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.
 Many options have long names starting with -f or with -W---for example,
 -fforce-mem, -fstrength-reduce, -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 -pipe -pass-exit-codes -x language -ObjC
 (APPLE ONLY) -ObjC++ (APPLE ONLY) -arch arch (APPLE ONLY) -v -###
 --help --target-help --version
 C Language Options
 -ansi -std=standard -aux-info filename -faltivec (APPLE ONLY)
 -fasm-blocks (APPLE ONLY) -fno-asm -fno-builtin -fno-builtin-func-
 tion -fhosted -ffreestanding -fms-extensions -trigraphs
 -no-integrated-cpp -traditional -traditional-cpp -fallow-sin-
 gle-precision -fcond-mismatch -fconstant-cfstrings (APPLE ONLY)
 -fpch-preprocess (APPLE ONLY) -fsigned-bitfields -fsigned-char
 -funsigned-bitfields -funsigned-char -fpascal-strings (APPLE ONLY)
 -fcoalesce (APPLE ONLY) -fweak-coalesced (APPLE ONLY) -Wno-#warn-
 ings (APPLE ONLY) -Wextra-tokens (APPLE ONLY) -Wpragma-once (APPLE
 ONLY) -Wnewline-eof (APPLE ONLY) -Wno-altivec-long-deprecated
 (APPLE ONLY) -fwritable-strings
 C++ Language Options
 -fabi-version=n -fno-access-control -fcheck-new -fconserve-space
 -fno-const-strings -fdollars-in-identifiers -fno-elide-construc-
 tors -fno-enforce-eh-specs -fexternal-templates -falt-exter-
 nal-templates -ffor-scope -fno-for-scope -fno-gnu-keywords
 -fno-implicit-templates -fno-implicit-inline-templates -fno-imple-
 ment-inlines -findirect-virtual-calls (APPLE ONLY) -fapple-kext
 (APPLE ONLY) -fcoalesce-templates (APPLE ONLY) -fms-extensions
 -fno-nonansi-builtins -fno-operator-names -fno-optional-diags
 -fpermissive -frepo -fno-rtti -fstats -ftemplate-depth-n
 -fuse-cxa-atexit -fvtable-gc -fno-weak -nostdinc++
 -fno-default-inline -Wabi -Wctor-dtor-privacy -Wnon-virtual-dtor
 -Wreorder -Weffc++ -Wno-deprecated -Wno-non-template-friend
 -Wold-style-cast -Woverloaded-virtual -Wno-pmf-conversions
 -Wsign-promo -Wsynth
 Objective-C Language Options
 -fconstant-string-class=class-name -fgnu-runtime -fnext-runtime
 -fno-nil-receivers (APPLE ONLY) -fobjc-direct-dispatch (APPLE ONLY)
 -fobjc-exceptions (APPLE ONLY) -freplace-objc-classes (APPLE ONLY)
 -fzero-link (APPLE ONLY) -gen-decls -Wno-protocol -Wselector -Wun-
 declared-selector
 Language Independent Options
 -fmessage-length=n -fdiagnostics-show-location=[once|every-line]
 Warning Options
 -fsyntax-only -pedantic -pedantic-errors -w -W -Wall -Waggre-
 gate-return -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment
 -Wconversion -Wno-deprecated-declarations -Wdisabled-optimization
 -Wno-div-by-zero -Werror -Wfloat-equal -Wformat -Wformat=2
 -Wformat-nonliteral -Wformat-security -Wimplicit -Wimplicit-int
 -Wimplicit-function-declaration -Werror-implicit-function-declara-
 tion -Wimport -Winline -Winvalid-pch -Wno-endif-labels
 -Wno-invalid-offsetof (APPLE ONLY) -Wlarger-than-len -Wlong-long
 -Wno-long-double (APPLE ONLY) -Wmain -Wmissing-braces -Wmiss-
 ing-format-attribute -Wmissing-noreturn -Wmost (APPLE ONLY)
 -Wno-multichar -Wno-format-extra-args -Wno-format-y2k -Wno-import
 -Wnonnull -Wpacked -Wpadded -Wparentheses -Wpointer-arith -Wre-
 dundant-decls -Wreturn-type -Wsequence-point -Wshadow -Wsign-com-
 pare -Wstrict-aliasing -Wswitch -Wswitch-default -Wswitch-enum
 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized -Wun-
 known-pragmas -Wunreachable-code -Wunused -Wunused-function
 -Wunused-label -Wunused-parameter -Wunused-value -Wunused-vari-
 able -Wwrite-strings
 C-only Warning Options
 -Wbad-function-cast -Wmissing-declarations -Wmissing-prototypes
 -Wnested-externs -Wstrict-prototypes -Wtraditional
 Debugging Options
 -dletters -dumpspecs -dumpmachine -dumpversion -fdump-unnumbered
 -fdump-translation-unit[-n] -fdump-class-hierarchy[-n]
 -fdump-tree-original[-n] -fdump-tree-optimized[-n]
 -fdump-tree-inlined[-n] -feliminate-dwarf2-dups -fmem-report
 -fprofile-arcs -fsched-verbose=n -ftest-coverage -ftime-report -g
 -glevel -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 -ggdb
 -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ -p -pg
 -print-file-name=library -print-libgcc-file-name
 -print-multi-directory -print-multi-lib -print-prog-name=program
 -print-search-dirs -Q -save-temps -time -fsave-repository=loca-
 tion -grepository
 Optimization Options
 -falign-functions=n -falign-jumps=n -falign-labels=n
 -falign-loops=n -falign-loops-max-skip=n -falign-jumps-max-skip=n
 -fbranch-probabilities -fcaller-saves -fcprop-registers -fcse-fol-
 low-jumps -fcse-skip-blocks -fdata-sections -fdelayed-branch
 -fdelete-null-pointer-checks -fexpensive-optimizations -ffast-math
 -ffloat-store -fforce-addr -fforce-mem -ffunction-sections -fgcse
 -fgcse-lm -fgcse-sm -floop-optimize -fcrossjumping -fif-conversion
 -fif-conversion2 -finline-functions -finline-limit=n
 -fkeep-inline-functions -fkeep-static-consts -fmerge-constants
 -fmerge-all-constants -fmove-all-movables -fnew-ra
 -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 -funsafe-math-opti-
 mizations -ffinite-math-only -fno-trapping-math -fno-zero-initial-
 ized-in-bss -fomit-frame-pointer -foptimize-register-move -fopti-
 mize-sibling-calls -fprefetch-loop-arrays -freduce-all-givs -freg-
 move -frename-registers -freorder-blocks -freorder-functions -fre-
 run-cse-after-loop -frerun-loop-opt -fschedule-insns -fsched-
 ule-insns2 -fno-sched-interblock -fno-sched-spec
 -fsched-spec-load -fsched-spec-load-dangerous -fsignaling-nans
 -fsingle-precision-constant -fssa -fssa-ccp -fssa-dce
 -fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps -fun-
 roll-all-loops -funroll-loops --param name=value -O -O0 -O1 -O2
 -O3 -Os -fast (APPLE ONLY)
 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 -M -MM -MF -MG -MP -MQ -MT -nostdinc -P -remap -depen-
 dency-file (APPLE ONLY) -trigraphs -undef -Umacro -Wp,option
 Assembler Option
 -Wa,option
 Linker Options
 object-file-name -llibrary -nostartfiles -nodefaultlibs -nost-
 dlib -no-c++filt (APPLE ONLY) -s -static -static-libgcc -shared
 -shared-libgcc -symbolic -Wl,option -Xlinker option -u symbol
 Directory Options
 -Bprefix -Idir -I- -Fdir (APPLE ONLY) -Ldir -specs=file
 Target Options
 -V version -b machine
 Machine Dependent 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-powerpc-gpopt -mpowerpc-gfxopt
 -mno-powerpc-gfxopt -mnew-mnemonics -mold-mnemonics -mfull-toc
 -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc -m64 -m32
 -mxl-call -mno-xl-call -mpe -malign-mac68k (APPLE ONLY)
 -malign-power (APPLE ONLY) -malign-natural (APPLE ONLY)
 -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-relocat-
 able-lib -mtoc -mno-toc -mlittle -mlittle-endian -mbig
 -mbig-endian -mdynamic-no-pic (APPLE ONLY) -mlong-branch (APPLE
 ONLY) -mcall-aix -mcall-sysv -mcall-netbsd -maix-struct-return
 -msvr4-struct-return -mabi=altivec -mabi=no-altivec -mabi=spe
 -mabi=no-spe -misel=yes -misel=no -mprototype -mno-prototype -msim
 -mmvme -mads -myellowknife -memb -msdata -msdata=opt -mvxworks
 -mwindiss -G num -pthread
 Darwin Options
 -all_load -allowable_client -arch -arch_errors_fatal -arch_only
 -bind_at_load -bundle -bundle_loader -client_name -compatibil-
 ity_version -current_version -dead_strip
 -no_dead_strip_inits_and_terms -dependency-file -dylib_file
 -dylinker_install_name -dynamic -dynamiclib -exported_symbols_list
 -filelist -flat_namespace -force_cpusubtype_ALL -force_flat_names-
 pace -headerpad_max_install_names -image_base -init -install_name
 -keep_private_externs -multi_module -multiply_defined -multi-
 ply_defined_unused -noall_load -nomultidefs -noprebind
 -noseglinkedit -pagezero_size -prebind -prebind_all_twolevel_mod-
 ules -private_bundle -read_only_relocs -sectalign -sectobjectsym-
 bols -whyload -seg1addr -sectcreate -sectobjectsymbols -sectorder
 -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_symbols_list -weak_reference_mismatches -whatsloaded
 -mone-byte-bool
 i386 and x86-64 Options
 -mcpu=cpu-type -march=cpu-type -mfpmath=unit -masm=dialect
 -mno-fancy-math-387 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib
 -mno-wide-multiply -mrtd -malign-double -mpreferred-stack-bound-
 ary=num -mmmx -msse -msse2 -m3dnow -mthreads -mno-align-stringops
 -minline-all-stringops -mpush-args -maccumulate-outgoing-args
 -m128bit-long-double -m96bit-long-double -mregparm=num
 -momit-leaf-frame-pointer -mno-red-zone -mcmodel=code-model -m32
 -m64
 Code Generation Options
 -fcall-saved-reg -fcall-used-reg -ffixed-reg -fexceptions
 -fnon-call-exceptions -funwind-tables -fasynchronous-unwind-tables
 -finhibit-size-directive -finstrument-functions -fno-common
 -fno-ident -fno-gnu-linker -fpcc-struct-return -fpic -fPIC
 -freg-struct-return -fshared-data -fshort-enums -fshort-double
 -fshort-wchar -fvolatile -fvolatile-global -fvolatile-static
 -fverbose-asm -fpack-struct -fstack-check -fstack-limit-regis-
 ter=reg -fstack-limit-symbol=sym -fargument-alias -fargu-
 ment-noalias -fargument-noalias-global -fleading-underscore
 -ftls-model=model -ftrapv -fbounds-check
 Options Controlling the Kind of Output
 Compilation can involve up to four stages: preprocessing, compilation
 proper, assembly and linking, always in that order. The first three
 stages apply to an individual source file, and end by producing an
 object file; linking combines all the object files (those newly com-
 piled, 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 library
 libobjc.a to make an Objective-C program work.
 file.mi
 Objective-C source code which should not be preprocessed.
 file.h
 C or C++ header file to be turned into a precompiled header.
 file.cc
 file.cp
 file.cxx
 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. (APPLE ONLY)
 file.mii
 Objective-C++ source code which should not be preprocessed. (APPLE
 ONLY)
 file.hh
 file.H
 C++ header file to be turned into a precompiled header.
 file.f
 file.for
 file.FOR
 Fortran source code which should not be preprocessed.
 file.F
 file.fpp
 file.FPP
 Fortran source code which must be preprocessed (with the tradi-
 tional preprocessor).
 file.r
 Fortran source code which must be preprocessed with a RATFOR pre-
 processor (not included with GCC).
 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. Apple's version of GCC runs the preprocessor on
 these files as well as those ending in .S.
 file.S
 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 cpp-output
 c++ c++-header c++-cpp-output
 objective-c objective-c-header objc-cpp-output
 objective-c++ (APPLE ONLY) objective-c++-header (APPLE ONLY)
 assembler assembler-with-cpp
 ada
 f77 f77-cpp-input ratfor
 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).
 -ObjC
 -ObjC++
 These are similar in effect to -x objective-c and -x objective-c++,
 but also cause the -ObjC flag to be passed to lldd(1), causing static
 archive libraries that define an Objective-C class or category to
 be linked in in their entirety. (APPLE ONLY)
 -arch arch
 Compile for the specified target architecture arch. The allowable
 values are i386 and ppc. Multiple options work, and direct the
 compiler to produce ``fat'' binaries including object code for each
 architecture specified with -arch. This option only works if
 assembler and libraries are available for each architecture speci-
 fied. (APPLE ONLY)
 -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.
 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 combinations
 (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 linking
 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-assem-
 bler 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.
 Since only one output file can be specified, it does not make sense
 to use -o when compiling more than one input file, unless you are
 producing an executable file as output.
 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, and all preprocessed C source on standard output.
 -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.
 --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 -W option is also specified 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.
 --version
 Display the version number and copyrights of the invoked GCC.
 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 or .H; prepro-
 cessed 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 name gcc).
 However, C++ programs often require class libraries as well as a com-
 piler that understands the C++ language---and under some circumstances,
 you might want to compile programs or header files from standard input,
 or otherwise without a suffix that flags them as C++ programs. You
 might also like to precompile a C header file with a .h extension to be
 used in C++ compilations. g++ is a program that calls GCC with the
 default language set to C++, and automatically specifies linking
 against the C++ library. On many systems, g++ is also installed with
 the name c++.
 When you compile C++ programs, you may specify many of the same com-
 mand-line options that you use for compiling programs in any language;
 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++ and Objective-C) that the compiler accepts:
 -ansi
 In C mode, support all ISO C90 programs. In C++ mode, remove GNU
 extensions that conflict with ISO C++.
 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 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 disables recognition 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 which 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 with -ansi is used.
 -std=
 Determine the language standard. This option is currently only
 supported when compiling C or C++. A value for this option must be
 provided; possible values are
 c89
 iso9899:1990
 ISO C90 (same as -ansi).
 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 <http://gcc.gnu.org/gcc-3.3/c99status/> for more infor-
 mation. The names c9x and iso9899:199x are deprecated.
 gnu89
 Default, ISO C90 plus GNU extensions (including some C99 fea-
 tures).
 gnu99
 gnu9x
 ISO C99 plus GNU extensions. 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.
 gnu++98
 The same as -std=c++98 plus GNU extensions. This is the
 default for C++ code.
 Even when this option is not specified, you can still use some of
 the features of newer standards in so far as they do not conflict
 with previous C standards. For example, you may use "__restrict__"
 even when -std=c99 is not specified.
 The -std options specifying some version of ISO C have the same
 effects as -ansi, except that features that were not in ISO C90 but
 are in the specified version (for example, // comments and the
 "inline" keyword in ISO C99) are not disabled.
 -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 lan-
 guage other than C.
 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 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 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.
 -faltivec
 Enable the AltiVec language extensions, as defined in Motorola's
 AltiVec PIM. This includes the recognition of "vector" and "pixel"
 as (context-dependent) keywords, the definition of built-in func-
 tions such as "vec_add", and other extensions. Note that unlike
 the option -maltivec, the extensions do not require the inclusion
 of any special header files. (APPLE ONLY)
 -fasm-blocks
 Enable the use of blocks and entire functions of assembly code
 within a C or C++ file. The syntax follows that used in CodeWar-
 rior. (APPLE ONLY)
 -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.
 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-func-
 tion option; if you wish to enable built-in functions 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.
 -fms-extensions
 Accept some non-standard constructs used in Microsoft header files.
 -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 (inter-
 nal 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++.
 -fpch-preprocess
 Enable PCH processing even when -E or -save-temps is used.
 -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 consistent:
 the basic integer types such as "int" are signed types.
 -fwritable-strings
 Store string constants in the writable data segment and don't
 uniquize them. This is for compatibility with old programs which
 assume they can write into string constants.
 Writing into string constants is a very bad idea; ``constants''
 should be constant.
 -fconstant-cfstrings
 Enable the automatic creation of a CoreFoundation-type constant
 string whenever a special builtin "__builtin__CFStringMakeCon-
 stantString" is called on a literal string, and for "@"..."" liter-
 als in Objective-C (thus overriding the -fconstant-string-class
 setting). This option will also be enabled if the environment
 variable "MACOSX_DEPLOYMENT_TARGET" exists and is set to "10.2" or
 greater. (APPLE ONLY)
 -fpascal-strings
 Allow Pascal-style string literals to be constructed. (APPLE ONLY)
 -fcoalesce
 Coalesce duplicated functions and data. The linker will discard all
 but one, saving space. Enabled by default. (APPLE ONLY)
 -fweak-coalesced
 Use the new OS X "weak_definitions" section attribute for coalesced
 items. A single "normal" definition will be chosen by the linker
 over any number of weakly-coalesced ones. (APPLE ONLY)
 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 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 specification.
 Therefore, the ABI obtained using version 0 will change as ABI bugs
 are fixed.
 The default is version 1.
 -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. The current
 Working Paper requires that "operator new" never return a null
 pointer, so this check is normally unnecessary.
 An alternative to using this option is to specify that your "opera-
 tor new" does not throw any exceptions; if you declare it tthhrrooww(()),
 G++ will check the return value. 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.
 -fno-const-strings
 Give string constants type "char *" instead of type "const char *".
 By default, G++ uses type "const char *" as required by the stan-
 dard. Even if you use -fno-const-strings, you cannot actually mod-
 ify the value of a string constant, unless you also use
 -fwritable-strings.
 This option might be removed in a future release of G++. For maxi-
 mum portability, you should structure your code so that it works
 with string constants that have type "const char *".
 -fdollars-in-identifiers
 Accept $ in identifiers. You can also explicitly prohibit use of $
 with the option -fno-dollars-in-identifiers. (GNU C allows $ by
 default on most target systems, but there are a few exceptions.)
 Traditional C allowed the character $ to form part of identifiers.
 However, ISO C and C++ forbid $ in identifiers.
 -fno-elide-constructors
 The C++ standard allows an implementation to omit creating a tempo-
 rary 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 check for violation of exception specifications at runtime.
 This option violates the C++ standard, but may be useful for reduc-
 ing code size in production builds, much like defining NDEBUG. The
 compiler will still optimize based on the exception specifications.
 -fexternal-templates
 instantiation; template instances are emitted or not according to
 the location of the template definition.
 This option is deprecated.
 -falt-external-templates
 Similar to -fexternal-templates, but template instances are emitted
 or not according to the place where they are first instantiated.
 This option is deprecated.
 -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 otherwise 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
 errors if these functions are not inlined everywhere they are
 called.
 -findirect-virtual-calls
 Do not make direct calls to virtual functions; instead, always go
 through the vtable. (APPLE ONLY)
 -fapple-kext
 Alter vtables, destructors, and other implementation details to
 more closely resemble the GCC 2.95 ABI. This is to make kernel
 extensions loadable by Darwin kernels, and is required to build any
 Darwin kernel extension. -fno-exceptions and -static must also be
 used with this flag. (APPLE ONLY)
 -fcoalesce-templates
 Mark instantiated templates as "coalesced": the linker will discard
 all but one, thus saving space. (APPLE ONLY)
 -fms-extensions
 Disable pedantic warnings about constructs used in MFC, such as
 implicit int and getting a pointer to member function via non-stan-
 dard 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 messages about nonconformant code from errors to warn-
 ings. By default, G++ effectively sets -pedantic-errors without
 -pedantic; this option reverses that. This behavior and this
 option are superseded by -pedantic, which works as it does for GNU
 C.
 -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.
 -fskip-unused-source
 Skip declarations in the input files that aren't actually needed.
 This flag doesn't change the meaning of correct source code, but it
 can suppress diagnostics about incorrect source code and suppress
 output of debugging information for the parts of the input that are
 skipped.
 -fstats
 Emit statistics about front-end processing at the end of the compi-
 lation. 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.
 -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". This option is not supported on Mac OS X.
 -fvtable-gc
 Emit special relocations for vtables and virtual function refer-
 ences so that the linker can identify unused virtual functions and
 zero out vtable slots that refer to them. This is most useful with
 -ffunction-sections and -Wl,--gc-sections, in order to also discard
 the functions themselves.
 This optimization requires GNU as and GNU ld. Not all systems sup-
 port this option. -Wl,--gc-sections is ignored without -static.
 -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 specific
 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++ 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 exam-
 ple:
 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 example:
 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 <typename Q>
 void f(typename Q::X) {}
 template <template <typename> class Q>
 void f(typename Q<int>::X) {}
 Instantiations of these templates may be mangled incorrectly.
 -Wctor-dtor-privacy (C++ only)
 Warn when a class seems unusable, because all the constructors or
 destructors in a class are private and the class has no friends or
 public static member functions. This warning is enabled by
 default.
 -Wnon-virtual-dtor (C++ only)
 Warn when a class declares a non-virtual destructor that should
 probably be virtual, because it looks like the class will be used
 polymorphically. This warning is enabled by -Wall.
 -Wreorder (C++ only)
 Warn when the order of member initializers given in the code does
 not match the order in which they must be executed. For instance:
 struct A {
 int i;
 int j;
 A(): j (0), i (1) { }
 };
 Here the compiler will warn that the member initializers for i and
 j will be rearranged to match the declaration order of the members.
 This warning is enabled by -Wall.
 The following -W... options are not affected by -Wall.
 -Weffc++ (C++ only)
 Warn about violations of the following style guidelines from Scott
 Meyers' Effective C++ book:
 * Item 11: Define a copy constructor and an assignment operator
 for classes with dynamically allocated memory.
 * Item 12: Prefer initialization to assignment in constructors.
 * Item 14: Make destructors virtual in base classes.
 * Item 15: Have "operator=" return a reference to *this.
 * Item 23: Don't try to return a reference when you must return
 an object.
 and about violations of the following style guidelines from Scott
 Meyers' More Effective C++ book:
 * Item 6: Distinguish between prefix and postfix forms of incre-
 ment and decrement operators.
 * Item 7: Never overload "&&", "||", or ",".
 If you use this option, you should be aware that the standard
 library headers do not obey all of these guidelines; you can use
 grep -v to filter out those warnings.
 -Wno-deprecated (C++ only)
 Do not warn about usage of deprecated features.
 -Wno-non-template-friend (C++ only)
 Disable warnings when non-templatized friend functions are declared
 within a template. With the advent of explicit template specifica-
 tion support in G++, if the name of the friend is an unqualified-id
 (i.e., friend foo(int)), the C++ language specification demands
 that the friend declare or define an ordinary, nontemplate func-
 tion. (Section 14.5.3). Before G++ implemented explicit specifi-
 cation, unqualified-ids could be interpreted as a particular spe-
 cialization of a templatized function. Because this non-conforming
 behavior is no longer the default behavior for G++, -Wnon-tem-
 plate-friend allows the compiler to check existing code for poten-
 tial trouble spots, and is on by default. This new compiler behav-
 ior can be turned off with -Wno-non-template-friend which keeps the
 conformant compiler code but disables the helpful warning.
 -Wold-style-cast (C++ only)
 Warn if an old-style (C-style) cast to a non-void type is used
 within a C++ program. The new-style casts (static_cast, reinter-
 pret_cast, and const_cast) are less vulnerable to unintended
 effects, and much easier to grep for.
 -Woverloaded-virtual (C++ only)
 Warn when a function declaration hides virtual functions from a
 base class. For example, in:
 struct A {
 virtual void f();
 };
 struct B: public A {
 void f(int);
 };
 the "A" class version of "f" is hidden in "B", and code like this:
 B* b;
 b->f();
 will fail to compile.
 -Wno-pmf-conversions (C++ only)
 Disable the diagnostic for converting a bound pointer to member
 function to a plain pointer.
 -Wsign-promo (C++ only)
 Warn when overload resolution chooses a promotion from unsigned or
 enumeral type to a signed type over a conversion to an unsigned
 type of the same size. Previous versions of G++ would try to pre-
 serve unsignedness, but the standard mandates the current behavior.
 -Wsynth (C++ only)
 Warn when G++'s synthesis behavior does not match that of cfront.
 For instance:
 struct A {
 operator int ();
 A& operator = (int);
 };
 main ()
 {
 A a,b;
 a = b;
 }
 In this example, G++ will synthesize a default A& operator = (const
 A&);, while cfront will use the user-defined operator =.
 Options Controlling Objective-C Dialect
 This section describes the command-line options that are only meaning-
 ful for Objective-C programs; but you can also use most of the GNU com-
 piler options regardless of what language your program is in. For
 example, you might compile a file "some_class.m" like this:
 gcc -g -fgnu-runtime -O -c some_class.m
 In this example, only -fgnu-runtime is an option meant only for Objec-
 tive-C programs; you can use the other options with any language sup-
 ported by GCC.
 Here is a list of options that are only for compiling Objective-C pro-
 grams:
 -fconstant-string-class=class-name
 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 used,
 and "NSConstantString" if the NeXT runtime is being used (see
 below). The -fconstant-cfstrings option, if also present, will
 override the -fconstant-string-class setting and cause "@"...""
 literals to be laid out as constant CoreFoundation strings.
 -fgnu-runtime
 Generate object code compatible with the standard GNU Objective-C
 runtime. This is the default for most types of systems.
 -fnext-runtime
 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) this option
 is used.
 -fno-nil-receivers (APPLE ONLY)
 Assume that all Objective-C message dispatches (e.g., "[receiver
 message:arg]") in this translation unit ensure that the receiver is
 not "nil". This allows for more efficient entry points in the run-
 time to be used. Currently, this option is only available in con-
 junction with the NeXT runtime.
 -fobjc-direct-dispatch (APPLE ONLY)
 For some functions (such as "objc_msgSend") called very frequently
 by Objective-C programs, special entry points exist in high memory
 that may be jumped to directly (e.g., via the "bla" instruction on
 the PowerPC) for improved performance. The -fobjc-direct-dispatch
 option will cause such jumps to be generated. This option is only
 available in conjunction with the NeXT runtime; furthermore, pro-
 grams built with the -fobjc-direct-dispatch option will only run on
 Mac OS X 10.4 (Tiger) or later systems.
 -fobjc-exceptions (APPLE ONLY)
 Enable syntactic support for structured exception handling in
 Objective-C, similar to what is offered by C++ and Java. This
 option will also be enabled if the environment variable
 "MACOSX_DEPLOYMENT_TARGET" exists and is set to "10.3" or greater.
 @try {
 ...
 @throw expr;
 ...
 }
 @catch (AnObjCClass *exc) {
 ...
 @throw expr;
 ...
 @throw;
 ...
 }
 @catch (AnotherClass *exc) {
 ...
 }
 @catch (id allOthers) {
 ...
 }
 @finally {
 ...
 @throw expr;
 ...
 }
 The @throw statement may appear anywhere in an Objective-C or
 Objective-C++ program; when used inside of a @catch block, the
 @throw may appear without an argument (as shown above), in which
 case the object caught by the @catch will be rethrown.
 Note that only (pointers to) Objective-C objects may be thrown and
 caught using this scheme. When an object is thrown, it will be
 caught by the nearest @catch clause capable of handling objects of
 that type, analogously to how "catch" blocks work in C++ and Java.
 A "@catch(id ...)" clause (as shown above) may also be provided to
 catch any and all Objective-C exceptions not caught by previous
 @catch clauses (if any).
 The @finally clause, if present, will be executed upon exit from
 the immediately preceding "@try ... @catch" section. This will
 happen regardless of whether any exceptions are thrown, caught or
 rethrown inside the "@try ... @catch" section, analogously to the
 behavior of the "finally" clause in Java.
 There are several caveats to using the new exception mechanism:
 * Although currently designed to be binary compatible with
 "NS_HANDLER"-style idioms provided by the "NSException" class,
 the new exceptions can only be used on Mac OS X 10.3 (Panther)
 and later systems, due to additional functionality needed in
 the (NeXT) Objective-C runtime.
 * As mentioned above, the new exceptions do not support handling
 types other than Objective-C objects. Furthermore, when used
 from Objective-C++, the Objective-C exception model does not
 interoperate with C++ exceptions at this time. This means you
 cannot @throw an exception from Objective-C and "catch" it in
 C++, or vice versa (i.e., "throw ... @catch").
 The -fobjc-exceptions switch also enables the use of synchroniza-
 tion blocks for thread-safe execution:
 ObjCClass *lockObject = ...;
 ...
 @synchronized (lockObject) {
 ...
 @throw expr;
 ...
 }
 Unlike Java, Objective-C does not allow for entire methods to be
 marked @synchronized. Note that throwing exceptions out of @syn-
 chronized blocks is allowed, and will cause the guarding object to
 be unlocked properly.
 -freplace-objc-classes (APPLE ONLY)
 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
 get initialized at load time, which improves run-time performance.
 Specifying the -freplace-objc-classes flag suppresses this behavior
 and causes calls to "objc_getClass("...")" to be retained. This is
 useful in Fix-and-Continue debugging mode, since it allows for
 individual class implementations to be modified during program exe-
 cution.
 -fzero-link (APPLE ONLY)
 Emit a special marker instructing lldd(1) not to statically link in
 the resulting object file, and allow ddyylldd(1) to load it in at run
 time instead. This is used in conjunction with the Zero Link
 debugging mode.
 -gen-decls
 Dump interface declarations for all classes seen in the source file
 to a file named sourcename.decl.
 -Wno-protocol
 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 every method
 not explicitly implemented in the class, even if a method implemen-
 tation is inherited from the superclass. If you use the "-Wno-pro-
 tocol" option, then methods inherited from the superclass are con-
 sidered to be implemented, and no warning is issued for them.
 -Wselector
 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. Additionally, a
 check is performed that for each selector appearing in a "@selec-
 tor(...)" expression, a corresponding method with that selector
 has been found during compilation. Because 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 during compilation, or because
 the "-fsyntax-only" option is being used.
 -Wundeclared-selector
 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 (explicitly, in an @inter-
 face or @protocol declaration, or implicitly, in an @implementation
 section) before the "@selector(...)" expression. This option
 always performs its checks as soon as a "@selector(...)" expression
 is found (while "-Wselector" only performs its checks in the final
 stage of compilation), and so additionally enforces the coding
 style convention that methods and selectors must be declared before
 being used.
 Options to Control Diagnostic Messages Formatting
 Traditionally, diagnostic messages have been formatted irrespective of
 the output device's aspect (e.g. its width, ...). The options
 described below can be used to control the diagnostic messages format-
 ting algorithm, e.g. how many characters per line, how often source
 location information should be reported. Right now, only the C++ front
 end can honor these options. However it is expected, in the near
 future, that the remaining front ends would be able to digest them cor-
 rectly.
 -fmessage-length=n
 Try to format error messages so that they fit on lines of about n
 characters. The default is 72 characters for g++ and 0 for the
 rest of the front ends supported by GCC. If n is zero, then no
 line-wrapping will be done; each error message will appear on a
 single line.
 -fdiagnostics-show-location=once
 Only meaningful in line-wrapping mode. Instructs the diagnostic
 messages reporter to emit once source location information; that
 is, in case the message is too long to fit on a single 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.
 -fdiagnostics-show-location=every-line
 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 breaking
 a message which is too long to fit on a single line.
 Options to Request or Suppress Warnings
 Warnings are diagnostic messages that report constructions which are
 not inherently erroneous but which are risky or suggest there may have
 been an error.
 You can request many specific warnings with options beginning -W, for
 example -Wimplicit to request warnings on implicit declarations. Each
 of these specific warning options also has a 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.
 The following options control the amount and kinds of warnings produced
 by GCC; for further, language-specific options also refer to @ref{C++
 Dialect Options} and @ref{Objective-C Dialect Options}.
 -fsyntax-only
 Check the code for syntax errors, but don't do anything beyond
 that.
 -pedantic
 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, follows the ver-
 sion of the ISO C standard specified by any -std option used.
 Valid ISO C and ISO C++ programs should compile properly with or
 without this option (though a rare few will require -ansi or a -std
 option specifying the required version of ISO C). However, without
 this option, certain GNU extensions and traditional C and C++ fea-
 tures are supported as well. With this option, they are rejected.
 -pedantic 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 "__extension__". How-
 ever, only system header files should use these escape routes;
 application programs should avoid them.
 Some users try to use -pedantic 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 those for
 which ISO C requires a diagnostic, and some others for which diag-
 nostics have been added.
 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 -pedantic. We don't have plans
 to support such a feature in the near future.
 Where the standard specified with -std represents a GNU extended
 dialect of C, such as gnu89 or gnu99, there is a corresponding base
 standard, the version of ISO C on which the GNU extended dialect is
 based. Warnings from -pedantic are given where they are required
 by the base standard. (It would not make sense for such warnings
 to be given only for features not in the 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.)
 -pedantic-errors
 Like -pedantic, except that errors are produced rather than warn-
 ings.
 -w Inhibit all warning messages.
 -Wno-import
 Inhibit warning messages about the use of #import.
 -Wno-#warnings
 Inhibit warning messages issued by #warning.
 -Wpragma-once
 -Wextra-tokens
 Warn about extra tokens at the end of prepreprocessor directives.
 (APPLE ONLY)
 -Wnewline-eof
 Warn about files missing a newline at the end of the file. (APPLE
 ONLY)
 -Wno-altivec-long-deprecated
 Do not warn about the use of the deprecated 'long' keyword in
 AltiVec data types. (APPLE ONLY)
 -Wchar-subscripts
 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.
 -Wcomment
 Warn whenever a comment-start sequence /* appears in a /* comment,
 or whenever a Backslash-Newline appears in a // comment.
 -Wformat
 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 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 standard) families.
 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 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. However, if
 -pedantic is used with -Wformat, warnings will be given about for-
 mat features not in the selected standard version (but not for
 "strfmon" formats, since those are not in any version of the C
 standard).
 Since -Wformat also checks for null format arguments for several
 functions, -Wformat also implies -Wnonnull.
 -Wformat is included in -Wall. For more control over some aspects
 of format checking, the options -Wno-format-y2k, -Wno-for-
 mat-extra-args, -Wno-format-zero-length, -Wformat-nonliteral,
 -Wformat-security, and -Wformat=2 are available, but are not
 included in -Wall.
 -Wno-format-y2k
 If -Wformat is specified, do not warn about "strftime" formats
 which may yield only a two-digit year.
 -Wno-format-extra-args
 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.
 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 what type
 to pass to "va_arg" to skip the unused arguments. However, in the
 case of "scanf" formats, this option will suppress the warning if
 the unused arguments are all pointers, since the Single Unix Speci-
 fication says that such unused arguments are allowed.
 -Wno-format-zero-length
 If -Wformat is specified, do not warn about zero-length formats.
 The C standard specifies that zero-length formats are allowed.
 -Wformat-nonliteral
 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".
 -Wformat-security
 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 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 contains %n. (This is cur-
 rently 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.)
 -Wformat=2
 Enable -Wformat plus format checks not included in -Wformat. Cur-
 rently equivalent to -Wformat -Wformat-nonliteral -Wformat-secu-
 rity.
 -Wnonnull
 Enable warning about passing a null pointer for arguments marked as
 requiring a non-null value by the "nonnull" function attribute.
 -Wnonnull is included in -Wall and -Wformat. It can be disabled
 with the -Wno-nonnull option.
 -Wimplicit-int
 Warn when a declaration does not specify a type.
 -Wimplicit-function-declaration
 -Werror-implicit-function-declaration
 Give a warning (or error) whenever a function is used before being
 declared.
 -Wimplicit
 Same as -Wimplicit-int and -Wimplicit-function-declaration.
 -Wmain
 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.
 -Wmissing-braces
 Warn if an aggregate or union initializer is not fully bracketed.
 In the following example, the initializer for a is not fully brack-
 eted, but that for b is fully bracketed.
 int a[2][2] = { 0, 1, 2, 3 };
 int b[2][2] = { { 0, 1 }, { 2, 3 } };
 -Wparentheses
 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
 often get confused about.
 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:
 {
 if (a)
 if (b)
 foo ();
 else
 bar ();
 }
 In 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 above example
 by indentation the programmer chose. When there is the potential
 for this confusion, GCC will issue a warning when this flag is
 specified. To eliminate the warning, add explicit braces around
 the innermost "if" statement so there is no way the "else" could
 belong to the enclosing "if". The resulting code would look like
 this:
 {
 if (a)
 {
 if (b)
 foo ();
 else
 bar ();
 }
 }
 -Wsequence-point
 Warn about code that may have undefined semantics because of viola-
 tions of sequence point rules in the C standard.
 The C standard defines the order in which expressions in a C pro-
 gram are evaluated in terms of sequence points, which represent a
 partial ordering between the execution of parts 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), after the evaluation of
 the first operand of a "&&", "||", "? :" or "," (comma) operator,
 before a function is called (but after the evaluation of its argu-
 ments and the expression denoting the called function), and in cer-
 tain other places. Other than as expressed by the sequence point
 rules, the order of evaluation of subexpressions of an expression
 is not specified. All 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 which the functions are called is not specified. How-
 ever, the standards committee have ruled that function calls do not
 overlap.
 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 standard specifies 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 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.
 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 posi-
 tive result, but in general it has been found fairly effective at
 detecting this sort of problem in programs.
 The present implementation of this option only works for C pro-
 grams. A future implementation may also work for C++ programs.
 The C standard is worded confusingly, therefore there is some
 debate over the precise meaning of the sequence point rules in sub-
 tle cases. Links to discussions of the problem, including proposed
 formal definitions, may be found on our readings page, at
 <http://gcc.gnu.org/readings/>.
 -Wreturn-type
 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".
 For C++, a function without return type always produces a diagnos-
 tic message, even when -Wno-return-type is specified. The only
 exceptions are main and functions defined in system headers.
 -Wswitch
 Warn whenever a "switch" statement has an index of enumeral type
 and lacks a "case" for one or more of the named codes of that enu-
 meration. (The presence of a "default" label prevents this warn-
 ing.) "case" labels outside the enumeration range also provoke
 warnings when this option is used.
 -Wswitch-default
 Warn whenever a "switch" statement does not have a "default" case.
 -Wswitch-enum
 Warn whenever a "switch" statement has an index of enumeral type
 and lacks a "case" for one or more of the named codes of that enu-
 meration. "case" labels outside the enumeration range also provoke
 warnings when this option is used.
 -Wtrigraphs
 Warn if any trigraphs are encountered that might change the meaning
 of the program (trigraphs within comments are not warned about).
 -Wunused-function
 Warn whenever a static function is declared but not defined or a
 non\-inline static function is unused.
 -Wunused-label
 Warn whenever a label is declared but not used.
 To suppress this warning use the unused attribute.
 -Wunused-parameter
 Warn whenever a function parameter is unused aside from its decla-
 ration.
 To suppress this warning use the unused attribute.
 -Wunused-variable
 Warn whenever a local variable or non-constant static variable is
 unused aside from its declaration
 To suppress this warning use the unused attribute.
 -Wunused-value
 Warn whenever a statement computes a result that is explicitly not
 used.
 To suppress this warning cast the expression to void.
 -Wunused
 All the above -Wunused options combined.
 In order to get a warning about an unused function parameter, you
 must either specify -W -Wunused or separately specify
 -Wunused-parameter.
 -Wuninitialized
 Warn if an automatic variable is used without first being initial-
 ized or if a variable may be clobbered by a "setjmp" call.
 These warnings are possible only in optimizing compilation, because
 they require data flow information that is computed only when opti-
 mizing. If you don't specify -O, you simply won't get these warn-
 ings.
 These warnings occur only for variables that are candidates for
 register allocation. Therefore, they do not occur for a variable
 that is declared "volatile", or whose address is taken, or whose
 size is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
 structures, unions or arrays, even when they are in registers.
 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 warn-
 ings are printed.
 These warnings are made optional because GCC is not smart enough to
 see all the reasons why the code might be correct despite appearing
 to have an error. Here is one example of how this can happen:
 {
 int x;
 switch (y)
 {
 case 1: x = 1;
 break;
 case 2: x = 4;
 break;
 case 3: x = 5;
 }
 foo (x);
 }
 If the value of "y" is always 1, 2 or 3, then "x" is always ini-
 tialized, but GCC doesn't know this. Here is another common case:
 {
 int save_y;
 if (change_y) save_y = y, y = new_y;
 ...
 if (change_y) y = save_y;
 }
 This has no bug because "save_y" is used only if it is set.
 This option also warns when a non-volatile automatic variable might
 be changed by a call to "longjmp". These warnings as well are pos-
 sible only in optimizing compilation.
 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 warning even
 when there is in fact no problem because "longjmp" cannot in fact
 be called at the place which would cause a problem.
 Some spurious warnings can be avoided if you declare all the func-
 tions you use that never return as "noreturn".
 -Wunknown-pragmas
 stood by GCC. If this command line option is used, warnings will
 even be issued for unknown pragmas in system header files. This is
 not the case if the warnings were only enabled by the -Wall command
 line option.
 -Wstrict-aliasing
 This option is only active when -fstrict-aliasing is active. It
 warns about code which might break the strict aliasing rules that
 the compiler is using for optimization. The warning does not catch
 all cases, but does attempt to catch the more common pitfalls. It
 is included in -Wall.
 -Wall
 All of the above -W options combined. This enables all the warn-
 ings 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 also enables some language-specific
 warnings described in @ref{C++ Dialect Options} and @ref{Objec-
 tive-C Dialect Options}.
 -Wmost
 This is equivalent to -Wall -Wno-parentheses. (APPLE ONLY)
 The following -W... options are not implied by -Wall. Some of them
 warn about constructions that users generally do not consider question-
 able, but which occasionally you might wish to 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.
 -W Print extra warning messages for these events:
 * A function can return either with or without a value. (Falling
 off the end of the function body is considered returning with-
 out a value.) For example, this function would evoke such a
 warning:
 foo (a)
 {
 if (a > 0)
 return a;
 }
 * An expression-statement or the left-hand side of a comma
 expression contains no side effects. To suppress the warning,
 cast the unused expression to void. For example, an expression
 such as x[i,j] will cause a warning, but x[(void)i,j] will not.
 * An unsigned value is compared against zero with < or <=.
 * 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.
 * Storage-class specifiers like "static" are not the first things
 in a declaration. According to the C Standard, this usage is
 obsolescent.
 * The return type of a function has a type qualifier such as
 "const". Such a type qualifier has no effect, since the value
 returned by a function is not an lvalue. (But don't warn about
 the GNU extension of "volatile void" return types. That exten-
 sion will be warned about if -pedantic is specified.)
 * If -Wall or -Wunused is also specified, warn about unused argu-
 ments.
 * A comparison between signed and unsigned values could produce
 an incorrect result when the signed value is converted to
 unsigned. (But don't warn if -Wno-sign-compare is also speci-
 fied.)
 * An aggregate has a partly bracketed initializer. For example,
 the following code would evoke such a warning, because braces
 are missing around the initializer for "x.h":
 struct s { int f, g; };
 struct t { struct s h; int i; };
 struct t x = { 1, 2, 3 };
 * An aggregate has an initializer which does not initialize all
 members. For example, the following code would cause such a
 warning, because "x.h" would be implicitly initialized to zero:
 struct s { int f, g, h; };
 struct s x = { 3, 4 };
 -Wno-div-by-zero
 Do not warn about compile-time integer division by zero. Floating
 point division by zero is not warned about, as it can be a legiti-
 mate way of obtaining infinities and NaNs.
 -Wsystem-headers
 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 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 using -Wall
 in conjunction with this option will not warn about unknown pragmas
 in system headers---for that, -Wunknown-pragmas must also be used.
 -Wfloat-equal
 Warn if floating point values are used in equality comparisons.
 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, 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 when producing
 output, but that's a different problem). In particular, instead of
 testing for equality, you would check to see whether the two values
 have ranges that overlap; and this is done with the relational
 operators, so equality comparisons are probably mistaken.
 -Wtraditional (C only)
 Warn about certain constructs that behave differently in tradi-
 tional and ISO C. Also warn about ISO C constructs that have no
 traditional C equivalent, and/or problematic constructs which
 should be avoided.
 * Macro parameters that appear within string literals in the
 macro body. In traditional C macro replacement takes place
 within string literals, but does not in ISO C.
 * In traditional C, some preprocessor directives did not exist.
 Traditional preprocessors would only consider a line to be a
 directive if the # appeared in column 1 on the line. Therefore
 -Wtraditional warns about directives that traditional C under-
 stands but would ignore because the # does not appear as the
 first character on the line. It also suggests you hide direc-
 them. Some traditional implementations would not recognize
 #elif, so it suggests avoiding it altogether.
 * A function-like macro that appears without arguments.
 * The unary plus operator.
 * 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
 defined in the system headers of most modern systems, e.g. the
 _MIN/_MAX macros in "<limits.h>". Use of these macros in user
 code might normally lead to spurious warnings, however gcc's
 integrated preprocessor has enough context to avoid warning in
 these cases.
 * A function declared external in one block and then used after
 the end of the block.
 * A "switch" statement has an operand of type "long".
 * A non-"static" function declaration follows a "static" one.
 This construct is not accepted by some traditional C compilers.
 * 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
 octal values, which typically represent bit patterns, are not
 warned about.
 * Usage of ISO string concatenation is detected.
 * Initialization of automatic aggregates.
 * Identifier conflicts with labels. Traditional C lacks a sepa-
 rate namespace for labels.
 * 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.
 "__STDC__" to avoid missing initializer warnings and relies on
 default initialization to zero in the traditional C case.
 * Conversions by prototypes between fixed/floating point values
 and vice versa. The absence of these prototypes when compiling
 with traditional C would cause serious problems. This is a
 subset of the possible conversion warnings, for the full set
 use -Wconversion.
 * Use of ISO C style function definitions. This warning inten-
 tionally is not issued for prototype declarations or variadic
 functions because these ISO C features will appear in your code
 when 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 exten-
 sion and thus not relevant to traditional C compatibility.
 -Wundef
 Warn if an undefined identifier is evaluated in an #if directive.
 -Wendif-labels
 Warn whenever an #else or an #endif are followed by text.
 -Wshadow
 Warn whenever a local variable shadows another local variable,
 parameter or global variable or whenever a built-in function is
 shadowed.
 -Wlarger-than-len
 Warn whenever an object of larger than len bytes is defined.
 -Wpointer-arith
 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 conve-
 nience in calculations with "void *" pointers and pointers to func-
 tions.
 -Wbad-function-cast (C only)
 Warn whenever a function call is cast to a non-matching type. For
 example, warn if "int malloc()" is cast to "anything *".
 -Wcast-qual
 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 *".
 -Wcast-align
 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 accessed at
 two- or four-byte boundaries.
 -Wwrite-strings
 When compiling C, give string constants the type "const
 char[length]" so that copying the address of one into a non-"const"
 "char *" pointer will get a warning; when compiling C++, warn about
 the deprecated conversion from string constants to "char *". These
 warnings will help you find at compile time code that can try to
 write into a string constant, but only if you have been very care-
 ful about using "const" in declarations and prototypes. Otherwise,
 it will just be a nuisance; this is why we did not make -Wall
 request these warnings.
 -Wconversion
 Warn if a prototype causes a type conversion that is different from
 what would happen to the same argument in the absence of a proto-
 type. This includes conversions of fixed point to floating and
 vice versa, and conversions changing the width or signedness of a
 fixed point argument except when the same as the default promotion.
 Also, warn if a negative integer constant expression is implicitly
 converted to an unsigned type. For example, warn about the assign-
 ment "x = -1" if "x" is unsigned. But do not warn about explicit
 casts like "(unsigned) -1".
 -Wsign-compare
 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 enabled by -W, and by -Wall in C++ only.
 -Waggregate-return
 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.)
 -Wstrict-prototypes (C only)
 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 which specifies the
 argument types.)
 -Wmissing-prototypes (C only)
 Warn if a global function is defined without a previous prototype
 declaration. This warning is issued even if the definition itself
 provides a prototype. The aim is to detect global functions that
 fail to be declared in header files.
 -Wmissing-declarations
 Warn if a global function is defined without a previous declara-
 tion. Do so even if the definition itself provides a prototype.
 Use this option to detect global functions that are not declared in
 header files.
 -Wmissing-noreturn
 Warn about functions which might be candidates for attribute "nore-
 turn". Note these are only possible candidates, not absolute ones.
 Care should be taken to manually verify functions actually do not
 ever return before adding the "noreturn" attribute, otherwise sub-
 tle code generation bugs could be introduced. You will not get a
 warning for "main" in hosted C environments.
 -Wmissing-format-attribute
 If -Wformat is enabled, also warn about functions which might be
 candidates for "format" attributes. Note these are only possible
 candidates, not absolute ones. GCC will guess that "format"
 attributes might be appropriate for any function that calls a func-
 tion like "vprintf" or "vscanf", but this might not always be the
 case, and some functions for which "format" attributes are appro-
 priate may not be detected. This option has no effect unless
 -Wformat is enabled (possibly by -Wall).
 -Wno-multichar
 Do not warn if a multicharacter constant ('FOOF') is used. Usually
 they indicate a typo in the user's code, as they have implementa-
 tion-defined values, and should not be used in portable code.
 -Wno-deprecated-declarations
 Do not warn about uses of functions, variables, and types marked as
 deprecated by using the "deprecated" attribute. (@pxref{Function
 Attributes}, @pxref{Variable Attributes}, @pxref{Type Attributes}.)
 -Wpacked
 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
 instance, in this code, the variable "f.x" in "struct bar" will be
 misaligned even though "struct bar" does not itself have the packed
 attribute:
 struct foo {
 int x;
 char a, b, c, d;
 } __attribute__((packed));
 struct bar {
 char z;
 struct foo f;
 };
 -Wpadded
 Warn if padding is included in a structure, either to align an ele-
 ment of the structure or to align the whole structure. Sometimes
 when this happens it is possible to rearrange the fields of the
 structure to reduce the padding and so make the structure smaller.
 -Wredundant-decls
 Warn if anything is declared more than once in the same scope, even
 in cases where multiple declaration is valid and changes nothing.
 -Wnested-externs (C only)
 Warn if an "extern" declaration is encountered within a function.
 -Wunreachable-code
 Warn if the compiler detects that code will never be executed.
 This option is intended to warn when the compiler detects that at
 least a whole line of source code will never be executed, because
 some condition is never satisfied or because it is after a proce-
 dure that never returns.
 It is possible for this option to produce a warning even though
 there are circumstances under which part of the affected line can
 be executed, so care should be taken when removing apparently-
 unreachable code.
 For instance, when a function is inlined, a warning may mean that
 the line is unreachable in only one inlined copy of the function.
 This option is not made part of -Wall because in a debugging ver-
 sion of a program there is often substantial code which checks cor-
 rect functioning of the program and is, hopefully, unreachable
 because the program does work. Another common use of unreachable
 code is to provide behavior which is selectable at compile-time.
 -Winline
 Warn if a function can not be inlined and it was declared as
 inline.
 -Wno-invalid-offsetof (C++ only)
 Suppress warnings from applying the offsetof macro to a non-POD
 type.
 -Wno-long-double
 Inhibit warning if the long double type is used. (APPLE ONLY)
 -Winvalid-pch
 Warn if a precompiled header is found in the search path but can't
 be used.
 -Wlong-long
 Warn if long long type is used. This is default. To inhibit the
 warning messages, use -Wno-long-long. Flags -Wlong-long and
 -Wno-long-long are taken into account only when -pedantic flag is
 used.
 -Wdisabled-optimization
 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 were unable to han-
 dle the code effectively. Often, the problem is that your code is
 too big or too complex; GCC will refuse to optimize programs when
 the optimization itself is likely to take inordinate amounts of
 time.
 -Werror
 Make all warnings into errors.
 Options for Debugging Your Program or GCC
 GCC has various special options that are used for debugging either your
 program or GCC:
 -g Produce debugging information in the operating system's native for-
 mat (stabs, COFF, XCOFF, or DWARF). GDB can work with this debug-
 ging information.
 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 will probably make other
 debuggers crash or refuse to read the program. If you want to con-
 trol for certain whether to generate the extra information, use
 -gstabs+ or -gstabs (see below).
 Unlike most other C compilers, GCC allows you to use -g with -O.
 The shortcuts taken by optimized code may occasionally produce sur-
 prising results: some variables you declared may not exist at all;
 flow of control may briefly move where you did not expect it; some
 statements may not be executed because they compute constant
 results or their values were already at hand; some statements may
 execute in different places because they were moved out of loops.
 Nevertheless it proves possible to debug optimized output. This
 makes it reasonable to use the optimizer for programs that might
 have bugs.
 The following options are useful when GCC is generated with the
 capability for more than one debugging format.
 -ggdb
 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 extensions
 if at all possible.
 -gstabs
 Produce debugging information in stabs format (if that is sup-
 ported), without GDB extensions. This is the format used by DBX on
 most BSD systems. On MIPS, Alpha and System V Release 4 systems
 this option produces stabs debugging output which is not understood
 by DBX or SDB. On System V Release 4 systems this option requires
 the GNU assembler.
 -gstabs+
 Produce debugging information in stabs format (if that is sup-
 ported), using GNU extensions understood only by the GNU debugger
 (GDB). The use of these extensions is likely to make other debug-
 gers crash or refuse to read the program.
 (Other debug formats, such as -gcoff, are not supported in Darwin
 or Mac OS X.)
 -glevel
 -ggdblevel
 -gstabslevel
 Request debugging information and also use level to specify how
 much information. The default level is 2.
 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, but no
 information about local variables and no line numbers.
 Level 3 includes extra information, such as all the macro defini-
 tions present in the program. Some debuggers support macro expan-
 sion when you use -g3.
 Note that in order to avoid confusion between DWARF1 debug level 2,
 and DWARF2, neither -gdwarf nor -gdwarf-2 accept a concatenated
 debug level. Instead use an additional -glevel option to change
 the debug level for DWARF1 or DWARF2.
 -feliminate-dwarf2-dups
 Compress DWARF2 debugging information by eliminating duplicated
 information about each symbol. This option only makes sense when
 generating DWARF2 debugging information with -gdwarf-2.
 -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 it when
 linking.
 -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 it when
 linking.
 -Q Makes the compiler print out each function name as it is compiled,
 and print some statistics about each pass when it finishes.
 -ftime-report
 Makes the compiler print some statistics about the time consumed by
 each pass when it finishes.
 -fmem-report
 Makes the compiler print some statistics about permanent memory
 allocation when it finishes.
 -fprofile-arcs
 Instrument arcs during compilation to generate coverage data or for
 profile-directed block ordering. During execution the program
 records how many times each branch is executed and how many times
 it is taken. When the compiled program exits it saves this data to
 a file called auxname.da for each source file. auxname is gener-
 ated from the name of the output file, if explicitly specified and
 it is not the final executable, otherwise it is the basename of the
 source file. In both cases any suffix is removed (e.g. foo.da for
 input file dir/foo.c, or dir/foo.da for output file specified as -o
 dir/foo.o).
 For profile-directed block ordering, compile the program with
 -fprofile-arcs plus optimization and code generation options, gen-
 erate the arc profile information by running the program on a
 selected workload, and then compile the program again with the same
 optimization and code generation options plus -fbranch-probabili-
 ties.
 The other use of -fprofile-arcs is for use with gcov, when it is
 used with the -ftest-coverage option.
 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 instru-
 mented: 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 added to the
 block; otherwise, a new basic block must be created to hold the
 instrumentation code.
 -ftest-coverage
 Create data files for the gcov code-coverage utility. See -fpro-
 file-arcs option above for a description of auxname.
 auxname.bb
 A mapping from basic blocks to line numbers, which gcov uses to
 associate basic block execution counts with line numbers.
 auxname.bbg
 A list of all arcs in the program flow graph. This allows gcov
 to reconstruct the program flow graph, so that it can compute
 all basic block and arc execution counts from the information
 in the auxname.da file.
 Use -ftest-coverage with -fprofile-arcs; the latter option adds
 instrumentation to the program, which then writes execution counts
 to another data file:
 auxname.da
 Runtime arc execution counts, used in conjunction with the arc
 information in the file auxname.bbg.
 Coverage data will map better to the source files if -ftest-cover-
 age is used without optimization.
 -dletters
 Says to make debugging dumps during compilation at times specified
 by letters. This is used for debugging the compiler. The file
 names for most of the dumps are made by appending a pass number and
 a word to the dumpname. dumpname is generated from the name of the
 output file, if explicitly specified and it is not an executable,
 otherwise it is the basename of the source file. In both cases any
 suffix is removed (e.g. foo.00.rtl or foo.01.sibling). Here are
 the possible letters for use in letters, and their meanings:
 A Annotate the assembler output with miscellaneous debugging
 information.
 b Dump after computing branch probabilities, to file.14.bp.
 B Dump after block reordering, to file.32.bbro.
 c Dump after instruction combination, to the file file.19.com-
 bine.
 C Dump after the first if conversion, to the file file.15.ce1.
 d Dump after delayed branch scheduling, to file.34.dbr.
 D Dump all macro definitions, at the end of preprocessing, in
 addition to normal output.
 e Dump after SSA optimizations, to file.04.ssa and file.07.ussa.
 E Dump after the second if conversion, to file.29.ce3.
 f Dump after life analysis, to file.18.life.
 F Dump after purging "ADDRESSOF" codes, to file.10.addressof.
 g Dump after global register allocation, to file.24.greg.
 h Dump after finalization of EH handling code, to file.02.eh.
 k Dump after reg-to-stack conversion, to file.31.stack.
 o Dump after post-reload optimizations, to file.25.postreload.
 G Dump after GCSE, to file.11.gcse.
 i Dump after sibling call optimizations, to file.01.sibling.
 j Dump after the first jump optimization, to file.03.jump.
 k Dump after conversion from registers to stack, to
 file.31.stack.
 l Dump after local register allocation, to file.23.lreg.
 L Dump after loop optimization, to file.12.loop.
 M Dump after performing the machine dependent reorganization
 pass, to file.33.mach.
 n Dump after register renumbering, to file.28.rnreg.
 N Dump after the register move pass, to file.21.regmove.
 r Dump after RTL generation, to file.00.rtl.
 R Dump after the second scheduling pass, to file.30.sched2.
 s Dump after CSE (including the jump optimization that sometimes
 follows CSE), to file.09.cse.
 S Dump after the first scheduling pass, to file.22.sched.
 t Dump after the second CSE pass (including the jump optimization
 that sometimes follows CSE), to file.17.cse2.
 u Dump after null pointer elimination pass to file.08.null.
 w Dump after the second flow pass, to file.26.flow2.
 X Dump after SSA dead code elimination, to file.06.ssadce.
 z Dump after the peephole pass, to file.27.peephole2.
 a Produce all the dumps listed above.
 m Print statistics on memory usage, at the end of the run, to
 standard error.
 p Annotate the assembler output with a comment indicating which
 pattern and alternative was used. The length of each instruc-
 tion is also printed.
 P Dump the RTL in the assembler output as a comment before each
 instruction. Also turns on -dp annotation.
 v For each of the other indicated dump files (except for
 file.00.rtl), dump a representation of the control flow graph
 suitable for viewing with VCG to file.pass.vcg.
 x Just generate RTL for a function instead of compiling it. Usu-
 ally used with r.
 y Dump debugging information during parsing, to standard error.
 -fdump-unnumbered
 When doing debugging dumps (see -d option above), suppress instruc-
 tion numbers and line number note output. This makes it more fea-
 sible to use diff on debugging dumps for compiler invocations with
 different options, in particular with and without -g.
 -fdump-translation-unit (C and C++ only)
 -fdump-translation-unit-options (C and C++ only)
 Dump a representation of the tree structure for the entire transla-
 tion unit to a file. The file name is made by appending .tu to the
 source file name. If the -options form is used, options controls
 the details of the dump as described for the -fdump-tree options.
 -fdump-class-hierarchy (C++ only)
 -fdump-class-hierarchy-options (C++ only)
 Dump a representation of each class's hierarchy and virtual func-
 tion table layout to a file. The file name is made by appending
 .class to the source file name. If the -options form is used,
 options controls the details of the dump as described for the
 -fdump-tree options.
 -fdump-tree-switch (C++ only)
 -fdump-tree-switch-options (C++ only)
 Control the dumping at various stages of processing the intermedi-
 ate language tree to a file. The file name is generated by append-
 ing a switch specific suffix to the source file name. If the
 -options form is used, options is a list of - separated options
 that control the details of the dump. Not all options are applica-
 ble to all dumps, those which are not meaningful will be ignored.
 The following options are available
 address
 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 environ-
 ment.
 slim
 Inhibit dumping of members of a scope or body of a function
 merely because that scope has been reached. Only dump such
 items when they are directly reachable by some other path.
 all Turn on all options.
 The following tree dumps are possible:
 original
 Dump before any tree based optimization, to file.original.
 optimized
 Dump after all tree based optimization, to file.optimized.
 inlined
 Dump after function inlining, to file.inlined.
 -fsched-verbose=n
 On targets that use instruction scheduling, this option controls
 the amount of debugging output the scheduler prints. This informa-
 tion is written to standard error, unless -dS or -dR is specified,
 in which case it is output to the usual dump listing file, .sched
 or .sched2 respectively. However for n greater than nine, the out-
 put is always printed to standard error.
 For n greater than zero, -fsched-verbose outputs the same informa-
 tion as -dRS. For n greater than one, it also output basic block
 probabilities, detailed 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 dependence info.
 -save-temps
 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 would produce
 files foo.i and foo.s, as well as foo.o. This creates a prepro-
 cessed foo.i output file even though the compiler now normally uses
 an integrated preprocessor.
 -time
 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). The output looks
 like this:
 # cc1 0.12 0.01
 # as 0.00 0.01
 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 behalf of
 the program. Both numbers are in seconds.
 -fsave-repository=location
 Creates separate symbol repository at location for given input
 header file. Separate repository contains only debugging symbols in
 stabs format.
 -grepository
 Instructs compiler to use separate symbol repository with debugging
 symbols. Compiler searches for such repositories in include paths.
 -print-file-name=library
 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 prints the
 file name.
 -print-multi-directory
 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.
 -print-multi-lib
 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 the
 @samp{-, without spaces between multiple switches. This is sup-
 posed to ease shell-processing.
 -print-prog-name=program
 Like -print-file-name, but searches for a program such as cpp.
 -print-libgcc-file-name
 Same as -print-file-name=libgcc.a.
 This is useful when you use -nostdlib or -nodefaultlibs but you do
 want to link with libgcc.a. You can do
 gcc -nostdlib <files>... `gcc -print-libgcc-file-name`
 -print-search-dirs
 Print the name of the configured installation directory and a list
 of program and library directories gcc will search---and don't do
 anything else.
 This is useful when gcc prints the error message installation prob-
 lem, cannot exec cpp0: No such file or directory. To resolve this
 you either need to put cpp0 and the other compiler 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 '/'.
 -dumpmachine
 Print the compiler's target machine (for example,
 i686-pc-linux-gnu)---and don't do anything else.
 -dumpversion
 Print the compiler version (for example, 3.0)---and don't do any-
 thing else.
 -dumpspecs
 Print the compiler's built-in specs---and don't do anything else.
 (This is used when GCC itself is being built.)
 Options That Control Optimization
 These options control various sorts of optimizations.
 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 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 would expect from the source code.
 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.
 Not all optimizations are controlled directly by a flag. Only opti-
 mizations that have a flag are listed.
 -O
 -O1 Optimize. Optimizing compilation takes somewhat more time, and a
 lot more memory for a large function.
 With -O, the compiler tries to reduce code size and execution time,
 without performing any optimizations that take a great deal of com-
 pilation time.
 In Apple's version of GCC, -fstrict-aliasing, -freorder-blocks, and
 -fsched-interblock are disabled by default when optimizing.
 -O2 Optimize even more. GCC performs nearly all supported optimiza-
 tions that do not involve a space-speed tradeoff. The compiler
 does not perform loop unrolling or function inlining when you spec-
 ify -O2. As compared to -O, this option increases both compilation
 time and the performance of the generated code.
 -O2 turns on all optimization flags specified by -O. It also turns
 on the following optimization flags: -fforce-mem -foptimize-sib-
 ling-calls -fstrength-reduce -fcse-follow-jumps -fcse-skip-blocks
 -frerun-cse-after-loop -frerun-loop-opt -fgcse -fgcse-lm
 -fgcse-sm -fdelete-null-pointer-checks -fexpensive-optimizations
 -fregmove -fschedule-insns -fschedule-insns2 -fsched-interblock
 -fsched-spec -fcaller-saves -fpeephole2 -freorder-blocks -fre-
 order-functions -fstrict-aliasing -falign-functions -falign-jumps
 -falign-loops -falign-labels
 Please note the warning under -fgcse about invoking -O2 on programs
 that use computed gotos.
 -O3 Optimize yet more. -O3 turns on all optimizations specified by -O2
 and also turns on the -finline-functions and -frename-registers
 options.
 -O0 Do not optimize. This is the default.
 -fast
 Optimize for maximum performance. -fast changes the overall opti-
 mization strategy of GCC in order to produce the fastest possible
 running code for PPC7450 and G5 architectures. By default, -fast
 optimizes for G5. Programs optimized for G5 will not run on
 PPC7450. To optimize for PPC7450, add -mcpu=7450 on command line.
 -fast currently enables the following optimization flags (for G5
 and PPC7450). These flags may change in the future. You cannot
 override any of these options if you use -fast except by setting
 -mcpu=7450. Note that -ffast-math, -fstrict-aliasing and
 -malign-natural are unsafe in some situations. To build shared
 libraries with -fast, specify -fPIC on command line.
 -O3 -funroll-loops -fstrict-aliasing -fsched-interblock
 -falign-loops=16 -falign-jumps=16 -falign-functions=16
 -falign-jumps-max-skip=15 -falign-loops-max-skip=15 -malign-natural
 -ffast-math -mdynamic-no-pic -mpowerpc-gpopt -force_cpusubtype_ALL
 -fstrict-aliasing -mtune=G5 -mcpu=G5 -mpowerpc64
 -Os Optimize for size. -Os enables all -O2 optimizations that do not
 typically increase code size. It also performs further optimiza-
 tions designed to reduce code size.
 -Os disables the following optimization flags: -falign-functions
 -falign-jumps -falign-loops -falign-labels -freorder-blocks
 -fprefetch-loop-arrays
 If you use multiple -O options, with or without level numbers, the
 last such option is the one that is effective.
 Options of the form -fflag specify machine-independent flags. Most
 flags have both positive and negative forms; the negative form of -ffoo
 would be -fno-foo. In the table below, only one of the forms is
 listed---the one you typically will use. You can figure out the other
 form by either removing no- or adding it.
 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-tuning'' of optimiza-
 tions to be performed is desired.
 -fno-default-inline
 Do not make member functions inline by default merely because they
 are defined inside the class scope (C++ only). Otherwise, when you
 specify -O, member functions defined inside class scope are com-
 piled inline by default; i.e., you don't need to add inline in
 front of the member function name.
 -fno-defer-pop
 Always pop the arguments to each function call as soon as that
 function returns. For machines which must pop arguments after a
 function call, the compiler normally lets arguments accumulate on
 the stack for several function calls and pops them all at once.
 Disabled at levels -O, -O2, -O3, -Os.
 -fforce-mem
 Force memory operands to be copied into registers before doing
 arithmetic on them. This produces better code by making all memory
 references potential common subexpressions. When they are not com-
 mon subexpressions, instruction combination should eliminate the
 separate register-load.
 Enabled at levels -O2, -O3, -Os.
 -fforce-addr
 Force memory address constants to be copied into registers before
 doing arithmetic on them. This may produce better code just as
 -fforce-mem may.
 -fomit-frame-pointer
 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 available in many
 functions. It also makes debugging impossible on some machines.
 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. The
 machine-description macro "FRAME_POINTER_REQUIRED" controls whether
 a target machine supports this flag.
 Enabled at levels -O, -O2, -O3, -Os.
 -foptimize-sibling-calls
 Optimize sibling and tail recursive calls.
 Enabled at levels -O2, -O3, -Os.
 -fno-inline
 Don't pay attention to the "inline" keyword. Normally this option
 is used to keep the compiler from expanding any functions inline.
 Note that if you are not optimizing, no functions can be expanded
 inline.
 -finline-functions
 Integrate all simple functions into their callers. The compiler
 heuristically decides which functions are simple enough to be worth
 integrating in this way.
 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.
 Enabled at level -O3.
 -finline-limit=n
 By default, gcc limits the size of functions that can be inlined.
 This flag allows the control of this limit for functions that are
 explicitly marked as inline (i.e., marked with the inline keyword
 or defined within the class definition in c++). n is the size of
 functions that can be inlined in number of pseudo instructions (not
 counting parameter handling). The default value of n is 600.
 Increasing this value can result in more inlined code at the cost
 of compilation time and memory consumption. Decreasing usually
 makes the compilation faster and less code will be inlined (which
 presumably means slower programs). This option is particularly
 useful for programs that use inlining heavily such as those based
 on recursive templates with C++.
 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 follows:
 @item max-inline-insns
 is set to I<n>.
 @item max-inline-insns-single
 is set to I<n>/2.
 @item max-inline-insns-single-auto
 is set to I<n>/2.
 @item min-inline-insns
 is set to 130 or I<n>/4, whichever is smaller.
 @item max-inline-insns-rtl
 is set to I<n>.
 Using -finline-limit=600 thus results in the default settings for
 these parameters. See below for a documentation of the individual
 parameters controlling inlining.
 Note: pseudo instruction represents, in this particular context, an
 abstract measurement of function's size. In no way, it represents
 a count of assembly instructions and as such its exact meaning
 might change from one release to an another.
 -fkeep-inline-functions
 Even if all calls to a given function are integrated, and the func-
 tion is declared "static", nevertheless output a separate run-time
 callable version of the function. This switch does not affect
 "extern inline" functions.
 -fkeep-static-consts
 Emit variables declared "static const" when optimization isn't
 turned on, even if the variables aren't referenced.
 GCC enables this option by default. If you want to force the com-
 piler to check if the variable was referenced, regardless of
 whether or not optimization is turned on, use the
 -fno-keep-static-consts option.
 -fmerge-constants
 Attempt to merge identical constants (string constants and floating
 point constants) across compilation units.
 This option is the default for optimized compilation if the assem-
 bler and linker support it. Use -fno-merge-constants to inhibit
 this behavior.
 Enabled at levels -O, -O2, -O3, -Os.
 -fmerge-all-constants
 Attempt to merge identical constants and identical variables.
 This option implies -fmerge-constants. In addition to -fmerge-con-
 stants this considers e.g. even constant initialized arrays or ini-
 tialized constant variables with integral or floating point types.
 Languages like C or C++ require each non-automatic variable to have
 distinct location, so using this option will result in non-conform-
 ing behavior.
 -fno-branch-count-reg
 Do not use ``decrement and branch'' instructions on a count regis-
 ter, but instead generate a sequence of instructions that decrement
 a register, compare it against zero, then branch based upon the
 result. This option is only meaningful on architectures that sup-
 port such instructions, which include x86, PowerPC, IA-64 and
 S/390.
 The default is -fbranch-count-reg, enabled when -fstrength-reduce
 is enabled.
 -fno-function-cse
 Do not put function addresses in registers; make each instruction
 that calls a constant function contain the function's address
 explicitly.
 This option results in less efficient code, but some strange hacks
 that alter the assembler output may be confused by the optimiza-
 tions performed when this option is not used.
 The default is -ffunction-cse
 -fno-zero-initialized-in-bss
 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.
 This option turns off this behavior because some programs explic-
 itly rely on variables going to the data section. E.g., so that
 the resulting executable can find the beginning of that section
 and/or make assumptions based on that.
 The default is -fzero-initialized-in-bss.
 -fstrength-reduce
 Perform the optimizations of loop strength reduction and elimina-
 tion of iteration variables.
 Enabled at levels -O2, -O3, -Os.
 -fthread-jumps
 Perform optimizations where we 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 destination of
 the second branch or a point immediately following it, depending on
 whether the condition is known to be true or false.
 Enabled at levels -O, -O2, -O3, -Os.
 -fcse-follow-jumps
 In common subexpression elimination, 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 with an "else"
 clause, CSE will follow the jump when the condition tested is
 false.
 Enabled at levels -O2, -O3, -Os.
 -fcse-skip-blocks
 This is similar to -fcse-follow-jumps, but causes CSE to follow
 jumps which conditionally skip over blocks. When CSE encounters a
 simple "if" statement with no else clause, -fcse-skip-blocks causes
 CSE to follow the jump around the body of the "if".
 Enabled at levels -O2, -O3, -Os.
 -frerun-cse-after-loop
 Re-run common subexpression elimination after loop optimizations
 has been performed.
 Enabled at levels -O2, -O3, -Os.
 -frerun-loop-opt
 Run the loop optimizer twice.
 Enabled at levels -O2, -O3, -Os.
 -fgcse
 Perform a global common subexpression elimination pass. This pass
 also performs global constant and copy propagation.
 Note: When compiling a program using computed gotos, a GCC exten-
 sion, you may get better runtime performance if you disable the
 global common subexpression elimination pass by adding -fno-gcse to
 the command line.
 Enabled at levels -O2, -O3, -Os.
 -fgcse-lm
 When -fgcse-lm is enabled, global common subexpression elimination
 will attempt to move loads which are only killed by stores into
 themselves. This allows a loop containing a load/store sequence to
 be changed to a load outside the loop, and a copy/store within the
 loop.
 Enabled by default when gcse is enabled.
 -fgcse-sm
 When -fgcse-sm is enabled, A store motion pass is run after global
 common subexpression elimination. This pass will attempt to move
 stores out of loops. When used in conjunction with -fgcse-lm,
 loops containing a load/store sequence can be changed to a load
 before the loop and a store after the loop.
 Enabled by default when gcse is enabled.
 -floop-optimize
 Perform loop optimizations: move constant expressions out of loops,
 simplify exit test conditions and optionally do strength-reduction
 and loop unrolling as well.
 Enabled at levels -O, -O2, -O3, -Os.
 -fcrossjumping
 Perform cross-jumping transformation. This transformation unifies
 equivalent code and save code size. The resulting code may or may
 not perform better than without cross-jumping.
 Enabled at levels -O, -O2, -O3, -Os.
 -fif-conversion
 Attempt to transform conditional jumps into branch-less equiva-
 lents. This include use of conditional moves, min, max, set flags
 and abs instructions, and some tricks doable by standard arith-
 metics. The use of conditional execution on chips where it is
 available is controlled by "if-conversion2".
 Enabled at levels -O, -O2, -O3, -Os.
 -fif-conversion2
 Use conditional execution (where available) to transform condi-
 tional jumps into branch-less equivalents.
 Enabled at levels -O, -O2, -O3, -Os.
 -fdelete-null-pointer-checks
 Use global dataflow analysis to identify and eliminate useless
 checks for null pointers. The compiler assumes that dereferencing
 a null pointer would have halted the program. If a pointer is
 checked after it has already been dereferenced, it cannot be null.
 In some environments, this assumption is not true, and programs can
 safely dereference null pointers. Use
 -fno-delete-null-pointer-checks to disable this optimization for
 programs which depend on that behavior.
 Enabled at levels -O2, -O3, -Os.
 -fexpensive-optimizations
 Perform a number of minor optimizations that are relatively expen-
 sive.
 Enabled at levels -O2, -O3, -Os.
 -foptimize-register-move
 -fregmove
 Attempt to reassign register numbers in move instructions and as
 operands of other simple instructions in order to maximize the
 amount of register tying. This is especially helpful on machines
 with two-operand instructions.
 Note -fregmove and -foptimize-register-move are the same optimiza-
 tion.
 Enabled at levels -O2, -O3, -Os.
 -fdelayed-branch
 If supported for the target machine, attempt to reorder instruc-
 tions to exploit instruction slots available after delayed branch
 instructions.
 Enabled at levels -O, -O2, -O3, -Os.
 -fschedule-insns
 If supported for the target machine, attempt to reorder instruc-
 tions to eliminate execution stalls due to required data being
 unavailable. This helps machines that have slow floating point or
 memory load instructions by allowing other instructions to be
 issued until the result of the load or floating point instruction
 is required.
 Enabled at levels -O2, -O3, -Os.
 -fschedule-insns2
 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 num-
 ber of registers and where memory load instructions take more than
 one cycle.
 Enabled at levels -O2, -O3, -Os.
 -fno-sched-interblock
 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.
 -fno-sched-spec
 Don't allow speculative motion of non-load instructions. This is
 normally enabled by default when scheduling before register alloca-
 tion, i.e. with -fschedule-insns or at -O2 or higher.
 -fsched-spec-load
 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.
 -fsched-spec-load-dangerous
 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.
 -fcaller-saves
 Enable values to be allocated in registers that will be clobbered
 by function calls, by emitting extra instructions to save and
 restore the registers around such calls. Such allocation is done
 only when it seems to result in better code than would otherwise be
 produced.
 This option is always enabled by default on certain machines, usu-
 ally those which have no call-preserved registers to use instead.
 Enabled at levels -O2, -O3, -Os.
 -fmove-all-movables
 Forces all invariant computations in loops to be moved outside the
 loop.
 -freduce-all-givs
 Forces all general-induction variables in loops to be
 strength-reduced.
 Note: When compiling programs written in Fortran, -fmove-all-mov-
 ables and -freduce-all-givs are enabled by default when you use the
 optimizer.
 These options may generate better or worse code; results are highly
 dependent on the structure of loops within the source code.
 These two options are intended to be removed someday, once they
 have helped determine the efficacy of various approaches to improv-
 ing loop optimizations.
 Please let us (<gcc@gcc.gnu.org> and <fortran@gnu.org>) know how
 use of these options affects the performance of your production
 code. We're very interested in code that runs slower when these
 options are enabled.
 -fno-peephole
 -fno-peephole2
 Disable any machine-specific peephole optimizations. The differ-
 ence between -fno-peephole and -fno-peephole2 is in how they are
 implemented in the compiler; some targets use one, some use the
 other, a few use both.
 -fpeephole is enabled by default. -fpeephole2 enabled at levels
 -O2, -O3, -Os.
 -fbranch-probabilities
 -fno-guess-branch-probability
 Do not guess branch probabilities using a randomized model.
 Sometimes gcc will opt to use a randomized model to guess branch
 probabilities, when none are available from either profiling feed-
 back (-fprofile-arcs) or __builtin_expect. This means that differ-
 ent runs of the compiler on the same program may produce different
 object code.
 In a hard real-time system, people don't want different runs of the
 compiler to produce code that has different behavior; minimizing
 non-determinism is of paramount import. This switch allows users
 to reduce non-determinism, possibly at the expense of inferior
 optimization.
 The default is -fguess-branch-probability at levels -O, -O2, -O3,
 -Os.
 -freorder-blocks
 Reorder basic blocks in the compiled function in order to reduce
 number of taken branches and improve code locality.
 Enabled at levels -O2, -O3, -Os.
 -freorder-functions
 Reorder basic blocks in the compiled function in order to reduce
 number of taken branches and improve code locality. This is imple-
 mented by using special subsections "text.hot" for most frequently
 executed functions and "text.unlikely" for unlikely executed func-
 tions. Reordering is done by the linker so object file format must
 support named sections and linker must place them in a reasonable
 way.
 Also profile feedback must be available in to make this option
 effective. See -fprofile-arcs for details.
 Enabled at levels -O2, -O3, -Os.
 -fstrict-aliasing
 Allows the compiler to assume the strictest aliasing rules applica-
 ble to the language being compiled. For C (and C++), this acti-
 vates optimizations based on the type of expressions. In particu-
 lar, 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 alias an
 "int", but not a "void*" or a "double". A character type may alias
 any other type.
 Pay special attention to code like this:
 union a_union {
 int i;
 double d;
 };
 int f() {
 a_union t;
 t.d = 3.0;
 return t.i;
 }
 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 the mem-
 ory is accessed through the union type. So, the code above will
 work as expected. However, this code might not:
 int f() {
 a_union t;
 int* ip;
 t.d = 3.0;
 ip = &t.i;
 return *ip;
 }
 Every language that wishes to perform language-specific alias anal-
 ysis should define a function that computes, given an "tree" node,
 an alias set for the node. Nodes in different alias sets are not
 allowed to alias. For an example, see the C front-end function
 "c_get_alias_set".
 Enabled at levels -O2, -O3, -Os.
 -falign-functions
 -falign-functions=n
 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 -falign-func-
 tions=24 would align to the next 32-byte boundary only if this can
 be done by skipping 23 bytes or less.
 -fno-align-functions and -falign-functions=1 are equivalent and
 mean that functions will not be aligned.
 Some assemblers only support this flag when n is a power of two; in
 that case, it is rounded up.
 If n is not specified, use a machine-dependent default.
 Enabled at levels -O2, -O3.
 -falign-labels
 -falign-labels=n
 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 the branch
 target is reached in the usual flow of the code.
 If -falign-loops or -falign-jumps are applicable and are greater
 than this value, then their values are used instead.
 If n is not specified, use a machine-dependent default which is
 very likely to be 1, meaning no alignment.
 Enabled at levels -O2, -O3.
 -falign-loops
 -falign-loops=n
 Align loops to a power-of-two boundary, skipping up to n bytes like
 -falign-functions. The hope is that the loop will be executed many
 times, which will make up for any execution of the dummy opera-
 tions.
 -falign-loops-max-skip
 -falign-loops-max-skip=n
 When aligning loops to a power-of-two boundary, only do so if can
 skip by up to n bytes.
 If n is not specified, use a machine-dependent default.
 Enabled at levels -O2, -O3.
 -falign-jumps
 -falign-jumps=n
 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 operations
 need be executed.
 -falign-jumps-max-skip
 -falign-jumps-max-skip=n
 When aligning branch targets to a power-of-two boundary, only do so
 if can skip by up to n bytes.
 If n is not specified, use a machine-dependent default.
 Enabled at levels -O2, -O3.
 -frename-registers
 Attempt to avoid false dependencies in scheduled code by making use
 of registers left over after register allocation. This optimiza-
 tion will most benefit processors with lots of registers. It can,
 however, make debugging impossible, since variables will no longer
 stay in a ``home register''.
 Enabled at levels -O3.
 -fno-cprop-registers
 After register allocation and post-register allocation instruction
 splitting, we perform a copy-propagation pass to try to reduce
 scheduling dependencies and occasionally eliminate the copy.
 Disabled at levels -O, -O2, -O3, -Os.
 The following options control compiler behavior regarding floating
 point arithmetic. These options trade off between speed and correct-
 ness. All must be specifically enabled.
 -ffloat-store
 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.
 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. 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 such programs, after
 modifying them to store all pertinent intermediate computations
 into variables.
 -ffast-math
 Sets -fno-math-errno, -funsafe-math-optimizations, -fno-trap-
 ping-math, -ffinite-math-only and -fno-signaling-nans.
 This option causes the preprocessor macro "__FAST_MATH__" to be
 defined.
 This option should never be turned on by any -O option since it can
 result in incorrect output for programs which depend on an exact
 implementation of IEEE or ISO rules/specifications for math func-
 tions.
 -fno-math-errno
 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 this flag
 for speed while maintaining IEEE arithmetic compatibility.
 This option should never be turned on by any -O option since it can
 result in incorrect output for programs which depend on an exact
 implementation of IEEE or ISO rules/specifications for math func-
 tions.
 The default is -fmath-errno.
 -funsafe-math-optimizations
 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 libraries
 or startup files that change the default FPU control word or other
 similar optimizations.
 This option should never be turned on by any -O option since it can
 result in incorrect output for programs which depend on an exact
 implementation of IEEE or ISO rules/specifications for math func-
 tions.
 The default is -fno-unsafe-math-optimizations.
 -ffinite-math-only
 Allow optimizations for floating-point arithmetic that assume that
 arguments and results are not NaNs or +-Infs.
 This option should never be turned on by any -O option since it can
 result in incorrect output for programs which depend on an exact
 implementation of IEEE or ISO rules/specifications.
 The default is -fno-finite-math-only.
 -fno-trapping-math
 Compile code assuming that floating-point operations cannot gener-
 ate user-visible traps. These traps include division by zero,
 overflow, underflow, inexact result and invalid operation. This
 option implies -fno-signaling-nans. Setting this option may allow
 faster code if one relies on ``non-stop'' IEEE arithmetic, for
 example.
 This option should never be turned on by any -O option since it can
 result in incorrect output for programs which depend on an exact
 implementation of IEEE or ISO rules/specifications for math func-
 tions.
 The default is -ftrapping-math.
 -fsignaling-nans
 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 excep-
 tions visible with signaling NaNs. This option implies -ftrap-
 ping-math.
 This option causes the preprocessor macro "__SUPPORT_SNAN__" to be
 defined.
 The default is -fno-signaling-nans.
 This option is experimental and does not currently guarantee to
 disable all GCC optimizations that affect signaling NaN behavior.
 -fsingle-precision-constant
 Treat floating point constant as single precision constant instead
 of implicitly converting it to double precision constant.
 The following options control optimizations that may improve perfor-
 mance, but are not enabled by any -O options. This section includes
 experimental options that may produce broken code.
 -fbranch-probabilities
 After running a program compiled with -fprofile-arcs, you can com-
 pile it a second time using -fbranch-probabilities, to improve
 optimizations based on the number of times each branch was taken.
 When the program compiled with -fprofile-arcs exits it saves arc
 execution counts to a file called sourcename.da for each source
 file The information in this data file is very dependent on the
 structure of the generated code, so you must use the same source
 code and the same optimization options for both compilations.
 With -fbranch-probabilities, GCC puts a REG_BR_PROB note on each
 JUMP_INSN and CALL_INSN. These can be used to improve optimiza-
 tion. Currently, they are only used in one place: in reorg.c,
 instead of guessing which path a branch is mostly to take, the
 REG_BR_PROB values are used to exactly determine which path is
 taken more often.
 -fnew-ra
 Use a graph coloring register allocator. Currently this option is
 meant for testing, so we are interested to hear about miscompila-
 tions with -fnew-ra.
 -ftracer
 Perform tail duplication to enlarge superblock size. This transfor-
 mation simplifies the control flow of the function allowing other
 optimizations to do better job.
 -funroll-loops
 Unroll loops whose number of iterations can be determined at com-
 pile time or upon entry to the loop. -funroll-loops implies both
 -fstrength-reduce and -frerun-cse-after-loop. This option makes
 code larger, and may or may not make it run faster.
 -funroll-all-loops
 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 -fun-
 roll-loops,
 -fprefetch-loop-arrays
 If supported by the target machine, generate instructions to
 prefetch memory to improve the performance of loops that access
 large arrays.
 Disabled at level -Os.
 -ffunction-sections
 -fdata-sections
 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 section's name
 in the output file.
 Use these options on systems where the linker can perform optimiza-
 tions to improve locality of reference in the instruction space.
 HPPA processors running HP-UX and SPARC processors running Solaris
 2 have linkers with such optimizations. Other systems using the
 ELF object format as well as AIX may have these optimizations in
 the future.
 Only use these options when there are significant benefits from
 doing so. When you specify these options, the assembler and linker
 will create larger object and executable files and will also be
 slower. You will not be able to 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.
 -fssa
 Perform optimizations in static single assignment form. Each func-
 tion's flow graph is translated into SSA form, optimizations are
 performed, and the flow graph is translated back from SSA form.
 Users should not specify this option, since it is not yet ready for
 production use.
 -fssa-ccp
 Perform Sparse Conditional Constant Propagation in SSA form.
 Requires -fssa. Like -fssa, this is an experimental feature.
 -fssa-dce
 Perform aggressive dead-code elimination in SSA form. Requires
 -fssa. Like -fssa, this is an experimental feature.
 --param name=value
 In some places, GCC uses various constants to control the amount of
 optimization that is done. For example, GCC will not inline func-
 tions that contain more that a certain number of instructions. You
 can control some of these constants on the command-line using the
 --param option.
 In each case, the value is an integer. The allowable choices for
 name are given in the following table:
 max-delay-slot-insn-search
 The maximum number of instructions to consider when looking for
 an instruction to fill a delay slot. If more than this arbi-
 trary number of instructions is searched, the time savings from
 filling the delay slot will be minimal so stop searching.
 Increasing values mean more aggressive optimization, making the
 compile time increase with probably small improvement in exe-
 cutable run time.
 max-delay-slot-live-search
 When trying to fill delay slots, the maximum number of instruc-
 tions to consider when searching for a block with valid live
 register information. Increasing this arbitrarily chosen value
 means more aggressive optimization, increasing the compile
 time. This parameter should be removed when the delay slot
 code is rewritten to maintain the control-flow graph.
 max-gcse-memory
 The approximate maximum amount of memory that will be allocated
 in order to perform the global common subexpression elimination
 optimization. If more memory than specified is required, the
 optimization will not be done.
 max-gcse-passes
 The maximum number of passes of GCSE to run.
 max-pending-list-length
 The maximum number of pending dependencies scheduling will
 allow before flushing the current state and starting over.
 Large functions with few branches or calls can create exces-
 sively large lists which needlessly consume memory and
 resources.
 max-inline-insns-single
 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
 tree inliner will consider for inlining. This only affects
 functions declared inline and methods implemented in a class
 declaration (C++). The default value is 300.
 max-inline-insns-auto
 When you use -finline-functions (included in -O3), a lot of
 functions that would otherwise not be considered for inlining
 by the compiler will be investigated. To those functions, a
 different (more restrictive) limit compared to functions
 declared inline can be applied. The default value is 300.
 max-inline-insns
 The tree inliner does decrease the allowable size for single
 functions to be inlined after we already inlined the number of
 instructions given here by repeated inlining. This number
 should be a factor of two or more larger than the single func-
 tion limit. Higher numbers result in better runtime perfor-
 mance, but incur higher compile-time resource (CPU time, mem-
 ory) requirements and result in larger binaries. Very high
 values are not advisable, as too large binaries may adversely
 affect runtime performance. The default value is 600.
 max-inline-slope
 After exceeding the maximum number of inlined instructions by
 repeated inlining, a linear function is used to decrease the
 allowable size for single functions. The slope of that func-
 tion is the negative reciprocal of the number specified here.
 The default value is 32.
 min-inline-insns
 The repeated inlining is throttled more and more by the linear
 function after exceeding the limit. To avoid too much throt-
 tling, a minimum for this function is specified here to allow
 repeated inlining for very small functions even when a lot of
 repeated inlining already has been done. The default value is
 130.
 max-inline-insns-rtl
 For languages that use the RTL inliner (this happens at a later
 stage than tree inlining), you can set the maximum allowable
 size (counted in RTL instructions) for the RTL inliner with
 this parameter. The default value is 600.
 max-unrolled-insns
 The maximum number of instructions that a loop should have if
 that loop is unrolled, and if the loop is unrolled, it deter-
 mines how many times the loop code is unrolled.
 hot-bb-count-fraction
 Select fraction of the maximal count of repetitions of basic
 block in program given basic block needs to have to be consid-
 ered hot.
 hot-bb-frequency-fraction
 Select fraction of the maximal frequency of executions of basic
 block in function given basic block needs to have to be consid-
 ered hot
 tracer-dynamic-coverage
 tracer-dynamic-coverage-feedback
 This value is used to limit superblock formation once the given
 percentage of executed instructions is covered. This limits
 unnecessary code size expansion.
 The tracer-dynamic-coverage-feedback is used only when profile
 feedback is available. The real profiles (as opposed to stati-
 cally estimated ones) are much less balanced allowing the
 threshold to be larger value.
 tracer-max-code-growth
 Stop tail duplication once code growth has reached given per-
 centage. This is rather hokey argument, as most of the dupli-
 cates will be eliminated later in cross jumping, so it may be
 set to much higher values than is the desired code growth.
 tracer-min-branch-ratio
 Stop reverse growth when the reverse probability of best edge
 is less than this threshold (in percent).
 tracer-min-branch-ratio
 tracer-min-branch-ratio-feedback
 Stop forward growth if the best edge do have probability lower
 than this threshold.
 Similarly to tracer-dynamic-coverage two values are present,
 one for compilation for profile feedback and one for compila-
 tion without. The value for compilation with profile feedback
 needs to be more conservative (higher) in order to make tracer
 effective.
 ggc-min-expand
 GCC uses a garbage collector to manage its own memory alloca-
 tion. This parameter specifies the minimum percentage by which
 the garbage collector's heap should be allowed to expand
 between collections. Tuning this may improve compilation
 speed; it has no effect on code generation.
 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, RLIMIT_RSS, RLIMIT_DATA
 and RLIMIT_AS. If GCC is not able to calculate RAM on a par-
 ticular platform, the lower bound of 30% is used. Setting this
 parameter and ggc-min-heapsize to zero causes a full collection
 to occur at every opportunity. This is extremely slow, but can
 be useful for debugging.
 ggc-min-heapsize
 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-heap-
 size. Again, tuning this may improve compilation speed, and
 has no effect on code generation.
 The default is RAM/8, with a lower bound of 4096 (four
 megabytes) and an upper bound of 131072 (128 megabytes). If
 "getrlimit" is available, the notion of "RAM" is the smallest
 of actual RAM, RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If GCC
 is not able to calculate RAM on a particular platform, the
 lower bound is used. Setting this parameter very large effec-
 tively disables garbage collection. Setting this parameter and
 ggc-min-expand to zero causes a full collection to occur at
 every opportunity.
 Options Controlling the Preprocessor
 These options control the C preprocessor, which is run on each C source
 file before actual compilation.
 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 compilation.
 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. 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 interface is undocumented and subject to change,
 so whenever possible you should avoid using -Wp and let the driver han-
 dle the options instead.
 -D name
 Predefine name as a macro, with definition 1.
 -D name=definition
 Predefine name as a macro, with definition definition. There are
 no restrictions on the contents of definition, but 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 syntax.
 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 shells,
 so you will need to quote the option. With sh and csh,
 -D'name(args...)=definition' works.
 -D and -U options are processed in the order they are given on the
 command line. All -imacros file and -include file options are pro-
 cessed after all -D and -U options.
 -U name
 Cancel any previous definition of name, either built in or provided
 with a -D option.
 -undef
 Do not predefine any system-specific macros. The common predefined
 macros remain defined.
 -I dir
 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 is a
 standard system include directory, the option is ignored to ensure
 that the default search order for system directories and the spe-
 cial treatment of system headers are not defeated .
 -o file
 Write output to file. This is the same as specifying file as the
 second non-option argument to cpp. gcc has a different interpreta-
 tion of a second non-option argument, so you must use -o to specify
 the output file.
 -Wall
 Turns on all optional warnings which are desirable for normal code.
 At present this is -Wcomment and -Wtrigraphs. Note that many of
 the preprocessor's warnings are on by default and have no options
 to control them.
 -Wcomment
 -Wcomments
 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.)
 -Wtrigraphs
 Warn if any trigraphs are encountered. This option used to take
 effect only if -trigraphs was also specified, but now works inde-
 pendently. Warnings are not given for trigraphs within comments,
 as they do not affect the meaning of the program.
 -Wtraditional
 Warn about certain constructs that behave differently in tradi-
 tional and ISO C. Also warn about ISO C constructs that have no
 traditional C equivalent, and problematic constructs which should
 be avoided.
 -Wimport
 Warn the first time #import is used.
 -Wundef
 Warn whenever an identifier which is not a macro is encountered in
 an #if directive, outside of defined. Such identifiers are
 replaced with zero.
 -Wunused-macros
 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 been
 used at the time it is redefined or undefined.
 Built-in macros, macros defined on the command line, and macros
 defined in include files are not warned about.
 Note: If a macro is actually used, but only used in skipped condi-
 tional blocks, then CPP will report it as unused. To avoid the
 warning in such a case, you might improve the scope of the macro's
 definition by, for example, moving it into the first skipped block.
 Alternatively, you could provide a dummy use with something like:
 #if defined the_macro_causing_the_warning
 #endif
 -Wendif-labels
 Warn whenever an #else or an #endif are followed by text. This
 usually happens in code of the form
 #if FOO
 ...
 #else FOO
 ...
 #endif FOO
 The second and third "FOO" should be in comments, but often are not
 in older programs. This warning is on by default.
 -Werror
 Make all warnings into hard errors. Source code which triggers
 warnings will be rejected.
 -Wsystem-headers
 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 to see
 them.
 -w Suppress all warnings, including those which GNU CPP issues by
 default.
 -pedantic
 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.
 -pedantic-errors
 Issue all the mandatory diagnostics, and make all mandatory diag-
 nostics into errors. This includes mandatory diagnostics that GCC
 issues without -pedantic but treats as warnings.
 -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 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.
 Unless specified explicitly (with -MT or -MQ), the object file name
 consists of the basename of the source file with any suffix
 replaced with object file suffix. If there are many included files
 then the rule is split into several lines using \-newline. The
 rule has no commands.
 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 file with
 -MF, or use an environment variable like DEPENDENCIES_OUTPUT.
 Debug output will still be sent to the regular output stream as
 normal.
 Passing -M to the driver implies -E, and suppresses warnings with
 an implicit -w.
 -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.
 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 slight
 change in semantics from GCC versions 3.0 and earlier.
 -MF file
 @anchor{-MF} 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.
 When used with the driver options -MD or -MMD, -MF overrides the
 default dependency output file.
 -dependency-file
 Like -MF. (APPLE ONLY)
 -MG In conjunction with an option such as -M requesting dependency gen-
 eration, -MG assumes missing header files are generated files and
 adds them to the dependency list without raising an error. The
 dependency filename is taken directly from the "#include" directive
 without prepending any path. -MG also suppresses preprocessed out-
 put, as a missing header file renders this useless.
 This feature is used in automatic updating of makefiles.
 -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 remove header
 files without updating the Makefile to match.
 This is typical output:
 test.o: test.c test.h
 test.h:
 -MT target
 Change the target of the rule emitted by dependency generation. By
 default CPP takes the name of the main input file, including any
 path, deletes any file suffix such as .c, and appends the plat-
 form's usual object suffix. The result is the target.
 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.
 For example, -MT '$(objpfx)foo.o' might give
 $(objpfx)foo.o: foo.c
 -MQ target
 Same as -MT, but it quotes any characters which are special to
 Make. -MQ '$(objpfx)foo.o' gives
 $$(objpfx)foo.o: foo.c
 The default target is automatically quoted, as if it were given
 with -MQ.
 -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 of .d,
 otherwise it take the basename of the input file and applies a .d
 suffix.
 If -MD is used in conjunction with -E, any -o switch is understood
 to specify the dependency output file (but @pxref{-MF}), but if
 used without -E, each -o is understood to specify a target object
 file.
 Since -E is not implied, -MD can be used to generate a dependency
 output file as a side-effect of the compilation process.
 -MMD
 Like -MD except mention only user header files, not system -header
 files.
 -fpch-deps
 When using precompiled headers, this flag will cause the depen-
 dency-output flags to also list the files from the precompiled
 header's dependencies. If not specified only the precompiled
 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.
 -x c
 -x c++
 -x objective-c
 -x objective-c++
 -x assembler-with-cpp
 Specify the source language: C, C++, Objective-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 none of these options, cpp will deduce the language from the
 extension of the source file: .c, .cc, .m, .mm, or .S. Some other
 common extensions for C++ and assembly are also recognized. If cpp
 does not recognize the extension, it will treat the file as C; this
 is the most generic mode.
 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
 option.
 -std=standard
 -ansi
 Specify the standard to which the code should conform. Currently
 CPP knows about C and C++ standards; others may be added in the
 future.
 standard may be one of:
 "iso9899:1990"
 "c89"
 The ISO C standard from 1990. c89 is the customary shorthand
 for this version of the standard.
 The -ansi option is equivalent to -std=c89.
 "iso9899:199409"
 The 1990 C standard, as amended in 1994.
 "iso9899:1999"
 "c99"
 "iso9899:199x"
 "c9x"
 The revised ISO C standard, published in December 1999. Before
 publication, this was known as C9X.
 "gnu89"
 The 1990 C standard plus GNU extensions. This is the default.
 "gnu99"
 "gnu9x"
 The 1999 C standard plus GNU extensions.
 "c++98"
 The 1998 ISO C++ standard plus amendments.
 "gnu++98"
 The same as -std=c++98 plus GNU extensions. This is the
 default for C++ code.
 -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 <file>". If
 additional directories are specified with -I options after the -I-,
 those directories are searched for all #include directives.
 In addition, -I- inhibits the use of the directory of the current
 file directory as the first search directory for "#include "file"".
 -nostdinc
 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.
 -nostdinc++
 Do not search for header files in the C++-specific standard direc-
 tories, but do still search the other standard directories. (This
 option is used when building the C++ library.)
 -include file
 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 the direc-
 tory containing the main source file. If not found there, it is
 searched for in the remainder of the "#include "..."" search chain
 as normal.
 If multiple -include options are given, the files are included in
 the order they appear on the command line.
 -imacros file
 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 also
 processing its declarations.
 All files specified by -imacros are processed before all files
 specified by -include.
 -idirafter dir
 Search dir for header files, but do it after all directories speci-
 fied with -I and the standard system directories have been
 exhausted. dir is treated as a system include directory.
 -iprefix prefix
 Specify prefix as the prefix for subsequent -iwithprefix options.
 If the prefix represents a directory, you should include the final
 /.
 -iwithprefix dir
 -iwithprefixbefore dir
 Append dir to the prefix specified previously with -iprefix, and
 add the resulting directory to the include search path. -iwithpre-
 fixbefore puts it in the same place -I would; -iwithprefix puts it
 where -idirafter would.
 Use of these options is discouraged.
 -isystem dir
 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 is applied
 to the standard system directories.
 -fpreprocessed
 Indicate to the preprocessor that the input file has already been
 preprocessed. This suppresses things like macro expansion, tri-
 graph conversion, escaped newline splicing, and processing of most
 directives. The preprocessor still recognizes and removes com-
 ments, so that you can pass a file preprocessed with -C to the com-
 piler without problems. In this mode the integrated preprocessor
 is little more than a tokenizer for the front ends.
 -fpreprocessed is implicit if the input file has one of the exten-
 sions .i, .ii or .mi. These are the extensions that GCC uses for
 preprocessed files created by -save-temps.
 -ftabstop=width
 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 than
 100, the option is ignored. The default is 8.
 -fno-show-column
 Do not print column numbers in diagnostics. This may be necessary
 if diagnostics are being scanned by a program that does not under-
 stand the column numbers, such as dejagnu.
 -A predicate=answer
 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 special
 characters.
 -A -predicate=answer
 Cancel an assertion with the predicate predicate and answer answer.
 -A- Cancel all predefined assertions and all assertions preceding it on
 the command line. Also, undefine all predefined macros and all
 macros preceding it on the command line. (This is a historical
 wart and may change in the future.)
 -dCHARS
 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 of GCC, and
 so are silently ignored. If you specify characters whose behavior
 conflicts, the result is undefined.
 M Instead of the normal output, generate a list of #define direc-
 tives for all the macros defined during the execution of the
 preprocessor, including predefined macros. This gives you a
 way of finding out what is predefined in your version of the
 preprocessor. Assuming you have no file foo.h, the command
 touch foo.h; cpp -dM foo.h
 will show all the predefined macros.
 D Like M except in two respects: it does not include the prede-
 fined macros, and it outputs both the #define directives and
 the result of preprocessing. Both kinds of output go to the
 standard output file.
 N Like D, but emit only the macro names, not their expansions.
 I Output #include directives in addition to the result of prepro-
 cessing.
 -P Inhibit generation of linemarkers in the output from the preproces-
 sor. This might be useful when running the preprocessor on some-
 thing that is not C code, and will be sent to a program which might
 be confused by the linemarkers.
 -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.
 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 be a
 directive line have the effect of turning that line into an ordi-
 nary source line, since the first token on the line is no longer a
 #.
 -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 expanded.
 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 from
 inadvertently commenting out the remainder of the source line.
 The -CC option is generally used to support lint comments.
 -gcc
 Define the macros __GNUC__, __GNUC_MINOR__ and __GNUC_PATCHLEVEL__.
 These are defined automatically when you use gcc -E; you can turn
 them off in that case with -no-gcc.
 -traditional-cpp
 Try to imitate the behavior of old-fashioned C preprocessors, as
 opposed to ISO C preprocessors.
 -trigraphs
 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 a charac-
 ter constant for a newline. By default, GCC ignores trigraphs, but
 in standard-conforming modes it converts them. See the -std and
 -ansi options.
 The nine trigraphs and their replacements are
 Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??-
 Replacement: [ ] { } # \ ^ | ~
 -remap
 Enable special code to work around file systems which only permit
 very short file names, such as MS-DOS.
 --help
 --target-help
 Print text describing all the command line options instead of pre-
 processing anything.
 -v Verbose mode. Print out GNU CPP's version number at the beginning
 of execution, and report the final form of the include path.
 -H Print the name of each header file used, in addition to other nor-
 mal activities. Each name is indented to show how deep in the
 #include stack it is. Precompiled header files are also printed,
 even if they are found to be invalid; an invalid precompiled header
 file is printed with ...x and a valid one with ...! .
 -version
 --version
 Print out GNU CPP's version number. With one dash, proceed to pre-
 process as normal. With two dashes, exit immediately.
 Passing Options to the Assembler
 You can pass options to the assembler.
 -Wa,option
 Pass option as an option to the assembler. If option contains com-
 mas, it is split into multiple options at the commas.
 Options for Linking
 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.
 In addition to the options listed below, Apple's GCC also accepts and
 passes nearly all of the options defined by the linker ld and by the
 library tool libtool. Common options include -framework, -dynamic,
 -bundle, -flat_namespace, and so forth. See the ld and libtool man
 pages for further details.
 object-file-name
 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 file
 contents.) If linking is done, these object files are used as
 input to the linker.
 -c
 -S
 -E If any of these options is used, then the linker is not run, and
 object file names should not be used as arguments.
 -llibrary
 -l library
 Search the library named library when linking. (The second alter-
 native with the library as a separate argument is only for POSIX
 compliance and is not recommended.)
 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 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.
 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 name.
 The directories searched include several standard system directo-
 ries plus any that you specify with -L.
 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 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 fash-
 ion. The only difference between using an -l option and specifying
 a file name is that -l surrounds library with lib and .a and
 searches several directories.
 -lobjc
 You need this special case of the -l option in order to link an
 Objective-C program.
 -nostartfiles
 Do not use the standard system startup files when linking. The
 standard system libraries are used normally, unless -nostdlib or
 -nodefaultlibs is used.
 -nodefaultlibs
 Do not use the standard system libraries when linking. Only the
 libraries you specify will be passed to the linker. The standard
 startup files are used normally, unless -nostartfiles is used. The
 compiler may generate calls to memcmp, memset, and memcpy for Sys-
 tem V (and ISO C) environments or to bcopy and bzero for BSD envi-
 ronments. These entries are usually resolved by entries in libc.
 These entry points should be supplied through some other mechanism
 when this option is specified.
 -nostdlib
 Do not use the standard system startup files or libraries when
 linking. No startup files and only the libraries you specify will
 be passed to the linker. The compiler may generate calls to mem-
 cmp, memset, and memcpy for System V (and ISO C) environments or to
 bcopy and bzero for BSD environments. These entries are usually
 resolved by entries in libc. These entry points should be supplied
 through some other mechanism when this option is specified.
 -no-c++filt
 By default all linker diagnostic output is piped through c++filt.
 This option suppresses that behavior. (APPLE ONLY)
 One of the standard libraries bypassed by -nostdlib and -nodefault-
 libs is libgcc.a, a library of internal subroutines that GCC uses
 to overcome shortcomings of particular machines, or special needs
 for some languages.
 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. This
 ensures that you have no unresolved references to internal GCC
 library subroutines. (For example, __main, used to ensure C++ con-
 structors will be called.)
 -s Remove all symbol table and relocation information from the exe-
 cutable.
 -static
 On systems that support dynamic linking, this prevents linking with
 the shared libraries. On other systems, this option has no effect.
 This option will not work on Mac OS X unless all of your libraries
 (including libgcc.a) have also been compiled with -static.
 -shared
 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 of options
 that were used to generate code (-fpic, -fPIC, or model suboptions)
 when you specify this option.[1]
 This option is not supported on Mac OS X.
 -shared-libgcc
 -static-libgcc
 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 compiler was con-
 figured, these options have no effect.
 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 exceptions
 across different shared libraries. In that case, each of the
 libraries as well as the application itself should use the shared
 libgcc.
 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 is the
 right thing to do.
 If, instead, you use the GCC driver to create shared libraries, you
 may find that they will not always be linked with the shared
 libgcc. If GCC finds, at its configuration time, that you have a
 GNU linker that does not support option --eh-frame-hdr, it will
 link the shared version of libgcc into shared libraries by default.
 Otherwise, it will take advantage of the linker and optimize 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 libraries, without incurring reloca-
 tion costs at library load time.
 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 using the
 option -shared-libgcc, such that it is linked with the shared
 libgcc.
 -symbolic
 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 systems sup-
 port this option.
 -Xlinker option
 Pass option as an option to the linker. You can use this to supply
 system-specific linker options which GCC does not know how to rec-
 ognize.
 If you want to pass an option that takes an argument, you must use
 -Xlinker twice, once for the option and once for the argument. For
 example, to pass -assert definitions, you must 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 linker expects.
 -Wl,option
 Pass option as an option to the linker. If option contains commas,
 it is split into multiple options at the commas.
 -u symbol
 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 modules.
 Options for Directory Search
 These options specify directories to search for header files, for
 libraries and for parts of the compiler:
 -Idir
 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 directories
 are searched before the system header file directories. However,
 you should not use this option to add directories that contain ven-
 dor-supplied system header files (use -isystem 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.
 If a standard system include directory, or a directory specified
 with -isystem, is also specified with -I, the -I option will be
 ignored. The directory will still be searched but as a system
 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 inadvertently
 changed. If you really need to change the search order for system
 directories, use the -nostdinc and/or -isystem options.
 -I- Any directories you specify with -I options before the -I- option
 are searched only for the case of #include "file"; they are not
 searched for #include <file>.
 If additional directories are specified with -I options after the
 -I-, these directories are searched for all #include directives.
 (Ordinarily all -I directories are used this way.)
 In addition, the -I- option inhibits the use of the current direc-
 tory (where the current input file came from) as the first search
 directory for #include "file". There is no way to override this
 effect of -I-. With -I. you can specify searching the directory
 which was current when the compiler was invoked. That is not
 exactly the same as what the preprocessor does by default, but it
 is often satisfactory.
 -I- does not inhibit the use of the standard system directories for
 header files. Thus, -I- and -nostdinc are independent.
 -Ldir
 Add directory dir to the list of directories to be searched for -l.
 -Fdir
 In Apple's version of GCC only, add the directory dir to the head
 of the list of directories to be searched for frameworks.
 The framework search algorithm is, for an inclusion of
 <Fmwk/Header.h>, to look for files named path/Fmwk.framework/Head-
 ers/Header.h or path/Fmwk.framework/PrivateHeaders/Header.h where
 path includes /System/Library/Frameworks/ /Library/Frameworks/, and
 /Local/Library/Frameworks/, plus any additional paths specified by
 -F.
 All the -F options are also passed to the linker.
 -Bprefix
 This option specifies where to find the executables, libraries,
 include files, and data files of the compiler itself.
 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/.
 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 was not
 specified, the driver tries two standard prefixes, which are
 /usr/lib/gcc/ and /usr/local/lib/gcc-lib/. 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 envi-
 ronment variable.
 The compiler will check to see if the path provided by the -B
 refers to a directory, and if necessary it will add a directory
 separator character at the end of the path.
 -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
 includes 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.
 The run-time support file libgcc.a can also be searched for using
 the -B prefix, if needed. If it is not found there, the two stan-
 dard prefixes above are tried, and that is all. The file is left
 out of the link if it is not found by those means.
 Another way to specify a prefix much like the -B prefix is to use
 the environment variable GCC_EXEC_PREFIX.
 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 will be replaced
 by [dir/]include. This is to help with boot-strapping the com-
 piler.
 -specs=file
 Process file after the compiler reads in the standard specs file,
 in order to override the defaults that the gcc driver program uses
 when determining what switches to pass to cc1, cc1plus, 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.
 Specifying Target Machine and Compiler Version
 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. Sometimes this is
 inconvenient, so GCC provides options that will switch to another
 cross-compiler or version.
 -b machine
 The argument machine specifies the target machine for compilation.
 The value to use for machine is the same as was specified as the
 machine type when configuring GCC as a cross-compiler. For exam-
 ple, if a cross-compiler was configured with configure i386v, mean-
 ing to compile for an 80386 running System V, then you would spec-
 ify -b i386v to run that cross compiler.
 -V version
 The argument version specifies which version of GCC to run. This
 is useful when multiple versions are installed. For example, ver-
 sion might be 2.0, meaning to run GCC version 2.0.
 The -V and -b options work by running the <machine>-gcc-<version> exe-
 cutable, so there's no real reason to use them if you can just run that
 directly.
 Hardware Models and Configurations
 Earlier we discussed the standard option -b which chooses among differ-
 ent installed compilers for completely different target machines, such
 as VAX vs. 68000 vs. 80386.
 In addition, each of these target machine types can have its own spe-
 cial options, starting with -m, to choose among various hardware models
 or configurations---for example, 68010 vs 68020, floating coprocessor
 or none. A single installed version of the compiler can compile for
 any model or configuration, according to the options specified.
 Some configurations of the compiler also support additional special
 options, usually for compatibility with other compilers on the same
 platform.
 These options are defined by the macro "TARGET_SWITCHES" in the machine
 description. The default for the options is also defined by that
 macro, which enables you to change the defaults.
 IBM RS/6000 and PowerPC Options
 These -m options are defined for the IBM RS/6000 and PowerPC:
 -mpower
 -mno-power
 -mpower2
 -mno-power2
 -mpowerpc
 -mno-powerpc
 -mpowerpc-gpopt
 -mno-powerpc-gpopt
 -mpowerpc-gfxopt
 -mno-powerpc-gfxopt
 -mpowerpc64
 -mno-powerpc64
 GCC supports two related instruction set architectures for the
 RS/6000 and PowerPC. The POWER instruction set are those instruc-
 tions supported by the rios chip set used in the original RS/6000
 systems and the PowerPC instruction set is the architecture of the
 Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and the IBM 4xx
 microprocessors.
 Neither architecture is a subset of the other. However there is a
 large common subset of instructions supported by both. An MQ reg-
 ister is included in processors supporting the POWER architecture.
 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 -mcpu=cpu_type
 overrides the specification of these options. We recommend you use
 the -mcpu=cpu_type option rather than the options listed above.
 The -mpower option allows GCC to generate instructions that are
 found only in the POWER architecture and to use the MQ register.
 Specifying -mpower2 implies -power and also allows GCC to generate
 instructions that are present in the POWER2 architecture but not
 the original POWER architecture.
 The -mpowerpc option allows GCC to generate instructions that are
 found only in the 32-bit subset of the PowerPC architecture. Spec-
 ifying -mpowerpc-gpopt implies -mpowerpc and also allows GCC to use
 the optional PowerPC architecture instructions in the General Pur-
 pose group, including floating-point square root. Specifying
 -mpowerpc-gfxopt implies -mpowerpc and also allows GCC to use the
 optional PowerPC architecture instructions in the Graphics group,
 including floating-point select.
 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 defaults to
 -mno-powerpc64.
 If you specify both -mno-power and -mno-powerpc, GCC will use only
 the instructions in the common subset of both architectures plus
 some special AIX common-mode calls, and will not use the MQ regis-
 ter. Specifying both -mpower and -mpowerpc permits GCC to use any
 instruction from either architecture and to allow use of the MQ
 register; specify this for the Motorola MPC601.
 -mnew-mnemonics
 -mold-mnemonics
 Select which mnemonics to use in the generated assembler code.
 With -mnew-mnemonics, GCC uses the assembler mnemonics defined for
 the PowerPC architecture. With -mold-mnemonics it uses the assem-
 bler mnemonics defined for the POWER architecture. Instructions
 defined in only one architecture have only one mnemonic; GCC uses
 that mnemonic irrespective of which of these options is specified.
 GCC defaults to the mnemonics appropriate for the architecture in
 use. Specifying -mcpu=cpu_type sometimes overrides the value of
 these option. Unless you are building a cross-compiler, you should
 normally not specify either -mnew-mnemonics or -mold-mnemonics, but
 should instead accept the default.
 -mcpu=cpu_type
 Set architecture type, register usage, choice of mnemonics, and
 instruction scheduling parameters for machine type cpu_type. Sup-
 ported values for cpu_type are rios, rios1, rsc, rios2, rs64a, 601,
 602, 603, 603e, 604, 604e, 620, 630, 740, 7400, 7450, 750, power,
 power2, powerpc, 403, 505, 801, 821, 823, and 860 and common.
 -mcpu=common selects a completely generic processor. Code gener-
 ated under this option will run on any POWER or PowerPC processor.
 GCC will use only the instructions in the common subset of both
 architectures, and will not use the MQ register. GCC assumes a
 generic processor model for scheduling purposes.
 -mcpu=power, -mcpu=power2, -mcpu=powerpc, and -mcpu=powerpc64 spec-
 ify generic POWER, POWER2, pure 32-bit PowerPC (i.e., not MPC601),
 and 64-bit PowerPC architecture machine types, with an appropriate,
 generic processor model assumed for scheduling purposes.
 The other options specify a specific processor. Code generated
 under those options will run best on that processor, and may not
 run at all on others.
 The -mcpu options automatically enable or disable other -m options
 as follows:
 common
 -mno-power, -mno-powerpc
 power
 power2
 rios1
 rios2
 rsc -mpower, -mno-powerpc, -mno-new-mnemonics
 powerpc
 rs64a
 602
 603
 603e
 604
 620
 630
 740
 7400
 7450
 750
 505 -mno-power, -mpowerpc, -mnew-mnemonics
 601 -mpower, -mpowerpc, -mnew-mnemonics
 403
 821
 860 -mno-power, -mpowerpc, -mnew-mnemonics, -msoft-float
 -mtune=cpu_type
 Set the instruction scheduling parameters for machine type
 cpu_type, but do not set the architecture type, register usage, or
 choice of mnemonics, as -mcpu=cpu_type would. The same values for
 cpu_type are used for -mtune as for -mcpu. If both are specified,
 the code generated will use the architecture, registers, and
 mnemonics set by -mcpu, but the scheduling parameters set by
 -mtune.
 -maltivec
 -mno-altivec
 These switches enable or disable the use of built-in functions that
 allow access to the AltiVec instruction set. You may also need to
 set -mabi=altivec to adjust the current ABI with AltiVec ABI
 enhancements.
 This option is not supported on Mac OS X; use -faltivec instead.
 -mabi=spe
 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.
 -mabi=no-spe
 Disable Booke SPE ABI extensions for the current ABI.
 -misel=yes/no
 -misel
 This switch enables or disables the generation of ISEL instruc-
 tions.
 -mfull-toc
 -mno-fp-in-toc
 -mno-sum-in-toc
 -mminimal-toc
 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 will allocate at least one TOC entry
 for each unique non-automatic variable reference in your program.
 GCC will also place floating-point constants in the TOC. However,
 only 16,384 entries are available in the TOC.
 If you receive a linker error message that saying you have over-
 flowed the available TOC space, you can reduce the amount of TOC
 space used with the -mno-fp-in-toc and -mno-sum-in-toc 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 cal-
 culate the sum of an address and a constant at 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 conserving TOC space.
 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 you
 specify this option, GCC will produce 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 executed
 code.
 -maix64
 -maix32
 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 and -mpowerpc, while -maix32
 disables the 64-bit ABI and implies -mno-powerpc64. GCC defaults
 to -maix32.
 -mxl-call
 -mno-xl-call
 On AIX, pass floating-point arguments to prototyped functions
 beyond the register save area (RSA) on the stack in addition to
 argument FPRs. 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 argu-
 ments than declared. AIX XL compilers access floating point argu-
 ments which do not fit in the RSA from the stack when a subroutine
 is compiled without optimization. Because always storing floating-
 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 AIX XL compilers without optimization.
 -mpe
 Support IBM RS/6000 SP Parallel Environment (PE). Link an applica-
 tion written to use message passing with special startup code to
 enable the application to run. The system must have PE installed
 in the standard location (/usr/lpp/ppe.poe/), or the specs file
 must be overridden with the -specs= option to specify the appropri-
 ate directory location. The Parallel Environment does not support
 threads, so the -mpe option and the -pthread option are incompati-
 ble.
 -malign-mac68k
 -malign-power
 -malign-natural
 The option -malign-mac68k causes structure fields to be aligned on
 2-byte boundaries, in order to be compatible with m68k compiler
 output. The option -malign-power is the standard alignment mode
 for the PowerPC. The option -malign-natural is an extension of
 PowerPC alignment that aligns larger data types such as doubles on
 their natural boundaries. (APPLE ONLY)
 -msoft-float
 -mhard-float
 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 linking.
 -mmultiple
 -mno-multiple
 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
 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 PPC740
 and PPC750 which permit the instructions usage in little endian
 mode.
 -mstring
 -mno-string
 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 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 in little endian
 mode. The exceptions are PPC740 and PPC750 which permit the
 instructions usage in little endian mode.
 -mupdate
 -mno-update
 Generate code that uses (does not use) the load or store instruc-
 tions that update the base register to the address of the calcu-
 lated memory location. These instructions are generated by
 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 stack
 frame across interrupts or signals may get corrupted data.
 -mfused-madd
 -mno-fused-madd
 Generate code that uses (does not use) the floating point multiply
 and accumulate instructions. These instructions are generated by
 default if hardware floating is used.
 -mno-bit-align
 -mbit-align
 On System V.4 and embedded PowerPC systems do not (do) force struc-
 tures and unions that contain bit-fields to be aligned to the base
 type of the bit-field.
 For example, by default a structure containing nothing but 8
 "unsigned" bit-fields of length 1 would be aligned to a 4 byte
 boundary and have a size of 4 bytes. By using -mno-bit-align, the
 structure would be aligned to a 1 byte boundary and be one byte in
 size.
 -mno-strict-align
 -mstrict-align
 On System V.4 and embedded PowerPC systems do not (do) assume that
 unaligned memory references will be handled by the system.
 -mrelocatable
 -mno-relocatable
 On embedded PowerPC systems generate code that allows (does not
 allow) the program to be relocated to a different address at run-
 time. If you use -mrelocatable on any module, all objects linked
 together must be compiled with -mrelocatable or -mrelocatable-lib.
 -mrelocatable-lib
 -mno-relocatable-lib
 On embedded PowerPC systems generate code that allows (does not
 allow) the program to be relocated to a different address at run-
 time. Modules compiled with -mrelocatable-lib can be linked with
 either modules compiled without -mrelocatable and -mrelocatable-lib
 or with modules compiled with the -mrelocatable options.
 -mno-toc
 -mtoc
 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.
 -mlittle
 -mlittle-endian
 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.
 -mbig
 -mbig-endian
 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.
 -mdynamic-no-pic
 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
 libraries. (APPLE ONLY)
 -mlong-branch
 On Darwin and Mac OS X systems, compile calls to use a 32-bit des-
 tination address. This is to support kernel extensions, which may
 load anywhere within the kernel address space. (APPLE ONLY)
 -mcall-sysv
 On System V.4 and embedded PowerPC systems compile code using call-
 ing conventions that adheres to the March 1995 draft of the System
 V Application Binary Interface, PowerPC processor supplement. This
 is the default unless you configured GCC using powerpc-*-eabiaix.
 -mcall-sysv-eabi
 Specify both -mcall-sysv and -meabi options.
 -mcall-sysv-noeabi
 Specify both -mcall-sysv and -mno-eabi options.
 -mcall-aix
 On System V.4 and embedded PowerPC systems compile code using call-
 ing conventions that are similar to those used on AIX. This is the
 default if you configured GCC using powerpc-*-eabiaix.
 -mcall-solaris
 On System V.4 and embedded PowerPC systems compile code for the
 Solaris operating system.
 -mcall-linux
 On System V.4 and embedded PowerPC systems compile code for the
 Linux-based GNU system.
 -mcall-gnu
 On System V.4 and embedded PowerPC systems compile code for the
 Hurd-based GNU system.
 -mcall-netbsd
 On System V.4 and embedded PowerPC systems compile code for the
 NetBSD operating system.
 -maix-struct-return
 Return all structures in memory (as specified by the AIX ABI).
 -msvr4-struct-return
 Return structures smaller than 8 bytes in registers (as specified
 by the SVR4 ABI).
 -mabi=altivec
 Extend the current ABI with AltiVec ABI extensions. This does not
 change the default ABI, instead it adds the AltiVec ABI extensions
 to the current ABI.
 This option is effectively permanently enabled on Mac OS X.
 -mabi=no-altivec
 Disable AltiVec ABI extensions for the current ABI.
 This option will not work on Mac OS X.
 -mprototype
 -mno-prototype
 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 prototyped
 call to set or clear bit 6 of the condition code register (CR) to
 indicate whether floating point values were passed in the floating
 point registers in case the function takes a variable arguments.
 With -mprototype, only calls to prototyped variable argument func-
 tions will set or clear the bit.
 -msim
 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. configura-
 tions.
 -mmvme
 On embedded PowerPC systems, assume that the startup module is
 called crt0.o and the standard C libraries are libmvme.a and
 libc.a.
 -mads
 On embedded PowerPC systems, assume that the startup module is
 called crt0.o and the standard C libraries are libads.a and libc.a.
 -myellowknife
 On embedded PowerPC systems, assume that the startup module is
 called crt0.o and the standard C libraries are libyk.a and libc.a.
 -mvxworks
 On System V.4 and embedded PowerPC systems, specify that you are
 compiling for a VxWorks system.
 -mwindiss
 Specify that you are compiling for the WindISS simulation environ-
 ment.
 -memb
 On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags
 header to indicate that eabi extended relocations are used.
 -meabi
 -mno-eabi
 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. Selecting -meabi
 means that the stack is aligned to an 8 byte boundary, a function
 "__eabi" is called to from "main" to set up the eabi environment,
 and the -msdata option can use both "r2" and "r13" to point to two
 separate small data areas. Selecting -mno-eabi means that the
 stack is aligned to a 16 byte boundary, do not call an initializa-
 tion function from "main", and the -msdata option will only use
 "r13" to point to a single small data area. The -meabi option is
 on by default if you configured GCC using one of the pow-
 erpc*-*-eabi* options.
 -msdata=eabi
 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 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 to the .sdata section. The
 -msdata=eabi option is incompatible with the -mrelocatable option.
 The -msdata=eabi option also sets the -memb option.
 -msdata=sysv
 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 in the .sbss
 section, which is adjacent to the .sdata section. The -msdata=sysv
 option is incompatible with the -mrelocatable option.
 -msdata=default
 -msdata
 On System V.4 and embedded PowerPC systems, if -meabi is used, com-
 pile code the same as -msdata=eabi, otherwise compile code the same
 as -msdata=sysv.
 -msdata-data
 On System V.4 and embedded PowerPC systems, put small global and
 static data in the .sdata section. Put small uninitialized global
 and static data in the .sbss section. Do not use register "r13" to
 address small data however. This is the default behavior unless
 other -msdata options are used.
 -msdata=none
 -mno-sdata
 On embedded PowerPC systems, put all initialized global and static
 data in the .data section, and all uninitialized data in the .bss
 section.
 -G num
 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. The -G
 num switch is also passed to the linker. All modules should be
 compiled with the same -G num value.
 -mregnames
 -mno-regnames
 On System V.4 and embedded PowerPC systems do (do not) emit regis-
 ter names in the assembly language output using symbolic forms.
 -mlongcall
 -mno-longcall
 Default to making all function calls via pointers, so that func-
 tions which reside further than 64 megabytes (67,108,864 bytes)
 from the current location can be called. This setting can be over-
 call(0)".
 Some linkers are capable of detecting out-of-range calls and gener-
 ating glue code on the fly. On these systems, long calls are
 unnecessary and generate slower code. As of this writing, the 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.
 In the future, we may cause GCC to ignore all longcall specifica-
 tions when the linker is known to generate glue.
 -pthread
 Adds support for multithreading with the pthreads library. This
 option sets flags for both the preprocessor and linker.
 Darwin Options
 -all_load
 Loads all members of static archive libraries. See man ld(1)  for
 more information.
 -arch_errors_fatal
 Cause the errors having to do with files that have the wrong archi-
 tecture to be fatal.
 -bind_at_load
 Causes the output file to be marked such that the dynamic linker
 will bind all undefined references when the file is loaded or
 launched.
 -bundle
 Produce a Mach-o bundle format file. See man ld(1)  for more infor-
 mation.
 -bundle_loader executable
 This specifies the executable that will be loading the build output
 file being linked. See man ld(1)  for more information.
 -mone-byte-bool
 Override the defaults for bool so that sizeof(bool)==1. By default
 sizeof(bool) is 4 when compiling for Darwin/PowerPC and 1 when com-
 piling for Darwin/x86, so this option has no effect on x86.
 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 mod-
 ules in a program, including system libraries. Use this switch to
 conform to a non-default data model.
 -allowable_client client_name
 -arch_only
 -client_name
 -compatibility_version
 -current_version
 -dead_strip
 -no_dead_strip_inits_and_terms
 -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
 -image_base
 -init
 -install_name
 -keep_private_externs
 -multi_module
 -multiply_defined
 -multiply_defined_unused
 -noall_load
 -nomultidefs
 -noprebind
 -noseglinkedit
 -pagezero_size
 -prebind
 -prebind_all_twolevel_modules
 -private_bundle
 -read_only_relocs
 -sectalign
 -sectobjectsymbols
 -whyload
 -seg1addr
 -sectcreate
 -sectobjectsymbols
 -sectorder
 -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_symbols_list
 -weak_reference_mismatches
 -whatsloaded
 This options are available for Darwin linker. Darwin linker man
 page describes them in detail.
 Intel 386 and AMD x86-64 Options
 These -m options are defined for the i386 and x86-64 family of comput-
 ers:
 -mcpu=cpu-type
 Tune to cpu-type everything applicable about the generated code,
 except for the ABI and the set of available instructions. The
 choices for cpu-type are i386, i486, i586, i686, pentium, pentium-
 mmx, pentiumpro, pentium2, pentium3, pentium4, k6, k6-2, k6-3,
 athlon, athlon-tbird, athlon-4, athlon-xp, athlon-mp, winchip-c6,
 winchip2 and c3.
 While picking a specific cpu-type will schedule things appropri-
 ately for that particular chip, the compiler will not generate any
 code that does not run on the i386 without the -march=cpu-type
 option being used. i586 is equivalent to pentium and i686 is
 equivalent to pentiumpro. k6 and athlon are the AMD chips as
 opposed to the Intel ones.
 -march=cpu-type
 Generate instructions for the machine type cpu-type. The choices
 for cpu-type are the same as for -mcpu. Moreover, specifying
 -march=cpu-type implies -mcpu=cpu-type.
 -m386
 -m486
 -mpentium
 -mpentiumpro
 These options are synonyms for -mcpu=i386, -mcpu=i486, -mcpu=pen-
 tium, and -mcpu=pentiumpro respectively. These synonyms are depre-
 cated.
 -mfpmath=unit
 generate floating point arithmetics for selected unit unit. the
 choices for unit are:
 387 Use the standard 387 floating point coprocessor present major-
 ity of chips and emulated otherwise. Code compiled with this
 option will run almost everywhere. The temporary results are
 computed in 80bit precision instead of precision specified by
 the type resulting in slightly different results compared to
 most of other chips. See -ffloat-store for more detailed
 description.
 This is the default choice for i386 compiler.
 sse Use scalar floating point instructions present in the SSE
 instruction set. This instruction set is supported by Pentium3
 and newer chips, in the AMD line by Athlon-4, Athlon-xp and
 Athlon-mp chips. The earlier version of SSE instruction set
 supports only single precision arithmetics, thus the double and
 extended precision arithmetics is still done using 387. Later
 version, present only in Pentium4 and the future AMD x86-64
 chips supports double precision arithmetics too.
 For i387 you need to use -march=cpu-type, -msse or -msse2
 switches to enable SSE extensions and make this option effec-
 tive. For x86-64 compiler, these extensions are enabled by
 default.
 The resulting code should be considerably faster in majority of
 cases and avoid the numerical instability problems of 387 code,
 but may break some existing code that expects temporaries to be
 80bit.
 This is the default choice for x86-64 compiler.
 sse,387
 Attempt to utilize both instruction sets at once. This effec-
 tively double the amount of available registers and on chips
 with separate execution units for 387 and SSE the execution
 resources too. Use this option with care, as it is still
 experimental, because gcc register allocator does not model
 separate functional units well resulting in instable perfor-
 mance.
 -masm=dialect
 Output asm instructions using selected dialect. Supported choices
 are intel or att (the default one).
 -mieee-fp
 -mno-ieee-fp
 Control whether or not the compiler uses IEEE floating point com-
 parisons. These handle correctly the case where the result of a
 comparison is unordered.
 -msoft-float
 Generate output containing library calls for floating point. Warn-
 ing: 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 make your
 own arrangements to provide suitable library functions for
 cross-compilation.
 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.
 -mno-fp-ret-in-387
 Do not use the FPU registers for return values of functions.
 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 FPU.
 The option -mno-fp-ret-in-387 causes such values to be returned in
 ordinary CPU registers instead.
 -mno-fancy-math-387
 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 FreeBSD, OpenBSD
 and NetBSD. This option is overridden when -march indicates that
 the target cpu will always have an FPU and so the instruction will
 not need emulation. As of revision 2.6.1, these instructions are
 not generated unless you also use the -funsafe-math-optimizations
 switch.
 -malign-double
 -mno-align-double
 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 will produce code that
 runs somewhat faster on a Pentium at the expense of more memory.
 Warning: if you use the -malign-double switch, structures contain-
 ing the above types will be aligned differently than the published
 application binary interface specifications for the 386 and will
 not be binary compatible with structures in code compiled without
 that switch.
 -m128bit-long-double
 Control the size of "long double" type. i386 application binary
 interface specify the size to be 12 bytes, while modern architec-
 tures (Pentium and newer) prefer "long double" aligned to 8 or 16
 byte boundary. This is impossible to reach with 12 byte long dou-
 bles in the array accesses.
 Warning: if you use the -m128bit-long-double switch, the structures
 and arrays containing "long double" will change their size as well
 as function calling convention for function taking "long double"
 will be modified.
 -m96bit-long-double
 Set the size of "long double" to 96 bits as required by the i386
 application binary interface. This is the default.
 -msvr3-shlib
 -mno-svr3-shlib
 Control whether GCC places uninitialized local variables into the
 "bss" or "data" segments. -msvr3-shlib places them into "bss".
 These options are meaningful only on System V Release 3.
 -mrtd
 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
 saves one instruction in the caller since there is no need to pop
 the arguments there.
 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 attribute cdecl.
 Warning: this calling convention is incompatible with the one nor-
 mally used on Unix, so you cannot use it if you need to call
 libraries compiled with the Unix compiler.
 Also, you must provide function prototypes for all functions that
 take variable numbers of arguments (including "printf"); otherwise
 incorrect code will be generated for calls to those functions.
 In addition, seriously incorrect code will result if you call a
 function with too many arguments. (Normally, extra arguments are
 harmlessly ignored.)
 -mregparm=num
 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 spe-
 cific function by using the function attribute regparm.
 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.
 -mpreferred-stack-boundary=num
 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), except when optimizing for
 code size (-Os), in which case the default is the minimum correct
 alignment (4 bytes for x86, and 8 bytes for x86-64).
 On Pentium and PentiumPro, "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 III, the
 Streaming SIMD Extension (SSE) data type "__m128" suffers similar
 penalties if it is not 16 byte aligned.
 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 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 will most likely misalign the stack.
 It is recommended that libraries that use callbacks always use the
 default setting.
 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, may want to
 reduce the preferred alignment to -mpreferred-stack-boundary=2.
 -mmmx
 -mno-mmx
 -msse
 -mno-sse
 -msse2
 -mno-sse2
 -m3dnow
 -mno-3dnow
 These switches enable or disable the use of built-in functions that
 allow direct access to the MMX, SSE and 3Dnow extensions of the
 instruction set.
 To have SSE/SSE2 instructions generated automatically from float-
 ing-point code, see -mfpmath=sse.
 -mpush-args
 -mno-push-args
 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 may improve
 performance because of improved scheduling and reduced dependen-
 cies.
 -maccumulate-outgoing-args
 If enabled, the maximum amount of space required for outgoing argu-
 ments will be computed in the function prologue. This is faster on
 most modern CPUs because of reduced dependencies, improved schedul-
 ing and reduced stack usage when preferred stack boundary is not
 equal to 2. The drawback is a notable increase in code size. This
 switch implies -mno-push-args.
 -mthreads
 Support thread-safe exception handling on Mingw32. Code that
 relies on thread-safe exception handling must compile and link all
 code with the -mthreads option. When compiling, -mthreads defines
 -D_MT; when linking, it links in a special thread helper library
 -lmingwthrd which cleans up per thread exception handling data.
 -mno-align-stringops
 Do not align destination of inlined string operations. This switch
 reduces code size and improves performance in case the destination
 is already aligned, but gcc don't know about it.
 -minline-all-stringops
 By default GCC inlines string operations only when destination is
 known to be aligned at least to 4 byte boundary. This enables more
 inlining, increase code size, but may improve performance of code
 that depends on fast memcpy, strlen and memset for short lengths.
 -momit-leaf-frame-pointer
 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 functions.
 The option -fomit-frame-pointer removes the frame pointer for all
 functions which might make debugging harder.
 These -m switches are supported in addition to the above on AMD x86-64
 processors in 64-bit environments.
 -m32
 -m64
 Generate code for a 32-bit or 64-bit environment. The 32-bit envi-
 ronment sets int, long and pointer to 32 bits and generates code
 that runs on any i386 system. The 64-bit environment sets int to
 32 bits and long and pointer to 64 bits and generates code for
 AMD's x86-64 architecture.
 -mno-red-zone
 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 loca-
 tion of the stack pointer that will not be modified by signal or
 interrupt handlers and therefore can be used for temporary data
 without adjusting the stack pointer. The flag -mno-red-zone dis-
 ables this red zone.
 -mcmodel=small
 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 linked.
 This is the default code model.
 -mcmodel=kernel
 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.
 -mcmodel=medium
 Generate code for the medium model: The program is linked in the
 lower 2 GB of the address space but symbols can be located anywhere
 in the address space. Programs can be statically or dynamically
 linked, but building of shared libraries are not supported with the
 medium model.
 -mcmodel=large
 Generate code for the large model: This model makes no assumptions
 about addresses and sizes of sections. Currently GCC does not
 implement this model.
 Options for Code Generation Conventions
 These machine-independent options control the interface conventions
 used in code generation.
 Most of them have both positive and negative forms; the negative form
 of -ffoo would be -fno-foo. In the table below, only one of the forms
 is listed---the one which is not the default. You can figure out the
 other form by either removing no- or adding it.
 -fbounds-check
 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 77
 front-ends, where this option defaults to true and false respec-
 tively.
 -ftrapv
 This option generates traps for signed overflow on addition, sub-
 traction, multiplication operations.
 -fexceptions
 Enable exception handling. Generates extra code needed to propa-
 gate exceptions. For some targets, this implies GCC will generate
 frame unwind information for all functions, which can produce sig-
 nificant data size overhead, although it does not affect execution.
 If you do not specify this option, GCC will enable it by default
 for languages like C++ which normally require exception handling,
 and disable 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 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.
 -fnon-call-exceptions
 Generate code that allows trapping instructions to throw excep-
 tions. Note that this requires platform-specific runtime support
 that does not exist everywhere. Moreover, it only allows trapping
 instructions to throw exceptions, i.e. memory references or float-
 ing point instructions. It does not allow exceptions to be thrown
 from arbitrary signal handlers such as "SIGALRM".
 -funwind-tables
 Similar to -fexceptions, except that it will just generate any
 needed static data, but will not affect the generated code in any
 other way. You will normally not enable this option; instead, a
 language processor that needs this handling would enable it on your
 behalf.
 -fasynchronous-unwind-tables
 Generate unwind table in dwarf2 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 (such as
 debugger or garbage collector).
 -fpcc-struct-return
 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 between GCC-
 compiled files and files compiled with other compilers, particu-
 larly the Portable C Compiler (pcc).
 The precise convention for returning structures in memory depends
 on the target configuration macros.
 Short structures and unions are those whose size and alignment
 match that of some integer type.
 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 binary
 interface.
 -freg-struct-return
 Return "struct" and "union" values in registers when possible.
 This is more efficient for small structures than
 -fpcc-struct-return.
 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
 -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.
 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 binary
 interface.
 -fshort-enums
 Allocate to an "enum" type only as many bytes as it needs for the
 declared range of possible values. Specifically, the "enum" type
 will be equivalent to the smallest integer type which has enough
 room.
 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 interface.
 -fshort-double
 Use the same size for "double" as for "float".
 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 interface.
 -fshort-wchar
 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.
 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 interface.
 -fshared-data
 Requests that the data and non-"const" variables of this compila-
 tion be shared data rather than private data. The distinction
 makes sense only on certain operating systems, where shared data is
 shared between processes running the same program, while private
 data exists in one copy per process.
 -fno-common
 In C, allocate even uninitialized global variables in the data sec-
 tion 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 will get an
 error when you link them. The only reason this might be useful is
 if you wish to verify that the program will work on other systems
 which always work this way.
 -fno-ident
 Ignore the #ident directive.
 -fno-gnu-linker
 Do not output global initializations (such as C++ constructors and
 destructors) in the form used by the GNU linker (on systems where
 the GNU linker is the standard method of handling them). Use this
 option when you want to use a non-GNU linker, which also requires
 using the collect2 program to make sure the system linker includes
 constructors and destructors. (collect2 is included in the GCC
 distribution.) For systems which must use collect2, the compiler
 driver gcc is configured to do this automatically.
 -finhibit-size-directive
 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. This
 option is used when compiling crtstuff.c; you should not need to
 use it for anything else.
 -fverbose-asm
 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 (per-
 haps while debugging the compiler itself).
 -fno-verbose-asm, the default, causes the extra information to be
 omitted and is useful when comparing two assembler files.
 -fvolatile
 Consider all memory references through pointers to be volatile.
 -fvolatile-global
 Consider all memory references to extern and global data items to
 be volatile. GCC does not consider static data items to be
 volatile because of this switch.
 -fvolatile-static
 Consider all memory references to static data to be volatile.
 -fpic
 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
 (GOT). The dynamic loader resolves the GOT entries when the pro-
 gram starts (the dynamic loader is not part of GCC; it is part of
 the operating system). If the GOT size for the linked 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 are 16k on the m88k,
 8k on the SPARC, and 32k on the m68k and RS/6000. The 386 has no
 such limit.)
 Position-independent code requires special support, and therefore
 works only on certain machines. For the 386, GCC supports PIC for
 System V but not for the Sun 386i. Code generated for the IBM
 RS/6000 is always position-independent.
 -fpic is not supported on Mac OS X.
 -fPIC
 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 difference on
 the m68k, m88k, and the SPARC.
 Position-independent code requires special support, and therefore
 works only on certain machines.
 -fPIC is the default on Darwin and Mac OS X.
 -ffixed-reg
 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).
 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.
 This flag does not have a negative form, because it specifies a
 three-way choice.
 -fcall-used-reg
 Treat the register named reg as an allocable register that is clob-
 bered by function calls. It may be allocated for temporaries or
 variables that do not live across a call. Functions compiled this
 way will not save and restore the register reg.
 It is an error to used this flag with the frame pointer or stack
 pointer. Use of this flag for other registers that have fixed per-
 vasive roles in the machine's execution model will produce disas-
 trous results.
 This flag does not have a negative form, because it specifies a
 three-way choice.
 -fcall-saved-reg
 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 will save and
 restore the register reg if they use it.
 It is an error to used this flag with the frame pointer or stack
 pointer. Use of this flag for other registers that have fixed per-
 vasive roles in the machine's execution model will produce disas-
 trous results.
 A different sort of disaster will result from the use of this flag
 for a register in which function values may be returned.
 This flag does not have a negative form, because it specifies a
 three-way choice.
 -fpack-struct
 Pack all structure members together without holes.
 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 conform to a
 non-default application binary interface.
 -finstrument-functions
 Generate instrumentation calls for entry and exit to functions.
 Just after function entry and just before function exit, the fol-
 lowing profiling functions will be called with the address of the
 current function and its call site. (On some platforms,
 "__builtin_return_address" does not work beyond the current func-
 tion, so the call site information may not be available to the pro-
 filing functions otherwise.)
 void __cyg_profile_func_enter (void *this_fn,
 void *call_site);
 void __cyg_profile_func_exit (void *this_fn,
 void *call_site);
 The first argument is the address of the start of the current func-
 tion, which may be looked up exactly in the symbol table.
 This instrumentation is also done for functions expanded inline in
 other functions. The profiling calls will indicate where, concep-
 tually, the inline function is entered and exited. This means that
 addressable versions of such functions must be available. If all
 your uses of a function are expanded inline, this may mean an addi-
 tional expansion of code size. If you use extern inline in your C
 code, an addressable version of such functions must be provided.
 (This is normally the case anyways, but if you get lucky and the
 optimizer always expands the functions inline, you might have got-
 ten away without providing static copies.)
 A function may be given the attribute "no_instrument_function", in
 which case this instrumentation will not be done. This can be
 used, for example, for the profiling functions listed above, high-
 priority interrupt routines, and any functions from which the pro-
 filing functions cannot safely be called (perhaps signal handlers,
 if the profiling routines generate output or allocate memory).
 -fstack-check
 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 only rarely need to specify
 it in a single-threaded environment since stack overflow is auto-
 matically detected on nearly all systems if there is only one
 stack.
 Note that this switch does not actually cause checking to be done;
 the operating system must do that. The switch causes generation of
 code to ensure that the operating system sees the stack being
 extended.
 -fstack-limit-register=reg
 -fstack-limit-symbol=sym
 -fno-stack-limit
 Generate code to ensure that the stack does not grow beyond a cer-
 tain value, either the value of a register or the address of a sym-
 bol. If the stack would grow beyond the value, a signal is raised.
 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.
 For instance, if the stack starts at absolute address 0x80000000
 and grows downwards, you can use the flags -fstack-limit-sym-
 bol=__stack_limit and -Wl,--defsym,__stack_limit=0x7ffe0000 to
 enforce a stack limit of 128KB. Note that this may only work with
 the GNU linker.
 -fargument-alias
 -fargument-noalias
 -fargument-noalias-global
 Specify the possible relationships among parameters and between
 parameters and global data.
 -fargument-alias specifies that arguments (parameters) may alias
 each other and may alias global storage.-fargument-noalias speci-
 fies that arguments do not alias each other, but may alias global
 storage.-fargument-noalias-global specifies that arguments do not
 alias each other and do not alias global storage.
 Each language will automatically use whatever option is required by
 the language standard. You should not need to use these options
 yourself.
 -fleading-underscore
 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.
 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 binary
 interface. Not all targets provide complete support for this
 switch.
 -ftls-model=model
 Alter the thread-local storage model to be used. The model argu-
 ment should be one of "global-dynamic", "local-dynamic", "ini-
 tial-exec" or "local-exec".
 The default without -fpic is "initial-exec"; with -fpic the default
 is "global-dynamic".

 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. Some are used to
 specify other aspects of the compilation environment.
 Note that you can also specify places to search using options such as
 -B, -I and -L. These take precedence over places specified using envi-
 ronment variables, which in turn take precedence over those specified
 by the configuration of GCC.
 LANG
 LC_CTYPE
 LC_MESSAGES
 LC_ALL
 These environment variables control the way that GCC uses localiza-
 tion information that allow GCC to work with different national
 conventions. GCC inspects the locale categories LC_CTYPE and
 LC_MESSAGES if it has been configured to do so. These locale cate-
 gories can be set to any value supported by your installation. A
 typical value is en_UK for English in the United Kingdom.
 The LC_CTYPE environment variable specifies character classifica-
 tion. GCC uses it to determine the character boundaries in a
 string; this is needed for some multibyte encodings that contain
 quote and escape characters that would otherwise be interpreted as
 a string end or escape.
 The LC_MESSAGES environment variable specifies the language to use
 in diagnostic messages.
 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 none of
 these variables are set, GCC defaults to traditional C English
 behavior.
 TMPDIR
 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 stage: for
 example, the output of the preprocessor, which is the input to the
 compiler proper.
 GCC_EXEC_PREFIX
 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 subprogram,
 but you can specify a prefix that ends with a slash if you wish.
 If GCC_EXEC_PREFIX is not set, GCC will attempt to figure out an
 appropriate prefix to use based on the pathname it was invoked
 with.
 If GCC cannot find the subprogram using the specified prefix, it
 tries looking in the usual places for the subprogram.
 The default value of GCC_EXEC_PREFIX is prefix/lib/gcc-lib/ where
 prefix is the value of "prefix" when you ran the configure script.
 Other prefixes specified with -B take precedence over this prefix.
 This prefix is also used for finding files such as crt0.o that are
 used for linking.
 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 /usr/local/lib/gcc-lib
 (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 -Bfoo/, GCC will search
 foo/bar where it would normally search /usr/local/lib/bar. These
 alternate directories are searched first; the standard directories
 come next.
 COMPILER_PATH
 The value of COMPILER_PATH is a colon-separated list of directo-
 ries, much like PATH. GCC tries the directories thus specified
 when searching for subprograms, if it can't find the subprograms
 using GCC_EXEC_PREFIX.
 LIBRARY_PATH
 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 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 with -L come
 first).
 LANG
 This variable is used to pass locale information to the compiler.
 One way in which this information is used is to determine the char-
 acter set to be used when character literals, string 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:
 C-JIS
 Recognize JIS characters.
 C-SJIS
 Recognize SJIS characters.
 C-EUCJP
 Recognize EUCJP characters.
 If LANG is not defined, or if it has some other value, then the
 compiler will use mblen and mbtowc as defined by the default locale
 to recognize and translate multibyte characters.
 Some additional environments variables affect the behavior of the pre-
 processor.
 CPATH
 C_INCLUDE_PATH
 CPLUS_INCLUDE_PATH
 OBJC_INCLUDE_PATH
 Each variable's value is a list of directories separated by a spe-
 cial character, much like PATH, in which to look for header files.
 The special character, "PATH_SEPARATOR", is target-dependent and
 determined at GCC build time. For Windows-based targets it is a
 semicolon, and for almost all other targets it is a colon.
 CPATH specifies a list of directories to be searched as if speci-
 fied with -I, but after any paths given with -I options on the com-
 mand line. This environment variable is used regardless of which
 language is being preprocessed.
 The remaining environment variables apply only when preprocessing
 the particular language indicated. Each specifies a list of direc-
 tories to be searched as if specified with -isystem, but after any
 paths given with -isystem options on the command line.
 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 value of
 CPATH is ":/special/include", that has the same effect as
 -I. -I/special/include.
 DEPENDENCIES_OUTPUT
 If this variable is set, its value specifies how to output depen-
 dencies for Make based on the non-system header files processed by
 the compiler. System header files are ignored in the dependency
 output.
 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 the form
 file target, in which case the rules are written to file file using
 target as the target name.
 In other words, this environment variable is equivalent to combin-
 ing the options -MM and -MF, with an optional -MT switch too.
 SUNPRO_DEPENDENCIES
 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 file is
 omitted.

 To report bugs to Apple, see <http://developer.apple.com/bugreporter/ >.

 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. Failing
 to supply the correct flags may lead to subtle defects. Supplying
 them in cases where they are not necessary is innocuous.

 gpl(7) , gfdl(7) , fsf-funding(7) , cpp(1) , gcov(1) , g77(1), as(1) , ld(1) ,
 gdb(1) , adb(1), dbx(1), sdb(1), gcc_select(1) and the Info entries for
 gcc, cpp, g77, as, ld, binutils and gdb.

 See the Info entry for gcc , or <http://gcc.gnu.org/onlinedocs/gcc/Con-tributors/ >, for 
 contributors to GCC.

 Copyright (c) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.2 or
 any later version published by the Free Software 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 below). A copy of the license is
 included in the gfdl(7)  man page.
 (a) The FSF's Front-Cover Text is:
 A GNU Manual
 (b) The FSF's Back-Cover Text is:
 You have freedom to copy and modify this GNU Manual, like GNU
 software. Copies published by the Free Software Foundation raise
 funds for GNU development.
gcc-3.3 2005年03月20日 

Mac OS X 10.4 - Generated Fri Apr 29 06:57:20 CDT 2005