GCC(1) GNU GCC(1) NAME gcc - GNU project C and C++ compiler SYNOPSIS gcc [-c|-S|-E] [-std=standard] [-g] [-pg] [-Olevel] [-Wwarn...] [-pedantic] [-Idir...] [-Ldir...] [-Dmacro[=defn]...] [-Umacro] [-foption...] [-mmachine-option...] [-o outfile] [@file] infile... Only the most useful options are listed here; see below for the remainder. g++ accepts mostly the same options as gcc. DESCRIPTION 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 option says not to run the linker. Then the output consists of object files output by the assembler. 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 are not docu- mented here, since you rarely need to use any of them. 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 the description for a particular option does not mention a source language, you can use that option with all supported languages. 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: -dr is very different from -d -r. 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 more than once, the directories are searched in the order specified. Also, the placement of the -l option is significant. Many options have long names starting with -f or with -W---for exam- ple, -fmove-loop-invariants, -Wformat and so on. Most of these have both positive and negative forms; the negative form of -ffoo would be -fno-foo. This manual documents only one of these two forms, whichever one is not the default. OPTIONS Option Summary Here is a summary of all the options, grouped by type. Explanations are in the following sections. Overall Options -c -S -E -o file -combine -pipe -pass-exit-codes -x language -v -### --help[=class] --target-help --version @file C Language Options -ansi -std=standard -fgnu89-inline -aux-info filename -fno-asm -fno-builtin -fno-builtin-function -fhosted -ffreestanding -fopenmp -fms-extensions -trigraphs -no-integrated-cpp -tradi- tional -traditional-cpp -fallow-single-precision -fcond-mismatch -flax-vector-conversions -fsigned-bitfields -fsigned-char -fun- signed-bitfields -funsigned-char C++ Language Options -fabi-version=n -fno-access-control -fcheck-new -fconserve-space -ffriend-injection -fno-elide-constructors -fno-enforce-eh-specs -ffor-scope -fno-for-scope -fno-gnu-keywords -fno-implicit-tem- plates -fno-implicit-inline-templates -fno-implement-inlines -fms-extensions -fno-nonansi-builtins -fno-operator-names -fno-optional-diags -fpermissive -frepo -fno-rtti -fstats -ftemplate-depth-n -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ -fno-default-inline -fvisibil- ity-inlines-hidden -fvisibility-ms-compat -Wabi -Wctor-dtor-pri- vacy -Wnon-virtual-dtor -Wreorder -Weffc++ -Wno-deprecated -Wstrict-null-sentinel -Wno-non-template-friend -Wold-style-cast -Woverloaded-virtual -Wno-pmf-conversions -Wsign-promo Objective-C and Objective-C++ Language Options -fconstant-string-class=class-name -fgnu-runtime -fnext-runtime -fno-nil-receivers -fobjc-call-cxx-cdtors -fobjc-direct-dispatch -fobjc-exceptions -fobjc-gc -freplace-objc-classes -fzero-link -gen-decls -Wassign-intercept -Wno-protocol -Wselector -Wstrict-selector-match -Wundeclared-selector Language Independent Options -fmessage-length=n -fdiagnostics-show-location=[once|every-line] -fdiagnostics-show-option Warning Options -fsyntax-only -pedantic -pedantic-errors -w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds -Wno-attributes -Wc++-compat -Wc++0x-compat -Wcast-align -Wcast-qual -Wchar-sub- scripts -Wclobbered -Wcomment -Wconversion -Wcoverage-mismatch -Wno-deprecated-declarations -Wdisabled-optimization -Wno-div-by-zero -Wempty-body -Wno-endif-labels -Werror -Wer- ror=* -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 -Wno-format-extra-args -Wformat-nonliteral -Wformat-security -Wformat-y2k -Wignored-qualifiers -Wimplicit -Wimplicit-func- tion-declaration -Wimplicit-int -Wimport -Wno-import -Winit-self -Winline -Wno-int-to-pointer-cast -Wno-invalid-off- setof -Winvalid-pch -Wlarger-than-len -Wunsafe-loop-optimizations -Wlogical-op -Wlong-long -Wmain -Wmissing-braces -Wmiss- ing-field-initializers -Wmissing-format-attribute -Wmiss- ing-include-dirs -Wmissing-noreturn -Wno-multichar -Wnonnull -Wno-overflow -Woverlength-strings -Wpacked -Wpadded -Wparenthe- ses -Wpointer-arith -Wno-pointer-to-int-cast -Wredundant-decls -Wreturn-type -Wsequence-point -Wshadow -Wsign-compare -Wsign-conversion -Wstack-protector -Wstrict-aliasing -Wstrict-aliasing=n -Wstrict-overflow -Wstrict-overflow=n -Wswitch -Wswitch-default -Wswitch-enum -Wsystem-headers -Wtrigraphs -Wtype-limits -Wundef -Wuninitialized -Wunknown-pragmas -Wno-pragmas -Wunreachable-code -Wunused -Wunused-function -Wunused-label -Wunused-parameter -Wunused-value -Wunused-vari- able -Wvariadic-macros -Wvla -Wvolatile-register-var -Wwrite-strings C and Objective-C-only Warning Options -Wbad-function-cast -Wmissing-declarations -Wmissing-parame- ter-type -Wmissing-prototypes -Wnested-externs -Wold-style-dec- laration -Wold-style-definition -Wstrict-prototypes -Wtradi- tional -Wtraditional-conversion -Wdeclaration-after-statement -Wpointer-sign Debugging Options -dletters -dumpspecs -dumpmachine -dumpversion -fdbg-cnt-list -fdbg-cnt=counter-value-list -fdump-noaddr -fdump-unnumbered -fdump-translation-unit[-n] -fdump-class-hierarchy[-n] -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline -fdump-tree-all -fdump-tree-original[-n] -fdump-tree-optimized[-n] -fdump-tree-cfg -fdump-tree-vcg -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-mud- flap[-n] -fdump-tree-dom[-n] -fdump-tree-dse[-n] -fdump-tree-phiopt[-n] -fdump-tree-forwprop[-n] -fdump-tree-copy- rename[-n] -fdump-tree-nrv -fdump-tree-vect -fdump-tree-sink -fdump-tree-sra[-n] -fdump-tree-salias -fdump-tree-fre[-n] -fdump-tree-vrp[-n] -ftree-vectorizer-verbose=n -fdump-tree-storeccp[-n] -feliminate-dwarf2-dups -felimi- nate-unused-debug-types -feliminate-unused-debug-symbols -femit-class-debug-always -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs -frandom-seed=string -fsched-verbose=n -ftest-coverage -ftime-report -fvar-tracking -g -glevel -gcoff -gdwarf-2 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ -fno-merge-debug-strings -fdebug-prefix-map=old=new -femit-struct-debug-baseonly -femit-struct-debug-reduced -femit-struct-debug-detailed[=spec-list] -p -pg -print-file-name=library -print-libgcc-file-name -print-multi-directory -print-multi-lib -print-prog-name=program -print-search-dirs -Q -print-sysroot-headers-suffix -save-temps -time Optimization Options -falign-functions[=n] -falign-jumps[=n] -falign-labels[=n] -falign-loops[=n] -fassociative-math -fauto-inc-dec -fbranch-prob- abilities -fbranch-target-load-optimize -fbranch-target-load-opti- mize2 -fbtr-bb-exclusive -fcaller-saves -fcheck-data-deps -fcprop-registers -fcrossjumping -fcse-follow-jumps -fcse-skip-blocks -fcx-limited-range -fdata-sections -fdce -fdce -fdelayed-branch -fdelete-null-pointer-checks -fdse -fdse -fearly-inlining -fexpensive-optimizations -ffast-math -ffi- nite-math-only -ffloat-store -fforward-propagate -ffunction-sec- tions -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgcse-sm -fif-conversion -fif-conversion2 -finline-functions -finline-func- tions-called-once -finline-limit=n -finline-small-functions -fipa-cp -fipa-marix-reorg -fipa-pta -fipa-pure-const -fipa-refer- ence -fipa-struct-reorg -fipa-type-escape -fivopts -fkeep-inline-functions -fkeep-static-consts -fmerge-all-constants -fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves -fmove-loop-invariants -fmudflap -fmudflapir -fmudflapth -fno-branch-count-reg -fno-default-inline -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 -fno-toplevel-reorder -fno-trap- ping-math -fno-zero-initialized-in-bss -fomit-frame-pointer -fop- timize-register-move -foptimize-sibling-calls -fpeel-loops -fpre- dictive-commoning -fprefetch-loop-arrays -fprofile-generate -fpro- file-use -fprofile-values -freciprocal-math -fregmove -fre- name-registers -freorder-blocks -freorder-blocks-and-partition -freorder-functions -frerun-cse-after-loop -freschedule-mod- ulo-scheduled-loops -frounding-math -frtl-abstract-sequences -fsched2-use-superblocks -fsched2-use-traces -fsched-spec-load -fsched-spec-load-dangerous -fsched-stalled-insns-dep[=n] -fsched-stalled-insns[=n] -fschedule-insns -fschedule-insns2 -fsection-anchors -fsee -fsignaling-nans -fsingle-precision-con- stant -fsplit-ivs-in-unroller -fsplit-wide-types -fstack-protector -fstack-protector-all -fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer -ftree-ccp -ftree-ch -ftree-copy-prop -ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-fre -ftree-loop-im -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize -ftree-parallelize-loops=n -ftree-pre -ftree-reassoc -ftree-salias -ftree-sink -ftree-sra -ftree-store-ccp -ftree-ter -ftree-vect-loop-version -ftree-vec- torize -ftree-vrp -funit-at-a-time -funroll-all-loops -fun- roll-loops -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb -fwhole-program --param name=value -O -O0 -O1 -O2 -O3 -Os Preprocessor Options -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 -isystem dir -imultilib dir -isysroot dir -M -MM -MF -MG -MP -MQ -MT -nostdinc -P -fworking-directory -remap -trigraphs -undef -Umacro -Wp,option -Xpreprocessor option Assembler Option -Wa,option -Xassembler option Linker Options object-file-name -llibrary -nostartfiles -nodefaultlibs -nost- dlib -pie -rdynamic -s -static -static-libgcc -shared -shared-libgcc -symbolic -Wl,option -Xlinker option -u symbol Directory Options -Bprefix -Idir -iquotedir -Ldir -specs=file -I- --sysroot=dir Target Options -V version -b machine Machine Dependent Options ARC Options -EB -EL -mmangle-cpu -mcpu=cpu -mtext=text-section -mdata=data-section -mrodata=readonly-data-section 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-pro- log -mno-sched-prolog -mlittle-endian -mbig-endian -mwords-lit- tle-endian -mfloat-abi=name -msoft-float -mhard-float -mfpe -mthumb-interwork -mno-thumb-interwork -mcpu=name -march=name -mfpu=name -mstructure-size-boundary=n -mabort-on-noreturn -mlong-calls -mno-long-calls -msingle-pic-base -mno-sin- gle-pic-base -mpic-register=reg -mnop-fun-dllimport -mcir- rus-fix-invalid-insns -mno-cirrus-fix-invalid-insns -mpoke-func- tion-name -mthumb -marm -mtpcs-frame -mtpcs-leaf-frame -mcaller-super-interworking -mcallee-super-interworking -mtp=name AVR Options -mmcu=mcu -msize -minit-stack=n -mno-interrupts -mcall-prologues -mno-tablejump -mtiny-stack -mint8 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 -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 -mno-long-calls -mfast-fp -min- line-plt 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 -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 CRX Options -mmac -mpush-args Darwin Options -all_load -allowable_client -arch -arch_errors_fatal -arch_only -bind_at_load -bundle -bun- dle_loader -client_name -compatibility_version -current_version -dead_strip -dependency-file -dylib_file -dylinker_install_name -dynamic -dynamiclib -exported_symbols_list -filelist -flat_namespace -force_cpusubtype_ALL -force_flat_namespace -headerpad_max_install_names -iframework -image_base -init -install_name -keep_private_externs -multi_module -multi- ply_defined -multiply_defined_unused -noall_load -no_dead_strip_inits_and_terms -nofixprebinding -nomultidefs -noprebind -noseglinkedit -pagezero_size -prebind -pre- bind_all_twolevel_modules -private_bundle -read_only_relocs -sectalign -sectobjectsymbols -whyload -seg1addr -sectcreate -sectobjectsymbols -sectorder -segaddr -segs_read_only_addr -segs_read_write_addr -seg_addr_table -seg_addr_table_filename -seglinkedit -segprot -segs_read_only_addr -segs_read_write_addr -single_module -static -sub_library -sub_umbrella -twolevel_namespace -umbrella -undefined -unexported_sym- bols_list -weak_reference_mismatches -whatsloaded -F -gused -gfull -mmacosx-version-min=version -mkernel -mone-byte-bool DEC Alpha Options -mno-fp-regs -msoft-float -malpha-as -mgas -mieee -mieee-with-inexact -mieee-conformant -mfp-trap-mode=mode -mfp-rounding-mode=mode -mtrap-precision=mode -mbuild-constants -mcpu=cpu-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 DEC Alpha/VMS Options -mvms-return-codes 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 -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 -mop- timize-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 -mno-nested-cond-exec -mtomcat-stats -mTLS -mtls -mcpu=cpu GNU/Linux Options -muclibc H8/300 Options -mrelax -mh -ms -mn -mint32 -malign-300 HPPA Options -march=architecture-type -mbig-switch -mdis- able-fpregs -mdisable-indexing -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld -mfixed-range=register-range -mjump-in-delay -mlinker-opt -mlong-calls -mlong-load-store -mno-big-switch -mno-disable-fpregs -mno-disable-indexing -mno-fast-indi- rect-calls -mno-gas -mno-jump-in-delay -mno-long-load-store -mno-portable-runtime -mno-soft-float -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 i386 and x86-64 Options -mtune=cpu-type -march=cpu-type -mfp- math=unit -masm=dialect -mno-fancy-math-387 -mno-fp-ret-in-387 -msoft-float -mno-wide-multiply -mrtd -malign-double -mpre- ferred-stack-boundary=num -mcx16 -msahf -mrecip -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -msse4a -m3dnow -mpopcnt -mabm -msse5 -mthreads -mno-align-stringops -min- line-all-stringops -mpush-args -maccumulate-outgoing-args -m128bit-long-double -m96bit-long-double -mregparm=num -mssereg- parm -mveclibabi=type -mpc32 -mpc64 -mpc80 -mstackrealign -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs -mcmodel=code-model -m32 -m64 -mlarge-data-threshold=num -mfused-madd -mno-fused-madd IA-64 Options -mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic -mvolatile-asm-stop -mregister-names -mno-sdata -mcon- stant-gp -mauto-pic -minline-float-divide-min-latency -minline-float-divide-max-throughput -min- line-int-divide-min-latency -minline-int-divide-max-throughput -minline-sqrt-min-latency -minline-sqrt-max-throughput -mno-dwarf2-asm -mearly-stop-bits -mfixed-range=register-range -mtls-size=tls-size -mtune=cpu-type -mt -pthread -milp32 -mlp64 -mno-sched-br-data-spec -msched-ar-data-spec -mno-sched-con- trol-spec -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec -msched-ldc -mno-sched-control-ldc -mno-sched-spec-verbose -mno-sched-prefer-non-data-spec-insns -mno-sched-prefer-non-control-spec-insns -mno-sched-count-spec-in-critical-path 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 -mflush-func=name -mno-flush-trap -mflush-trap=number -G num M32C Options -mcpu=cpu -msim -memregs=number 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 -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 -mno-sep-data -mshared-library-id=n -mid-shared-library -mno-id-shared-library M68hc1x Options -m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 -mauto-incdec -minmax -mlong-calls -mshort -msoft-reg-count=count MCore Options -mhardlit -mno-hardlit -mdiv -mno-div -mre- lax-immediates -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields -m4byte-functions -mno-4byte-functions -mcallgraph-data -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment MIPS Options -EL -EB -march=arch -mtune=arch -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 -mips16 -mno-mips16 -mflip-mips16 -minterlink-mips16 -mno-interlink-mips16 -mabi=abi -mabicalls -mno-abicalls -mshared -mno-shared -mxgot -mno-xgot -mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float -msin- gle-float -mdouble-float -mdsp -mno-dsp -mdspr2 -mno-dspr2 -msmartmips -mno-smartmips -mpaired-single -mno-paired-single -mdmx -mno-mdmx -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc -mlong64 -mlong32 -msym32 -mno-sym32 -Gnum -mlo- cal-sdata -mno-local-sdata -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt -membedded-data -mno-embedded-data -muninit-const-in-rodata -mno-uninit-const-in-rodata -mcode-read- able=setting -msplit-addresses -mno-split-addresses -mex- plicit-relocs -mno-explicit-relocs -mcheck-zero-division -mno-check-zero-division -mdivide-traps -mdivide-breaks -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 -mflush-func=func -mno-flush-func -mbranch-cost=num -mbranch-likely -mno-branch-likely -mfp-exceptions -mno-fp-excep- tions -mvr4130-align -mno-vr4130-align MMIX Options -mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu -mabi=mmixware -mzero-extend -mknuthdiv -mto- plevel-symbols -melf -mbranch-predict -mno-branch-predict -mbase-addresses -mno-base-addresses -msingle-exit -mno-sin- gle-exit MN10300 Options -mmult-bug -mno-mult-bug -mam33 -mno-am33 -mam33-2 -mno-am33-2 -mreturn-pointer-on-d0 -mno-crt0 -mrelax MT Options -mno-crt0 -mbacc -msim -march=cpu-type 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 -mab- shi -mno-abshi -mbranch-expensive -mbranch-cheap -msplit -mno-split -munix-asm -mdec-asm PowerPC Options See RS/6000 and PowerPC Options. RS/6000 and PowerPC Options -mcpu=cpu-type -mtune=cpu-type -mpower -mno-power -mpower2 -mno-power2 -mpowerpc -mpowerpc64 -mno-powerpc -maltivec -mno-altivec -mpowerpc-gpopt -mno-pow- erpc-gpopt -mpowerpc-gfxopt -mno-powerpc-gfxopt -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp -mnew-mnemonics -mold-mnemonics -mfull-toc -mminimal-toc -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 -mstring -mno-string -mupdate -mno-update -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align -mstrict-align -mno-strict-align -mrelocatable -mno-relocatable -mrelocatable-lib -mno-relocatable-lib -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian -mdy- namic-no-pic -maltivec -mswdiv -mpriori- tize-restricted-insns=priority -msched-costly-dep=dependence_type -minsert-sched-nops=scheme -mcall-sysv -mcall-netbsd -maix-struct-return -msvr4-struct-return -mabi=abi-type -mse- cure-plt -mbss-plt -misel -mno-isel -misel=yes -misel=no -mspe -mno-spe -mspe=yes -mspe=no -mpaired -mvrsave -mno-vrsave -mmulhw -mno-mulhw -mdlmzb -mno-dlmzb -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double -mprototype -mno-proto- type -msim -mmvme -mads -myellowknife -memb -msdata -msdata=opt -mvxworks -mwindiss -G num -pthread S/390 and zSeries Options -mtune=cpu-type -march=cpu-type -mhard-float -msoft-float -mlong-double-64 -mlong-double-128 -mbackchain -mno-backchain -mpacked-stack -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 -mwarn-dynamic- stack -mstack-size -mstack-guard Score Options -meb -mel -mnhwloop -muls -mmac -mscore5 -mscore5u -mscore7 -mscore7d SH Options -m1 -m2 -m2e -m3 -m3e -m4-nofpu -m4-single-only -m4-single -m4 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al -m5-64media -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 -misize -minline-ic_invalidate -mpadstruct -mspace -mprefergot -musermode -multcost=number -mdiv=strategy -mdi- vsi3_libfunc=name -madjust-unroll -mindexed-addressing -mgettr- cost=number -mpt-fixed -minvalid-symbols SPARC Options -mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model -m32 -m64 -mapp-regs -mno-app-regs -mfaster-structs -mno-faster-structs -mfpu -mno-fpu -mhard-float -msoft-float -mhard-quad-float -msoft-quad-float -mimpure-text -mno-impure-text -mlittle-endian -mstack-bias -mno-stack-bias -munaligned-doubles -mno-unaligned-doubles -mv8plus -mno-v8plus -mvis -mno-vis -threads -pthreads -pthread SPU Options -mwarn-reloc -merror-reloc -msafe-dma -munsafe-dma -mbranch-hints -msmall-mem -mlarge-mem -mstdmain -mfixed-range=register-range System V Options -Qy -Qn -YP,paths -Ym,dir V850 Options -mlong-calls -mno-long-calls -mep -mno-ep -mpro- log-function -mno-prolog-function -mspace -mtda=n -msda=n -mzda=n -mapp-regs -mno-app-regs -mdisable-callt -mno-dis- able-callt -mv850e1 -mv850e -mv850 -mbig-switch VAX Options -mg -mgnu -munix VxWorks Options -mrtp -non-static -Bstatic -Bdynamic -Xbind-lazy -Xbind-now x86-64 Options See i386 and x86-64 Options. Xstormy16 Options -msim Xtensa Options -mconst16 -mno-const16 -mfused-madd -mno-fused-madd -mtext-section-literals -mno-text-section-liter- als -mtarget-align -mno-target-align -mlongcalls -mno-longcalls zSeries Options See S/390 and zSeries Options. Code Generation Options -fcall-saved-reg -fcall-used-reg -ffixed-reg -fexceptions -fnon-call-exceptions -funwind-tables -fasyn- chronous-unwind-tables -finhibit-size-directive -finstru- ment-functions -finstrument-functions-exclude-func- tion-list=sym,sym,... -finstrument-func- tions-exclude-file-list=file,file,... -fno-common -fno-ident -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] -fstack-check -fstack-limit-register=reg -fstack-limit-symbol=sym -fno-stack-limit -fargument-alias -fargument-noalias -fargu- ment-noalias-global -fargument-noalias-anything -fleading-under- score -ftls-model=model -ftrapv -fwrapv -fbounds-check -fvisi- bility Options Controlling the Kind of Output 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 several assem- bler input files, or into one assembler input file; then each assem- bler input file produces an object file, and linking combines all the object files (those newly compiled, and those specified as input) into an executable file. For any given input file, the file name suffix determines what kind of compilation is done: file.c C source code which must be preprocessed. file.i C source code which should not be preprocessed. file.ii C++ source code which should not be preprocessed. file.m Objective-C source code. Note that you must link with the libobjc library to make an Objective-C program work. file.mi Objective-C source code which should not be preprocessed. file.mm file.M 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. file.mii Objective-C++ source code which should not be preprocessed. file.h C, C++, Objective-C or Objective-C++ header file to be turned into a precompiled header. file.cc file.cp file.cxx file.cpp file.CPP file.c++ file.C C++ source code which must be preprocessed. Note that in .cxx, the last two letters must both be literally x. Likewise, .C refers to a literal capital C. file.mm file.M Objective-C++ source code which must be preprocessed. file.mii Objective-C++ source code which should not be preprocessed. file.hh file.H file.hp file.hxx file.hpp file.HPP file.h++ file.tcc C++ header file to be turned into a precompiled header. file.f file.for file.FOR Fixed form Fortran source code which should not be preprocessed. file.F file.fpp file.FPP Fixed form Fortran source code which must be preprocessed (with the traditional preprocessor). file.f90 file.f95 Free form Fortran source code which should not be preprocessed. file.F90 file.F95 Free form Fortran source code which must be preprocessed (with the traditional preprocessor). file.ads Ada source code file which contains a library unit declaration (a declaration of a package, subprogram, or generic, or a generic instantiation), or a library unit renaming declaration (a package, generic, or subprogram renaming declaration). Such files are also called specs. file.adb Ada source code file containing a library unit body (a subprogram or package body). Such files are also called bodies. file.s Assembler code. file.S file.sx Assembler code which must be preprocessed. other An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way. You can specify the input language explicitly with the -x option: -x language 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 files until the next -x option. Possible values for language are: c c-header c-cpp-output c++ c++-header c++-cpp-output objective-c objective-c-header objective-c-cpp-output objective-c++ objective-c++-header objective-c++-cpp-output assembler assembler-with-cpp ada f95 f95-cpp-input java treelang -x none 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). -pass-exit-codes Normally the gcc program will exit 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 will instead return with numeri- cally highest error produced by any phase that returned an error indication. The C, C++, and Fortran frontends return 4, if an internal compiler error is encountered. 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 some combina- tions (for example, -x cpp-output -E) instruct gcc to do nothing at all. -c Compile or assemble the source files, but do not link. The link- ing stage simply is not done. The ultimate output is in the form of an object file for each source file. By default, the object file name for a source file is made by replacing the suffix .c, .i, .s, etc., with .o. Unrecognized input files, not requiring compilation or assembly, are ignored. -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. By default, the assembler file name for a source file is made by replacing the suffix .c, .i, etc., with .s. Input files that don't require compilation are ignored. -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. Input files which don't require preprocessing are ignored. -o file Place output in file file. This applies regardless to whatever sort of output is being produced, whether it be an executable file, an object file, an assembler file or preprocessed C code. 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 source.suffix.gch, and all preprocessed C source on standard out- put. -v Print (on standard error output) the commands executed to run the stages of compilation. Also print the version number of the com- piler driver program and of the preprocessor and the compiler proper. -### Like -v except the commands are not executed and all command argu- ments are quoted. This is useful for shell scripts to capture the driver-generated command lines. -pipe 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 the GNU assembler has no trouble. -combine If you are compiling multiple source files, this option tells the driver to pass all the source files to the compiler at once (for those languages for which the compiler can handle this). This will allow intermodule analysis (IMA) to be performed by the com- piler. Currently the only language for which this is supported is C. If you pass source files for multiple languages to the driver, using this option, the driver will invoke the compiler(s) that support IMA once each, passing each compiler all the source files appropriate for it. For those languages that do not support IMA this option will be ignored, and the compiler will be invoked once for each source file in that language. If you use this option in conjunction with -save-temps, the compiler will generate multiple pre-processed files (one for each source file), but only one (com- bined) .o or .s file. --help Print (on the standard output) a description of the command line options understood by gcc. If the -v option is also specified then --help will also be passed on to the various processes invoked 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 which have no documentation associated with them will also be displayed. --target-help Print (on the standard output) a description of target-specific command line options for each tool. For some targets extra tar- get-specific information may also be printed. --help=class[,qualifier] Print (on the standard output) a description of the command line options understood by the compiler that fit into a specific class. The class can be one of optimizers, warnings, target, params, or language: optimizers This will display all of the optimization options supported by the compiler. warnings This will display all of the options controlling warning mes- sages produced by the compiler. target This will display target-specific options. Unlike the --tar- get-help option however, target-specific options of the linker and assembler will not be displayed. This is because those tools do not currently support the extended --help= syntax. params This will display the values recognized by the --param option. language This will display the options supported for language, where language is the name of one of the languages supported in this version of GCC. common This will display the options that are common to all lan- guages. It is possible to further refine the output of the --help= option by adding a comma separated list of qualifiers after the class. These can be any from the following list: undocumented Display only those options which are undocumented. joined Display options which take an argument that appears after an equal sign in the same continuous piece of text, such as: --help=target. separate Display options which take an argument that appears as a sepa- rate word following the original option, such as: -o output- file. Thus for example to display all the undocumented target-specific switches supported by the compiler the following can be used: --help=target,undocumented 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 an argument), which have a description the following can be used: --help=warnings,^joined,^undocumented A class can also be used as a qualifier, although this usually restricts the output by so much that there is nothing to display. One case where it does work however is when one of the classes is target. So for example to display all the target-specific opti- mization options the following can be used: --help=target,optimizers The --help= option can be repeated on the command line. Each suc- cessive use will display its requested class of options, skipping those that have already been displayed. 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 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). Here is a truncated example from the ARM port of gcc: % gcc -Q -mabi=2 --help=target -c The following options are target specific: -mabi= 2 -mabort-on-noreturn [disabled] -mapcs [disabled] The output is sensitive to the effects of previous command line options, so for example it is possible to find out which optimiza- tions are enabled at -O2 by using: -O2 --help=optimizers Alternatively you can discover which binary optimizations are enabled by -O3 by using: gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts diff /tmp/O2-opts /tmp/O3-opts | grep enabled --version Display the version number and copyrights of the invoked GCC. @file 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 liter- ally, and not removed. Options in file are separated by whitespace. A whitespace charac- ter may be included in an option by surrounding the entire option in either single or double quotes. Any character (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 recursively. Compiling C++ Programs 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 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 com- piling C programs (usually with the name gcc). However, the use of gcc does not add the C++ library. g++ is a pro- gram that calls GCC and treats .c, .h and .i files as C++ source files instead of C source files unless -x is used, and automatically speci- fies linking against the C++ library. 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 installed with the name c++. When you compile C++ programs, you may specify many of the same command-line options that you use for compiling programs in any lan- guage; or command-line options meaningful for C and related languages; or options that are meaningful only for C++ programs. Options Controlling C Dialect 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: -ansi In C mode, this is equivalent to -std=c89. In C++ mode, it is equivalent to -std=c++98. This turns off certain features of GCC that are incompatible with ISO C90 (when compiling C code), or of standard C++ (when compil- ing C++ code), such as the "asm" and "typeof" keywords, and prede- fined 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 disables recog- nition of C++ style // comments as well as the "inline" keyword. 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 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 -ansi. The -ansi option does not cause non-ISO programs to be rejected gratuitously. For that, -pedantic is required in addition to -ansi. 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 the ISO standard doesn't call for; this is to avoid interfering with any programs that might use these names for other things. Functions that would normally be built in but do not have seman- tics defined by ISO C (such as "alloca" and "ffs") are not built- in functions when -ansi is used. -std= Determine the language standard. This option is currently only supported when compiling C or C++. The compiler can accept several base standards, such as c89 or c++98, and GNU dialects of those standards, such as gnu89 or gnu++98. By specifing a base standard, the compiler will accept all programs following that standard and those using GNU exten- sions that do not contradict it. For example, -std=c89 turns off certain features of GCC that are incompatible with ISO C90, 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, by specifing a GNU dialect of a standard, all features the compiler support are enabled, even when those features change the meaning of the base standard and some strict-conforming programs may be rejected. The particular standard is used by -pedantic to identify which fea- tures are GNU extensions given that version of the standard. For example -std=gnu89 -pedantic would warn about C++ style // com- ments, while -std=gnu99 -pedantic would not. A value for this option must be provided; possible values are c89 iso9899:1990 Support all ISO C90 programs (certain GNU extensions that con- flict with ISO C90 are disabled). Same as -ansi for C code. iso9899:199409 ISO C90 as modified in amendment 1. c99 c9x iso9899:1999 iso9899:199x ISO C99. Note that this standard is not yet fully supported; see for more information. The names c9x and iso9899:199x are deprecated. gnu89 GNU dialect of ISO C90 (including some C99 features). This is the default for C code. gnu99 gnu9x GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC, this will become the default. The name gnu9x is depre- cated. c++98 The 1998 ISO C++ standard plus amendments. Same as -ansi for C++ code. gnu++98 GNU dialect of -std=c++98. This is the default for C++ code. c++0x The working draft of the upcoming ISO C++0x standard. This option enables experimental features that are likely to be included in C++0x. The working draft is constantly changing, and any feature that is enabled by this flag may be removed from future versions of GCC if it is not part of the C++0x standard. gnu++0x GNU dialect of -std=c++0x. This option enables experimental features that may be removed in future versions of GCC. -fgnu89-inline The option -fgnu89-inline tells GCC to use the traditional GNU semantics for "inline" functions when in C99 mode. This option is accepted and ignored by GCC versions 4.1.3 up to but not including 4.3. In GCC versions 4.3 and later it changes the behavior of GCC in C99 mode. Using this option is roughly equivalent to adding the "gnu_inline" function attribute to all inline functions. The option -fno-gnu89-inline explicitly tells GCC to use the C99 semantics for "inline" when in C99 or gnu99 mode (i.e., it speci- fies the default behavior). This option was first supported in GCC 4.3. This option is not supported in C89 or gnu89 mode. The preprocessor macros "__GNUC_GNU_INLINE__" and "__GNUC_STDC_INLINE__" may be used to check which semantics are in effect for "inline" functions. -aux-info filename Output to the given filename prototyped declarations for all func- tions declared and/or defined in a translation unit, including those in header files. This option is silently ignored in any language other than C. Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declara- tion was implicit, prototyped or unprototyped (I, N for new or O for old, respectively, in the first character after the line num- ber and the colon), and whether it came from a declaration or a definition (C or F, respectively, in the following 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. -fno-asm 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 implies -fno-asm. 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 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. -fno-builtin -fno-builtin-function Don't recognize built-in functions that do not begin with __builtin_ as prefix. GCC normally generates special code to handle certain built-in functions more efficiently; for instance, calls to "alloca" may become single instructions that adjust the stack directly, and 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 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 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, warnings are given with -Wformat for bad calls to "printf", when "printf" is built in, and "strlen" is known not to modify global memory. 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 this is not built-in in this version of GCC, this option is ignored. There is no corresponding -fbuiltin-function option; if you wish to enable built-in func- tions selectively when using -fno-builtin or -ffreestanding, you may define macros such as: #define abs(n) __builtin_abs ((n)) #define strcpy(d, s) __builtin_strcpy ((d), (s)) -fhosted Assert that compilation takes place in 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 return type of "int". Examples are nearly everything except a kernel. This is equivalent to -fno-freestanding. -ffreestanding Assert that compilation takes place in a freestanding environment. This implies -fno-builtin. A freestanding environment is one in which the standard library may not exist, and program startup may not necessarily be at "main". The most obvious example is an OS kernel. This is equivalent to -fno-hosted. -fopenmp Enable handling of OpenMP directives "#pragma omp" in C/C++ and "!$omp" in Fortran. When -fopenmp is specified, the compiler gen- erates parallel code according to the OpenMP Application Program Interface v2.5 . This option implies -pthread, and thus is only supported on targets that have support for -pthread. -fms-extensions Accept some non-standard constructs used in Microsoft header files. Some cases of unnamed fields in structures and unions are only accepted with this option. -trigraphs Support ISO C trigraphs. The -ansi option (and -std options for strict ISO C conformance) implies -trigraphs. -no-integrated-cpp Performs a compilation in two passes: preprocessing and compiling. This option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the -B option. The user supplied compilation step can then add in an additional preprocessing step after normal preprocessing but before compiling. The default is to use the integrated cpp (internal cpp) The semantics of this option will change if "cc1", "cc1plus", and "cc1obj" are merged. -traditional -traditional-cpp 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 mode. See the GNU CPP manual for details. -fcond-mismatch 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++. -flax-vector-conversions Allow implicit conversions between vectors with differing numbers of elements and/or incompatible element types. This option should not be used for new code. -funsigned-char Let the type "char" be unsigned, like "unsigned char". 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. 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 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 default. 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. -fsigned-char Let the type "char" be signed, like "signed char". 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. -fsigned-bitfields -funsigned-bitfields -fno-signed-bitfields -fno-unsigned-bitfields 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 consis- tent: the basic integer types such as "int" are signed types. Options Controlling C++ Dialect This section describes the command-line options that are only meaning- ful for C++ programs; but you can also use most of the GNU compiler options regardless of what language your program is in. For example, you might compile a file "firstClass.C" like this: g++ -g -frepo -O -c firstClass.C 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. Here is a list of options that are only for compiling C++ programs: -fabi-version=n Use version n of the C++ ABI. Version 2 is the version of the C++ ABI that first appeared in G++ 3.4. Version 1 is the version of the C++ ABI that first appeared in G++ 3.2. Version 0 will always be the version that conforms most closely to the C++ ABI specifi- cation. Therefore, the ABI obtained using version 0 will change as ABI bugs are fixed. The default is version 2. -fno-access-control Turn off all access checking. This switch is mainly useful for working around bugs in the access control code. -fcheck-new 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 "operator new" will only return 0 if it is declared throw(), in which case the compiler will always check the return value even without this option. In all other cases, when "operator new" has a non-empty exception specification, memory exhaustion is sig- nalled by throwing "std::bad_alloc". See also new (nothrow). -fconserve-space Put uninitialized or runtime-initialized global variables into the common segment, as C does. This saves space in the executable at the cost of not diagnosing duplicate definitions. If you compile with this flag and your program mysteriously crashes after "main()" has completed, you may have an object that is being destroyed twice because two definitions were merged. This option is no longer useful on most targets, now that support has been added for putting variables into BSS without making them common. -ffriend-injection 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 in the old Annotated C++ Reference Manual, and versions of G++ before 4.1 always worked that way. However, in ISO C++ a friend function which is not declared in an enclosing scope can only be found using argument dependent lookup. This option causes friends to be injected as they were in earlier releases. This option is for compatibility, and may be removed in a future release of G++. -fno-elide-constructors The C++ standard allows an implementation to omit creating a tem- porary which is only used to initialize another object of the same type. Specifying this option disables that optimization, and forces G++ to call the copy constructor in all cases. -fno-enforce-eh-specs Don't generate code to check for violation of exception specifica- tions at runtime. This option violates the C++ standard, but may be useful for reducing code size in production builds, much like defining NDEBUG. This does not give user code permission to throw exceptions in violation of the exception specifications; the com- piler will still optimize based on the specifications, so throwing an unexpected exception will result in undefined behavior. -ffor-scope -fno-for-scope 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, 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++. The default if neither flag is given to follow the standard, but to allow and give a warning for old-style code that would other- wise be invalid, or have different behavior. -fno-gnu-keywords 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. -fno-implicit-templates Never emit code for non-inline templates which are instantiated implicitly (i.e. by use); only emit code for explicit instantia- tions. -fno-implicit-inline-templates Don't emit code for implicit instantiations of inline templates, either. The default is to handle inlines differently so that com- piles with and without optimization will need the same set of explicit instantiations. -fno-implement-inlines To save space, do not emit out-of-line copies of inline functions controlled by #pragma implementation. This will cause linker errors if these functions are not inlined everywhere they are called. -fms-extensions Disable pedantic warnings about constructs used in MFC, such as implicit int and getting a pointer to member function via non- standard syntax. -fno-nonansi-builtins 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. -fno-operator-names Do not treat the operator name keywords "and", "bitand", "bitor", "compl", "not", "or" and "xor" as synonyms as keywords. -fno-optional-diags 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 class. -fpermissive Downgrade some diagnostics about nonconformant code from errors to warnings. Thus, using -fpermissive will allow some nonconforming code to compile. -frepo Enable automatic template instantiation at link time. This option also implies -fno-implicit-templates. -fno-rtti Disable generation of information about every class with virtual functions for use by the C++ runtime type identification features (dynamic_cast and typeid). If you don't use those parts of the language, you can save some space by using this flag. Note that exception handling uses the same information, but it will generate it as needed. The dynamic_cast operator can still be used for casts that do not require runtime type information, i.e. casts to "void *" or to unambiguous base classes. -fstats Emit statistics about front-end processing at the end of the com- pilation. This information is generally only useful to the G++ development team. -ftemplate-depth-n Set the maximum instantiation depth for template classes to n. A limit on the template instantiation depth is needed to detect end- less recursions during template class instantiation. ANSI/ISO C++ conforming programs must not rely on a maximum depth greater than 17. -fno-threadsafe-statics 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 doesn't need to be thread-safe. -fuse-cxa-atexit 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 handling of static destructors, but will only work if your C library supports "__cxa_atexit". -fno-use-cxa-get-exception-ptr Don't use the "__cxa_get_exception_ptr" runtime routine. This will cause "std::uncaught_exception" to be incorrect, but is nec- essary if the runtime routine is not available. -fvisibility-inlines-hidden This switch declares that the user does not attempt to compare pointers to inline methods where the addresses of the two func- tions were taken in different shared objects. The effect of this is that GCC may, effectively, mark inline meth- ods with "__attribute__ ((visibility ("hidden")))" so that they do not appear in the export table of a DSO and do not require 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 mas- sively reduces the size of the dynamic export table when the library makes heavy use of templates. 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 that the function is defined in only one shared object. 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, you might mark it as having default visibility. Marking the enclosing class with explicit visibility will have no effect. Explicitly instantiated inline methods are unaffected by this option as their linkage might otherwise cross a shared library boundary. -fvisibility-ms-compat This flag attempts to use visibility settings to make GCC's C++ linkage model compatible with that of Microsoft Visual Studio. The flag makes these changes to GCC's linkage model: 1. It sets the default visibility to "hidden", like -fvisibil- ity=hidden. 2. Types, but not their members, are not hidden by default. 3. The One Definition Rule is relaxed for types without explicit visibility specifications which are defined in more than one different shared object: those declarations are permitted if they would have been permitted when this option was not used. In new code it is better to use -fvisibility=hidden and export those classes which are intended to be externally visible. Unfor- tunately it is possible for code to rely, perhaps accidentally, on the Visual Studio behavior. Among the consequences of these changes are that static data mem- bers of the same type with the same name but defined in different shared objects will be different, so changing one will not change the other; and that pointers to function members defined in dif- ferent shared objects may not compare equal. When this flag is given, it is a violation of the ODR to define types with the same name differently. -fno-weak Do not use weak symbol support, even if it is provided by the linker. By default, G++ will use weak symbols if they are avail- able. This option exists only for testing, and should not be used by end-users; it will result in inferior code and has no benefits. This option may be removed in a future release of G++. -nostdinc++ Do not search for header files in the standard directories spe- cific to C++, but do still search the other standard directories. (This option is used when building the C++ library.) In addition, these optimization, warning, and code generation options have meanings only for C++ programs: -fno-default-inline Do not assume inline for functions defined inside a class scope. Note that these functions will have linkage like inline func- tions; they just won't be inlined by default. -Wabi (C++ and Objective-C++ only) Warn when G++ generates code that is probably not compatible with the vendor-neutral C++ ABI. 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 cases where warnings are emitted even though the code that is generated will be compatible. 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. The known incompatibilities at this point include: * Incorrect handling of tail-padding for bit-fields. G++ may attempt to pack data into the same byte as a base class. For example: struct A { virtual void f(); int f1 : 1; }; struct B : public A { int f2 : 1; }; In this case, G++ will place "B::f2" into the same byte as"A::f1"; other compilers will not. You can avoid this prob- lem by explicitly padding "A" so that its size is a multiple of the byte size on your platform; that will cause G++ and other compilers to layout "B" identically. * Incorrect handling of tail-padding for virtual bases. G++ does not use tail padding when laying out virtual bases. For example: struct A { virtual void f(); char c1; }; struct B { B(); char c2; }; struct C : public A, public virtual B {}; In this case, G++ will not place "B" into the tail-padding for "A"; other compilers will. You can avoid this problem by explicitly padding "A" so that its size is a multiple of its alignment (ignoring virtual base classes); that will cause G++ and other compilers to layout "C" identically. * Incorrect handling of bit-fields with declared widths greater than that of their underlying types, when the bit-fields appear in a union. For example: union U { int i : 4096; }; Assuming that an "int" does not have 4096 bits, G++ will make the union too small by the number of bits in an "int". * Empty classes can be placed at incorrect offsets. For exam- ple: struct A {}; struct B { A a; virtual void f (); }; struct C : public B, public A {}; G++ will place the "A" base class of "C" at a nonzero offset; it should be placed at offset zero. G++ mistakenly believes that the "A" data member of "B" is already at offset zero. * Names of template functions whose types involve "typename" or template template parameters can be mangled incorrectly. template void f(typename Q::X) {} template