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man gcc-3.3(1)
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GCC(1)                                GNU                               GCC(1)


       gcc - GNU project C and C++ compiler


       gcc [-c|-S|-E] [-std=standard]
           [-g] [-pg] [-Olevel]
           [-Wwarn...] [-pedantic]
           [-Idir...] [-Ldir...]
           [-Dmacro[=defn]...] [-Umacro]
           [-foption...] [-mmachine-option...]
           [-o outfile] infile...

       Only the most useful options are listed here; see below for the remain-
       der.  g++ accepts mostly the same options as gcc.

       Note: In Apple's version of GCC, both cc and gcc are actually symbolic
       links to gcc-3.3, while c++ and g++ are links to g++-3.3, unless the
       ggcccc_sseelleecctt(1) command has been used to point them at another compiler

       Note that Apple's GCC includes a number of extensions to standard GCC
       (flagged below with ``APPLE ONLY''), and that not all generic GCC
       options are available or supported on Darwin / Mac OS X.  In particu-
       lar, Apple does not currently support the compilation of Fortran, Ada,
       or Java, although there are third parties who have made these work.


       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.


       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-

       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

       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

           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

       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:

           C source code which must be preprocessed.

           C source code which should not be preprocessed.

           C++ source code which should not be preprocessed.

           Objective-C source code.  Note that you must link with the library
           libobjc.a to make an Objective-C program work.

           Objective-C source code which should not be preprocessed.

           C or C++ header file to be turned into a precompiled header.
           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.
           Objective-C++ source code which must be preprocessed.  (APPLE ONLY)

           Objective-C++ source code which should not be preprocessed.  (APPLE

           C++ header file to be turned into a precompiled header.

           Fortran source code which should not be preprocessed.

           Fortran source code which must be preprocessed (with the tradi-
           tional preprocessor).

           Fortran source code which must be preprocessed with a RATFOR pre-
           processor (not included with GCC).
           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.

           Ada source code file containing a library unit body (a subprogram
           or package body).  Such files are also called bodies.

           Assembler code.  Apple's version of GCC runs the preprocessor on
           these files as well as those ending in .S.

           Assembler code which must be preprocessed.

           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
                   f77  f77-cpp-input  ratfor

       -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).

           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)

           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

       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

           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.

           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.

           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.

           Print (on the standard output) a description of target specific
           command line options for each tool.

           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:

           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

           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.

           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

               ISO C90 (same as -ansi).

               ISO C90 as modified in amendment 1.

               ISO C99.  Note that this standard is not yet fully supported;
               see <> for more infor-
               mation.  The names c9x and iso9899:199x are deprecated.

               Default, ISO C90 plus GNU extensions (including some C99 fea-

               ISO C99 plus GNU extensions.  When ISO C99 is fully implemented
               in GCC, this will become the default.  The name gnu9x is depre-

               The 1998 ISO C++ standard plus amendments.

               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

           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)

           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)

           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

           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

           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))

           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.

           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.

           Accept some non-standard constructs used in Microsoft header files.

           Support ISO C trigraphs.  The -ansi option (and -std options for
           strict ISO C conformance) implies -trigraphs.

           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.

           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.

           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++.

           Enable PCH processing even when -E or -save-temps is used.

           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

           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.

           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.

           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.

           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.

           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)

           Allow Pascal-style string literals to be constructed.  (APPLE ONLY)

           Coalesce duplicated functions and data. The linker will discard all
           but one, saving space.  Enabled by default. (APPLE ONLY)

           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:

           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.

           Turn off all access checking.  This switch is mainly useful for
           working around bugs in the access control code.

           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).

           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

           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

           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 *".

           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.

           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.

           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.

           instantiation; template instances are emitted or not according to
           the location of the template definition.

           This option is deprecated.

           Similar to -fexternal-templates, but template instances are emitted
           or not according to the place where they are first instantiated.

           This option is deprecated.

           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.

           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.

           Never emit code for non-inline templates which are instantiated
           implicitly (i.e. by use); only emit code for explicit instantia-

           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.

           To save space, do not emit out-of-line copies of inline functions
           errors if these functions are not inlined everywhere they are

           Do not make direct calls to virtual functions; instead, always go
           through the vtable. (APPLE ONLY)

           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)

           Mark instantiated templates as "coalesced": the linker will discard
           all but one, thus saving space. (APPLE ONLY)

           Disable pedantic warnings about constructs used in MFC, such as
           implicit int and getting a pointer to member function via non-stan-
           dard syntax.

           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.

           Do not treat the operator name keywords "and", "bitand", "bitor",
           "compl", "not", "or" and "xor" as synonyms as keywords.

           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.

           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

           Enable automatic template instantiation at link time.  This option
           also implies -fno-implicit-templates.

           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.

           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

           Emit statistics about front-end processing at the end of the compi-
           lation.  This information is generally only useful to the G++
           development team.

           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

           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.

           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.

           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++.

           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:

           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

                       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-

                       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

       -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;

           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-

           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.

           Generate object code compatible with the standard GNU Objective-C
           runtime.  This is the default for most types of systems.

           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;
                     @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-

       -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.

           Dump interface declarations for all classes seen in the source file
           to a file named sourcename.decl.

           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.

           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.

           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-

           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.

           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.

           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}.

           Check the code for syntax errors, but don't do anything beyond

           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.)

           Like -pedantic, except that errors are produced rather than warn-

       -w  Inhibit all warning messages.

           Inhibit warning messages about the use of #import.

           Inhibit warning messages issued by #warning.


           Warn about extra tokens at the end of prepreprocessor directives.
           (APPLE ONLY)

           Warn about files missing a newline at the end of the file.  (APPLE

           Do not warn about the use of the deprecated 'long' keyword in
           AltiVec data types.  (APPLE ONLY)

           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.

           Warn whenever a comment-start sequence /* appears in a /* comment,
           or whenever a Backslash-Newline appears in a // comment.

           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

           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.

           If -Wformat is specified, do not warn about "strftime" formats
           which may yield only a two-digit year.

           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.

           If -Wformat is specified, do not warn about zero-length formats.
           The C standard specifies that zero-length formats are allowed.

           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".

           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.)

           Enable -Wformat plus format checks not included in -Wformat.  Cur-
           rently equivalent to -Wformat -Wformat-nonliteral -Wformat-secu-

           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.

           Warn when a declaration does not specify a type.

           Give a warning (or error) whenever a function is used before being

           Same as -Wimplicit-int and -Wimplicit-function-declaration.

           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.

           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 } };

           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 ();
                       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

                     if (a)
                         if (b)
                           foo ();
                           bar ();

           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

           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

           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

           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.

           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.

           Warn whenever a "switch" statement does not have a "default" case.

           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.

           Warn if any trigraphs are encountered that might change the meaning
           of the program (trigraphs within comments are not warned about).

           Warn whenever a static function is declared but not defined or a
           non\-inline static function is unused.

           Warn whenever a label is declared but not used.

           To suppress this warning use the unused attribute.

           Warn whenever a function parameter is unused aside from its decla-

           To suppress this warning use the unused attribute.

           Warn whenever a local variable or non-constant static variable is
           unused aside from its declaration

           To suppress this warning use the unused attribute.

           Warn whenever a statement computes a result that is explicitly not

           To suppress this warning cast the expression to void.

           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

           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-

           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;
                       case 2: x = 4;
                       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".

           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.

           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.

           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}.

           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

                       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

           *   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-

           *   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-

           *   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 };

           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.

           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.

           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.

           Warn if an undefined identifier is evaluated in an #if directive.

           Warn whenever an #else or an #endif are followed by text.

           Warn whenever a local variable shadows another local variable,
           parameter or global variable or whenever a built-in function is

           Warn whenever an object of larger than len bytes is defined.

           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-

       -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 *".

           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 *".

           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.

           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.

           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".

           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.

           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.

           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.

           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.

           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).

           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.

           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}.)

           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

                   struct foo {
                     int x;
                     char a, b, c, d;
                   } __attribute__((packed));
                   struct bar {
                     char z;
                     struct foo f;

           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.

           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.

           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.

           Warn if a function can not be inlined and it was declared as

       -Wno-invalid-offsetof (C++ only)
           Suppress warnings from applying the offsetof macro to a non-POD

           Inhibit warning if the long double type is used. (APPLE ONLY)

           Warn if a precompiled header is found in the search path but can't
           be used.

           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

           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

           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.

           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.

           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.

           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.)

           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.

           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

       -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

       -Q  Makes the compiler print out each function name as it is compiled,
           and print some statistics about each pass when it finishes.

           Makes the compiler print some statistics about the time consumed by
           each pass when it finishes.

           Makes the compiler print some statistics about permanent memory
           allocation when it finishes.

           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

           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-

           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.

           Create data files for the gcov code-coverage utility.  See -fpro-
           file-arcs option above for a description of auxname.

               A mapping from basic blocks to line numbers, which gcov uses to
               associate basic block execution counts with line numbers.

               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:

               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.

           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

           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

           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

           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

           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

           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.

           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

               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-

               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:

               Dump before any tree based optimization, to file.original.

               Dump after all tree based optimization, to file.optimized.

               Dump after function inlining, to file.inlined.

           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.

           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.

           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.

           Creates separate symbol repository at location for given input
           header file. Separate repository contains only debugging symbols in
           stabs format.

           Instructs compiler to use separate symbol repository with debugging
           symbols. Compiler searches for such repositories in include paths.

           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 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 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.

           Like -print-file-name, but searches for a program such as cpp.

           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 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 '/'.

           Print the compiler's target machine (for example,
           i686-pc-linux-gnu)---and don't do anything else.

           Print the compiler version (for example, 3.0)---and don't do any-
           thing else.

           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.

       -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

       -O0 Do not optimize.  This is the default.

           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

           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.

           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.

           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.

           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.

           Force memory address constants to be copied into registers before
           doing arithmetic on them.  This may produce better code just as
           -fforce-mem may.

           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.

           Optimize sibling and tail recursive calls.

           Enabled at levels -O2, -O3, -Os.

           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

           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.

           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.

           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.

           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.

           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.

           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.

           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

           The default is -fbranch-count-reg, enabled when -fstrength-reduce
           is enabled.

           Do not put function addresses in registers; make each instruction
           that calls a constant function contain the function's address

           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

           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.

           Perform the optimizations of loop strength reduction and elimina-
           tion of iteration variables.

           Enabled at levels -O2, -O3, -Os.

           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.

           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

           Enabled at levels -O2, -O3, -Os.

           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.

           Re-run common subexpression elimination after loop optimizations
           has been performed.

           Enabled at levels -O2, -O3, -Os.

           Run the loop optimizer twice.

           Enabled at levels -O2, -O3, -Os.

           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.

           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

           Enabled by default when gcse is enabled.

           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.

           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.

           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.

           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.

           Use conditional execution (where available) to transform condi-
           tional jumps into branch-less equivalents.

           Enabled at levels -O, -O2, -O3, -Os.

           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.

           Perform a number of minor optimizations that are relatively expen-

           Enabled at levels -O2, -O3, -Os.

           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-

           Enabled at levels -O2, -O3, -Os.

           If supported for the target machine, attempt to reorder instruc-
           tions to exploit instruction slots available after delayed branch

           Enabled at levels -O, -O2, -O3, -Os.

           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.

           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.

           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.

           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.

           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.

           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.

           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

           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.

           Forces all invariant computations in loops to be moved outside the

           Forces all general-induction variables in loops to be

           Note: When compiling programs written in Fortran, -fmove-all-mov-
           ables and -freduce-all-givs are enabled by default when you use the

           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 (<> and <>) 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.

           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.

           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

           The default is -fguess-branch-probability at levels -O, -O2, -O3,

           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.

           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 "" 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

           Also profile feedback must be available in to make this option
           effective.  See -fprofile-arcs for details.

           Enabled at levels -O2, -O3, -Os.

           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

           Enabled at levels -O2, -O3, -Os.

           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.

           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.

           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-

           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.

           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.

           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.

           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.

           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.

           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.

           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

           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-

           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-

           The default is -fmath-errno.

           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-

           The default is -fno-unsafe-math-optimizations.

           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.

           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

           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-

           The default is -ftrapping-math.

           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-

           This option causes the preprocessor macro "__SUPPORT_SNAN__" to be

           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.

           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.

           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.

           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.

           Perform tail duplication to enlarge superblock size. This transfor-
           mation simplifies the control flow of the function allowing other
           optimizations to do better job.

           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.

           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-

           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.

           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.

           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.

           Perform Sparse Conditional Constant Propagation in SSA form.
           Requires -fssa.  Like -fssa, this is an experimental feature.

           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:

               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.

               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.

               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.

               The maximum number of passes of GCSE to run.

               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

               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.

               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.

               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.

               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.

               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

               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.

               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.

               Select fraction of the maximal count of repetitions of basic
               block in program given basic block needs to have to be consid-
               ered hot.

               Select fraction of the maximal frequency of executions of basic
               block in function given basic block needs to have to be consid-
               ered hot

               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.

               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.

               Stop reverse growth when the reverse probability of best edge
               is less than this threshold (in percent).

               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

               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.

               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.

           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.

           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.

           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.)

           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.

           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.

           Warn the first time #import is used.

           Warn whenever an identifier which is not a macro is encountered in
           an #if directive, outside of defined.  Such identifiers are
           replaced with zero.

           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

           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.

           Make all warnings into hard errors.  Source code which triggers
           warnings will be rejected.

           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

       -w  Suppress all warnings, including those which GNU CPP issues by

           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.

           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

           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

           When used with the driver options -MD or -MMD, -MF overrides the
           default dependency output 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


       -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

           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

           Since -E is not implied, -MD can be used to generate a dependency
           output file as a side-effect of the compilation process.

           Like -MD except mention only user header files, not system -header

           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

           Specify the standard to which the code should conform.  Currently
           CPP knows about C and C++ standards; others may be added in the

           standard may be one of:

               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.

               The 1990 C standard, as amended in 1994.

               The revised ISO C standard, published in December 1999.  Before
               publication, this was known as C9X.

               The 1990 C standard plus GNU extensions.  This is the default.

               The 1999 C standard plus GNU extensions.

               The 1998 ISO C++ standard plus amendments.

               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"".

           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.

           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.

           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.

           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.

           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

       -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.)

           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-

       -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.

           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.

           Try to imitate the behavior of old-fashioned C preprocessors, as
           opposed to ISO C preprocessors.

           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:      [    ]    {    }    #    \    ^    |    ~

           Enable special code to work around file systems which only permit
           very short file names, such as MS-DOS.

           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 ...! .

           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.

           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.

           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.

       -E  If any of these options is used, then the linker is not run, and
           object file names should not be used as arguments.

       -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.

           You need this special case of the -l option in order to link an
           Objective-C program.

           Do not use the standard system startup files when linking.  The
           standard system libraries are used normally, unless -nostdlib or
           -nodefaultlibs is used.

           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.

           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.

           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-

           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.

           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.

           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

           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

           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-

           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.

           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:

           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.

           Add directory dir to the list of directories to be searched for -l.

           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

           All the -F options are also passed to the linker.

           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-

           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

       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

       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:

           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

           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

           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.

           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.

           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:

               -mno-power, -mno-powerpc

           rsc -mpower, -mno-powerpc, -mno-new-mnemonics

           505 -mno-power, -mpowerpc, -mnew-mnemonics

           601 -mpower, -mpowerpc, -mnew-mnemonics

           860 -mno-power, -mpowerpc, -mnew-mnemonics, -msoft-float

           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

           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

           This option is not supported on Mac OS X; use -faltivec instead.

           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.

           Disable Booke SPE ABI extensions for the current ABI.

           This switch enables or disables the generation of ISEL instruc-

           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

           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.

           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.

           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-

           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)

           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.

           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

           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.

           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.

           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.

           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

           On System V.4 and embedded PowerPC systems do not (do) assume that
           unaligned memory references will be handled by the system.

           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.

           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.

           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.

           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.

           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.

           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)

           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)

           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.

           Specify both -mcall-sysv and -meabi options.

           Specify both -mcall-sysv and -mno-eabi options.

           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.

           On System V.4 and embedded PowerPC systems compile code for the
           Solaris operating system.

           On System V.4 and embedded PowerPC systems compile code for the
           Linux-based GNU system.

           On System V.4 and embedded PowerPC systems compile code for the
           Hurd-based GNU system.

           On System V.4 and embedded PowerPC systems compile code for the
           NetBSD operating system.

           Return all structures in memory (as specified by the AIX ABI).

           Return structures smaller than 8 bytes in registers (as specified
           by the SVR4 ABI).

           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.

           Disable AltiVec ABI extensions for the current ABI.

           This option will not work on Mac OS X.

           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.

           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-

           On embedded PowerPC systems, assume that the startup module is
           called crt0.o and the standard C libraries are libmvme.a and

           On embedded PowerPC systems, assume that the startup module is
           called crt0.o and the standard C libraries are libads.a and libc.a.

           On embedded PowerPC systems, assume that the startup module is
           called crt0.o and the standard C libraries are libyk.a and libc.a.

           On System V.4 and embedded PowerPC systems, specify that you are
           compiling for a VxWorks system.

           Specify that you are compiling for the WindISS simulation environ-

           On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags
           header to indicate that eabi extended relocations are used.

           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.

           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.

           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.

           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.

           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.

           On embedded PowerPC systems, put all initialized global and static
           data in the .data section, and all uninitialized data in the .bss

       -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.

           On System V.4 and embedded PowerPC systems do (do not) emit regis-
           ter names in the assembly language output using symbolic forms.

           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-

           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.

           Adds support for multithreading with the pthreads library.  This
           option sets flags for both the preprocessor and linker.

       Darwin Options

           Loads all members of static archive libraries.  See man ld(1) for
           more information.

           Cause the errors having to do with files that have the wrong archi-
           tecture to be fatal.

           Causes the output file to be marked such that the dynamic linker
           will bind all undefined references when the file is loaded or

           Produce a Mach-o bundle format file.  See man ld(1) for more infor-

       -bundle_loader executable
           This specifies the executable that will be loading the build output
           file being linked. See man ld(1) for more information.

           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
           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-

           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.

           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.

           These options are synonyms for -mcpu=i386, -mcpu=i486, -mcpu=pen-
           tium, and -mcpu=pentiumpro respectively.  These synonyms are depre-

           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

               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

               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

               This is the default choice for x86-64 compiler.

               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-

           Output asm instructions using selected dialect. Supported choices
           are intel or att (the default one).

           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.

           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

           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.

           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.

           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

           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.

           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.

           Set the size of "long double" to 96 bits as required by the i386
           application binary interface.  This is the default.

           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.

           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.)

           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.

           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.

           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.

           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-

           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.

           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.

           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.

           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.

           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.

           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.

           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.

           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.

           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.

           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.

           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.

           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-

           This option generates traps for signed overflow on addition, sub-
           traction, multiplication operations.

           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.

           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".

           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

           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).

           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

           Return "struct" and "union" values in registers when possible.
           This is more efficient for small structures than

           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

           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

           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.

           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.

           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.

           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.

           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.

           Ignore the #ident directive.

           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.

           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.

           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.

           Consider all memory references through pointers to be volatile.

           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.

           Consider all memory references to static data to be volatile.

           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.

           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.

           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.

           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.

           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.

           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.

           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).

           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

           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

           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.

           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

           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

           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.

           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

           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.

           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

           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.

           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.

           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

           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

               Recognize JIS characters.

               Recognize SJIS characters.

               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-

           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.

           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

           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.

           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


       To report bugs to Apple, see <>.


       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 <>, 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                           2005-03-20                            

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