498 sign-dependent rounding modes. 3499 The default is -fno-rounding-math. 3500 This option is experimental and does not currently guarantee to disable all GCC optimizations that are affected by rounding mode. Future versions of GCC may provide finer control of this 3501 setting using C99's "FENV_ACCESS" pragma. This command-line option will be used to specify the default state for "FENV_ACCESS". 3502 -fsignaling-nans 3503 Compile code assuming that IEEE signaling NaNs may generate user-visible traps during floating-point operations. Setting this option disables optimizations that may change the number of 3504 exceptions visible with signaling NaNs. This option implies -ftrapping-math. 3505 This option causes the preprocessor macro "__SUPPORT_SNAN__" to be defined. 3506 The default is -fno-signaling-nans. 3507 This option is experimental and does not currently guarantee to disable all GCC optimizations that affect signaling NaN behavior. 3508 -fsingle-precision-constant 3509 Treat floating-point constants as single precision instead of implicitly converting them to double-precision constants. 3510 -fcx-limited-range 3511 When enabled, this option states that a range reduction step is not needed when performing complex division. Also, there is no checking whether the result of a complex multiplication or 3512 division is "NaN + I*NaN", with an attempt to rescue the situation in that case. The default is -fno-cx-limited-range, but is enabled by -ffast-math. 3513 This option controls the default setting of the ISO C99 "CX_LIMITED_RANGE" pragma. Nevertheless, the option applies to all languages. 3514 -fcx-fortran-rules 3515 Complex multiplication and division follow Fortran rules. Range reduction is done as part of complex division, but there is no checking whether the result of a complex multiplication or 3516 division is "NaN + I*NaN", with an attempt to rescue the situation in that case. 3517 The default is -fno-cx-fortran-rules. 3518 The following options control optimizations that may improve performance, but are not enabled by any -O options. This section includes experimental options that may produce broken code. 3519 -fbranch-probabilities 3520 After running a program compiled with -fprofile-arcs, you can compile it a second time using -fbranch-probabilities, to improve optimizations based on the number of times each branch was 3521 taken. When a program compiled with -fprofile-arcs exits, it saves arc execution counts to a file called sourcename.gcda for each source file. The information in this data file is very 3522 dependent on the structure of the generated code, so you must use the same source code and the same optimization options for both compilations. 3523 With -fbranch-probabilities, GCC puts a REG_BR_PROB note on each JUMP_INSN and CALL_INSN. These can be used to improve optimization. Currently, they are only used in one place: in reorg.c, 3524 instead of guessing which path a branch is most likely to take, the REG_BR_PROB values are used to exactly determine which path is taken more often. 3525 -fprofile-values 3526 If combined with -fprofile-arcs, it adds code so that some data about values of expressions in the program is gathered. 3527 With -fbranch-probabilities, it reads back the data gathered from profiling values of expressions for usage in optimizations. 3528 Enabled with -fprofile-generate and -fprofile-use. 3529 -fprofile-reorder-functions 3530 Function reordering based on profile instrumentation collects first time of execution of a function and orders these functions in ascending order. 3531 Enabled with -fprofile-use. 3532 -fvpt 3533 If combined with -fprofile-arcs, this option instructs the compiler to add code to gather information about values of expressions. 3534 With -fbranch-probabilities, it reads back the data gathered and actually performs the optimizations based on them. Currently the optimizations include specialization of division operations 3535 using the knowledge about the value of the denominator. 3536 -frename-registers 3537 Attempt to avoid false dependencies in scheduled code by making use of registers left over after register allocation. This optimization most benefits processors with lots of registers. 3538 Depending on the debug information format adopted by the target, however, it can make debugging impossible, since variables no longer stay in a "home register". 3539 Enabled by default with -funroll-loops and -fpeel-loops. 3540 -fschedule-fusion 3541 Performs a target dependent pass over the instruction stream to schedule instructions of same type together because target machine can execute them more efficiently if they are adjacent to 3542 each other in the instruction flow. 3543 Enabled at levels -O2, -O3, -Os. 3544 -ftracer 3545 Perform tail duplication to enlarge superblock size. This transformation simplifies the control flow of the function allowing other optimizations to do a better job. 3546 Enabled with -fprofile-use. 3547 -funroll-loops 3548 Unroll loops whose number of iterations can be determined at compile time or upon entry to the loop. -funroll-loops implies -frerun-cse-after-loop, -fweb and -frename-registers. It also 3549 turns on complete loop peeling (i.e. complete removal of loops with a small constant number of iterations). This option makes code larger, and may or may not make it run faster. 3550 Enabled with -fprofile-use. 3551 -funroll-all-loops 3552 Unroll all loops, even if their number of iterations is uncertain when the loop is entered. This usually makes programs run more slowly. -funroll-all-loops implies the same options as 3553 -funroll-loops. 3554 -fpeel-loops 3555 Peels loops for which there is enough information that they do not roll much (from profile feedback). It also turns on complete loop peeling (i.e. complete removal of loops with small 3556 constant number of iterations). 3557 Enabled with -fprofile-use. 3558 -fmove-loop-invariants 3559 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled at level -O1 3560 -funswitch-loops 3561 Move branches with loop invariant conditions out of the loop, with duplicates of the loop on both branches (modified according to result of the condition). 3562 -ffunction-sections 3563 -fdata-sections 3564 Place each function or data item into its own section in the output file if the target supports arbitrary sections. The name of the function or the name of the data item determines the 3565 section's name in the output file. 3566 Use these options on systems where the linker can perform optimizations to improve locality of reference in the instruction space. Most systems using the ELF object format and SPARC 3567 processors running Solaris 2 have linkers with such optimizations. AIX may have these optimizations in the future. 3568 Only use these options when there are significant benefits from doing so. When you specify these options, the assembler and linker create larger object and executable files and are also 3569 slower. You cannot use gprof on all systems if you specify this option, and you may have problems with debugging if you specify both this option and -g. 3570 -fbranch-target-load-optimize 3571 Perform branch target register load optimization before prologue / epilogue threading. The use of target registers can typically be exposed only during reload, thus hoisting loads out of 3572 loops and doing inter-block scheduling needs a separate optimization pass. 3573 -fbranch-target-load-optimize2 3574 Perform branch target register load optimization after prologue / epilogue threading. 3575 -fbtr-bb-exclusive 3576 When performing branch target register load optimization, don't reuse branch target registers within any basic block. 3577 -fstack-protector 3578 Emit extra code to check for buffer overflows, such as stack smashing attacks. This is done by adding a guard variable to functions with vulnerable objects. This includes functions that 3579 call "alloca", and functions with buffers larger than 8 bytes. The guards are initialized when a function is entered and then checked when the function exits. If a guard check fails, an 3580 error message is printed and the program exits. 3581 -fstack-protector-all 3582 Like -fstack-protector except that all functions are protected. 3583 -fstack-protector-strong 3584 Like -fstack-protector but includes additional functions to be protected --- those that have local array definitions, or have references to local frame addresses. 3585 -fstack-protector-explicit 3586 Like -fstack-protector but only protects those functions which have the "stack_protect" attribute 3587 -fstdarg-opt 3588 Optimize the prologue of variadic argument functions with respect to usage of those arguments. 3589 -fsection-anchors 3590 Try to reduce the number of symbolic address calculations by using shared "anchor" symbols to address nearby objects. This transformation can help to reduce the number of GOT entries and 3591 GOT accesses on some targets. 3592 For example, the implementation of the following function "foo": 3593 static int a, b, c; 3594 int foo (void) { return a + b + c; } 3595 usually calculates the addresses of all three variables, but if you compile it with -fsection-anchors, it accesses the variables from a common anchor point instead. The effect is similar to 3596 the following pseudocode (which isn't valid C): 3597 int foo (void) 3598 { 3599 register int *xr = &x; 3600 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; 3601 } 3602 Not all targets support this option. 3603 --param name=value 3604 In some places, GCC uses various constants to control the amount of optimization that is done. For example, GCC does not inline functions that contain more than a certain number of 3605 instructions. You can control some of these constants on the command line using the --param option. 3606 The names of specific parameters, and the meaning of the values, are tied to the internals of the compiler, and are subject to change without notice in future releases. 3607 In each case, the value is an integer. The allowable choices for name are: 3608 predictable-branch-outcome 3609 When branch is predicted to be taken with probability lower than this threshold (in percent), then it is considered well predictable. The default is 10. 3610 max-crossjump-edges 3611 The maximum number of incoming edges to consider for cross-jumping. The algorithm used by -fcrossjumping is O(N^2) in the number of edges incoming to each block. Increasing values mean 3612 more aggressive optimization, making the compilation time increase with probably small improvement in executable size. 3613 min-crossjump-insns 3614 The minimum number of instructions that must be matched at the end of two blocks before cross-jumping is performed on them. This value is ignored in the case where all instructions in 3615 the block being cross-jumped from are matched. The default value is 5. 3616 max-grow-copy-bb-insns 3617 The maximum code size expansion factor when copying basic blocks instead of jumping. The expansion is relative to a jump instruction. The default value is 8. 3618 max-goto-duplication-insns 3619 The maximum number of instructions to duplicate to a block that jumps to a computed goto. To avoid O(N^2) behavior in a number of passes, GCC factors computed gotos early in the 3620 compilation process, and unfactors them as late as possible. Only computed jumps at the end of a basic blocks with no more than max-goto-duplication-insns are unfactored. The default 3621 value is 8. 3622 max-delay-slot-insn-search 3623 The maximum number of instructions to consider when looking for an instruction to fill a delay slot. If more than this arbitrary number of instructions are searched, the time savings 3624 from filling the delay slot are minimal, so stop searching. Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in 3625 execution time. 3626 max-delay-slot-live-search 3627 When trying to fill delay slots, the maximum number of instructions to consider when searching for a block with valid live register information. Increasing this arbitrarily chosen value 3628 means more aggressive optimization, increasing the compilation time. This parameter should be removed when the delay slot code is rewritten to maintain the control-flow graph. 3629 max-gcse-memory 3630 The approximate maximum amount of memory that can be allocated in order to perform the global common subexpression elimination optimization. If more memory than specified is required, 3631 the optimization is not done. 3632 max-gcse-insertion-ratio 3633 If the ratio of expression insertions to deletions is larger than this value for any expression, then RTL PRE inserts or removes the expression and thus leaves partially redundant 3634 computations in the instruction stream. The default value is 20. 3635 max-pending-list-length 3636 The maximum number of pending dependencies scheduling allows before flushing the current state and starting over. Large functions with few branches or calls can create excessively large 3637 lists which needlessly consume memory and resources. 3638 max-modulo-backtrack-attempts 3639 The maximum number of backtrack attempts the scheduler should make when modulo scheduling a loop. Larger values can exponentially increase compilation time. 3640 max-inline-insns-single 3641 Several parameters control the tree inliner used in GCC. This number sets the maximum number of instructions (counted in GCC's internal representation) in a single function that the 3642 tree inliner considers for inlining. This only affects functions declared inline and methods implemented in a class declaration (C++). The default value is 400. 3643 max-inline-insns-auto 3644 When you use -finline-functions (included in -O3), a lot of functions that would otherwise not be considered for inlining by the compiler are investigated. To those functions, a 3645 different (more restrictive) limit compared to functions declared inline can be applied. The default value is 40. 3646 inline-min-speedup 3647 When estimated performance improvement of caller + callee runtime exceeds this threshold (in precent), the function can be inlined regardless the limit on --param max-inline-insns-single 3648 and --param max-inline-insns-auto. 3649 large-function-insns 3650 The limit specifying really large functions. For functions larger than this limit after inlining, inlining is constrained by --param large-function-growth. This parameter is useful 3651 primarily to avoid extreme compilation time caused by non-linear algorithms used by the back end. The default value is 2700. 3652 large-function-growth 3653 Specifies maximal growth of large function caused by inlining in percents. The default value is 100 which limits large function growth to 2.0 times the original size. 3654 large-unit-insns 3655 The limit specifying large translation unit. Growth caused by inlining of units larger than this limit is limited by --param inline-unit-growth. For small units this might be too 3656 tight. For example, consider a unit consisting of function A that is inline and B that just calls A three times. If B is small relative to A, the growth of unit is 300\% and yet such 3657 inlining is very sane. For very large units consisting of small inlineable functions, however, the overall unit growth limit is needed to avoid exponential explosion of code size. Thus 3658 for smaller units, the size is increased to --param large-unit-insns before applying --param inline-unit-growth. The default is 10000. 3659 inline-unit-growth 3660 Specifies maximal overall growth of the compilation unit caused by inlining. The default value is 20 which limits unit growth to 1.2 times the original size. Cold functions (either 3661 marked cold via an attribute or by profile feedback) are not accounted into the unit size. 3662 ipcp-unit-growth 3663 Specifies maximal overall growth of the compilation unit caused by interprocedural constant propagation. The default value is 10 which limits unit growth to 1.1 times the original size. 3664 large-stack-frame 3665 The limit specifying large stack frames. While inlining the algorithm is trying to not grow past this limit too much. The default value is 256 bytes. 3666 large-stack-frame-growth 3667 Specifies maximal growth of large stack frames caused by inlining in percents. The default value is 1000 which limits large stack frame growth to 11 times the original size. 3668 max-inline-insns-recursive 3669 max-inline-insns-recursive-auto 3670 Specifies the maximum number of instructions an out-of-line copy of a self-recursive inline function can grow into by performing recursive inlining. 3671 --param max-inline-insns-recursive applies to functions declared inline. For functions not declared inline, recursive inlining happens only when -finline-functions (included in -O3) is 3672 enabled; --param max-inline-insns-recursive-auto applies instead. The default value is 450. 3673 max-inline-recursive-depth 3674 max-inline-recursive-depth-auto 3675 Specifies the maximum recursion depth used for recursive inlining. 3676 --param max-inline-recursive-depth applies to functions declared inline. For functions not declared inline, recursive inlining happens only when -finline-functions (included in -O3) is 3677 enabled; --param max-inline-recursive-depth-auto applies instead. The default value is 8. 3678 min-inline-recursive-probability 3679 Recursive inlining is profitable only for function having deep recursion in average and can hurt for function having little recursion depth by increasing the prologue size or complexity 3680 of function body to other optimizers. 3681 When profile feedback is available (see -fprofile-generate) the actual recursion depth can be guessed from probability that function recurses via a given call expression. This parameter 3682 limits inlining only to call expressions whose probability exceeds the given threshold (in percents). The default value is 10. 3683 early-inlining-insns 3684 Specify growth that the early inliner can make. In effect it increases the amount of inlining for code having a large abstraction penalty. The default value is 14. 3685 max-early-inliner-iterations 3686 Limit of iterations of the early inliner. This basically bounds the number of nested indirect calls the early inliner can resolve. Deeper chains are still handled by late inlining. 3687 comdat-sharing-probability 3688 Probability (in percent) that C++ inline function with comdat visibility are shared across multiple compilation units. The default value is 20. 3689 profile-func-internal-id 3690 A parameter to control whether to use function internal id in profile database lookup. If the value is 0, the compiler uses an id that is based on function assembler name and filename, 3691 which makes old profile data more tolerant to source changes such as function reordering etc. The default value is 0. 3692 min-vect-loop-bound 3693 The minimum number of iterations under which loops are not vectorized when -ftree-vectorize is used. The number of iterations after vectorization needs to be greater than the value 3694 specified by this option to allow vectorization. The default value is 0. 3695 gcse-cost-distance-ratio 3696 Scaling factor in calculation of maximum distance an expression can be moved by GCSE optimizations. This is currently supported only in the code hoisting pass. The bigger the ratio, 3697 the more aggressive code hoisting is with simple expressions, i.e., the expressions that have cost less than gcse-unrestricted-cost. Specifying 0 disables hoisting of simple 3698 expressions. The default value is 10. 3699 gcse-unrestricted-cost 3700 Cost, roughly measured as the cost of a single typical machine instruction, at which GCSE optimizations do not constrain the distance an expression can travel. This is currently 3701 supported only in the code hoisting pass. The lesser the cost, the more aggressive code hoisting is. Specifying 0 allows all expressions to travel unrestricted distances. The default 3702 value is 3. 3703 max-hoist-depth 3704 The depth of search in the dominator tree for expressions to hoist. This is used to avoid quadratic behavior in hoisting algorithm. The value of 0 does not limit on the search, but may 3705 slow down compilation of huge functions. The default value is 30. 3706 max-tail-merge-comparisons 3707 The maximum amount of similar bbs to compare a bb with. This is used to avoid quadratic behavior in tree tail merging. The default value is 10. 3708 max-tail-merge-iterations 3709 The maximum amount of iterations of the pass over the function. This is used to limit compilation time in tree tail merging. The default value is 2. 3710 max-unrolled-insns 3711 The maximum number of instructions that a loop may have to be unrolled. If a loop is unrolled, this parameter also determines how many times the loop code is unrolled. 3712 max-average-unrolled-insns 3713 The maximum number of instructions biased by probabilities of their execution that a loop may have to be unrolled. If a loop is unrolled, this parameter also determines how many times 3714 the loop code is unrolled. 3715 max-unroll-times 3716 The maximum number of unrollings of a single loop. 3717 max-peeled-insns 3718 The maximum number of instructions that a loop may have to be peeled. If a loop is peeled, this parameter also determines how many times the loop code is peeled. 3719 max-peel-times 3720 The maximum number of peelings of a single loop. 3721 max-peel-branches 3722 The maximum number of branches on the hot path through the peeled sequence. 3723 max-completely-peeled-insns 3724 The maximum number of insns of a completely peeled loop. 3725 max-completely-peel-times 3726 The maximum number of iterations of a loop to be suitable for complete peeling. 3727 max-completely-peel-loop-nest-depth 3728 The maximum depth of a loop nest suitable for complete peeling. 3729 max-unswitch-insns 3730 The maximum number of insns of an unswitched loop. 3731 max-unswitch-level 3732 The maximum number of branches unswitched in a single loop. 3733 lim-expensive 3734 The minimum cost of an expensive expression in the loop invariant motion. 3735 iv-consider-all-candidates-bound 3736 Bound on number of candidates for induction variables, below which all candidates are considered for each use in induction variable optimizations. If there are more candidates than 3737 this, only the most relevant ones are considered to avoid quadratic time complexity. 3738 iv-max-considered-uses 3739 The induction variable optimizations give up on loops that contain more induction variable uses. 3740 iv-always-prune-cand-set-bound 3741 If the number of candidates in the set is smaller than this value, always try to remove unnecessary ivs from the set when adding a new one. 3742 scev-max-expr-size 3743 Bound on size of expressions used in the scalar evolutions analyzer. Large expressions slow the analyzer. 3744 scev-max-expr-complexity 3745 Bound on the complexity of the expressions in the scalar evolutions analyzer. Complex expressions slow the analyzer. 3746 omega-max-vars 3747 The maximum number of variables in an Omega constraint system. The default value is 128. 3748 omega-max-geqs 3749 The maximum number of inequalities in an Omega constraint system. The default value is 256. 3750 omega-max-eqs 3751 The maximum number of equalities in an Omega constraint system. The default value is 128. 3752 omega-max-wild-cards 3753 The maximum number of wildcard variables that the Omega solver is able to insert. The default value is 18. 3754 omega-hash-table-size 3755 The size of the hash table in the Omega solver. The default value is 550. 3756 omega-max-keys 3757 The maximal number of keys used by the Omega solver. The default value is 500. 3758 omega-eliminate-redundant-constraints 3759 When set to 1, use expensive methods to eliminate all redundant constraints. The default value is 0. 3760 vect-max-version-for-alignment-checks 3761 The maximum number of run-time checks that can be performed when doing loop versioning for alignment in the vectorizer. 3762 vect-max-version-for-alias-checks 3763 The maximum number of run-time checks that can be performed when doing loop versioning for alias in the vectorizer. 3764 vect-max-peeling-for-alignment 3765 The maximum number of loop peels to enhance access alignment for vectorizer. Value -1 means 'no limit'. 3766 max-iterations-to-track 3767 The maximum number of iterations of a loop the brute-force algorithm for analysis of the number of iterations of the loop tries to evaluate. 3768 hot-bb-count-ws-permille 3769 A basic block profile count is considered hot if it contributes to the given permillage (i.e. 0...1000) of the entire profiled execution. 3770 hot-bb-frequency-fraction 3771 Select fraction of the entry block frequency of executions of basic block in function given basic block needs to have to be considered hot. 3772 max-predicted-iterations 3773 The maximum number of loop iterations we predict statically. This is useful in cases where a function contains a single loop with known bound and another loop with unknown bound. The 3774 known number of iterations is predicted correctly, while the unknown number of iterations average to roughly 10. This means that the loop without bounds appears artificially cold 3775 relative to the other one. 3776 builtin-expect-probability 3777 Control the probability of the expression having the specified value. This parameter takes a percentage (i.e. 0 ... 100) as input. The default probability of 90 is obtained empirically. 3778 align-threshold 3779 Select fraction of the maximal frequency of executions of a basic block in a function to align the basic block. 3780 align-loop-iterations 3781 A loop expected to iterate at least the selected number of iterations is aligned. 3782 tracer-dynamic-coverage 3783 tracer-dynamic-coverage-feedback 3784 This value is used to limit superblock formation once the given percentage of executed instructions is covered. This limits unnecessary code size expansion. 3785 The tracer-dynamic-coverage-feedback parameter is used only when profile feedback is available. The real profiles (as opposed to statically estimated ones) are much less balanced 3786 allowing the threshold to be larger value. 3787 tracer-max-code-growth 3788 Stop tail duplication once code growth has reached given percentage. This is a rather artificial limit, as most of the duplicates are eliminated later in cross jumping, so it may be set 3789 to much higher values than is the desired code growth. 3790 tracer-min-branch-ratio 3791 Stop reverse growth when the reverse probability of best edge is less than this threshold (in percent). 3792 tracer-min-branch-ratio 3793 tracer-min-branch-ratio-feedback 3794 Stop forward growth if the best edge has probability lower than this threshold. 3795 Similarly to tracer-dynamic-coverage two values are present, one for compilation for profile feedback and one for compilation without. The value for compilation with profile feedback 3796 needs to be more conservative (higher) in order to make tracer effective. 3797 max-cse-path-length 3798 The maximum number of basic blocks on path that CSE considers. The default is 10. 3799 max-cse-insns 3800 The maximum number of instructions CSE processes before flushing. The default is 1000. 3801 ggc-min-expand 3802 GCC uses a garbage collector to manage its own memory allocation. This parameter specifies the minimum percentage by which the garbage collector's heap should be allowed to expand 3803 between collections. Tuning this may improve compilation speed; it has no effect on code generation. 3804 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when RAM >= 1GB. If "getrlimit" is available, the notion of "RAM" is the smallest of actual RAM and "RLIMIT_DATA" or 3805 "RLIMIT_AS". If GCC is not able to calculate RAM on a particular platform, the lower bound of 30% is used. Setting this parameter and ggc-min-heapsize to zero causes a full collection 3806 to occur at every opportunity. This is extremely slow, but can be useful for debugging. 3807 ggc-min-heapsize 3808 Minimum size of the garbage collector's heap before it begins bothering to collect garbage. The first collection occurs after the heap expands by ggc-min-expand% beyond ggc-min- 3809 heapsize. Again, tuning this may improve compilation speed, and has no effect on code generation. 3810 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but with a lower bound of 4096 (four megabytes) and an 3811 upper bound of 131072 (128 megabytes). If GCC is not able to calculate RAM on a particular platform, the lower bound is used. Setting this parameter very large effectively disables 3812 garbage collection. Setting this parameter and ggc-min-expand to zero causes a full collection to occur at every opportunity. 3813 max-reload-search-insns 3814 The maximum number of instruction reload should look backward for equivalent register. Increasing values mean more aggressive optimization, making the compilation time increase with 3815 probably slightly better performance. The default value is 100. 3816 max-cselib-memory-locations 3817 The maximum number of memory locations cselib should take into account. Increasing values mean more aggressive optimization, making the compilation time increase with probably slightly 3818 better performance. The default value is 500. 3819 reorder-blocks-duplicate 3820 reorder-blocks-duplicate-feedback 3821 Used by the basic block reordering pass to decide whether to use unconditional branch or duplicate the code on its destination. Code is duplicated when its estimated size is smaller 3822 than this value multiplied by the estimated size of unconditional jump in the hot spots of the program. 3823 The reorder-block-duplicate-feedback parameter is used only when profile feedback is available. It may be set to higher values than reorder-block-duplicate since information about the 3824 hot spots is more accurate. 3825 max-sched-ready-insns 3826 The maximum number of instructions ready to be issued the scheduler should consider at any given time during the first scheduling pass. Increasing values mean more thorough searches, 3827 making the compilation time increase with probably little benefit. The default value is 100. 3828 max-sched-region-blocks 3829 The maximum number of blocks in a region to be considered for interblock scheduling. The default value is 10. 3830 max-pipeline-region-blocks 3831 The maximum number of blocks in a region to be considered for pipelining in the selective scheduler. The default value is 15. 3832 max-sched-region-insns 3833 The maximum number of insns in a region to be considered for interblock scheduling. The default value is 100. 3834 max-pipeline-region-insns 3835 The maximum number of insns in a region to be considered for pipelining in the selective scheduler. The default value is 200. 3836 min-spec-prob 3837 The minimum probability (in percents) of reaching a source block for interblock speculative scheduling. The default value is 40. 3838 max-sched-extend-regions-iters 3839 The maximum number of iterations through CFG to extend regions. A value of 0 (the default) disables region extensions. 3840 max-sched-insn-conflict-delay 3841 The maximum conflict delay for an insn to be considered for speculative motion. The default value is 3. 3842 sched-spec-prob-cutoff 3843 The minimal probability of speculation success (in percents), so that speculative insns are scheduled. The default value is 40. 3844 sched-spec-state-edge-prob-cutoff 3845 The minimum probability an edge must have for the scheduler to save its state across it. The default value is 10. 3846 sched-mem-true-dep-cost 3847 Minimal distance (in CPU cycles) between store and load targeting same memory locations. The default value is 1. 3848 selsched-max-lookahead 3849 The maximum size of the lookahead window of selective scheduling. It is a depth of search for available instructions. The default value is 50. 3850 selsched-max-sched-times 3851 The maximum number of times that an instruction is scheduled during selective scheduling. This is the limit on the number of iterations through which the instruction may be pipelined. 3852 The default value is 2. 3853 selsched-max-insns-to-rename 3854 The maximum number of best instructions in the ready list that are considered for renaming in the selective scheduler. The default value is 2. 3855 sms-min-sc 3856 The minimum value of stage count that swing modulo scheduler generates. The default value is 2. 3857 max-last-value-rtl 3858 The maximum size measured as number of RTLs that can be recorded in an expression in combiner for a pseudo register as last known value of that register. The default is 10000. 3859 max-combine-insns 3860 The maximum number of instructions the RTL combiner tries to combine. The default value is 2 at -Og and 4 otherwise. 3861 integer-share-limit 3862 Small integer constants can use a shared data structure, reducing the compiler's memory usage and increasing its speed. This sets the maximum value of a shared integer constant. The 3863 default value is 256. 3864 ssp-buffer-size 3865 The minimum size of buffers (i.e. arrays) that receive stack smashing protection when -fstack-protection is used. 3866 min-size-for-stack-sharing 3867 The minimum size of variables taking part in stack slot sharing when not optimizing. The default value is 32. 3868 max-jump-thread-duplication-stmts 3869 Maximum number of statements allowed in a block that needs to be duplicated when threading jumps. 3870 max-fields-for-field-sensitive 3871 Maximum number of fields in a structure treated in a field sensitive manner during pointer analysis. The default is zero for -O0 and -O1, and 100 for -Os, -O2, and -O3. 3872 prefetch-latency 3873 Estimate on average number of instructions that are executed before prefetch finishes. The distance prefetched ahead is proportional to this constant. Increasing this number may also 3874 lead to less streams being prefetched (see simultaneous-prefetches). 3875 simultaneous-prefetches 3876 Maximum number of prefetches that can run at the same time. 3877 l1-cache-line-size 3878 The size of cache line in L1 cache, in bytes. 3879 l1-cache-size 3880 The size of L1 cache, in kilobytes. 3881 l2-cache-size 3882 The size of L2 cache, in kilobytes. 3883 min-insn-to-prefetch-ratio 3884 The minimum ratio between the number of instructions and the number of prefetches to enable prefetching in a loop. 3885 prefetch-min-insn-to-mem-ratio 3886 The minimum ratio between the number of instructions and the number of memory references to enable prefetching in a loop. 3887 use-canonical-types 3888 Whether the compiler should use the "canonical" type system. By default, this should always be 1, which uses a more efficient internal mechanism for comparing types in C++ and 3889 Objective-C++. However, if bugs in the canonical type system are causing compilation failures, set this value to 0 to disable canonical types. 3890 switch-conversion-max-branch-ratio 3891 Switch initialization conversion refuses to create arrays that are bigger than switch-conversion-max-branch-ratio times the number of branches in the switch. 3892 max-partial-antic-length 3893 Maximum length of the partial antic set computed during the tree partial redundancy elimination optimization (-ftree-pre) when optimizing at -O3 and above. For some sorts of source code 3894 the enhanced partial redundancy elimination optimization can run away, consuming all of the memory available on the host machine. This parameter sets a limit on the length of the sets 3895 that are computed, which prevents the runaway behavior. Setting a value of 0 for this parameter allows an unlimited set length. 3896 sccvn-max-scc-size 3897 Maximum size of a strongly connected component (SCC) during SCCVN processing. If this limit is hit, SCCVN processing for the whole function is not done and optimizations depending on it 3898 are disabled. The default maximum SCC size is 10000. 3899 sccvn-max-alias-queries-per-access 3900 Maximum number of alias-oracle queries we perform when looking for redundancies for loads and stores. If this limit is hit the search is aborted and the load or store is not considered 3901 redundant. The number of queries is algorithmically limited to the number of stores on all paths from the load to the function entry. The default maxmimum number of queries is 1000. 3902 ira-max-loops-num 3903 IRA uses regional register allocation by default. If a function contains more loops than the number given by this parameter, only at most the given number of the most frequently- 3904 executed loops form regions for regional register allocation. The default value of the parameter is 100. 3905 ira-max-conflict-table-size 3906 Although IRA uses a sophisticated algorithm to compress the conflict table, the table can still require excessive amounts of memory for huge functions. If the conflict table for a 3907 function could be more than the size in MB given by this parameter, the register allocator instead uses a faster, simpler, and lower-quality algorithm that does not require building a 3908 pseudo-register conflict table. The default value of the parameter is 2000. 3909 ira-loop-reserved-regs 3910 IRA can be used to evaluate more accurate register pressure in loops for decisions to move loop invariants (see -O3). The number of available registers reserved for some other purposes 3911 is given by this parameter. The default value of the parameter is 2, which is the minimal number of registers needed by typical instructions. This value is the best found from numerous 3912 experiments. 3913 lra-inheritance-ebb-probability-cutoff 3914 LRA tries to reuse values reloaded in registers in subsequent insns. This optimization is called inheritance. EBB is used as a region to do this optimization. The parameter defines a 3915 minimal fall-through edge probability in percentage used to add BB to inheritance EBB in LRA. The default value of the parameter is 40. The value was chosen from numerous runs of 3916 SPEC2000 on x86-64. 3917 loop-invariant-max-bbs-in-loop 3918 Loop invariant motion can be very expensive, both in compilation time and in amount of needed compile-time memory, with very large loops. Loops with more basic blocks than this 3919 parameter won't have loop invariant motion optimization performed on them. The default value of the parameter is 1000 for -O1 and 10000 for -O2 and above. 3920 loop-max-datarefs-for-datadeps 3921 Building data dapendencies is expensive for very large loops. This parameter limits the number of data references in loops that are considered for data dependence analysis. These large 3922 loops are no handled by the optimizations using loop data dependencies. The default value is 1000. 3923 max-vartrack-size 3924 Sets a maximum number of hash table slots to use during variable tracking dataflow analysis of any function. If this limit is exceeded with variable tracking at assignments enabled, 3925 analysis for that function is retried without it, after removing all debug insns from the function. If the limit is exceeded even without debug insns, var tracking analysis is 3926 completely disabled for the function. Setting the parameter to zero makes it unlimited. 3927 max-vartrack-expr-depth 3928 Sets a maximum number of recursion levels when attempting to map variable names or debug temporaries to value expressions. This trades compilation time for more complete debug 3929 information. If this is set too low, value expressions that are available and could be represented in debug information may end up not being used; setting this higher may enable the 3930 compiler to find more complex debug expressions, but compile time and memory use may grow. The default is 12. 3931 min-nondebug-insn-uid 3932 Use uids starting at this parameter for nondebug insns. The range below the parameter is reserved exclusively for debug insns created by -fvar-tracking-assignments, but debug insns may 3933 get (non-overlapping) uids above it if the reserved range is exhausted. 3934 ipa-sra-ptr-growth-factor 3935 IPA-SRA replaces a pointer to an aggregate with one or more new parameters only when their cumulative size is less or equal to ipa-sra-ptr-growth-factor times the size of the original 3936 pointer parameter. 3937 sra-max-scalarization-size-Ospeed 3938 sra-max-scalarization-size-Osize 3939 The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA) aim to replace scalar parts of aggregates with uses of independent scalar variables. These parameters control the maximum 3940 size, in storage units, of aggregate which is considered for replacement when compiling for speed (sra-max-scalarization-size-Ospeed) or size (sra-max-scalarization-size-Osize) 3941 respectively. 3942 tm-max-aggregate-size 3943 When making copies of thread-local variables in a transaction, this parameter specifies the size in bytes after which variables are saved with the logging functions as opposed to 3944 save/restore code sequence pairs. This option only applies when using -fgnu-tm. 3945 graphite-max-nb-scop-params 3946 To avoid exponential effects in the Graphite loop transforms, the number of parameters in a Static Control Part (SCoP) is bounded. The default value is 10 parameters. A variable whose 3947 value is unknown at compilation time and defined outside a SCoP is a parameter of the SCoP. 3948 graphite-max-bbs-per-function 3949 To avoid exponential effects in the detection of SCoPs, the size of the functions analyzed by Graphite is bounded. The default value is 100 basic blocks. 3950 loop-block-tile-size 3951 Loop blocking or strip mining transforms, enabled with -floop-block or -floop-strip-mine, strip mine each loop in the loop nest by a given number of iterations. The strip length can be 3952 changed using the loop-block-tile-size parameter. The default value is 51 iterations. 3953 loop-unroll-jam-size 3954 Specify the unroll factor for the -floop-unroll-and-jam option. The default value is 4. 3955 loop-unroll-jam-depth 3956 Specify the dimension to be unrolled (counting from the most inner loop) for the -floop-unroll-and-jam. The default value is 2. 3957 ipa-cp-value-list-size 3958 IPA-CP attempts to track all possible values and types passed to a function's parameter in order to propagate them and perform devirtualization. ipa-cp-value-list-size is the maximum 3959 number of values and types it stores per one formal parameter of a function. 3960 ipa-cp-eval-threshold 3961 IPA-CP calculates its own score of cloning profitability heuristics and performs those cloning opportunities with scores that exceed ipa-cp-eval-threshold. 3962 ipa-cp-recursion-penalty 3963 Percentage penalty the recursive functions will receive when they are evaluated for cloning. 3964 ipa-cp-single-call-penalty 3965 Percentage penalty functions containg a single call to another function will receive when they are evaluated for cloning. 3966 ipa-max-agg-items 3967 IPA-CP is also capable to propagate a number of scalar values passed in an aggregate. ipa-max-agg-items controls the maximum number of such values per one parameter. 3968 ipa-cp-loop-hint-bonus 3969 When IPA-CP determines that a cloning candidate would make the number of iterations of a loop known, it adds a bonus of ipa-cp-loop-hint-bonus to the profitability score of the 3970 candidate. 3971 ipa-cp-array-index-hint-bonus 3972 When IPA-CP determines that a cloning candidate would make the index of an array access known, it adds a bonus of ipa-cp-array-index-hint-bonus to the profitability score of the 3973 candidate. 3974 ipa-max-aa-steps 3975 During its analysis of function bodies, IPA-CP employs alias analysis in order to track values pointed to by function parameters. In order not spend too much time analyzing huge 3976 functions, it gives up and consider all memory clobbered after examining ipa-max-aa-steps statements modifying memory. 3977 lto-partitions 3978 Specify desired number of partitions produced during WHOPR compilation. The number of partitions should exceed the number of CPUs used for compilation. The default value is 32. 3979 lto-minpartition 3980 Size of minimal partition for WHOPR (in estimated instructions). This prevents expenses of splitting very small programs into too many partitions. 3981 cxx-max-namespaces-for-diagnostic-help 3982 The maximum number of namespaces to consult for suggestions when C++ name lookup fails for an identifier. The default is 1000. 3983 sink-frequency-threshold 3984 The maximum relative execution frequency (in percents) of the target block relative to a statement's original block to allow statement sinking of a statement. Larger numbers result in 3985 more aggressive statement sinking. The default value is 75. A small positive adjustment is applied for statements with memory operands as those are even more profitable so sink. 3986 max-stores-to-sink 3987 The maximum number of conditional stores paires that can be sunk. Set to 0 if either vectorization (-ftree-vectorize) or if-conversion (-ftree-loop-if-convert) is disabled. The default 3988 is 2. 3989 allow-store-data-races 3990 Allow optimizers to introduce new data races on stores. Set to 1 to allow, otherwise to 0. This option is enabled by default at optimization level -Ofast. 3991 case-values-threshold 3992 The smallest number of different values for which it is best to use a jump-table instead of a tree of conditional branches. If the value is 0, use the default for the machine. The 3993 default is 0. 3994 tree-reassoc-width 3995 Set the maximum number of instructions executed in parallel in reassociated tree. This parameter overrides target dependent heuristics used by default if has non zero value. 3996 sched-pressure-algorithm 3997 Choose between the two available implementations of -fsched-pressure. Algorithm 1 is the original implementation and is the more likely to prevent instructions from being reordered. 3998 Algorithm 2 was designed to be a compromise between the relatively conservative approach taken by algorithm 1 and the rather aggressive approach taken by the default scheduler. It 3999 relies more heavily on having a regular register file and accurate register pressure classes. See haifa-sched.c in the GCC sources for more details. 4000 The default choice depends on the target. 4001 max-slsr-cand-scan 4002 Set the maximum number of existing candidates that are considered when seeking a basis for a new straight-line strength reduction candidate. 4003 asan-globals 4004 Enable buffer overflow detection for global objects. This kind of protection is enabled by default if you are using -fsanitize=address option. To disable global objects protection use 4005 --param asan-globals=0. 4006 asan-stack 4007 Enable buffer overflow detection for stack objects. This kind of protection is enabled by default when using-fsanitize=address. To disable stack protection use --param asan-stack=0 4008 option. 4009 asan-instrument-reads 4010 Enable buffer overflow detection for memory reads. This kind of protection is enabled by default when using -fsanitize=address. To disable memory reads protection use --param 4011 asan-instrument-reads=0. 4012 asan-instrument-writes 4013 Enable buffer overflow detection for memory writes. This kind of protection is enabled by default when using -fsanitize=address. To disable memory writes protection use --param 4014 asan-instrument-writes=0 option. 4015 asan-memintrin 4016 Enable detection for built-in functions. This kind of protection is enabled by default when using -fsanitize=address. To disable built-in functions protection use --param 4017 asan-memintrin=0. 4018 asan-use-after-return 4019 Enable detection of use-after-return. This kind of protection is enabled by default when using -fsanitize=address option. To disable use-after-return detection use --param 4020 asan-use-after-return=0. 4021 asan-instrumentation-with-call-threshold 4022 If number of memory accesses in function being instrumented is greater or equal to this number, use callbacks instead of inline checks. E.g. to disable inline code use --param 4023 asan-instrumentation-with-call-threshold=0. 4024 chkp-max-ctor-size 4025 Static constructors generated by Pointer Bounds Checker may become very large and significantly increase compile time at optimization level -O1 and higher. This parameter is a maximum 4026 nubmer of statements in a single generated constructor. Default value is 5000. 4027 max-fsm-thread-path-insns 4028 Maximum number of instructions to copy when duplicating blocks on a finite state automaton jump thread path. The default is 100. 4029 max-fsm-thread-length 4030 Maximum number of basic blocks on a finite state automaton jump thread path. The default is 10. 4031 max-fsm-thread-paths 4032 Maximum number of new jump thread paths to create for a finite state automaton. The default is 50. 4033 Options Controlling the Preprocessor 4034 These options control the C preprocessor, which is run on each C source file before actual compilation. 4035 If you use the -E option, nothing is done except preprocessing. Some of these options make sense only together with -E because they cause the preprocessor output to be unsuitable for actual 4036 compilation. 4037 -Wp,option 4038 You can use -Wp,option to bypass the compiler driver and pass option directly through to the preprocessor. If option contains commas, it is split into multiple options at the commas. 4039 However, many options are modified, translated or interpreted by the compiler driver before being passed to the preprocessor, and -Wp forcibly bypasses this phase. The preprocessor's direct 4040 interface is undocumented and subject to change, so whenever possible you should avoid using -Wp and let the driver handle the options instead. 4041 -Xpreprocessor option 4042 Pass option as an option to the preprocessor. You can use this to supply system-specific preprocessor options that GCC does not recognize. 4043 If you want to pass an option that takes an argument, you must use -Xpreprocessor twice, once for the option and once for the argument. 4044 -no-integrated-cpp 4045 Perform preprocessing as a separate pass before compilation. By default, GCC performs preprocessing as an integrated part of input tokenization and parsing. If this option is provided, the 4046 appropriate language front end (cc1, cc1plus, or cc1obj for C, C++, and Objective-C, respectively) is instead invoked twice, once for preprocessing only and once for actual compilation of 4047 the preprocessed input. This option may be useful in conjunction with the -B or -wrapper options to specify an alternate preprocessor or perform additional processing of the program source 4048 between normal preprocessing and compilation. 4049 -D name 4050 Predefine name as a macro, with definition 1. 4051 -D name=definition 4052 The contents of definition are tokenized and processed as if they appeared during translation phase three in a #define directive. In particular, the definition will be truncated by embedded 4053 newline characters. 4054 If you are invoking the preprocessor from a shell or shell-like program you may need to use the shell's quoting syntax to protect characters such as spaces that have a meaning in the shell 4055 syntax. 4056 If you wish to define a function-like macro on the command line, write its argument list with surrounding parentheses before the equals sign (if any). Parentheses are meaningful to most 4057 shells, so you will need to quote the option. With sh and csh, -D'name(args...)=definition' works. 4058 -D and -U options are processed in the order they are given on the command line. All -imacros file and -include file options are processed after all -D and -U options. 4059 -U name 4060 Cancel any previous definition of name, either built in or provided with a -D option. 4061 -undef 4062 Do not predefine any system-specific or GCC-specific macros. The standard predefined macros remain defined. 4063 -I dir 4064 Add the directory dir to the list of directories to be searched for header files. Directories named by -I are searched before the standard system include directories. If the directory dir 4065 is a standard system include directory, the option is ignored to ensure that the default search order for system directories and the special treatment of system headers are not defeated . 4066 If dir begins with "=", then the "=" will be replaced by the sysroot prefix; see --sysroot and -isysroot. 4067 -o file 4068 Write output to file. This is the same as specifying file as the second non-option argument to cpp. gcc has a different interpretation of a second non-option argument, so you must use -o 4069 to specify the output file. 4070 -Wall 4071 Turns on all optional warnings which are desirable for normal code. At present this is -Wcomment, -Wtrigraphs, -Wmultichar and a warning about integer promotion causing a change of sign in 4072 "#if" expressions. Note that many of the preprocessor's warnings are on by default and have no options to control them. 4073 -Wcomment 4074 -Wcomments 4075 Warn whenever a comment-start sequence /* appears in a /* comment, or whenever a backslash-newline appears in a // comment. (Both forms have the same effect.) 4076 -Wtrigraphs 4077 Most trigraphs in comments cannot affect the meaning of the program. However, a trigraph that would form an escaped newline (??/ at the end of a line) can, by changing where the comment 4078 begins or ends. Therefore, only trigraphs that would form escaped newlines produce warnings inside a comment. 4079 This option is implied by -Wall. If -Wall is not given, this option is still enabled unless trigraphs are enabled. To get trigraph conversion without warnings, but get the other -Wall 4080 warnings, use -trigraphs -Wall -Wno-trigraphs. 4081 -Wtraditional 4082 Warn about certain constructs that behave differently in traditional and ISO C. Also warn about ISO C constructs that have no traditional C equivalent, and problematic constructs which 4083 should be avoided. 4084 -Wundef 4085 Warn whenever an identifier which is not a macro is encountered in an #if directive, outside of defined. Such identifiers are replaced with zero. 4086 -Wunused-macros 4087 Warn about macros defined in the main file that are unused. A macro is used if it is expanded or tested for existence at least once. The preprocessor will also warn if the macro has not 4088 been used at the time it is redefined or undefined. 4089 Built-in macros, macros defined on the command line, and macros defined in include files are not warned about. 4090 Note: If a macro is actually used, but only used in skipped conditional blocks, then CPP will report it as unused. To avoid the warning in such a case, you might improve the scope of the 4091 macro's definition by, for example, moving it into the first skipped block. Alternatively, you could provide a dummy use with something like: 4092 #if defined the_macro_causing_the_warning 4093 #endif 4094 -Wendif-labels 4095 Warn whenever an #else or an #endif are followed by text. This usually happens in code of the form 4096 #if FOO 4097 ... 4098 #else FOO 4099 ... 4100 #endif FOO 4101 The second and third "FOO" should be in comments, but often are not in older programs. This warning is on by default. 4102 -Werror 4103 Make all warnings into hard errors. Source code which triggers warnings will be rejected. 4104 -Wsystem-headers 4105 Issue warnings for code in system headers. These are normally unhelpful in finding bugs in your own code, therefore suppressed. If you are responsible for the system library, you may want 4106 to see them. 4107 -w Suppress all warnings, including those which GNU CPP issues by default. 4108 -pedantic 4109 Issue all the mandatory diagnostics listed in the C standard. Some of them are left out by default, since they trigger frequently on harmless code. 4110 -pedantic-errors 4111 Issue all the mandatory diagnostics, and make all mandatory diagnostics into errors. This includes mandatory diagnostics that GCC issues without -pedantic but treats as warnings. 4112 -M Instead of outputting the result of preprocessing, output a rule suitable for make describing the dependencies of the main source file. The preprocessor outputs one make rule containing the 4113 object file name for that source file, a colon, and the names of all the included files, including those coming from -include or -imacros command-line options. 4114 Unless specified explicitly (with -MT or -MQ), the object file name consists of the name of the source file with any suffix replaced with object file suffix and with any leading directory 4115 parts removed. If there are many included files then the rule is split into several lines using \-newline. The rule has no commands. 4116 This option does not suppress the preprocessor's debug output, such as -dM. To avoid mixing such debug output with the dependency rules you should explicitly specify the dependency output 4117 file with -MF, or use an environment variable like DEPENDENCIES_OUTPUT. Debug output will still be sent to the regular output stream as normal. 4118 Passing -M to the driver implies -E, and suppresses warnings with an implicit -w. 4119 -MM Like -M but do not mention header files that are found in system header directories, nor header files that are included, directly or indirectly, from such a header. 4120 This implies that the choice of angle brackets or double quotes in an #include directive does not in itself determine whether that header will appear in -MM dependency output. This is a 4121 slight change in semantics from GCC versions 3.0 and earlier. 4122 -MF file 4123 When used with -M or -MM, specifies a file to write the dependencies to. If no -MF switch is given the preprocessor sends the rules to the same place it would have sent preprocessed output. 4124 When used with the driver options -MD or -MMD, -MF overrides the default dependency output file. 4125 -MG In conjunction with an option such as -M requesting dependency generation, -MG assumes missing header files are generated files and adds them to the dependency list without raising an error. 4126 The dependency filename is taken directly from the "#include" directive without prepending any path. -MG also suppresses preprocessed output, as a missing header file renders this useless. 4127 This feature is used in automatic updating of makefiles. 4128 -MP This option instructs CPP to add a phony target for each dependency other than the main file, causing each to depend on nothing. These dummy rules work around errors make gives if you 4129 remove header files without updating the Makefile to match. 4130 This is typical output: 4131 test.o: test.c test.h 4132 test.h: 4133 -MT target 4134 Change the target of the rule emitted by dependency generation. By default CPP takes the name of the main input file, deletes any directory components and any file suffix such as .c, and 4135 appends the platform's usual object suffix. The result is the target. 4136 An -MT option will set the target to be exactly the string you specify. If you want multiple targets, you can specify them as a single argument to -MT, or use multiple -MT options. 4137 For example, -MT '$(objpfx)foo.o' might give 4138 $(objpfx)foo.o: foo.c 4139 -MQ target 4140 Same as -MT, but it quotes any characters which are special to Make. -MQ '$(objpfx)foo.o' gives 4141 $$(objpfx)foo.o: foo.c 4142 The default target is automatically quoted, as if it were given with -MQ. 4143 -MD -MD is equivalent to -M -MF file, except that -E is not implied. The driver determines file based on whether an -o option is given. If it is, the driver uses its argument but with a suffix 4144 of .d, otherwise it takes the name of the input file, removes any directory components and suffix, and applies a .d suffix. 4145 If -MD is used in conjunction with -E, any -o switch is understood to specify the dependency output file, but if used without -E, each -o is understood to specify a target object file. 4146 Since -E is not implied, -MD can be used to generate a dependency output file as a side-effect of the compilation process. 4147 -MMD 4148 Like -MD except mention only user header files, not system header files. 4149 -fpch-deps 4150 When using precompiled headers, this flag will cause the dependency-output flags to also list the files from the precompiled header's dependencies. If not specified only the precompiled 4151 header would be listed and not the files that were used to create it because those files are not consulted when a precompiled header is used. 4152 -fpch-preprocess 4153 This option allows use of a precompiled header together with -E. It inserts a special "#pragma", "#pragma GCC pch_preprocess "filename"" in the output to mark the place where the 4154 precompiled header was found, and its filename. When -fpreprocessed is in use, GCC recognizes this "#pragma" and loads the PCH. 4155 This option is off by default, because the resulting preprocessed output is only really suitable as input to GCC. It is switched on by -save-temps. 4156 You should not write this "#pragma" in your own code, but it is safe to edit the filename if the PCH file is available in a different location. The filename may be absolute or it may be 4157 relative to GCC's current directory. 4158 -x c 4159 -x c++ 4160 -x objective-c 4161 -x assembler-with-cpp 4162 Specify the source language: C, C++, Objective-C, or assembly. This has nothing to do with standards conformance or extensions; it merely selects which base syntax to expect. If you give 4163 none of these options, cpp will deduce the language from the extension of the source file: .c, .cc, .m, or .S. Some other common extensions for C++ and assembly are also recognized. If cpp 4164 does not recognize the extension, it will treat the file as C; this is the most generic mode. 4165 Note: Previous versions of cpp accepted a -lang option which selected both the language and the standards conformance level. This option has been removed, because it conflicts with the -l 4166 option. 4167 -std=standard 4168 -ansi 4169 Specify the standard to which the code should conform. Currently CPP knows about C and C++ standards; others may be added in the future. 4170 standard may be one of: 4171 "c90" 4172 "c89" 4173 "iso9899:1990" 4174 The ISO C standard from 1990. c90 is the customary shorthand for this version of the standard. 4175 The -ansi option is equivalent to -std=c90. 4176 "iso9899:199409" 4177 The 1990 C standard, as amended in 1994. 4178 "iso9899:1999" 4179 "c99" 4180 "iso9899:199x" 4181 "c9x" 4182 The revised ISO C standard, published in December 1999. Before publication, this was known as C9X. 4183 "iso9899:2011" 4184 "c11" 4185 "c1x" 4186 The revised ISO C standard, published in December 2011. Before publication, this was known as C1X. 4187 "gnu90" 4188 "gnu89" 4189 The 1990 C standard plus GNU extensions. This is the default. 4190 "gnu99" 4191 "gnu9x" 4192 The 1999 C standard plus GNU extensions. 4193 "gnu11" 4194 "gnu1x" 4195 The 2011 C standard plus GNU extensions. 4196 "c++98" 4197 The 1998 ISO C++ standard plus amendments. 4198 "gnu++98" 4199 The same as -std=c++98 plus GNU extensions. This is the default for C++ code. 4200 -I- Split the include path. Any directories specified with -I options before -I- are searched only for headers requested with "#include "file""; they are not searched for "#include ". If 4201 additional directories are specified with -I options after the -I-, those directories are searched for all #include directives. 4202 In addition, -I- inhibits the use of the directory of the current file directory as the first search directory for "#include "file"". This option has been deprecated. 4203 -nostdinc 4204 Do not search the standard system directories for header files. Only the directories you have specified with -I options (and the directory of the current file, if appropriate) are searched. 4205 -nostdinc++ 4206 Do not search for header files in the C++-specific standard directories, but do still search the other standard directories. (This option is used when building the C++ library.) 4207 -include file 4208 Process file as if "#include "file"" appeared as the first line of the primary source file. However, the first directory searched for file is the preprocessor's working directory instead of 4209 the directory containing the main source file. If not found there, it is searched for in the remainder of the "#include "..."" search chain as normal. 4210 If multiple -include options are given, the files are included in the order they appear on the command line. 4211 -imacros file 4212 Exactly like -include, except that any output produced by scanning file is thrown away. Macros it defines remain defined. This allows you to acquire all the macros from a header without 4213 also processing its declarations. 4214 All files specified by -imacros are processed before all files specified by -include. 4215 -idirafter dir 4216 Search dir for header files, but do it after all directories specified with -I and the standard system directories have been exhausted. dir is treated as a system include directory. If dir 4217 begins with "=", then the "=" will be replaced by the sysroot prefix; see --sysroot and -isysroot. 4218 -iprefix prefix 4219 Specify prefix as the prefix for subsequent -iwithprefix options. If the prefix represents a directory, you should include the final /. 4220 -iwithprefix dir 4221 -iwithprefixbefore dir 4222 Append dir to the prefix specified previously with -iprefix, and add the resulting directory to the include search path. -iwithprefixbefore puts it in the same place -I would; -iwithprefix 4223 puts it where -idirafter would. 4224 -isysroot dir 4225 This option is like the --sysroot option, but applies only to header files (except for Darwin targets, where it applies to both header files and libraries). See the --sysroot option for 4226 more information. 4227 -imultilib dir 4228 Use dir as a subdirectory of the directory containing target-specific C++ headers. 4229 -isystem dir 4230 Search dir for header files, after all directories specified by -I but before the standard system directories. Mark it as a system directory, so that it gets the same special treatment as 4231 is applied to the standard system directories. If dir begins with "=", then the "=" will be replaced by the sysroot prefix; see --sysroot and -isysroot. 4232 -iquote dir 4233 Search dir only for header files requested with "#include "file""; they are not searched for "#include ", before all directories specified by -I and before the standard system 4234 directories. If dir begins with "=", then the "=" will be replaced by the sysroot prefix; see --sysroot and -isysroot. 4235 -fdirectives-only 4236 When preprocessing, handle directives, but do not expand macros. 4237 The option's behavior depends on the -E and -fpreprocessed options. 4238 With -E, preprocessing is limited to the handling of directives such as "#define", "#ifdef", and "#error". Other preprocessor operations, such as macro expansion and trigraph conversion are 4239 not performed. In addition, the -dD option is implicitly enabled. 4240 With -fpreprocessed, predefinition of command line and most builtin macros is disabled. Macros such as "__LINE__", which are contextually dependent, are handled normally. This enables 4241 compilation of files previously preprocessed with "-E -fdirectives-only". 4242 With both -E and -fpreprocessed, the rules for -fpreprocessed take precedence. This enables full preprocessing of files previously preprocessed with "-E -fdirectives-only". 4243 -fdollars-in-identifiers 4244 Accept $ in identifiers. 4245 -fextended-identifiers 4246 Accept universal character names in identifiers. This option is enabled by default for C99 (and later C standard versions) and C++. 4247 -fno-canonical-system-headers 4248 When preprocessing, do not shorten system header paths with canonicalization. 4249 -fpreprocessed 4250 Indicate to the preprocessor that the input file has already been preprocessed. This suppresses things like macro expansion, trigraph conversion, escaped newline splicing, and processing of 4251 most directives. The preprocessor still recognizes and removes comments, so that you can pass a file preprocessed with -C to the compiler without problems. In this mode the integrated 4252 preprocessor is little more than a tokenizer for the front ends. 4253 -fpreprocessed is implicit if the input file has one of the extensions .i, .ii or .mi. These are the extensions that GCC uses for preprocessed files created by -save-temps. 4254 -ftabstop=width 4255 Set the distance between tab stops. This helps the preprocessor report correct column numbers in warnings or errors, even if tabs appear on the line. If the value is less than 1 or greater 4256 than 100, the option is ignored. The default is 8. 4257 -fdebug-cpp 4258 This option is only useful for debugging GCC. When used with -E, dumps debugging information about location maps. Every token in the output is preceded by the dump of the map its location 4259 belongs to. The dump of the map holding the location of a token would be: 4260 {"P":F;"F":F;"L":;"C":;"S":;"M":;"E":,"loc":} 4261 When used without -E, this option has no effect. 4262 -ftrack-macro-expansion[=level] 4263 Track locations of tokens across macro expansions. This allows the compiler to emit diagnostic about the current macro expansion stack when a compilation error occurs in a macro expansion. 4264 Using this option makes the preprocessor and the compiler consume more memory. The level parameter can be used to choose the level of precision of token location tracking thus decreasing the 4265 memory consumption if necessary. Value 0 of level de-activates this option just as if no -ftrack-macro-expansion was present on the command line. Value 1 tracks tokens locations in a 4266 degraded mode for the sake of minimal memory overhead. In this mode all tokens resulting from the expansion of an argument of a function-like macro have the same location. Value 2 tracks 4267 tokens locations completely. This value is the most memory hungry. When this option is given no argument, the default parameter value is 2. 4268 Note that "-ftrack-macro-expansion=2" is activated by default. 4269 -fexec-charset=charset 4270 Set the execution character set, used for string and character constants. The default is UTF-8. charset can be any encoding supported by the system's "iconv" library routine. 4271 -fwide-exec-charset=charset 4272 Set the wide execution character set, used for wide string and character constants. The default is UTF-32 or UTF-16, whichever corresponds to the width of "wchar_t". As with 4273 -fexec-charset, charset can be any encoding supported by the system's "iconv" library routine; however, you will have problems with encodings that do not fit exactly in "wchar_t". 4274 -finput-charset=charset 4275 Set the input character set, used for translation from the character set of the input file to the source character set used by GCC. If the locale does not specify, or GCC cannot get this 4276 information from the locale, the default is UTF-8. This can be overridden by either the locale or this command-line option. Currently the command-line option takes precedence if there's a 4277 conflict. charset can be any encoding supported by the system's "iconv" library routine. 4278 -fworking-directory 4279 Enable generation of linemarkers in the preprocessor output that will let the compiler know the current working directory at the time of preprocessing. When this option is enabled, the 4280 preprocessor will emit, after the initial linemarker, a second linemarker with the current working directory followed by two slashes. GCC will use this directory, when it's present in the 4281 preprocessed input, as the directory emitted as the current working directory in some debugging information formats. This option is implicitly enabled if debugging information is enabled, 4282 but this can be inhibited with the negated form -fno-working-directory. If the -P flag is present in the command line, this option has no effect, since no "#line" directives are emitted 4283 whatsoever. 4284 -fno-show-column 4285 Do not print column numbers in diagnostics. This may be necessary if diagnostics are being scanned by a program that does not understand the column numbers, such as dejagnu. 4286 -A predicate=answer 4287 Make an assertion with the predicate predicate and answer answer. This form is preferred to the older form -A predicate(answer), which is still supported, because it does not use shell 4288 special characters. 4289 -A -predicate=answer 4290 Cancel an assertion with the predicate predicate and answer answer. 4291 -dCHARS 4292 CHARS is a sequence of one or more of the following characters, and must not be preceded by a space. Other characters are interpreted by the compiler proper, or reserved for future versions 4293 of GCC, and so are silently ignored. If you specify characters whose behavior conflicts, the result is undefined. 4294 M Instead of the normal output, generate a list of #define directives for all the macros defined during the execution of the preprocessor, including predefined macros. This gives you a 4295 way of finding out what is predefined in your version of the preprocessor. Assuming you have no file foo.h, the command 4296 touch foo.h; cpp -dM foo.h 4297 will show all the predefined macros. 4298 If you use -dM without the -E option, -dM is interpreted as a synonym for -fdump-rtl-mach. 4299 D Like M except in two respects: it does not include the predefined macros, and it outputs both the #define directives and the result of preprocessing. Both kinds of output go to the 4300 standard output file. 4301 N Like D, but emit only the macro names, not their expansions. 4302 I Output #include directives in addition to the result of preprocessing. 4303 U Like D except that only macros that are expanded, or whose definedness is tested in preprocessor directives, are output; the output is delayed until the use or test of the macro; and 4304 #undef directives are also output for macros tested but undefined at the time. 4305 -P Inhibit generation of linemarkers in the output from the preprocessor. This might be useful when running the preprocessor on something that is not C code, and will be sent to a program 4306 which might be confused by the linemarkers. 4307 -C Do not discard comments. All comments are passed through to the output file, except for comments in processed directives, which are deleted along with the directive. 4308 You should be prepared for side effects when using -C; it causes the preprocessor to treat comments as tokens in their own right. For example, comments appearing at the start of what would 4309 be a directive line have the effect of turning that line into an ordinary source line, since the first token on the line is no longer a #. 4310 -CC Do not discard comments, including during macro expansion. This is like -C, except that comments contained within macros are also passed through to the output file where the macro is 4311 expanded. 4312 In addition to the side-effects of the -C option, the -CC option causes all C++-style comments inside a macro to be converted to C-style comments. This is to prevent later use of that macro 4313 from inadvertently commenting out the remainder of the source line. 4314 The -CC option is generally used to support lint comments. 4315 -traditional-cpp 4316 Try to imitate the behavior of old-fashioned C preprocessors, as opposed to ISO C preprocessors. 4317 -trigraphs 4318 Process trigraph sequences. These are three-character sequences, all starting with ??, that are defined by ISO C to stand for single characters. For example, ??/ stands for \, so '??/n' is 4319 a character constant for a newline. By default, GCC ignores trigraphs, but in standard-conforming modes it converts them. See the -std and -ansi options. 4320 The nine trigraphs and their replacements are 4321 Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??- 4322 Replacement: [ ] { } # \ ^ | ~ 4323 -remap 4324 Enable special code to work around file systems which only permit very short file names, such as MS-DOS. 4325 --help 4326 --target-help 4327 Print text describing all the command-line options instead of preprocessing anything. 4328 -v Verbose mode. Print out GNU CPP's version number at the beginning of execution, and report the final form of the include path. 4329 -H Print the name of each header file used, in addition to other normal activities. Each name is indented to show how deep in the #include stack it is. Precompiled header files are also 4330 printed, even if they are found to be invalid; an invalid precompiled header file is printed with ...x and a valid one with ...! . 4331 -version 4332 --version 4333 Print out GNU CPP's version number. With one dash, proceed to preprocess as normal. With two dashes, exit immediately. 4334 Passing Options to the Assembler 4335 You can pass options to the assembler. 4336 -Wa,option 4337 Pass option as an option to the assembler. If option contains commas, it is split into multiple options at the commas. 4338 -Xassembler option 4339 Pass option as an option to the assembler. You can use this to supply system-specific assembler options that GCC does not recognize. 4340 If you want to pass an option that takes an argument, you must use -Xassembler twice, once for the option and once for the argument. 4341 Options for Linking 4342 These options come into play when the compiler links object files into an executable output file. They are meaningless if the compiler is not doing a link step. 4343 object-file-name 4344 A file name that does not end in a special recognized suffix is considered to name an object file or library. (Object files are distinguished from libraries by the linker according to the 4345 file contents.) If linking is done, these object files are used as input to the linker. 4346 -c 4347 -S 4348 -E If any of these options is used, then the linker is not run, and object file names should not be used as arguments. 4349 -fuse-ld=bfd 4350 Use the bfd linker instead of the default linker. 4351 -fuse-ld=gold 4352 Use the gold linker instead of the default linker. 4353 -llibrary 4354 -l library 4355 Search the library named library when linking. (The second alternative with the library as a separate argument is only for POSIX compliance and is not recommended.) 4356 It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, foo.o -lz bar.o 4357 searches library z after file foo.o but before bar.o. If bar.o refers to functions in z, those functions may not be loaded. 4358 The linker searches a standard list of directories for the library, which is actually a file named liblibrary.a. The linker then uses this file as if it had been specified precisely by 4359 name. 4360 The directories searched include several standard system directories plus any that you specify with -L. 4361 Normally the files found this way are library files---archive files whose members are object files. The linker handles an archive file by scanning through it for members which define 4362 symbols that have so far been referenced but not defined. But if the file that is found is an ordinary object file, it is linked in the usual fashion. The only difference between using an 4363 -l option and specifying a file name is that -l surrounds library with lib and .a and searches several directories. 4364 -lobjc 4365 You need this special case of the -l option in order to link an Objective-C or Objective-C++ program. 4366 -nostartfiles 4367 Do not use the standard system startup files when linking. The standard system libraries are used normally, unless -nostdlib or -nodefaultlibs is used. 4368 -nodefaultlibs 4369 Do not use the standard system libraries when linking. Only the libraries you specify are passed to the linker, and options specifying linkage of the system libraries, such as 4370 -static-libgcc or -shared-libgcc, are ignored. The standard startup files are used normally, unless -nostartfiles is used. 4371 The compiler may generate calls to "memcmp", "memset", "memcpy" and "memmove". These entries are usually resolved by entries in libc. These entry points should be supplied through some 4372 other mechanism when this option is specified. 4373 -nostdlib 4374 Do not use the standard system startup files or libraries when linking. No startup files and only the libraries you specify are passed to the linker, and options specifying linkage of the 4375 system libraries, such as -static-libgcc or -shared-libgcc, are ignored. 4376 The compiler may generate calls to "memcmp", "memset", "memcpy" and "memmove". These entries are usually resolved by entries in libc. These entry points should be supplied through some 4377 other mechanism when this option is specified. 4378 One of the standard libraries bypassed by -nostdlib and -nodefaultlibs is libgcc.a, a library of internal subroutines which GCC uses to overcome shortcomings of particular machines, or 4379 special needs for some languages. 4380 In most cases, you need libgcc.a even when you want to avoid other standard libraries. In other words, when you specify -nostdlib or -nodefaultlibs you should usually specify -lgcc as well. 4381 This ensures that you have no unresolved references to internal GCC library subroutines. (An example of such an internal subroutine is "__main", used to ensure C++ constructors are called.) 4382 -pie 4383 Produce a position independent executable on targets that support it. For predictable results, you must also specify the same set of options used for compilation (-fpie, -fPIE, or model 4384 suboptions) when you specify this linker option. 4385 -rdynamic 4386 Pass the flag -export-dynamic to the ELF linker, on targets that support it. This instructs the linker to add all symbols, not only used ones, to the dynamic symbol table. This option is 4387 needed for some uses of "dlopen" or to allow obtaining backtraces from within a program. 4388 -s Remove all symbol table and relocation information from the executable. 4389 -static 4390 On systems that support dynamic linking, this prevents linking with the shared libraries. On other systems, this option has no effect. 4391 -shared 4392 Produce a shared object which can then be linked with other objects to form an executable. Not all systems support this option. For predictable results, you must also specify the same set 4393 of options used for compilation (-fpic, -fPIC, or model suboptions) when you specify this linker option.[1] 4394 -shared-libgcc 4395 -static-libgcc 4396 On systems that provide libgcc as a shared library, these options force the use of either the shared or static version, respectively. If no shared version of libgcc was built when the 4397 compiler was configured, these options have no effect. 4398 There are several situations in which an application should use the shared libgcc instead of the static version. The most common of these is when the application wishes to throw and catch 4399 exceptions across different shared libraries. In that case, each of the libraries as well as the application itself should use the shared libgcc. 4400 Therefore, the G++ and GCJ drivers automatically add -shared-libgcc whenever you build a shared library or a main executable, because C++ and Java programs typically use exceptions, so this 4401 is the right thing to do. 4402 If, instead, you use the GCC driver to create shared libraries, you may find that they are not always linked with the shared libgcc. If GCC finds, at its configuration time, that you have a 4403 non-GNU linker or a GNU linker that does not support option --eh-frame-hdr, it links the shared version of libgcc into shared libraries by default. Otherwise, it takes advantage of the 4404 linker and optimizes away the linking with the shared version of libgcc, linking with the static version of libgcc by default. This allows exceptions to propagate through such shared 4405 libraries, without incurring relocation costs at library load time. 4406 However, if a library or main executable is supposed to throw or catch exceptions, you must link it using the G++ or GCJ driver, as appropriate for the languages used in the program, or 4407 using the option -shared-libgcc, such that it is linked with the shared libgcc. 4408 -static-libasan 4409 When the -fsanitize=address option is used to link a program, the GCC driver automatically links against libasan. If libasan is available as a shared library, and the -static option is not 4410 used, then this links against the shared version of libasan. The -static-libasan option directs the GCC driver to link libasan statically, without necessarily linking other libraries 4411 statically. 4412 -static-libtsan 4413 When the -fsanitize=thread option is used to link a program, the GCC driver automatically links against libtsan. If libtsan is available as a shared library, and the -static option is not 4414 used, then this links against the shared version of libtsan. The -static-libtsan option directs the GCC driver to link libtsan statically, without necessarily linking other libraries 4415 statically. 4416 -static-liblsan 4417 When the -fsanitize=leak option is used to link a program, the GCC driver automatically links against liblsan. If liblsan is available as a shared library, and the -static option is not 4418 used, then this links against the shared version of liblsan. The -static-liblsan option directs the GCC driver to link liblsan statically, without necessarily linking other libraries 4419 statically. 4420 -static-libubsan 4421 When the -fsanitize=undefined option is used to link a program, the GCC driver automatically links against libubsan. If libubsan is available as a shared library, and the -static option is 4422 not used, then this links against the shared version of libubsan. The -static-libubsan option directs the GCC driver to link libubsan statically, without necessarily linking other libraries 4423 statically. 4424 -static-libmpx 4425 When the -fcheck-pointer bounds and -mmpx options are used to link a program, the GCC driver automatically links against libmpx. If libmpx is available as a shared library, and the -static 4426 option is not used, then this links against the shared version of libmpx. The -static-libmpx option directs the GCC driver to link libmpx statically, without necessarily linking other 4427 libraries statically. 4428 -static-libmpxwrappers 4429 When the -fcheck-pointer bounds and -mmpx options are used to link a program without also using -fno-chkp-use-wrappers, the GCC driver automatically links against libmpxwrappers. If 4430 libmpxwrappers is available as a shared library, and the -static option is not used, then this links against the shared version of libmpxwrappers. The -static-libmpxwrappers option directs 4431 the GCC driver to link libmpxwrappers statically, without necessarily linking other libraries statically. 4432 -static-libstdc++ 4433 When the g++ program is used to link a C++ program, it normally automatically links against libstdc++. If libstdc++ is available as a shared library, and the -static option is not used, 4434 then this links against the shared version of libstdc++. That is normally fine. However, it is sometimes useful to freeze the version of libstdc++ used by the program without going all the 4435 way to a fully static link. The -static-libstdc++ option directs the g++ driver to link libstdc++ statically, without necessarily linking other libraries statically. 4436 -symbolic 4437 Bind references to global symbols when building a shared object. Warn about any unresolved references (unless overridden by the link editor option -Xlinker -z -Xlinker defs). Only a few 4438 systems support this option. 4439 -T script 4440 Use script as the linker script. This option is supported by most systems using the GNU linker. On some targets, such as bare-board targets without an operating system, the -T option may 4441 be required when linking to avoid references to undefined symbols. 4442 -Xlinker option 4443 Pass option as an option to the linker. You can use this to supply system-specific linker options that GCC does not recognize. 4444 If you want to pass an option that takes a separate argument, you must use -Xlinker twice, once for the option and once for the argument. For example, to pass -assert definitions, you must 4445 write -Xlinker -assert -Xlinker definitions. It does not work to write -Xlinker "-assert definitions", because this passes the entire string as a single argument, which is not what the 4446 linker expects. 4447 When using the GNU linker, it is usually more convenient to pass arguments to linker options using the option=value syntax than as separate arguments. For example, you can specify -Xlinker 4448 -Map=output.map rather than -Xlinker -Map -Xlinker output.map. Other linkers may not support this syntax for command-line options. 4449 -Wl,option 4450 Pass option as an option to the linker. If option contains commas, it is split into multiple options at the commas. You can use this syntax to pass an argument to the option. For example, 4451 -Wl,-Map,output.map passes -Map output.map to the linker. When using the GNU linker, you can also get the same effect with -Wl,-Map=output.map. 4452 -u symbol 4453 Pretend the symbol symbol is undefined, to force linking of library modules to define it. You can use -u multiple times with different symbols to force loading of additional library 4454 modules. 4455 -z keyword 4456 -z is passed directly on to the linker along with the keyword keyword. See the section in the documentation of your linker for permitted values and their meanings. 4457 Options for Directory Search 4458 These options specify directories to search for header files, for libraries and for parts of the compiler: 4459 -Idir 4460 Add the directory dir to the head of the list of directories to be searched for header files. This can be used to override a system header file, substituting your own version, since these 4461 directories are searched before the system header file directories. However, you should not use this option to add directories that contain vendor-supplied system header files (use -isystem 4462 for that). If you use more than one -I option, the directories are scanned in left-to-right order; the standard system directories come after. 4463 If a standard system include directory, or a directory specified with -isystem, is also specified with -I, the -I option is ignored. The directory is still searched but as a system 4464 directory at its normal position in the system include chain. This is to ensure that GCC's procedure to fix buggy system headers and the ordering for the "include_next" directive are not 4465 inadvertently changed. If you really need to change the search order for system directories, use the -nostdinc and/or -isystem options. 4466 -iplugindir=dir 4467 Set the directory to search for plugins that are passed by -fplugin=name instead of -fplugin=path/name.so. This option is not meant to be used by the user, but only passed by the driver. 4468 -iquotedir 4469 Add the directory dir to the head of the list of directories to be searched for header files only for the case of "#include "file""; they are not searched for "#include ", otherwise 4470 just like -I. 4471 -Ldir 4472 Add directory dir to the list of directories to be searched for -l. 4473 -Bprefix 4474 This option specifies where to find the executables, libraries, include files, and data files of the compiler itself. 4475 The compiler driver program runs one or more of the subprograms cpp, cc1, as and ld. It tries prefix as a prefix for each program it tries to run, both with and without machine/version/. 4476 For each subprogram to be run, the compiler driver first tries the -B prefix, if any. If that name is not found, or if -B is not specified, the driver tries two standard prefixes, 4477 /usr/lib/gcc/ and /usr/local/lib/gcc/. If neither of those results in a file name that is found, the unmodified program name is searched for using the directories specified in your PATH 4478 environment variable. 4479 The compiler checks to see if the path provided by -B refers to a directory, and if necessary it adds a directory separator character at the end of the path. 4480 -B prefixes that effectively specify directory names also apply to libraries in the linker, because the compiler translates these options into -L options for the linker. They also apply to 4481 include files in the preprocessor, because the compiler translates these options into -isystem options for the preprocessor. In this case, the compiler appends include to the prefix. 4482 The runtime support file libgcc.a can also be searched for using the -B prefix, if needed. If it is not found there, the two standard prefixes above are tried, and that is all. The file is 4483 left out of the link if it is not found by those means. 4484 Another way to specify a prefix much like the -B prefix is to use the environment variable GCC_EXEC_PREFIX. 4485 As a special kludge, if the path provided by -B is [dir/]stageN/, where N is a number in the range 0 to 9, then it is replaced by [dir/]include. This is to help with boot-strapping the 4486 compiler. 4487 -specs=file 4488 Process file after the compiler reads in the standard specs file, in order to override the defaults which the gcc driver program uses when determining what switches to pass to cc1, cc1plus, 4489 as, ld, etc. More than one -specs=file can be specified on the command line, and they are processed in order, from left to right. 4490 --sysroot=dir 4491 Use dir as the logical root directory for headers and libraries. For example, if the compiler normally searches for headers in /usr/include and libraries in /usr/lib, it instead searches 4492 dir/usr/include and dir/usr/lib. 4493 If you use both this option and the -isysroot option, then the --sysroot option applies to libraries, but the -isysroot option applies to header files. 4494 The GNU linker (beginning with version 2.16) has the necessary support for this option. If your linker does not support this option, the header file aspect of --sysroot still works, but the 4495 library aspect does not. 4496 --no-sysroot-suffix 4497 For some targets, a suffix is added to the root directory specified with --sysroot, depending on the other options used, so that headers may for example be found in dir/suffix/usr/include 4498 instead of dir/usr/include. This option disables the addition of such a suffix. 4499 -I- This option has been deprecated. Please use -iquote instead for -I directories before the -I- and remove the -I- option. Any directories you specify with -I options before the -I- option 4500 are searched only for the case of "#include "file""; they are not searched for "#include ". 4501 If additional directories are specified with -I options after the -I- option, these directories are searched for all "#include" directives. (Ordinarily all -I directories are used this 4502 way.) 4503 In addition, the -I- option inhibits the use of the current directory (where the current input file came from) as the first search directory for "#include "file"". There is no way to 4504 override this effect of -I-. With -I. you can specify searching the directory that is current when the compiler is invoked. That is not exactly the same as what the preprocessor does by 4505 default, but it is often satisfactory. 4506 -I- does not inhibit the use of the standard system directories for header files. Thus, -I- and -nostdinc are independent. 4507 Specifying Target Machine and Compiler Version 4508 The usual way to run GCC is to run the executable called gcc, or machine-gcc when cross-compiling, or machine-gcc-version to run a version other than the one that was installed last. 4509 Hardware Models and Configurations 4510 Each target machine types can have its own special options, starting with -m, to choose among various hardware models or configurations---for example, 68010 vs 68020, floating coprocessor or 4511 none. A single installed version of the compiler can compile for any model or configuration, according to the options specified. 4512 Some configurations of the compiler also support additional special options, usually for compatibility with other compilers on the same platform. 4513 AArch64 Options 4514 These options are defined for AArch64 implementations: 4515 -mabi=name 4516 Generate code for the specified data model. Permissible values are ilp32 for SysV-like data model where int, long int and pointer are 32-bit, and lp64 for SysV-like data model where int is 4517 32-bit, but long int and pointer are 64-bit. 4518 The default depends on the specific target configuration. Note that the LP64 and ILP32 ABIs are not link-compatible; you must compile your entire program with the same ABI, and link with a 4519 compatible set of libraries. 4520 -mbig-endian 4521 Generate big-endian code. This is the default when GCC is configured for an aarch64_be-*-* target. 4522 -mgeneral-regs-only 4523 Generate code which uses only the general registers. 4524 -mlittle-endian 4525 Generate little-endian code. This is the default when GCC is configured for an aarch64-*-* but not an aarch64_be-*-* target. 4526 -mcmodel=tiny 4527 Generate code for the tiny code model. The program and its statically defined symbols must be within 1GB of each other. Pointers are 64 bits. Programs can be statically or dynamically 4528 linked. This model is not fully implemented and mostly treated as small. 4529 -mcmodel=small 4530 Generate code for the small code model. The program and its statically defined symbols must be within 4GB of each other. Pointers are 64 bits. Programs can be statically or dynamically 4531 linked. This is the default code model. 4532 -mcmodel=large 4533 Generate code for the large code model. This makes no assumptions about addresses and sizes of sections. Pointers are 64 bits. Programs can be statically linked only. 4534 -mstrict-align 4535 Do not assume that unaligned memory references are handled by the system. 4536 -momit-leaf-frame-pointer 4537 -mno-omit-leaf-frame-pointer 4538 Omit or keep the frame pointer in leaf functions. The former behaviour is the default. 4539 -mtls-dialect=desc 4540 Use TLS descriptors as the thread-local storage mechanism for dynamic accesses of TLS variables. This is the default. 4541 -mtls-dialect=traditional 4542 Use traditional TLS as the thread-local storage mechanism for dynamic accesses of TLS variables. 4543 -mfix-cortex-a53-835769 4544 -mno-fix-cortex-a53-835769 4545 Enable or disable the workaround for the ARM Cortex-A53 erratum number 835769. This involves inserting a NOP instruction between memory instructions and 64-bit integer multiply-accumulate 4546 instructions. 4547 -mfix-cortex-a53-843419 4548 -mno-fix-cortex-a53-843419 4549 Enable or disable the workaround for the ARM Cortex-A53 erratum number 843419. This erratum workaround is made at link time and this will only pass the corresponding flag to the linker. 4550 -march=name 4551 Specify the name of the target architecture, optionally suffixed by one or more feature modifiers. This option has the form -march=arch{+[no]feature}*, where the only permissible value for 4552 arch is armv8-a. The permissible values for feature are documented in the sub-section below. 4553 Where conflicting feature modifiers are specified, the right-most feature is used. 4554 GCC uses this name to determine what kind of instructions it can emit when generating assembly code. 4555 Where -march is specified without either of -mtune or -mcpu also being specified, the code is tuned to perform well across a range of target processors implementing the target architecture. 4556 -mtune=name 4557 Specify the name of the target processor for which GCC should tune the performance of the code. Permissible values for this option are: generic, cortex-a53, cortex-a57, cortex-a72, 4558 exynos-m1, thunderx, xgene1. 4559 Additionally, this option can specify that GCC should tune the performance of the code for a big.LITTLE system. Permissible values for this option are: cortex-a57.cortex-a53, 4560 cortex-a72.cortex-a53. 4561 Where none of -mtune=, -mcpu= or -march= are specified, the code is tuned to perform well across a range of target processors. 4562 This option cannot be suffixed by feature modifiers. 4563 -mcpu=name 4564 Specify the name of the target processor, optionally suffixed by one or more feature modifiers. This option has the form -mcpu=cpu{+[no]feature}*, where the permissible values for cpu are 4565 the same as those available for -mtune. 4566 The permissible values for feature are documented in the sub-section below. 4567 Where conflicting feature modifiers are specified, the right-most feature is used. 4568 GCC uses this name to determine what kind of instructions it can emit when generating assembly code (as if by -march) and to determine the target processor for which to tune for performance 4569 (as if by -mtune). Where this option is used in conjunction with -march or -mtune, those options take precedence over the appropriate part of this option. 4570 -march and -mcpu Feature Modifiers 4571 Feature modifiers used with -march and -mcpu can be one the following: 4572 crc Enable CRC extension. 4573 crypto 4574 Enable Crypto extension. This implies Advanced SIMD is enabled. 4575 fp Enable floating-point instructions. 4576 simd 4577 Enable Advanced SIMD instructions. This implies floating-point instructions are enabled. This is the default for all current possible values for options -march and -mcpu=. 4578 Adapteva Epiphany Options 4579 These -m options are defined for Adapteva Epiphany: 4580 -mhalf-reg-file 4581 Don't allocate any register in the range "r32"..."r63". That allows code to run on hardware variants that lack these registers. 4582 -mprefer-short-insn-regs 4583 Preferrentially allocate registers that allow short instruction generation. This can result in increased instruction count, so this may either reduce or increase overall code size. 4584 -mbranch-cost=num 4585 Set the cost of branches to roughly num "simple" instructions. This cost is only a heuristic and is not guaranteed to produce consistent results across releases. 4586 -mcmove 4587 Enable the generation of conditional moves. 4588 -mnops=num 4589 Emit num NOPs before every other generated instruction. 4590 -mno-soft-cmpsf 4591 For single-precision floating-point comparisons, emit an "fsub" instruction and test the flags. This is faster than a software comparison, but can get incorrect results in the presence of 4592 NaNs, or when two different small numbers are compared such that their difference is calculated as zero. The default is -msoft-cmpsf, which uses slower, but IEEE-compliant, software 4593 comparisons. 4594 -mstack-offset=num 4595 Set the offset between the top of the stack and the stack pointer. E.g., a value of 8 means that the eight bytes in the range "sp+0...sp+7" can be used by leaf functions without stack 4596 allocation. Values other than 8 or 16 are untested and unlikely to work. Note also that this option changes the ABI; compiling a program with a different stack offset than the libraries 4597 have been compiled with generally does not work. This option can be useful if you want to evaluate if a different stack offset would give you better code, but to actually use a different 4598 stack offset to build working programs, it is recommended to configure the toolchain with the appropriate --with-stack-offset=num option. 4599 -mno-round-nearest 4600 Make the scheduler assume that the rounding mode has been set to truncating. The default is -mround-nearest. 4601 -mlong-calls 4602 If not otherwise specified by an attribute, assume all calls might be beyond the offset range of the "b" / "bl" instructions, and therefore load the function address into a register before 4603 performing a (otherwise direct) call. This is the default. 4604 -mshort-calls 4605 If not otherwise specified by an attribute, assume all direct calls are in the range of the "b" / "bl" instructions, so use these instructions for direct calls. The default is -mlong-calls. 4606 -msmall16 4607 Assume addresses can be loaded as 16-bit unsigned values. This does not apply to function addresses for which -mlong-calls semantics are in effect. 4608 -mfp-mode=mode 4609 Set the prevailing mode of the floating-point unit. This determines the floating-point mode that is provided and expected at function call and return time. Making this mode match the mode 4610 you predominantly need at function start can make your programs smaller and faster by avoiding unnecessary mode switches. 4611 mode can be set to one the following values: 4612 caller 4613 Any mode at function entry is valid, and retained or restored when the function returns, and when it calls other functions. This mode is useful for compiling libraries or other 4614 compilation units you might want to incorporate into different programs with different prevailing FPU modes, and the convenience of being able to use a single object file outweighs the 4615 size and speed overhead for any extra mode switching that might be needed, compared with what would be needed with a more specific choice of prevailing FPU mode. 4616 truncate 4617 This is the mode used for floating-point calculations with truncating (i.e. round towards zero) rounding mode. That includes conversion from floating point to integer. 4618 round-nearest 4619 This is the mode used for floating-point calculations with round-to-nearest-or-even rounding mode. 4620 int This is the mode used to perform integer calculations in the FPU, e.g. integer multiply, or integer multiply-and-accumulate. 4621 The default is -mfp-mode=caller 4622 -mnosplit-lohi 4623 -mno-postinc 4624 -mno-postmodify 4625 Code generation tweaks that disable, respectively, splitting of 32-bit loads, generation of post-increment addresses, and generation of post-modify addresses. The defaults are msplit-lohi, 4626 -mpost-inc, and -mpost-modify. 4627 -mnovect-double 4628 Change the preferred SIMD mode to SImode. The default is -mvect-double, which uses DImode as preferred SIMD mode. 4629 -max-vect-align=num 4630 The maximum alignment for SIMD vector mode types. num may be 4 or 8. The default is 8. Note that this is an ABI change, even though many library function interfaces are unaffected if they 4631 don't use SIMD vector modes in places that affect size and/or alignment of relevant types. 4632 -msplit-vecmove-early 4633 Split vector moves into single word moves before reload. In theory this can give better register allocation, but so far the reverse seems to be generally the case. 4634 -m1reg-reg 4635 Specify a register to hold the constant -1, which makes loading small negative constants and certain bitmasks faster. Allowable values for reg are r43 and r63, which specify use of that 4636 register as a fixed register, and none, which means that no register is used for this purpose. The default is -m1reg-none. 4637 ARC Options 4638 The following options control the architecture variant for which code is being compiled: 4639 -mbarrel-shifter 4640 Generate instructions supported by barrel shifter. This is the default unless -mcpu=ARC601 is in effect. 4641 -mcpu=cpu 4642 Set architecture type, register usage, and instruction scheduling parameters for cpu. There are also shortcut alias options available for backward compatibility and convenience. Supported 4643 values for cpu are 4644 ARC600 4645 Compile for ARC600. Aliases: -mA6, -mARC600. 4646 ARC601 4647 Compile for ARC601. Alias: -mARC601. 4648 ARC700 4649 Compile for ARC700. Aliases: -mA7, -mARC700. This is the default when configured with --with-cpu=arc700. 4650 -mdpfp 4651 -mdpfp-compact 4652 FPX: Generate Double Precision FPX instructions, tuned for the compact implementation. 4653 -mdpfp-fast 4654 FPX: Generate Double Precision FPX instructions, tuned for the fast implementation. 4655 -mno-dpfp-lrsr 4656 Disable LR and SR instructions from using FPX extension aux registers. 4657 -mea 4658 Generate Extended arithmetic instructions. Currently only "divaw", "adds", "subs", and "sat16" are supported. This is always enabled for -mcpu=ARC700. 4659 -mno-mpy 4660 Do not generate mpy instructions for ARC700. 4661 -mmul32x16 4662 Generate 32x16 bit multiply and mac instructions. 4663 -mmul64 4664 Generate mul64 and mulu64 instructions. Only valid for -mcpu=ARC600. 4665 -mnorm 4666 Generate norm instruction. This is the default if -mcpu=ARC700 is in effect. 4667 -mspfp 4668 -mspfp-compact 4669 FPX: Generate Single Precision FPX instructions, tuned for the compact implementation. 4670 -mspfp-fast 4671 FPX: Generate Single Precision FPX instructions, tuned for the fast implementation. 4672 -msimd 4673 Enable generation of ARC SIMD instructions via target-specific builtins. Only valid for -mcpu=ARC700. 4674 -msoft-float 4675 This option ignored; it is provided for compatibility purposes only. Software floating point code is emitted by default, and this default can overridden by FPX options; mspfp, mspfp- 4676 compact, or mspfp-fast for single precision, and mdpfp, mdpfp-compact, or mdpfp-fast for double precision. 4677 -mswap 4678 Generate swap instructions. 4679 The following options are passed through to the assembler, and also define preprocessor macro symbols. 4680 -mdsp-packa 4681 Passed down to the assembler to enable the DSP Pack A extensions. Also sets the preprocessor symbol "__Xdsp_packa". 4682 -mdvbf 4683 Passed down to the assembler to enable the dual viterbi butterfly extension. Also sets the preprocessor symbol "__Xdvbf". 4684 -mlock 4685 Passed down to the assembler to enable the Locked Load/Store Conditional extension. Also sets the preprocessor symbol "__Xlock". 4686 -mmac-d16 4687 Passed down to the assembler. Also sets the preprocessor symbol "__Xxmac_d16". 4688 -mmac-24 4689 Passed down to the assembler. Also sets the preprocessor symbol "__Xxmac_24". 4690 -mrtsc 4691 Passed down to the assembler to enable the 64-bit Time-Stamp Counter extension instruction. Also sets the preprocessor symbol "__Xrtsc". 4692 -mswape 4693 Passed down to the assembler to enable the swap byte ordering extension instruction. Also sets the preprocessor symbol "__Xswape". 4694 -mtelephony 4695 Passed down to the assembler to enable dual and single operand instructions for telephony. Also sets the preprocessor symbol "__Xtelephony". 4696 -mxy 4697 Passed down to the assembler to enable the XY Memory extension. Also sets the preprocessor symbol "__Xxy". 4698 The following options control how the assembly code is annotated: 4699 -misize 4700 Annotate assembler instructions with estimated addresses. 4701 -mannotate-align 4702 Explain what alignment considerations lead to the decision to make an instruction short or long. 4703 The following options are passed through to the linker: 4704 -marclinux 4705 Passed through to the linker, to specify use of the "arclinux" emulation. This option is enabled by default in tool chains built for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when 4706 profiling is not requested. 4707 -marclinux_prof 4708 Passed through to the linker, to specify use of the "arclinux_prof" emulation. This option is enabled by default in tool chains built for "arc-linux-uclibc" and "arceb-linux-uclibc" targets 4709 when profiling is requested. 4710 The following options control the semantics of generated code: 4711 -mepilogue-cfi 4712 Enable generation of call frame information for epilogues. 4713 -mno-epilogue-cfi 4714 Disable generation of call frame information for epilogues. 4715 -mlong-calls 4716 Generate call insns as register indirect calls, thus providing access to the full 32-bit address range. 4717 -mmedium-calls 4718 Don't use less than 25 bit addressing range for calls, which is the offset available for an unconditional branch-and-link instruction. Conditional execution of function calls is suppressed, 4719 to allow use of the 25-bit range, rather than the 21-bit range with conditional branch-and-link. This is the default for tool chains built for "arc-linux-uclibc" and "arceb-linux-uclibc" 4720 targets. 4721 -mno-sdata 4722 Do not generate sdata references. This is the default for tool chains built for "arc-linux-uclibc" and "arceb-linux-uclibc" targets. 4723 -mucb-mcount 4724 Instrument with mcount calls as used in UCB code. I.e. do the counting in the callee, not the caller. By default ARC instrumentation counts in the caller. 4725 -mvolatile-cache 4726 Use ordinarily cached memory accesses for volatile references. This is the default. 4727 -mno-volatile-cache 4728 Enable cache bypass for volatile references. 4729 The following options fine tune code generation: 4730 -malign-call 4731 Do alignment optimizations for call instructions. 4732 -mauto-modify-reg 4733 Enable the use of pre/post modify with register displacement. 4734 -mbbit-peephole 4735 Enable bbit peephole2. 4736 -mno-brcc 4737 This option disables a target-specific pass in arc_reorg to generate "BRcc" instructions. It has no effect on "BRcc" generation driven by the combiner pass. 4738 -mcase-vector-pcrel 4739 Use pc-relative switch case tables - this enables case table shortening. This is the default for -Os. 4740 -mcompact-casesi 4741 Enable compact casesi pattern. This is the default for -Os. 4742 -mno-cond-exec 4743 Disable ARCompact specific pass to generate conditional execution instructions. Due to delay slot scheduling and interactions between operand numbers, literal sizes, instruction lengths, 4744 and the support for conditional execution, the target-independent pass to generate conditional execution is often lacking, so the ARC port has kept a special pass around that tries to find 4745 more conditional execution generating opportunities after register allocation, branch shortening, and delay slot scheduling have been done. This pass generally, but not always, improves 4746 performance and code size, at the cost of extra compilation time, which is why there is an option to switch it off. If you have a problem with call instructions exceeding their allowable 4747 offset range because they are conditionalized, you should consider using -mmedium-calls instead. 4748 -mearly-cbranchsi 4749 Enable pre-reload use of the cbranchsi pattern. 4750 -mexpand-adddi 4751 Expand "adddi3" and "subdi3" at rtl generation time into "add.f", "adc" etc. 4752 -mindexed-loads 4753 Enable the use of indexed loads. This can be problematic because some optimizers then assume that indexed stores exist, which is not the case. 4754 -mlra 4755 Enable Local Register Allocation. This is still experimental for ARC, so by default the compiler uses standard reload (i.e. -mno-lra). 4756 -mlra-priority-none 4757 Don't indicate any priority for target registers. 4758 -mlra-priority-compact 4759 Indicate target register priority for r0..r3 / r12..r15. 4760 -mlra-priority-noncompact 4761 Reduce target regsiter priority for r0..r3 / r12..r15. 4762 -mno-millicode 4763 When optimizing for size (using -Os), prologues and epilogues that have to save or restore a large number of registers are often shortened by using call to a special function in libgcc; this 4764 is referred to as a millicode call. As these calls can pose performance issues, and/or cause linking issues when linking in a nonstandard way, this option is provided to turn off millicode 4765 call generation. 4766 -mmixed-code 4767 Tweak register allocation to help 16-bit instruction generation. This generally has the effect of decreasing the average instruction size while increasing the instruction count. 4768 -mq-class 4769 Enable 'q' instruction alternatives. This is the default for -Os. 4770 -mRcq 4771 Enable Rcq constraint handling - most short code generation depends on this. This is the default. 4772 -mRcw 4773 Enable Rcw constraint handling - ccfsm condexec mostly depends on this. This is the default. 4774 -msize-level=level 4775 Fine-tune size optimization with regards to instruction lengths and alignment. The recognized values for level are: 4776 0 No size optimization. This level is deprecated and treated like 1. 4777 1 Short instructions are used opportunistically. 4778 2 In addition, alignment of loops and of code after barriers are dropped. 4779 3 In addition, optional data alignment is dropped, and the option Os is enabled. 4780 This defaults to 3 when -Os is in effect. Otherwise, the behavior when this is not set is equivalent to level 1. 4781 -mtune=cpu 4782 Set instruction scheduling parameters for cpu, overriding any implied by -mcpu=. 4783 Supported values for cpu are 4784 ARC600 4785 Tune for ARC600 cpu. 4786 ARC601 4787 Tune for ARC601 cpu. 4788 ARC700 4789 Tune for ARC700 cpu with standard multiplier block. 4790 ARC700-xmac 4791 Tune for ARC700 cpu with XMAC block. 4792 ARC725D 4793 Tune for ARC725D cpu. 4794 ARC750D 4795 Tune for ARC750D cpu. 4796 -mmultcost=num 4797 Cost to assume for a multiply instruction, with 4 being equal to a normal instruction. 4798 -munalign-prob-threshold=probability 4799 Set probability threshold for unaligning branches. When tuning for ARC700 and optimizing for speed, branches without filled delay slot are preferably emitted unaligned and long, unless 4800 profiling indicates that the probability for the branch to be taken is below probability. The default is (REG_BR_PROB_BASE/2), i.e. 5000. 4801 The following options are maintained for backward compatibility, but are now deprecated and will be removed in a future release: 4802 -margonaut 4803 Obsolete FPX. 4804 -mbig-endian 4805 -EB Compile code for big endian targets. Use of these options is now deprecated. Users wanting big-endian code, should use the "arceb-elf32" and "arceb-linux-uclibc" targets when building the 4806 tool chain, for which big-endian is the default. 4807 -mlittle-endian 4808 -EL Compile code for little endian targets. Use of these options is now deprecated. Users wanting little-endian code should use the "arc-elf32" and "arc-linux-uclibc" targets when building the 4809 tool chain, for which little-endian is the default. 4810 -mbarrel_shifter 4811 Replaced by -mbarrel-shifter. 4812 -mdpfp_compact 4813 Replaced by -mdpfp-compact. 4814 -mdpfp_fast 4815 Replaced by -mdpfp-fast. 4816 -mdsp_packa 4817 Replaced by -mdsp-packa. 4818 -mEA 4819 Replaced by -mea. 4820 -mmac_24 4821 Replaced by -mmac-24. 4822 -mmac_d16 4823 Replaced by -mmac-d16. 4824 -mspfp_compact 4825 Replaced by -mspfp-compact. 4826 -mspfp_fast 4827 Replaced by -mspfp-fast. 4828 -mtune=cpu 4829 Values arc600, arc601, arc700 and arc700-xmac for cpu are replaced by ARC600, ARC601, ARC700 and ARC700-xmac respectively 4830 -multcost=num 4831 Replaced by -mmultcost. 4832 ARM Options 4833 These -m options are defined for the ARM port: 4834 -mabi=name 4835 Generate code for the specified ABI. Permissible values are: apcs-gnu, atpcs, aapcs, aapcs-linux and iwmmxt. 4836 -mapcs-frame 4837 Generate a stack frame that is compliant with the ARM Procedure Call Standard for all functions, even if this is not strictly necessary for correct execution of the code. Specifying 4838 -fomit-frame-pointer with this option causes the stack frames not to be generated for leaf functions. The default is -mno-apcs-frame. This option is deprecated. 4839 -mapcs 4840 This is a synonym for -mapcs-frame and is deprecated. 4841 -mthumb-interwork 4842 Generate code that supports calling between the ARM and Thumb instruction sets. Without this option, on pre-v5 architectures, the two instruction sets cannot be reliably used inside one 4843 program. The default is -mno-thumb-interwork, since slightly larger code is generated when -mthumb-interwork is specified. In AAPCS configurations this option is meaningless. 4844 -mno-sched-prolog 4845 Prevent the reordering of instructions in the function prologue, or the merging of those instruction with the instructions in the function's body. This means that all functions start with a 4846 recognizable set of instructions (or in fact one of a choice from a small set of different function prologues), and this information can be used to locate the start of functions inside an 4847 executable piece of code. The default is -msched-prolog. 4848 -mfloat-abi=name 4849 Specifies which floating-point ABI to use. Permissible values are: soft, softfp and hard. 4850 Specifying soft causes GCC to generate output containing library calls for floating-point operations. softfp allows the generation of code using hardware floating-point instructions, but 4851 still uses the soft-float calling conventions. hard allows generation of floating-point instructions and uses FPU-specific calling conventions. 4852 The default depends on the specific target configuration. Note that the hard-float and soft-float ABIs are not link-compatible; you must compile your entire program with the same ABI, and 4853 link with a compatible set of libraries. 4854 -mlittle-endian 4855 Generate code for a processor running in little-endian mode. This is the default for all standard configurations. 4856 -mbig-endian 4857 Generate code for a processor running in big-endian mode; the default is to compile code for a little-endian processor. 4858 -march=name 4859 This specifies the name of the target ARM architecture. GCC uses this name to determine what kind of instructions it can emit when generating assembly code. This option can be used in 4860 conjunction with or instead of the -mcpu= option. Permissible names are: armv2, armv2a, armv3, armv3m, armv4, armv4t, armv5, armv5t, armv5e, armv5te, armv6, armv6j, armv6t2, armv6z, 4861 armv6zk, armv6-m, armv7, armv7-a, armv7-r, armv7-m, armv7e-m, armv7ve, armv8-a, armv8-a+crc, iwmmxt, iwmmxt2, ep9312. 4862 -march=armv7ve is the armv7-a architecture with virtualization extensions. 4863 -march=armv8-a+crc enables code generation for the ARMv8-A architecture together with the optional CRC32 extensions. 4864 -march=native causes the compiler to auto-detect the architecture of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. 4865 If the auto-detect is unsuccessful the option has no effect. 4866 -mtune=name 4867 This option specifies the name of the target ARM processor for which GCC should tune the performance of the code. For some ARM implementations better performance can be obtained by using 4868 this option. Permissible names are: arm2, arm250, arm3, arm6, arm60, arm600, arm610, arm620, arm7, arm7m, arm7d, arm7dm, arm7di, arm7dmi, arm70, arm700, arm700i, arm710, arm710c, arm7100, 4869 arm720, arm7500, arm7500fe, arm7tdmi, arm7tdmi-s, arm710t, arm720t, arm740t, strongarm, strongarm110, strongarm1100, strongarm1110, arm8, arm810, arm9, arm9e, arm920, arm920t, arm922t, 4870 arm946e-s, arm966e-s, arm968e-s, arm926ej-s, arm940t, arm9tdmi, arm10tdmi, arm1020t, arm1026ej-s, arm10e, arm1020e, arm1022e, arm1136j-s, arm1136jf-s, mpcore, mpcorenovfp, arm1156t2-s, 4871 arm1156t2f-s, arm1176jz-s, arm1176jzf-s, cortex-a5, cortex-a7, cortex-a8, cortex-a9, cortex-a12, cortex-a15, cortex-a53, cortex-a57, cortex-a72, cortex-r4, cortex-r4f, cortex-r5, cortex-r7, 4872 cortex-m7, cortex-m4, cortex-m3, cortex-m1, cortex-m0, cortex-m0plus, cortex-m1.small-multiply, cortex-m0.small-multiply, cortex-m0plus.small-multiply, exynos-m1, marvell-pj4, xscale, 4873 iwmmxt, iwmmxt2, ep9312, fa526, fa626, fa606te, fa626te, fmp626, fa726te, xgene1. 4874 Additionally, this option can specify that GCC should tune the performance of the code for a big.LITTLE system. Permissible names are: cortex-a15.cortex-a7, cortex-a57.cortex-a53, 4875 cortex-a72.cortex-a53. 4876 -mtune=generic-arch specifies that GCC should tune the performance for a blend of processors within architecture arch. The aim is to generate code that run well on the current most popular 4877 processors, balancing between optimizations that benefit some CPUs in the range, and avoiding performance pitfalls of other CPUs. The effects of this option may change in future GCC 4878 versions as CPU models come and go. 4879 -mtune=native causes the compiler to auto-detect the CPU of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the 4880 auto-detect is unsuccessful the option has no effect. 4881 -mcpu=name 4882 This specifies the name of the target ARM processor. GCC uses this name to derive the name of the target ARM architecture (as if specified by -march) and the ARM processor type for which to 4883 tune for performance (as if specified by -mtune). Where this option is used in conjunction with -march or -mtune, those options take precedence over the appropriate part of this option. 4884 Permissible names for this option are the same as those for -mtune. 4885 -mcpu=generic-arch is also permissible, and is equivalent to -march=arch -mtune=generic-arch. See -mtune for more information. 4886 -mcpu=native causes the compiler to auto-detect the CPU of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the 4887 auto-detect is unsuccessful the option has no effect. 4888 -mfpu=name 4889 This specifies what floating-point hardware (or hardware emulation) is available on the target. Permissible names are: vfp, vfpv3, vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16, vfpv3xd, 4890 vfpv3xd-fp16, neon, neon-fp16, vfpv4, vfpv4-d16, fpv4-sp-d16, neon-vfpv4, fpv5-d16, fpv5-sp-d16, fp-armv8, neon-fp-armv8, and crypto-neon-fp-armv8. 4891 If -msoft-float is specified this specifies the format of floating-point values. 4892 If the selected floating-point hardware includes the NEON extension (e.g. -mfpu=neon), note that floating-point operations are not generated by GCC's auto-vectorization pass unless 4893 -funsafe-math-optimizations is also specified. This is because NEON hardware does not fully implement the IEEE 754 standard for floating-point arithmetic (in particular denormal values are 4894 treated as zero), so the use of NEON instructions may lead to a loss of precision. 4895 -mfp16-format=name 4896 Specify the format of the "__fp16" half-precision floating-point type. Permissible names are none, ieee, and alternative; the default is none, in which case the "__fp16" type is not 4897 defined. 4898 -mstructure-size-boundary=n 4899 The sizes of all structures and unions are rounded up to a multiple of the number of bits set by this option. Permissible values are 8, 32 and 64. The default value varies for different 4900 toolchains. For the COFF targeted toolchain the default value is 8. A value of 64 is only allowed if the underlying ABI supports it. 4901 Specifying a larger number can produce faster, more efficient code, but can also increase the size of the program. Different values are potentially incompatible. Code compiled with one 4902 value cannot necessarily expect to work with code or libraries compiled with another value, if they exchange information using structures or unions. 4903 -mabort-on-noreturn 4904 Generate a call to the function "abort" at the end of a "noreturn" function. It is executed if the function tries to return. 4905 -mlong-calls 4906 -mno-long-calls 4907 Tells the compiler to perform function calls by first loading the address of the function into a register and then performing a subroutine call on this register. This switch is needed if 4908 the target function lies outside of the 64-megabyte addressing range of the offset-based version of subroutine call instruction. 4909 Even if this switch is enabled, not all function calls are turned into long calls. The heuristic is that static functions, functions that have the "short_call" attribute, functions that are 4910 inside the scope of a "#pragma no_long_calls" directive, and functions whose definitions have already been compiled within the current compilation unit are not turned into long calls. The 4911 exceptions to this rule are that weak function definitions, functions with the "long_call" attribute or the "section" attribute, and functions that are within the scope of a "#pragma 4912 long_calls" directive are always turned into long calls. 4913 This feature is not enabled by default. Specifying -mno-long-calls restores the default behavior, as does placing the function calls within the scope of a "#pragma long_calls_off" 4914 directive. Note these switches have no effect on how the compiler generates code to handle function calls via function pointers. 4915 -msingle-pic-base 4916 Treat the register used for PIC addressing as read-only, rather than loading it in the prologue for each function. The runtime system is responsible for initializing this register with an 4917 appropriate value before execution begins. 4918 -mpic-register=reg 4919 Specify the register to be used for PIC addressing. For standard PIC base case, the default is any suitable register determined by compiler. For single PIC base case, the default is R9 if 4920 target is EABI based or stack-checking is enabled, otherwise the default is R10. 4921 -mpic-data-is-text-relative 4922 Assume that each data segments are relative to text segment at load time. Therefore, it permits addressing data using PC-relative operations. This option is on by default for targets other 4923 than VxWorks RTP. 4924 -mpoke-function-name 4925 Write the name of each function into the text section, directly preceding the function prologue. The generated code is similar to this: 4926 t0 4927 .ascii "arm_poke_function_name", 0 4928 .align 4929 t1 4930 .word 0xff000000 + (t1 - t0) 4931 arm_poke_function_name 4932 mov ip, sp 4933 stmfd sp!, {fp, ip, lr, pc} 4934 sub fp, ip, #4 4935 When performing a stack backtrace, code can inspect the value of "pc" stored at "fp + 0". If the trace function then looks at location "pc - 12" and the top 8 bits are set, then we know 4936 that there is a function name embedded immediately preceding this location and has length "((pc[-3]) & 0xff000000)". 4937 -mthumb 4938 -marm 4939 Select between generating code that executes in ARM and Thumb states. The default for most configurations is to generate code that executes in ARM state, but the default can be changed by 4940 configuring GCC with the --with-mode=state configure option. 4941 -mtpcs-frame 4942 Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all non-leaf functions. (A leaf function is one that does not call any other functions.) The default is 4943 -mno-tpcs-frame. 4944 -mtpcs-leaf-frame 4945 Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all leaf functions. (A leaf function is one that does not call any other functions.) The default is 4946 -mno-apcs-leaf-frame. 4947 -mcallee-super-interworking 4948 Gives all externally visible functions in the file being compiled an ARM instruction set header which switches to Thumb mode before executing the rest of the function. This allows these 4949 functions to be called from non-interworking code. This option is not valid in AAPCS configurations because interworking is enabled by default. 4950 -mcaller-super-interworking 4951 Allows calls via function pointers (including virtual functions) to execute correctly regardless of whether the target code has been compiled for interworking or not. There is a small 4952 overhead in the cost of executing a function pointer if this option is enabled. This option is not valid in AAPCS configurations because interworking is enabled by default. 4953 -mtp=name 4954 Specify the access model for the thread local storage pointer. The valid models are soft, which generates calls to "__aeabi_read_tp", cp15, which fetches the thread pointer from "cp15" 4955 directly (supported in the arm6k architecture), and auto, which uses the best available method for the selected processor. The default setting is auto. 4956 -mtls-dialect=dialect 4957 Specify the dialect to use for accessing thread local storage. Two dialects are supported---gnu and gnu2. The gnu dialect selects the original GNU scheme for supporting local and global 4958 dynamic TLS models. The gnu2 dialect selects the GNU descriptor scheme, which provides better performance for shared libraries. The GNU descriptor scheme is compatible with the original 4959 scheme, but does require new assembler, linker and library support. Initial and local exec TLS models are unaffected by this option and always use the original scheme. 4960 -mword-relocations 4961 Only generate absolute relocations on word-sized values (i.e. R_ARM_ABS32). This is enabled by default on targets (uClinux, SymbianOS) where the runtime loader imposes this restriction, and 4962 when -fpic or -fPIC is specified. 4963 -mfix-cortex-m3-ldrd 4964 Some Cortex-M3 cores can cause data corruption when "ldrd" instructions with overlapping destination and base registers are used. This option avoids generating these instructions. This 4965 option is enabled by default when -mcpu=cortex-m3 is specified. 4966 -munaligned-access 4967 -mno-unaligned-access 4968 Enables (or disables) reading and writing of 16- and 32- bit values from addresses that are not 16- or 32- bit aligned. By default unaligned access is disabled for all pre-ARMv6 and all 4969 ARMv6-M architectures, and enabled for all other architectures. If unaligned access is not enabled then words in packed data structures are accessed a byte at a time. 4970 The ARM attribute "Tag_CPU_unaligned_access" is set in the generated object file to either true or false, depending upon the setting of this option. If unaligned access is enabled then the 4971 preprocessor symbol "__ARM_FEATURE_UNALIGNED" is also defined. 4972 -mneon-for-64bits 4973 Enables using Neon to handle scalar 64-bits operations. This is disabled by default since the cost of moving data from core registers to Neon is high. 4974 -mslow-flash-data 4975 Assume loading data from flash is slower than fetching instruction. Therefore literal load is minimized for better performance. This option is only supported when compiling for ARMv7 4976 M-profile and off by default. 4977 -masm-syntax-unified 4978 Assume inline assembler is using unified asm syntax. The default is currently off which implies divided syntax. Currently this option is available only for Thumb1 and has no effect on ARM 4979 state and Thumb2. However, this may change in future releases of GCC. Divided syntax should be considered deprecated. 4980 -mrestrict-it 4981 Restricts generation of IT blocks to conform to the rules of ARMv8. IT blocks can only contain a single 16-bit instruction from a select set of instructions. This option is on by default 4982 for ARMv8 Thumb mode. 4983 -mprint-tune-info 4984 Print CPU tuning information as comment in assembler file. This is an option used only for regression testing of the compiler and not intended for ordinary use in compiling code. This 4985 option is disabled by default. 4986 AVR Options 4987 These options are defined for AVR implementations: 4988 -mmcu=mcu 4989 Specify Atmel AVR instruction set architectures (ISA) or MCU type. 4990 The default for this option is@tie{}avr2. 4991 GCC supports the following AVR devices and ISAs: 4992 "avr2" 4993 "Classic" devices with up to 8@tie{}KiB of program memory. mcu@tie{}= "attiny22", "attiny26", "at90c8534", "at90s2313", "at90s2323", "at90s2333", "at90s2343", "at90s4414", "at90s4433", 4994 "at90s4434", "at90s8515", "at90s8535". 4995 "avr25" 4996 "Classic" devices with up to 8@tie{}KiB of program memory and with the "MOVW" instruction. mcu@tie{}= "ata5272", "ata6616c", "attiny13", "attiny13a", "attiny2313", "attiny2313a", 4997 "attiny24", "attiny24a", "attiny25", "attiny261", "attiny261a", "attiny43u", "attiny4313", "attiny44", "attiny44a", "attiny441", "attiny45", "attiny461", "attiny461a", "attiny48", 4998 "attiny828", "attiny84", "attiny84a", "attiny841", "attiny85", "attiny861", "attiny861a", "attiny87", "attiny88", "at86rf401". 4999 "avr3" 5000 "Classic" devices with 16@tie{}KiB up to 64@tie{}KiB of program memory. mcu@tie{}= "at43usb355", "at76c711". 5001 "avr31" 5002 "Classic" devices with 128@tie{}KiB of program memory. mcu@tie{}= "atmega103", "at43usb320". 5003 "avr35" 5004 "Classic" devices with 16@tie{}KiB up to 64@tie{}KiB of program memory and with the "MOVW" instruction. mcu@tie{}= "ata5505", "ata6617c", "ata664251", "atmega16u2", "atmega32u2", 5005 "atmega8u2", "attiny1634", "attiny167", "at90usb162", "at90usb82". 5006 "avr4" 5007 "Enhanced" devices with up to 8@tie{}KiB of program memory. mcu@tie{}= "ata6285", "ata6286", "ata6289", "ata6612c", "atmega48", "atmega48a", "atmega48p", "atmega48pa", "atmega8", 5008 "atmega8a", "atmega8hva", "atmega8515", "atmega8535", "atmega88", "atmega88a", "atmega88p", "atmega88pa", "at90pwm1", "at90pwm2", "at90pwm2b", "at90pwm3", "at90pwm3b", "at90pwm81". 5009 "avr5" 5010 "Enhanced" devices with 16@tie{}KiB up to 64@tie{}KiB of program memory. mcu@tie{}= "ata5702m322", "ata5782", "ata5790", "ata5790n", "ata5795", "ata5831", "ata6613c", "ata6614q", 5011 "atmega16", "atmega16a", "atmega16hva", "atmega16hva2", "atmega16hvb", "atmega16hvbrevb", "atmega16m1", "atmega16u4", "atmega161", "atmega162", "atmega163", "atmega164a", "atmega164p", 5012 "atmega164pa", "atmega165", "atmega165a", "atmega165p", "atmega165pa", "atmega168", "atmega168a", "atmega168p", "atmega168pa", "atmega169", "atmega169a", "atmega169p", "atmega169pa", 5013 "atmega32", "atmega32a", "atmega32c1", "atmega32hvb", "atmega32hvbrevb", "atmega32m1", "atmega32u4", "atmega32u6", "atmega323", "atmega324a", "atmega324p", "atmega324pa", "atmega325", 5014 "atmega325a", "atmega325p", "atmega325pa", "atmega3250", "atmega3250a", "atmega3250p", "atmega3250pa", "atmega328", "atmega328p", "atmega329", "atmega329a", "atmega329p", "atmega329pa", 5015 "atmega3290", "atmega3290a", "atmega3290p", "atmega3290pa", "atmega406", "atmega64", "atmega64a", "atmega64c1", "atmega64hve", "atmega64hve2", "atmega64m1", "atmega64rfr2", "atmega640", 5016 "atmega644", "atmega644a", "atmega644p", "atmega644pa", "atmega644rfr2", "atmega645", "atmega645a", "atmega645p", "atmega6450", "atmega6450a", "atmega6450p", "atmega649", "atmega649a", 5017 "atmega649p", "atmega6490", "atmega6490a", "atmega6490p", "at90can32", "at90can64", "at90pwm161", "at90pwm216", "at90pwm316", "at90scr100", "at90usb646", "at90usb647", "at94k", "m3000". 5018 "avr51" 5019 "Enhanced" devices with 128@tie{}KiB of program memory. mcu@tie{}= "atmega128", "atmega128a", "atmega128rfa1", "atmega128rfr2", "atmega1280", "atmega1281", "atmega1284", "atmega1284p", 5020 "atmega1284rfr2", "at90can128", "at90usb1286", "at90usb1287". 5021 "avr6" 5022 "Enhanced" devices with 3-byte PC, i.e. with more than 128@tie{}KiB of program memory. mcu@tie{}= "atmega256rfr2", "atmega2560", "atmega2561", "atmega2564rfr2". 5023 "avrxmega2" 5024 "XMEGA" devices with more than 8@tie{}KiB and up to 64@tie{}KiB of program memory. mcu@tie{}= "atxmega16a4", "atxmega16a4u", "atxmega16c4", "atxmega16d4", "atxmega16e5", "atxmega32a4", 5025 "atxmega32a4u", "atxmega32c3", "atxmega32c4", "atxmega32d3", "atxmega32d4", "atxmega32e5", "atxmega8e5". 5026 "avrxmega4" 5027 "XMEGA" devices with more than 64@tie{}KiB and up to 128@tie{}KiB of program memory. mcu@tie{}= "atxmega64a3", "atxmega64a3u", "atxmega64a4u", "atxmega64b1", "atxmega64b3", 5028 "atxmega64c3", "atxmega64d3", "atxmega64d4". 5029 "avrxmega5" 5030 "XMEGA" devices with more than 64@tie{}KiB and up to 128@tie{}KiB of program memory and more than 64@tie{}KiB of RAM. mcu@tie{}= "atxmega64a1", "atxmega64a1u". 5031 "avrxmega6" 5032 "XMEGA" devices with more than 128@tie{}KiB of program memory. mcu@tie{}= "atxmega128a3", "atxmega128a3u", "atxmega128b1", "atxmega128b3", "atxmega128c3", "atxmega128d3", 5033 "atxmega128d4", "atxmega192a3", "atxmega192a3u", "atxmega192c3", "atxmega192d3", "atxmega256a3", "atxmega256a3b", "atxmega256a3bu", "atxmega256a3u", "atxmega256c3", "atxmega256d3", 5034 "atxmega384c3", "atxmega384d3". 5035 "avrxmega7" 5036 "XMEGA" devices with more than 128@tie{}KiB of program memory and more than 64@tie{}KiB of RAM. mcu@tie{}= "atxmega128a1", "atxmega128a1u", "atxmega128a4u". 5037 "avrtiny" 5038 "TINY" Tiny core devices with 512@tie{}B up to 4@tie{}KiB of program memory. mcu@tie{}= "attiny10", "attiny20", "attiny4", "attiny40", "attiny5", "attiny9". 5039 "avr1" 5040 This ISA is implemented by the minimal AVR core and supported for assembler only. mcu@tie{}= "attiny11", "attiny12", "attiny15", "attiny28", "at90s1200". 5041 -maccumulate-args 5042 Accumulate outgoing function arguments and acquire/release the needed stack space for outgoing function arguments once in function prologue/epilogue. Without this option, outgoing arguments 5043 are pushed before calling a function and popped afterwards. 5044 Popping the arguments after the function call can be expensive on AVR so that accumulating the stack space might lead to smaller executables because arguments need not to be removed from the 5045 stack after such a function call. 5046 This option can lead to reduced code size for functions that perform several calls to functions that get their arguments on the stack like calls to printf-like functions. 5047 -mbranch-cost=cost 5048 Set the branch costs for conditional branch instructions to cost. Reasonable values for cost are small, non-negative integers. The default branch cost is 0. 5049 -mcall-prologues 5050 Functions prologues/epilogues are expanded as calls to appropriate subroutines. Code size is smaller. 5051 -mint8 5052 Assume "int" to be 8-bit integer. This affects the sizes of all types: a "char" is 1 byte, an "int" is 1 byte, a "long" is 2 bytes, and "long long" is 4 bytes. Please note that this option 5053 does not conform to the C standards, but it results in smaller code size. 5054 -mn-flash=num 5055 Assume that the flash memory has a size of num times 64@tie{}KiB. 5056 -mno-interrupts 5057 Generated code is not compatible with hardware interrupts. Code size is smaller. 5058 -mrelax 5059 Try to replace "CALL" resp. "JMP" instruction by the shorter "RCALL" resp. "RJMP" instruction if applicable. Setting -mrelax just adds the --mlink-relax option to the assembler's command 5060 line and the --relax option to the linker's command line. 5061 Jump relaxing is performed by the linker because jump offsets are not known before code is located. Therefore, the assembler code generated by the compiler is the same, but the instructions 5062 in the executable may differ from instructions in the assembler code. 5063 Relaxing must be turned on if linker stubs are needed, see the section on "EIND" and linker stubs below. 5064 -mrmw 5065 Assume that the device supports the Read-Modify-Write instructions "XCH", "LAC", "LAS" and "LAT". 5066 -msp8 5067 Treat the stack pointer register as an 8-bit register, i.e. assume the high byte of the stack pointer is zero. In general, you don't need to set this option by hand. 5068 This option is used internally by the compiler to select and build multilibs for architectures "avr2" and "avr25". These architectures mix devices with and without "SPH". For any setting 5069 other than -mmcu=avr2 or -mmcu=avr25 the compiler driver adds or removes this option from the compiler proper's command line, because the compiler then knows if the device or architecture 5070 has an 8-bit stack pointer and thus no "SPH" register or not. 5071 -mstrict-X 5072 Use address register "X" in a way proposed by the hardware. This means that "X" is only used in indirect, post-increment or pre-decrement addressing. 5073 Without this option, the "X" register may be used in the same way as "Y" or "Z" which then is emulated by additional instructions. For example, loading a value with "X+const" addressing 5074 with a small non-negative "const < 64" to a register Rn is performed as 5075 adiw r26, const ; X += const 5076 ld , X ; = *X 5077 sbiw r26, const ; X -= const 5078 -mtiny-stack 5079 Only change the lower 8@tie{}bits of the stack pointer. 5080 -nodevicelib 5081 Don't link against AVR-LibC's device specific library "libdev.a". 5082 -Waddr-space-convert 5083 Warn about conversions between address spaces in the case where the resulting address space is not contained in the incoming address space. 5084 "EIND" and Devices with More Than 128 Ki Bytes of Flash 5085 Pointers in the implementation are 16@tie{}bits wide. The address of a function or label is represented as word address so that indirect jumps and calls can target any code address in the range 5086 of 64@tie{}Ki words. 5087 In order to facilitate indirect jump on devices with more than 128@tie{}Ki bytes of program memory space, there is a special function register called "EIND" that serves as most significant part 5088 of the target address when "EICALL" or "EIJMP" instructions are used. 5089 Indirect jumps and calls on these devices are handled as follows by the compiler and are subject to some limitations: 5090 * The compiler never sets "EIND". 5091 * The compiler uses "EIND" implicitely in "EICALL"/"EIJMP" instructions or might read "EIND" directly in order to emulate an indirect call/jump by means of a "RET" instruction. 5092 * The compiler assumes that "EIND" never changes during the startup code or during the application. In particular, "EIND" is not saved/restored in function or interrupt service routine 5093 prologue/epilogue. 5094 * For indirect calls to functions and computed goto, the linker generates stubs. Stubs are jump pads sometimes also called trampolines. Thus, the indirect call/jump jumps to such a stub. The 5095 stub contains a direct jump to the desired address. 5096 * Linker relaxation must be turned on so that the linker generates the stubs correctly in all situations. See the compiler option -mrelax and the linker option --relax. There are corner cases 5097 where the linker is supposed to generate stubs but aborts without relaxation and without a helpful error message. 5098 * The default linker script is arranged for code with "EIND = 0". If code is supposed to work for a setup with "EIND != 0", a custom linker script has to be used in order to place the 5099 sections whose name start with ".trampolines" into the segment where "EIND" points to. 5100 * The startup code from libgcc never sets "EIND". Notice that startup code is a blend of code from libgcc and AVR-LibC. For the impact of AVR-LibC on "EIND", see the AVR-LibC user manual 5101 ("http://nongnu.org/avr-libc/user-manual/"). 5102 * It is legitimate for user-specific startup code to set up "EIND" early, for example by means of initialization code located in section ".init3". Such code runs prior to general startup code 5103 that initializes RAM and calls constructors, but after the bit of startup code from AVR-LibC that sets "EIND" to the segment where the vector table is located. 5104 #include 5105 static void 5106 __attribute__((section(".init3"),naked,used,no_instrument_function)) 5107 init3_set_eind (void) 5108 { 5109 __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t" 5110 "out %i0,r24" :: "n" (&EIND) : "r24","memory"); 5111 } 5112 The "__trampolines_start" symbol is defined in the linker script. 5113 * Stubs are generated automatically by the linker if the following two conditions are met: 5114 - 5115 (short for generate stubs) like so: 5116 LDI r24, lo8(gs()) 5117 LDI r25, hi8(gs()) 5118 - 5119 outside the segment where the stubs are located. 5120 * The compiler emits such "gs" modifiers for code labels in the following situations: 5121 - 5122 - 5123 - 5124 command-line option. 5125 - 5126 tables you can specify the -fno-jump-tables command-line option. 5127 - 5128 - 5129 * Jumping to non-symbolic addresses like so is not supported: 5130 int main (void) 5131 { 5132 /* Call function at word address 0x2 */ 5133 return ((int(*)(void)) 0x2)(); 5134 } 5135 Instead, a stub has to be set up, i.e. the function has to be called through a symbol ("func_4" in the example): 5136 int main (void) 5137 { 5138 extern int func_4 (void); 5139 /* Call function at byte address 0x4 */ 5140 return func_4(); 5141 } 5142 and the application be linked with -Wl,--defsym,func_4=0x4. Alternatively, "func_4" can be defined in the linker script. 5143 Handling of the "RAMPD", "RAMPX", "RAMPY" and "RAMPZ" Special Function Registers 5144 Some AVR devices support memories larger than the 64@tie{}KiB range that can be accessed with 16-bit pointers. To access memory locations outside this 64@tie{}KiB range, the contentent of a 5145 "RAMP" register is used as high part of the address: The "X", "Y", "Z" address register is concatenated with the "RAMPX", "RAMPY", "RAMPZ" special function register, respectively, to get a wide 5146 address. Similarly, "RAMPD" is used together with direct addressing. 5147 * The startup code initializes the "RAMP" special function registers with zero. 5148 * If a AVR Named Address Spaces,named address space other than generic or "__flash" is used, then "RAMPZ" is set as needed before the operation. 5149 * If the device supports RAM larger than 64@tie{}KiB and the compiler needs to change "RAMPZ" to accomplish an operation, "RAMPZ" is reset to zero after the operation. 5150 * If the device comes with a specific "RAMP" register, the ISR prologue/epilogue saves/restores that SFR and initializes it with zero in case the ISR code might (implicitly) use it. 5151 * RAM larger than 64@tie{}KiB is not supported by GCC for AVR targets. If you use inline assembler to read from locations outside the 16-bit address range and change one of the "RAMP" 5152 registers, you must reset it to zero after the access. 5153 AVR Built-in Macros 5154 GCC defines several built-in macros so that the user code can test for the presence or absence of features. Almost any of the following built-in macros are deduced from device capabilities and 5155 thus triggered by the -mmcu= command-line option. 5156 For even more AVR-specific built-in macros see AVR Named Address Spaces and AVR Built-in Functions. 5157 "__AVR_ARCH__" 5158 Build-in macro that resolves to a decimal number that identifies the architecture and depends on the -mmcu=mcu option. Possible values are: 5159 2, 25, 3, 31, 35, 4, 5, 51, 6 5160 for mcu="avr2", "avr25", "avr3", "avr31", "avr35", "avr4", "avr5", "avr51", "avr6", 5161 respectively and 5162 100, 102, 104, 105, 106, 107 5163 for mcu="avrtiny", "avrxmega2", "avrxmega4", "avrxmega5", "avrxmega6", "avrxmega7", respectively. If mcu specifies a device, this built-in macro is set accordingly. For example, with 5164 -mmcu=atmega8 the macro is defined to 4. 5165 "__AVR_Device__" 5166 Setting -mmcu=device defines this built-in macro which reflects the device's name. For example, -mmcu=atmega8 defines the built-in macro "__AVR_ATmega8__", -mmcu=attiny261a defines 5167 "__AVR_ATtiny261A__", etc. 5168 The built-in macros' names follow the scheme "__AVR_Device__" where Device is the device name as from the AVR user manual. The difference between Device in the built-in macro and device in 5169 -mmcu=device is that the latter is always lowercase. 5170 If device is not a device but only a core architecture like avr51, this macro is not defined. 5171 "__AVR_DEVICE_NAME__" 5172 Setting -mmcu=device defines this built-in macro to the device's name. For example, with -mmcu=atmega8 the macro is defined to "atmega8". 5173 If device is not a device but only a core architecture like avr51, this macro is not defined. 5174 "__AVR_XMEGA__" 5175 The device / architecture belongs to the XMEGA family of devices. 5176 "__AVR_HAVE_ELPM__" 5177 The device has the the "ELPM" instruction. 5178 "__AVR_HAVE_ELPMX__" 5179 The device has the "ELPM Rn,Z" and "ELPM Rn,Z+" instructions. 5180 "__AVR_HAVE_MOVW__" 5181 The device has the "MOVW" instruction to perform 16-bit register-register moves. 5182 "__AVR_HAVE_LPMX__" 5183 The device has the "LPM Rn,Z" and "LPM Rn,Z+" instructions. 5184 "__AVR_HAVE_MUL__" 5185 The device has a hardware multiplier. 5186 "__AVR_HAVE_JMP_CALL__" 5187 The device has the "JMP" and "CALL" instructions. This is the case for devices with at least 16@tie{}KiB of program memory. 5188 "__AVR_HAVE_EIJMP_EICALL__" 5189 "__AVR_3_BYTE_PC__" 5190 The device has the "EIJMP" and "EICALL" instructions. This is the case for devices with more than 128@tie{}KiB of program memory. This also means that the program counter (PC) is 5191 3@tie{}bytes wide. 5192 "__AVR_2_BYTE_PC__" 5193 The program counter (PC) is 2@tie{}bytes wide. This is the case for devices with up to 128@tie{}KiB of program memory. 5194 "__AVR_HAVE_8BIT_SP__" 5195 "__AVR_HAVE_16BIT_SP__" 5196 The stack pointer (SP) register is treated as 8-bit respectively 16-bit register by the compiler. The definition of these macros is affected by -mtiny-stack. 5197 "__AVR_HAVE_SPH__" 5198 "__AVR_SP8__" 5199 The device has the SPH (high part of stack pointer) special function register or has an 8-bit stack pointer, respectively. The definition of these macros is affected by -mmcu= and in the 5200 cases of -mmcu=avr2 and -mmcu=avr25 also by -msp8. 5201 "__AVR_HAVE_RAMPD__" 5202 "__AVR_HAVE_RAMPX__" 5203 "__AVR_HAVE_RAMPY__" 5204 "__AVR_HAVE_RAMPZ__" 5205 The device has the "RAMPD", "RAMPX", "RAMPY", "RAMPZ" special function register, respectively. 5206 "__NO_INTERRUPTS__" 5207 This macro reflects the -mno-interrupts command-line option. 5208 "__AVR_ERRATA_SKIP__" 5209 "__AVR_ERRATA_SKIP_JMP_CALL__" 5210 Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit instructions because of a hardware erratum. Skip instructions are "SBRS", "SBRC", "SBIS", "SBIC" and "CPSE". The second macro 5211 is only defined if "__AVR_HAVE_JMP_CALL__" is also set. 5212 "__AVR_ISA_RMW__" 5213 The device has Read-Modify-Write instructions (XCH, LAC, LAS and LAT). 5214 "__AVR_SFR_OFFSET__=offset" 5215 Instructions that can address I/O special function registers directly like "IN", "OUT", "SBI", etc. may use a different address as if addressed by an instruction to access RAM like "LD" or 5216 "STS". This offset depends on the device architecture and has to be subtracted from the RAM address in order to get the respective I/O@tie{}address. 5217 "__WITH_AVRLIBC__" 5218 The compiler is configured to be used together with AVR-Libc. See the --with-avrlibc configure option. 5219 Blackfin Options 5220 -mcpu=cpu[-sirevision] 5221 Specifies the name of the target Blackfin processor. Currently, cpu can be one of bf512, bf514, bf516, bf518, bf522, bf523, bf524, bf525, bf526, bf527, bf531, bf532, bf533, bf534, bf536, 5222 bf537, bf538, bf539, bf542, bf544, bf547, bf548, bf549, bf542m, bf544m, bf547m, bf548m, bf549m, bf561, bf592. 5223 The optional sirevision specifies the silicon revision of the target Blackfin processor. Any workarounds available for the targeted silicon revision are enabled. If sirevision is none, no 5224 workarounds are enabled. If sirevision is any, all workarounds for the targeted processor are enabled. The "__SILICON_REVISION__" macro is defined to two hexadecimal digits representing 5225 the major and minor numbers in the silicon revision. If sirevision is none, the "__SILICON_REVISION__" is not defined. If sirevision is any, the "__SILICON_REVISION__" is defined to be 5226 0xffff. If this optional sirevision is not used, GCC assumes the latest known silicon revision of the targeted Blackfin processor. 5227 GCC defines a preprocessor macro for the specified cpu. For the bfin-elf toolchain, this option causes the hardware BSP provided by libgloss to be linked in if -msim is not given. 5228 Without this option, bf532 is used as the processor by default. 5229 Note that support for bf561 is incomplete. For bf561, only the preprocessor macro is defined. 5230 -msim 5231 Specifies that the program will be run on the simulator. This causes the simulator BSP provided by libgloss to be linked in. This option has effect only for bfin-elf toolchain. Certain 5232 other options, such as -mid-shared-library and -mfdpic, imply -msim. 5233 -momit-leaf-frame-pointer 5234 Don't keep the frame pointer in a register for leaf functions. This avoids the instructions to save, set up and restore frame pointers and makes an extra register available in leaf 5235 functions. The option -fomit-frame-pointer removes the frame pointer for all functions, which might make debugging harder. 5236 -mspecld-anomaly 5237 When enabled, the compiler ensures that the generated code does not contain speculative loads after jump instructions. If this option is used, "__WORKAROUND_SPECULATIVE_LOADS" is defined. 5238 -mno-specld-anomaly 5239 Don't generate extra code to prevent speculative loads from occurring. 5240 -mcsync-anomaly 5241 When enabled, the compiler ensures that the generated code does not contain CSYNC or SSYNC instructions too soon after conditional branches. If this option is used, 5242 "__WORKAROUND_SPECULATIVE_SYNCS" is defined. 5243 -mno-csync-anomaly 5244 Don't generate extra code to prevent CSYNC or SSYNC instructions from occurring too soon after a conditional branch. 5245 -mlow-64k 5246 When enabled, the compiler is free to take advantage of the knowledge that the entire program fits into the low 64k of memory. 5247 -mno-low-64k 5248 Assume that the program is arbitrarily large. This is the default. 5249 -mstack-check-l1 5250 Do stack checking using information placed into L1 scratchpad memory by the uClinux kernel. 5251 -mid-shared-library 5252 Generate code that supports shared libraries via the library ID method. This allows for execute in place and shared libraries in an environment without virtual memory management. This 5253 option implies -fPIC. With a bfin-elf target, this option implies -msim. 5254 -mno-id-shared-library 5255 Generate code that doesn't assume ID-based shared libraries are being used. This is the default. 5256 -mleaf-id-shared-library 5257 Generate code that supports shared libraries via the library ID method, but assumes that this library or executable won't link against any other ID shared libraries. That allows the 5258 compiler to use faster code for jumps and calls. 5259 -mno-leaf-id-shared-library 5260 Do not assume that the code being compiled won't link against any ID shared libraries. Slower code is generated for jump and call insns. 5261 -mshared-library-id=n 5262 Specifies the identification number of the ID-based shared library being compiled. Specifying a value of 0 generates more compact code; specifying other values forces the allocation of that 5263 number to the current library but is no more space- or time-efficient than omitting this option. 5264 -msep-data 5265 Generate code that allows the data segment to be located in a different area of memory from the text segment. This allows for execute in place in an environment without virtual memory 5266 management by eliminating relocations against the text section. 5267 -mno-sep-data 5268 Generate code that assumes that the data segment follows the text segment. This is the default. 5269 -mlong-calls 5270 -mno-long-calls 5271 Tells the compiler to perform function calls by first loading the address of the function into a register and then performing a subroutine call on this register. This switch is needed if 5272 the target function lies outside of the 24-bit addressing range of the offset-based version of subroutine call instruction. 5273 This feature is not enabled by default. Specifying -mno-long-calls restores the default behavior. Note these switches have no effect on how the compiler generates code to handle function 5274 calls via function pointers. 5275 -mfast-fp 5276 Link with the fast floating-point library. This library relaxes some of the IEEE floating-point standard's rules for checking inputs against Not-a-Number (NAN), in the interest of 5277 performance. 5278 -minline-plt 5279 Enable inlining of PLT entries in function calls to functions that are not known to bind locally. It has no effect without -mfdpic. 5280 -mmulticore 5281 Build a standalone application for multicore Blackfin processors. This option causes proper start files and link scripts supporting multicore to be used, and defines the macro 5282 "__BFIN_MULTICORE". It can only be used with -mcpu=bf561[-sirevision]. 5283 This option can be used with -mcorea or -mcoreb, which selects the one-application-per-core programming model. Without -mcorea or -mcoreb, the single-application/dual-core programming model 5284 is used. In this model, the main function of Core B should be named as "coreb_main". 5285 If this option is not used, the single-core application programming model is used. 5286 -mcorea 5287 Build a standalone application for Core A of BF561 when using the one-application-per-core programming model. Proper start files and link scripts are used to support Core A, and the macro 5288 "__BFIN_COREA" is defined. This option can only be used in conjunction with -mmulticore. 5289 -mcoreb 5290 Build a standalone application for Core B of BF561 when using the one-application-per-core programming model. Proper start files and link scripts are used to support Core B, and the macro 5291 "__BFIN_COREB" is defined. When this option is used, "coreb_main" should be used instead of "main". This option can only be used in conjunction with -mmulticore. 5292 -msdram 5293 Build a standalone application for SDRAM. Proper start files and link scripts are used to put the application into SDRAM, and the macro "__BFIN_SDRAM" is defined. The loader should 5294 initialize SDRAM before loading the application. 5295 -micplb 5296 Assume that ICPLBs are enabled at run time. This has an effect on certain anomaly workarounds. For Linux targets, the default is to assume ICPLBs are enabled; for standalone applications 5297 the default is off. 5298 C6X Options 5299 -march=name 5300 This specifies the name of the target architecture. GCC uses this name to determine what kind of instructions it can emit when generating assembly code. Permissible names are: c62x, c64x, 5301 c64x+, c67x, c67x+, c674x. 5302 -mbig-endian 5303 Generate code for a big-endian target. 5304 -mlittle-endian 5305 Generate code for a little-endian target. This is the default. 5306 -msim 5307 Choose startup files and linker script suitable for the simulator. 5308 -msdata=default 5309 Put small global and static data in the ".neardata" section, which is pointed to by register "B14". Put small uninitialized global and static data in the ".bss" section, which is adjacent 5310 to the ".neardata" section. Put small read-only data into the ".rodata" section. The corresponding sections used for large pieces of data are ".fardata", ".far" and ".const". 5311 -msdata=all 5312 Put all data, not just small objects, into the sections reserved for small data, and use addressing relative to the "B14" register to access them. 5313 -msdata=none 5314 Make no use of the sections reserved for small data, and use absolute addresses to access all data. Put all initialized global and static data in the ".fardata" section, and all 5315 uninitialized data in the ".far" section. Put all constant data into the ".const" section. 5316 CRIS Options 5317 These options are defined specifically for the CRIS ports. 5318 -march=architecture-type 5319 -mcpu=architecture-type 5320 Generate code for the specified architecture. The choices for architecture-type are v3, v8 and v10 for respectively ETRAX 4, ETRAX 100, and ETRAX 100 LX. Default is v0 except for cris- 5321 axis-linux-gnu, where the default is v10. 5322 -mtune=architecture-type 5323 Tune to architecture-type everything applicable about the generated code, except for the ABI and the set of available instructions. The choices for architecture-type are the same as for 5324 -march=architecture-type. 5325 -mmax-stack-frame=n 5326 Warn when the stack frame of a function exceeds n bytes. 5327 -metrax4 5328 -metrax100 5329 The options -metrax4 and -metrax100 are synonyms for -march=v3 and -march=v8 respectively. 5330 -mmul-bug-workaround 5331 -mno-mul-bug-workaround 5332 Work around a bug in the "muls" and "mulu" instructions for CPU models where it applies. This option is active by default. 5333 -mpdebug 5334 Enable CRIS-specific verbose debug-related information in the assembly code. This option also has the effect of turning off the #NO_APP formatted-code indicator to the assembler at the 5335 beginning of the assembly file. 5336 -mcc-init 5337 Do not use condition-code results from previous instruction; always emit compare and test instructions before use of condition codes. 5338 -mno-side-effects 5339 Do not emit instructions with side effects in addressing modes other than post-increment. 5340 -mstack-align 5341 -mno-stack-align 5342 -mdata-align 5343 -mno-data-align 5344 -mconst-align 5345 -mno-const-align 5346 These options (no- options) arrange (eliminate arrangements) for the stack frame, individual data and constants to be aligned for the maximum single data access size for the chosen CPU 5347 model. The default is to arrange for 32-bit alignment. ABI details such as structure layout are not affected by these options. 5348 -m32-bit 5349 -m16-bit 5350 -m8-bit 5351 Similar to the stack- data- and const-align options above, these options arrange for stack frame, writable data and constants to all be 32-bit, 16-bit or 8-bit aligned. The default is 5352 32-bit alignment. 5353 -mno-prologue-epilogue 5354 -mprologue-epilogue 5355 With -mno-prologue-epilogue, the normal function prologue and epilogue which set up the stack frame are omitted and no return instructions or return sequences are generated in the code. Use 5356 this option only together with visual inspection of the compiled code: no warnings or errors are generated when call-saved registers must be saved, or storage for local variables needs to be 5357 allocated. 5358 -mno-gotplt 5359 -mgotplt 5360 With -fpic and -fPIC, don't generate (do generate) instruction sequences that load addresses for functions from the PLT part of the GOT rather than (traditional on other architectures) calls 5361 to the PLT. The default is -mgotplt. 5362 -melf 5363 Legacy no-op option only recognized with the cris-axis-elf and cris-axis-linux-gnu targets. 5364 -mlinux 5365 Legacy no-op option only recognized with the cris-axis-linux-gnu target. 5366 -sim 5367 This option, recognized for the cris-axis-elf, arranges to link with input-output functions from a simulator library. Code, initialized data and zero-initialized data are allocated 5368 consecutively. 5369 -sim2 5370 Like -sim, but pass linker options to locate initialized data at 0x40000000 and zero-initialized data at 0x80000000. 5371 CR16 Options 5372 These options are defined specifically for the CR16 ports. 5373 -mmac 5374 Enable the use of multiply-accumulate instructions. Disabled by default. 5375 -mcr16cplus 5376 -mcr16c 5377 Generate code for CR16C or CR16C+ architecture. CR16C+ architecture is default. 5378 -msim 5379 Links the library libsim.a which is in compatible with simulator. Applicable to ELF compiler only. 5380 -mint32 5381 Choose integer type as 32-bit wide. 5382 -mbit-ops 5383 Generates "sbit"/"cbit" instructions for bit manipulations. 5384 -mdata-model=model 5385 Choose a data model. The choices for model are near, far or medium. medium is default. However, far is not valid with -mcr16c, as the CR16C architecture does not support the far data model. 5386 Darwin Options 5387 These options are defined for all architectures running the Darwin operating system. 5388 FSF GCC on Darwin does not create "fat" object files; it creates an object file for the single architecture that GCC was built to target. Apple's GCC on Darwin does create "fat" files if 5389 multiple -arch options are used; it does so by running the compiler or linker multiple times and joining the results together with lipo. 5390 The subtype of the file created (like ppc7400 or ppc970 or i686) is determined by the flags that specify the ISA that GCC is targeting, like -mcpu or -march. The -force_cpusubtype_ALL option 5391 can be used to override this. 5392 The Darwin tools vary in their behavior when presented with an ISA mismatch. The assembler, as, only permits instructions to be used that are valid for the subtype of the file it is generating, 5393 so you cannot put 64-bit instructions in a ppc750 object file. The linker for shared libraries, /usr/bin/libtool, fails and prints an error if asked to create a shared library with a less 5394 restrictive subtype than its input files (for instance, trying to put a ppc970 object file in a ppc7400 library). The linker for executables, ld, quietly gives the executable the most 5395 restrictive subtype of any of its input files. 5396 -Fdir 5397 Add the framework directory dir to the head of the list of directories to be searched for header files. These directories are interleaved with those specified by -I options and are scanned 5398 in a left-to-right order. 5399 A framework directory is a directory with frameworks in it. A framework is a directory with a Headers and/or PrivateHeaders directory contained directly in it that ends in .framework. The 5400 name of a framework is the name of this directory excluding the .framework. Headers associated with the framework are found in one of those two directories, with Headers being searched 5401 first. A subframework is a framework directory that is in a framework's Frameworks directory. Includes of subframework headers can only appear in a header of a framework that contains the 5402 subframework, or in a sibling subframework header. Two subframeworks are siblings if they occur in the same framework. A subframework should not have the same name as a framework; a 5403 warning is issued if this is violated. Currently a subframework cannot have subframeworks; in the future, the mechanism may be extended to support this. The standard frameworks can be 5404 found in /System/Library/Frameworks and /Library/Frameworks. An example include looks like "#include ", where Framework denotes the name of the framework and header.h is 5405 found in the PrivateHeaders or Headers directory. 5406 -iframeworkdir 5407 Like -F except the directory is a treated as a system directory. The main difference between this -iframework and -F is that with -iframework the compiler does not warn about constructs 5408 contained within header files found via dir. This option is valid only for the C family of languages. 5409 -gused 5410 Emit debugging information for symbols that are used. For stabs debugging format, this enables -feliminate-unused-debug-symbols. This is by default ON. 5411 -gfull 5412 Emit debugging information for all symbols and types. 5413 -mmacosx-version-min=version 5414 The earliest version of MacOS X that this executable will run on is version. Typical values of version include 10.1, 10.2, and 10.3.9. 5415 If the compiler was built to use the system's headers by default, then the default for this option is the system version on which the compiler is running, otherwise the default is to make 5416 choices that are compatible with as many systems and code bases as possible. 5417 -mkernel 5418 Enable kernel development mode. The -mkernel option sets -static, -fno-common, -fno-use-cxa-atexit, -fno-exceptions, -fno-non-call-exceptions, -fapple-kext, -fno-weak and -fno-rtti where 5419 applicable. This mode also sets -mno-altivec, -msoft-float, -fno-builtin and -mlong-branch for PowerPC targets. 5420 -mone-byte-bool 5421 Override the defaults for "bool" so that "sizeof(bool)==1". By default "sizeof(bool)" is 4 when compiling for Darwin/PowerPC and 1 when compiling for Darwin/x86, so this option has no 5422 effect on x86. 5423 Warning: The -mone-byte-bool switch causes GCC to generate code that is not binary compatible with code generated without that switch. Using this switch may require recompiling all other 5424 modules in a program, including system libraries. Use this switch to conform to a non-default data model. 5425 -mfix-and-continue 5426 -ffix-and-continue 5427 -findirect-data 5428 Generate code suitable for fast turnaround development, such as to allow GDB to dynamically load .o files into already-running programs. -findirect-data and -ffix-and-continue are provided 5429 for backwards compatibility. 5430 -all_load 5431 Loads all members of static archive libraries. See man ld(1) for more information. 5432 -arch_errors_fatal 5433 Cause the errors having to do with files that have the wrong architecture to be fatal. 5434 -bind_at_load 5435 Causes the output file to be marked such that the dynamic linker will bind all undefined references when the file is loaded or launched. 5436 -bundle 5437 Produce a Mach-o bundle format file. See man ld(1) for more information. 5438 -bundle_loader executable 5439 This option specifies the executable that will load the build output file being linked. See man ld(1) for more information. 5440 -dynamiclib 5441 When passed this option, GCC produces a dynamic library instead of an executable when linking, using the Darwin libtool command. 5442 -force_cpusubtype_ALL 5443 This causes GCC's output file to have the ALL subtype, instead of one controlled by the -mcpu or -march option. 5444 -allowable_client client_name 5445 -client_name 5446 -compatibility_version 5447 -current_version 5448 -dead_strip 5449 -dependency-file 5450 -dylib_file 5451 -dylinker_install_name 5452 -dynamic 5453 -exported_symbols_list 5454 -filelist 5455 -flat_namespace 5456 -force_flat_namespace 5457 -headerpad_max_install_names 5458 -image_base 5459 -init 5460 -install_name 5461 -keep_private_externs 5462 -multi_module 5463 -multiply_defined 5464 -multiply_defined_unused 5465 -noall_load 5466 -no_dead_strip_inits_and_terms 5467 -nofixprebinding 5468 -nomultidefs 5469 -noprebind 5470 -noseglinkedit 5471 -pagezero_size 5472 -prebind 5473 -prebind_all_twolevel_modules 5474 -private_bundle 5475 -read_only_relocs 5476 -sectalign 5477 -sectobjectsymbols 5478 -whyload 5479 -seg1addr 5480 -sectcreate 5481 -sectobjectsymbols 5482 -sectorder 5483 -segaddr 5484 -segs_read_only_addr 5485 -segs_read_write_addr 5486 -seg_addr_table 5487 -seg_addr_table_filename 5488 -seglinkedit 5489 -segprot 5490 -segs_read_only_addr 5491 -segs_read_write_addr 5492 -single_module 5493 -static 5494 -sub_library 5495 -sub_umbrella 5496 -twolevel_namespace 5497 -umbrella 5498 -undefined 5499 -unexported_symbols_list 5500 -weak_reference_mismatches 5501 -whatsloaded 5502 These options are passed to the Darwin linker. The Darwin linker man page describes them in detail. 5503 DEC Alpha Options 5504 These -m options are defined for the DEC Alpha implementations: 5505 -mno-soft-float 5506 -msoft-float 5507 Use (do not use) the hardware floating-point instructions for floating-point operations. When -msoft-float is specified, functions in libgcc.a are used to perform floating-point operations. 5508 Unless they are replaced by routines that emulate the floating-point operations, or compiled in such a way as to call such emulations routines, these routines issue floating-point 5509 operations. If you are compiling for an Alpha without floating-point operations, you must ensure that the library is built so as not to call them. 5510 Note that Alpha implementations without floating-point operations are required to have floating-point registers. 5511 -mfp-reg 5512 -mno-fp-regs 5513 Generate code that uses (does not use) the floating-point register set. -mno-fp-regs implies -msoft-float. If the floating-point register set is not used, floating-point operands are 5514 passed in integer registers as if they were integers and floating-point results are passed in $0 instead of $f0. This is a non-standard calling sequence, so any function with a floating- 5515 point argument or return value called by code compiled with -mno-fp-regs must also be compiled with that option. 5516 A typical use of this option is building a kernel that does not use, and hence need not save and restore, any floating-point registers. 5517 -mieee 5518 The Alpha architecture implements floating-point hardware optimized for maximum performance. It is mostly compliant with the IEEE floating-point standard. However, for full compliance, 5519 software assistance is required. This option generates code fully IEEE-compliant code except that the inexact-flag is not maintained (see below). If this option is turned on, the 5520 preprocessor macro "_IEEE_FP" is defined during compilation. The resulting code is less efficient but is able to correctly support denormalized numbers and exceptional IEEE values such as 5521 not-a-number and plus/minus infinity. Other Alpha compilers call this option -ieee_with_no_inexact. 5522 -mieee-with-inexact 5523 This is like -mieee except the generated code also maintains the IEEE inexact-flag. Turning on this option causes the generated code to implement fully-compliant IEEE math. In addition to 5524 "_IEEE_FP", "_IEEE_FP_EXACT" is defined as a preprocessor macro. On some Alpha implementations the resulting code may execute significantly slower than the code generated by default. Since 5525 there is very little code that depends on the inexact-flag, you should normally not specify this option. Other Alpha compilers call this option -ieee_with_inexact. 5526 -mfp-trap-mode=trap-mode 5527 This option controls what floating-point related traps are enabled. Other Alpha compilers call this option -fptm trap-mode. The trap mode can be set to one of four values: 5528 n This is the default (normal) setting. The only traps that are enabled are the ones that cannot be disabled in software (e.g., division by zero trap). 5529 u In addition to the traps enabled by n, underflow traps are enabled as well. 5530 su Like u, but the instructions are marked to be safe for software completion (see Alpha architecture manual for details). 5531 sui Like su, but inexact traps are enabled as well. 5532 -mfp-rounding-mode=rounding-mode 5533 Selects the IEEE rounding mode. Other Alpha compilers call this option -fprm rounding-mode. The rounding-mode can be one of: 5534 n Normal IEEE rounding mode. Floating-point numbers are rounded towards the nearest machine number or towards the even machine number in case of a tie. 5535 m Round towards minus infinity. 5536 c Chopped rounding mode. Floating-point numbers are rounded towards zero. 5537 d Dynamic rounding mode. A field in the floating-point control register (fpcr, see Alpha architecture reference manual) controls the rounding mode in effect. The C library initializes 5538 this register for rounding towards plus infinity. Thus, unless your program modifies the fpcr, d corresponds to round towards plus infinity. 5539 -mtrap-precision=trap-precision 5540 In the Alpha architecture, floating-point traps are imprecise. This means without software assistance it is impossible to recover from a floating trap and program execution normally needs 5541 to be terminated. GCC can generate code that can assist operating system trap handlers in determining the exact location that caused a floating-point trap. Depending on the requirements of 5542 an application, different levels of precisions can be selected: 5543 p Program precision. This option is the default and means a trap handler can only identify which program caused a floating-point exception. 5544 f Function precision. The trap handler can determine the function that caused a floating-point exception. 5545 i Instruction precision. The trap handler can determine the exact instruction that caused a floating-point exception. 5546 Other Alpha compilers provide the equivalent options called -scope_safe and -resumption_safe. 5547 -mieee-conformant 5548 This option marks the generated code as IEEE conformant. You must not use this option unless you also specify -mtrap-precision=i and either -mfp-trap-mode=su or -mfp-trap-mode=sui. Its 5549 only effect is to emit the line .eflag 48 in the function prologue of the generated assembly file. 5550 -mbuild-constants 5551 Normally GCC examines a 32- or 64-bit integer constant to see if it can construct it from smaller constants in two or three instructions. If it cannot, it outputs the constant as a literal 5552 and generates code to load it from the data segment at run time. 5553 Use this option to require GCC to construct all integer constants using code, even if it takes more instructions (the maximum is six). 5554 You typically use this option to build a shared library dynamic loader. Itself a shared library, it must relocate itself in memory before it can find the variables and constants in its own 5555 data segment. 5556 -mbwx 5557 -mno-bwx 5558 -mcix 5559 -mno-cix 5560 -mfix 5561 -mno-fix 5562 -mmax 5563 -mno-max 5564 Indicate whether GCC should generate code to use the optional BWX, CIX, FIX and MAX instruction sets. The default is to use the instruction sets supported by the CPU type specified via 5565 -mcpu= option or that of the CPU on which GCC was built if none is specified. 5566 -mfloat-vax 5567 -mfloat-ieee 5568 Generate code that uses (does not use) VAX F and G floating-point arithmetic instead of IEEE single and double precision. 5569 -mexplicit-relocs 5570 -mno-explicit-relocs 5571 Older Alpha assemblers provided no way to generate symbol relocations except via assembler macros. Use of these macros does not allow optimal instruction scheduling. GNU binutils as of 5572 version 2.12 supports a new syntax that allows the compiler to explicitly mark which relocations should apply to which instructions. This option is mostly useful for debugging, as GCC 5573 detects the capabilities of the assembler when it is built and sets the default accordingly. 5574 -msmall-data 5575 -mlarge-data 5576 When -mexplicit-relocs is in effect, static data is accessed via gp-relative relocations. When -msmall-data is used, objects 8 bytes long or smaller are placed in a small data area (the 5577 ".sdata" and ".sbss" sections) and are accessed via 16-bit relocations off of the $gp register. This limits the size of the small data area to 64KB, but allows the variables to be directly 5578 accessed via a single instruction. 5579 The default is -mlarge-data. With this option the data area is limited to just below 2GB. Programs that require more than 2GB of data must use "malloc" or "mmap" to allocate the data in 5580 the heap instead of in the program's data segment. 5581 When generating code for shared libraries, -fpic implies -msmall-data and -fPIC implies -mlarge-data. 5582 -msmall-text 5583 -mlarge-text 5584 When -msmall-text is used, the compiler assumes that the code of the entire program (or shared library) fits in 4MB, and is thus reachable with a branch instruction. When -msmall-data is 5585 used, the compiler can assume that all local symbols share the same $gp value, and thus reduce the number of instructions required for a function call from 4 to 1. 5586 The default is -mlarge-text. 5587 -mcpu=cpu_type 5588 Set the instruction set and instruction scheduling parameters for machine type cpu_type. You can specify either the EV style name or the corresponding chip number. GCC supports scheduling 5589 parameters for the EV4, EV5 and EV6 family of processors and chooses the default values for the instruction set from the processor you specify. If you do not specify a processor type, GCC 5590 defaults to the processor on which the compiler was built. 5591 Supported values for cpu_type are 5592 ev4 5593 ev45 5594 21064 5595 Schedules as an EV4 and has no instruction set extensions. 5596 ev5 5597 21164 5598 Schedules as an EV5 and has no instruction set extensions. 5599 ev56 5600 21164a 5601 Schedules as an EV5 and supports the BWX extension. 5602 pca56 5603 21164pc 5604 21164PC 5605 Schedules as an EV5 and supports the BWX and MAX extensions. 5606 ev6 5607 21264 5608 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions. 5609 ev67 5610 21264a 5611 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions. 5612 Native toolchains also support the value native, which selects the best architecture option for the host processor. -mcpu=native has no effect if GCC does not recognize the processor. 5613 -mtune=cpu_type 5614 Set only the instruction scheduling parameters for machine type cpu_type. The instruction set is not changed. 5615 Native toolchains also support the value native, which selects the best architecture option for the host processor. -mtune=native has no effect if GCC does not recognize the processor. 5616 -mmemory-latency=time 5617 Sets the latency the scheduler should assume for typical memory references as seen by the application. This number is highly dependent on the memory access patterns used by the application 5618 and the size of the external cache on the machine. 5619 Valid options for time are 5620 number 5621 A decimal number representing clock cycles. 5622 L1 5623 L2 5624 L3 5625 main 5626 The compiler contains estimates of the number of clock cycles for "typical" EV4 & EV5 hardware for the Level 1, 2 & 3 caches (also called Dcache, Scache, and Bcache), as well as to main 5627 memory. Note that L3 is only valid for EV5. 5628 FR30 Options 5629 These options are defined specifically for the FR30 port. 5630 -msmall-model 5631 Use the small address space model. This can produce smaller code, but it does assume that all symbolic values and addresses fit into a 20-bit range. 5632 -mno-lsim 5633 Assume that runtime support has been provided and so there is no need to include the simulator library (libsim.a) on the linker command line. 5634 FRV Options 5635 -mgpr-32 5636 Only use the first 32 general-purpose registers. 5637 -mgpr-64 5638 Use all 64 general-purpose registers. 5639 -mfpr-32 5640 Use only the first 32 floating-point registers. 5641 -mfpr-64 5642 Use all 64 floating-point registers. 5643 -mhard-float 5644 Use hardware instructions for floating-point operations. 5645 -msoft-float 5646 Use library routines for floating-point operations. 5647 -malloc-cc 5648 Dynamically allocate condition code registers. 5649 -mfixed-cc 5650 Do not try to dynamically allocate condition code registers, only use "icc0" and "fcc0". 5651 -mdword 5652 Change ABI to use double word insns. 5653 -mno-dword 5654 Do not use double word instructions. 5655 -mdouble 5656 Use floating-point double instructions. 5657 -mno-double 5658 Do not use floating-point double instructions. 5659 -mmedia 5660 Use media instructions. 5661 -mno-media 5662 Do not use media instructions. 5663 -mmuladd 5664 Use multiply and add/subtract instructions. 5665 -mno-muladd 5666 Do not use multiply and add/subtract instructions. 5667 -mfdpic 5668 Select the FDPIC ABI, which uses function descriptors to represent pointers to functions. Without any PIC/PIE-related options, it implies -fPIE. With -fpic or -fpie, it assumes GOT entries 5669 and small data are within a 12-bit range from the GOT base address; with -fPIC or -fPIE, GOT offsets are computed with 32 bits. With a bfin-elf target, this option implies -msim. 5670 -minline-plt 5671 Enable inlining of PLT entries in function calls to functions that are not known to bind locally. It has no effect without -mfdpic. It's enabled by default if optimizing for speed and 5672 compiling for shared libraries (i.e., -fPIC or -fpic), or when an optimization option such as -O3 or above is present in the command line. 5673 -mTLS 5674 Assume a large TLS segment when generating thread-local code. 5675 -mtls 5676 Do not assume a large TLS segment when generating thread-local code. 5677 -mgprel-ro 5678 Enable the use of "GPREL" relocations in the FDPIC ABI for data that is known to be in read-only sections. It's enabled by default, except for -fpic or -fpie: even though it may help make 5679 the global offset table smaller, it trades 1 instruction for 4. With -fPIC or -fPIE, it trades 3 instructions for 4, one of which may be shared by multiple symbols, and it avoids the need 5680 for a GOT entry for the referenced symbol, so it's more likely to be a win. If it is not, -mno-gprel-ro can be used to disable it. 5681 -multilib-library-pic 5682 Link with the (library, not FD) pic libraries. It's implied by -mlibrary-pic, as well as by -fPIC and -fpic without -mfdpic. You should never have to use it explicitly. 5683 -mlinked-fp 5684 Follow the EABI requirement of always creating a frame pointer whenever a stack frame is allocated. This option is enabled by default and can be disabled with -mno-linked-fp. 5685 -mlong-calls 5686 Use indirect addressing to call functions outside the current compilation unit. This allows the functions to be placed anywhere within the 32-bit address space. 5687 -malign-labels 5688 Try to align labels to an 8-byte boundary by inserting NOPs into the previous packet. This option only has an effect when VLIW packing is enabled. It doesn't create new packets; it merely 5689 adds NOPs to existing ones. 5690 -mlibrary-pic 5691 Generate position-independent EABI code. 5692 -macc-4 5693 Use only the first four media accumulator registers. 5694 -macc-8 5695 Use all eight media accumulator registers. 5696 -mpack 5697 Pack VLIW instructions. 5698 -mno-pack 5699 Do not pack VLIW instructions. 5700 -mno-eflags 5701 Do not mark ABI switches in e_flags. 5702 -mcond-move 5703 Enable the use of conditional-move instructions (default). 5704 This switch is mainly for debugging the compiler and will likely be removed in a future version. 5705 -mno-cond-move 5706 Disable the use of conditional-move instructions. 5707 This switch is mainly for debugging the compiler and will likely be removed in a future version. 5708 -mscc 5709 Enable the use of conditional set instructions (default). 5710 This switch is mainly for debugging the compiler and will likely be removed in a future version. 5711 -mno-scc 5712 Disable the use of conditional set instructions. 5713 This switch is mainly for debugging the compiler and will likely be removed in a future version. 5714 -mcond-exec 5715 Enable the use of conditional execution (default). 5716 This switch is mainly for debugging the compiler and will likely be removed in a future version. 5717 -mno-cond-exec 5718 Disable the use of conditional execution. 5719 This switch is mainly for debugging the compiler and will likely be removed in a future version. 5720 -mvliw-branch 5721 Run a pass to pack branches into VLIW instructions (default). 5722 This switch is mainly for debugging the compiler and will likely be removed in a future version. 5723 -mno-vliw-branch 5724 Do not run a pass to pack branches into VLIW instructions. 5725 This switch is mainly for debugging the compiler and will likely be removed in a future version. 5726 -mmulti-cond-exec 5727 Enable optimization of "&&" and "||" in conditional execution (default). 5728 This switch is mainly for debugging the compiler and will likely be removed in a future version. 5729 -mno-multi-cond-exec 5730 Disable optimization of "&&" and "||" in conditional execution. 5731 This switch is mainly for debugging the compiler and will likely be removed in a future version. 5732 -mnested-cond-exec 5733 Enable nested conditional execution optimizations (default). 5734 This switch is mainly for debugging the compiler and will likely be removed in a future version. 5735 -mno-nested-cond-exec 5736 Disable nested conditional execution optimizations. 5737 This switch is mainly for debugging the compiler and will likely be removed in a future version. 5738 -moptimize-membar 5739 This switch removes redundant "membar" instructions from the compiler-generated code. It is enabled by default. 5740 -mno-optimize-membar 5741 This switch disables the automatic removal of redundant "membar" instructions from the generated code. 5742 -mtomcat-stats 5743 Cause gas to print out tomcat statistics. 5744 -mcpu=cpu 5745 Select the processor type for which to generate code. Possible values are frv, fr550, tomcat, fr500, fr450, fr405, fr400, fr300 and simple. 5746 GNU/Linux Options 5747 These -m options are defined for GNU/Linux targets: 5748 -mglibc 5749 Use the GNU C library. This is the default except on *-*-linux-*uclibc* and *-*-linux-*android* targets. 5750 -muclibc 5751 Use uClibc C library. This is the default on *-*-linux-*uclibc* targets. 5752 -mbionic 5753 Use Bionic C library. This is the default on *-*-linux-*android* targets. 5754 -mandroid 5755 Compile code compatible with Android platform. This is the default on *-*-linux-*android* targets. 5756 When compiling, this option enables -mbionic, -fPIC, -fno-exceptions and -fno-rtti by default. When linking, this option makes the GCC driver pass Android-specific options to the linker. 5757 Finally, this option causes the preprocessor macro "__ANDROID__" to be defined. 5758 -tno-android-cc 5759 Disable compilation effects of -mandroid, i.e., do not enable -mbionic, -fPIC, -fno-exceptions and -fno-rtti by default. 5760 -tno-android-ld 5761 Disable linking effects of -mandroid, i.e., pass standard Linux linking options to the linker. 5762 H8/300 Options 5763 These -m options are defined for the H8/300 implementations: 5764 -mrelax 5765 Shorten some address references at link time, when possible; uses the linker option -relax. 5766 -mh Generate code for the H8/300H. 5767 -ms Generate code for the H8S. 5768 -mn Generate code for the H8S and H8/300H in the normal mode. This switch must be used either with -mh or -ms. 5769 -ms2600 5770 Generate code for the H8S/2600. This switch must be used with -ms. 5771 -mexr 5772 Extended registers are stored on stack before execution of function with monitor attribute. Default option is -mexr. This option is valid only for H8S targets. 5773 -mno-exr 5774 Extended registers are not stored on stack before execution of function with monitor attribute. Default option is -mno-exr. This option is valid only for H8S targets. 5775 -mint32 5776 Make "int" data 32 bits by default. 5777 -malign-300 5778 On the H8/300H and H8S, use the same alignment rules as for the H8/300. The default for the H8/300H and H8S is to align longs and floats on 4-byte boundaries. -malign-300 causes them to be 5779 aligned on 2-byte boundaries. This option has no effect on the H8/300. 5780 HPPA Options 5781 These -m options are defined for the HPPA family of computers: 5782 -march=architecture-type 5783 Generate code for the specified architecture. The choices for architecture-type are 1.0 for PA 1.0, 1.1 for PA 1.1, and 2.0 for PA 2.0 processors. Refer to /usr/lib/sched.models on an HP- 5784 UX system to determine the proper architecture option for your machine. Code compiled for lower numbered architectures runs on higher numbered architectures, but not the other way around. 5785 -mpa-risc-1-0 5786 -mpa-risc-1-1 5787 -mpa-risc-2-0 5788 Synonyms for -march=1.0, -march=1.1, and -march=2.0 respectively. 5789 -mjump-in-delay 5790 This option is ignored and provided for compatibility purposes only. 5791 -mdisable-fpregs 5792 Prevent floating-point registers from being used in any manner. This is necessary for compiling kernels that perform lazy context switching of floating-point registers. If you use this 5793 option and attempt to perform floating-point operations, the compiler aborts. 5794 -mdisable-indexing 5795 Prevent the compiler from using indexing address modes. This avoids some rather obscure problems when compiling MIG generated code under MACH. 5796 -mno-space-regs 5797 Generate code that assumes the target has no space registers. This allows GCC to generate faster indirect calls and use unscaled index address modes. 5798 Such code is suitable for level 0 PA systems and kernels. 5799 -mfast-indirect-calls 5800 Generate code that assumes calls never cross space boundaries. This allows GCC to emit code that performs faster indirect calls. 5801 This option does not work in the presence of shared libraries or nested functions. 5802 -mfixed-range=register-range 5803 Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling kernel code. A register 5804 range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. 5805 -mlong-load-store 5806 Generate 3-instruction load and store sequences as sometimes required by the HP-UX 10 linker. This is equivalent to the +k option to the HP compilers. 5807 -mportable-runtime 5808 Use the portable calling conventions proposed by HP for ELF systems. 5809 -mgas 5810 Enable the use of assembler directives only GAS understands. 5811 -mschedule=cpu-type 5812 Schedule code according to the constraints for the machine type cpu-type. The choices for cpu-type are 700 7100, 7100LC, 7200, 7300 and 8000. Refer to /usr/lib/sched.models on an HP-UX 5813 system to determine the proper scheduling option for your machine. The default scheduling is 8000. 5814 -mlinker-opt 5815 Enable the optimization pass in the HP-UX linker. Note this makes symbolic debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9 linkers in which they give bogus error 5816 messages when linking some programs. 5817 -msoft-float 5818 Generate output containing library calls for floating point. Warning: the requisite libraries are not available for all HPPA targets. Normally the facilities of the machine's usual C 5819 compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. 5820 -msoft-float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. In particular, you need to compile libgcc.a, 5821 the library that comes with GCC, with -msoft-float in order for this to work. 5822 -msio 5823 Generate the predefine, "_SIO", for server IO. The default is -mwsio. This generates the predefines, "__hp9000s700", "__hp9000s700__" and "_WSIO", for workstation IO. These options are 5824 available under HP-UX and HI-UX. 5825 -mgnu-ld 5826 Use options specific to GNU ld. This passes -shared to ld when building a shared library. It is the default when GCC is configured, explicitly or implicitly, with the GNU linker. This 5827 option does not affect which ld is called; it only changes what parameters are passed to that ld. The ld that is called is determined by the --with-ld configure option, GCC's program search 5828 path, and finally by the user's PATH. The linker used by GCC can be printed using which `gcc -print-prog-name=ld`. This option is only available on the 64-bit HP-UX GCC, i.e. configured 5829 with hppa*64*-*-hpux*. 5830 -mhp-ld 5831 Use options specific to HP ld. This passes -b to ld when building a shared library and passes +Accept TypeMismatch to ld on all links. It is the default when GCC is configured, explicitly 5832 or implicitly, with the HP linker. This option does not affect which ld is called; it only changes what parameters are passed to that ld. The ld that is called is determined by the 5833 --with-ld configure option, GCC's program search path, and finally by the user's PATH. The linker used by GCC can be printed using which `gcc -print-prog-name=ld`. This option is only 5834 available on the 64-bit HP-UX GCC, i.e. configured with hppa*64*-*-hpux*. 5835 -mlong-calls 5836 Generate code that uses long call sequences. This ensures that a call is always able to reach linker generated stubs. The default is to generate long calls only when the distance from the 5837 call site to the beginning of the function or translation unit, as the case may be, exceeds a predefined limit set by the branch type being used. The limits for normal calls are 7,600,000 5838 and 240,000 bytes, respectively for the PA 2.0 and PA 1.X architectures. Sibcalls are always limited at 240,000 bytes. 5839 Distances are measured from the beginning of functions when using the -ffunction-sections option, or when using the -mgas and -mno-portable-runtime options together under HP-UX with the SOM 5840 linker. 5841 It is normally not desirable to use this option as it degrades performance. However, it may be useful in large applications, particularly when partial linking is used to build the 5842 application. 5843 The types of long calls used depends on the capabilities of the assembler and linker, and the type of code being generated. The impact on systems that support long absolute calls, and long 5844 pic symbol-difference or pc-relative calls should be relatively small. However, an indirect call is used on 32-bit ELF systems in pic code and it is quite long. 5845 -munix=unix-std 5846 Generate compiler predefines and select a startfile for the specified UNIX standard. The choices for unix-std are 93, 95 and 98. 93 is supported on all HP-UX versions. 95 is available on 5847 HP-UX 10.10 and later. 98 is available on HP-UX 11.11 and later. The default values are 93 for HP-UX 10.00, 95 for HP-UX 10.10 though to 11.00, and 98 for HP-UX 11.11 and later. 5848 -munix=93 provides the same predefines as GCC 3.3 and 3.4. -munix=95 provides additional predefines for "XOPEN_UNIX" and "_XOPEN_SOURCE_EXTENDED", and the startfile unix95.o. -munix=98 5849 provides additional predefines for "_XOPEN_UNIX", "_XOPEN_SOURCE_EXTENDED", "_INCLUDE__STDC_A1_SOURCE" and "_INCLUDE_XOPEN_SOURCE_500", and the startfile unix98.o. 5850 It is important to note that this option changes the interfaces for various library routines. It also affects the operational behavior of the C library. Thus, extreme care is needed in 5851 using this option. 5852 Library code that is intended to operate with more than one UNIX standard must test, set and restore the variable "__xpg4_extended_mask" as appropriate. Most GNU software doesn't provide 5853 this capability. 5854 -nolibdld 5855 Suppress the generation of link options to search libdld.sl when the -static option is specified on HP-UX 10 and later. 5856 -static 5857 The HP-UX implementation of setlocale in libc has a dependency on libdld.sl. There isn't an archive version of libdld.sl. Thus, when the -static option is specified, special link options 5858 are needed to resolve this dependency. 5859 On HP-UX 10 and later, the GCC driver adds the necessary options to link with libdld.sl when the -static option is specified. This causes the resulting binary to be dynamic. On the 64-bit 5860 port, the linkers generate dynamic binaries by default in any case. The -nolibdld option can be used to prevent the GCC driver from adding these link options. 5861 -threads 5862 Add support for multithreading with the dce thread library under HP-UX. This option sets flags for both the preprocessor and linker. 5863 IA-64 Options 5864 These are the -m options defined for the Intel IA-64 architecture. 5865 -mbig-endian 5866 Generate code for a big-endian target. This is the default for HP-UX. 5867 -mlittle-endian 5868 Generate code for a little-endian target. This is the default for AIX5 and GNU/Linux. 5869 -mgnu-as 5870 -mno-gnu-as 5871 Generate (or don't) code for the GNU assembler. This is the default. 5872 -mgnu-ld 5873 -mno-gnu-ld 5874 Generate (or don't) code for the GNU linker. This is the default. 5875 -mno-pic 5876 Generate code that does not use a global pointer register. The result is not position independent code, and violates the IA-64 ABI. 5877 -mvolatile-asm-stop 5878 -mno-volatile-asm-stop 5879 Generate (or don't) a stop bit immediately before and after volatile asm statements. 5880 -mregister-names 5881 -mno-register-names 5882 Generate (or don't) in, loc, and out register names for the stacked registers. This may make assembler output more readable. 5883 -mno-sdata 5884 -msdata 5885 Disable (or enable) optimizations that use the small data section. This may be useful for working around optimizer bugs. 5886 -mconstant-gp 5887 Generate code that uses a single constant global pointer value. This is useful when compiling kernel code. 5888 -mauto-pic 5889 Generate code that is self-relocatable. This implies -mconstant-gp. This is useful when compiling firmware code. 5890 -minline-float-divide-min-latency 5891 Generate code for inline divides of floating-point values using the minimum latency algorithm. 5892 -minline-float-divide-max-throughput 5893 Generate code for inline divides of floating-point values using the maximum throughput algorithm. 5894 -mno-inline-float-divide 5895 Do not generate inline code for divides of floating-point values. 5896 -minline-int-divide-min-latency 5897 Generate code for inline divides of integer values using the minimum latency algorithm. 5898 -minline-int-divide-max-throughput 5899 Generate code for inline divides of integer values using the maximum throughput algorithm. 5900 -mno-inline-int-divide 5901 Do not generate inline code for divides of integer values. 5902 -minline-sqrt-min-latency 5903 Generate code for inline square roots using the minimum latency algorithm. 5904 -minline-sqrt-max-throughput 5905 Generate code for inline square roots using the maximum throughput algorithm. 5906 -mno-inline-sqrt 5907 Do not generate inline code for "sqrt". 5908 -mfused-madd 5909 -mno-fused-madd 5910 Do (don't) generate code that uses the fused multiply/add or multiply/subtract instructions. The default is to use these instructions. 5911 -mno-dwarf2-asm 5912 -mdwarf2-asm 5913 Don't (or do) generate assembler code for the DWARF 2 line number debugging info. This may be useful when not using the GNU assembler. 5914 -mearly-stop-bits 5915 -mno-early-stop-bits 5916 Allow stop bits to be placed earlier than immediately preceding the instruction that triggered the stop bit. This can improve instruction scheduling, but does not always do so. 5917 -mfixed-range=register-range 5918 Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling kernel code. A register 5919 range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. 5920 -mtls-size=tls-size 5921 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and 64. 5922 -mtune=cpu-type 5923 Tune the instruction scheduling for a particular CPU, Valid values are itanium, itanium1, merced, itanium2, and mckinley. 5924 -milp32 5925 -mlp64 5926 Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long and pointer to 32 bits. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits. 5927 These are HP-UX specific flags. 5928 -mno-sched-br-data-spec 5929 -msched-br-data-spec 5930 (Dis/En)able data speculative scheduling before reload. This results in generation of "ld.a" instructions and the corresponding check instructions ("ld.c" / "chk.a"). The default is 5931 'disable'. 5932 -msched-ar-data-spec 5933 -mno-sched-ar-data-spec 5934 (En/Dis)able data speculative scheduling after reload. This results in generation of "ld.a" instructions and the corresponding check instructions ("ld.c" / "chk.a"). The default is 5935 'enable'. 5936 -mno-sched-control-spec 5937 -msched-control-spec 5938 (Dis/En)able control speculative scheduling. This feature is available only during region scheduling (i.e. before reload). This results in generation of the "ld.s" instructions and the 5939 corresponding check instructions "chk.s". The default is 'disable'. 5940 -msched-br-in-data-spec 5941 -mno-sched-br-in-data-spec 5942 (En/Dis)able speculative scheduling of the instructions that are dependent on the data speculative loads before reload. This is effective only with -msched-br-data-spec enabled. The 5943 default is 'enable'. 5944 -msched-ar-in-data-spec 5945 -mno-sched-ar-in-data-spec 5946 (En/Dis)able speculative scheduling of the instructions that are dependent on the data speculative loads after reload. This is effective only with -msched-ar-data-spec enabled. The default 5947 is 'enable'. 5948 -msched-in-control-spec 5949 -mno-sched-in-control-spec 5950 (En/Dis)able speculative scheduling of the instructions that are dependent on the control speculative loads. This is effective only with -msched-control-spec enabled. The default is 5951 'enable'. 5952 -mno-sched-prefer-non-data-spec-insns 5953 -msched-prefer-non-data-spec-insns 5954 If enabled, data-speculative instructions are chosen for schedule only if there are no other choices at the moment. This makes the use of the data speculation much more conservative. The 5955 default is 'disable'. 5956 -mno-sched-prefer-non-control-spec-insns 5957 -msched-prefer-non-control-spec-insns 5958 If enabled, control-speculative instructions are chosen for schedule only if there are no other choices at the moment. This makes the use of the control speculation much more conservative. 5959 The default is 'disable'. 5960 -mno-sched-count-spec-in-critical-path 5961 -msched-count-spec-in-critical-path 5962 If enabled, speculative dependencies are considered during computation of the instructions priorities. This makes the use of the speculation a bit more conservative. The default is 5963 'disable'. 5964 -msched-spec-ldc 5965 Use a simple data speculation check. This option is on by default. 5966 -msched-control-spec-ldc 5967 Use a simple check for control speculation. This option is on by default. 5968 -msched-stop-bits-after-every-cycle 5969 Place a stop bit after every cycle when scheduling. This option is on by default. 5970 -msched-fp-mem-deps-zero-cost 5971 Assume that floating-point stores and loads are not likely to cause a conflict when placed into the same instruction group. This option is disabled by default. 5972 -msel-sched-dont-check-control-spec 5973 Generate checks for control speculation in selective scheduling. This flag is disabled by default. 5974 -msched-max-memory-insns=max-insns 5975 Limit on the number of memory insns per instruction group, giving lower priority to subsequent memory insns attempting to schedule in the same instruction group. Frequently useful to prevent 5976 cache bank conflicts. The default value is 1. 5977 -msched-max-memory-insns-hard-limit 5978 Makes the limit specified by msched-max-memory-insns a hard limit, disallowing more than that number in an instruction group. Otherwise, the limit is "soft", meaning that non-memory 5979 operations are preferred when the limit is reached, but memory operations may still be scheduled. 5980 LM32 Options 5981 These -m options are defined for the LatticeMico32 architecture: 5982 -mbarrel-shift-enabled 5983 Enable barrel-shift instructions. 5984 -mdivide-enabled 5985 Enable divide and modulus instructions. 5986 -mmultiply-enabled 5987 Enable multiply instructions. 5988 -msign-extend-enabled 5989 Enable sign extend instructions. 5990 -muser-enabled 5991 Enable user-defined instructions. 5992 M32C Options 5993 -mcpu=name 5994 Select the CPU for which code is generated. name may be one of r8c for the R8C/Tiny series, m16c for the M16C (up to /60) series, m32cm for the M16C/80 series, or m32c for the M32C/80 5995 series. 5996 -msim 5997 Specifies that the program will be run on the simulator. This causes an alternate runtime library to be linked in which supports, for example, file I/O. You must not use this option when 5998 generating programs that will run on real hardware; you must provide your own runtime library for whatever I/O functions are needed. 5999 -memregs=number 6000 Specifies the number of memory-based pseudo-registers GCC uses during code generation. These pseudo-registers are used like real registers, so there is a tradeoff between GCC's ability to 6001 fit the code into available registers, and the performance penalty of using memory instead of registers. Note that all modules in a program must be compiled with the same value for this 6002 option. Because of that, you must not use this option with GCC's default runtime libraries. 6003 M32R/D Options 6004 These -m options are defined for Renesas M32R/D architectures: 6005 -m32r2 6006 Generate code for the M32R/2. 6007 -m32rx 6008 Generate code for the M32R/X. 6009 -m32r 6010 Generate code for the M32R. This is the default. 6011 -mmodel=small 6012 Assume all objects live in the lower 16MB of memory (so that their addresses can be loaded with the "ld24" instruction), and assume all subroutines are reachable with the "bl" instruction. 6013 This is the default. 6014 The addressability of a particular object can be set with the "model" attribute. 6015 -mmodel=medium 6016 Assume objects may be anywhere in the 32-bit address space (the compiler generates "seth/add3" instructions to load their addresses), and assume all subroutines are reachable with the "bl" 6017 instruction. 6018 -mmodel=large 6019 Assume objects may be anywhere in the 32-bit address space (the compiler generates "seth/add3" instructions to load their addresses), and assume subroutines may not be reachable with the 6020 "bl" instruction (the compiler generates the much slower "seth/add3/jl" instruction sequence). 6021 -msdata=none 6022 Disable use of the small data area. Variables are put into one of ".data", ".bss", or ".rodata" (unless the "section" attribute has been specified). This is the default. 6023 The small data area consists of sections ".sdata" and ".sbss". Objects may be explicitly put in the small data area with the "section" attribute using one of these sections. 6024 -msdata=sdata 6025 Put small global and static data in the small data area, but do not generate special code to reference them. 6026 -msdata=use 6027 Put small global and static data in the small data area, and generate special instructions to reference them. 6028 -G num 6029 Put global and static objects less than or equal to num bytes into the small data or BSS sections instead of the normal data or BSS sections. The default value of num is 8. The -msdata 6030 option must be set to one of sdata or use for this option to have any effect. 6031 All modules should be compiled with the same -G num value. Compiling with different values of num may or may not work; if it doesn't the linker gives an error message---incorrect code is 6032 not generated. 6033 -mdebug 6034 Makes the M32R-specific code in the compiler display some statistics that might help in debugging programs. 6035 -malign-loops 6036 Align all loops to a 32-byte boundary. 6037 -mno-align-loops 6038 Do not enforce a 32-byte alignment for loops. This is the default. 6039 -missue-rate=number 6040 Issue number instructions per cycle. number can only be 1 or 2. 6041 -mbranch-cost=number 6042 number can only be 1 or 2. If it is 1 then branches are preferred over conditional code, if it is 2, then the opposite applies. 6043 -mflush-trap=number 6044 Specifies the trap number to use to flush the cache. The default is 12. Valid numbers are between 0 and 15 inclusive. 6045 -mno-flush-trap 6046 Specifies that the cache cannot be flushed by using a trap. 6047 -mflush-func=name 6048 Specifies the name of the operating system function to call to flush the cache. The default is _flush_cache, but a function call is only used if a trap is not available. 6049 -mno-flush-func 6050 Indicates that there is no OS function for flushing the cache. 6051 M680x0 Options 6052 These are the -m options defined for M680x0 and ColdFire processors. The default settings depend on which architecture was selected when the compiler was configured; the defaults for the most 6053 common choices are given below. 6054 -march=arch 6055 Generate code for a specific M680x0 or ColdFire instruction set architecture. Permissible values of arch for M680x0 architectures are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32. 6056 ColdFire architectures are selected according to Freescale's ISA classification and the permissible values are: isaa, isaaplus, isab and isac. 6057 GCC defines a macro "__mcfarch__" whenever it is generating code for a ColdFire target. The arch in this macro is one of the -march arguments given above. 6058 When used together, -march and -mtune select code that runs on a family of similar processors but that is optimized for a particular microarchitecture. 6059 -mcpu=cpu 6060 Generate code for a specific M680x0 or ColdFire processor. The M680x0 cpus are: 68000, 68010, 68020, 68030, 68040, 68060, 68302, 68332 and cpu32. The ColdFire cpus are given by the table 6061 below, which also classifies the CPUs into families: 6062 Family : -mcpu arguments 6063 51 : 51 51ac 51ag 51cn 51em 51je 51jf 51jg 51jm 51mm 51qe 51qm 6064 5206 : 5202 5204 5206 6065 5206e : 5206e 6066 5208 : 5207 5208 6067 5211a : 5210a 5211a 6068 5213 : 5211 5212 5213 6069 5216 : 5214 5216 6070 52235 : 52230 52231 52232 52233 52234 52235 6071 5225 : 5224 5225 6072 52259 : 52252 52254 52255 52256 52258 52259 6073 5235 : 5232 5233 5234 5235 523x 6074 5249 : 5249 6075 5250 : 5250 6076 5271 : 5270 5271 6077 5272 : 5272 6078 5275 : 5274 5275 6079 5282 : 5280 5281 5282 528x 6080 53017 : 53011 53012 53013 53014 53015 53016 53017 6081 5307 : 5307 6082 5329 : 5327 5328 5329 532x 6083 5373 : 5372 5373 537x 6084 5407 : 5407 6085 5475 : 5470 5471 5472 5473 5474 5475 547x 5480 5481 5482 5483 5484 5485 6086 -mcpu=cpu overrides -march=arch if arch is compatible with cpu. Other combinations of -mcpu and -march are rejected. 6087 GCC defines the macro "__mcf_cpu_cpu" when ColdFire target cpu is selected. It also defines "__mcf_family_family", where the value of family is given by the table above. 6088 -mtune=tune 6089 Tune the code for a particular microarchitecture within the constraints set by -march and -mcpu. The M680x0 microarchitectures are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32. The 6090 ColdFire microarchitectures are: cfv1, cfv2, cfv3, cfv4 and cfv4e. 6091 You can also use -mtune=68020-40 for code that needs to run relatively well on 68020, 68030 and 68040 targets. -mtune=68020-60 is similar but includes 68060 targets as well. These two 6092 options select the same tuning decisions as -m68020-40 and -m68020-60 respectively. 6093 GCC defines the macros "__mcarch" and "__mcarch__" when tuning for 680x0 architecture arch. It also defines "mcarch" unless either -ansi or a non-GNU -std option is used. If GCC is tuning 6094 for a range of architectures, as selected by -mtune=68020-40 or -mtune=68020-60, it defines the macros for every architecture in the range. 6095 GCC also defines the macro "__muarch__" when tuning for ColdFire microarchitecture uarch, where uarch is one of the arguments given above. 6096 -m68000 6097 -mc68000 6098 Generate output for a 68000. This is the default when the compiler is configured for 68000-based systems. It is equivalent to -march=68000. 6099 Use this option for microcontrollers with a 68000 or EC000 core, including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356. 6100 -m68010 6101 Generate output for a 68010. This is the default when the compiler is configured for 68010-based systems. It is equivalent to -march=68010. 6102 -m68020 6103 -mc68020 6104 Generate output for a 68020. This is the default when the compiler is configured for 68020-based systems. It is equivalent to -march=68020. 6105 -m68030 6106 Generate output for a 68030. This is the default when the compiler is configured for 68030-based systems. It is equivalent to -march=68030. 6107 -m68040 6108 Generate output for a 68040. This is the default when the compiler is configured for 68040-based systems. It is equivalent to -march=68040. 6109 This option inhibits the use of 68881/68882 instructions that have to be emulated by software on the 68040. Use this option if your 68040 does not have code to emulate those instructions. 6110 -m68060 6111 Generate output for a 68060. This is the default when the compiler is configured for 68060-based systems. It is equivalent to -march=68060. 6112 This option inhibits the use of 68020 and 68881/68882 instructions that have to be emulated by software on the 68060. Use this option if your 68060 does not have code to emulate those 6113 instructions. 6114 -mcpu32 6115 Generate output for a CPU32. This is the default when the compiler is configured for CPU32-based systems. It is equivalent to -march=cpu32. 6116 Use this option for microcontrollers with a CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334, 68336, 68340, 68341, 68349 and 68360. 6117 -m5200 6118 Generate output for a 520X ColdFire CPU. This is the default when the compiler is configured for 520X-based systems. It is equivalent to -mcpu=5206, and is now deprecated in favor of that 6119 option. 6120 Use this option for microcontroller with a 5200 core, including the MCF5202, MCF5203, MCF5204 and MCF5206. 6121 -m5206e 6122 Generate output for a 5206e ColdFire CPU. The option is now deprecated in favor of the equivalent -mcpu=5206e. 6123 -m528x 6124 Generate output for a member of the ColdFire 528X family. The option is now deprecated in favor of the equivalent -mcpu=528x. 6125 -m5307 6126 Generate output for a ColdFire 5307 CPU. The option is now deprecated in favor of the equivalent -mcpu=5307. 6127 -m5407 6128 Generate output for a ColdFire 5407 CPU. The option is now deprecated in favor of the equivalent -mcpu=5407. 6129 -mcfv4e 6130 Generate output for a ColdFire V4e family CPU (e.g. 547x/548x). This includes use of hardware floating-point instructions. The option is equivalent to -mcpu=547x, and is now deprecated in 6131 favor of that option. 6132 -m68020-40 6133 Generate output for a 68040, without using any of the new instructions. This results in code that can run relatively efficiently on either a 68020/68881 or a 68030 or a 68040. The 6134 generated code does use the 68881 instructions that are emulated on the 68040. 6135 The option is equivalent to -march=68020 -mtune=68020-40. 6136 -m68020-60 6137 Generate output for a 68060, without using any of the new instructions. This results in code that can run relatively efficiently on either a 68020/68881 or a 68030 or a 68040. The 6138 generated code does use the 68881 instructions that are emulated on the 68060. 6139 The option is equivalent to -march=68020 -mtune=68020-60. 6140 -mhard-float 6141 -m68881 6142 Generate floating-point instructions. This is the default for 68020 and above, and for ColdFire devices that have an FPU. It defines the macro "__HAVE_68881__" on M680x0 targets and 6143 "__mcffpu__" on ColdFire targets. 6144 -msoft-float 6145 Do not generate floating-point instructions; use library calls instead. This is the default for 68000, 68010, and 68832 targets. It is also the default for ColdFire devices that have no 6146 FPU. 6147 -mdiv 6148 -mno-div 6149 Generate (do not generate) ColdFire hardware divide and remainder instructions. If -march is used without -mcpu, the default is "on" for ColdFire architectures and "off" for M680x0 6150 architectures. Otherwise, the default is taken from the target CPU (either the default CPU, or the one specified by -mcpu). For example, the default is "off" for -mcpu=5206 and "on" for 6151 -mcpu=5206e. 6152 GCC defines the macro "__mcfhwdiv__" when this option is enabled. 6153 -mshort 6154 Consider type "int" to be 16 bits wide, like "short int". Additionally, parameters passed on the stack are also aligned to a 16-bit boundary even on targets whose API mandates promotion to 6155 32-bit. 6156 -mno-short 6157 Do not consider type "int" to be 16 bits wide. This is the default. 6158 -mnobitfield 6159 -mno-bitfield 6160 Do not use the bit-field instructions. The -m68000, -mcpu32 and -m5200 options imply -mnobitfield. 6161 -mbitfield 6162 Do use the bit-field instructions. The -m68020 option implies -mbitfield. This is the default if you use a configuration designed for a 68020. 6163 -mrtd 6164 Use a different function-calling convention, in which functions that take a fixed number of arguments return with the "rtd" instruction, which pops their arguments while returning. This 6165 saves one instruction in the caller since there is no need to pop the arguments there. 6166 This calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler. 6167 Also, you must provide function prototypes for all functions that take variable numbers of arguments (including "printf"); otherwise incorrect code is generated for calls to those functions. 6168 In addition, seriously incorrect code results if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.) 6169 The "rtd" instruction is supported by the 68010, 68020, 68030, 68040, 68060 and CPU32 processors, but not by the 68000 or 5200. 6170 -mno-rtd 6171 Do not use the calling conventions selected by -mrtd. This is the default. 6172 -malign-int 6173 -mno-align-int 6174 Control whether GCC aligns "int", "long", "long long", "float", "double", and "long double" variables on a 32-bit boundary (-malign-int) or a 16-bit boundary (-mno-align-int). Aligning 6175 variables on 32-bit boundaries produces code that runs somewhat faster on processors with 32-bit busses at the expense of more memory. 6176 Warning: if you use the -malign-int switch, GCC aligns structures containing the above types differently than most published application binary interface specifications for the m68k. 6177 -mpcrel 6178 Use the pc-relative addressing mode of the 68000 directly, instead of using a global offset table. At present, this option implies -fpic, allowing at most a 16-bit offset for pc-relative 6179 addressing. -fPIC is not presently supported with -mpcrel, though this could be supported for 68020 and higher processors. 6180 -mno-strict-align 6181 -mstrict-align 6182 Do not (do) assume that unaligned memory references are handled by the system. 6183 -msep-data 6184 Generate code that allows the data segment to be located in a different area of memory from the text segment. This allows for execute-in-place in an environment without virtual memory 6185 management. This option implies -fPIC. 6186 -mno-sep-data 6187 Generate code that assumes that the data segment follows the text segment. This is the default. 6188 -mid-shared-library 6189 Generate code that supports shared libraries via the library ID method. This allows for execute-in-place and shared libraries in an environment without virtual memory management. This 6190 option implies -fPIC. 6191 -mno-id-shared-library 6192 Generate code that doesn't assume ID-based shared libraries are being used. This is the default. 6193 -mshared-library-id=n 6194 Specifies the identification number of the ID-based shared library being compiled. Specifying a value of 0 generates more compact code; specifying other values forces the allocation of that 6195 number to the current library, but is no more space- or time-efficient than omitting this option. 6196 -mxgot 6197 -mno-xgot 6198 When generating position-independent code for ColdFire, generate code that works if the GOT has more than 8192 entries. This code is larger and slower than code generated without this 6199 option. On M680x0 processors, this option is not needed; -fPIC suffices. 6200 GCC normally uses a single instruction to load values from the GOT. While this is relatively efficient, it only works if the GOT is smaller than about 64k. Anything larger causes the 6201 linker to report an error such as: 6202 relocation truncated to fit: R_68K_GOT16O foobar 6203 If this happens, you should recompile your code with -mxgot. It should then work with very large GOTs. However, code generated with -mxgot is less efficient, since it takes 4 instructions 6204 to fetch the value of a global symbol. 6205 Note that some linkers, including newer versions of the GNU linker, can create multiple GOTs and sort GOT entries. If you have such a linker, you should only need to use -mxgot when 6206 compiling a single object file that accesses more than 8192 GOT entries. Very few do. 6207 These options have no effect unless GCC is generating position-independent code. 6208 MCore Options 6209 These are the -m options defined for the Motorola M*Core processors. 6210 -mhardlit 6211 -mno-hardlit 6212 Inline constants into the code stream if it can be done in two instructions or less. 6213 -mdiv 6214 -mno-div 6215 Use the divide instruction. (Enabled by default). 6216 -mrelax-immediate 6217 -mno-relax-immediate 6218 Allow arbitrary-sized immediates in bit operations. 6219 -mwide-bitfields 6220 -mno-wide-bitfields 6221 Always treat bit-fields as "int"-sized. 6222 -m4byte-functions 6223 -mno-4byte-functions 6224 Force all functions to be aligned to a 4-byte boundary. 6225 -mcallgraph-data 6226 -mno-callgraph-data 6227 Emit callgraph information. 6228 -mslow-bytes 6229 -mno-slow-bytes 6230 Prefer word access when reading byte quantities. 6231 -mlittle-endian 6232 -mbig-endian 6233 Generate code for a little-endian target. 6234 -m210 6235 -m340 6236 Generate code for the 210 processor. 6237 -mno-lsim 6238 Assume that runtime support has been provided and so omit the simulator library (libsim.a) from the linker command line. 6239 -mstack-increment=size 6240 Set the maximum amount for a single stack increment operation. Large values can increase the speed of programs that contain functions that need a large amount of stack space, but they can 6241 also trigger a segmentation fault if the stack is extended too much. The default value is 0x1000. 6242 MeP Options 6243 -mabsdiff 6244 Enables the "abs" instruction, which is the absolute difference between two registers. 6245 -mall-opts 6246 Enables all the optional instructions---average, multiply, divide, bit operations, leading zero, absolute difference, min/max, clip, and saturation. 6247 -maverage 6248 Enables the "ave" instruction, which computes the average of two registers. 6249 -mbased=n 6250 Variables of size n bytes or smaller are placed in the ".based" section by default. Based variables use the $tp register as a base register, and there is a 128-byte limit to the ".based" 6251 section. 6252 -mbitops 6253 Enables the bit operation instructions---bit test ("btstm"), set ("bsetm"), clear ("bclrm"), invert ("bnotm"), and test-and-set ("tas"). 6254 -mc=name 6255 Selects which section constant data is placed in. name may be tiny, near, or far. 6256 -mclip 6257 Enables the "clip" instruction. Note that -mclip is not useful unless you also provide -mminmax. 6258 -mconfig=name 6259 Selects one of the built-in core configurations. Each MeP chip has one or more modules in it; each module has a core CPU and a variety of coprocessors, optional instructions, and 6260 peripherals. The "MeP-Integrator" tool, not part of GCC, provides these configurations through this option; using this option is the same as using all the corresponding command-line 6261 options. The default configuration is default. 6262 -mcop 6263 Enables the coprocessor instructions. By default, this is a 32-bit coprocessor. Note that the coprocessor is normally enabled via the -mconfig= option. 6264 -mcop32 6265 Enables the 32-bit coprocessor's instructions. 6266 -mcop64 6267 Enables the 64-bit coprocessor's instructions. 6268 -mivc2 6269 Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor. 6270 -mdc 6271 Causes constant variables to be placed in the ".near" section. 6272 -mdiv 6273 Enables the "div" and "divu" instructions. 6274 -meb 6275 Generate big-endian code. 6276 -mel 6277 Generate little-endian code. 6278 -mio-volatile 6279 Tells the compiler that any variable marked with the "io" attribute is to be considered volatile. 6280 -ml Causes variables to be assigned to the ".far" section by default. 6281 -mleadz 6282 Enables the "leadz" (leading zero) instruction. 6283 -mm Causes variables to be assigned to the ".near" section by default. 6284 -mminmax 6285 Enables the "min" and "max" instructions. 6286 -mmult 6287 Enables the multiplication and multiply-accumulate instructions. 6288 -mno-opts 6289 Disables all the optional instructions enabled by -mall-opts. 6290 -mrepeat 6291 Enables the "repeat" and "erepeat" instructions, used for low-overhead looping. 6292 -ms Causes all variables to default to the ".tiny" section. Note that there is a 65536-byte limit to this section. Accesses to these variables use the %gp base register. 6293 -msatur 6294 Enables the saturation instructions. Note that the compiler does not currently generate these itself, but this option is included for compatibility with other tools, like "as". 6295 -msdram 6296 Link the SDRAM-based runtime instead of the default ROM-based runtime. 6297 -msim 6298 Link the simulator run-time libraries. 6299 -msimnovec 6300 Link the simulator runtime libraries, excluding built-in support for reset and exception vectors and tables. 6301 -mtf 6302 Causes all functions to default to the ".far" section. Without this option, functions default to the ".near" section. 6303 -mtiny=n 6304 Variables that are n bytes or smaller are allocated to the ".tiny" section. These variables use the $gp base register. The default for this option is 4, but note that there's a 65536-byte 6305 limit to the ".tiny" section. 6306 MicroBlaze Options 6307 -msoft-float 6308 Use software emulation for floating point (default). 6309 -mhard-float 6310 Use hardware floating-point instructions. 6311 -mmemcpy 6312 Do not optimize block moves, use "memcpy". 6313 -mno-clearbss 6314 This option is deprecated. Use -fno-zero-initialized-in-bss instead. 6315 -mcpu=cpu-type 6316 Use features of, and schedule code for, the given CPU. Supported values are in the format vX.YY.Z, where X is a major version, YY is the minor version, and Z is compatibility code. Example 6317 values are v3.00.a, v4.00.b, v5.00.a, v5.00.b, v5.00.b, v6.00.a. 6318 -mxl-soft-mul 6319 Use software multiply emulation (default). 6320 -mxl-soft-div 6321 Use software emulation for divides (default). 6322 -mxl-barrel-shift 6323 Use the hardware barrel shifter. 6324 -mxl-pattern-compare 6325 Use pattern compare instructions. 6326 -msmall-divides 6327 Use table lookup optimization for small signed integer divisions. 6328 -mxl-stack-check 6329 This option is deprecated. Use -fstack-check instead. 6330 -mxl-gp-opt 6331 Use GP-relative ".sdata"/".sbss" sections. 6332 -mxl-multiply-high 6333 Use multiply high instructions for high part of 32x32 multiply. 6334 -mxl-float-convert 6335 Use hardware floating-point conversion instructions. 6336 -mxl-float-sqrt 6337 Use hardware floating-point square root instruction. 6338 -mbig-endian 6339 Generate code for a big-endian target. 6340 -mlittle-endian 6341 Generate code for a little-endian target. 6342 -mxl-reorder 6343 Use reorder instructions (swap and byte reversed load/store). 6344 -mxl-mode-app-model 6345 Select application model app-model. Valid models are 6346 executable 6347 normal executable (default), uses startup code crt0.o. 6348 xmdstub 6349 for use with Xilinx Microprocessor Debugger (XMD) based software intrusive debug agent called xmdstub. This uses startup file crt1.o and sets the start address of the program to 0x800. 6350 bootstrap 6351 for applications that are loaded using a bootloader. This model uses startup file crt2.o which does not contain a processor reset vector handler. This is suitable for transferring 6352 control on a processor reset to the bootloader rather than the application. 6353 novectors 6354 for applications that do not require any of the MicroBlaze vectors. This option may be useful for applications running within a monitoring application. This model uses crt3.o as a 6355 startup file. 6356 Option -xl-mode-app-model is a deprecated alias for -mxl-mode-app-model. 6357 MIPS Options 6358 -EB Generate big-endian code. 6359 -EL Generate little-endian code. This is the default for mips*el-*-* configurations. 6360 -march=arch 6361 Generate code that runs on arch, which can be the name of a generic MIPS ISA, or the name of a particular processor. The ISA names are: mips1, mips2, mips3, mips4, mips32, mips32r2, 6362 mips32r3, mips32r5, mips32r6, mips64, mips64r2, mips64r3, mips64r5 and mips64r6. The processor names are: 4kc, 4km, 4kp, 4ksc, 4kec, 4kem, 4kep, 4ksd, 5kc, 5kf, 20kc, 24kc, 24kf2_1, 6363 24kf1_1, 24kec, 24kef2_1, 24kef1_1, 34kc, 34kf2_1, 34kf1_1, 34kn, 74kc, 74kf2_1, 74kf1_1, 74kf3_2, 1004kc, 1004kf2_1, 1004kf1_1, loongson2e, loongson2f, loongson3a, m4k, m14k, m14kc, m14ke, 6364 m14kec, octeon, octeon+, octeon2, octeon3, orion, p5600, r2000, r3000, r3900, r4000, r4400, r4600, r4650, r4700, r6000, r8000, rm7000, rm9000, r10000, r12000, r14000, r16000, sb1, sr71000, 6365 vr4100, vr4111, vr4120, vr4130, vr4300, vr5000, vr5400, vr5500, xlr and xlp. The special value from-abi selects the most compatible architecture for the selected ABI (that is, mips1 for 6366 32-bit ABIs and mips3 for 64-bit ABIs). 6367 The native Linux/GNU toolchain also supports the value native, which selects the best architecture option for the host processor. -march=native has no effect if GCC does not recognize the 6368 processor. 6369 In processor names, a final 000 can be abbreviated as k (for example, -march=r2k). Prefixes are optional, and vr may be written r. 6370 Names of the form nf2_1 refer to processors with FPUs clocked at half the rate of the core, names of the form nf1_1 refer to processors with FPUs clocked at the same rate as the core, and 6371 names of the form nf3_2 refer to processors with FPUs clocked a ratio of 3:2 with respect to the core. For compatibility reasons, nf is accepted as a synonym for nf2_1 while nx and bfx are 6372 accepted as synonyms for nf1_1. 6373 GCC defines two macros based on the value of this option. The first is "_MIPS_ARCH", which gives the name of target architecture, as a string. The second has the form "_MIPS_ARCH_foo", 6374 where foo is the capitalized value of "_MIPS_ARCH". For example, -march=r2000 sets "_MIPS_ARCH" to "r2000" and defines the macro "_MIPS_ARCH_R2000". 6375 Note that the "_MIPS_ARCH" macro uses the processor names given above. In other words, it has the full prefix and does not abbreviate 000 as k. In the case of from-abi, the macro names the 6376 resolved architecture (either "mips1" or "mips3"). It names the default architecture when no -march option is given. 6377 -mtune=arch 6378 Optimize for arch. Among other things, this option controls the way instructions are scheduled, and the perceived cost of arithmetic operations. The list of arch values is the same as for 6379 -march. 6380 When this option is not used, GCC optimizes for the processor specified by -march. By using -march and -mtune together, it is possible to generate code that runs on a family of processors, 6381 but optimize the code for one particular member of that family. 6382 -mtune defines the macros "_MIPS_TUNE" and "_MIPS_TUNE_foo", which work in the same way as the -march ones described above. 6383 -mips1 6384 Equivalent to -march=mips1. 6385 -mips2 6386 Equivalent to -march=mips2. 6387 -mips3 6388 Equivalent to -march=mips3. 6389 -mips4 6390 Equivalent to -march=mips4. 6391 -mips32 6392 Equivalent to -march=mips32. 6393 -mips32r3 6394 Equivalent to -march=mips32r3. 6395 -mips32r5 6396 Equivalent to -march=mips32r5. 6397 -mips32r6 6398 Equivalent to -march=mips32r6. 6399 -mips64 6400 Equivalent to -march=mips64. 6401 -mips64r2 6402 Equivalent to -march=mips64r2. 6403 -mips64r3 6404 Equivalent to -march=mips64r3. 6405 -mips64r5 6406 Equivalent to -march=mips64r5. 6407 -mips64r6 6408 Equivalent to -march=mips64r6. 6409 -mips16 6410 -mno-mips16 6411 Generate (do not generate) MIPS16 code. If GCC is targeting a MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE. 6412 MIPS16 code generation can also be controlled on a per-function basis by means of "mips16" and "nomips16" attributes. 6413 -mflip-mips16 6414 Generate MIPS16 code on alternating functions. This option is provided for regression testing of mixed MIPS16/non-MIPS16 code generation, and is not intended for ordinary use in compiling 6415 user code. 6416 -minterlink-compressed 6417 -mno-interlink-compressed 6418 Require (do not require) that code using the standard (uncompressed) MIPS ISA be link-compatible with MIPS16 and microMIPS code, and vice versa. 6419 For example, code using the standard ISA encoding cannot jump directly to MIPS16 or microMIPS code; it must either use a call or an indirect jump. -minterlink-compressed therefore disables 6420 direct jumps unless GCC knows that the target of the jump is not compressed. 6421 -minterlink-mips16 6422 -mno-interlink-mips16 6423 Aliases of -minterlink-compressed and -mno-interlink-compressed. These options predate the microMIPS ASE and are retained for backwards compatibility. 6424 -mabi=32 6425 -mabi=o64 6426 -mabi=n32 6427 -mabi=64 6428 -mabi=eabi 6429 Generate code for the given ABI. 6430 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally generates 64-bit code when you select a 64-bit architecture, but you can use -mgp32 to get 32-bit code instead. 6431 For information about the O64 ABI, see . 6432 GCC supports a variant of the o32 ABI in which floating-point registers are 64 rather than 32 bits wide. You can select this combination with -mabi=32 -mfp64. This ABI relies on the 6433 "mthc1" and "mfhc1" instructions and is therefore only supported for MIPS32R2, MIPS32R3 and MIPS32R5 processors. 6434 The register assignments for arguments and return values remain the same, but each scalar value is passed in a single 64-bit register rather than a pair of 32-bit registers. For example, 6435 scalar floating-point values are returned in $f0 only, not a $f0/$f1 pair. The set of call-saved registers also remains the same in that the even-numbered double-precision registers are 6436 saved. 6437 Two additional variants of the o32 ABI are supported to enable a transition from 32-bit to 64-bit registers. These are FPXX (-mfpxx) and FP64A (-mfp64 -mno-odd-spreg). The FPXX extension 6438 mandates that all code must execute correctly when run using 32-bit or 64-bit registers. The code can be interlinked with either FP32 or FP64, but not both. The FP64A extension is similar 6439 to the FP64 extension but forbids the use of odd-numbered single-precision registers. This can be used in conjunction with the "FRE" mode of FPUs in MIPS32R5 processors and allows both FP32 6440 and FP64A code to interlink and run in the same process without changing FPU modes. 6441 -mabicalls 6442 -mno-abicalls 6443 Generate (do not generate) code that is suitable for SVR4-style dynamic objects. -mabicalls is the default for SVR4-based systems. 6444 -mshared 6445 -mno-shared 6446 Generate (do not generate) code that is fully position-independent, and that can therefore be linked into shared libraries. This option only affects -mabicalls. 6447 All -mabicalls code has traditionally been position-independent, regardless of options like -fPIC and -fpic. However, as an extension, the GNU toolchain allows executables to use absolute 6448 accesses for locally-binding symbols. It can also use shorter GP initialization sequences and generate direct calls to locally-defined functions. This mode is selected by -mno-shared. 6449 -mno-shared depends on binutils 2.16 or higher and generates objects that can only be linked by the GNU linker. However, the option does not affect the ABI of the final executable; it only 6450 affects the ABI of relocatable objects. Using -mno-shared generally makes executables both smaller and quicker. 6451 -mshared is the default. 6452 -mplt 6453 -mno-plt 6454 Assume (do not assume) that the static and dynamic linkers support PLTs and copy relocations. This option only affects -mno-shared -mabicalls. For the n64 ABI, this option has no effect 6455 without -msym32. 6456 You can make -mplt the default by configuring GCC with --with-mips-plt. The default is -mno-plt otherwise. 6457 -mxgot 6458 -mno-xgot 6459 Lift (do not lift) the usual restrictions on the size of the global offset table. 6460 GCC normally uses a single instruction to load values from the GOT. While this is relatively efficient, it only works if the GOT is smaller than about 64k. Anything larger causes the 6461 linker to report an error such as: 6462 relocation truncated to fit: R_MIPS_GOT16 foobar 6463 If this happens, you should recompile your code with -mxgot. This works with very large GOTs, although the code is also less efficient, since it takes three instructions to fetch the value 6464 of a global symbol. 6465 Note that some linkers can create multiple GOTs. If you have such a linker, you should only need to use -mxgot when a single object file accesses more than 64k's worth of GOT entries. Very 6466 few do. 6467 These options have no effect unless GCC is generating position independent code. 6468 -mgp32 6469 Assume that general-purpose registers are 32 bits wide. 6470 -mgp64 6471 Assume that general-purpose registers are 64 bits wide. 6472 -mfp32 6473 Assume that floating-point registers are 32 bits wide. 6474 -mfp64 6475 Assume that floating-point registers are 64 bits wide. 6476 -mfpxx 6477 Do not assume the width of floating-point registers. 6478 -mhard-float 6479 Use floating-point coprocessor instructions. 6480 -msoft-float 6481 Do not use floating-point coprocessor instructions. Implement floating-point calculations using library calls instead. 6482 -mno-float 6483 Equivalent to -msoft-float, but additionally asserts that the program being compiled does not perform any floating-point operations. This option is presently supported only by some bare- 6484 metal MIPS configurations, where it may select a special set of libraries that lack all floating-point support (including, for example, the floating-point "printf" formats). If code 6485 compiled with -mno-float accidentally contains floating-point operations, it is likely to suffer a link-time or run-time failure. 6486 -msingle-float 6487 Assume that the floating-point coprocessor only supports single-precision operations. 6488 -mdouble-float 6489 Assume that the floating-point coprocessor supports double-precision operations. This is the default. 6490 -modd-spreg 6491 -mno-odd-spreg 6492 Enable the use of odd-numbered single-precision floating-point registers for the o32 ABI. This is the default for processors that are known to support these registers. When using the o32 6493 FPXX ABI, -mno-odd-spreg is set by default. 6494 -mabs=2008 6495 -mabs=legacy 6496 These options control the treatment of the special not-a-number (NaN) IEEE 754 floating-point data with the "abs.fmt" and "neg.fmt" machine instructions. 6497 By default or when -mabs=legacy is used the legacy treatment is selected. In this case these instructions are considered arithmetic and avoided where correct operation is required and the 6498 input operand might be a NaN. A longer sequence of instructions that manipulate the sign bit of floating-point datum manually is used instead unless the -ffinite-math-only option has also 6499 been specified. 6500 The -mabs=2008 option selects the IEEE 754-2008 treatment. In this case these instructions are considered non-arithmetic and therefore operating correctly in all cases, including in 6501 particular where the input operand is a NaN. These instructions are therefore always used for the respective operations. 6502 -mnan=2008 6503 -mnan=legacy 6504 These options control the encoding of the special not-a-number (NaN) IEEE 754 floating-point data. 6505 The -mnan=legacy option selects the legacy encoding. In this case quiet NaNs (qNaNs) are denoted by the first bit of their trailing significand field being 0, whereas signalling NaNs 6506 (sNaNs) are denoted by the first bit of their trailing significand field being 1. 6507 The -mnan=2008 option selects the IEEE 754-2008 encoding. In this case qNaNs are denoted by the first bit of their trailing significand field being 1, whereas sNaNs are denoted by the first 6508 bit of their trailing significand field being 0. 6509 The default is -mnan=legacy unless GCC has been configured with --with-nan=2008. 6510 -mllsc 6511 -mno-llsc 6512 Use (do not use) ll, sc, and sync instructions to implement atomic memory built-in functions. When neither option is specified, GCC uses the instructions if the target architecture supports 6513 them. 6514 -mllsc is useful if the runtime environment can emulate the instructions and -mno-llsc can be useful when compiling for nonstandard ISAs. You can make either option the default by 6515 configuring GCC with --with-llsc and --without-llsc respectively. --with-llsc is the default for some configurations; see the installation documentation for details. 6516 -mdsp 6517 -mno-dsp 6518 Use (do not use) revision 1 of the MIPS DSP ASE. 6519 This option defines the preprocessor macro "__mips_dsp". It also defines "__mips_dsp_rev" to 1. 6520 -mdspr2 6521 -mno-dspr2 6522 Use (do not use) revision 2 of the MIPS DSP ASE. 6523 This option defines the preprocessor macros "__mips_dsp" and "__mips_dspr2". It also defines "__mips_dsp_rev" to 2. 6524 -msmartmips 6525 -mno-smartmips 6526 Use (do not use) the MIPS SmartMIPS ASE. 6527 -mpaired-single 6528 -mno-paired-single 6529 Use (do not use) paired-single floating-point instructions. 6530 This option requires hardware floating-point support to be enabled. 6531 -mdmx 6532 -mno-mdmx 6533 Use (do not use) MIPS Digital Media Extension instructions. This option can only be used when generating 64-bit code and requires hardware floating-point support to be enabled. 6534 -mips3d 6535 -mno-mips3d 6536 Use (do not use) the MIPS-3D ASE. The option -mips3d implies -mpaired-single. 6537 -mmicromips 6538 -mno-micromips 6539 Generate (do not generate) microMIPS code. 6540 MicroMIPS code generation can also be controlled on a per-function basis by means of "micromips" and "nomicromips" attributes. 6541 -mmt 6542 -mno-mt 6543 Use (do not use) MT Multithreading instructions. 6544 -mmcu 6545 -mno-mcu 6546 Use (do not use) the MIPS MCU ASE instructions. 6547 -meva 6548 -mno-eva 6549 Use (do not use) the MIPS Enhanced Virtual Addressing instructions. 6550 -mvirt 6551 -mno-virt 6552 Use (do not use) the MIPS Virtualization Application Specific instructions. 6553 -mxpa 6554 -mno-xpa 6555 Use (do not use) the MIPS eXtended Physical Address (XPA) instructions. 6556 -mlong64 6557 Force "long" types to be 64 bits wide. See -mlong32 for an explanation of the default and the way that the pointer size is determined. 6558 -mlong32 6559 Force "long", "int", and pointer types to be 32 bits wide. 6560 The default size of "int"s, "long"s and pointers depends on the ABI. All the supported ABIs use 32-bit "int"s. The n64 ABI uses 64-bit "long"s, as does the 64-bit EABI; the others use 6561 32-bit "long"s. Pointers are the same size as "long"s, or the same size as integer registers, whichever is smaller. 6562 -msym32 6563 -mno-sym32 6564 Assume (do not assume) that all symbols have 32-bit values, regardless of the selected ABI. This option is useful in combination with -mabi=64 and -mno-abicalls because it allows GCC to 6565 generate shorter and faster references to symbolic addresses. 6566 -G num 6567 Put definitions of externally-visible data in a small data section if that data is no bigger than num bytes. GCC can then generate more efficient accesses to the data; see -mgpopt for 6568 details. 6569 The default -G option depends on the configuration. 6570 -mlocal-sdata 6571 -mno-local-sdata 6572 Extend (do not extend) the -G behavior to local data too, such as to static variables in C. -mlocal-sdata is the default for all configurations. 6573 If the linker complains that an application is using too much small data, you might want to try rebuilding the less performance-critical parts with -mno-local-sdata. You might also want to 6574 build large libraries with -mno-local-sdata, so that the libraries leave more room for the main program. 6575 -mextern-sdata 6576 -mno-extern-sdata 6577 Assume (do not assume) that externally-defined data is in a small data section if the size of that data is within the -G limit. -mextern-sdata is the default for all configurations. 6578 If you compile a module Mod with -mextern-sdata -G num -mgpopt, and Mod references a variable Var that is no bigger than num bytes, you must make sure that Var is placed in a small data 6579 section. If Var is defined by another module, you must either compile that module with a high-enough -G setting or attach a "section" attribute to Var's definition. If Var is common, you 6580 must link the application with a high-enough -G setting. 6581 The easiest way of satisfying these restrictions is to compile and link every module with the same -G option. However, you may wish to build a library that supports several different small 6582 data limits. You can do this by compiling the library with the highest supported -G setting and additionally using -mno-extern-sdata to stop the library from making assumptions about 6583 externally-defined data. 6584 -mgpopt 6585 -mno-gpopt 6586 Use (do not use) GP-relative accesses for symbols that are known to be in a small data section; see -G, -mlocal-sdata and -mextern-sdata. -mgpopt is the default for all configurations. 6587 -mno-gpopt is useful for cases where the $gp register might not hold the value of "_gp". For example, if the code is part of a library that might be used in a boot monitor, programs that 6588 call boot monitor routines pass an unknown value in $gp. (In such situations, the boot monitor itself is usually compiled with -G0.) 6589 -mno-gpopt implies -mno-local-sdata and -mno-extern-sdata. 6590 -membedded-data 6591 -mno-embedded-data 6592 Allocate variables to the read-only data section first if possible, then next in the small data section if possible, otherwise in data. This gives slightly slower code than the default, but 6593 reduces the amount of RAM required when executing, and thus may be preferred for some embedded systems. 6594 -muninit-const-in-rodata 6595 -mno-uninit-const-in-rodata 6596 Put uninitialized "const" variables in the read-only data section. This option is only meaningful in conjunction with -membedded-data. 6597 -mcode-readable=setting 6598 Specify whether GCC may generate code that reads from executable sections. There are three possible settings: 6599 -mcode-readable=yes 6600 Instructions may freely access executable sections. This is the default setting. 6601 -mcode-readable=pcrel 6602 MIPS16 PC-relative load instructions can access executable sections, but other instructions must not do so. This option is useful on 4KSc and 4KSd processors when the code TLBs have the 6603 Read Inhibit bit set. It is also useful on processors that can be configured to have a dual instruction/data SRAM interface and that, like the M4K, automatically redirect PC-relative 6604 loads to the instruction RAM. 6605 -mcode-readable=no 6606 Instructions must not access executable sections. This option can be useful on targets that are configured to have a dual instruction/data SRAM interface but that (unlike the M4K) do 6607 not automatically redirect PC-relative loads to the instruction RAM. 6608 -msplit-addresses 6609 -mno-split-addresses 6610 Enable (disable) use of the "%hi()" and "%lo()" assembler relocation operators. This option has been superseded by -mexplicit-relocs but is retained for backwards compatibility. 6611 -mexplicit-relocs 6612 -mno-explicit-relocs 6613 Use (do not use) assembler relocation operators when dealing with symbolic addresses. The alternative, selected by -mno-explicit-relocs, is to use assembler macros instead. 6614 -mexplicit-relocs is the default if GCC was configured to use an assembler that supports relocation operators. 6615 -mcheck-zero-division 6616 -mno-check-zero-division 6617 Trap (do not trap) on integer division by zero. 6618 The default is -mcheck-zero-division. 6619 -mdivide-traps 6620 -mdivide-breaks 6621 MIPS systems check for division by zero by generating either a conditional trap or a break instruction. Using traps results in smaller code, but is only supported on MIPS II and later. 6622 Also, some versions of the Linux kernel have a bug that prevents trap from generating the proper signal ("SIGFPE"). Use -mdivide-traps to allow conditional traps on architectures that 6623 support them and -mdivide-breaks to force the use of breaks. 6624 The default is usually -mdivide-traps, but this can be overridden at configure time using --with-divide=breaks. Divide-by-zero checks can be completely disabled using 6625 -mno-check-zero-division. 6626 -mmemcpy 6627 -mno-memcpy 6628 Force (do not force) the use of "memcpy" for non-trivial block moves. The default is -mno-memcpy, which allows GCC to inline most constant-sized copies. 6629 -mlong-calls 6630 -mno-long-calls 6631 Disable (do not disable) use of the "jal" instruction. Calling functions using "jal" is more efficient but requires the caller and callee to be in the same 256 megabyte segment. 6632 This option has no effect on abicalls code. The default is -mno-long-calls. 6633 -mmad 6634 -mno-mad 6635 Enable (disable) use of the "mad", "madu" and "mul" instructions, as provided by the R4650 ISA. 6636 -mimadd 6637 -mno-imadd 6638 Enable (disable) use of the "madd" and "msub" integer instructions. The default is -mimadd on architectures that support "madd" and "msub" except for the 74k architecture where it was found 6639 to generate slower code. 6640 -mfused-madd 6641 -mno-fused-madd 6642 Enable (disable) use of the floating-point multiply-accumulate instructions, when they are available. The default is -mfused-madd. 6643 On the R8000 CPU when multiply-accumulate instructions are used, the intermediate product is calculated to infinite precision and is not subject to the FCSR Flush to Zero bit. This may be 6644 undesirable in some circumstances. On other processors the result is numerically identical to the equivalent computation using separate multiply, add, subtract and negate instructions. 6645 -nocpp 6646 Tell the MIPS assembler to not run its preprocessor over user assembler files (with a .s suffix) when assembling them. 6647 -mfix-24k 6648 -mno-fix-24k 6649 Work around the 24K E48 (lost data on stores during refill) errata. The workarounds are implemented by the assembler rather than by GCC. 6650 -mfix-r4000 6651 -mno-fix-r4000 6652 Work around certain R4000 CPU errata: 6653 - A double-word or a variable shift may give an incorrect result if executed immediately after starting an integer division. 6654 - A double-word or a variable shift may give an incorrect result if executed while an integer multiplication is in progress. 6655 - An integer division may give an incorrect result if started in a delay slot of a taken branch or a jump. 6656 -mfix-r4400 6657 -mno-fix-r4400 6658 Work around certain R4400 CPU errata: 6659 - A double-word or a variable shift may give an incorrect result if executed immediately after starting an integer division. 6660 -mfix-r10000 6661 -mno-fix-r10000 6662 Work around certain R10000 errata: 6663 - "ll"/"sc" sequences may not behave atomically on revisions prior to 3.0. They may deadlock on revisions 2.6 and earlier. 6664 This option can only be used if the target architecture supports branch-likely instructions. -mfix-r10000 is the default when -march=r10000 is used; -mno-fix-r10000 is the default 6665 otherwise. 6666 -mfix-rm7000 6667 -mno-fix-rm7000 6668 Work around the RM7000 "dmult"/"dmultu" errata. The workarounds are implemented by the assembler rather than by GCC. 6669 -mfix-vr4120 6670 -mno-fix-vr4120 6671 Work around certain VR4120 errata: 6672 - "dmultu" does not always produce the correct result. 6673 - "div" and "ddiv" do not always produce the correct result if one of the operands is negative. 6674 The workarounds for the division errata rely on special functions in libgcc.a. At present, these functions are only provided by the "mips64vr*-elf" configurations. 6675 Other VR4120 errata require a NOP to be inserted between certain pairs of instructions. These errata are handled by the assembler, not by GCC itself. 6676 -mfix-vr4130 6677 Work around the VR4130 "mflo"/"mfhi" errata. The workarounds are implemented by the assembler rather than by GCC, although GCC avoids using "mflo" and "mfhi" if the VR4130 "macc", "macchi", 6678 "dmacc" and "dmacchi" instructions are available instead. 6679 -mfix-sb1 6680 -mno-fix-sb1 6681 Work around certain SB-1 CPU core errata. (This flag currently works around the SB-1 revision 2 "F1" and "F2" floating-point errata.) 6682 -mr10k-cache-barrier=setting 6683 Specify whether GCC should insert cache barriers to avoid the side-effects of speculation on R10K processors. 6684 In common with many processors, the R10K tries to predict the outcome of a conditional branch and speculatively executes instructions from the "taken" branch. It later aborts these 6685 instructions if the predicted outcome is wrong. However, on the R10K, even aborted instructions can have side effects. 6686 This problem only affects kernel stores and, depending on the system, kernel loads. As an example, a speculatively-executed store may load the target memory into cache and mark the cache 6687 line as dirty, even if the store itself is later aborted. If a DMA operation writes to the same area of memory before the "dirty" line is flushed, the cached data overwrites the DMA-ed 6688 data. See the R10K processor manual for a full description, including other potential problems. 6689 One workaround is to insert cache barrier instructions before every memory access that might be speculatively executed and that might have side effects even if aborted. 6690 -mr10k-cache-barrier=setting controls GCC's implementation of this workaround. It assumes that aborted accesses to any byte in the following regions does not have side effects: 6691 1. the memory occupied by the current function's stack frame; 6692 2. the memory occupied by an incoming stack argument; 6693 3. the memory occupied by an object with a link-time-constant address. 6694 It is the kernel's responsibility to ensure that speculative accesses to these regions are indeed safe. 6695 If the input program contains a function declaration such as: 6696 void foo (void); 6697 then the implementation of "foo" must allow "j foo" and "jal foo" to be executed speculatively. GCC honors this restriction for functions it compiles itself. It expects non-GCC functions 6698 (such as hand-written assembly code) to do the same. 6699 The option has three forms: 6700 -mr10k-cache-barrier=load-store 6701 Insert a cache barrier before a load or store that might be speculatively executed and that might have side effects even if aborted. 6702 -mr10k-cache-barrier=store 6703 Insert a cache barrier before a store that might be speculatively executed and that might have side effects even if aborted. 6704 -mr10k-cache-barrier=none 6705 Disable the insertion of cache barriers. This is the default setting. 6706 -mflush-func=func 6707 -mno-flush-func 6708 Specifies the function to call to flush the I and D caches, or to not call any such function. If called, the function must take the same arguments as the common "_flush_func", that is, the 6709 address of the memory range for which the cache is being flushed, the size of the memory range, and the number 3 (to flush both caches). The default depends on the target GCC was configured 6710 for, but commonly is either "_flush_func" or "__cpu_flush". 6711 mbranch-cost=num 6712 Set the cost of branches to roughly num "simple" instructions. This cost is only a heuristic and is not guaranteed to produce consistent results across releases. A zero cost redundantly 6713 selects the default, which is based on the -mtune setting. 6714 -mbranch-likely 6715 -mno-branch-likely 6716 Enable or disable use of Branch Likely instructions, regardless of the default for the selected architecture. By default, Branch Likely instructions may be generated if they are supported 6717 by the selected architecture. An exception is for the MIPS32 and MIPS64 architectures and processors that implement those architectures; for those, Branch Likely instructions are not be 6718 generated by default because the MIPS32 and MIPS64 architectures specifically deprecate their use. 6719 -mfp-exceptions 6720 -mno-fp-exceptions 6721 Specifies whether FP exceptions are enabled. This affects how FP instructions are scheduled for some processors. The default is that FP exceptions are enabled. 6722 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting 64-bit code, then we can use both FP pipes. Otherwise, we can only use one FP pipe. 6723 -mvr4130-align 6724 -mno-vr4130-align 6725 The VR4130 pipeline is two-way superscalar, but can only issue two instructions together if the first one is 8-byte aligned. When this option is enabled, GCC aligns pairs of instructions 6726 that it thinks should execute in parallel. 6727 This option only has an effect when optimizing for the VR4130. It normally makes code faster, but at the expense of making it bigger. It is enabled by default at optimization level -O3. 6728 -msynci 6729 -mno-synci 6730 Enable (disable) generation of "synci" instructions on architectures that support it. The "synci" instructions (if enabled) are generated when "__builtin___clear_cache" is compiled. 6731 This option defaults to -mno-synci, but the default can be overridden by configuring GCC with --with-synci. 6732 When compiling code for single processor systems, it is generally safe to use "synci". However, on many multi-core (SMP) systems, it does not invalidate the instruction caches on all cores 6733 and may lead to undefined behavior. 6734 -mrelax-pic-calls 6735 -mno-relax-pic-calls 6736 Try to turn PIC calls that are normally dispatched via register $25 into direct calls. This is only possible if the linker can resolve the destination at link-time and if the destination is 6737 within range for a direct call. 6738 -mrelax-pic-calls is the default if GCC was configured to use an assembler and a linker that support the ".reloc" assembly directive and -mexplicit-relocs is in effect. With 6739 -mno-explicit-relocs, this optimization can be performed by the assembler and the linker alone without help from the compiler. 6740 -mmcount-ra-address 6741 -mno-mcount-ra-address 6742 Emit (do not emit) code that allows "_mcount" to modify the calling function's return address. When enabled, this option extends the usual "_mcount" interface with a new ra-address 6743 parameter, which has type "intptr_t *" and is passed in register $12. "_mcount" can then modify the return address by doing both of the following: 6744 * Returning the new address in register $31. 6745 * Storing the new address in "*ra-address", if ra-address is nonnull. 6746 The default is -mno-mcount-ra-address. 6747 MMIX Options 6748 These options are defined for the MMIX: 6749 -mlibfuncs 6750 -mno-libfuncs 6751 Specify that intrinsic library functions are being compiled, passing all values in registers, no matter the size. 6752 -mepsilon 6753 -mno-epsilon 6754 Generate floating-point comparison instructions that compare with respect to the "rE" epsilon register. 6755 -mabi=mmixware 6756 -mabi=gnu 6757 Generate code that passes function parameters and return values that (in the called function) are seen as registers $0 and up, as opposed to the GNU ABI which uses global registers $231 and 6758 up. 6759 -mzero-extend 6760 -mno-zero-extend 6761 When reading data from memory in sizes shorter than 64 bits, use (do not use) zero-extending load instructions by default, rather than sign-extending ones. 6762 -mknuthdiv 6763 -mno-knuthdiv 6764 Make the result of a division yielding a remainder have the same sign as the divisor. With the default, -mno-knuthdiv, the sign of the remainder follows the sign of the dividend. Both 6765 methods are arithmetically valid, the latter being almost exclusively used. 6766 -mtoplevel-symbols 6767 -mno-toplevel-symbols 6768 Prepend (do not prepend) a : to all global symbols, so the assembly code can be used with the "PREFIX" assembly directive. 6769 -melf 6770 Generate an executable in the ELF format, rather than the default mmo format used by the mmix simulator. 6771 -mbranch-predict 6772 -mno-branch-predict 6773 Use (do not use) the probable-branch instructions, when static branch prediction indicates a probable branch. 6774 -mbase-addresses 6775 -mno-base-addresses 6776 Generate (do not generate) code that uses base addresses. Using a base address automatically generates a request (handled by the assembler and the linker) for a constant to be set up in a 6777 global register. The register is used for one or more base address requests within the range 0 to 255 from the value held in the register. The generally leads to short and fast code, but 6778 the number of different data items that can be addressed is limited. This means that a program that uses lots of static data may require -mno-base-addresses. 6779 -msingle-exit 6780 -mno-single-exit 6781 Force (do not force) generated code to have a single exit point in each function. 6782 MN10300 Options 6783 These -m options are defined for Matsushita MN10300 architectures: 6784 -mmult-bug 6785 Generate code to avoid bugs in the multiply instructions for the MN10300 processors. This is the default. 6786 -mno-mult-bug 6787 Do not generate code to avoid bugs in the multiply instructions for the MN10300 processors. 6788 -mam33 6789 Generate code using features specific to the AM33 processor. 6790 -mno-am33 6791 Do not generate code using features specific to the AM33 processor. This is the default. 6792 -mam33-2 6793 Generate code using features specific to the AM33/2.0 processor. 6794 -mam34 6795 Generate code using features specific to the AM34 processor. 6796 -mtune=cpu-type 6797 Use the timing characteristics of the indicated CPU type when scheduling instructions. This does not change the targeted processor type. The CPU type must be one of mn10300, am33, am33-2 6798 or am34. 6799 -mreturn-pointer-on-d0 6800 When generating a function that returns a pointer, return the pointer in both "a0" and "d0". Otherwise, the pointer is returned only in "a0", and attempts to call such functions without a 6801 prototype result in errors. Note that this option is on by default; use -mno-return-pointer-on-d0 to disable it. 6802 -mno-crt0 6803 Do not link in the C run-time initialization object file. 6804 -mrelax 6805 Indicate to the linker that it should perform a relaxation optimization pass to shorten branches, calls and absolute memory addresses. This option only has an effect when used on the 6806 command line for the final link step. 6807 This option makes symbolic debugging impossible. 6808 -mliw 6809 Allow the compiler to generate Long Instruction Word instructions if the target is the AM33 or later. This is the default. This option defines the preprocessor macro "__LIW__". 6810 -mnoliw 6811 Do not allow the compiler to generate Long Instruction Word instructions. This option defines the preprocessor macro "__NO_LIW__". 6812 -msetlb 6813 Allow the compiler to generate the SETLB and Lcc instructions if the target is the AM33 or later. This is the default. This option defines the preprocessor macro "__SETLB__". 6814 -mnosetlb 6815 Do not allow the compiler to generate SETLB or Lcc instructions. This option defines the preprocessor macro "__NO_SETLB__". 6816 Moxie Options 6817 -meb 6818 Generate big-endian code. This is the default for moxie-*-* configurations. 6819 -mel 6820 Generate little-endian code. 6821 -mmul.x 6822 Generate mul.x and umul.x instructions. This is the default for moxiebox-*-* configurations. 6823 -mno-crt0 6824 Do not link in the C run-time initialization object file. 6825 MSP430 Options 6826 These options are defined for the MSP430: 6827 -masm-hex 6828 Force assembly output to always use hex constants. Normally such constants are signed decimals, but this option is available for testsuite and/or aesthetic purposes. 6829 -mmcu= 6830 Select the MCU to target. This is used to create a C preprocessor symbol based upon the MCU name, converted to upper case and pre- and post-fixed with __. This in turn is used by the 6831 msp430.h header file to select an MCU-specific supplementary header file. 6832 The option also sets the ISA to use. If the MCU name is one that is known to only support the 430 ISA then that is selected, otherwise the 430X ISA is selected. A generic MCU name of 6833 msp430 can also be used to select the 430 ISA. Similarly the generic msp430x MCU name selects the 430X ISA. 6834 In addition an MCU-specific linker script is added to the linker command line. The script's name is the name of the MCU with .ld appended. Thus specifying -mmcu=xxx on the gcc command line 6835 defines the C preprocessor symbol "__XXX__" and cause the linker to search for a script called xxx.ld. 6836 This option is also passed on to the assembler. 6837 -mcpu= 6838 Specifies the ISA to use. Accepted values are msp430, msp430x and msp430xv2. This option is deprecated. The -mmcu= option should be used to select the ISA. 6839 -msim 6840 Link to the simulator runtime libraries and linker script. Overrides any scripts that would be selected by the -mmcu= option. 6841 -mlarge 6842 Use large-model addressing (20-bit pointers, 32-bit "size_t"). 6843 -msmall 6844 Use small-model addressing (16-bit pointers, 16-bit "size_t"). 6845 -mrelax 6846 This option is passed to the assembler and linker, and allows the linker to perform certain optimizations that cannot be done until the final link. 6847 mhwmult= 6848 Describes the type of hardware multiply supported by the target. Accepted values are none for no hardware multiply, 16bit for the original 16-bit-only multiply supported by early MCUs. 6849 32bit for the 16/32-bit multiply supported by later MCUs and f5series for the 16/32-bit multiply supported by F5-series MCUs. A value of auto can also be given. This tells GCC to deduce 6850 the hardware multiply support based upon the MCU name provided by the -mmcu option. If no -mmcu option is specified then 32bit hardware multiply support is assumed. auto is the default 6851 setting. 6852 Hardware multiplies are normally performed by calling a library routine. This saves space in the generated code. When compiling at -O3 or higher however the hardware multiplier is invoked 6853 inline. This makes for bigger, but faster code. 6854 The hardware multiply routines disable interrupts whilst running and restore the previous interrupt state when they finish. This makes them safe to use inside interrupt handlers as well as 6855 in normal code. 6856 -minrt 6857 Enable the use of a minimum runtime environment - no static initializers or constructors. This is intended for memory-constrained devices. The compiler includes special symbols in some 6858 objects that tell the linker and runtime which code fragments are required. 6859 NDS32 Options 6860 These options are defined for NDS32 implementations: 6861 -mbig-endian 6862 Generate code in big-endian mode. 6863 -mlittle-endian 6864 Generate code in little-endian mode. 6865 -mreduced-regs 6866 Use reduced-set registers for register allocation. 6867 -mfull-regs 6868 Use full-set registers for register allocation. 6869 -mcmov 6870 Generate conditional move instructions. 6871 -mno-cmov 6872 Do not generate conditional move instructions. 6873 -mperf-ext 6874 Generate performance extension instructions. 6875 -mno-perf-ext 6876 Do not generate performance extension instructions. 6877 -mv3push 6878 Generate v3 push25/pop25 instructions. 6879 -mno-v3push 6880 Do not generate v3 push25/pop25 instructions. 6881 -m16-bit 6882 Generate 16-bit instructions. 6883 -mno-16-bit 6884 Do not generate 16-bit instructions. 6885 -misr-vector-size=num 6886 Specify the size of each interrupt vector, which must be 4 or 16. 6887 -mcache-block-size=num 6888 Specify the size of each cache block, which must be a power of 2 between 4 and 512. 6889 -march=arch 6890 Specify the name of the target architecture. 6891 -mcmodel=code-model 6892 Set the code model to one of 6893 small 6894 All the data and read-only data segments must be within 512KB addressing space. The text segment must be within 16MB addressing space. 6895 medium 6896 The data segment must be within 512KB while the read-only data segment can be within 4GB addressing space. The text segment should be still within 16MB addressing space. 6897 large 6898 All the text and data segments can be within 4GB addressing space. 6899 -mctor-dtor 6900 Enable constructor/destructor feature. 6901 -mrelax 6902 Guide linker to relax instructions. 6903 Nios II Options 6904 These are the options defined for the Altera Nios II processor. 6905 -G num 6906 Put global and static objects less than or equal to num bytes into the small data or BSS sections instead of the normal data or BSS sections. The default value of num is 8. 6907 -mgpopt=option 6908 -mgpopt 6909 -mno-gpopt 6910 Generate (do not generate) GP-relative accesses. The following option names are recognized: 6911 none 6912 Do not generate GP-relative accesses. 6913 local 6914 Generate GP-relative accesses for small data objects that are not external or weak. Also use GP-relative addressing for objects that have been explicitly placed in a small data section 6915 via a "section" attribute. 6916 global 6917 As for local, but also generate GP-relative accesses for small data objects that are external or weak. If you use this option, you must ensure that all parts of your program (including 6918 libraries) are compiled with the same -G setting. 6919 data 6920 Generate GP-relative accesses for all data objects in the program. If you use this option, the entire data and BSS segments of your program must fit in 64K of memory and you must use an 6921 appropriate linker script to allocate them within the addressible range of the global pointer. 6922 all Generate GP-relative addresses for function pointers as well as data pointers. If you use this option, the entire text, data, and BSS segments of your program must fit in 64K of memory 6923 and you must use an appropriate linker script to allocate them within the addressible range of the global pointer. 6924 -mgpopt is equivalent to -mgpopt=local, and -mno-gpopt is equivalent to -mgpopt=none. 6925 The default is -mgpopt except when -fpic or -fPIC is specified to generate position-independent code. Note that the Nios II ABI does not permit GP-relative accesses from shared libraries. 6926 You may need to specify -mno-gpopt explicitly when building programs that include large amounts of small data, including large GOT data sections. In this case, the 16-bit offset for GP- 6927 relative addressing may not be large enough to allow access to the entire small data section. 6928 -mel 6929 -meb 6930 Generate little-endian (default) or big-endian (experimental) code, respectively. 6931 -mbypass-cache 6932 -mno-bypass-cache 6933 Force all load and store instructions to always bypass cache by using I/O variants of the instructions. The default is not to bypass the cache. 6934 -mno-cache-volatile 6935 -mcache-volatile 6936 Volatile memory access bypass the cache using the I/O variants of the load and store instructions. The default is not to bypass the cache. 6937 -mno-fast-sw-div 6938 -mfast-sw-div 6939 Do not use table-based fast divide for small numbers. The default is to use the fast divide at -O3 and above. 6940 -mno-hw-mul 6941 -mhw-mul 6942 -mno-hw-mulx 6943 -mhw-mulx 6944 -mno-hw-div 6945 -mhw-div 6946 Enable or disable emitting "mul", "mulx" and "div" family of instructions by the compiler. The default is to emit "mul" and not emit "div" and "mulx". 6947 -mcustom-insn=N 6948 -mno-custom-insn 6949 Each -mcustom-insn=N option enables use of a custom instruction with encoding N when generating code that uses insn. For example, -mcustom-fadds=253 generates custom instruction 253 for 6950 single-precision floating-point add operations instead of the default behavior of using a library call. 6951 The following values of insn are supported. Except as otherwise noted, floating-point operations are expected to be implemented with normal IEEE 754 semantics and correspond directly to the 6952 C operators or the equivalent GCC built-in functions. 6953 Single-precision floating point: 6954 fadds, fsubs, fdivs, fmuls 6955 Binary arithmetic operations. 6956 fnegs 6957 Unary negation. 6958 fabss 6959 Unary absolute value. 6960 fcmpeqs, fcmpges, fcmpgts, fcmples, fcmplts, fcmpnes 6961 Comparison operations. 6962 fmins, fmaxs 6963 Floating-point minimum and maximum. These instructions are only generated if -ffinite-math-only is specified. 6964 fsqrts 6965 Unary square root operation. 6966 fcoss, fsins, ftans, fatans, fexps, flogs 6967 Floating-point trigonometric and exponential functions. These instructions are only generated if -funsafe-math-optimizations is also specified. 6968 Double-precision floating point: 6969 faddd, fsubd, fdivd, fmuld 6970 Binary arithmetic operations. 6971 fnegd 6972 Unary negation. 6973 fabsd 6974 Unary absolute value. 6975 fcmpeqd, fcmpged, fcmpgtd, fcmpled, fcmpltd, fcmpned 6976 Comparison operations. 6977 fmind, fmaxd 6978 Double-precision minimum and maximum. These instructions are only generated if -ffinite-math-only is specified. 6979 fsqrtd 6980 Unary square root operation. 6981 fcosd, fsind, ftand, fatand, fexpd, flogd 6982 Double-precision trigonometric and exponential functions. These instructions are only generated if -funsafe-math-optimizations is also specified. 6983 Conversions: 6984 fextsd 6985 Conversion from single precision to double precision. 6986 ftruncds 6987 Conversion from double precision to single precision. 6988 fixsi, fixsu, fixdi, fixdu 6989 Conversion from floating point to signed or unsigned integer types, with truncation towards zero. 6990 round 6991 Conversion from single-precision floating point to signed integer, rounding to the nearest integer and ties away from zero. This corresponds to the "__builtin_lroundf" function when 6992 -fno-math-errno is used. 6993 floatis, floatus, floatid, floatud 6994 Conversion from signed or unsigned integer types to floating-point types. 6995 In addition, all of the following transfer instructions for internal registers X and Y must be provided to use any of the double-precision floating-point instructions. Custom instructions 6996 taking two double-precision source operands expect the first operand in the 64-bit register X. The other operand (or only operand of a unary operation) is given to the custom arithmetic 6997 instruction with the least significant half in source register src1 and the most significant half in src2. A custom instruction that returns a double-precision result returns the most 6998 significant 32 bits in the destination register and the other half in 32-bit register Y. GCC automatically generates the necessary code sequences to write register X and/or read register Y 6999 when double-precision floating-point instructions are used. 7000 fwrx 7001 Write src1 into the least significant half of X and src2 into the most significant half of X. 7002 fwry 7003 Write src1 into Y. 7004 frdxhi, frdxlo 7005 Read the most or least (respectively) significant half of X and store it in dest. 7006 frdy 7007 Read the value of Y and store it into dest. 7008 Note that you can gain more local control over generation of Nios II custom instructions by using the "target("custom-insn=N")" and "target("no-custom-insn")" function attributes or pragmas. 7009 -mcustom-fpu-cfg=name 7010 This option enables a predefined, named set of custom instruction encodings (see -mcustom-insn above). Currently, the following sets are defined: 7011 -mcustom-fpu-cfg=60-1 is equivalent to: -mcustom-fmuls=252 -mcustom-fadds=253 -mcustom-fsubs=254 -fsingle-precision-constant 7012 -mcustom-fpu-cfg=60-2 is equivalent to: -mcustom-fmuls=252 -mcustom-fadds=253 -mcustom-fsubs=254 -mcustom-fdivs=255 -fsingle-precision-constant 7013 -mcustom-fpu-cfg=72-3 is equivalent to: -mcustom-floatus=243 -mcustom-fixsi=244 -mcustom-floatis=245 -mcustom-fcmpgts=246 -mcustom-fcmples=249 -mcustom-fcmpeqs=250 -mcustom-fcmpnes=251 7014 -mcustom-fmuls=252 -mcustom-fadds=253 -mcustom-fsubs=254 -mcustom-fdivs=255 -fsingle-precision-constant 7015 Custom instruction assignments given by individual -mcustom-insn= options override those given by -mcustom-fpu-cfg=, regardless of the order of the options on the command line. 7016 Note that you can gain more local control over selection of a FPU configuration by using the "target("custom-fpu-cfg=name")" function attribute or pragma. 7017 These additional -m options are available for the Altera Nios II ELF (bare-metal) target: 7018 -mhal 7019 Link with HAL BSP. This suppresses linking with the GCC-provided C runtime startup and termination code, and is typically used in conjunction with -msys-crt0= to specify the location of the 7020 alternate startup code provided by the HAL BSP. 7021 -msmallc 7022 Link with a limited version of the C library, -lsmallc, rather than Newlib. 7023 -msys-crt0=startfile 7024 startfile is the file name of the startfile (crt0) to use when linking. This option is only useful in conjunction with -mhal. 7025 -msys-lib=systemlib 7026 systemlib is the library name of the library that provides low-level system calls required by the C library, e.g. "read" and "write". This option is typically used to link with a library 7027 provided by a HAL BSP. 7028 Nvidia PTX Options 7029 These options are defined for Nvidia PTX: 7030 -m32 7031 -m64 7032 Generate code for 32-bit or 64-bit ABI. 7033 -mmainkernel 7034 Link in code for a __main kernel. This is for stand-alone instead of offloading execution. 7035 PDP-11 Options 7036 These options are defined for the PDP-11: 7037 -mfpu 7038 Use hardware FPP floating point. This is the default. (FIS floating point on the PDP-11/40 is not supported.) 7039 -msoft-float 7040 Do not use hardware floating point. 7041 -mac0 7042 Return floating-point results in ac0 (fr0 in Unix assembler syntax). 7043 -mno-ac0 7044 Return floating-point results in memory. This is the default. 7045 -m40 7046 Generate code for a PDP-11/40. 7047 -m45 7048 Generate code for a PDP-11/45. This is the default. 7049 -m10 7050 Generate code for a PDP-11/10. 7051 -mbcopy-builtin 7052 Use inline "movmemhi" patterns for copying memory. This is the default. 7053 -mbcopy 7054 Do not use inline "movmemhi" patterns for copying memory. 7055 -mint16 7056 -mno-int32 7057 Use 16-bit "int". This is the default. 7058 -mint32 7059 -mno-int16 7060 Use 32-bit "int". 7061 -mfloat64 7062 -mno-float32 7063 Use 64-bit "float". This is the default. 7064 -mfloat32 7065 -mno-float64 7066 Use 32-bit "float". 7067 -mabshi 7068 Use "abshi2" pattern. This is the default. 7069 -mno-abshi 7070 Do not use "abshi2" pattern. 7071 -mbranch-expensive 7072 Pretend that branches are expensive. This is for experimenting with code generation only. 7073 -mbranch-cheap 7074 Do not pretend that branches are expensive. This is the default. 7075 -munix-asm 7076 Use Unix assembler syntax. This is the default when configured for pdp11-*-bsd. 7077 -mdec-asm 7078 Use DEC assembler syntax. This is the default when configured for any PDP-11 target other than pdp11-*-bsd. 7079 picoChip Options 7080 These -m options are defined for picoChip implementations: 7081 -mae=ae_type 7082 Set the instruction set, register set, and instruction scheduling parameters for array element type ae_type. Supported values for ae_type are ANY, MUL, and MAC. 7083 -mae=ANY selects a completely generic AE type. Code generated with this option runs on any of the other AE types. The code is not as efficient as it would be if compiled for a specific AE 7084 type, and some types of operation (e.g., multiplication) do not work properly on all types of AE. 7085 -mae=MUL selects a MUL AE type. This is the most useful AE type for compiled code, and is the default. 7086 -mae=MAC selects a DSP-style MAC AE. Code compiled with this option may suffer from poor performance of byte (char) manipulation, since the DSP AE does not provide hardware support for byte 7087 load/stores. 7088 -msymbol-as-address 7089 Enable the compiler to directly use a symbol name as an address in a load/store instruction, without first loading it into a register. Typically, the use of this option generates larger 7090 programs, which run faster than when the option isn't used. However, the results vary from program to program, so it is left as a user option, rather than being permanently enabled. 7091 -mno-inefficient-warnings 7092 Disables warnings about the generation of inefficient code. These warnings can be generated, for example, when compiling code that performs byte-level memory operations on the MAC AE type. 7093 The MAC AE has no hardware support for byte-level memory operations, so all byte load/stores must be synthesized from word load/store operations. This is inefficient and a warning is 7094 generated to indicate that you should rewrite the code to avoid byte operations, or to target an AE type that has the necessary hardware support. This option disables these warnings. 7095 PowerPC Options 7096 These are listed under 7097 RL78 Options 7098 -msim 7099 Links in additional target libraries to support operation within a simulator. 7100 -mmul=none 7101 -mmul=g13 7102 -mmul=rl78 7103 Specifies the type of hardware multiplication support to be used. The default is none, which uses software multiplication functions. The g13 option is for the hardware multiply/divide 7104 peripheral only on the RL78/G13 targets. The rl78 option is for the standard hardware multiplication defined in the RL78 software manual. 7105 -m64bit-doubles 7106 -m32bit-doubles 7107 Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits (-m32bit-doubles) in size. The default is -m32bit-doubles. 7108 IBM RS/6000 and PowerPC Options 7109 These -m options are defined for the IBM RS/6000 and PowerPC: 7110 -mpowerpc-gpopt 7111 -mno-powerpc-gpopt 7112 -mpowerpc-gfxopt 7113 -mno-powerpc-gfxopt 7114 -mpowerpc64 7115 -mno-powerpc64 7116 -mmfcrf 7117 -mno-mfcrf 7118 -mpopcntb 7119 -mno-popcntb 7120 -mpopcntd 7121 -mno-popcntd 7122 -mfprnd 7123 -mno-fprnd 7124 -mcmpb 7125 -mno-cmpb 7126 -mmfpgpr 7127 -mno-mfpgpr 7128 -mhard-dfp 7129 -mno-hard-dfp 7130 You use these options to specify which instructions are available on the processor you are using. The default value of these options is determined when configuring GCC. Specifying the 7131 -mcpu=cpu_type overrides the specification of these options. We recommend you use the -mcpu=cpu_type option rather than the options listed above. 7132 Specifying -mpowerpc-gpopt allows GCC to use the optional PowerPC architecture instructions in the General Purpose group, including floating-point square root. Specifying -mpowerpc-gfxopt 7133 allows GCC to use the optional PowerPC architecture instructions in the Graphics group, including floating-point select. 7134 The -mmfcrf option allows GCC to generate the move from condition register field instruction implemented on the POWER4 processor and other processors that support the PowerPC V2.01 7135 architecture. The -mpopcntb option allows GCC to generate the popcount and double-precision FP reciprocal estimate instruction implemented on the POWER5 processor and other processors that 7136 support the PowerPC V2.02 architecture. The -mpopcntd option allows GCC to generate the popcount instruction implemented on the POWER7 processor and other processors that support the 7137 PowerPC V2.06 architecture. The -mfprnd option allows GCC to generate the FP round to integer instructions implemented on the POWER5+ processor and other processors that support the PowerPC 7138 V2.03 architecture. The -mcmpb option allows GCC to generate the compare bytes instruction implemented on the POWER6 processor and other processors that support the PowerPC V2.05 7139 architecture. The -mmfpgpr option allows GCC to generate the FP move to/from general-purpose register instructions implemented on the POWER6X processor and other processors that support the 7140 extended PowerPC V2.05 architecture. The -mhard-dfp option allows GCC to generate the decimal floating-point instructions implemented on some POWER processors. 7141 The -mpowerpc64 option allows GCC to generate the additional 64-bit instructions that are found in the full PowerPC64 architecture and to treat GPRs as 64-bit, doubleword quantities. GCC 7142 defaults to -mno-powerpc64. 7143 -mcpu=cpu_type 7144 Set architecture type, register usage, and instruction scheduling parameters for machine type cpu_type. Supported values for cpu_type are 401, 403, 405, 405fp, 440, 440fp, 464, 464fp, 476, 7145 476fp, 505, 601, 602, 603, 603e, 604, 604e, 620, 630, 740, 7400, 7450, 750, 801, 821, 823, 860, 970, 8540, a2, e300c2, e300c3, e500mc, e500mc64, e5500, e6500, ec603e, G3, G4, G5, titan, 7146 power3, power4, power5, power5+, power6, power6x, power7, power8, powerpc, powerpc64, powerpc64le, and rs64. 7147 -mcpu=powerpc, -mcpu=powerpc64, and -mcpu=powerpc64le specify pure 32-bit PowerPC (either endian), 64-bit big endian PowerPC and 64-bit little endian PowerPC architecture machine types, with 7148 an appropriate, generic processor model assumed for scheduling purposes. 7149 The other options specify a specific processor. Code generated under those options runs best on that processor, and may not run at all on others. 7150 The -mcpu options automatically enable or disable the following options: 7151 -maltivec -mfprnd -mhard-float -mmfcrf -mmultiple -mpopcntb -mpopcntd -mpowerpc64 -mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float -msimple-fpu -mstring -mmulhw 7152 -mdlmzb -mmfpgpr -mvsx -mcrypto -mdirect-move -mpower8-fusion -mpower8-vector -mquad-memory -mquad-memory-atomic 7153 The particular options set for any particular CPU varies between compiler versions, depending on what setting seems to produce optimal code for that CPU; it doesn't necessarily reflect the 7154 actual hardware's capabilities. If you wish to set an individual option to a particular value, you may specify it after the -mcpu option, like -mcpu=970 -mno-altivec. 7155 On AIX, the -maltivec and -mpowerpc64 options are not enabled or disabled by the -mcpu option at present because AIX does not have full support for these options. You may still enable or 7156 disable them individually if you're sure it'll work in your environment. 7157 -mtune=cpu_type 7158 Set the instruction scheduling parameters for machine type cpu_type, but do not set the architecture type or register usage, as -mcpu=cpu_type does. The same values for cpu_type are used 7159 for -mtune as for -mcpu. If both are specified, the code generated uses the architecture and registers set by -mcpu, but the scheduling parameters set by -mtune. 7160 -mcmodel=small 7161 Generate PowerPC64 code for the small model: The TOC is limited to 64k. 7162 -mcmodel=medium 7163 Generate PowerPC64 code for the medium model: The TOC and other static data may be up to a total of 4G in size. 7164 -mcmodel=large 7165 Generate PowerPC64 code for the large model: The TOC may be up to 4G in size. Other data and code is only limited by the 64-bit address space. 7166 -maltivec 7167 -mno-altivec 7168 Generate code that uses (does not use) AltiVec instructions, and also enable the use of built-in functions that allow more direct access to the AltiVec instruction set. You may also need to 7169 set -mabi=altivec to adjust the current ABI with AltiVec ABI enhancements. 7170 When -maltivec is used, rather than -maltivec=le or -maltivec=be, the element order for Altivec intrinsics such as "vec_splat", "vec_extract", and "vec_insert" match array element order 7171 corresponding to the endianness of the target. That is, element zero identifies the leftmost element in a vector register when targeting a big-endian platform, and identifies the rightmost 7172 element in a vector register when targeting a little-endian platform. 7173 -maltivec=be 7174 Generate Altivec instructions using big-endian element order, regardless of whether the target is big- or little-endian. This is the default when targeting a big-endian platform. 7175 The element order is used to interpret element numbers in Altivec intrinsics such as "vec_splat", "vec_extract", and "vec_insert". By default, these match array element order corresponding 7176 to the endianness for the target. 7177 -maltivec=le 7178 Generate Altivec instructions using little-endian element order, regardless of whether the target is big- or little-endian. This is the default when targeting a little-endian platform. 7179 This option is currently ignored when targeting a big-endian platform. 7180 The element order is used to interpret element numbers in Altivec intrinsics such as "vec_splat", "vec_extract", and "vec_insert". By default, these match array element order corresponding 7181 to the endianness for the target. 7182 -mvrsave 7183 -mno-vrsave 7184 Generate VRSAVE instructions when generating AltiVec code. 7185 -mgen-cell-microcode 7186 Generate Cell microcode instructions. 7187 -mwarn-cell-microcode 7188 Warn when a Cell microcode instruction is emitted. An example of a Cell microcode instruction is a variable shift. 7189 -msecure-plt 7190 Generate code that allows ld and ld.so to build executables and shared libraries with non-executable ".plt" and ".got" sections. This is a PowerPC 32-bit SYSV ABI option. 7191 -mbss-plt 7192 Generate code that uses a BSS ".plt" section that ld.so fills in, and requires ".plt" and ".got" sections that are both writable and executable. This is a PowerPC 32-bit SYSV ABI option. 7193 -misel 7194 -mno-isel 7195 This switch enables or disables the generation of ISEL instructions. 7196 -misel=yes/no 7197 This switch has been deprecated. Use -misel and -mno-isel instead. 7198 -mspe 7199 -mno-spe 7200 This switch enables or disables the generation of SPE simd instructions. 7201 -mpaired 7202 -mno-paired 7203 This switch enables or disables the generation of PAIRED simd instructions. 7204 -mspe=yes/no 7205 This option has been deprecated. Use -mspe and -mno-spe instead. 7206 -mvsx 7207 -mno-vsx 7208 Generate code that uses (does not use) vector/scalar (VSX) instructions, and also enable the use of built-in functions that allow more direct access to the VSX instruction set. 7209 -mcrypto 7210 -mno-crypto 7211 Enable the use (disable) of the built-in functions that allow direct access to the cryptographic instructions that were added in version 2.07 of the PowerPC ISA. 7212 -mdirect-move 7213 -mno-direct-move 7214 Generate code that uses (does not use) the instructions to move data between the general purpose registers and the vector/scalar (VSX) registers that were added in version 2.07 of the 7215 PowerPC ISA. 7216 -mpower8-fusion 7217 -mno-power8-fusion 7218 Generate code that keeps (does not keeps) some integer operations adjacent so that the instructions can be fused together on power8 and later processors. 7219 -mpower8-vector 7220 -mno-power8-vector 7221 Generate code that uses (does not use) the vector and scalar instructions that were added in version 2.07 of the PowerPC ISA. Also enable the use of built-in functions that allow more 7222 direct access to the vector instructions. 7223 -mquad-memory 7224 -mno-quad-memory 7225 Generate code that uses (does not use) the non-atomic quad word memory instructions. The -mquad-memory option requires use of 64-bit mode. 7226 -mquad-memory-atomic 7227 -mno-quad-memory-atomic 7228 Generate code that uses (does not use) the atomic quad word memory instructions. The -mquad-memory-atomic option requires use of 64-bit mode. 7229 -mupper-regs-df 7230 -mno-upper-regs-df 7231 Generate code that uses (does not use) the scalar double precision instructions that target all 64 registers in the vector/scalar floating point register set that were added in version 2.06 7232 of the PowerPC ISA. -mupper-regs-df is turned on by default if you use any of the -mcpu=power7, -mcpu=power8, or -mvsx options. 7233 -mupper-regs-sf 7234 -mno-upper-regs-sf 7235 Generate code that uses (does not use) the scalar single precision instructions that target all 64 registers in the vector/scalar floating point register set that were added in version 2.07 7236 of the PowerPC ISA. -mupper-regs-sf is turned on by default if you use either of the -mcpu=power8 or -mpower8-vector options. 7237 -mupper-regs 7238 -mno-upper-regs 7239 Generate code that uses (does not use) the scalar instructions that target all 64 registers in the vector/scalar floating point register set, depending on the model of the machine. 7240 If the -mno-upper-regs option is used, it turns off both -mupper-regs-sf and -mupper-regs-df options. 7241 -mfloat-gprs=yes/single/double/no 7242 -mfloat-gprs 7243 This switch enables or disables the generation of floating-point operations on the general-purpose registers for architectures that support it. 7244 The argument yes or single enables the use of single-precision floating-point operations. 7245 The argument double enables the use of single and double-precision floating-point operations. 7246 The argument no disables floating-point operations on the general-purpose registers. 7247 This option is currently only available on the MPC854x. 7248 -m32 7249 -m64 7250 Generate code for 32-bit or 64-bit environments of Darwin and SVR4 targets (including GNU/Linux). The 32-bit environment sets int, long and pointer to 32 bits and generates code that runs 7251 on any PowerPC variant. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits, and generates code for PowerPC64, as for -mpowerpc64. 7252 -mfull-toc 7253 -mno-fp-in-toc 7254 -mno-sum-in-toc 7255 -mminimal-toc 7256 Modify generation of the TOC (Table Of Contents), which is created for every executable file. The -mfull-toc option is selected by default. In that case, GCC allocates at least one TOC 7257 entry for each unique non-automatic variable reference in your program. GCC also places floating-point constants in the TOC. However, only 16,384 entries are available in the TOC. 7258 If you receive a linker error message that saying you have overflowed the available TOC space, you can reduce the amount of TOC space used with the -mno-fp-in-toc and -mno-sum-in-toc 7259 options. -mno-fp-in-toc prevents GCC from putting floating-point constants in the TOC and -mno-sum-in-toc forces GCC to generate code to calculate the sum of an address and a constant at 7260 run time instead of putting that sum into the TOC. You may specify one or both of these options. Each causes GCC to produce very slightly slower and larger code at the expense of 7261 conserving TOC space. 7262 If you still run out of space in the TOC even when you specify both of these options, specify -mminimal-toc instead. This option causes GCC to make only one TOC entry for every file. When 7263 you specify this option, GCC produces code that is slower and larger but which uses extremely little TOC space. You may wish to use this option only on files that contain less frequently- 7264 executed code. 7265 -maix64 7266 -maix32 7267 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit "long" type, and the infrastructure needed to support them. Specifying -maix64 implies -mpowerpc64, while -maix32 7268 disables the 64-bit ABI and implies -mno-powerpc64. GCC defaults to -maix32. 7269 -mxl-compat 7270 -mno-xl-compat 7271 Produce code that conforms more closely to IBM XL compiler semantics when using AIX-compatible ABI. Pass floating-point arguments to prototyped functions beyond the register save area (RSA) 7272 on the stack in addition to argument FPRs. Do not assume that most significant double in 128-bit long double value is properly rounded when comparing values and converting to double. Use 7273 XL symbol names for long double support routines. 7274 The AIX calling convention was extended but not initially documented to handle an obscure K&R C case of calling a function that takes the address of its arguments with fewer arguments than 7275 declared. IBM XL compilers access floating-point arguments that do not fit in the RSA from the stack when a subroutine is compiled without optimization. Because always storing floating- 7276 point arguments on the stack is inefficient and rarely needed, this option is not enabled by default and only is necessary when calling subroutines compiled by IBM XL compilers without 7277 optimization. 7278 -mpe 7279 Support IBM RS/6000 SP Parallel Environment (PE). Link an application written to use message passing with special startup code to enable the application to run. The system must have PE 7280 installed in the standard location (/usr/lpp/ppe.poe/), or the specs file must be overridden with the -specs= option to specify the appropriate directory location. The Parallel Environment 7281 does not support threads, so the -mpe option and the -pthread option are incompatible. 7282 -malign-natural 7283 -malign-power 7284 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option -malign-natural overrides the ABI-defined alignment of larger types, such as floating-point doubles, on their natural size- 7285 based boundary. The option -malign-power instructs GCC to follow the ABI-specified alignment rules. GCC defaults to the standard alignment defined in the ABI. 7286 On 64-bit Darwin, natural alignment is the default, and -malign-power is not supported. 7287 -msoft-float 7288 -mhard-float 7289 Generate code that does not use (uses) the floating-point register set. Software floating-point emulation is provided if you use the -msoft-float option, and pass the option to GCC when 7290 linking. 7291 -msingle-float 7292 -mdouble-float 7293 Generate code for single- or double-precision floating-point operations. -mdouble-float implies -msingle-float. 7294 -msimple-fpu 7295 Do not generate "sqrt" and "div" instructions for hardware floating-point unit. 7296 -mfpu=name 7297 Specify type of floating-point unit. Valid values for name are sp_lite (equivalent to -msingle-float -msimple-fpu), dp_lite (equivalent to -mdouble-float -msimple-fpu), sp_full (equivalent 7298 to -msingle-float), and dp_full (equivalent to -mdouble-float). 7299 -mxilinx-fpu 7300 Perform optimizations for the floating-point unit on Xilinx PPC 405/440. 7301 -mmultiple 7302 -mno-multiple 7303 Generate code that uses (does not use) the load multiple word instructions and the store multiple word instructions. These instructions are generated by default on POWER systems, and not 7304 generated on PowerPC systems. Do not use -mmultiple on little-endian PowerPC systems, since those instructions do not work when the processor is in little-endian mode. The exceptions are 7305 PPC740 and PPC750 which permit these instructions in little-endian mode. 7306 -mstring 7307 -mno-string 7308 Generate code that uses (does not use) the load string instructions and the store string word instructions to save multiple registers and do small block moves. These instructions are 7309 generated by default on POWER systems, and not generated on PowerPC systems. Do not use -mstring on little-endian PowerPC systems, since those instructions do not work when the processor is 7310 in little-endian mode. The exceptions are PPC740 and PPC750 which permit these instructions in little-endian mode. 7311 -mupdate 7312 -mno-update 7313 Generate code that uses (does not use) the load or store instructions that update the base register to the address of the calculated memory location. These instructions are generated by 7314 default. If you use -mno-update, there is a small window between the time that the stack pointer is updated and the address of the previous frame is stored, which means code that walks the 7315 stack frame across interrupts or signals may get corrupted data. 7316 -mavoid-indexed-addresses 7317 -mno-avoid-indexed-addresses 7318 Generate code that tries to avoid (not avoid) the use of indexed load or store instructions. These instructions can incur a performance penalty on Power6 processors in certain situations, 7319 such as when stepping through large arrays that cross a 16M boundary. This option is enabled by default when targeting Power6 and disabled otherwise. 7320 -mfused-madd 7321 -mno-fused-madd 7322 Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. The machine- 7323 dependent -mfused-madd option is now mapped to the machine-independent -ffp-contract=fast option, and -mno-fused-madd is mapped to -ffp-contract=off. 7324 -mmulhw 7325 -mno-mulhw 7326 Generate code that uses (does not use) the half-word multiply and multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors. These instructions are generated by default 7327 when targeting those processors. 7328 -mdlmzb 7329 -mno-dlmzb 7330 Generate code that uses (does not use) the string-search dlmzb instruction on the IBM 405, 440, 464 and 476 processors. This instruction is generated by default when targeting those 7331 processors. 7332 -mno-bit-align 7333 -mbit-align 7334 On System V.4 and embedded PowerPC systems do not (do) force structures and unions that contain bit-fields to be aligned to the base type of the bit-field. 7335 For example, by default a structure containing nothing but 8 "unsigned" bit-fields of length 1 is aligned to a 4-byte boundary and has a size of 4 bytes. By using -mno-bit-align, the 7336 structure is aligned to a 1-byte boundary and is 1 byte in size. 7337 -mno-strict-align 7338 -mstrict-align 7339 On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory references are handled by the system. 7340 -mrelocatable 7341 -mno-relocatable 7342 Generate code that allows (does not allow) a static executable to be relocated to a different address at run time. A simple embedded PowerPC system loader should relocate the entire 7343 contents of ".got2" and 4-byte locations listed in the ".fixup" section, a table of 32-bit addresses generated by this option. For this to work, all objects linked together must be compiled 7344 with -mrelocatable or -mrelocatable-lib. -mrelocatable code aligns the stack to an 8-byte boundary. 7345 -mrelocatable-lib 7346 -mno-relocatable-lib 7347 Like -mrelocatable, -mrelocatable-lib generates a ".fixup" section to allow static executables to be relocated at run time, but -mrelocatable-lib does not use the smaller stack alignment of 7348 -mrelocatable. Objects compiled with -mrelocatable-lib may be linked with objects compiled with any combination of the -mrelocatable options. 7349 -mno-toc 7350 -mtoc 7351 On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains a pointer to a global area pointing to the addresses used in the program. 7352 -mlittle 7353 -mlittle-endian 7354 On System V.4 and embedded PowerPC systems compile code for the processor in little-endian mode. The -mlittle-endian option is the same as -mlittle. 7355 -mbig 7356 -mbig-endian 7357 On System V.4 and embedded PowerPC systems compile code for the processor in big-endian mode. The -mbig-endian option is the same as -mbig. 7358 -mdynamic-no-pic 7359 On Darwin and Mac OS X systems, compile code so that it is not relocatable, but that its external references are relocatable. The resulting code is suitable for applications, but not shared 7360 libraries. 7361 -msingle-pic-base 7362 Treat the register used for PIC addressing as read-only, rather than loading it in the prologue for each function. The runtime system is responsible for initializing this register with an 7363 appropriate value before execution begins. 7364 -mprioritize-restricted-insns=priority 7365 This option controls the priority that is assigned to dispatch-slot restricted instructions during the second scheduling pass. The argument priority takes the value 0, 1, or 2 to assign no, 7366 highest, or second-highest (respectively) priority to dispatch-slot restricted instructions. 7367 -msched-costly-dep=dependence_type 7368 This option controls which dependences are considered costly by the target during instruction scheduling. The argument dependence_type takes one of the following values: 7369 no No dependence is costly. 7370 all All dependences are costly. 7371 true_store_to_load 7372 A true dependence from store to load is costly. 7373 store_to_load 7374 Any dependence from store to load is costly. 7375 number 7376 Any dependence for which the latency is greater than or equal to number is costly. 7377 -minsert-sched-nops=scheme 7378 This option controls which NOP insertion scheme is used during the second scheduling pass. The argument scheme takes one of the following values: 7379 no Don't insert NOPs. 7380 pad Pad with NOPs any dispatch group that has vacant issue slots, according to the scheduler's grouping. 7381 regroup_exact 7382 Insert NOPs to force costly dependent insns into separate groups. Insert exactly as many NOPs as needed to force an insn to a new group, according to the estimated processor grouping. 7383 number 7384 Insert NOPs to force costly dependent insns into separate groups. Insert number NOPs to force an insn to a new group. 7385 -mcall-sysv 7386 On System V.4 and embedded PowerPC systems compile code using calling conventions that adhere to the March 1995 draft of the System V Application Binary Interface, PowerPC processor 7387 supplement. This is the default unless you configured GCC using powerpc-*-eabiaix. 7388 -mcall-sysv-eabi 7389 -mcall-eabi 7390 Specify both -mcall-sysv and -meabi options. 7391 -mcall-sysv-noeabi 7392 Specify both -mcall-sysv and -mno-eabi options. 7393 -mcall-aixdesc 7394 On System V.4 and embedded PowerPC systems compile code for the AIX operating system. 7395 -mcall-linux 7396 On System V.4 and embedded PowerPC systems compile code for the Linux-based GNU system. 7397 -mcall-freebsd 7398 On System V.4 and embedded PowerPC systems compile code for the FreeBSD operating system. 7399 -mcall-netbsd 7400 On System V.4 and embedded PowerPC systems compile code for the NetBSD operating system. 7401 -mcall-openbsd 7402 On System V.4 and embedded PowerPC systems compile code for the OpenBSD operating system. 7403 -maix-struct-return 7404 Return all structures in memory (as specified by the AIX ABI). 7405 -msvr4-struct-return 7406 Return structures smaller than 8 bytes in registers (as specified by the SVR4 ABI). 7407 -mabi=abi-type 7408 Extend the current ABI with a particular extension, or remove such extension. Valid values are altivec, no-altivec, spe, no-spe, ibmlongdouble, ieeelongdouble, elfv1, elfv2. 7409 -mabi=spe 7410 Extend the current ABI with SPE ABI extensions. This does not change the default ABI, instead it adds the SPE ABI extensions to the current ABI. 7411 -mabi=no-spe 7412 Disable Book-E SPE ABI extensions for the current ABI. 7413 -mabi=ibmlongdouble 7414 Change the current ABI to use IBM extended-precision long double. This is a PowerPC 32-bit SYSV ABI option. 7415 -mabi=ieeelongdouble 7416 Change the current ABI to use IEEE extended-precision long double. This is a PowerPC 32-bit Linux ABI option. 7417 -mabi=elfv1 7418 Change the current ABI to use the ELFv1 ABI. This is the default ABI for big-endian PowerPC 64-bit Linux. Overriding the default ABI requires special system support and is likely to fail 7419 in spectacular ways. 7420 -mabi=elfv2 7421 Change the current ABI to use the ELFv2 ABI. This is the default ABI for little-endian PowerPC 64-bit Linux. Overriding the default ABI requires special system support and is likely to 7422 fail in spectacular ways. 7423 -mprototype 7424 -mno-prototype 7425 On System V.4 and embedded PowerPC systems assume that all calls to variable argument functions are properly prototyped. Otherwise, the compiler must insert an instruction before every non- 7426 prototyped call to set or clear bit 6 of the condition code register ("CR") to indicate whether floating-point values are passed in the floating-point registers in case the function takes 7427 variable arguments. With -mprototype, only calls to prototyped variable argument functions set or clear the bit. 7428 -msim 7429 On embedded PowerPC systems, assume that the startup module is called sim-crt0.o and that the standard C libraries are libsim.a and libc.a. This is the default for powerpc-*-eabisim 7430 configurations. 7431 -mmvme 7432 On embedded PowerPC systems, assume that the startup module is called crt0.o and the standard C libraries are libmvme.a and libc.a. 7433 -mads 7434 On embedded PowerPC systems, assume that the startup module is called crt0.o and the standard C libraries are libads.a and libc.a. 7435 -myellowknife 7436 On embedded PowerPC systems, assume that the startup module is called crt0.o and the standard C libraries are libyk.a and libc.a. 7437 -mvxworks 7438 On System V.4 and embedded PowerPC systems, specify that you are compiling for a VxWorks system. 7439 -memb 7440 On embedded PowerPC systems, set the "PPC_EMB" bit in the ELF flags header to indicate that eabi extended relocations are used. 7441 -meabi 7442 -mno-eabi 7443 On System V.4 and embedded PowerPC systems do (do not) adhere to the Embedded Applications Binary Interface (EABI), which is a set of modifications to the System V.4 specifications. 7444 Selecting -meabi means that the stack is aligned to an 8-byte boundary, a function "__eabi" is called from "main" to set up the EABI environment, and the -msdata option can use both "r2" and 7445 "r13" to point to two separate small data areas. Selecting -mno-eabi means that the stack is aligned to a 16-byte boundary, no EABI initialization function is called from "main", and the 7446 -msdata option only uses "r13" to point to a single small data area. The -meabi option is on by default if you configured GCC using one of the powerpc*-*-eabi* options. 7447 -msdata=eabi 7448 On System V.4 and embedded PowerPC systems, put small initialized "const" global and static data in the ".sdata2" section, which is pointed to by register "r2". Put small initialized 7449 non-"const" global and static data in the ".sdata" section, which is pointed to by register "r13". Put small uninitialized global and static data in the ".sbss" section, which is adjacent 7450 to the ".sdata" section. The -msdata=eabi option is incompatible with the -mrelocatable option. The -msdata=eabi option also sets the -memb option. 7451 -msdata=sysv 7452 On System V.4 and embedded PowerPC systems, put small global and static data in the ".sdata" section, which is pointed to by register "r13". Put small uninitialized global and static data 7453 in the ".sbss" section, which is adjacent to the ".sdata" section. The -msdata=sysv option is incompatible with the -mrelocatable option. 7454 -msdata=default 7455 -msdata 7456 On System V.4 and embedded PowerPC systems, if -meabi is used, compile code the same as -msdata=eabi, otherwise compile code the same as -msdata=sysv. 7457 -msdata=data 7458 On System V.4 and embedded PowerPC systems, put small global data in the ".sdata" section. Put small uninitialized global data in the ".sbss" section. Do not use register "r13" to address 7459 small data however. This is the default behavior unless other -msdata options are used. 7460 -msdata=none 7461 -mno-sdata 7462 On embedded PowerPC systems, put all initialized global and static data in the ".data" section, and all uninitialized data in the ".bss" section. 7463 -mblock-move-inline-limit=num 7464 Inline all block moves (such as calls to "memcpy" or structure copies) less than or equal to num bytes. The minimum value for num is 32 bytes on 32-bit targets and 64 bytes on 64-bit 7465 targets. The default value is target-specific. 7466 -G num 7467 On embedded PowerPC systems, put global and static items less than or equal to num bytes into the small data or BSS sections instead of the normal data or BSS section. By default, num is 8. 7468 The -G num switch is also passed to the linker. All modules should be compiled with the same -G num value. 7469 -mregnames 7470 -mno-regnames 7471 On System V.4 and embedded PowerPC systems do (do not) emit register names in the assembly language output using symbolic forms. 7472 -mlongcall 7473 -mno-longcall 7474 By default assume that all calls are far away so that a longer and more expensive calling sequence is required. This is required for calls farther than 32 megabytes (33,554,432 bytes) from 7475 the current location. A short call is generated if the compiler knows the call cannot be that far away. This setting can be overridden by the "shortcall" function attribute, or by "#pragma 7476 longcall(0)". 7477 Some linkers are capable of detecting out-of-range calls and generating glue code on the fly. On these systems, long calls are unnecessary and generate slower code. As of this writing, the 7478 AIX linker can do this, as can the GNU linker for PowerPC/64. It is planned to add this feature to the GNU linker for 32-bit PowerPC systems as well. 7479 On Darwin/PPC systems, "#pragma longcall" generates "jbsr callee, L42", plus a branch island (glue code). The two target addresses represent the callee and the branch island. The 7480 Darwin/PPC linker prefers the first address and generates a "bl callee" if the PPC "bl" instruction reaches the callee directly; otherwise, the linker generates "bl L42" to call the branch 7481 island. The branch island is appended to the body of the calling function; it computes the full 32-bit address of the callee and jumps to it. 7482 On Mach-O (Darwin) systems, this option directs the compiler emit to the glue for every direct call, and the Darwin linker decides whether to use or discard it. 7483 In the future, GCC may ignore all longcall specifications when the linker is known to generate glue. 7484 -mtls-markers 7485 -mno-tls-markers 7486 Mark (do not mark) calls to "__tls_get_addr" with a relocation specifying the function argument. The relocation allows the linker to reliably associate function call with argument setup 7487 instructions for TLS optimization, which in turn allows GCC to better schedule the sequence. 7488 -pthread 7489 Adds support for multithreading with the pthreads library. This option sets flags for both the preprocessor and linker. 7490 -mrecip 7491 -mno-recip 7492 This option enables use of the reciprocal estimate and reciprocal square root estimate instructions with additional Newton-Raphson steps to increase precision instead of doing a divide or 7493 square root and divide for floating-point arguments. You should use the -ffast-math option when using -mrecip (or at least -funsafe-math-optimizations, -finite-math-only, -freciprocal-math 7494 and -fno-trapping-math). Note that while the throughput of the sequence is generally higher than the throughput of the non-reciprocal instruction, the precision of the sequence can be 7495 decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994) for reciprocal square roots. 7496 -mrecip=opt 7497 This option controls which reciprocal estimate instructions may be used. opt is a comma-separated list of options, which may be preceded by a "!" to invert the option: 7498 all Enable all estimate instructions. 7499 default 7500 Enable the default instructions, equivalent to -mrecip. 7501 none 7502 Disable all estimate instructions, equivalent to -mno-recip. 7503 div Enable the reciprocal approximation instructions for both single and double precision. 7504 divf 7505 Enable the single-precision reciprocal approximation instructions. 7506 divd 7507 Enable the double-precision reciprocal approximation instructions. 7508 rsqrt 7509 Enable the reciprocal square root approximation instructions for both single and double precision. 7510 rsqrtf 7511 Enable the single-precision reciprocal square root approximation instructions. 7512 rsqrtd 7513 Enable the double-precision reciprocal square root approximation instructions. 7514 So, for example, -mrecip=all,!rsqrtd enables all of the reciprocal estimate instructions, except for the "FRSQRTE", "XSRSQRTEDP", and "XVRSQRTEDP" instructions which handle the double- 7515 precision reciprocal square root calculations. 7516 -mrecip-precision 7517 -mno-recip-precision 7518 Assume (do not assume) that the reciprocal estimate instructions provide higher-precision estimates than is mandated by the PowerPC ABI. Selecting -mcpu=power6, -mcpu=power7 or -mcpu=power8 7519 automatically selects -mrecip-precision. The double-precision square root estimate instructions are not generated by default on low-precision machines, since they do not provide an estimate 7520 that converges after three steps. 7521 -mveclibabi=type 7522 Specifies the ABI type to use for vectorizing intrinsics using an external library. The only type supported at present is mass, which specifies to use IBM's Mathematical Acceleration 7523 Subsystem (MASS) libraries for vectorizing intrinsics using external libraries. GCC currently emits calls to "acosd2", "acosf4", "acoshd2", "acoshf4", "asind2", "asinf4", "asinhd2", 7524 "asinhf4", "atan2d2", "atan2f4", "atand2", "atanf4", "atanhd2", "atanhf4", "cbrtd2", "cbrtf4", "cosd2", "cosf4", "coshd2", "coshf4", "erfcd2", "erfcf4", "erfd2", "erff4", "exp2d2", "exp2f4", 7525 "expd2", "expf4", "expm1d2", "expm1f4", "hypotd2", "hypotf4", "lgammad2", "lgammaf4", "log10d2", "log10f4", "log1pd2", "log1pf4", "log2d2", "log2f4", "logd2", "logf4", "powd2", "powf4", 7526 "sind2", "sinf4", "sinhd2", "sinhf4", "sqrtd2", "sqrtf4", "tand2", "tanf4", "tanhd2", and "tanhf4" when generating code for power7. Both -ftree-vectorize and -funsafe-math-optimizations 7527 must also be enabled. The MASS libraries must be specified at link time. 7528 -mfriz 7529 -mno-friz 7530 Generate (do not generate) the "friz" instruction when the -funsafe-math-optimizations option is used to optimize rounding of floating-point values to 64-bit integer and back to floating 7531 point. The "friz" instruction does not return the same value if the floating-point number is too large to fit in an integer. 7532 -mpointers-to-nested-functions 7533 -mno-pointers-to-nested-functions 7534 Generate (do not generate) code to load up the static chain register ("r11") when calling through a pointer on AIX and 64-bit Linux systems where a function pointer points to a 3-word 7535 descriptor giving the function address, TOC value to be loaded in register "r2", and static chain value to be loaded in register "r11". The -mpointers-to-nested-functions is on by default. 7536 You cannot call through pointers to nested functions or pointers to functions compiled in other languages that use the static chain if you use -mno-pointers-to-nested-functions. 7537 -msave-toc-indirect 7538 -mno-save-toc-indirect 7539 Generate (do not generate) code to save the TOC value in the reserved stack location in the function prologue if the function calls through a pointer on AIX and 64-bit Linux systems. If the 7540 TOC value is not saved in the prologue, it is saved just before the call through the pointer. The -mno-save-toc-indirect option is the default. 7541 -mcompat-align-parm 7542 -mno-compat-align-parm 7543 Generate (do not generate) code to pass structure parameters with a maximum alignment of 64 bits, for compatibility with older versions of GCC. 7544 Older versions of GCC (prior to 4.9.0) incorrectly did not align a structure parameter on a 128-bit boundary when that structure contained a member requiring 128-bit alignment. This is 7545 corrected in more recent versions of GCC. This option may be used to generate code that is compatible with functions compiled with older versions of GCC. 7546 The -mno-compat-align-parm option is the default. 7547 RX Options 7548 These command-line options are defined for RX targets: 7549 -m64bit-doubles 7550 -m32bit-doubles 7551 Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits (-m32bit-doubles) in size. The default is -m32bit-doubles. Note RX floating-point hardware only works on 32-bit values, 7552 which is why the default is -m32bit-doubles. 7553 -fpu 7554 -nofpu 7555 Enables (-fpu) or disables (-nofpu) the use of RX floating-point hardware. The default is enabled for the RX600 series and disabled for the RX200 series. 7556 Floating-point instructions are only generated for 32-bit floating-point values, however, so the FPU hardware is not used for doubles if the -m64bit-doubles option is used. 7557 Note If the -fpu option is enabled then -funsafe-math-optimizations is also enabled automatically. This is because the RX FPU instructions are themselves unsafe. 7558 -mcpu=name 7559 Selects the type of RX CPU to be targeted. Currently three types are supported, the generic RX600 and RX200 series hardware and the specific RX610 CPU. The default is RX600. 7560 The only difference between RX600 and RX610 is that the RX610 does not support the "MVTIPL" instruction. 7561 The RX200 series does not have a hardware floating-point unit and so -nofpu is enabled by default when this type is selected. 7562 -mbig-endian-data 7563 -mlittle-endian-data 7564 Store data (but not code) in the big-endian format. The default is -mlittle-endian-data, i.e. to store data in the little-endian format. 7565 -msmall-data-limit=N 7566 Specifies the maximum size in bytes of global and static variables which can be placed into the small data area. Using the small data area can lead to smaller and faster code, but the size 7567 of area is limited and it is up to the programmer to ensure that the area does not overflow. Also when the small data area is used one of the RX's registers (usually "r13") is reserved for 7568 use pointing to this area, so it is no longer available for use by the compiler. This could result in slower and/or larger code if variables are pushed onto the stack instead of being held 7569 in this register. 7570 Note, common variables (variables that have not been initialized) and constants are not placed into the small data area as they are assigned to other sections in the output executable. 7571 The default value is zero, which disables this feature. Note, this feature is not enabled by default with higher optimization levels (-O2 etc) because of the potentially detrimental effects 7572 of reserving a register. It is up to the programmer to experiment and discover whether this feature is of benefit to their program. See the description of the -mpid option for a 7573 description of how the actual register to hold the small data area pointer is chosen. 7574 -msim 7575 -mno-sim 7576 Use the simulator runtime. The default is to use the libgloss board-specific runtime. 7577 -mas100-syntax 7578 -mno-as100-syntax 7579 When generating assembler output use a syntax that is compatible with Renesas's AS100 assembler. This syntax can also be handled by the GAS assembler, but it has some restrictions so it is 7580 not generated by default. 7581 -mmax-constant-size=N 7582 Specifies the maximum size, in bytes, of a constant that can be used as an operand in a RX instruction. Although the RX instruction set does allow constants of up to 4 bytes in length to be 7583 used in instructions, a longer value equates to a longer instruction. Thus in some circumstances it can be beneficial to restrict the size of constants that are used in instructions. 7584 Constants that are too big are instead placed into a constant pool and referenced via register indirection. 7585 The value N can be between 0 and 4. A value of 0 (the default) or 4 means that constants of any size are allowed. 7586 -mrelax 7587 Enable linker relaxation. Linker relaxation is a process whereby the linker attempts to reduce the size of a program by finding shorter versions of various instructions. Disabled by 7588 default. 7589 -mint-register=N 7590 Specify the number of registers to reserve for fast interrupt handler functions. The value N can be between 0 and 4. A value of 1 means that register "r13" is reserved for the exclusive 7591 use of fast interrupt handlers. A value of 2 reserves "r13" and "r12". A value of 3 reserves "r13", "r12" and "r11", and a value of 4 reserves "r13" through "r10". A value of 0, the 7592 default, does not reserve any registers. 7593 -msave-acc-in-interrupts 7594 Specifies that interrupt handler functions should preserve the accumulator register. This is only necessary if normal code might use the accumulator register, for example because it 7595 performs 64-bit multiplications. The default is to ignore the accumulator as this makes the interrupt handlers faster. 7596 -mpid 7597 -mno-pid 7598 Enables the generation of position independent data. When enabled any access to constant data is done via an offset from a base address held in a register. This allows the location of 7599 constant data to be determined at run time without requiring the executable to be relocated, which is a benefit to embedded applications with tight memory constraints. Data that can be 7600 modified is not affected by this option. 7601 Note, using this feature reserves a register, usually "r13", for the constant data base address. This can result in slower and/or larger code, especially in complicated functions. 7602 The actual register chosen to hold the constant data base address depends upon whether the -msmall-data-limit and/or the -mint-register command-line options are enabled. Starting with 7603 register "r13" and proceeding downwards, registers are allocated first to satisfy the requirements of -mint-register, then -mpid and finally -msmall-data-limit. Thus it is possible for the 7604 small data area register to be "r8" if both -mint-register=4 and -mpid are specified on the command line. 7605 By default this feature is not enabled. The default can be restored via the -mno-pid command-line option. 7606 -mno-warn-multiple-fast-interrupts 7607 -mwarn-multiple-fast-interrupts 7608 Prevents GCC from issuing a warning message if it finds more than one fast interrupt handler when it is compiling a file. The default is to issue a warning for each extra fast interrupt 7609 handler found, as the RX only supports one such interrupt. 7610 Note: The generic GCC command-line option -ffixed-reg has special significance to the RX port when used with the "interrupt" function attribute. This attribute indicates a function intended to 7611 process fast interrupts. GCC ensures that it only uses the registers "r10", "r11", "r12" and/or "r13" and only provided that the normal use of the corresponding registers have been restricted 7612 via the -ffixed-reg or -mint-register command-line options. 7613 S/390 and zSeries Options 7614 These are the -m options defined for the S/390 and zSeries architecture. 7615 -mhard-float 7616 -msoft-float 7617 Use (do not use) the hardware floating-point instructions and registers for floating-point operations. When -msoft-float is specified, functions in libgcc.a are used to perform floating- 7618 point operations. When -mhard-float is specified, the compiler generates IEEE floating-point instructions. This is the default. 7619 -mhard-dfp 7620 -mno-hard-dfp 7621 Use (do not use) the hardware decimal-floating-point instructions for decimal-floating-point operations. When -mno-hard-dfp is specified, functions in libgcc.a are used to perform decimal- 7622 floating-point operations. When -mhard-dfp is specified, the compiler generates decimal-floating-point hardware instructions. This is the default for -march=z9-ec or higher. 7623 -mlong-double-64 7624 -mlong-double-128 7625 These switches control the size of "long double" type. A size of 64 bits makes the "long double" type equivalent to the "double" type. This is the default. 7626 -mbackchain 7627 -mno-backchain 7628 Store (do not store) the address of the caller's frame as backchain pointer into the callee's stack frame. A backchain may be needed to allow debugging using tools that do not understand 7629 DWARF 2 call frame information. When -mno-packed-stack is in effect, the backchain pointer is stored at the bottom of the stack frame; when -mpacked-stack is in effect, the backchain is 7630 placed into the topmost word of the 96/160 byte register save area. 7631 In general, code compiled with -mbackchain is call-compatible with code compiled with -mmo-backchain; however, use of the backchain for debugging purposes usually requires that the whole 7632 binary is built with -mbackchain. Note that the combination of -mbackchain, -mpacked-stack and -mhard-float is not supported. In order to build a linux kernel use -msoft-float. 7633 The default is to not maintain the backchain. 7634 -mpacked-stack 7635 -mno-packed-stack 7636 Use (do not use) the packed stack layout. When -mno-packed-stack is specified, the compiler uses the all fields of the 96/160 byte register save area only for their default purpose; unused 7637 fields still take up stack space. When -mpacked-stack is specified, register save slots are densely packed at the top of the register save area; unused space is reused for other purposes, 7638 allowing for more efficient use of the available stack space. However, when -mbackchain is also in effect, the topmost word of the save area is always used to store the backchain, and the 7639 return address register is always saved two words below the backchain. 7640 As long as the stack frame backchain is not used, code generated with -mpacked-stack is call-compatible with code generated with -mno-packed-stack. Note that some non-FSF releases of GCC 7641 2.95 for S/390 or zSeries generated code that uses the stack frame backchain at run time, not just for debugging purposes. Such code is not call-compatible with code compiled with 7642 -mpacked-stack. Also, note that the combination of -mbackchain, -mpacked-stack and -mhard-float is not supported. In order to build a linux kernel use -msoft-float. 7643 The default is to not use the packed stack layout. 7644 -msmall-exec 7645 -mno-small-exec 7646 Generate (or do not generate) code using the "bras" instruction to do subroutine calls. This only works reliably if the total executable size does not exceed 64k. The default is to use the 7647 "basr" instruction instead, which does not have this limitation. 7648 -m64 7649 -m31 7650 When -m31 is specified, generate code compliant to the GNU/Linux for S/390 ABI. When -m64 is specified, generate code compliant to the GNU/Linux for zSeries ABI. This allows GCC in 7651 particular to generate 64-bit instructions. For the s390 targets, the default is -m31, while the s390x targets default to -m64. 7652 -mzarch 7653 -mesa 7654 When -mzarch is specified, generate code using the instructions available on z/Architecture. When -mesa is specified, generate code using the instructions available on ESA/390. Note that 7655 -mesa is not possible with -m64. When generating code compliant to the GNU/Linux for S/390 ABI, the default is -mesa. When generating code compliant to the GNU/Linux for zSeries ABI, the 7656 default is -mzarch. 7657 -mmvcle 7658 -mno-mvcle 7659 Generate (or do not generate) code using the "mvcle" instruction to perform block moves. When -mno-mvcle is specified, use a "mvc" loop instead. This is the default unless optimizing for 7660 size. 7661 -mdebug 7662 -mno-debug 7663 Print (or do not print) additional debug information when compiling. The default is to not print debug information. 7664 -march=cpu-type 7665 Generate code that runs on cpu-type, which is the name of a system representing a certain processor type. Possible values for cpu-type are g5, g6, z900, z990, z9-109, z9-ec, z10, z196, 7666 zEC12, and z13. When generating code using the instructions available on z/Architecture, the default is -march=z900. Otherwise, the default is -march=g5. 7667 -mtune=cpu-type 7668 Tune to cpu-type everything applicable about the generated code, except for the ABI and the set of available instructions. The list of cpu-type values is the same as for -march. The 7669 default is the value used for -march. 7670 -mtpf-trace 7671 -mno-tpf-trace 7672 Generate code that adds (does not add) in TPF OS specific branches to trace routines in the operating system. This option is off by default, even when compiling for the TPF OS. 7673 -mfused-madd 7674 -mno-fused-madd 7675 Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. 7676 -mwarn-framesize=framesize 7677 Emit a warning if the current function exceeds the given frame size. Because this is a compile-time check it doesn't need to be a real problem when the program runs. It is intended to 7678 identify functions that most probably cause a stack overflow. It is useful to be used in an environment with limited stack size e.g. the linux kernel. 7679 -mwarn-dynamicstack 7680 Emit a warning if the function calls "alloca" or uses dynamically-sized arrays. This is generally a bad idea with a limited stack size. 7681 -mstack-guard=stack-guard 7682 -mstack-size=stack-size 7683 If these options are provided the S/390 back end emits additional instructions in the function prologue that trigger a trap if the stack size is stack-guard bytes above the stack-size 7684 (remember that the stack on S/390 grows downward). If the stack-guard option is omitted the smallest power of 2 larger than the frame size of the compiled function is chosen. These options 7685 are intended to be used to help debugging stack overflow problems. The additionally emitted code causes only little overhead and hence can also be used in production-like systems without 7686 greater performance degradation. The given values have to be exact powers of 2 and stack-size has to be greater than stack-guard without exceeding 64k. In order to be efficient the extra 7687 code makes the assumption that the stack starts at an address aligned to the value given by stack-size. The stack-guard option can only be used in conjunction with stack-size. 7688 -mhotpatch=pre-halfwords,post-halfwords 7689 If the hotpatch option is enabled, a "hot-patching" function prologue is generated for all functions in the compilation unit. The funtion label is prepended with the given number of two- 7690 byte NOP instructions (pre-halfwords, maximum 1000000). After the label, 2 * post-halfwords bytes are appended, using the largest NOP like instructions the architecture allows (maximum 7691 1000000). 7692 If both arguments are zero, hotpatching is disabled. 7693 This option can be overridden for individual functions with the "hotpatch" attribute. 7694 Score Options 7695 These options are defined for Score implementations: 7696 -meb 7697 Compile code for big-endian mode. This is the default. 7698 -mel 7699 Compile code for little-endian mode. 7700 -mnhwloop 7701 Disable generation of "bcnz" instructions. 7702 -muls 7703 Enable generation of unaligned load and store instructions. 7704 -mmac 7705 Enable the use of multiply-accumulate instructions. Disabled by default. 7706 -mscore5 7707 Specify the SCORE5 as the target architecture. 7708 -mscore5u 7709 Specify the SCORE5U of the target architecture. 7710 -mscore7 7711 Specify the SCORE7 as the target architecture. This is the default. 7712 -mscore7d 7713 Specify the SCORE7D as the target architecture. 7714 SH Options 7715 These -m options are defined for the SH implementations: 7716 -m1 Generate code for the SH1. 7717 -m2 Generate code for the SH2. 7718 -m2e 7719 Generate code for the SH2e. 7720 -m2a-nofpu 7721 Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way that the floating-point unit is not used. 7722 -m2a-single-only 7723 Generate code for the SH2a-FPU, in such a way that no double-precision floating-point operations are used. 7724 -m2a-single 7725 Generate code for the SH2a-FPU assuming the floating-point unit is in single-precision mode by default. 7726 -m2a 7727 Generate code for the SH2a-FPU assuming the floating-point unit is in double-precision mode by default. 7728 -m3 Generate code for the SH3. 7729 -m3e 7730 Generate code for the SH3e. 7731 -m4-nofpu 7732 Generate code for the SH4 without a floating-point unit. 7733 -m4-single-only 7734 Generate code for the SH4 with a floating-point unit that only supports single-precision arithmetic. 7735 -m4-single 7736 Generate code for the SH4 assuming the floating-point unit is in single-precision mode by default. 7737 -m4 Generate code for the SH4. 7738 -m4-100 7739 Generate code for SH4-100. 7740 -m4-100-nofpu 7741 Generate code for SH4-100 in such a way that the floating-point unit is not used. 7742 -m4-100-single 7743 Generate code for SH4-100 assuming the floating-point unit is in single-precision mode by default. 7744 -m4-100-single-only 7745 Generate code for SH4-100 in such a way that no double-precision floating-point operations are used. 7746 -m4-200 7747 Generate code for SH4-200. 7748 -m4-200-nofpu 7749 Generate code for SH4-200 without in such a way that the floating-point unit is not used. 7750 -m4-200-single 7751 Generate code for SH4-200 assuming the floating-point unit is in single-precision mode by default. 7752 -m4-200-single-only 7753 Generate code for SH4-200 in such a way that no double-precision floating-point operations are used. 7754 -m4-300 7755 Generate code for SH4-300. 7756 -m4-300-nofpu 7757 Generate code for SH4-300 without in such a way that the floating-point unit is not used. 7758 -m4-300-single 7759 Generate code for SH4-300 in such a way that no double-precision floating-point operations are used. 7760 -m4-300-single-only 7761 Generate code for SH4-300 in such a way that no double-precision floating-point operations are used. 7762 -m4-340 7763 Generate code for SH4-340 (no MMU, no FPU). 7764 -m4-500 7765 Generate code for SH4-500 (no FPU). Passes -isa=sh4-nofpu to the assembler. 7766 -m4a-nofpu 7767 Generate code for the SH4al-dsp, or for a SH4a in such a way that the floating-point unit is not used. 7768 -m4a-single-only 7769 Generate code for the SH4a, in such a way that no double-precision floating-point operations are used. 7770 -m4a-single 7771 Generate code for the SH4a assuming the floating-point unit is in single-precision mode by default. 7772 -m4a 7773 Generate code for the SH4a. 7774 -m4al 7775 Same as -m4a-nofpu, except that it implicitly passes -dsp to the assembler. GCC doesn't generate any DSP instructions at the moment. 7776 -m5-32media 7777 Generate 32-bit code for SHmedia. 7778 -m5-32media-nofpu 7779 Generate 32-bit code for SHmedia in such a way that the floating-point unit is not used. 7780 -m5-64media 7781 Generate 64-bit code for SHmedia. 7782 -m5-64media-nofpu 7783 Generate 64-bit code for SHmedia in such a way that the floating-point unit is not used. 7784 -m5-compact 7785 Generate code for SHcompact. 7786 -m5-compact-nofpu 7787 Generate code for SHcompact in such a way that the floating-point unit is not used. 7788 -mb Compile code for the processor in big-endian mode. 7789 -ml Compile code for the processor in little-endian mode. 7790 -mdalign 7791 Align doubles at 64-bit boundaries. Note that this changes the calling conventions, and thus some functions from the standard C library do not work unless you recompile it first with 7792 -mdalign. 7793 -mrelax 7794 Shorten some address references at link time, when possible; uses the linker option -relax. 7795 -mbigtable 7796 Use 32-bit offsets in "switch" tables. The default is to use 16-bit offsets. 7797 -mbitops 7798 Enable the use of bit manipulation instructions on SH2A. 7799 -mfmovd 7800 Enable the use of the instruction "fmovd". Check -mdalign for alignment constraints. 7801 -mrenesas 7802 Comply with the calling conventions defined by Renesas. 7803 -mno-renesas 7804 Comply with the calling conventions defined for GCC before the Renesas conventions were available. This option is the default for all targets of the SH toolchain. 7805 -mnomacsave 7806 Mark the "MAC" register as call-clobbered, even if -mrenesas is given. 7807 -mieee 7808 -mno-ieee 7809 Control the IEEE compliance of floating-point comparisons, which affects the handling of cases where the result of a comparison is unordered. By default -mieee is implicitly enabled. If 7810 -ffinite-math-only is enabled -mno-ieee is implicitly set, which results in faster floating-point greater-equal and less-equal comparisons. The implcit settings can be overridden by 7811 specifying either -mieee or -mno-ieee. 7812 -minline-ic_invalidate 7813 Inline code to invalidate instruction cache entries after setting up nested function trampolines. This option has no effect if -musermode is in effect and the selected code generation 7814 option (e.g. -m4) does not allow the use of the "icbi" instruction. If the selected code generation option does not allow the use of the "icbi" instruction, and -musermode is not in effect, 7815 the inlined code manipulates the instruction cache address array directly with an associative write. This not only requires privileged mode at run time, but it also fails if the cache line 7816 had been mapped via the TLB and has become unmapped. 7817 -misize 7818 Dump instruction size and location in the assembly code. 7819 -mpadstruct 7820 This option is deprecated. It pads structures to multiple of 4 bytes, which is incompatible with the SH ABI. 7821 -matomic-model=model 7822 Sets the model of atomic operations and additional parameters as a comma separated list. For details on the atomic built-in functions see __atomic Builtins. The following models and 7823 parameters are supported: 7824 none 7825 Disable compiler generated atomic sequences and emit library calls for atomic operations. This is the default if the target is not "sh*-*-linux*". 7826 soft-gusa 7827 Generate GNU/Linux compatible gUSA software atomic sequences for the atomic built-in functions. The generated atomic sequences require additional support from the interrupt/exception 7828 handling code of the system and are only suitable for SH3* and SH4* single-core systems. This option is enabled by default when the target is "sh*-*-linux*" and SH3* or SH4*. When the 7829 target is SH4A, this option also partially utilizes the hardware atomic instructions "movli.l" and "movco.l" to create more efficient code, unless strict is specified. 7830 soft-tcb 7831 Generate software atomic sequences that use a variable in the thread control block. This is a variation of the gUSA sequences which can also be used on SH1* and SH2* targets. The 7832 generated atomic sequences require additional support from the interrupt/exception handling code of the system and are only suitable for single-core systems. When using this model, the 7833 gbr-offset= parameter has to be specified as well. 7834 soft-imask 7835 Generate software atomic sequences that temporarily disable interrupts by setting "SR.IMASK = 1111". This model works only when the program runs in privileged mode and is only suitable 7836 for single-core systems. Additional support from the interrupt/exception handling code of the system is not required. This model is enabled by default when the target is "sh*-*-linux*" 7837 and SH1* or SH2*. 7838 hard-llcs 7839 Generate hardware atomic sequences using the "movli.l" and "movco.l" instructions only. This is only available on SH4A and is suitable for multi-core systems. Since the hardware 7840 instructions support only 32 bit atomic variables access to 8 or 16 bit variables is emulated with 32 bit accesses. Code compiled with this option is also compatible with other software 7841 atomic model interrupt/exception handling systems if executed on an SH4A system. Additional support from the interrupt/exception handling code of the system is not required for this 7842 model. 7843 gbr-offset= 7844 This parameter specifies the offset in bytes of the variable in the thread control block structure that should be used by the generated atomic sequences when the soft-tcb model has been 7845 selected. For other models this parameter is ignored. The specified value must be an integer multiple of four and in the range 0-1020. 7846 strict 7847 This parameter prevents mixed usage of multiple atomic models, even if they are compatible, and makes the compiler generate atomic sequences of the specified model only. 7848 -mtas 7849 Generate the "tas.b" opcode for "__atomic_test_and_set". Notice that depending on the particular hardware and software configuration this can degrade overall performance due to the operand 7850 cache line flushes that are implied by the "tas.b" instruction. On multi-core SH4A processors the "tas.b" instruction must be used with caution since it can result in data corruption for 7851 certain cache configurations. 7852 -mprefergot 7853 When generating position-independent code, emit function calls using the Global Offset Table instead of the Procedure Linkage Table. 7854 -musermode 7855 -mno-usermode 7856 Don't allow (allow) the compiler generating privileged mode code. Specifying -musermode also implies -mno-inline-ic_invalidate if the inlined code would not work in user mode. -musermode 7857 is the default when the target is "sh*-*-linux*". If the target is SH1* or SH2* -musermode has no effect, since there is no user mode. 7858 -multcost=number 7859 Set the cost to assume for a multiply insn. 7860 -mdiv=strategy 7861 Set the division strategy to be used for integer division operations. For SHmedia strategy can be one of: 7862 fp Performs the operation in floating point. This has a very high latency, but needs only a few instructions, so it might be a good choice if your code has enough easily-exploitable ILP to 7863 allow the compiler to schedule the floating-point instructions together with other instructions. Division by zero causes a floating-point exception. 7864 inv Uses integer operations to calculate the inverse of the divisor, and then multiplies the dividend with the inverse. This strategy allows CSE and hoisting of the inverse calculation. 7865 Division by zero calculates an unspecified result, but does not trap. 7866 inv:minlat 7867 A variant of inv where, if no CSE or hoisting opportunities have been found, or if the entire operation has been hoisted to the same place, the last stages of the inverse calculation are 7868 intertwined with the final multiply to reduce the overall latency, at the expense of using a few more instructions, and thus offering fewer scheduling opportunities with other code. 7869 call 7870 Calls a library function that usually implements the inv:minlat strategy. This gives high code density for "m5-*media-nofpu" compilations. 7871 call2 7872 Uses a different entry point of the same library function, where it assumes that a pointer to a lookup table has already been set up, which exposes the pointer load to CSE and code 7873 hoisting optimizations. 7874 inv:call 7875 inv:call2 7876 inv:fp 7877 Use the inv algorithm for initial code generation, but if the code stays unoptimized, revert to the call, call2, or fp strategies, respectively. Note that the potentially-trapping side 7878 effect of division by zero is carried by a separate instruction, so it is possible that all the integer instructions are hoisted out, but the marker for the side effect stays where it 7879 is. A recombination to floating-point operations or a call is not possible in that case. 7880 inv20u 7881 inv20l 7882 Variants of the inv:minlat strategy. In the case that the inverse calculation is not separated from the multiply, they speed up division where the dividend fits into 20 bits (plus sign 7883 where applicable) by inserting a test to skip a number of operations in this case; this test slows down the case of larger dividends. inv20u assumes the case of a such a small dividend 7884 to be unlikely, and inv20l assumes it to be likely. 7885 For targets other than SHmedia strategy can be one of: 7886 call-div1 7887 Calls a library function that uses the single-step division instruction "div1" to perform the operation. Division by zero calculates an unspecified result and does not trap. This is 7888 the default except for SH4, SH2A and SHcompact. 7889 call-fp 7890 Calls a library function that performs the operation in double precision floating point. Division by zero causes a floating-point exception. This is the default for SHcompact with FPU. 7891 Specifying this for targets that do not have a double precision FPU defaults to "call-div1". 7892 call-table 7893 Calls a library function that uses a lookup table for small divisors and the "div1" instruction with case distinction for larger divisors. Division by zero calculates an unspecified 7894 result and does not trap. This is the default for SH4. Specifying this for targets that do not have dynamic shift instructions defaults to "call-div1". 7895 When a division strategy has not been specified the default strategy is selected based on the current target. For SH2A the default strategy is to use the "divs" and "divu" instructions 7896 instead of library function calls. 7897 -maccumulate-outgoing-args 7898 Reserve space once for outgoing arguments in the function prologue rather than around each call. Generally beneficial for performance and size. Also needed for unwinding to avoid changing 7899 the stack frame around conditional code. 7900 -mdivsi3_libfunc=name 7901 Set the name of the library function used for 32-bit signed division to name. This only affects the name used in the call and inv:call division strategies, and the compiler still expects 7902 the same sets of input/output/clobbered registers as if this option were not present. 7903 -mfixed-range=register-range 7904 Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator can not use. This is useful when compiling kernel code. A register 7905 range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. 7906 -mindexed-addressing 7907 Enable the use of the indexed addressing mode for SHmedia32/SHcompact. This is only safe if the hardware and/or OS implement 32-bit wrap-around semantics for the indexed addressing mode. 7908 The architecture allows the implementation of processors with 64-bit MMU, which the OS could use to get 32-bit addressing, but since no current hardware implementation supports this or any 7909 other way to make the indexed addressing mode safe to use in the 32-bit ABI, the default is -mno-indexed-addressing. 7910 -mgettrcost=number 7911 Set the cost assumed for the "gettr" instruction to number. The default is 2 if -mpt-fixed is in effect, 100 otherwise. 7912 -mpt-fixed 7913 Assume "pt*" instructions won't trap. This generally generates better-scheduled code, but is unsafe on current hardware. The current architecture definition says that "ptabs" and "ptrel" 7914 trap when the target anded with 3 is 3. This has the unintentional effect of making it unsafe to schedule these instructions before a branch, or hoist them out of a loop. For example, 7915 "__do_global_ctors", a part of libgcc that runs constructors at program startup, calls functions in a list which is delimited by -1. With the -mpt-fixed option, the "ptabs" is done before 7916 testing against -1. That means that all the constructors run a bit more quickly, but when the loop comes to the end of the list, the program crashes because "ptabs" loads -1 into a target 7917 register. 7918 Since this option is unsafe for any hardware implementing the current architecture specification, the default is -mno-pt-fixed. Unless specified explicitly with -mgettrcost, -mno-pt-fixed 7919 also implies -mgettrcost=100; this deters register allocation from using target registers for storing ordinary integers. 7920 -minvalid-symbols 7921 Assume symbols might be invalid. Ordinary function symbols generated by the compiler are always valid to load with "movi"/"shori"/"ptabs" or "movi"/"shori"/"ptrel", but with assembler 7922 and/or linker tricks it is possible to generate symbols that cause "ptabs" or "ptrel" to trap. This option is only meaningful when -mno-pt-fixed is in effect. It prevents cross-basic-block 7923 CSE, hoisting and most scheduling of symbol loads. The default is -mno-invalid-symbols. 7924 -mbranch-cost=num 7925 Assume num to be the cost for a branch instruction. Higher numbers make the compiler try to generate more branch-free code if possible. If not specified the value is selected depending on 7926 the processor type that is being compiled for. 7927 -mzdcbranch 7928 -mno-zdcbranch 7929 Assume (do not assume) that zero displacement conditional branch instructions "bt" and "bf" are fast. If -mzdcbranch is specified, the compiler prefers zero displacement branch code 7930 sequences. This is enabled by default when generating code for SH4 and SH4A. It can be explicitly disabled by specifying -mno-zdcbranch. 7931 -mcbranch-force-delay-slot 7932 Force the usage of delay slots for conditional branches, which stuffs the delay slot with a "nop" if a suitable instruction can't be found. By default this option is disabled. It can be 7933 enabled to work around hardware bugs as found in the original SH7055. 7934 -mfused-madd 7935 -mno-fused-madd 7936 Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. The machine- 7937 dependent -mfused-madd option is now mapped to the machine-independent -ffp-contract=fast option, and -mno-fused-madd is mapped to -ffp-contract=off. 7938 -mfsca 7939 -mno-fsca 7940 Allow or disallow the compiler to emit the "fsca" instruction for sine and cosine approximations. The option -mfsca must be used in combination with -funsafe-math-optimizations. It is 7941 enabled by default when generating code for SH4A. Using -mno-fsca disables sine and cosine approximations even if -funsafe-math-optimizations is in effect. 7942 -mfsrra 7943 -mno-fsrra 7944 Allow or disallow the compiler to emit the "fsrra" instruction for reciprocal square root approximations. The option -mfsrra must be used in combination with -funsafe-math-optimizations and 7945 -ffinite-math-only. It is enabled by default when generating code for SH4A. Using -mno-fsrra disables reciprocal square root approximations even if -funsafe-math-optimizations and 7946 -ffinite-math-only are in effect. 7947 -mpretend-cmove 7948 Prefer zero-displacement conditional branches for conditional move instruction patterns. This can result in faster code on the SH4 processor. 7949 Solaris 2 Options 7950 These -m options are supported on Solaris 2: 7951 -mclear-hwcap 7952 -mclear-hwcap tells the compiler to remove the hardware capabilities generated by the Solaris assembler. This is only necessary when object files use ISA extensions not supported by the 7953 current machine, but check at runtime whether or not to use them. 7954 -mimpure-text 7955 -mimpure-text, used in addition to -shared, tells the compiler to not pass -z text to the linker when linking a shared object. Using this option, you can link position-dependent code into a 7956 shared object. 7957 -mimpure-text suppresses the "relocations remain against allocatable but non-writable sections" linker error message. However, the necessary relocations trigger copy-on-write, and the 7958 shared object is not actually shared across processes. Instead of using -mimpure-text, you should compile all source code with -fpic or -fPIC. 7959 These switches are supported in addition to the above on Solaris 2: 7960 -pthreads 7961 Add support for multithreading using the POSIX threads library. This option sets flags for both the preprocessor and linker. This option does not affect the thread safety of object code 7962 produced by the compiler or that of libraries supplied with it. 7963 -pthread 7964 This is a synonym for -pthreads. 7965 SPARC Options 7966 These -m options are supported on the SPARC: 7967 -mno-app-regs 7968 -mapp-regs 7969 Specify -mapp-regs to generate output using the global registers 2 through 4, which the SPARC SVR4 ABI reserves for applications. Like the global register 1, each global register 2 through 7970 4 is then treated as an allocable register that is clobbered by function calls. This is the default. 7971 To be fully SVR4 ABI-compliant at the cost of some performance loss, specify -mno-app-regs. You should compile libraries and system software with this option. 7972 -mflat 7973 -mno-flat 7974 With -mflat, the compiler does not generate save/restore instructions and uses a "flat" or single register window model. This model is compatible with the regular register window model. 7975 The local registers and the input registers (0--5) are still treated as "call-saved" registers and are saved on the stack as needed. 7976 With -mno-flat (the default), the compiler generates save/restore instructions (except for leaf functions). This is the normal operating mode. 7977 -mfpu 7978 -mhard-float 7979 Generate output containing floating-point instructions. This is the default. 7980 -mno-fpu 7981 -msoft-float 7982 Generate output containing library calls for floating point. Warning: the requisite libraries are not available for all SPARC targets. Normally the facilities of the machine's usual C 7983 compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. The embedded 7984 targets sparc-*-aout and sparclite-*-* do provide software floating-point support. 7985 -msoft-float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. In particular, you need to compile libgcc.a, 7986 the library that comes with GCC, with -msoft-float in order for this to work. 7987 -mhard-quad-float 7988 Generate output containing quad-word (long double) floating-point instructions. 7989 -msoft-quad-float 7990 Generate output containing library calls for quad-word (long double) floating-point instructions. The functions called are those specified in the SPARC ABI. This is the default. 7991 As of this writing, there are no SPARC implementations that have hardware support for the quad-word floating-point instructions. They all invoke a trap handler for one of these 7992 instructions, and then the trap handler emulates the effect of the instruction. Because of the trap handler overhead, this is much slower than calling the ABI library routines. Thus the 7993 -msoft-quad-float option is the default. 7994 -mno-unaligned-doubles 7995 -munaligned-doubles 7996 Assume that doubles have 8-byte alignment. This is the default. 7997 With -munaligned-doubles, GCC assumes that doubles have 8-byte alignment only if they are contained in another type, or if they have an absolute address. Otherwise, it assumes they have 7998 4-byte alignment. Specifying this option avoids some rare compatibility problems with code generated by other compilers. It is not the default because it results in a performance loss, 7999 especially for floating-point code. 8000 -muser-mode 8001 -mno-user-mode 8002 Do not generate code that can only run in supervisor mode. This is relevant only for the "casa" instruction emitted for the LEON3 processor. The default is -mno-user-mode. 8003 -mno-faster-structs 8004 -mfaster-structs 8005 With -mfaster-structs, the compiler assumes that structures should have 8-byte alignment. This enables the use of pairs of "ldd" and "std" instructions for copies in structure assignment, 8006 in place of twice as many "ld" and "st" pairs. However, the use of this changed alignment directly violates the SPARC ABI. Thus, it's intended only for use on targets where the developer 8007 acknowledges that their resulting code is not directly in line with the rules of the ABI. 8008 -mcpu=cpu_type 8009 Set the instruction set, register set, and instruction scheduling parameters for machine type cpu_type. Supported values for cpu_type are v7, cypress, v8, supersparc, hypersparc, leon, 8010 leon3, leon3v7, sparclite, f930, f934, sparclite86x, sparclet, tsc701, v9, ultrasparc, ultrasparc3, niagara, niagara2, niagara3 and niagara4. 8011 Native Solaris and GNU/Linux toolchains also support the value native, which selects the best architecture option for the host processor. -mcpu=native has no effect if GCC does not 8012 recognize the processor. 8013 Default instruction scheduling parameters are used for values that select an architecture and not an implementation. These are v7, v8, sparclite, sparclet, v9. 8014 Here is a list of each supported architecture and their supported implementations. 8015 v7 cypress, leon3v7 8016 v8 supersparc, hypersparc, leon, leon3 8017 sparclite 8018 f930, f934, sparclite86x 8019 sparclet 8020 tsc701 8021 v9 ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4 8022 By default (unless configured otherwise), GCC generates code for the V7 variant of the SPARC architecture. With -mcpu=cypress, the compiler additionally optimizes it for the Cypress CY7C602 8023 chip, as used in the SPARCStation/SPARCServer 3xx series. This is also appropriate for the older SPARCStation 1, 2, IPX etc. 8024 With -mcpu=v8, GCC generates code for the V8 variant of the SPARC architecture. The only difference from V7 code is that the compiler emits the integer multiply and integer divide 8025 instructions which exist in SPARC-V8 but not in SPARC-V7. With -mcpu=supersparc, the compiler additionally optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and 8026 2000 series. 8027 With -mcpu=sparclite, GCC generates code for the SPARClite variant of the SPARC architecture. This adds the integer multiply, integer divide step and scan ("ffs") instructions which exist 8028 in SPARClite but not in SPARC-V7. With -mcpu=f930, the compiler additionally optimizes it for the Fujitsu MB86930 chip, which is the original SPARClite, with no FPU. With -mcpu=f934, the 8029 compiler additionally optimizes it for the Fujitsu MB86934 chip, which is the more recent SPARClite with FPU. 8030 With -mcpu=sparclet, GCC generates code for the SPARClet variant of the SPARC architecture. This adds the integer multiply, multiply/accumulate, integer divide step and scan ("ffs") 8031 instructions which exist in SPARClet but not in SPARC-V7. With -mcpu=tsc701, the compiler additionally optimizes it for the TEMIC SPARClet chip. 8032 With -mcpu=v9, GCC generates code for the V9 variant of the SPARC architecture. This adds 64-bit integer and floating-point move instructions, 3 additional floating-point condition code 8033 registers and conditional move instructions. With -mcpu=ultrasparc, the compiler additionally optimizes it for the Sun UltraSPARC I/II/IIi chips. With -mcpu=ultrasparc3, the compiler 8034 additionally optimizes it for the Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With -mcpu=niagara, the compiler additionally optimizes it for Sun UltraSPARC T1 chips. With 8035 -mcpu=niagara2, the compiler additionally optimizes it for Sun UltraSPARC T2 chips. With -mcpu=niagara3, the compiler additionally optimizes it for Sun UltraSPARC T3 chips. With 8036 -mcpu=niagara4, the compiler additionally optimizes it for Sun UltraSPARC T4 chips. 8037 -mtune=cpu_type 8038 Set the instruction scheduling parameters for machine type cpu_type, but do not set the instruction set or register set that the option -mcpu=cpu_type does. 8039 The same values for -mcpu=cpu_type can be used for -mtune=cpu_type, but the only useful values are those that select a particular CPU implementation. Those are cypress, supersparc, 8040 hypersparc, leon, leon3, leon3v7, f930, f934, sparclite86x, tsc701, ultrasparc, ultrasparc3, niagara, niagara2, niagara3 and niagara4. With native Solaris and GNU/Linux toolchains, native 8041 can also be used. 8042 -mv8plus 8043 -mno-v8plus 8044 With -mv8plus, GCC generates code for the SPARC-V8+ ABI. The difference from the V8 ABI is that the global and out registers are considered 64 bits wide. This is enabled by default on 8045 Solaris in 32-bit mode for all SPARC-V9 processors. 8046 -mvis 8047 -mno-vis 8048 With -mvis, GCC generates code that takes advantage of the UltraSPARC Visual Instruction Set extensions. The default is -mno-vis. 8049 -mvis2 8050 -mno-vis2 8051 With -mvis2, GCC generates code that takes advantage of version 2.0 of the UltraSPARC Visual Instruction Set extensions. The default is -mvis2 when targeting a cpu that supports such 8052 instructions, such as UltraSPARC-III and later. Setting -mvis2 also sets -mvis. 8053 -mvis3 8054 -mno-vis3 8055 With -mvis3, GCC generates code that takes advantage of version 3.0 of the UltraSPARC Visual Instruction Set extensions. The default is -mvis3 when targeting a cpu that supports such 8056 instructions, such as niagara-3 and later. Setting -mvis3 also sets -mvis2 and -mvis. 8057 -mcbcond 8058 -mno-cbcond 8059 With -mcbcond, GCC generates code that takes advantage of compare-and-branch instructions, as defined in the Sparc Architecture 2011. The default is -mcbcond when targeting a cpu that 8060 supports such instructions, such as niagara-4 and later. 8061 -mpopc 8062 -mno-popc 8063 With -mpopc, GCC generates code that takes advantage of the UltraSPARC population count instruction. The default is -mpopc when targeting a cpu that supports such instructions, such as 8064 Niagara-2 and later. 8065 -mfmaf 8066 -mno-fmaf 8067 With -mfmaf, GCC generates code that takes advantage of the UltraSPARC Fused Multiply-Add Floating-point extensions. The default is -mfmaf when targeting a cpu that supports such 8068 instructions, such as Niagara-3 and later. 8069 -mfix-at697f 8070 Enable the documented workaround for the single erratum of the Atmel AT697F processor (which corresponds to erratum #13 of the AT697E processor). 8071 -mfix-ut699 8072 Enable the documented workarounds for the floating-point errata and the data cache nullify errata of the UT699 processor. 8073 These -m options are supported in addition to the above on SPARC-V9 processors in 64-bit environments: 8074 -m32 8075 -m64 8076 Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long and pointer to 32 bits. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits. 8077 -mcmodel=which 8078 Set the code model to one of 8079 medlow 8080 The Medium/Low code model: 64-bit addresses, programs must be linked in the low 32 bits of memory. Programs can be statically or dynamically linked. 8081 medmid 8082 The Medium/Middle code model: 64-bit addresses, programs must be linked in the low 44 bits of memory, the text and data segments must be less than 2GB in size and the data segment must 8083 be located within 2GB of the text segment. 8084 medany 8085 The Medium/Anywhere code model: 64-bit addresses, programs may be linked anywhere in memory, the text and data segments must be less than 2GB in size and the data segment must be located 8086 within 2GB of the text segment. 8087 embmedany 8088 The Medium/Anywhere code model for embedded systems: 64-bit addresses, the text and data segments must be less than 2GB in size, both starting anywhere in memory (determined at link 8089 time). The global register %g4 points to the base of the data segment. Programs are statically linked and PIC is not supported. 8090 -mmemory-model=mem-model 8091 Set the memory model in force on the processor to one of 8092 default 8093 The default memory model for the processor and operating system. 8094 rmo Relaxed Memory Order 8095 pso Partial Store Order 8096 tso Total Store Order 8097 sc Sequential Consistency 8098 These memory models are formally defined in Appendix D of the Sparc V9 architecture manual, as set in the processor's "PSTATE.MM" field. 8099 -mstack-bias 8100 -mno-stack-bias 8101 With -mstack-bias, GCC assumes that the stack pointer, and frame pointer if present, are offset by -2047 which must be added back when making stack frame references. This is the default in 8102 64-bit mode. Otherwise, assume no such offset is present. 8103 SPU Options 8104 These -m options are supported on the SPU: 8105 -mwarn-reloc 8106 -merror-reloc 8107 The loader for SPU does not handle dynamic relocations. By default, GCC gives an error when it generates code that requires a dynamic relocation. -mno-error-reloc disables the error, 8108 -mwarn-reloc generates a warning instead. 8109 -msafe-dma 8110 -munsafe-dma 8111 Instructions that initiate or test completion of DMA must not be reordered with respect to loads and stores of the memory that is being accessed. With -munsafe-dma you must use the 8112 "volatile" keyword to protect memory accesses, but that can lead to inefficient code in places where the memory is known to not change. Rather than mark the memory as volatile, you can use 8113 -msafe-dma to tell the compiler to treat the DMA instructions as potentially affecting all memory. 8114 -mbranch-hints 8115 By default, GCC generates a branch hint instruction to avoid pipeline stalls for always-taken or probably-taken branches. A hint is not generated closer than 8 instructions away from its 8116 branch. There is little reason to disable them, except for debugging purposes, or to make an object a little bit smaller. 8117 -msmall-mem 8118 -mlarge-mem 8119 By default, GCC generates code assuming that addresses are never larger than 18 bits. With -mlarge-mem code is generated that assumes a full 32-bit address. 8120 -mstdmain 8121 By default, GCC links against startup code that assumes the SPU-style main function interface (which has an unconventional parameter list). With -mstdmain, GCC links your program against 8122 startup code that assumes a C99-style interface to "main", including a local copy of "argv" strings. 8123 -mfixed-range=register-range 8124 Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling kernel code. A register 8125 range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. 8126 -mea32 8127 -mea64 8128 Compile code assuming that pointers to the PPU address space accessed via the "__ea" named address space qualifier are either 32 or 64 bits wide. The default is 32 bits. As this is an ABI- 8129 changing option, all object code in an executable must be compiled with the same setting. 8130 -maddress-space-conversion 8131 -mno-address-space-conversion 8132 Allow/disallow treating the "__ea" address space as superset of the generic address space. This enables explicit type casts between "__ea" and generic pointer as well as implicit 8133 conversions of generic pointers to "__ea" pointers. The default is to allow address space pointer conversions. 8134 -mcache-size=cache-size 8135 This option controls the version of libgcc that the compiler links to an executable and selects a software-managed cache for accessing variables in the "__ea" address space with a particular 8136 cache size. Possible options for cache-size are 8, 16, 32, 64 and 128. The default cache size is 64KB. 8137 -matomic-updates 8138 -mno-atomic-updates 8139 This option controls the version of libgcc that the compiler links to an executable and selects whether atomic updates to the software-managed cache of PPU-side variables are used. If you 8140 use atomic updates, changes to a PPU variable from SPU code using the "__ea" named address space qualifier do not interfere with changes to other PPU variables residing in the same cache 8141 line from PPU code. If you do not use atomic updates, such interference may occur; however, writing back cache lines is more efficient. The default behavior is to use atomic updates. 8142 -mdual-nops 8143 -mdual-nops=n 8144 By default, GCC inserts nops to increase dual issue when it expects it to increase performance. n can be a value from 0 to 10. A smaller n inserts fewer nops. 10 is the default, 0 is the 8145 same as -mno-dual-nops. Disabled with -Os. 8146 -mhint-max-nops=n 8147 Maximum number of nops to insert for a branch hint. A branch hint must be at least 8 instructions away from the branch it is affecting. GCC inserts up to n nops to enforce this, otherwise 8148 it does not generate the branch hint. 8149 -mhint-max-distance=n 8150 The encoding of the branch hint instruction limits the hint to be within 256 instructions of the branch it is affecting. By default, GCC makes sure it is within 125. 8151 -msafe-hints 8152 Work around a hardware bug that causes the SPU to stall indefinitely. By default, GCC inserts the "hbrp" instruction to make sure this stall won't happen. 8153 Options for System V 8154 These additional options are available on System V Release 4 for compatibility with other compilers on those systems: 8155 -G Create a shared object. It is recommended that -symbolic or -shared be used instead. 8156 -Qy Identify the versions of each tool used by the compiler, in a ".ident" assembler directive in the output. 8157 -Qn Refrain from adding ".ident" directives to the output file (this is the default). 8158 -YP,dirs 8159 Search the directories dirs, and no others, for libraries specified with -l. 8160 -Ym,dir 8161 Look in the directory dir to find the M4 preprocessor. The assembler uses this option. 8162 TILE-Gx Options 8163 These -m options are supported on the TILE-Gx: 8164 -mcmodel=small 8165 Generate code for the small model. The distance for direct calls is limited to 500M in either direction. PC-relative addresses are 32 bits. Absolute addresses support the full address 8166 range. 8167 -mcmodel=large 8168 Generate code for the large model. There is no limitation on call distance, pc-relative addresses, or absolute addresses. 8169 -mcpu=name 8170 Selects the type of CPU to be targeted. Currently the only supported type is tilegx. 8171 -m32 8172 -m64 8173 Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long, and pointer to 32 bits. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits. 8174 -mbig-endian 8175 -mlittle-endian 8176 Generate code in big/little endian mode, respectively. 8177 TILEPro Options 8178 These -m options are supported on the TILEPro: 8179 -mcpu=name 8180 Selects the type of CPU to be targeted. Currently the only supported type is tilepro. 8181 -m32 8182 Generate code for a 32-bit environment, which sets int, long, and pointer to 32 bits. This is the only supported behavior so the flag is essentially ignored. 8183 V850 Options 8184 These -m options are defined for V850 implementations: 8185 -mlong-calls 8186 -mno-long-calls 8187 Treat all calls as being far away (near). If calls are assumed to be far away, the compiler always loads the function's address into a register, and calls indirect through the pointer. 8188 -mno-ep 8189 -mep 8190 Do not optimize (do optimize) basic blocks that use the same index pointer 4 or more times to copy pointer into the "ep" register, and use the shorter "sld" and "sst" instructions. The -mep 8191 option is on by default if you optimize. 8192 -mno-prolog-function 8193 -mprolog-function 8194 Do not use (do use) external functions to save and restore registers at the prologue and epilogue of a function. The external functions are slower, but use less code space if more than one 8195 function saves the same number of registers. The -mprolog-function option is on by default if you optimize. 8196 -mspace 8197 Try to make the code as small as possible. At present, this just turns on the -mep and -mprolog-function options. 8198 -mtda=n 8199 Put static or global variables whose size is n bytes or less into the tiny data area that register "ep" points to. The tiny data area can hold up to 256 bytes in total (128 bytes for byte 8200 references). 8201 -msda=n 8202 Put static or global variables whose size is n bytes or less into the small data area that register "gp" points to. The small data area can hold up to 64 kilobytes. 8203 -mzda=n 8204 Put static or global variables whose size is n bytes or less into the first 32 kilobytes of memory. 8205 -mv850 8206 Specify that the target processor is the V850. 8207 -mv850e3v5 8208 Specify that the target processor is the V850E3V5. The preprocessor constant "__v850e3v5__" is defined if this option is used. 8209 -mv850e2v4 8210 Specify that the target processor is the V850E3V5. This is an alias for the -mv850e3v5 option. 8211 -mv850e2v3 8212 Specify that the target processor is the V850E2V3. The preprocessor constant "__v850e2v3__" is defined if this option is used. 8213 -mv850e2 8214 Specify that the target processor is the V850E2. The preprocessor constant "__v850e2__" is defined if this option is used. 8215 -mv850e1 8216 Specify that the target processor is the V850E1. The preprocessor constants "__v850e1__" and "__v850e__" are defined if this option is used. 8217 -mv850es 8218 Specify that the target processor is the V850ES. This is an alias for the -mv850e1 option. 8219 -mv850e 8220 Specify that the target processor is the V850E. The preprocessor constant "__v850e__" is defined if this option is used. 8221 If neither -mv850 nor -mv850e nor -mv850e1 nor -mv850e2 nor -mv850e2v3 nor -mv850e3v5 are defined then a default target processor is chosen and the relevant __v850*__ preprocessor constant 8222 is defined. 8223 The preprocessor constants "__v850" and "__v851__" are always defined, regardless of which processor variant is the target. 8224 -mdisable-callt 8225 -mno-disable-callt 8226 This option suppresses generation of the "CALLT" instruction for the v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the v850 architecture. 8227 This option is enabled by default when the RH850 ABI is in use (see -mrh850-abi), and disabled by default when the GCC ABI is in use. If "CALLT" instructions are being generated then the C 8228 preprocessor symbol "__V850_CALLT__" is defined. 8229 -mrelax 8230 -mno-relax 8231 Pass on (or do not pass on) the -mrelax command-line option to the assembler. 8232 -mlong-jumps 8233 -mno-long-jumps 8234 Disable (or re-enable) the generation of PC-relative jump instructions. 8235 -msoft-float 8236 -mhard-float 8237 Disable (or re-enable) the generation of hardware floating point instructions. This option is only significant when the target architecture is V850E2V3 or higher. If hardware floating 8238 point instructions are being generated then the C preprocessor symbol "__FPU_OK__" is defined, otherwise the symbol "__NO_FPU__" is defined. 8239 -mloop 8240 Enables the use of the e3v5 LOOP instruction. The use of this instruction is not enabled by default when the e3v5 architecture is selected because its use is still experimental. 8241 -mrh850-abi 8242 -mghs 8243 Enables support for the RH850 version of the V850 ABI. This is the default. With this version of the ABI the following rules apply: 8244 * Integer sized structures and unions are returned via a memory pointer rather than a register. 8245 * Large structures and unions (more than 8 bytes in size) are passed by value. 8246 * Functions are aligned to 16-bit boundaries. 8247 * The -m8byte-align command-line option is supported. 8248 * The -mdisable-callt command-line option is enabled by default. The -mno-disable-callt command-line option is not supported. 8249 When this version of the ABI is enabled the C preprocessor symbol "__V850_RH850_ABI__" is defined. 8250 -mgcc-abi 8251 Enables support for the old GCC version of the V850 ABI. With this version of the ABI the following rules apply: 8252 * Integer sized structures and unions are returned in register "r10". 8253 * Large structures and unions (more than 8 bytes in size) are passed by reference. 8254 * Functions are aligned to 32-bit boundaries, unless optimizing for size. 8255 * The -m8byte-align command-line option is not supported. 8256 * The -mdisable-callt command-line option is supported but not enabled by default. 8257 When this version of the ABI is enabled the C preprocessor symbol "__V850_GCC_ABI__" is defined. 8258 -m8byte-align 8259 -mno-8byte-align 8260 Enables support for "double" and "long long" types to be aligned on 8-byte boundaries. The default is to restrict the alignment of all objects to at most 4-bytes. When -m8byte-align is in 8261 effect the C preprocessor symbol "__V850_8BYTE_ALIGN__" is defined. 8262 -mbig-switch 8263 Generate code suitable for big switch tables. Use this option only if the assembler/linker complain about out of range branches within a switch table. 8264 -mapp-regs 8265 This option causes r2 and r5 to be used in the code generated by the compiler. This setting is the default. 8266 -mno-app-regs 8267 This option causes r2 and r5 to be treated as fixed registers. 8268 VAX Options 8269 These -m options are defined for the VAX: 8270 -munix 8271 Do not output certain jump instructions ("aobleq" and so on) that the Unix assembler for the VAX cannot handle across long ranges. 8272 -mgnu 8273 Do output those jump instructions, on the assumption that the GNU assembler is being used. 8274 -mg Output code for G-format floating-point numbers instead of D-format. 8275 Visium Options 8276 -mdebug 8277 A program which performs file I/O and is destined to run on an MCM target should be linked with this option. It causes the libraries libc.a and libdebug.a to be linked. The program should 8278 be run on the target under the control of the GDB remote debugging stub. 8279 -msim 8280 A program which performs file I/O and is destined to run on the simulator should be linked with option. This causes libraries libc.a and libsim.a to be linked. 8281 -mfpu 8282 -mhard-float 8283 Generate code containing floating-point instructions. This is the default. 8284 -mno-fpu 8285 -msoft-float 8286 Generate code containing library calls for floating-point. 8287 -msoft-float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. In particular, you need to compile libgcc.a, 8288 the library that comes with GCC, with -msoft-float in order for this to work. 8289 -mcpu=cpu_type 8290 Set the instruction set, register set, and instruction scheduling parameters for machine type cpu_type. Supported values for cpu_type are mcm, gr5 and gr6. 8291 mcm is a synonym of gr5 present for backward compatibility. 8292 By default (unless configured otherwise), GCC generates code for the GR5 variant of the Visium architecture. 8293 With -mcpu=gr6, GCC generates code for the GR6 variant of the Visium architecture. The only difference from GR5 code is that the compiler will generate block move instructions. 8294 -mtune=cpu_type 8295 Set the instruction scheduling parameters for machine type cpu_type, but do not set the instruction set or register set that the option -mcpu=cpu_type would. 8296 -msv-mode 8297 Generate code for the supervisor mode, where there are no restrictions on the access to general registers. This is the default. 8298 -muser-mode 8299 Generate code for the user mode, where the access to some general registers is forbidden: on the GR5, registers r24 to r31 cannot be accessed in this mode; on the GR6, only registers r29 to 8300 r31 are affected. 8301 VMS Options 8302 These -m options are defined for the VMS implementations: 8303 -mvms-return-codes 8304 Return VMS condition codes from "main". The default is to return POSIX-style condition (e.g. error) codes. 8305 -mdebug-main=prefix 8306 Flag the first routine whose name starts with prefix as the main routine for the debugger. 8307 -mmalloc64 8308 Default to 64-bit memory allocation routines. 8309 -mpointer-size=size 8310 Set the default size of pointers. Possible options for size are 32 or short for 32 bit pointers, 64 or long for 64 bit pointers, and no for supporting only 32 bit pointers. The later option 8311 disables "pragma pointer_size". 8312 VxWorks Options 8313 The options in this section are defined for all VxWorks targets. Options specific to the target hardware are listed with the other options for that target. 8314 -mrtp 8315 GCC can generate code for both VxWorks kernels and real time processes (RTPs). This option switches from the former to the latter. It also defines the preprocessor macro "__RTP__". 8316 -non-static 8317 Link an RTP executable against shared libraries rather than static libraries. The options -static and -shared can also be used for RTPs; -static is the default. 8318 -Bstatic 8319 -Bdynamic 8320 These options are passed down to the linker. They are defined for compatibility with Diab. 8321 -Xbind-lazy 8322 Enable lazy binding of function calls. This option is equivalent to -Wl,-z,now and is defined for compatibility with Diab. 8323 -Xbind-now 8324 Disable lazy binding of function calls. This option is the default and is defined for compatibility with Diab. 8325 x86 Options 8326 These -m options are defined for the x86 family of computers. 8327 -march=cpu-type 8328 Generate instructions for the machine type cpu-type. In contrast to -mtune=cpu-type, which merely tunes the generated code for the specified cpu-type, -march=cpu-type allows GCC to generate 8329 code that may not run at all on processors other than the one indicated. Specifying -march=cpu-type implies -mtune=cpu-type. 8330 The choices for cpu-type are: 8331 native 8332 This selects the CPU to generate code for at compilation time by determining the processor type of the compiling machine. Using -march=native enables all instruction subsets supported 8333 by the local machine (hence the result might not run on different machines). Using -mtune=native produces code optimized for the local machine under the constraints of the selected 8334 instruction set. 8335 i386 8336 Original Intel i386 CPU. 8337 i486 8338 Intel i486 CPU. (No scheduling is implemented for this chip.) 8339 i586 8340 pentium 8341 Intel Pentium CPU with no MMX support. 8342 pentium-mmx 8343 Intel Pentium MMX CPU, based on Pentium core with MMX instruction set support. 8344 pentiumpro 8345 Intel Pentium Pro CPU. 8346 i686 8347 When used with -march, the Pentium Pro instruction set is used, so the code runs on all i686 family chips. When used with -mtune, it has the same meaning as generic. 8348 pentium2 8349 Intel Pentium II CPU, based on Pentium Pro core with MMX instruction set support. 8350 pentium3 8351 pentium3m 8352 Intel Pentium III CPU, based on Pentium Pro core with MMX and SSE instruction set support. 8353 pentium-m 8354 Intel Pentium M; low-power version of Intel Pentium III CPU with MMX, SSE and SSE2 instruction set support. Used by Centrino notebooks. 8355 pentium4 8356 pentium4m 8357 Intel Pentium 4 CPU with MMX, SSE and SSE2 instruction set support. 8358 prescott 8359 Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2 and SSE3 instruction set support. 8360 nocona 8361 Improved version of Intel Pentium 4 CPU with 64-bit extensions, MMX, SSE, SSE2 and SSE3 instruction set support. 8362 core2 8363 Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3 instruction set support. 8364 nehalem 8365 Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2 and POPCNT instruction set support. 8366 westmere 8367 Intel Westmere CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES and PCLMUL instruction set support. 8368 sandybridge 8369 Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AES and PCLMUL instruction set support. 8370 ivybridge 8371 Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AES, PCLMUL, FSGSBASE, RDRND and F16C instruction set support. 8372 haswell 8373 Intel Haswell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2 and F16C instruction set 8374 support. 8375 broadwell 8376 Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX and 8377 PREFETCHW instruction set support. 8378 bonnell 8379 Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3 and SSSE3 instruction set support. 8380 silvermont 8381 Intel Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PCLMUL and RDRND instruction set support. 8382 knl Intel Knight's Landing CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, 8383 ADCX, PREFETCHW, AVX512F, AVX512PF, AVX512ER and AVX512CD instruction set support. 8384 k6 AMD K6 CPU with MMX instruction set support. 8385 k6-2 8386 k6-3 8387 Improved versions of AMD K6 CPU with MMX and 3DNow! instruction set support. 8388 athlon 8389 athlon-tbird 8390 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow! and SSE prefetch instructions support. 8391 athlon-4 8392 athlon-xp 8393 athlon-mp 8394 Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow! and full SSE instruction set support. 8395 k8 8396 opteron 8397 athlon64 8398 athlon-fx 8399 Processors based on the AMD K8 core with x86-64 instruction set support, including the AMD Opteron, Athlon 64, and Athlon 64 FX processors. (This supersets MMX, SSE, SSE2, 3DNow!, 8400 enhanced 3DNow! and 64-bit instruction set extensions.) 8401 k8-sse3 8402 opteron-sse3 8403 athlon64-sse3 8404 Improved versions of AMD K8 cores with SSE3 instruction set support. 8405 amdfam10 8406 barcelona 8407 CPUs based on AMD Family 10h cores with x86-64 instruction set support. (This supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!, enhanced 3DNow!, ABM and 64-bit instruction set extensions.) 8408 bdver1 8409 CPUs based on AMD Family 15h cores with x86-64 instruction set support. (This supersets FMA4, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM 8410 and 64-bit instruction set extensions.) 8411 bdver2 8412 AMD Family 15h core based CPUs with x86-64 instruction set support. (This supersets BMI, TBM, F16C, FMA, FMA4, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, 8413 SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.) 8414 bdver3 8415 AMD Family 15h core based CPUs with x86-64 instruction set support. (This supersets BMI, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, 8416 SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions. 8417 bdver4 8418 AMD Family 15h core based CPUs with x86-64 instruction set support. (This supersets BMI, BMI2, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, AVX2, XOP, LWP, AES, PCL_MUL, CX16, MOVBE, MMX, SSE, 8419 SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions. 8420 btver1 8421 CPUs based on AMD Family 14h cores with x86-64 instruction set support. (This supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A, CX16, ABM and 64-bit instruction set extensions.) 8422 btver2 8423 CPUs based on AMD Family 16h cores with x86-64 instruction set support. This includes MOVBE, F16C, BMI, AVX, PCL_MUL, AES, SSE4.2, SSE4.1, CX16, ABM, SSE4A, SSSE3, SSE3, SSE2, SSE, MMX 8424 and 64-bit instruction set extensions. 8425 winchip-c6 8426 IDT WinChip C6 CPU, dealt in same way as i486 with additional MMX instruction set support. 8427 winchip2 8428 IDT WinChip 2 CPU, dealt in same way as i486 with additional MMX and 3DNow! instruction set support. 8429 c3 VIA C3 CPU with MMX and 3DNow! instruction set support. (No scheduling is implemented for this chip.) 8430 c3-2 8431 VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set support. (No scheduling is implemented for this chip.) 8432 geode 8433 AMD Geode embedded processor with MMX and 3DNow! instruction set support. 8434 -mtune=cpu-type 8435 Tune to cpu-type everything applicable about the generated code, except for the ABI and the set of available instructions. While picking a specific cpu-type schedules things appropriately 8436 for that particular chip, the compiler does not generate any code that cannot run on the default machine type unless you use a -march=cpu-type option. For example, if GCC is configured for 8437 i686-pc-linux-gnu then -mtune=pentium4 generates code that is tuned for Pentium 4 but still runs on i686 machines. 8438 The choices for cpu-type are the same as for -march. In addition, -mtune supports 2 extra choices for cpu-type: 8439 generic 8440 Produce code optimized for the most common IA32/AMD64/EM64T processors. If you know the CPU on which your code will run, then you should use the corresponding -mtune or -march option 8441 instead of -mtune=generic. But, if you do not know exactly what CPU users of your application will have, then you should use this option. 8442 As new processors are deployed in the marketplace, the behavior of this option will change. Therefore, if you upgrade to a newer version of GCC, code generation controlled by this 8443 option will change to reflect the processors that are most common at the time that version of GCC is released. 8444 There is no -march=generic option because -march indicates the instruction set the compiler can use, and there is no generic instruction set applicable to all processors. In contrast, 8445 -mtune indicates the processor (or, in this case, collection of processors) for which the code is optimized. 8446 intel 8447 Produce code optimized for the most current Intel processors, which are Haswell and Silvermont for this version of GCC. If you know the CPU on which your code will run, then you should 8448 use the corresponding -mtune or -march option instead of -mtune=intel. But, if you want your application performs better on both Haswell and Silvermont, then you should use this option. 8449 As new Intel processors are deployed in the marketplace, the behavior of this option will change. Therefore, if you upgrade to a newer version of GCC, code generation controlled by this 8450 option will change to reflect the most current Intel processors at the time that version of GCC is released. 8451 There is no -march=intel option because -march indicates the instruction set the compiler can use, and there is no common instruction set applicable to all processors. In contrast, 8452 -mtune indicates the processor (or, in this case, collection of processors) for which the code is optimized. 8453 -mcpu=cpu-type 8454 A deprecated synonym for -mtune. 8455 -mfpmath=unit 8456 Generate floating-point arithmetic for selected unit unit. The choices for unit are: 8457 387 Use the standard 387 floating-point coprocessor present on the majority of chips and emulated otherwise. Code compiled with this option runs almost everywhere. The temporary results 8458 are computed in 80-bit precision instead of the precision specified by the type, resulting in slightly different results compared to most of other chips. See -ffloat-store for more 8459 detailed description. 8460 This is the default choice for x86-32 targets. 8461 sse Use scalar floating-point instructions present in the SSE instruction set. This instruction set is supported by Pentium III and newer chips, and in the AMD line by Athlon-4, Athlon XP 8462 and Athlon MP chips. The earlier version of the SSE instruction set supports only single-precision arithmetic, thus the double and extended-precision arithmetic are still done using 8463 387. A later version, present only in Pentium 4 and AMD x86-64 chips, supports double-precision arithmetic too. 8464 For the x86-32 compiler, you must use -march=cpu-type, -msse or -msse2 switches to enable SSE extensions and make this option effective. For the x86-64 compiler, these extensions are 8465 enabled by default. 8466 The resulting code should be considerably faster in the majority of cases and avoid the numerical instability problems of 387 code, but may break some existing code that expects 8467 temporaries to be 80 bits. 8468 This is the default choice for the x86-64 compiler. 8469 sse,387 8470 sse+387 8471 both 8472 Attempt to utilize both instruction sets at once. This effectively doubles the amount of available registers, and on chips with separate execution units for 387 and SSE the execution 8473 resources too. Use this option with care, as it is still experimental, because the GCC register allocator does not model separate functional units well, resulting in unstable 8474 performance. 8475 -masm=dialect 8476 Output assembly instructions using selected dialect. Also affects which dialect is used for basic "asm" and extended "asm". Supported choices (in dialect order) are att or intel. The 8477 default is att. Darwin does not support intel. 8478 -mieee-fp 8479 -mno-ieee-fp 8480 Control whether or not the compiler uses IEEE floating-point comparisons. These correctly handle the case where the result of a comparison is unordered. 8481 -msoft-float 8482 Generate output containing library calls for floating point. 8483 Warning: the requisite libraries are not part of GCC. Normally the facilities of the machine's usual C compiler are used, but this can't be done directly in cross-compilation. You must 8484 make your own arrangements to provide suitable library functions for cross-compilation. 8485 On machines where a function returns floating-point results in the 80387 register stack, some floating-point opcodes may be emitted even if -msoft-float is used. 8486 -mno-fp-ret-in-387 8487 Do not use the FPU registers for return values of functions. 8488 The usual calling convention has functions return values of types "float" and "double" in an FPU register, even if there is no FPU. The idea is that the operating system should emulate an 8489 FPU. 8490 The option -mno-fp-ret-in-387 causes such values to be returned in ordinary CPU registers instead. 8491 -mno-fancy-math-387 8492 Some 387 emulators do not support the "sin", "cos" and "sqrt" instructions for the 387. Specify this option to avoid generating those instructions. This option is the default on OpenBSD 8493 and NetBSD. This option is overridden when -march indicates that the target CPU always has an FPU and so the instruction does not need emulation. These instructions are not generated 8494 unless you also use the -funsafe-math-optimizations switch. 8495 -malign-double 8496 -mno-align-double 8497 Control whether GCC aligns "double", "long double", and "long long" variables on a two-word boundary or a one-word boundary. Aligning "double" variables on a two-word boundary produces code 8498 that runs somewhat faster on a Pentium at the expense of more memory. 8499 On x86-64, -malign-double is enabled by default. 8500 Warning: if you use the -malign-double switch, structures containing the above types are aligned differently than the published application binary interface specifications for the x86-32 and 8501 are not binary compatible with structures in code compiled without that switch. 8502 -m96bit-long-double 8503 -m128bit-long-double 8504 These switches control the size of "long double" type. The x86-32 application binary interface specifies the size to be 96 bits, so -m96bit-long-double is the default in 32-bit mode. 8505 Modern architectures (Pentium and newer) prefer "long double" to be aligned to an 8- or 16-byte boundary. In arrays or structures conforming to the ABI, this is not possible. So specifying 8506 -m128bit-long-double aligns "long double" to a 16-byte boundary by padding the "long double" with an additional 32-bit zero. 8507 In the x86-64 compiler, -m128bit-long-double is the default choice as its ABI specifies that "long double" is aligned on 16-byte boundary. 8508 Notice that neither of these options enable any extra precision over the x87 standard of 80 bits for a "long double". 8509 Warning: if you override the default value for your target ABI, this changes the size of structures and arrays containing "long double" variables, as well as modifying the function calling 8510 convention for functions taking "long double". Hence they are not binary-compatible with code compiled without that switch. 8511 -mlong-double-64 8512 -mlong-double-80 8513 -mlong-double-128 8514 These switches control the size of "long double" type. A size of 64 bits makes the "long double" type equivalent to the "double" type. This is the default for 32-bit Bionic C library. A 8515 size of 128 bits makes the "long double" type equivalent to the "__float128" type. This is the default for 64-bit Bionic C library. 8516 Warning: if you override the default value for your target ABI, this changes the size of structures and arrays containing "long double" variables, as well as modifying the function calling 8517 convention for functions taking "long double". Hence they are not binary-compatible with code compiled without that switch. 8518 -malign-data=type 8519 Control how GCC aligns variables. Supported values for type are compat uses increased alignment value compatible uses GCC 4.8 and earlier, abi uses alignment value as specified by the 8520 psABI, and cacheline uses increased alignment value to match the cache line size. compat is the default. 8521 -mlarge-data-threshold=threshold 8522 When -mcmodel=medium is specified, data objects larger than threshold are placed in the large data section. This value must be the same across all objects linked into the binary, and 8523 defaults to 65535. 8524 -mrtd 8525 Use a different function-calling convention, in which functions that take a fixed number of arguments return with the "ret num" instruction, which pops their arguments while returning. This 8526 saves one instruction in the caller since there is no need to pop the arguments there. 8527 You can specify that an individual function is called with this calling sequence with the function attribute "stdcall". You can also override the -mrtd option by using the function 8528 attribute "cdecl". 8529 Warning: this calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler. 8530 Also, you must provide function prototypes for all functions that take variable numbers of arguments (including "printf"); otherwise incorrect code is generated for calls to those functions. 8531 In addition, seriously incorrect code results if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.) 8532 -mregparm=num 8533 Control how many registers are used to pass integer arguments. By default, no registers are used to pass arguments, and at most 3 registers can be used. You can control this behavior for a 8534 specific function by using the function attribute "regparm". 8535 Warning: if you use this switch, and num is nonzero, then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules. 8536 -msseregparm 8537 Use SSE register passing conventions for float and double arguments and return values. You can control this behavior for a specific function by using the function attribute "sseregparm". 8538 Warning: if you use this switch then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules. 8539 -mvect8-ret-in-mem 8540 Return 8-byte vectors in memory instead of MMX registers. This is the default on Solaris@tie{}8 and 9 and VxWorks to match the ABI of the Sun Studio compilers until version 12. Later 8541 compiler versions (starting with Studio 12 Update@tie{}1) follow the ABI used by other x86 targets, which is the default on Solaris@tie{}10 and later. Only use this option if you need to 8542 remain compatible with existing code produced by those previous compiler versions or older versions of GCC. 8543 -mpc32 8544 -mpc64 8545 -mpc80 8546 Set 80387 floating-point precision to 32, 64 or 80 bits. When -mpc32 is specified, the significands of results of floating-point operations are rounded to 24 bits (single precision); -mpc64 8547 rounds the significands of results of floating-point operations to 53 bits (double precision) and -mpc80 rounds the significands of results of floating-point operations to 64 bits (extended 8548 double precision), which is the default. When this option is used, floating-point operations in higher precisions are not available to the programmer without setting the FPU control word 8549 explicitly. 8550 Setting the rounding of floating-point operations to less than the default 80 bits can speed some programs by 2% or more. Note that some mathematical libraries assume that extended- 8551 precision (80-bit) floating-point operations are enabled by default; routines in such libraries could suffer significant loss of accuracy, typically through so-called "catastrophic 8552 cancellation", when this option is used to set the precision to less than extended precision. 8553 -mstackrealign 8554 Realign the stack at entry. On the x86, the -mstackrealign option generates an alternate prologue and epilogue that realigns the run-time stack if necessary. This supports mixing legacy 8555 codes that keep 4-byte stack alignment with modern codes that keep 16-byte stack alignment for SSE compatibility. See also the attribute "force_align_arg_pointer", applicable to individual 8556 functions. 8557 -mpreferred-stack-boundary=num 8558 Attempt to keep the stack boundary aligned to a 2 raised to num byte boundary. If -mpreferred-stack-boundary is not specified, the default is 4 (16 bytes or 128 bits). 8559 Warning: When generating code for the x86-64 architecture with SSE extensions disabled, -mpreferred-stack-boundary=3 can be used to keep the stack boundary aligned to 8 byte boundary. Since 8560 x86-64 ABI require 16 byte stack alignment, this is ABI incompatible and intended to be used in controlled environment where stack space is important limitation. This option leads to wrong 8561 code when functions compiled with 16 byte stack alignment (such as functions from a standard library) are called with misaligned stack. In this case, SSE instructions may lead to misaligned 8562 memory access traps. In addition, variable arguments are handled incorrectly for 16 byte aligned objects (including x87 long double and __int128), leading to wrong results. You must build 8563 all modules with -mpreferred-stack-boundary=3, including any libraries. This includes the system libraries and startup modules. 8564 -mincoming-stack-boundary=num 8565 Assume the incoming stack is aligned to a 2 raised to num byte boundary. If -mincoming-stack-boundary is not specified, the one specified by -mpreferred-stack-boundary is used. 8566 On Pentium and Pentium Pro, "double" and "long double" values should be aligned to an 8-byte boundary (see -malign-double) or suffer significant run time performance penalties. On Pentium 8567 III, the Streaming SIMD Extension (SSE) data type "__m128" may not work properly if it is not 16-byte aligned. 8568 To ensure proper alignment of this values on the stack, the stack boundary must be as aligned as that required by any value stored on the stack. Further, every function must be generated 8569 such that it keeps the stack aligned. Thus calling a function compiled with a higher preferred stack boundary from a function compiled with a lower preferred stack boundary most likely 8570 misaligns the stack. It is recommended that libraries that use callbacks always use the default setting. 8571 This extra alignment does consume extra stack space, and generally increases code size. Code that is sensitive to stack space usage, such as embedded systems and operating system kernels, 8572 may want to reduce the preferred alignment to -mpreferred-stack-boundary=2. 8573 -mmmx 8574 -msse 8575 -msse2 8576 -msse3 8577 -mssse3 8578 -msse4 8579 -msse4a 8580 -msse4.1 8581 -msse4.2 8582 -mavx 8583 -mavx2 8584 -mavx512f 8585 -mavx512pf 8586 -mavx512er 8587 -mavx512cd 8588 -msha 8589 -maes 8590 -mpclmul 8591 -mclfushopt 8592 -mfsgsbase 8593 -mrdrnd 8594 -mf16c 8595 -mfma 8596 -mfma4 8597 -mno-fma4 8598 -mprefetchwt1 8599 -mxop 8600 -mlwp 8601 -m3dnow 8602 -mpopcnt 8603 -mabm 8604 -mbmi 8605 -mbmi2 8606 -mlzcnt 8607 -mfxsr 8608 -mxsave 8609 -mxsaveopt 8610 -mxsavec 8611 -mxsaves 8612 -mrtm 8613 -mtbm 8614 -mmpx 8615 -mmwaitx 8616 These switches enable the use of instructions in the MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, AVX, AVX2, AVX512F, AVX512PF, AVX512ER, AVX512CD, SHA, AES, PCLMUL, FSGSBASE, RDRND, F16C, FMA, 8617 SSE4A, FMA4, XOP, LWP, ABM, BMI, BMI2, FXSR, XSAVE, XSAVEOPT, LZCNT, RTM, MPX, MWAITX or 3DNow! extended instruction sets. Each has a corresponding -mno- option to disable use of these 8618 instructions. 8619 These extensions are also available as built-in functions: see x86 Built-in Functions, for details of the functions enabled and disabled by these switches. 8620 To generate SSE/SSE2 instructions automatically from floating-point code (as opposed to 387 instructions), see -mfpmath=sse. 8621 GCC depresses SSEx instructions when -mavx is used. Instead, it generates new AVX instructions or AVX equivalence for all SSEx instructions when needed. 8622 These options enable GCC to use these extended instructions in generated code, even without -mfpmath=sse. Applications that perform run-time CPU detection must compile separate files for 8623 each supported architecture, using the appropriate flags. In particular, the file containing the CPU detection code should be compiled without these options. 8624 -mdump-tune-features 8625 This option instructs GCC to dump the names of the x86 performance tuning features and default settings. The names can be used in -mtune-ctrl=feature-list. 8626 -mtune-ctrl=feature-list 8627 This option is used to do fine grain control of x86 code generation features. feature-list is a comma separated list of feature names. See also -mdump-tune-features. When specified, the 8628 feature is turned on if it is not preceded with ^, otherwise, it is turned off. -mtune-ctrl=feature-list is intended to be used by GCC developers. Using it may lead to code paths not 8629 covered by testing and can potentially result in compiler ICEs or runtime errors. 8630 -mno-default 8631 This option instructs GCC to turn off all tunable features. See also -mtune-ctrl=feature-list and -mdump-tune-features. 8632 -mcld 8633 This option instructs GCC to emit a "cld" instruction in the prologue of functions that use string instructions. String instructions depend on the DF flag to select between autoincrement or 8634 autodecrement mode. While the ABI specifies the DF flag to be cleared on function entry, some operating systems violate this specification by not clearing the DF flag in their exception 8635 dispatchers. The exception handler can be invoked with the DF flag set, which leads to wrong direction mode when string instructions are used. This option can be enabled by default on 8636 32-bit x86 targets by configuring GCC with the --enable-cld configure option. Generation of "cld" instructions can be suppressed with the -mno-cld compiler option in this case. 8637 -mvzeroupper 8638 This option instructs GCC to emit a "vzeroupper" instruction before a transfer of control flow out of the function to minimize the AVX to SSE transition penalty as well as remove unnecessary 8639 "zeroupper" intrinsics. 8640 -mprefer-avx128 8641 This option instructs GCC to use 128-bit AVX instructions instead of 256-bit AVX instructions in the auto-vectorizer. 8642 -mcx16 8643 This option enables GCC to generate "CMPXCHG16B" instructions. "CMPXCHG16B" allows for atomic operations on 128-bit double quadword (or oword) data types. This is useful for high- 8644 resolution counters that can be updated by multiple processors (or cores). This instruction is generated as part of atomic built-in functions: see __sync Builtins or __atomic Builtins for 8645 details. 8646 -msahf 8647 This option enables generation of "SAHF" instructions in 64-bit code. Early Intel Pentium 4 CPUs with Intel 64 support, prior to the introduction of Pentium 4 G1 step in December 2005, 8648 lacked the "LAHF" and "SAHF" instructions which are supported by AMD64. These are load and store instructions, respectively, for certain status flags. In 64-bit mode, the "SAHF" 8649 instruction is used to optimize "fmod", "drem", and "remainder" built-in functions; see Other Builtins for details. 8650 -mmovbe 8651 This option enables use of the "movbe" instruction to implement "__builtin_bswap32" and "__builtin_bswap64". 8652 -mcrc32 8653 This option enables built-in functions "__builtin_ia32_crc32qi", "__builtin_ia32_crc32hi", "__builtin_ia32_crc32si" and "__builtin_ia32_crc32di" to generate the "crc32" machine instruction. 8654 -mrecip 8655 This option enables use of "RCPSS" and "RSQRTSS" instructions (and their vectorized variants "RCPPS" and "RSQRTPS") with an additional Newton-Raphson step to increase precision instead of 8656 "DIVSS" and "SQRTSS" (and their vectorized variants) for single-precision floating-point arguments. These instructions are generated only when -funsafe-math-optimizations is enabled 8657 together with -finite-math-only and -fno-trapping-math. Note that while the throughput of the sequence is higher than the throughput of the non-reciprocal instruction, the precision of the 8658 sequence can be decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994). 8659 Note that GCC implements "1.0f/sqrtf(x)" in terms of "RSQRTSS" (or "RSQRTPS") already with -ffast-math (or the above option combination), and doesn't need -mrecip. 8660 Also note that GCC emits the above sequence with additional Newton-Raphson step for vectorized single-float division and vectorized "sqrtf(x)" already with -ffast-math (or the above option 8661 combination), and doesn't need -mrecip. 8662 -mrecip=opt 8663 This option controls which reciprocal estimate instructions may be used. opt is a comma-separated list of options, which may be preceded by a ! to invert the option: 8664 all Enable all estimate instructions. 8665 default 8666 Enable the default instructions, equivalent to -mrecip. 8667 none 8668 Disable all estimate instructions, equivalent to -mno-recip. 8669 div Enable the approximation for scalar division. 8670 vec-div 8671 Enable the approximation for vectorized division. 8672 sqrt 8673 Enable the approximation for scalar square root. 8674 vec-sqrt 8675 Enable the approximation for vectorized square root. 8676 So, for example, -mrecip=all,!sqrt enables all of the reciprocal approximations, except for square root. 8677 -mveclibabi=type 8678 Specifies the ABI type to use for vectorizing intrinsics using an external library. Supported values for type are svml for the Intel short vector math library and acml for the AMD math core 8679 library. To use this option, both -ftree-vectorize and -funsafe-math-optimizations have to be enabled, and an SVML or ACML ABI-compatible library must be specified at link time. 8680 GCC currently emits calls to "vmldExp2", "vmldLn2", "vmldLog102", "vmldLog102", "vmldPow2", "vmldTanh2", "vmldTan2", "vmldAtan2", "vmldAtanh2", "vmldCbrt2", "vmldSinh2", "vmldSin2", 8681 "vmldAsinh2", "vmldAsin2", "vmldCosh2", "vmldCos2", "vmldAcosh2", "vmldAcos2", "vmlsExp4", "vmlsLn4", "vmlsLog104", "vmlsLog104", "vmlsPow4", "vmlsTanh4", "vmlsTan4", "vmlsAtan4", 8682 "vmlsAtanh4", "vmlsCbrt4", "vmlsSinh4", "vmlsSin4", "vmlsAsinh4", "vmlsAsin4", "vmlsCosh4", "vmlsCos4", "vmlsAcosh4" and "vmlsAcos4" for corresponding function type when -mveclibabi=svml is 8683 used, and "__vrd2_sin", "__vrd2_cos", "__vrd2_exp", "__vrd2_log", "__vrd2_log2", "__vrd2_log10", "__vrs4_sinf", "__vrs4_cosf", "__vrs4_expf", "__vrs4_logf", "__vrs4_log2f", "__vrs4_log10f" 8684 and "__vrs4_powf" for the corresponding function type when -mveclibabi=acml is used. 8685 -mabi=name 8686 Generate code for the specified calling convention. Permissible values are sysv for the ABI used on GNU/Linux and other systems, and ms for the Microsoft ABI. The default is to use the 8687 Microsoft ABI when targeting Microsoft Windows and the SysV ABI on all other systems. You can control this behavior for specific functions by using the function attributes "ms_abi" and 8688 "sysv_abi". 8689 -mtls-dialect=type 8690 Generate code to access thread-local storage using the gnu or gnu2 conventions. gnu is the conservative default; gnu2 is more efficient, but it may add compile- and run-time requirements 8691 that cannot be satisfied on all systems. 8692 -mpush-args 8693 -mno-push-args 8694 Use PUSH operations to store outgoing parameters. This method is shorter and usually equally fast as method using SUB/MOV operations and is enabled by default. In some cases disabling it 8695 may improve performance because of improved scheduling and reduced dependencies. 8696 -maccumulate-outgoing-args 8697 If enabled, the maximum amount of space required for outgoing arguments is computed in the function prologue. This is faster on most modern CPUs because of reduced dependencies, improved 8698 scheduling and reduced stack usage when the preferred stack boundary is not equal to 2. The drawback is a notable increase in code size. This switch implies -mno-push-args. 8699 -mthreads 8700 Support thread-safe exception handling on MinGW. Programs that rely on thread-safe exception handling must compile and link all code with the -mthreads option. When compiling, -mthreads 8701 defines -D_MT; when linking, it links in a special thread helper library -lmingwthrd which cleans up per-thread exception-handling data. 8702 -mno-align-stringops 8703 Do not align the destination of inlined string operations. This switch reduces code size and improves performance in case the destination is already aligned, but GCC doesn't know about it. 8704 -minline-all-stringops 8705 By default GCC inlines string operations only when the destination is known to be aligned to least a 4-byte boundary. This enables more inlining and increases code size, but may improve 8706 performance of code that depends on fast "memcpy", "strlen", and "memset" for short lengths. 8707 -minline-stringops-dynamically 8708 For string operations of unknown size, use run-time checks with inline code for small blocks and a library call for large blocks. 8709 -mstringop-strategy=alg 8710 Override the internal decision heuristic for the particular algorithm to use for inlining string operations. The allowed values for alg are: 8711 rep_byte 8712 rep_4byte 8713 rep_8byte 8714 Expand using i386 "rep" prefix of the specified size. 8715 byte_loop 8716 loop 8717 unrolled_loop 8718 Expand into an inline loop. 8719 libcall 8720 Always use a library call. 8721 -mmemcpy-strategy=strategy 8722 Override the internal decision heuristic to decide if "__builtin_memcpy" should be inlined and what inline algorithm to use when the expected size of the copy operation is known. strategy is 8723 a comma-separated list of alg:max_size:dest_align triplets. alg is specified in -mstringop-strategy, max_size specifies the max byte size with which inline algorithm alg is allowed. For 8724 the last triplet, the max_size must be "-1". The max_size of the triplets in the list must be specified in increasing order. The minimal byte size for alg is 0 for the first triplet and 8725 "max_size + 1" of the preceding range. 8726 -mmemset-strategy=strategy 8727 The option is similar to -mmemcpy-strategy= except that it is to control "__builtin_memset" expansion. 8728 -momit-leaf-frame-pointer 8729 Don't keep the frame pointer in a register for leaf functions. This avoids the instructions to save, set up, and restore frame pointers and makes an extra register available in leaf 8730 functions. The option -fomit-leaf-frame-pointer removes the frame pointer for leaf functions, which might make debugging harder. 8731 -mtls-direct-seg-refs 8732 -mno-tls-direct-seg-refs 8733 Controls whether TLS variables may be accessed with offsets from the TLS segment register (%gs for 32-bit, %fs for 64-bit), or whether the thread base pointer must be added. Whether or not 8734 this is valid depends on the operating system, and whether it maps the segment to cover the entire TLS area. 8735 For systems that use the GNU C Library, the default is on. 8736 -msse2avx 8737 -mno-sse2avx 8738 Specify that the assembler should encode SSE instructions with VEX prefix. The option -mavx turns this on by default. 8739 -mfentry 8740 -mno-fentry 8741 If profiling is active (-pg), put the profiling counter call before the prologue. Note: On x86 architectures the attribute "ms_hook_prologue" isn't possible at the moment for -mfentry and 8742 -pg. 8743 -mrecord-mcount 8744 -mno-record-mcount 8745 If profiling is active (-pg), generate a __mcount_loc section that contains pointers to each profiling call. This is useful for automatically patching and out calls. 8746 -mnop-mcount 8747 -mno-nop-mcount 8748 If profiling is active (-pg), generate the calls to the profiling functions as nops. This is useful when they should be patched in later dynamically. This is likely only useful together with 8749 -mrecord-mcount. 8750 -mskip-rax-setup 8751 -mno-skip-rax-setup 8752 When generating code for the x86-64 architecture with SSE extensions disabled, -skip-rax-setup can be used to skip setting up RAX register when there are no variable arguments passed in 8753 vector registers. 8754 Warning: Since RAX register is used to avoid unnecessarily saving vector registers on stack when passing variable arguments, the impacts of this option are callees may waste some stack 8755 space, misbehave or jump to a random location. GCC 4.4 or newer don't have those issues, regardless the RAX register value. 8756 -m8bit-idiv 8757 -mno-8bit-idiv 8758 On some processors, like Intel Atom, 8-bit unsigned integer divide is much faster than 32-bit/64-bit integer divide. This option generates a run-time check. If both dividend and divisor 8759 are within range of 0 to 255, 8-bit unsigned integer divide is used instead of 32-bit/64-bit integer divide. 8760 -mavx256-split-unaligned-load 8761 -mavx256-split-unaligned-store 8762 Split 32-byte AVX unaligned load and store. 8763 -mstack-protector-guard=guard 8764 Generate stack protection code using canary at guard. Supported locations are global for global canary or tls for per-thread canary in the TLS block (the default). This option has effect 8765 only when -fstack-protector or -fstack-protector-all is specified. 8766 These -m switches are supported in addition to the above on x86-64 processors in 64-bit environments. 8767 -m32 8768 -m64 8769 -mx32 8770 -m16 8771 Generate code for a 16-bit, 32-bit or 64-bit environment. The -m32 option sets "int", "long", and pointer types to 32 bits, and generates code that runs on any i386 system. 8772 The -m64 option sets "int" to 32 bits and "long" and pointer types to 64 bits, and generates code for the x86-64 architecture. For Darwin only the -m64 option also turns off the -fno-pic 8773 and -mdynamic-no-pic options. 8774 The -mx32 option sets "int", "long", and pointer types to 32 bits, and generates code for the x86-64 architecture. 8775 The -m16 option is the same as -m32, except for that it outputs the ".code16gcc" assembly directive at the beginning of the assembly output so that the binary can run in 16-bit mode. 8776 -mno-red-zone 8777 Do not use a so-called "red zone" for x86-64 code. The red zone is mandated by the x86-64 ABI; it is a 128-byte area beyond the location of the stack pointer that is not modified by signal 8778 or interrupt handlers and therefore can be used for temporary data without adjusting the stack pointer. The flag -mno-red-zone disables this red zone. 8779 -mcmodel=small 8780 Generate code for the small code model: the program and its symbols must be linked in the lower 2 GB of the address space. Pointers are 64 bits. Programs can be statically or dynamically 8781 linked. This is the default code model. 8782 -mcmodel=kernel 8783 Generate code for the kernel code model. The kernel runs in the negative 2 GB of the address space. This model has to be used for Linux kernel code. 8784 -mcmodel=medium 8785 Generate code for the medium model: the program is linked in the lower 2 GB of the address space. Small symbols are also placed there. Symbols with sizes larger than -mlarge-data-threshold 8786 are put into large data or BSS sections and can be located above 2GB. Programs can be statically or dynamically linked. 8787 -mcmodel=large 8788 Generate code for the large model. This model makes no assumptions about addresses and sizes of sections. 8789 -maddress-mode=long 8790 Generate code for long address mode. This is only supported for 64-bit and x32 environments. It is the default address mode for 64-bit environments. 8791 -maddress-mode=short 8792 Generate code for short address mode. This is only supported for 32-bit and x32 environments. It is the default address mode for 32-bit and x32 environments. 8793 x86 Windows Options 8794 These additional options are available for Microsoft Windows targets: 8795 -mconsole 8796 This option specifies that a console application is to be generated, by instructing the linker to set the PE header subsystem type required for console applications. This option is 8797 available for Cygwin and MinGW targets and is enabled by default on those targets. 8798 -mdll 8799 This option is available for Cygwin and MinGW targets. It specifies that a DLL---a dynamic link library---is to be generated, enabling the selection of the required runtime startup object 8800 and entry point. 8801 -mnop-fun-dllimport 8802 This option is available for Cygwin and MinGW targets. It specifies that the "dllimport" attribute should be ignored. 8803 -mthread 8804 This option is available for MinGW targets. It specifies that MinGW-specific thread support is to be used. 8805 -municode 8806 This option is available for MinGW-w64 targets. It causes the "UNICODE" preprocessor macro to be predefined, and chooses Unicode-capable runtime startup code. 8807 -mwin32 8808 This option is available for Cygwin and MinGW targets. It specifies that the typical Microsoft Windows predefined macros are to be set in the pre-processor, but does not influence the 8809 choice of runtime library/startup code. 8810 -mwindows 8811 This option is available for Cygwin and MinGW targets. It specifies that a GUI application is to be generated by instructing the linker to set the PE header subsystem type appropriately. 8812 -fno-set-stack-executable 8813 This option is available for MinGW targets. It specifies that the executable flag for the stack used by nested functions isn't set. This is necessary for binaries running in kernel mode of 8814 Microsoft Windows, as there the User32 API, which is used to set executable privileges, isn't available. 8815 -fwritable-relocated-rdata 8816 This option is available for MinGW and Cygwin targets. It specifies that relocated-data in read-only section is put into .data section. This is a necessary for older runtimes not 8817 supporting modification of .rdata sections for pseudo-relocation. 8818 -mpe-aligned-commons 8819 This option is available for Cygwin and MinGW targets. It specifies that the GNU extension to the PE file format that permits the correct alignment of COMMON variables should be used when 8820 generating code. It is enabled by default if GCC detects that the target assembler found during configuration supports the feature. 8821 See also under x86 Options for standard options. 8822 Xstormy16 Options 8823 These options are defined for Xstormy16: 8824 -msim 8825 Choose startup files and linker script suitable for the simulator. 8826 Xtensa Options 8827 These options are supported for Xtensa targets: 8828 -mconst16 8829 -mno-const16 8830 Enable or disable use of "CONST16" instructions for loading constant values. The "CONST16" instruction is currently not a standard option from Tensilica. When enabled, "CONST16" 8831 instructions are always used in place of the standard "L32R" instructions. The use of "CONST16" is enabled by default only if the "L32R" instruction is not available. 8832 -mfused-madd 8833 -mno-fused-madd 8834 Enable or disable use of fused multiply/add and multiply/subtract instructions in the floating-point option. This has no effect if the floating-point option is not also enabled. Disabling 8835 fused multiply/add and multiply/subtract instructions forces the compiler to use separate instructions for the multiply and add/subtract operations. This may be desirable in some cases 8836 where strict IEEE 754-compliant results are required: the fused multiply add/subtract instructions do not round the intermediate result, thereby producing results with more bits of precision 8837 than specified by the IEEE standard. Disabling fused multiply add/subtract instructions also ensures that the program output is not sensitive to the compiler's ability to combine multiply 8838 and add/subtract operations. 8839 -mserialize-volatile 8840 -mno-serialize-volatile 8841 When this option is enabled, GCC inserts "MEMW" instructions before "volatile" memory references to guarantee sequential consistency. The default is -mserialize-volatile. Use 8842 -mno-serialize-volatile to omit the "MEMW" instructions. 8843 -mforce-no-pic 8844 For targets, like GNU/Linux, where all user-mode Xtensa code must be position-independent code (PIC), this option disables PIC for compiling kernel code. 8845 -mtext-section-literals 8846 -mno-text-section-literals 8847 These options control the treatment of literal pools. The default is -mno-text-section-literals, which places literals in a separate section in the output file. This allows the literal 8848 pool to be placed in a data RAM/ROM, and it also allows the linker to combine literal pools from separate object files to remove redundant literals and improve code size. With 8849 -mtext-section-literals, the literals are interspersed in the text section in order to keep them as close as possible to their references. This may be necessary for large assembly files. 8850 -mtarget-align 8851 -mno-target-align 8852 When this option is enabled, GCC instructs the assembler to automatically align instructions to reduce branch penalties at the expense of some code density. The assembler attempts to widen 8853 density instructions to align branch targets and the instructions following call instructions. If there are not enough preceding safe density instructions to align a target, no widening is 8854 performed. The default is -mtarget-align. These options do not affect the treatment of auto-aligned instructions like "LOOP", which the assembler always aligns, either by widening density 8855 instructions or by inserting NOP instructions. 8856 -mlongcalls 8857 -mno-longcalls 8858 When this option is enabled, GCC instructs the assembler to translate direct calls to indirect calls unless it can determine that the target of a direct call is in the range allowed by the 8859 call instruction. This translation typically occurs for calls to functions in other source files. Specifically, the assembler translates a direct "CALL" instruction into an "L32R" followed 8860 by a "CALLX" instruction. The default is -mno-longcalls. This option should be used in programs where the call target can potentially be out of range. This option is implemented in the 8861 assembler, not the compiler, so the assembly code generated by GCC still shows direct call instructions---look at the disassembled object code to see the actual instructions. Note that the 8862 assembler uses an indirect call for every cross-file call, not just those that really are out of range. 8863 zSeries Options 8864 These are listed under 8865 Options for Code Generation Conventions 8866 These machine-independent options control the interface conventions used in code generation. 8867 Most of them have both positive and negative forms; the negative form of -ffoo is -fno-foo. In the table below, only one of the forms is listed---the one that is not the default. You can 8868 figure out the other form by either removing no- or adding it. 8869 -fbounds-check 8870 For front ends that support it, generate additional code to check that indices used to access arrays are within the declared range. This is currently only supported by the Java and Fortran 8871 front ends, where this option defaults to true and false respectively. 8872 -fstack-reuse=reuse-level 8873 This option controls stack space reuse for user declared local/auto variables and compiler generated temporaries. reuse_level can be all, named_vars, or none. all enables stack reuse for 8874 all local variables and temporaries, named_vars enables the reuse only for user defined local variables with names, and none disables stack reuse completely. The default value is all. The 8875 option is needed when the program extends the lifetime of a scoped local variable or a compiler generated temporary beyond the end point defined by the language. When a lifetime of a 8876 variable ends, and if the variable lives in memory, the optimizing compiler has the freedom to reuse its stack space with other temporaries or scoped local variables whose live range does 8877 not overlap with it. Legacy code extending local lifetime is likely to break with the stack reuse optimization. 8878 For example, 8879 int *p; 8880 { 8881 int local1; 8882 p = &local1; 8883 local1 = 10; 8884 .... 8885 } 8886 { 8887 int local2; 8888 local2 = 20; 8889 ... 8890 } 8891 if (*p == 10) // out of scope use of local1 8892 { 8893 } 8894 Another example: 8895 struct A 8896 { 8897 A(int k) : i(k), j(k) { } 8898 int i; 8899 int j; 8900 }; 8901 A *ap; 8902 void foo(const A& ar) 8903 { 8904 ap = &ar; 8905 } 8906 void bar() 8907 { 8908 foo(A(10)); // temp object's lifetime ends when foo returns 8909 { 8910 A a(20); 8911 .... 8912 } 8913 ap->i+= 10; // ap references out of scope temp whose space 8914 // is reused with a. What is the value of ap->i? 8915 } 8916 The lifetime of a compiler generated temporary is well defined by the C++ standard. When a lifetime of a temporary ends, and if the temporary lives in memory, the optimizing compiler has the 8917 freedom to reuse its stack space with other temporaries or scoped local variables whose live range does not overlap with it. However some of the legacy code relies on the behavior of older 8918 compilers in which temporaries' stack space is not reused, the aggressive stack reuse can lead to runtime errors. This option is used to control the temporary stack reuse optimization. 8919 -ftrapv 8920 This option generates traps for signed overflow on addition, subtraction, multiplication operations. 8921 -fwrapv 8922 This option instructs the compiler to assume that signed arithmetic overflow of addition, subtraction and multiplication wraps around using twos-complement representation. This flag enables 8923 some optimizations and disables others. This option is enabled by default for the Java front end, as required by the Java language specification. 8924 -fexceptions 8925 Enable exception handling. Generates extra code needed to propagate exceptions. For some targets, this implies GCC generates frame unwind information for all functions, which can produce 8926 significant data size overhead, although it does not affect execution. If you do not specify this option, GCC enables it by default for languages like C++ that normally require exception 8927 handling, and disables it for languages like C that do not normally require it. However, you may need to enable this option when compiling C code that needs to interoperate properly with 8928 exception handlers written in C++. You may also wish to disable this option if you are compiling older C++ programs that don't use exception handling. 8929 -fnon-call-exceptions 8930 Generate code that allows trapping instructions to throw exceptions. Note that this requires platform-specific runtime support that does not exist everywhere. Moreover, it only allows 8931 trapping instructions to throw exceptions, i.e. memory references or floating-point instructions. It does not allow exceptions to be thrown from arbitrary signal handlers such as "SIGALRM". 8932 -fdelete-dead-exceptions 8933 Consider that instructions that may throw exceptions but don't otherwise contribute to the execution of the program can be optimized away. This option is enabled by default for the Ada 8934 front end, as permitted by the Ada language specification. Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels. 8935 -funwind-tables 8936 Similar to -fexceptions, except that it just generates any needed static data, but does not affect the generated code in any other way. You normally do not need to enable this option; 8937 instead, a language processor that needs this handling enables it on your behalf. 8938 -fasynchronous-unwind-tables 8939 Generate unwind table in DWARF 2 format, if supported by target machine. The table is exact at each instruction boundary, so it can be used for stack unwinding from asynchronous events 8940 (such as debugger or garbage collector). 8941 -fno-gnu-unique 8942 On systems with recent GNU assembler and C library, the C++ compiler uses the "STB_GNU_UNIQUE" binding to make sure that definitions of template static data members and static local 8943 variables in inline functions are unique even in the presence of "RTLD_LOCAL"; this is necessary to avoid problems with a library used by two different "RTLD_LOCAL" plugins depending on a 8944 definition in one of them and therefore disagreeing with the other one about the binding of the symbol. But this causes "dlclose" to be ignored for affected DSOs; if your program relies on 8945 reinitialization of a DSO via "dlclose" and "dlopen", you can use -fno-gnu-unique. 8946 -fpcc-struct-return 8947 Return "short" "struct" and "union" values in memory like longer ones, rather than in registers. This convention is less efficient, but it has the advantage of allowing intercallability 8948 between GCC-compiled files and files compiled with other compilers, particularly the Portable C Compiler (pcc). 8949 The precise convention for returning structures in memory depends on the target configuration macros. 8950 Short structures and unions are those whose size and alignment match that of some integer type. 8951 Warning: code compiled with the -fpcc-struct-return switch is not binary compatible with code compiled with the -freg-struct-return switch. Use it to conform to a non-default application 8952 binary interface. 8953 -freg-struct-return 8954 Return "struct" and "union" values in registers when possible. This is more efficient for small structures than -fpcc-struct-return. 8955 If you specify neither -fpcc-struct-return nor -freg-struct-return, GCC defaults to whichever convention is standard for the target. If there is no standard convention, GCC defaults to 8956 -fpcc-struct-return, except on targets where GCC is the principal compiler. In those cases, we can choose the standard, and we chose the more efficient register return alternative. 8957 Warning: code compiled with the -freg-struct-return switch is not binary compatible with code compiled with the -fpcc-struct-return switch. Use it to conform to a non-default application 8958 binary interface. 8959 -fshort-enums 8960 Allocate to an "enum" type only as many bytes as it needs for the declared range of possible values. Specifically, the "enum" type is equivalent to the smallest integer type that has enough 8961 room. 8962 Warning: the -fshort-enums switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary 8963 interface. 8964 -fshort-double 8965 Use the same size for "double" as for "float". 8966 Warning: the -fshort-double switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary 8967 interface. 8968 -fshort-wchar 8969 Override the underlying type for "wchar_t" to be "short unsigned int" instead of the default for the target. This option is useful for building programs to run under WINE. 8970 Warning: the -fshort-wchar switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary 8971 interface. 8972 -fno-common 8973 In C code, controls the placement of uninitialized global variables. Unix C compilers have traditionally permitted multiple definitions of such variables in different compilation units by 8974 placing the variables in a common block. This is the behavior specified by -fcommon, and is the default for GCC on most targets. On the other hand, this behavior is not required by ISO C, 8975 and on some targets may carry a speed or code size penalty on variable references. The -fno-common option specifies that the compiler should place uninitialized global variables in the data 8976 section of the object file, rather than generating them as common blocks. This has the effect that if the same variable is declared (without "extern") in two different compilations, you get 8977 a multiple-definition error when you link them. In this case, you must compile with -fcommon instead. Compiling with -fno-common is useful on targets for which it provides better 8978 performance, or if you wish to verify that the program will work on other systems that always treat uninitialized variable declarations this way. 8979 -fno-ident 8980 Ignore the "#ident" directive. 8981 -finhibit-size-directive 8982 Don't output a ".size" assembler directive, or anything else that would cause trouble if the function is split in the middle, and the two halves are placed at locations far apart in memory. 8983 This option is used when compiling crtstuff.c; you should not need to use it for anything else. 8984 -fverbose-asm 8985 Put extra commentary information in the generated assembly code to make it more readable. This option is generally only of use to those who actually need to read the generated assembly code 8986 (perhaps while debugging the compiler itself). 8987 -fno-verbose-asm, the default, causes the extra information to be omitted and is useful when comparing two assembler files. 8988 -frecord-gcc-switches 8989 This switch causes the command line used to invoke the compiler to be recorded into the object file that is being created. This switch is only implemented on some targets and the exact 8990 format of the recording is target and binary file format dependent, but it usually takes the form of a section containing ASCII text. This switch is related to the -fverbose-asm switch, but 8991 that switch only records information in the assembler output file as comments, so it never reaches the object file. See also -grecord-gcc-switches for another way of storing compiler 8992 options into the object file. 8993 -fpic 8994 Generate position-independent code (PIC) suitable for use in a shared library, if supported for the target machine. Such code accesses all constant addresses through a global offset table 8995 (GOT). The dynamic loader resolves the GOT entries when the program starts (the dynamic loader is not part of GCC; it is part of the operating system). If the GOT size for the linked 8996 executable exceeds a machine-specific maximum size, you get an error message from the linker indicating that -fpic does not work; in that case, recompile with -fPIC instead. (These maximums 8997 are 8k on the SPARC and 32k on the m68k and RS/6000. The x86 has no such limit.) 8998 Position-independent code requires special support, and therefore works only on certain machines. For the x86, GCC supports PIC for System V but not for the Sun 386i. Code generated for 8999 the IBM RS/6000 is always position-independent. 9000 When this flag is set, the macros "__pic__" and "__PIC__" are defined to 1. 9001 -fPIC 9002 If supported for the target machine, emit position-independent code, suitable for dynamic linking and avoiding any limit on the size of the global offset table. This option makes a 9003 difference on the m68k, PowerPC and SPARC. 9004 Position-independent code requires special support, and therefore works only on certain machines. 9005 When this flag is set, the macros "__pic__" and "__PIC__" are defined to 2. 9006 -fpie 9007 -fPIE 9008 These options are similar to -fpic and -fPIC, but generated position independent code can be only linked into executables. Usually these options are used when -pie GCC option is used during 9009 linking. 9010 -fpie and -fPIE both define the macros "__pie__" and "__PIE__". The macros have the value 1 for -fpie and 2 for -fPIE. 9011 -fno-jump-tables 9012 Do not use jump tables for switch statements even where it would be more efficient than other code generation strategies. This option is of use in conjunction with -fpic or -fPIC for 9013 building code that forms part of a dynamic linker and cannot reference the address of a jump table. On some targets, jump tables do not require a GOT and this option is not needed. 9014 -ffixed-reg 9015 Treat the register named reg as a fixed register; generated code should never refer to it (except perhaps as a stack pointer, frame pointer or in some other fixed role). 9016 reg must be the name of a register. The register names accepted are machine-specific and are defined in the "REGISTER_NAMES" macro in the machine description macro file. 9017 This flag does not have a negative form, because it specifies a three-way choice. 9018 -fcall-used-reg 9019 Treat the register named reg as an allocable register that is clobbered by function calls. It may be allocated for temporaries or variables that do not live across a call. Functions 9020 compiled this way do not save and restore the register reg. 9021 It is an error to use this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model produces 9022 disastrous results. 9023 This flag does not have a negative form, because it specifies a three-way choice. 9024 -fcall-saved-reg 9025 Treat the register named reg as an allocable register saved by functions. It may be allocated even for temporaries or variables that live across a call. Functions compiled this way save 9026 and restore the register reg if they use it. 9027 It is an error to use this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model produces 9028 disastrous results. 9029 A different sort of disaster results from the use of this flag for a register in which function values may be returned. 9030 This flag does not have a negative form, because it specifies a three-way choice. 9031 -fpack-struct[=n] 9032 Without a value specified, pack all structure members together without holes. When a value is specified (which must be a small power of two), pack structure members according to this value, 9033 representing the maximum alignment (that is, objects with default alignment requirements larger than this are output potentially unaligned at the next fitting location. 9034 Warning: the -fpack-struct switch causes GCC to generate code that is not binary compatible with code generated without that switch. Additionally, it makes the code suboptimal. Use it to 9035 conform to a non-default application binary interface. 9036 -finstrument-functions 9037 Generate instrumentation calls for entry and exit to functions. Just after function entry and just before function exit, the following profiling functions are called with the address of the 9038 current function and its call site. (On some platforms, "__builtin_return_address" does not work beyond the current function, so the call site information may not be available to the 9039 profiling functions otherwise.) 9040 void __cyg_profile_func_enter (void *this_fn, 9041 void *call_site); 9042 void __cyg_profile_func_exit (void *this_fn, 9043 void *call_site); 9044 The first argument is the address of the start of the current function, which may be looked up exactly in the symbol table. 9045 This instrumentation is also done for functions expanded inline in other functions. The profiling calls indicate where, conceptually, the inline function is entered and exited. This means 9046 that addressable versions of such functions must be available. If all your uses of a function are expanded inline, this may mean an additional expansion of code size. If you use "extern 9047 inline" in your C code, an addressable version of such functions must be provided. (This is normally the case anyway, but if you get lucky and the optimizer always expands the functions 9048 inline, you might have gotten away without providing static copies.) 9049 A function may be given the attribute "no_instrument_function", in which case this instrumentation is not done. This can be used, for example, for the profiling functions listed above, 9050 high-priority interrupt routines, and any functions from which the profiling functions cannot safely be called (perhaps signal handlers, if the profiling routines generate output or allocate 9051 memory). 9052 -finstrument-functions-exclude-file-list=file,file,... 9053 Set the list of functions that are excluded from instrumentation (see the description of -finstrument-functions). If the file that contains a function definition matches with one of file, 9054 then that function is not instrumented. The match is done on substrings: if the file parameter is a substring of the file name, it is considered to be a match. 9055 For example: 9056 -finstrument-functions-exclude-file-list=/bits/stl,include/sys 9057 excludes any inline function defined in files whose pathnames contain /bits/stl or include/sys. 9058 If, for some reason, you want to include letter , in one of sym, write ,. For example, -finstrument-functions-exclude-file-list=',,tmp' (note the single quote surrounding the option). 9059 -finstrument-functions-exclude-function-list=sym,sym,... 9060 This is similar to -finstrument-functions-exclude-file-list, but this option sets the list of function names to be excluded from instrumentation. The function name to be matched is its 9061 user-visible name, such as "vector blah(const vector &)", not the internal mangled name (e.g., "_Z4blahRSt6vectorIiSaIiEE"). The match is done on substrings: if the sym parameter 9062 is a substring of the function name, it is considered to be a match. For C99 and C++ extended identifiers, the function name must be given in UTF-8, not using universal character names. 9063 -fstack-check 9064 Generate code to verify that you do not go beyond the boundary of the stack. You should specify this flag if you are running in an environment with multiple threads, but you only rarely 9065 need to specify it in a single-threaded environment since stack overflow is automatically detected on nearly all systems if there is only one stack. 9066 Note that this switch does not actually cause checking to be done; the operating system or the language runtime must do that. The switch causes generation of code to ensure that they see 9067 the stack being extended. 9068 You can additionally specify a string parameter: no means no checking, generic means force the use of old-style checking, specific means use the best checking method and is equivalent to 9069 bare -fstack-check. 9070 Old-style checking is a generic mechanism that requires no specific target support in the compiler but comes with the following drawbacks: 9071 1. Modified allocation strategy for large objects: they are always allocated dynamically if their size exceeds a fixed threshold. 9072 2. Fixed limit on the size of the static frame of functions: when it is topped by a particular function, stack checking is not reliable and a warning is issued by the compiler. 9073 3. Inefficiency: because of both the modified allocation strategy and the generic implementation, code performance is hampered. 9074 Note that old-style stack checking is also the fallback method for specific if no target support has been added in the compiler. 9075 -fstack-limit-register=reg 9076 -fstack-limit-symbol=sym 9077 -fno-stack-limit 9078 Generate code to ensure that the stack does not grow beyond a certain value, either the value of a register or the address of a symbol. If a larger stack is required, a signal is raised at 9079 run time. For most targets, the signal is raised before the stack overruns the boundary, so it is possible to catch the signal without taking special precautions. 9080 For instance, if the stack starts at absolute address 0x80000000 and grows downwards, you can use the flags -fstack-limit-symbol=__stack_limit and -Wl,--defsym,__stack_limit=0x7ffe0000 to 9081 enforce a stack limit of 128KB. Note that this may only work with the GNU linker. 9082 -fsplit-stack 9083 Generate code to automatically split the stack before it overflows. The resulting program has a discontiguous stack which can only overflow if the program is unable to allocate any more 9084 memory. This is most useful when running threaded programs, as it is no longer necessary to calculate a good stack size to use for each thread. This is currently only implemented for the 9085 x86 targets running GNU/Linux. 9086 When code compiled with -fsplit-stack calls code compiled without -fsplit-stack, there may not be much stack space available for the latter code to run. If compiling all code, including 9087 library code, with -fsplit-stack is not an option, then the linker can fix up these calls so that the code compiled without -fsplit-stack always has a large stack. Support for this is 9088 implemented in the gold linker in GNU binutils release 2.21 and later. 9089 -fleading-underscore 9090 This option and its counterpart, -fno-leading-underscore, forcibly change the way C symbols are represented in the object file. One use is to help link with legacy assembly code. 9091 Warning: the -fleading-underscore switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application 9092 binary interface. Not all targets provide complete support for this switch. 9093 -ftls-model=model 9094 Alter the thread-local storage model to be used. The model argument should be one of global-dynamic, local-dynamic, initial-exec or local-exec. Note that the choice is subject to 9095 optimization: the compiler may use a more efficient model for symbols not visible outside of the translation unit, or if -fpic is not given on the command line. 9096 The default without -fpic is initial-exec; with -fpic the default is global-dynamic. 9097 -fvisibility=[default|internal|hidden|protected] 9098 Set the default ELF image symbol visibility to the specified option---all symbols are marked with this unless overridden within the code. Using this feature can very substantially improve 9099 linking and load times of shared object libraries, produce more optimized code, provide near-perfect API export and prevent symbol clashes. It is strongly recommended that you use this in 9100 any shared objects you distribute. 9101 Despite the nomenclature, default always means public; i.e., available to be linked against from outside the shared object. protected and internal are pretty useless in real-world usage so 9102 the only other commonly used option is hidden. The default if -fvisibility isn't specified is default, i.e., make every symbol public. 9103 A good explanation of the benefits offered by ensuring ELF symbols have the correct visibility is given by "How To Write Shared Libraries" by Ulrich Drepper (which can be found at 9104 )---however a superior solution made possible by this option to marking things hidden when the default is public is to make the default hidden and mark 9105 things public. This is the norm with DLLs on Windows and with -fvisibility=hidden and "__attribute__ ((visibility("default")))" instead of "__declspec(dllexport)" you get almost identical 9106 semantics with identical syntax. This is a great boon to those working with cross-platform projects. 9107 For those adding visibility support to existing code, you may find "#pragma GCC visibility" of use. This works by you enclosing the declarations you wish to set visibility for with (for 9108 example) "#pragma GCC visibility push(hidden)" and "#pragma GCC visibility pop". Bear in mind that symbol visibility should be viewed as part of the API interface contract and thus all new 9109 code should always specify visibility when it is not the default; i.e., declarations only for use within the local DSO should always be marked explicitly as hidden as so to avoid PLT 9110 indirection overheads---making this abundantly clear also aids readability and self-documentation of the code. Note that due to ISO C++ specification requirements, "operator new" and 9111 "operator delete" must always be of default visibility. 9112 Be aware that headers from outside your project, in particular system headers and headers from any other library you use, may not be expecting to be compiled with visibility other than the 9113 default. You may need to explicitly say "#pragma GCC visibility push(default)" before including any such headers. 9114 "extern" declarations are not affected by -fvisibility, so a lot of code can be recompiled with -fvisibility=hidden with no modifications. However, this means that calls to "extern" 9115 functions with no explicit visibility use the PLT, so it is more effective to use "__attribute ((visibility))" and/or "#pragma GCC visibility" to tell the compiler which "extern" 9116 declarations should be treated as hidden. 9117 Note that -fvisibility does affect C++ vague linkage entities. This means that, for instance, an exception class that is be thrown between DSOs must be explicitly marked with default 9118 visibility so that the type_info nodes are unified between the DSOs. 9119 An overview of these techniques, their benefits and how to use them is at . 9120 -fstrict-volatile-bitfields 9121 This option should be used if accesses to volatile bit-fields (or other structure fields, although the compiler usually honors those types anyway) should use a single access of the width of 9122 the field's type, aligned to a natural alignment if possible. For example, targets with memory-mapped peripheral registers might require all such accesses to be 16 bits wide; with this flag 9123 you can declare all peripheral bit-fields as "unsigned short" (assuming short is 16 bits on these targets) to force GCC to use 16-bit accesses instead of, perhaps, a more efficient 32-bit 9124 access. 9125 If this option is disabled, the compiler uses the most efficient instruction. In the previous example, that might be a 32-bit load instruction, even though that accesses bytes that do not 9126 contain any portion of the bit-field, or memory-mapped registers unrelated to the one being updated. 9127 In some cases, such as when the "packed" attribute is applied to a structure field, it may not be possible to access the field with a single read or write that is correctly aligned for the 9128 target machine. In this case GCC falls back to generating multiple accesses rather than code that will fault or truncate the result at run time. 9129 Note: Due to restrictions of the C/C++11 memory model, write accesses are not allowed to touch non bit-field members. It is therefore recommended to define all bits of the field's type as 9130 bit-field members. 9131 The default value of this option is determined by the application binary interface for the target processor. 9132 -fsync-libcalls 9133 This option controls whether any out-of-line instance of the "__sync" family of functions may be used to implement the C++11 "__atomic" family of functions. 9134 The default value of this option is enabled, thus the only useful form of the option is -fno-sync-libcalls. This option is used in the implementation of the libatomic runtime library. 9135 ENVIRONMENT 9136 This section describes several environment variables that affect how GCC operates. Some of them work by specifying directories or prefixes to use when searching for various kinds of files. 9137 Some are used to specify other aspects of the compilation environment. 9138 Note that you can also specify places to search using options such as -B, -I and -L. These take precedence over places specified using environment variables, which in turn take precedence over 9139 those specified by the configuration of GCC. 9140 LANG 9141 LC_CTYPE 9142 LC_MESSAGES 9143 LC_ALL 9144 These environment variables control the way that GCC uses localization information which allows GCC to work with different national conventions. GCC inspects the locale categories LC_CTYPE 9145 and LC_MESSAGES if it has been configured to do so. These locale categories can be set to any value supported by your installation. A typical value is en_GB.UTF-8 for English in the United 9146 Kingdom encoded in UTF-8. 9147 The LC_CTYPE environment variable specifies character classification. GCC uses it to determine the character boundaries in a string; this is needed for some multibyte encodings that contain 9148 quote and escape characters that are otherwise interpreted as a string end or escape. 9149 The LC_MESSAGES environment variable specifies the language to use in diagnostic messages. 9150 If the LC_ALL environment variable is set, it overrides the value of LC_CTYPE and LC_MESSAGES; otherwise, LC_CTYPE and LC_MESSAGES default to the value of the LANG environment variable. If 9151 none of these variables are set, GCC defaults to traditional C English behavior. 9152 TMPDIR 9153 If TMPDIR is set, it specifies the directory to use for temporary files. GCC uses temporary files to hold the output of one stage of compilation which is to be used as input to the next 9154 stage: for example, the output of the preprocessor, which is the input to the compiler proper. 9155 GCC_COMPARE_DEBUG 9156 Setting GCC_COMPARE_DEBUG is nearly equivalent to passing -fcompare-debug to the compiler driver. See the documentation of this option for more details. 9157 GCC_EXEC_PREFIX 9158 If GCC_EXEC_PREFIX is set, it specifies a prefix to use in the names of the subprograms executed by the compiler. No slash is added when this prefix is combined with the name of a 9159 subprogram, but you can specify a prefix that ends with a slash if you wish. 9160 If GCC_EXEC_PREFIX is not set, GCC attempts to figure out an appropriate prefix to use based on the pathname it is invoked with. 9161 If GCC cannot find the subprogram using the specified prefix, it tries looking in the usual places for the subprogram. 9162 The default value of GCC_EXEC_PREFIX is prefix/lib/gcc/ where prefix is the prefix to the installed compiler. In many cases prefix is the value of "prefix" when you ran the configure script. 9163 Other prefixes specified with -B take precedence over this prefix. 9164 This prefix is also used for finding files such as crt0.o that are used for linking. 9165 In addition, the prefix is used in an unusual way in finding the directories to search for header files. For each of the standard directories whose name normally begins with 9166 /usr/local/lib/gcc (more precisely, with the value of GCC_INCLUDE_DIR), GCC tries replacing that beginning with the specified prefix to produce an alternate directory name. Thus, with 9167 -Bfoo/, GCC searches foo/bar just before it searches the standard directory /usr/local/lib/bar. If a standard directory begins with the configured prefix then the value of prefix is 9168 replaced by GCC_EXEC_PREFIX when looking for header files. 9169 COMPILER_PATH 9170 The value of COMPILER_PATH is a colon-separated list of directories, much like PATH. GCC tries the directories thus specified when searching for subprograms, if it can't find the 9171 subprograms using GCC_EXEC_PREFIX. 9172 LIBRARY_PATH 9173 The value of LIBRARY_PATH is a colon-separated list of directories, much like PATH. When configured as a native compiler, GCC tries the directories thus specified when searching for special 9174 linker files, if it can't find them using GCC_EXEC_PREFIX. Linking using GCC also uses these directories when searching for ordinary libraries for the -l option (but directories specified 9175 with -L come first). 9176 LANG 9177 This variable is used to pass locale information to the compiler. One way in which this information is used is to determine the character set to be used when character literals, string 9178 literals and comments are parsed in C and C++. When the compiler is configured to allow multibyte characters, the following values for LANG are recognized: 9179 C-JIS 9180 Recognize JIS characters. 9181 C-SJIS 9182 Recognize SJIS characters. 9183 C-EUCJP 9184 Recognize EUCJP characters. 9185 If LANG is not defined, or if it has some other value, then the compiler uses "mblen" and "mbtowc" as defined by the default locale to recognize and translate multibyte characters. 9186 Some additional environment variables affect the behavior of the preprocessor. 9187 CPATH 9188 C_INCLUDE_PATH 9189 CPLUS_INCLUDE_PATH 9190 OBJC_INCLUDE_PATH 9191 Each variable's value is a list of directories separated by a special character, much like PATH, in which to look for header files. The special character, "PATH_SEPARATOR", is target- 9192 dependent and determined at GCC build time. For Microsoft Windows-based targets it is a semicolon, and for almost all other targets it is a colon. 9193 CPATH specifies a list of directories to be searched as if specified with -I, but after any paths given with -I options on the command line. This environment variable is used regardless of 9194 which language is being preprocessed. 9195 The remaining environment variables apply only when preprocessing the particular language indicated. Each specifies a list of directories to be searched as if specified with -isystem, but 9196 after any paths given with -isystem options on the command line. 9197 In all these variables, an empty element instructs the compiler to search its current working directory. Empty elements can appear at the beginning or end of a path. For instance, if the 9198 value of CPATH is ":/special/include", that has the same effect as -I. -I/special/include. 9199 DEPENDENCIES_OUTPUT 9200 If this variable is set, its value specifies how to output dependencies for Make based on the non-system header files processed by the compiler. System header files are ignored in the 9201 dependency output. 9202 The value of DEPENDENCIES_OUTPUT can be just a file name, in which case the Make rules are written to that file, guessing the target name from the source file name. Or the value can have 9203 the form file target, in which case the rules are written to file file using target as the target name. 9204 In other words, this environment variable is equivalent to combining the options -MM and -MF, with an optional -MT switch too. 9205 SUNPRO_DEPENDENCIES 9206 This variable is the same as DEPENDENCIES_OUTPUT (see above), except that system header files are not ignored, so it implies -M rather than -MM. However, the dependence on the main input 9207 file is omitted. 9208 BUGS 9209 For instructions on reporting bugs, see . 9210 FOOTNOTES 9211 1. On some systems, gcc -shared needs to build supplementary stub code for constructors to work. On multi-libbed systems, gcc -shared must select the correct support libraries to link against. 9212 Failing to supply the correct flags may lead to subtle defects. Supplying them in cases where they are not necessary is innocuous. 9213 SEE ALSO 9214 gpl(7), gfdl(7), fsf-funding(7), cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1) and the Info entries for gcc, cpp, as, ld, binutils and gdb. 9215 AUTHOR 9216 See the Info entry for gcc, or , for contributors to GCC. 9217 COPYRIGHT 9218 Copyright (c) 1988-2015 Free Software Foundation, Inc. 9219 Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software 9220 Foundation; with the Invariant Sections being "GNU General Public License" and "Funding Free Software", the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see 9221 below). A copy of the license is included in the gfdl(7) man page. 9222 (a) The FSF's Front-Cover Text is: 9223 A GNU Manual 9224 (b) The FSF's Back-Cover Text is: 9225 You have freedom to copy and modify this GNU Manual, like GNU 9226 software. Copies published by the Free Software Foundation raise 9227 funds for GNU development. 9228 gcc-5.2.0 2015-07-16 GCC(1)