-This is doc/gcc.info, produced by makeinfo version 4.5 from
+This is doc/gcc.info, produced by makeinfo version 4.11 from
doc/gcc.texi.
INFO-DIR-SECTION Programming
Introduction
************
- This manual documents how to use the GNU compilers, as well as their
+This manual documents how to use the GNU compilers, as well as their
features and incompatibilities, and how to report bugs. It corresponds
to GCC version 3.2.3. The internals of the GNU compilers, including
how to port them to new targets and some information about how to write
\1f
File: gcc.info, Node: G++ and GCC, Next: Standards, Prev: Top, Up: Top
-Compile C, C++, Objective-C, Ada, Fortran, or Java
-**************************************************
+1 Compile C, C++, Objective-C, Ada, Fortran, or Java
+****************************************************
- Several versions of the compiler (C, C++, Objective-C, Ada, Fortran,
+Several versions of the compiler (C, C++, Objective-C, Ada, Fortran,
and Java) are integrated; this is why we use the name "GNU Compiler
Collection". GCC can compile programs written in any of these
languages. The Ada, Fortran, and Java compilers are described in
\1f
File: gcc.info, Node: Standards, Next: Invoking GCC, Prev: G++ and GCC, Up: Top
-Language Standards Supported by GCC
-***********************************
+2 Language Standards Supported by GCC
+*************************************
- For each language compiled by GCC for which there is a standard, GCC
+For each language compiled by GCC for which there is a standard, GCC
attempts to follow one or more versions of that standard, possibly with
some exceptions, and possibly with some extensions.
\1f
File: gcc.info, Node: Invoking GCC, Next: C Implementation, Prev: Standards, Up: Top
-GCC Command Options
-*******************
+3 GCC Command Options
+*********************
- When you invoke GCC, it normally does preprocessing, compilation,
+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
\1f
File: gcc.info, Node: Option Summary, Next: Overall Options, Up: Invoking GCC
-Option Summary
-==============
+3.1 Option Summary
+==================
- Here is a summary of all the options, grouped by type. Explanations
-are in the following sections.
+Here is a summary of all the options, grouped by type. Explanations are
+in the following sections.
_Overall Options_
*Note Options Controlling the Kind of Output: Overall Options.
- -c -S -E -o FILE -pipe -pass-exit-codes -x LANGUAGE
+ -c -S -E -o FILE -pipe -pass-exit-codes -x LANGUAGE
-v -### --help --target-help --version
_C Language Options_
*Note Options Controlling C Dialect: C Dialect Options.
- -ansi -std=STANDARD -aux-info FILENAME
- -fno-asm -fno-builtin -fno-builtin-FUNCTION
- -fhosted -ffreestanding
- -trigraphs -no-integrated-cpp -traditional -traditional-cpp
- -fallow-single-precision -fcond-mismatch
- -fsigned-bitfields -fsigned-char
- -funsigned-bitfields -funsigned-char
+ -ansi -std=STANDARD -aux-info FILENAME
+ -fno-asm -fno-builtin -fno-builtin-FUNCTION
+ -fhosted -ffreestanding
+ -trigraphs -no-integrated-cpp -traditional -traditional-cpp
+ -fallow-single-precision -fcond-mismatch
+ -fsigned-bitfields -fsigned-char
+ -funsigned-bitfields -funsigned-char
-fwritable-strings
_C++ Language Options_
*Note Options Controlling C++ Dialect: C++ Dialect Options.
- -fno-access-control -fcheck-new -fconserve-space
- -fno-const-strings -fdollars-in-identifiers
- -fno-elide-constructors
- -fno-enforce-eh-specs -fexternal-templates
- -falt-external-templates
- -ffor-scope -fno-for-scope -fno-gnu-keywords
- -fno-implicit-templates
- -fno-implicit-inline-templates
- -fno-implement-inlines -fms-extensions
- -fno-nonansi-builtins -fno-operator-names
- -fno-optional-diags -fpermissive
- -frepo -fno-rtti -fstats -ftemplate-depth-N
- -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
+ -fno-access-control -fcheck-new -fconserve-space
+ -fno-const-strings -fdollars-in-identifiers
+ -fno-elide-constructors
+ -fno-enforce-eh-specs -fexternal-templates
+ -falt-external-templates
+ -ffor-scope -fno-for-scope -fno-gnu-keywords
+ -fno-implicit-templates
+ -fno-implicit-inline-templates
+ -fno-implement-inlines -fms-extensions
+ -fno-nonansi-builtins -fno-operator-names
+ -fno-optional-diags -fpermissive
+ -frepo -fno-rtti -fstats -ftemplate-depth-N
+ -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_
*Note Options Controlling Objective-C Dialect: Objective-C Dialect
Options.
- -fconstant-string-class=CLASS-NAME
- -fgnu-runtime -fnext-runtime -gen-decls
+ -fconstant-string-class=CLASS-NAME
+ -fgnu-runtime -fnext-runtime -gen-decls
-Wno-protocol -Wselector
_Language Independent Options_
*Note Options to Control Diagnostic Messages Formatting: Language
Independent Options.
- -fmessage-length=N
+ -fmessage-length=N
-fdiagnostics-show-location=[once|every-line]
_Warning Options_
*Note Options to Request or Suppress Warnings: Warning Options.
- -fsyntax-only -pedantic -pedantic-errors
- -w -W -Wall -Waggregate-return
- -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment
- -Wconversion -Wno-deprecated-declarations
- -Wdisabled-optimization -Wdiv-by-zero -Werror
- -Wfloat-equal -Wformat -Wformat=2
- -Wformat-nonliteral -Wformat-security
- -Wimplicit -Wimplicit-int
- -Wimplicit-function-declaration
- -Werror-implicit-function-declaration
- -Wimport -Winline
- -Wlarger-than-LEN -Wlong-long
- -Wmain -Wmissing-braces
- -Wmissing-format-attribute -Wmissing-noreturn
- -Wmultichar -Wno-format-extra-args -Wno-format-y2k
- -Wno-import -Wpacked -Wpadded
- -Wparentheses -Wpointer-arith -Wredundant-decls
- -Wreturn-type -Wsequence-point -Wshadow
- -Wsign-compare -Wswitch -Wsystem-headers
- -Wtrigraphs -Wundef -Wuninitialized
- -Wunknown-pragmas -Wunreachable-code
- -Wunused -Wunused-function -Wunused-label -Wunused-parameter
+ -fsyntax-only -pedantic -pedantic-errors
+ -w -W -Wall -Waggregate-return
+ -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment
+ -Wconversion -Wno-deprecated-declarations
+ -Wdisabled-optimization -Wdiv-by-zero -Werror
+ -Wfloat-equal -Wformat -Wformat=2
+ -Wformat-nonliteral -Wformat-security
+ -Wimplicit -Wimplicit-int
+ -Wimplicit-function-declaration
+ -Werror-implicit-function-declaration
+ -Wimport -Winline
+ -Wlarger-than-LEN -Wlong-long
+ -Wmain -Wmissing-braces
+ -Wmissing-format-attribute -Wmissing-noreturn
+ -Wmultichar -Wno-format-extra-args -Wno-format-y2k
+ -Wno-import -Wpacked -Wpadded
+ -Wparentheses -Wpointer-arith -Wredundant-decls
+ -Wreturn-type -Wsequence-point -Wshadow
+ -Wsign-compare -Wswitch -Wsystem-headers
+ -Wtrigraphs -Wundef -Wuninitialized
+ -Wunknown-pragmas -Wunreachable-code
+ -Wunused -Wunused-function -Wunused-label -Wunused-parameter
-Wunused-value -Wunused-variable -Wwrite-strings
_C-only Warning Options_
- -Wbad-function-cast -Wmissing-declarations
- -Wmissing-prototypes -Wnested-externs
+ -Wbad-function-cast -Wmissing-declarations
+ -Wmissing-prototypes -Wnested-externs
-Wstrict-prototypes -Wtraditional
_Debugging Options_
*Note Options for Debugging Your Program or GCC: 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]
- -fmem-report -fpretend-float
- -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
+ -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]
+ -fmem-report -fpretend-float
+ -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
_Optimization Options_
*Note Options that Control Optimization: Optimize Options.
- -falign-functions=N -falign-jumps=N
- -falign-labels=N -falign-loops=N
- -fbounds-check
- -fbranch-probabilities -fcaller-saves -fcprop-registers
- -fcse-follow-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
- -finline-functions -finline-limit=N -fkeep-inline-functions
- -fkeep-static-consts -fmerge-constants -fmerge-all-constants
- -fmove-all-movables -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-optimizations -fno-trapping-math
- -fomit-frame-pointer -foptimize-register-move
- -foptimize-sibling-calls -fprefetch-loop-arrays
- -freduce-all-givs -fregmove -frename-registers
- -frerun-cse-after-loop -frerun-loop-opt
- -fschedule-insns -fschedule-insns2
- -fno-sched-interblock -fno-sched-spec
- -fsched-spec-load -fsched-spec-load-dangerous
- -fsingle-precision-constant -fssa -fssa-ccp -fssa-dce
- -fstrength-reduce -fstrict-aliasing -fthread-jumps
- -ftrapv -funroll-all-loops -funroll-loops
+ -falign-functions=N -falign-jumps=N
+ -falign-labels=N -falign-loops=N
+ -fbounds-check
+ -fbranch-probabilities -fcaller-saves -fcprop-registers
+ -fcse-follow-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
+ -finline-functions -finline-limit=N -fkeep-inline-functions
+ -fkeep-static-consts -fmerge-constants -fmerge-all-constants
+ -fmove-all-movables -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-optimizations -fno-trapping-math
+ -fomit-frame-pointer -foptimize-register-move
+ -foptimize-sibling-calls -fprefetch-loop-arrays
+ -freduce-all-givs -fregmove -frename-registers
+ -frerun-cse-after-loop -frerun-loop-opt
+ -fschedule-insns -fschedule-insns2
+ -fno-sched-interblock -fno-sched-spec
+ -fsched-spec-load -fsched-spec-load-dangerous
+ -fsingle-precision-constant -fssa -fssa-ccp -fssa-dce
+ -fstrength-reduce -fstrict-aliasing -fthread-jumps
+ -ftrapv -funroll-all-loops -funroll-loops
--param NAME=VALUE
-O -O0 -O1 -O2 -O3 -Os
_Preprocessor Options_
*Note Options Controlling the Preprocessor: 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
+ -$ -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
-trigraphs -undef -UMACRO -Wp,OPTION
_Assembler Option_
_Linker Options_
*Note Options for Linking: Link Options.
- OBJECT-FILE-NAME -lLIBRARY
- -nostartfiles -nodefaultlibs -nostdlib
- -s -static -static-libgcc -shared -shared-libgcc -symbolic
- -Wl,OPTION -Xlinker OPTION
+ OBJECT-FILE-NAME -lLIBRARY
+ -nostartfiles -nodefaultlibs -nostdlib
+ -s -static -static-libgcc -shared -shared-libgcc -symbolic
+ -Wl,OPTION -Xlinker OPTION
-u SYMBOL
_Directory Options_
*Note Hardware Models and Configurations: Submodel Options.
_M680x0 Options_
- -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040
- -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020
- -mfpa -mnobitfield -mrtd -mshort -msoft-float -mpcrel
+ -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040
+ -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020
+ -mfpa -mnobitfield -mrtd -mshort -msoft-float -mpcrel
-malign-int -mstrict-align
_M68hc1x Options_
- -m6811 -m6812 -m68hc11 -m68hc12
+ -m6811 -m6812 -m68hc11 -m68hc12
-mauto-incdec -mshort -msoft-reg-count=COUNT
_VAX Options_
-mg -mgnu -munix
_SPARC Options_
- -mcpu=CPU-TYPE
- -mtune=CPU-TYPE
- -mcmodel=CODE-MODEL
- -m32 -m64
- -mapp-regs -mbroken-saverestore -mcypress
- -mfaster-structs -mflat
- -mfpu -mhard-float -mhard-quad-float
- -mimpure-text -mlive-g0 -mno-app-regs
- -mno-faster-structs -mno-flat -mno-fpu
- -mno-impure-text -mno-stack-bias -mno-unaligned-doubles
- -msoft-float -msoft-quad-float -msparclite -mstack-bias
+ -mcpu=CPU-TYPE
+ -mtune=CPU-TYPE
+ -mcmodel=CODE-MODEL
+ -m32 -m64
+ -mapp-regs -mbroken-saverestore -mcypress
+ -mfaster-structs -mflat
+ -mfpu -mhard-float -mhard-quad-float
+ -mimpure-text -mlive-g0 -mno-app-regs
+ -mno-faster-structs -mno-flat -mno-fpu
+ -mno-impure-text -mno-stack-bias -mno-unaligned-doubles
+ -msoft-float -msoft-quad-float -msparclite -mstack-bias
-msupersparc -munaligned-doubles -mv8
_Convex Options_
- -mc1 -mc2 -mc32 -mc34 -mc38
- -margcount -mnoargcount
- -mlong32 -mlong64
+ -mc1 -mc2 -mc32 -mc34 -mc38
+ -margcount -mnoargcount
+ -mlong32 -mlong64
-mvolatile-cache -mvolatile-nocache
_AMD29K Options_
- -m29000 -m29050 -mbw -mnbw -mdw -mndw
- -mlarge -mnormal -msmall
- -mkernel-registers -mno-reuse-arg-regs
- -mno-stack-check -mno-storem-bug
- -mreuse-arg-regs -msoft-float -mstack-check
+ -m29000 -m29050 -mbw -mnbw -mdw -mndw
+ -mlarge -mnormal -msmall
+ -mkernel-registers -mno-reuse-arg-regs
+ -mno-stack-check -mno-storem-bug
+ -mreuse-arg-regs -msoft-float -mstack-check
-mstorem-bug -muser-registers
_ARM Options_
- -mapcs-frame -mno-apcs-frame
- -mapcs-26 -mapcs-32
- -mapcs-stack-check -mno-apcs-stack-check
- -mapcs-float -mno-apcs-float
- -mapcs-reentrant -mno-apcs-reentrant
- -msched-prolog -mno-sched-prolog
- -mlittle-endian -mbig-endian -mwords-little-endian
- -malignment-traps -mno-alignment-traps
- -msoft-float -mhard-float -mfpe
- -mthumb-interwork -mno-thumb-interwork
- -mcpu=NAME -march=NAME -mfpe=NAME
- -mstructure-size-boundary=N
- -mbsd -mxopen -mno-symrename
- -mabort-on-noreturn
- -mlong-calls -mno-long-calls
- -msingle-pic-base -mno-single-pic-base
- -mpic-register=REG
- -mnop-fun-dllimport
- -mpoke-function-name
- -mthumb -marm
- -mtpcs-frame -mtpcs-leaf-frame
+ -mapcs-frame -mno-apcs-frame
+ -mapcs-26 -mapcs-32
+ -mapcs-stack-check -mno-apcs-stack-check
+ -mapcs-float -mno-apcs-float
+ -mapcs-reentrant -mno-apcs-reentrant
+ -msched-prolog -mno-sched-prolog
+ -mlittle-endian -mbig-endian -mwords-little-endian
+ -malignment-traps -mno-alignment-traps
+ -msoft-float -mhard-float -mfpe
+ -mthumb-interwork -mno-thumb-interwork
+ -mcpu=NAME -march=NAME -mfpe=NAME
+ -mstructure-size-boundary=N
+ -mbsd -mxopen -mno-symrename
+ -mabort-on-noreturn
+ -mlong-calls -mno-long-calls
+ -msingle-pic-base -mno-single-pic-base
+ -mpic-register=REG
+ -mnop-fun-dllimport
+ -mpoke-function-name
+ -mthumb -marm
+ -mtpcs-frame -mtpcs-leaf-frame
-mcaller-super-interworking -mcallee-super-interworking
_MN10200 Options_
-mrelax
_MN10300 Options_
- -mmult-bug -mno-mult-bug
- -mam33 -mno-am33
+ -mmult-bug -mno-mult-bug
+ -mam33 -mno-am33
-mno-crt0 -mrelax
_M32R/D Options_
- -m32rx -m32r -mcode-model=MODEL-TYPE -msdata=SDATA-TYPE
+ -m32rx -m32r -mcode-model=MODEL-TYPE -msdata=SDATA-TYPE
-G NUM
_M88K Options_
- -m88000 -m88100 -m88110 -mbig-pic
- -mcheck-zero-division -mhandle-large-shift
- -midentify-revision -mno-check-zero-division
- -mno-ocs-debug-info -mno-ocs-frame-position
- -mno-optimize-arg-area -mno-serialize-volatile
- -mno-underscores -mocs-debug-info
- -mocs-frame-position -moptimize-arg-area
- -mserialize-volatile -mshort-data-NUM -msvr3
- -msvr4 -mtrap-large-shift -muse-div-instruction
+ -m88000 -m88100 -m88110 -mbig-pic
+ -mcheck-zero-division -mhandle-large-shift
+ -midentify-revision -mno-check-zero-division
+ -mno-ocs-debug-info -mno-ocs-frame-position
+ -mno-optimize-arg-area -mno-serialize-volatile
+ -mno-underscores -mocs-debug-info
+ -mocs-frame-position -moptimize-arg-area
+ -mserialize-volatile -mshort-data-NUM -msvr3
+ -msvr4 -mtrap-large-shift -muse-div-instruction
-mversion-03.00 -mwarn-passed-structs
_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
- -msoft-float -mhard-float -mmultiple -mno-multiple
- -mstring -mno-string -mupdate -mno-update
- -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align
- -mstrict-align -mno-strict-align -mrelocatable
- -mno-relocatable -mrelocatable-lib -mno-relocatable-lib
- -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian
- -mcall-aix -mcall-sysv -mcall-netbsd
- -maix-struct-return -msvr4-struct-return
- -mabi=altivec -mabi=no-altivec
- -mprototype -mno-prototype
- -msim -mmvme -mads -myellowknife -memb -msdata
+ -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
+ -msoft-float -mhard-float -mmultiple -mno-multiple
+ -mstring -mno-string -mupdate -mno-update
+ -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align
+ -mstrict-align -mno-strict-align -mrelocatable
+ -mno-relocatable -mrelocatable-lib -mno-relocatable-lib
+ -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian
+ -mcall-aix -mcall-sysv -mcall-netbsd
+ -maix-struct-return -msvr4-struct-return
+ -mabi=altivec -mabi=no-altivec
+ -mprototype -mno-prototype
+ -msim -mmvme -mads -myellowknife -memb -msdata
-msdata=OPT -mvxworks -G NUM -pthread
_RT Options_
- -mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs
- -mfull-fp-blocks -mhc-struct-return -min-line-mul
+ -mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs
+ -mfull-fp-blocks -mhc-struct-return -min-line-mul
-mminimum-fp-blocks -mnohc-struct-return
_MIPS Options_
- -mabicalls -march=CPU-TYPE -mtune=CPU=TYPE
- -mcpu=CPU-TYPE -membedded-data -muninit-const-in-rodata
- -membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd
- -mgas -mgp32 -mgp64
- -mgpopt -mhalf-pic -mhard-float -mint64 -mips1
- -mips2 -mips3 -mips4 -mlong64 -mlong32 -mlong-calls -mmemcpy
- -mmips-as -mmips-tfile -mno-abicalls
- -mno-embedded-data -mno-uninit-const-in-rodata
- -mno-embedded-pic -mno-gpopt -mno-long-calls
- -mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats
- -mrnames -msoft-float
- -m4650 -msingle-float -mmad
- -mstats -EL -EB -G NUM -nocpp
- -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi
+ -mabicalls -march=CPU-TYPE -mtune=CPU=TYPE
+ -mcpu=CPU-TYPE -membedded-data -muninit-const-in-rodata
+ -membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd
+ -mgas -mgp32 -mgp64
+ -mgpopt -mhalf-pic -mhard-float -mint64 -mips1
+ -mips2 -mips3 -mips4 -mlong64 -mlong32 -mlong-calls -mmemcpy
+ -mmips-as -mmips-tfile -mno-abicalls
+ -mno-embedded-data -mno-uninit-const-in-rodata
+ -mno-embedded-pic -mno-gpopt -mno-long-calls
+ -mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats
+ -mrnames -msoft-float
+ -m4650 -msingle-float -mmad
+ -mstats -EL -EB -G NUM -nocpp
+ -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi
-mfix7000 -mno-crt0 -mflush-func=FUNC -mno-flush-func
_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-boundary=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
+ -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-boundary=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
+ -mcmodel=CODE-MODEL
-m32 -m64
_HPPA Options_
- -march=ARCHITECTURE-TYPE
- -mbig-switch -mdisable-fpregs -mdisable-indexing
- -mfast-indirect-calls -mgas -mjump-in-delay
- -mlong-load-store -mno-big-switch -mno-disable-fpregs
- -mno-disable-indexing -mno-fast-indirect-calls -mno-gas
- -mno-jump-in-delay -mno-long-load-store
- -mno-portable-runtime -mno-soft-float
- -mno-space-regs -msoft-float -mpa-risc-1-0
- -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime
+ -march=ARCHITECTURE-TYPE
+ -mbig-switch -mdisable-fpregs -mdisable-indexing
+ -mfast-indirect-calls -mgas -mjump-in-delay
+ -mlong-load-store -mno-big-switch -mno-disable-fpregs
+ -mno-disable-indexing -mno-fast-indirect-calls -mno-gas
+ -mno-jump-in-delay -mno-long-load-store
+ -mno-portable-runtime -mno-soft-float
+ -mno-space-regs -msoft-float -mpa-risc-1-0
+ -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime
-mschedule=CPU-TYPE -mspace-regs
_Intel 960 Options_
- -mCPU-TYPE -masm-compat -mclean-linkage
- -mcode-align -mcomplex-addr -mleaf-procedures
- -mic-compat -mic2.0-compat -mic3.0-compat
- -mintel-asm -mno-clean-linkage -mno-code-align
- -mno-complex-addr -mno-leaf-procedures
- -mno-old-align -mno-strict-align -mno-tail-call
- -mnumerics -mold-align -msoft-float -mstrict-align
+ -mCPU-TYPE -masm-compat -mclean-linkage
+ -mcode-align -mcomplex-addr -mleaf-procedures
+ -mic-compat -mic2.0-compat -mic3.0-compat
+ -mintel-asm -mno-clean-linkage -mno-code-align
+ -mno-complex-addr -mno-leaf-procedures
+ -mno-old-align -mno-strict-align -mno-tail-call
+ -mnumerics -mold-align -msoft-float -mstrict-align
-mtail-call
_DEC Alpha Options_
- -mno-fp-regs -msoft-float -malpha-as -mgas
- -mieee -mieee-with-inexact -mieee-conformant
- -mfp-trap-mode=MODE -mfp-rounding-mode=MODE
- -mtrap-precision=MODE -mbuild-constants
- -mcpu=CPU-TYPE -mtune=CPU-TYPE
- -mbwx -mmax -mfix -mcix
- -mfloat-vax -mfloat-ieee
- -mexplicit-relocs -msmall-data -mlarge-data
+ -mno-fp-regs -msoft-float -malpha-as -mgas
+ -mieee -mieee-with-inexact -mieee-conformant
+ -mfp-trap-mode=MODE -mfp-rounding-mode=MODE
+ -mtrap-precision=MODE -mbuild-constants
+ -mcpu=CPU-TYPE -mtune=CPU-TYPE
+ -mbwx -mmax -mfix -mcix
+ -mfloat-vax -mfloat-ieee
+ -mexplicit-relocs -msmall-data -mlarge-data
-mmemory-latency=TIME
_DEC Alpha/VMS Options_
-mrelax -mh -ms -mint32 -malign-300
_SH Options_
- -m1 -m2 -m3 -m3e
- -m4-nofpu -m4-single-only -m4-single -m4
- -m5-64media -m5-64media-nofpu
- -m5-32media -m5-32media-nofpu
- -m5-compact -m5-compact-nofpu
- -mb -ml -mdalign -mrelax
- -mbigtable -mfmovd -mhitachi -mnomacsave
- -mieee -misize -mpadstruct -mspace
+ -m1 -m2 -m3 -m3e
+ -m4-nofpu -m4-single-only -m4-single -m4
+ -m5-64media -m5-64media-nofpu
+ -m5-32media -m5-32media-nofpu
+ -m5-compact -m5-compact-nofpu
+ -mb -ml -mdalign -mrelax
+ -mbigtable -mfmovd -mhitachi -mnomacsave
+ -mieee -misize -mpadstruct -mspace
-mprefergot -musermode
_System V Options_
-Qy -Qn -YP,PATHS -Ym,DIR
_ARC Options_
- -EB -EL
- -mmangle-cpu -mcpu=CPU -mtext=TEXT-SECTION
+ -EB -EL
+ -mmangle-cpu -mcpu=CPU -mtext=TEXT-SECTION
-mdata=DATA-SECTION -mrodata=READONLY-DATA-SECTION
_TMS320C3x/C4x Options_
- -mcpu=CPU -mbig -msmall -mregparm -mmemparm
- -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload
- -mrpts=COUNT -mrptb -mdb -mloop-unsigned
+ -mcpu=CPU -mbig -msmall -mregparm -mmemparm
+ -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload
+ -mrpts=COUNT -mrptb -mdb -mloop-unsigned
-mparallel-insns -mparallel-mpy -mpreserve-float
_V850 Options_
- -mlong-calls -mno-long-calls -mep -mno-ep
- -mprolog-function -mno-prolog-function -mspace
- -mtda=N -msda=N -mzda=N
+ -mlong-calls -mno-long-calls -mep -mno-ep
+ -mprolog-function -mno-prolog-function -mspace
+ -mtda=N -msda=N -mzda=N
-mv850 -mbig-switch
_NS32K Options_
- -m32032 -m32332 -m32532 -m32081 -m32381
- -mmult-add -mnomult-add -msoft-float -mrtd -mnortd
- -mregparam -mnoregparam -msb -mnosb
+ -m32032 -m32332 -m32532 -m32081 -m32381
+ -mmult-add -mnomult-add -msoft-float -mrtd -mnortd
+ -mregparam -mnoregparam -msb -mnosb
-mbitfield -mnobitfield -mhimem -mnohimem
_AVR Options_
- -mmcu=MCU -msize -minit-stack=N -mno-interrupts
+ -mmcu=MCU -msize -minit-stack=N -mno-interrupts
-mcall-prologues -mno-tablejump -mtiny-stack
_MCore Options_
- -mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates
- -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields
- -m4byte-functions -mno-4byte-functions -mcallgraph-data
- -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim
+ -mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates
+ -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields
+ -m4byte-functions -mno-4byte-functions -mcallgraph-data
+ -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim
-mlittle-endian -mbig-endian -m210 -m340 -mstack-increment
_MMIX Options_
- -mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu
- -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols
- -melf -mbranch-predict -mno-branch-predict -mbase-addresses
+ -mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu
+ -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols
+ -melf -mbranch-predict -mno-branch-predict -mbase-addresses
-mno-base-addresses
_IA-64 Options_
- -mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic
- -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata
- -mconstant-gp -mauto-pic -minline-divide-min-latency
- -minline-divide-max-throughput -mno-dwarf2-asm
+ -mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic
+ -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata
+ -mconstant-gp -mauto-pic -minline-divide-min-latency
+ -minline-divide-max-throughput -mno-dwarf2-asm
-mfixed-range=REGISTER-RANGE
_D30V Options_
- -mextmem -mextmemory -monchip -mno-asm-optimize
+ -mextmem -mextmemory -monchip -mno-asm-optimize
-masm-optimize -mbranch-cost=N -mcond-exec=N
_S/390 and zSeries Options_
- -mhard-float -msoft-float -mbackchain -mno-backchain
- -msmall-exec -mno-small-exec -mmvcle -mno-mvcle
+ -mhard-float -msoft-float -mbackchain -mno-backchain
+ -msmall-exec -mno-small-exec -mmvcle -mno-mvcle
-m64 -m31 -mdebug -mno-debug
_CRIS Options_
- -mcpu=CPU -march=CPU -mtune=CPU
- -mmax-stack-frame=N -melinux-stacksize=N
- -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects
- -mstack-align -mdata-align -mconst-align
- -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt
+ -mcpu=CPU -march=CPU -mtune=CPU
+ -mmax-stack-frame=N -melinux-stacksize=N
+ -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects
+ -mstack-align -mdata-align -mconst-align
+ -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt
-melf -maout -melinux -mlinux -sim -sim2
_PDP-11 Options_
- -mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10
- -mbcopy -mbcopy-builtin -mint32 -mno-int16
- -mint16 -mno-int32 -mfloat32 -mno-float64
- -mfloat64 -mno-float32 -mabshi -mno-abshi
- -mbranch-expensive -mbranch-cheap
+ -mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10
+ -mbcopy -mbcopy-builtin -mint32 -mno-int16
+ -mint16 -mno-int32 -mfloat32 -mno-float64
+ -mfloat64 -mno-float32 -mabshi -mno-abshi
+ -mbranch-expensive -mbranch-cheap
-msplit -mno-split -munix-asm -mdec-asm
_Xstormy16 Options_
-msim
_Xtensa Options_
- -mbig-endian -mlittle-endian
- -mdensity -mno-density
- -mmac16 -mno-mac16
- -mmul16 -mno-mul16
- -mmul32 -mno-mul32
- -mnsa -mno-nsa
- -mminmax -mno-minmax
- -msext -mno-sext
- -mbooleans -mno-booleans
- -mhard-float -msoft-float
- -mfused-madd -mno-fused-madd
- -mserialize-volatile -mno-serialize-volatile
- -mtext-section-literals -mno-text-section-literals
- -mtarget-align -mno-target-align
+ -mbig-endian -mlittle-endian
+ -mdensity -mno-density
+ -mmac16 -mno-mac16
+ -mmul16 -mno-mul16
+ -mmul32 -mno-mul32
+ -mnsa -mno-nsa
+ -mminmax -mno-minmax
+ -msext -mno-sext
+ -mbooleans -mno-booleans
+ -mhard-float -msoft-float
+ -mfused-madd -mno-fused-madd
+ -mserialize-volatile -mno-serialize-volatile
+ -mtext-section-literals -mno-text-section-literals
+ -mtarget-align -mno-target-align
-mlongcalls -mno-longcalls
_Code Generation Options_
*Note Options for Code Generation Conventions: Code Gen 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-register=REG -fstack-limit-symbol=SYM
- -fargument-alias -fargument-noalias
+ -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-register=REG -fstack-limit-symbol=SYM
+ -fargument-alias -fargument-noalias
-fargument-noalias-global -fleading-underscore
\1f
File: gcc.info, Node: Overall Options, Next: Invoking G++, Prev: Option Summary, Up: Invoking GCC
-Options Controlling the Kind of Output
-======================================
+3.2 Options Controlling the Kind of Output
+==========================================
- Compilation can involve up to four stages: preprocessing, compilation
+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
\1f
File: gcc.info, Node: Invoking G++, Next: C Dialect Options, Prev: Overall Options, Up: Invoking GCC
-Compiling C++ Programs
-======================
+3.3 Compiling C++ Programs
+==========================
- C++ source files conventionally use one of the suffixes `.C', `.cc',
+C++ source files conventionally use one of the suffixes `.C', `.cc',
`.cpp', `.c++', `.cp', or `.cxx'; preprocessed C++ files use the suffix
`.ii'. GCC recognizes files with these names and compiles them as C++
programs even if you call the compiler the same way as for compiling C
Dialect: C++ Dialect Options, for explanations of options that are
meaningful only for C++ programs.
+\1f
+File: gcc.info, Node: C Dialect Options, Next: C++ Dialect Options, Prev: Invoking G++, Up: Invoking GCC
+
+3.4 Options Controlling C Dialect
+=================================
+
+The following options control the dialect of C (or languages derived
+from C, such as C++ and Objective-C) that the compiler accepts:
+
+`-ansi'
+ In C mode, support all ISO C89 programs. In C++ mode, remove GNU
+ extensions that conflict with ISO C++.
+
+ This turns off certain features of GCC that are incompatible with
+ ISO C89 (when compiling C code), or of standard C++ (when
+ compiling C++ code), such as the `asm' and `typeof' keywords, and
+ predefined macros such as `unix' and `vax' that identify the type
+ of system you are using. It also enables the undesirable and
+ rarely used ISO trigraph feature. For the C compiler, it disables
+ recognition of C++ style `//' comments as well as the `inline'
+ keyword.
+
+ The alternate keywords `__asm__', `__extension__', `__inline__'
+ and `__typeof__' continue to work despite `-ansi'. You would not
+ want to use them in an ISO C program, of course, but it is useful
+ to put them in header files that might be included in compilations
+ done with `-ansi'. Alternate predefined macros such as `__unix__'
+ and `__vax__' are also available, with or without `-ansi'.
+
+ The `-ansi' option does not cause non-ISO programs to be rejected
+ gratuitously. For that, `-pedantic' is required in addition to
+ `-ansi'. *Note Warning Options::.
+
+ 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
+ semantics defined by ISO C (such as `alloca' and `ffs') are not
+ built-in functions with `-ansi' is used. *Note Other built-in
+ functions provided by GCC: Other Builtins, for details of the
+ functions affected.
+
+`-std='
+ Determine the language standard. This option is currently only
+ supported when compiling C. A value for this option must be
+ provided; possible values are
+
+ `c89'
+ `iso9899:1990'
+ ISO C89 (same as `-ansi').
+
+ `iso9899:199409'
+ ISO C89 as modified in amendment 1.
+
+ `c99'
+ `c9x'
+ `iso9899:1999'
+ `iso9899:199x'
+ ISO C99. Note that this standard is not yet fully supported;
+ see `http://gcc.gnu.org/gcc-3.1/c99status.html' for more
+ information. The names `c9x' and `iso9899:199x' are
+ deprecated.
+
+ `gnu89'
+ Default, ISO C89 plus GNU extensions (including some C99
+ features).
+
+ `gnu99'
+
+ `gnu9x'
+ ISO C99 plus GNU extensions. When ISO C99 is fully
+ implemented in GCC, this will become the default. The name
+ `gnu9x' is deprecated.
+
+
+ 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 C89
+ but are in the specified version (for example, `//' comments and
+ the `inline' keyword in ISO C99) are not disabled.
+
+ *Note Language Standards Supported by GCC: Standards, for details
+ of these standard versions.
+
+`-aux-info FILENAME'
+ Output to the given filename prototyped declarations for all
+ functions declared and/or defined in a translation unit, including
+ those in header files. This option is silently ignored in any
+ language other than C.
+
+ Besides declarations, the file indicates, in comments, the origin
+ of each declaration (source file and line), whether the
+ declaration was implicit, prototyped or unprototyped (`I', `N' for
+ new or `O' for old, respectively, in the first character after the
+ line number and the colon), and whether it came from a declaration
+ or a definition (`C' or `F', respectively, in the following
+ character). In the case of function definitions, a K&R-style list
+ of arguments followed by their declarations is also provided,
+ inside comments, after the declaration.
+
+`-fno-asm'
+ Do not recognize `asm', `inline' or `typeof' as a keyword, so that
+ code can use these words as identifiers. You can use the keywords
+ `__asm__', `__inline__' and `__typeof__' instead. `-ansi' implies
+ `-fno-asm'.
+
+ In C++, this switch only affects the `typeof' keyword, since `asm'
+ and `inline' are standard keywords. You may want to use the
+ `-fno-gnu-keywords' flag instead, which has the same effect. In
+ C99 mode (`-std=c99' or `-std=gnu99'), this switch only affects
+ the `asm' and `typeof' keywords, since `inline' is a standard
+ keyword in ISO C99.
+
+`-fno-builtin'
+`-fno-builtin-FUNCTION (C and Objective-C only)'
+ Don't recognize built-in functions that do not begin with
+ `__builtin_' as prefix. *Note Other built-in functions provided
+ by GCC: Other Builtins, for details of the functions affected,
+ including those which are not built-in functions when `-ansi' or
+ `-std' options for strict ISO C conformance are used because they
+ do not have an ISO standard meaning.
+
+ GCC normally generates special code to handle certain built-in
+ functions more efficiently; for instance, calls to `alloca' may
+ become single instructions that adjust the stack directly, and
+ calls to `memcpy' may become inline copy loops. The resulting
+ code is often both smaller and faster, but since the function
+ calls no longer appear as such, you cannot set a breakpoint on
+ those calls, nor can you change the behavior of the functions by
+ linking with a different library.
+
+ In C++, `-fno-builtin' is always in effect. The `-fbuiltin'
+ option has no effect. Therefore, in C++, the only way to get the
+ optimization benefits of built-in functions is to call the function
+ using the `__builtin_' prefix. The GNU C++ Standard Library uses
+ built-in functions to implement many functions (like
+ `std::strchr'), so that you automatically get efficient code.
+
+ With the `-fno-builtin-FUNCTION' option, not available when
+ compiling C++, only the built-in function FUNCTION is disabled.
+ FUNCTION must not begin with `__builtin_'. If a function is named
+ this is not built-in in this version of GCC, this option is
+ ignored. There is no corresponding `-fbuiltin-FUNCTION' option;
+ if you wish to enable built-in functions selectively when using
+ `-fno-builtin' or `-ffreestanding', you may define macros such as:
+
+ #define abs(n) __builtin_abs ((n))
+ #define strcpy(d, s) __builtin_strcpy ((d), (s))
+
+`-fhosted'
+ Assert that compilation takes place in a hosted environment. This
+ implies `-fbuiltin'. A hosted environment is one in which the
+ entire standard library is available, and in which `main' has a
+ return type of `int'. Examples are nearly everything except a
+ kernel. This is equivalent to `-fno-freestanding'.
+
+`-ffreestanding'
+ Assert that compilation takes place in a freestanding environment.
+ This implies `-fno-builtin'. A freestanding environment is one in
+ which the standard library may not exist, and program startup may
+ not necessarily be at `main'. The most obvious example is an OS
+ kernel. This is equivalent to `-fno-hosted'.
+
+ *Note Language Standards Supported by GCC: Standards, for details
+ of freestanding and hosted environments.
+
+`-trigraphs'
+ Support ISO C trigraphs. The `-ansi' option (and `-std' options
+ for strict ISO C conformance) implies `-trigraphs'.
+
+`-no-integrated-cpp'
+ Invoke the external cpp during compilation. The default is to use
+ the integrated cpp (internal cpp). This option also allows a
+ user-supplied cpp via the `-B' option. This flag is applicable in
+ both C and C++ modes.
+
+ We do not guarantee to retain this option in future, and we may
+ change its semantics.
+
+`-traditional'
+ Attempt to support some aspects of traditional C compilers.
+ Specifically:
+
+ * All `extern' declarations take effect globally even if they
+ are written inside of a function definition. This includes
+ implicit declarations of functions.
+
+ * The newer keywords `typeof', `inline', `signed', `const' and
+ `volatile' are not recognized. (You can still use the
+ alternative keywords such as `__typeof__', `__inline__', and
+ so on.)
+
+ * Comparisons between pointers and integers are always allowed.
+
+ * Integer types `unsigned short' and `unsigned char' promote to
+ `unsigned int'.
+
+ * Out-of-range floating point literals are not an error.
+
+ * Certain constructs which ISO regards as a single invalid
+ preprocessing number, such as `0xe-0xd', are treated as
+ expressions instead.
+
+ * String "constants" are not necessarily constant; they are
+ stored in writable space, and identical looking constants are
+ allocated separately. (This is the same as the effect of
+ `-fwritable-strings'.)
+
+ * All automatic variables not declared `register' are preserved
+ by `longjmp'. Ordinarily, GNU C follows ISO C: automatic
+ variables not declared `volatile' may be clobbered.
+
+ * The character escape sequences `\x' and `\a' evaluate as the
+ literal characters `x' and `a' respectively. Without
+ `-traditional', `\x' is a prefix for the hexadecimal
+ representation of a character, and `\a' produces a bell.
+
+ This option is deprecated and may be removed.
+
+ You may wish to use `-fno-builtin' as well as `-traditional' if
+ your program uses names that are normally GNU C built-in functions
+ for other purposes of its own.
+
+ You cannot use `-traditional' if you include any header files that
+ rely on ISO C features. Some vendors are starting to ship systems
+ with ISO C header files and you cannot use `-traditional' on such
+ systems to compile files that include any system headers.
+
+ The `-traditional' option also enables `-traditional-cpp'.
+
+`-traditional-cpp'
+ Attempt to support some aspects of traditional C preprocessors.
+ See the GNU CPP manual for details.
+
+`-fcond-mismatch'
+ Allow conditional expressions with mismatched types in the second
+ and third arguments. The value of such an expression is void.
+ This option is not supported for C++.
+
+`-funsigned-char'
+ Let the type `char' be unsigned, like `unsigned char'.
+
+ Each kind of machine has a default for what `char' should be. It
+ is either like `unsigned char' by default or like `signed char' by
+ default.
+
+ Ideally, a portable program should always use `signed char' or
+ `unsigned char' when it depends on the signedness of an object.
+ But many programs have been written to use plain `char' and expect
+ it to be signed, or expect it to be unsigned, depending on the
+ machines they were written for. This option, and its inverse, let
+ you make such a program work with the opposite default.
+
+ The type `char' is always a distinct type from each of `signed
+ char' or `unsigned char', even though its behavior is always just
+ like one of those two.
+
+`-fsigned-char'
+ Let the type `char' be signed, like `signed char'.
+
+ Note that this is equivalent to `-fno-unsigned-char', which is the
+ negative form of `-funsigned-char'. Likewise, the option
+ `-fno-signed-char' is equivalent to `-funsigned-char'.
+
+`-fsigned-bitfields'
+`-funsigned-bitfields'
+`-fno-signed-bitfields'
+`-fno-unsigned-bitfields'
+ These options control whether a bit-field is signed or unsigned,
+ when the declaration does not use either `signed' or `unsigned'.
+ By default, such a bit-field is signed, because this is
+ consistent: the basic integer types such as `int' are signed types.
+
+ However, when `-traditional' is used, bit-fields are all unsigned
+ no matter what.
+
+`-fwritable-strings'
+ Store string constants in the writable data segment and don't
+ uniquize them. This is for compatibility with old programs which
+ assume they can write into string constants. The option
+ `-traditional' also has this effect.
+
+ Writing into string constants is a very bad idea; "constants"
+ should be constant.
+
+`-fallow-single-precision'
+ Do not promote single precision math operations to double
+ precision, even when compiling with `-traditional'.
+
+ Traditional K&R C promotes all floating point operations to double
+ precision, regardless of the sizes of the operands. On the
+ architecture for which you are compiling, single precision may be
+ faster than double precision. If you must use `-traditional',
+ but want to use single precision operations when the operands are
+ single precision, use this option. This option has no effect
+ when compiling with ISO or GNU C conventions (the default).
+
+\1f
+File: gcc.info, Node: C++ Dialect Options, Next: Objective-C Dialect Options, Prev: C Dialect Options, Up: Invoking GCC
+
+3.5 Options Controlling C++ Dialect
+===================================
+
+This section describes the command-line options that are only meaningful
+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:
+
+`-fno-access-control'
+ Turn off all access checking. This switch is mainly useful for
+ working around bugs in the access control code.
+
+`-fcheck-new'
+ Check that the pointer returned by `operator new' is non-null
+ before attempting to modify the storage allocated. The current
+ Working Paper requires that `operator new' never return a null
+ pointer, so this check is normally unnecessary.
+
+ An alternative to using this option is to specify that your
+ `operator new' does not throw any exceptions; if you declare it
+ `throw()', G++ will check the return value. See also `new
+ (nothrow)'.
+
+`-fconserve-space'
+ Put uninitialized or runtime-initialized global variables into the
+ common segment, as C does. This saves space in the executable at
+ the cost of not diagnosing duplicate definitions. If you compile
+ with this flag and your program mysteriously crashes after
+ `main()' has completed, you may have an object that is being
+ destroyed twice because two definitions were merged.
+
+ This option is no longer useful on most targets, now that support
+ has been added for putting variables into BSS without making them
+ common.
+
+`-fno-const-strings'
+ Give string constants type `char *' instead of type `const char
+ *'. By default, G++ uses type `const char *' as required by the
+ standard. Even if you use `-fno-const-strings', you cannot
+ actually modify the value of a string constant, unless you also use
+ `-fwritable-strings'.
+
+ This option might be removed in a future release of G++. For
+ maximum portability, you should structure your code so that it
+ works with string constants that have type `const char *'.
+
+`-fdollars-in-identifiers'
+ Accept `$' in identifiers. You can also explicitly prohibit use of
+ `$' with the option `-fno-dollars-in-identifiers'. (GNU C allows
+ `$' by default on most target systems, but there are a few
+ exceptions.) Traditional C allowed the character `$' to form part
+ of identifiers. However, ISO C and C++ forbid `$' in identifiers.
+
+`-fno-elide-constructors'
+ The C++ standard allows an implementation to omit creating a
+ temporary which is only used to initialize another object of the
+ same type. Specifying this option disables that optimization, and
+ forces G++ to call the copy constructor in all cases.
+
+`-fno-enforce-eh-specs'
+ Don't check for violation of exception specifications at runtime.
+ This option violates the C++ standard, but may be useful for
+ reducing code size in production builds, much like defining
+ `NDEBUG'. The compiler will still optimize based on the exception
+ specifications.
+
+`-fexternal-templates'
+ Cause `#pragma interface' and `implementation' to apply to
+ template instantiation; template instances are emitted or not
+ according to the location of the template definition. *Note
+ Template Instantiation::, for more information.
+
+ This option is deprecated.
+
+`-falt-external-templates'
+ Similar to `-fexternal-templates', but template instances are
+ emitted or not according to the place where they are first
+ instantiated. *Note Template Instantiation::, for more
+ information.
+
+ This option is deprecated.
+
+`-ffor-scope'
+`-fno-for-scope'
+ If `-ffor-scope' is specified, the scope of variables declared in
+ a for-init-statement is limited to the `for' loop itself, as
+ specified by the C++ standard. If `-fno-for-scope' is specified,
+ the scope of variables declared in a for-init-statement extends to
+ the end of the enclosing scope, as was the case in old versions of
+ G++, and other (traditional) implementations of C++.
+
+ The default if neither flag is given to follow the standard, but
+ to allow and give a warning for old-style code that would
+ otherwise be invalid, or have different behavior.
+
+`-fno-gnu-keywords'
+ Do not recognize `typeof' as a keyword, so that code can use this
+ word as an identifier. You can use the keyword `__typeof__'
+ instead. `-ansi' implies `-fno-gnu-keywords'.
+
+`-fno-implicit-templates'
+ Never emit code for non-inline templates which are instantiated
+ implicitly (i.e. by use); only emit code for explicit
+ instantiations. *Note Template Instantiation::, for more
+ information.
+
+`-fno-implicit-inline-templates'
+ Don't emit code for implicit instantiations of inline templates,
+ either. The default is to handle inlines differently so that
+ compiles with and without optimization will need the same set of
+ explicit instantiations.
+
+`-fno-implement-inlines'
+ To save space, do not emit out-of-line copies of inline functions
+ controlled by `#pragma implementation'. This will cause linker
+ errors if these functions are not inlined everywhere they are
+ called.
+
+`-fms-extensions'
+ Disable pedantic warnings about constructs used in MFC, such as
+ implicit int and getting a pointer to member function via
+ non-standard syntax.
+
+`-fno-nonansi-builtins'
+ Disable built-in declarations of functions that are not mandated by
+ ANSI/ISO C. These include `ffs', `alloca', `_exit', `index',
+ `bzero', `conjf', and other related functions.
+
+`-fno-operator-names'
+ Do not treat the operator name keywords `and', `bitand', `bitor',
+ `compl', `not', `or' and `xor' as synonyms as keywords.
+
+`-fno-optional-diags'
+ Disable diagnostics that the standard says a compiler does not
+ need to issue. Currently, the only such diagnostic issued by G++
+ is the one for a name having multiple meanings within a class.
+
+`-fpermissive'
+ Downgrade messages about nonconformant code from errors to
+ warnings. By default, G++ effectively sets `-pedantic-errors'
+ without `-pedantic'; this option reverses that. This behavior and
+ this option are superseded by `-pedantic', which works as it does
+ for GNU C.
+
+`-frepo'
+ Enable automatic template instantiation at link time. This option
+ also implies `-fno-implicit-templates'. *Note Template
+ Instantiation::, for more information.
+
+`-fno-rtti'
+ Disable generation of information about every class with virtual
+ functions for use by the C++ runtime type identification features
+ (`dynamic_cast' and `typeid'). If you don't use those parts of
+ the language, you can save some space by using this flag. Note
+ that exception handling uses the same information, but it will
+ generate it as needed.
+
+`-fstats'
+ Emit statistics about front-end processing at the end of the
+ compilation. This information is generally only useful to the G++
+ development team.
+
+`-ftemplate-depth-N'
+ Set the maximum instantiation depth for template classes to N. A
+ limit on the template instantiation depth is needed to detect
+ endless recursions during template class instantiation. ANSI/ISO
+ C++ conforming programs must not rely on a maximum depth greater
+ than 17.
+
+`-fuse-cxa-atexit'
+ Register destructors for objects with static storage duration with
+ the `__cxa_atexit' function rather than the `atexit' function.
+ This option is required for fully standards-compliant handling of
+ static destructors, but will only work if your C library supports
+ `__cxa_atexit'.
+
+`-fvtable-gc'
+ Emit special relocations for vtables and virtual function
+ references 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
+ support this option. `-Wl,--gc-sections' is ignored without
+ `-static'.
+
+`-fno-weak'
+ Do not use weak symbol support, even if it is provided by the
+ linker. By default, G++ will use weak symbols if they are
+ available. This option exists only for testing, and should not be
+ used by end-users; it will result in inferior code and has no
+ benefits. This option may be removed in a future release of G++.
+
+`-nostdinc++'
+ Do not search for header files in the standard directories
+ specific to C++, but do still search the other standard
+ directories. (This option is used when building the C++ library.)
+
+ In addition, these optimization, warning, and code generation options
+have meanings only for C++ programs:
+
+`-fno-default-inline'
+ Do not assume `inline' for functions defined inside a class scope.
+ *Note Options That Control Optimization: Optimize Options. Note
+ that these functions will have linkage like inline functions; 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 incompatibilites at this point include:
+
+ * Incorrect handling of tail-padding for bit-fields. G++ may
+ attempt to pack data into the same byte as a base class. For
+ example:
+
+ struct A { virtual void f(); int f1 : 1; };
+ struct B : public A { int f2 : 1; };
+
+ In this case, G++ will place `B::f2' into the same byte
+ as`A::f1'; other compilers will not. You can avoid this
+ problem by explicitly padding `A' so that its size is a
+ multiple of the byte size on your platform; that will cause
+ G++ and other compilers to layout `B' identically.
+
+ * Incorrect handling of tail-padding for virtual bases. G++
+ does not use tail padding when laying out virtual bases. For
+ example:
+
+ struct A { virtual void f(); char c1; };
+ struct B { B(); char c2; };
+ struct C : public A, public virtual B {};
+
+ In this case, G++ will not place `B' into the tail-padding for
+ `A'; other compilers will. You can avoid this problem by
+ explicitly padding `A' so that its size is a multiple of its
+ alignment (ignoring virtual base classes); that will cause
+ G++ and other compilers to layout `C' identically.
+
+
+`-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.
+
+`-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.
+
+`-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.
+
+ 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
+ increment 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. *Note 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
+ specification 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 function. (Section 14.5.3). Before G++
+ implemented explicit specification, unqualified-ids could be
+ interpreted as a particular specialization of a templatized
+ function. Because this non-conforming behavior is no longer the
+ default behavior for G++, `-Wnon-template-friend' allows the
+ compiler to check existing code for potential trouble spots, and
+ is on by default. This new compiler behavior can be turned off
+ with `-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',
+ `reinterpret_cast', and `const_cast') are less vulnerable to
+ unintended effects, and much easier to grep for.
+
+`-Woverloaded-virtual (C++ only)'
+ Warn when a function declaration hides virtual functions from a
+ base class. For example, in:
+
+ struct A {
+ virtual void f();
+ };
+
+ struct B: public A {
+ void f(int);
+ };
+
+ the `A' class version of `f' is hidden in `B', and code like this:
+
+ B* b;
+ b->f();
+
+ will fail to compile.
+
+`-Wno-pmf-conversions (C++ only)'
+ Disable the diagnostic for converting a bound pointer to member
+ function to a plain pointer.
+
+`-Wsign-promo (C++ only)'
+ Warn when overload resolution chooses a promotion from unsigned or
+ enumeral type to a signed type over a conversion to an unsigned
+ type of the same size. Previous versions of G++ would try to
+ preserve 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 ='.
+
+\1f
+File: gcc.info, Node: Objective-C Dialect Options, Next: Language Independent Options, Prev: C++ Dialect Options, Up: Invoking GCC
+
+3.6 Options Controlling Objective-C Dialect
+===========================================
+
+This section describes the command-line options that are only meaningful
+for Objective-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 `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
+Objective-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 Objective-C
+programs:
+
+`-fconstant-string-class=CLASS-NAME'
+ Use CLASS-NAME as the name of the class to instantiate for each
+ literal string specified with the syntax `@"..."'. The default
+ class name is `NXConstantString'.
+
+`-fgnu-runtime'
+ Generate object code compatible with the standard GNU Objective-C
+ runtime. This is the default for most types of systems.
+
+`-fnext-runtime'
+ Generate output compatible with the NeXT runtime. This is the
+ default for NeXT-based systems, including Darwin and Mac OS X.
+
+`-gen-decls'
+ Dump interface declarations for all classes seen in the source
+ file to a file named `SOURCENAME.decl'.
+
+`-Wno-protocol'
+ Do not warn if methods required by a protocol are not implemented
+ in the class adopting it.
+
+`-Wselector'
+ Warn if a selector has multiple methods of different types defined.
+
+
+\1f
+File: gcc.info, Node: Language Independent Options, Next: Warning Options, Prev: Objective-C Dialect Options, Up: Invoking GCC
+
+3.7 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 formatting
+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 correctly.
+
+`-fmessage-length=N'
+ Try to format error messages so that they fit on lines of about N
+ characters. The default is 72 characters for `g++' and 0 for the
+ rest of the front ends supported by GCC. If N is zero, then no
+ line-wrapping will be done; each error message will appear on a
+ single line.
+
+`-fdiagnostics-show-location=once'
+ Only meaningful in line-wrapping mode. Instructs the diagnostic
+ messages reporter to emit _once_ source location information; that
+ is, in case the message is too long to fit on a single physical
+ line and has to be wrapped, the source location won't be emitted
+ (as prefix) again, over and over, in subsequent continuation
+ lines. This is the default behavior.
+
+`-fdiagnostics-show-location=every-line'
+ Only meaningful in line-wrapping mode. Instructs the diagnostic
+ messages reporter to emit the same source location information (as
+ prefix) for physical lines that result from the process of breaking
+ a message which is too long to fit on a single line.
+
+
+\1f
+File: gcc.info, Node: Warning Options, Next: Debugging Options, Prev: Language Independent Options, Up: Invoking GCC
+
+3.8 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
+*note C++ Dialect Options:: and *note Objective-C Dialect Options::.
+
+`-fsyntax-only'
+ Check the code for syntax errors, but don't do anything beyond
+ that.
+
+`-pedantic'
+ Issue all the warnings demanded by strict ISO C and ISO C++;
+ reject all programs that use forbidden extensions, and some other
+ programs that do not follow ISO C and ISO C++. For ISO C, follows
+ the version 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++ features 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__'. However, only system header files should use
+ these escape routes; application programs should avoid them.
+ *Note Alternate Keywords::.
+
+ 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
+ diagnostics have been added.
+
+ A feature to report any failure to conform to ISO C might be
+ useful in some instances, but would require considerable
+ additional work and would be quite different from `-pedantic'. We
+ don't have plans to support such a feature in the near future.
+
+ Where the standard specified with `-std' represents a GNU extended
+ dialect of C, such as `gnu89' or `gnu99', there is a corresponding
+ "base standard", the version of ISO C on which the GNU extended
+ dialect is based. Warnings from `-pedantic' are given where they
+ are required by the base standard. (It would not make sense for
+ such warnings to be given only for features not in the specified
+ GNU C dialect, since by definition the GNU dialects of C include
+ all features the compiler supports with the given option, and
+ there would be nothing to warn about.)
+
+`-pedantic-errors'
+ Like `-pedantic', except that errors are produced rather than
+ warnings.
+
+`-w'
+ Inhibit all warning messages.
+
+`-Wno-import'
+ Inhibit warning messages about the use of `#import'.
+
+`-Wchar-subscripts'
+ Warn if an array subscript has type `char'. This is a common cause
+ of error, as programmers often forget that this type is signed on
+ some machines.
+
+`-Wcomment'
+ Warn whenever a comment-start sequence `/*' appears in a `/*'
+ comment, or whenever a Backslash-Newline appears in a `//' comment.
+
+`-Wformat'
+ Check calls to `printf' and `scanf', etc., to make sure that the
+ arguments supplied have types appropriate to the format string
+ specified, and that the conversions specified in the format string
+ make sense. This includes standard functions, and others
+ specified by format attributes (*note Function 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 C89 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 format features not in the selected standard version
+ (but not for `strfmon' formats, since those are not in any version
+ of the C standard). *Note Options Controlling C Dialect: C
+ Dialect Options.
+
+ `-Wformat' is included in `-Wall'. For more control over some
+ aspects of format checking, the options `-Wno-format-y2k',
+ `-Wno-format-extra-args', `-Wformat-nonliteral',
+ `-Wformat-security' and `-Wformat=2' are available, but are not
+ included in `-Wall'.
+
+`-Wno-format-y2k'
+ If `-Wformat' is specified, do not warn about `strftime' formats
+ which may yield only a two-digit year.
+
+`-Wno-format-extra-args'
+ If `-Wformat' is specified, do not warn about excess arguments to a
+ `printf' or `scanf' format function. The C standard specifies
+ that such arguments are ignored.
+
+ Where the unused arguments lie between used arguments that are
+ specified with `$' operand number specifications, normally
+ warnings are still given, since the implementation could not know
+ what type to pass to `va_arg' to skip the unused arguments.
+ However, in the case of `scanf' formats, this option will suppress
+ the warning if the unused arguments are all pointers, since the
+ Single Unix Specification says that such unused arguments are
+ allowed.
+
+`-Wformat-nonliteral'
+ If `-Wformat' is specified, also warn if the format string is not a
+ string literal and so cannot be checked, unless the format function
+ takes its format arguments as a `va_list'.
+
+`-Wformat-security'
+ If `-Wformat' is specified, also warn about uses of format
+ functions that represent possible security problems. At present,
+ this warns about calls to `printf' and `scanf' functions where the
+ format string is not a string literal and there are no format
+ arguments, as in `printf (foo);'. This may be a security hole if
+ the format string came from untrusted input and contains `%n'.
+ (This is currently a subset of what `-Wformat-nonliteral' warns
+ about, but in future warnings may be added to `-Wformat-security'
+ that are not included in `-Wformat-nonliteral'.)
+
+`-Wformat=2'
+ Enable `-Wformat' plus format checks not included in `-Wformat'.
+ Currently equivalent to `-Wformat -Wformat-nonliteral
+ -Wformat-security'.
+
+`-Wimplicit-int'
+ Warn when a declaration does not specify a type.
+
+`-Wimplicit-function-declaration'
+`-Werror-implicit-function-declaration'
+ Give a warning (or error) whenever a function is used before being
+ declared.
+
+`-Wimplicit'
+ Same as `-Wimplicit-int' and `-Wimplicit-function-declaration'.
+
+`-Wmain'
+ Warn if the type of `main' is suspicious. `main' should be a
+ function with external linkage, returning int, taking either zero
+ arguments, two, or three arguments of appropriate types.
+
+`-Wmissing-braces'
+ Warn if an aggregate or union initializer is not fully bracketed.
+ In the following example, the initializer for `a' is not fully
+ bracketed, but that for `b' is fully bracketed.
+
+ int a[2][2] = { 0, 1, 2, 3 };
+ int b[2][2] = { { 0, 1 }, { 2, 3 } };
+
+`-Wparentheses'
+ Warn if parentheses are omitted in certain contexts, such as when
+ there is an assignment in a context where a truth value is
+ expected, or when operators are nested whose precedence people
+ often get confused about.
+
+ Also warn about constructions where there may be confusion to which
+ `if' statement an `else' branch belongs. Here is an example of
+ such a case:
+
+ {
+ if (a)
+ if (b)
+ foo ();
+ else
+ bar ();
+ }
+
+ In C, every `else' branch belongs to the innermost possible `if'
+ statement, which in this example is `if (b)'. This is often not
+ what the programmer expected, as illustrated in the above example
+ by indentation the programmer chose. When there is the potential
+ for this confusion, GCC will issue a warning when this flag is
+ specified. To eliminate the warning, add explicit braces around
+ the innermost `if' statement so there is no way the `else' could
+ belong to the enclosing `if'. The resulting code would look like
+ this:
+
+ {
+ if (a)
+ {
+ if (b)
+ foo ();
+ else
+ bar ();
+ }
+ }
+
+`-Wsequence-point'
+ Warn about code that may have undefined semantics because of
+ violations of sequence point rules in the C standard.
+
+ The C standard defines the order in which expressions in a C
+ program 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 arguments and the expression denoting the called
+ function), and in certain other places. Other than as expressed
+ by the sequence point rules, the order of evaluation of
+ subexpressions of an expression is not specified. All 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. However, the standards
+ committee have ruled that function calls do not overlap.
+
+ It is not specified when between sequence points modifications to
+ the values of objects take effect. Programs whose behavior
+ depends on this have undefined behavior; the C standard specifies
+ that "Between the previous and next sequence point an object shall
+ have its stored value modified at most once by the evaluation of
+ an expression. Furthermore, the prior value shall be read only to
+ determine the value to be stored.". If a program breaks these
+ rules, the results on any particular implementation are entirely
+ unpredictable.
+
+ Examples of code with undefined behavior are `a = a++;', `a[n] =
+ b[n++]' and `a[i++] = i;'. Some more complicated cases are not
+ diagnosed by this option, and it may give an occasional false
+ positive 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
+ programs. 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
+ subtle cases. Links to discussions of the problem, including
+ proposed formal definitions, may be found on our readings page, at
+ `http://gcc.gnu.org/readings.html'.
+
+`-Wreturn-type'
+ Warn whenever a function is defined with a return-type that
+ defaults to `int'. Also warn about any `return' statement with no
+ return-value in a function whose return-type is not `void'.
+
+ For C++, a function without return type always produces a
+ diagnostic message, even when `-Wno-return-type' is specified.
+ The only exceptions are `main' and functions defined in system
+ headers.
+
+`-Wswitch'
+ Warn whenever a `switch' statement has an index of enumeral type
+ and lacks a `case' for one or more of the named codes of that
+ enumeration. (The presence of a `default' label prevents this
+ warning.) `case' labels outside the enumeration range also
+ provoke warnings when this option is used.
+
+`-Wtrigraphs'
+ Warn if any trigraphs are encountered that might change the
+ meaning of the program (trigraphs within comments are not warned
+ about).
+
+`-Wunused-function'
+ Warn whenever a static function is declared but not defined or a
+ non\-inline static function is unused.
+
+`-Wunused-label'
+ Warn whenever a label is declared but not used.
+
+ To suppress this warning use the `unused' attribute (*note
+ Variable Attributes::).
+
+`-Wunused-parameter'
+ Warn whenever a function parameter is unused aside from its
+ declaration.
+
+ To suppress this warning use the `unused' attribute (*note
+ Variable Attributes::).
+
+`-Wunused-variable'
+ Warn whenever a local variable or non-constant static variable is
+ unused aside from its declaration
+
+ To suppress this warning use the `unused' attribute (*note
+ Variable Attributes::).
+
+`-Wunused-value'
+ Warn whenever a statement computes a result that is explicitly not
+ used.
+
+ To suppress this warning cast the expression to `void'.
+
+`-Wunused'
+ All all the above `-Wunused' options combined.
+
+ In order to get a warning about an unused function parameter, you
+ must either specify `-W -Wunused' or separately specify
+ `-Wunused-parameter'.
+
+`-Wuninitialized'
+ Warn if an automatic variable is used without first being
+ initialized 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 optimizing. If you don't specify `-O', you simply won't get
+ these warnings.
+
+ 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
+ warnings are printed.
+
+ These warnings are made optional because GCC is not smart enough
+ to see all the reasons why the code might be correct despite
+ appearing to have an error. Here is one example of how this can
+ happen:
+
+ {
+ int x;
+ switch (y)
+ {
+ case 1: x = 1;
+ break;
+ case 2: x = 4;
+ break;
+ case 3: x = 5;
+ }
+ foo (x);
+ }
+
+ If the value of `y' is always 1, 2 or 3, then `x' is always
+ initialized, 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 possible 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
+ functions you use that never return as `noreturn'. *Note Function
+ Attributes::.
+
+`-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:
+
+`-Wunknown-pragmas'
+ Warn when a #pragma directive is encountered which is not
+ understood 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.
+
+`-Wall'
+ All of the above `-W' options combined. This enables all the
+ warnings about constructions that some users consider
+ questionable, and that are easy to avoid (or modify to prevent the
+ warning), even in conjunction with macros.
+
+`-Wdiv-by-zero'
+ Warn about compile-time integer division by zero. This is
+ default. To inhibit the warning messages, use `-Wno-div-by-zero'.
+ Floating point division by zero is not warned about, as it can be
+ a legitimate way of obtaining infinities and NaNs.
+
+`-Wmultichar'
+ Warn if a multicharacter constant (`'FOOF'') is used. This is
+ default. To inhibit the warning messages, use `-Wno-multichar'.
+ Usually they indicate a typo in the user's code, as they have
+ implementation-defined values, and should not be used in portable
+ code.
+
+`-Wsystem-headers'
+ Print warning messages for constructs found in system header files.
+ Warnings from system headers are normally suppressed, on the
+ assumption that they usually do not indicate real problems and
+ would only make the compiler output harder to read. Using this
+ command line option tells GCC to emit warnings from system headers
+ as if they occurred in user code. However, note that using
+ `-Wall' in conjunction with this option will _not_ warn about
+ unknown pragmas in system headers--for that, `-Wunknown-pragmas'
+ must also be used.
+
+ The following `-W...' options are not implied by `-Wall'. Some of
+them warn about constructions that users generally do not consider
+questionable, but which occasionally you might wish to 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 without a value.) For example, this function would
+ evoke such a warning:
+
+ foo (a)
+ {
+ if (a > 0)
+ return a;
+ }
+
+ * An expression-statement or the left-hand side of a comma
+ expression contains no side effects. To suppress the
+ warning, cast the unused expression to void. For example, an
+ expression such as `x[i,j]' will cause a warning, but
+ `x[(void)i,j]' will not.
+
+ * An unsigned value is compared against zero with `<' or `<='.
+
+ * A comparison like `x<=y<=z' appears; this is equivalent to
+ `(x<=y ? 1 : 0) <= z', which is a different interpretation
+ from that of ordinary mathematical notation.
+
+ * Storage-class specifiers like `static' are not the first
+ things in a declaration. According to the C Standard, this
+ usage is obsolescent.
+
+ * The return type of a function has a type qualifier such as
+ `const'. Such a type qualifier has no effect, since the
+ value returned by a function is not an lvalue. (But don't
+ warn about the GNU extension of `volatile void' return types.
+ That extension will be warned about if `-pedantic' is
+ specified.)
+
+ * If `-Wall' or `-Wunused' is also specified, warn about unused
+ arguments.
+
+ * 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
+ specified.)
+
+ * 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 };
+
+`-Wfloat-equal'
+ Warn if floating point values are used in equality comparisons.
+
+ The idea behind this is that sometimes it is convenient (for the
+ programmer) to consider floating-point values as approximations to
+ infinitely precise real numbers. If you are doing this, then you
+ need to compute (by analysing 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
+ traditional 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 understands but would ignore because the `#'
+ does not appear as the first character on the line. It also
+ suggests you hide directives like `#pragma' not understood by
+ traditional C by indenting 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
+ separate 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'.
+
+`-Wundef'
+ Warn if an undefined identifier is evaluated in an `#if' directive.
+
+`-Wshadow'
+ Warn whenever a local variable shadows another local variable,
+ parameter or global variable or whenever a built-in function is
+ shadowed.
+
+`-Wlarger-than-LEN'
+ Warn whenever an object of larger than LEN bytes is defined.
+
+`-Wpointer-arith'
+ Warn about anything that depends on the "size of" a function type
+ or of `void'. GNU C assigns these types a size of 1, for
+ convenience in calculations with `void *' pointers and pointers to
+ functions.
+
+`-Wbad-function-cast (C only)'
+ Warn whenever a function call is cast to a non-matching type. For
+ example, warn if `int malloc()' is cast to `anything *'.
+
+`-Wcast-qual'
+ Warn whenever a pointer is cast so as to remove a type qualifier
+ from the target type. For example, warn if a `const char *' is
+ cast to an ordinary `char *'.
+
+`-Wcast-align'
+ Warn whenever a pointer is cast such that the required alignment
+ of the target is increased. For example, warn if a `char *' is
+ cast to an `int *' on machines where integers can only be accessed
+ at two- or four-byte boundaries.
+
+`-Wwrite-strings'
+ When compiling C, give string constants the type `const
+ char[LENGTH]' so that copying the address of one into a
+ non-`const' `char *' pointer will get a warning; when compiling
+ C++, warn about the deprecated conversion from string constants to
+ `char *'. These warnings will help you find at compile time code
+ that can try to write into a string constant, but only if you have
+ been very careful about using `const' in declarations and
+ prototypes. Otherwise, it will just be a nuisance; this is why we
+ did not make `-Wall' request these warnings.
+
+`-Wconversion'
+ Warn if a prototype causes a type conversion that is different
+ from what would happen to the same argument in the absence of a
+ prototype. 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
+ assignment `x = -1' if `x' is unsigned. But do not warn about
+ explicit casts like `(unsigned) -1'.
+
+`-Wsign-compare'
+ Warn when a comparison between signed and unsigned values could
+ produce an incorrect result when the signed value is converted to
+ unsigned. This warning is also enabled by `-W'; to get the other
+ warnings of `-W' without this warning, use `-W -Wno-sign-compare'.
+
+`-Waggregate-return'
+ Warn if any functions that return structures or unions are defined
+ or called. (In languages where you can return an array, this also
+ elicits a warning.)
+
+`-Wstrict-prototypes (C only)'
+ Warn if a function is declared or defined without specifying the
+ argument types. (An old-style function definition is permitted
+ without a warning if preceded by a declaration which specifies the
+ argument types.)
+
+`-Wmissing-prototypes (C only)'
+ Warn if a global function is defined without a previous prototype
+ declaration. This warning is issued even if the definition itself
+ provides a prototype. The aim is to detect global functions that
+ fail to be declared in header files.
+
+`-Wmissing-declarations'
+ Warn if a global function is defined without a previous
+ declaration. Do so even if the definition itself provides a
+ prototype. Use this option to detect global functions that are
+ not declared in header files.
+
+`-Wmissing-noreturn'
+ Warn about functions which might be candidates for attribute
+ `noreturn'. 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 subtle code generation bugs could be introduced. You
+ will not get a warning for `main' in hosted C environments.
+
+`-Wmissing-format-attribute'
+ If `-Wformat' is enabled, also warn about functions which might be
+ candidates for `format' attributes. Note these are only possible
+ candidates, not absolute ones. GCC will guess that `format'
+ attributes might be appropriate for any function that calls a
+ function like `vprintf' or `vscanf', but this might not always be
+ the case, and some functions for which `format' attributes are
+ appropriate may not be detected. This option has no effect unless
+ `-Wformat' is enabled (possibly by `-Wall').
+
+`-Wno-deprecated-declarations'
+ Do not warn about uses of functions, variables, and types marked as
+ deprecated by using the `deprecated' attribute. (*note Function
+ Attributes::, *note Variable Attributes::, *note Type
+ Attributes::.)
+
+`-Wpacked'
+ Warn if a structure is given the packed attribute, but the packed
+ attribute has no effect on the layout or size of the structure.
+ Such structures may be mis-aligned for little benefit. For
+ instance, in this code, the variable `f.x' in `struct bar' will be
+ misaligned even though `struct bar' does not itself have the
+ packed attribute:
+
+ struct foo {
+ int x;
+ char a, b, c, d;
+ } __attribute__((packed));
+ struct bar {
+ char z;
+ struct foo f;
+ };
+
+`-Wpadded'
+ Warn if padding is included in a structure, either to align an
+ element of the structure or to align the whole structure.
+ Sometimes when this happens it is possible to rearrange the fields
+ of the structure to reduce the padding and so make the structure
+ smaller.
+
+`-Wredundant-decls'
+ Warn if anything is declared more than once in the same scope,
+ even in cases where multiple declaration is valid and changes
+ nothing.
+
+`-Wnested-externs (C only)'
+ Warn if an `extern' declaration is encountered within a function.
+
+`-Wunreachable-code'
+ Warn if the compiler detects that code will never be executed.
+
+ This option is intended to warn when the compiler detects that at
+ least a whole line of source code will never be executed, because
+ some condition is never satisfied or because it is after a
+ procedure 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
+ version of a program there is often substantial code which checks
+ correct functioning of the program and is, hopefully, unreachable
+ because the program does work. Another common use of unreachable
+ code is to provide behavior which is selectable at compile-time.
+
+`-Winline'
+ Warn if a function can not be inlined and it was declared as
+ inline.
+
+`-Wlong-long'
+ Warn if `long long' type is used. This is default. To inhibit
+ the warning messages, use `-Wno-long-long'. Flags `-Wlong-long'
+ and `-Wno-long-long' are taken into account only when `-pedantic'
+ flag is used.
+
+`-Wdisabled-optimization'
+ Warn if a requested optimization pass is disabled. This warning
+ does not generally indicate that there is anything wrong with your
+ code; it merely indicates that GCC's optimizers were unable to
+ handle the code effectively. Often, the problem is that your code
+ is too big or too complex; GCC will refuse to optimize programs
+ when the optimization itself is likely to take inordinate amounts
+ of time.
+
+`-Werror'
+ Make all warnings into errors.
+
+\1f
+File: gcc.info, Node: Debugging Options, Next: Optimize Options, Prev: Warning Options, Up: Invoking GCC
+
+3.9 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
+ format (stabs, COFF, XCOFF, or DWARF). GDB can work with this
+ debugging 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
+ control for certain whether to generate the extra information, use
+ `-gstabs+', `-gstabs', `-gxcoff+', `-gxcoff', `-gdwarf-1+',
+ `-gdwarf-1', or `-gvms' (see below).
+
+ Unlike most other C compilers, GCC allows you to use `-g' with
+ `-O'. The shortcuts taken by optimized code may occasionally
+ produce surprising results: some variables you declared may not
+ exist at all; flow of control may briefly move where you did not
+ expect it; some statements may not be executed because they
+ compute constant results or their values were already at hand;
+ some statements may execute in different places because they were
+ moved out of loops.
+
+ Nevertheless it proves possible to debug optimized output. This
+ makes it reasonable to use the optimizer for programs that might
+ have bugs.
+
+ The following options are useful when GCC is generated with the
+ capability for more than one debugging format.
+
+`-ggdb'
+ Produce debugging information for use by GDB. This means to use
+ the most expressive format available (DWARF 2, stabs, or the
+ native format if neither of those are supported), including GDB
+ extensions if at all possible.
+
+`-gstabs'
+ Produce debugging information in stabs format (if that is
+ supported), without GDB extensions. This is the format used by
+ DBX on most BSD systems. On MIPS, Alpha and System V Release 4
+ systems this option produces stabs debugging output which is not
+ understood by DBX or SDB. On System V Release 4 systems this
+ option requires the GNU assembler.
+
+`-gstabs+'
+ Produce debugging information in stabs format (if that is
+ supported), using GNU extensions understood only by the GNU
+ debugger (GDB). The use of these extensions is likely to make
+ other debuggers crash or refuse to read the program.
+
+`-gcoff'
+ Produce debugging information in COFF format (if that is
+ supported). This is the format used by SDB on most System V
+ systems prior to System V Release 4.
+
+`-gxcoff'
+ Produce debugging information in XCOFF format (if that is
+ supported). This is the format used by the DBX debugger on IBM
+ RS/6000 systems.
+
+`-gxcoff+'
+ Produce debugging information in XCOFF format (if that is
+ supported), using GNU extensions understood only by the GNU
+ debugger (GDB). The use of these extensions is likely to make
+ other debuggers crash or refuse to read the program, and may cause
+ assemblers other than the GNU assembler (GAS) to fail with an
+ error.
+
+`-gdwarf'
+ Produce debugging information in DWARF version 1 format (if that is
+ supported). This is the format used by SDB on most System V
+ Release 4 systems.
+
+`-gdwarf+'
+ Produce debugging information in DWARF version 1 format (if that is
+ supported), using GNU extensions understood only by the GNU
+ debugger (GDB). The use of these extensions is likely to make
+ other debuggers crash or refuse to read the program.
+
+`-gdwarf-2'
+ Produce debugging information in DWARF version 2 format (if that is
+ supported). This is the format used by DBX on IRIX 6.
+
+`-gvms'
+ Produce debugging information in VMS debug format (if that is
+ supported). This is the format used by DEBUG on VMS systems.
+
+`-gLEVEL'
+`-ggdbLEVEL'
+`-gstabsLEVEL'
+`-gcoffLEVEL'
+`-gxcoffLEVEL'
+`-gvmsLEVEL'
+ 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
+ definitions present in the program. Some debuggers support macro
+ expansion 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.
+
+`-p'
+ Generate extra code to write profile information suitable for the
+ analysis program `prof'. You must use this option when compiling
+ the source files you want data about, and you must also use it when
+ linking.
+
+`-pg'
+ Generate extra code to write profile information suitable for the
+ analysis program `gprof'. You must use this option when compiling
+ the source files you want data about, and you must also use it when
+ linking.
+
+`-Q'
+ Makes the compiler print out each function name as it is compiled,
+ and print some statistics about each pass when it finishes.
+
+`-ftime-report'
+ Makes the compiler print some statistics about the time consumed
+ by each pass when it finishes.
+
+`-fmem-report'
+ Makes the compiler print some statistics about permanent memory
+ allocation when it finishes.
+
+`-fprofile-arcs'
+ Instrument "arcs" during compilation to generate coverage data or
+ for profile-directed block ordering. During execution the program
+ records how many times each branch is executed and how many times
+ it is taken. When the compiled program exits it saves this data
+ to a file called `SOURCENAME.da' for each source file.
+
+ For profile-directed block ordering, compile the program with
+ `-fprofile-arcs' plus optimization and code generation options,
+ generate 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-probabilities' (*note Options that Control Optimization:
+ Optimize Options.).
+
+ 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
+ instrumented: the compiler adds code to count the number of times
+ that these arcs are executed. When an arc is the only exit or
+ only entrance to a block, the instrumentation code can be added to
+ the block; otherwise, a new basic block must be created to hold
+ the instrumentation code.
+
+`-ftest-coverage'
+ Create data files for the `gcov' code-coverage utility (*note
+ `gcov'--a Test Coverage Program: Gcov.). The data file names
+ begin with the name of your source file:
+
+ `SOURCENAME.bb'
+ A mapping from basic blocks to line numbers, which `gcov'
+ uses to associate basic block execution counts with line
+ numbers.
+
+ `SOURCENAME.bbg'
+ A list of all arcs in the program flow graph. This allows
+ `gcov' to reconstruct the program flow graph, so that it can
+ compute all basic block and arc execution counts from the
+ information in the `SOURCENAME.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:
+
+ `SOURCENAME.da'
+ Runtime arc execution counts, used in conjunction with the arc
+ information in the file `SOURCENAME.bbg'.
+
+ Coverage data will map better to the source files if
+ `-ftest-coverage' is used without optimization.
+
+`-dLETTERS'
+ Says to make debugging dumps during compilation at times specified
+ by LETTERS. This is used for debugging the compiler. The file
+ names for most of the dumps are made by appending a pass number
+ and a word to the source file name (e.g. `foo.c.00.rtl' or
+ `foo.c.01.sibling'). Here are the possible letters for use in
+ LETTERS, and their meanings:
+
+ `A'
+ Annotate the assembler output with miscellaneous debugging
+ information.
+
+ `b'
+ Dump after computing branch probabilities, to `FILE.14.bp'.
+
+ `B'
+ Dump after block reordering, to `FILE.29.bbro'.
+
+ `c'
+ Dump after instruction combination, to the file
+ `FILE.16.combine'.
+
+ `C'
+ Dump after the first if conversion, to the file `FILE.17.ce'.
+
+ `d'
+ Dump after delayed branch scheduling, to `FILE.31.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.26.ce2'.
+
+ `f'
+ Dump after life analysis, to `FILE.15.life'.
+
+ `F'
+ Dump after purging `ADDRESSOF' codes, to `FILE.09.addressof'.
+
+ `g'
+ Dump after global register allocation, to `FILE.21.greg'.
+
+ `h'
+ Dump after finalization of EH handling code, to `FILE.02.eh'.
+
+ `k'
+ Dump after reg-to-stack conversion, to `FILE.28.stack'.
+
+ `o'
+ Dump after post-reload optimizations, to `FILE.22.postreload'.
+
+ `G'
+ Dump after GCSE, to `FILE.10.gcse'.
+
+ `i'
+ Dump after sibling call optimizations, to `FILE.01.sibling'.
+
+ `j'
+ Dump after the first jump optimization, to `FILE.03.jump'.
+
+ `k'
+ Dump after conversion from registers to stack, to
+ `FILE.32.stack'.
+
+ `l'
+ Dump after local register allocation, to `FILE.20.lreg'.
+
+ `L'
+ Dump after loop optimization, to `FILE.11.loop'.
+
+ `M'
+ Dump after performing the machine dependent reorganisation
+ pass, to `FILE.30.mach'.
+
+ `n'
+ Dump after register renumbering, to `FILE.25.rnreg'.
+
+ `N'
+ Dump after the register move pass, to `FILE.18.regmove'.
+
+ `r'
+ Dump after RTL generation, to `FILE.00.rtl'.
+
+ `R'
+ Dump after the second scheduling pass, to `FILE.27.sched2'.
+
+ `s'
+ Dump after CSE (including the jump optimization that
+ sometimes follows CSE), to `FILE.08.cse'.
+
+ `S'
+ Dump after the first scheduling pass, to `FILE.19.sched'.
+
+ `t'
+ Dump after the second CSE pass (including the jump
+ optimization that sometimes follows CSE), to `FILE.12.cse2'.
+
+ `w'
+ Dump after the second flow pass, to `FILE.23.flow2'.
+
+ `X'
+ Dump after SSA dead code elimination, to `FILE.06.ssadce'.
+
+ `z'
+ Dump after the peephole pass, to `FILE.24.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
+ instruction 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.
+ Usually used with `r'.
+
+ `y'
+ Dump debugging information during parsing, to standard error.
+
+`-fdump-unnumbered'
+ When doing debugging dumps (see `-d' option above), suppress
+ instruction numbers and line number note output. This makes it
+ more feasible 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
+ translation 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
+ function 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
+ intermediate language tree to a file. The file name is generated
+ by appending 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
+ applicable to all dumps, those which are not meaningful will be
+ ignored. The following options are available
+
+ `address'
+ Print the address of each node. Usually this is not
+ meaningful as it changes according to the environment and
+ source file. Its primary use is for tying up a dump file with
+ a debug environment.
+
+ `slim'
+ Inhibit dumping of members of a scope or body of a function
+ merely because that scope has been reached. Only dump such
+ items when they are directly reachable by some other path.
+
+ `all'
+ Turn on all options.
+
+ The following tree dumps are possible:
+ `original'
+ Dump before any tree based optimization, to `FILE.original'.
+
+ `optimized'
+ Dump after all tree based optimization, to `FILE.optimized'.
+
+ `inlined'
+ Dump after function inlining, to `FILE.inlined'.
+
+`-fsched-verbose=N'
+ On targets that use instruction scheduling, this option controls
+ the amount of debugging output the scheduler prints. This
+ information 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 output is always printed to standard error.
+
+ For N greater than zero, `-fsched-verbose' outputs the same
+ information 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.
+
+`-fpretend-float'
+ When running a cross-compiler, pretend that the target machine
+ uses the same floating point format as the host machine. This
+ causes incorrect output of the actual floating constants, but the
+ actual instruction sequence will probably be the same as GCC would
+ make when running on the target machine.
+
+`-save-temps'
+ Store the usual "temporary" intermediate files permanently; place
+ them in the current directory and name them based on the source
+ file. Thus, compiling `foo.c' with `-c -save-temps' would produce
+ files `foo.i' and `foo.s', as well as `foo.o'. This creates a
+ preprocessed `foo.i' output file even though the compiler now
+ normally uses an integrated preprocessor.
+
+`-time'
+ Report the CPU time taken by each subprocess in the compilation
+ sequence. For C source files, this is the compiler proper and
+ assembler (plus the linker if linking is done). The output looks
+ like this:
+
+ # cc1 0.12 0.01
+ # as 0.00 0.01
+
+ The first number on each line is the "user time," that is time
+ spent executing the program itself. The second number is "system
+ time," time spent executing operating system routines on behalf of
+ the program. Both numbers are in seconds.
+
+`-print-file-name=LIBRARY'
+ Print the full absolute name of the library file LIBRARY that
+ would be used when linking--and don't do anything else. With this
+ option, GCC does not compile or link anything; it just prints the
+ file name.
+
+`-print-multi-directory'
+ Print the directory name corresponding to the multilib selected by
+ any other switches present in the command line. This directory is
+ supposed to exist in `GCC_EXEC_PREFIX'.
+
+`-print-multi-lib'
+ Print the mapping from multilib directory names to compiler
+ switches that enable them. The directory name is separated from
+ the switches by `;', and each switch starts with an `@' instead of
+ the `-', without spaces between multiple switches. This is
+ supposed to ease shell-processing.
+
+`-print-prog-name=PROGRAM'
+ Like `-print-file-name', but searches for a program such as `cpp'.
+
+`-print-libgcc-file-name'
+ Same as `-print-file-name=libgcc.a'.
+
+ This is useful when you use `-nostdlib' or `-nodefaultlibs' but
+ you do want to link with `libgcc.a'. You can do
+
+ gcc -nostdlib FILES... `gcc -print-libgcc-file-name`
+
+`-print-search-dirs'
+ Print the name of the configured installation directory and a list
+ of program and library directories gcc will search--and don't do
+ anything else.
+
+ This is useful when gcc prints the error message `installation
+ problem, 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 '/'. *Note Environment
+ Variables::.
+
+`-dumpmachine'
+ Print the compiler's target machine (for example,
+ `i686-pc-linux-gnu')--and don't do anything else.
+
+`-dumpversion'
+ Print the compiler version (for example, `3.0')--and don't do
+ anything else.
+
+`-dumpspecs'
+ Print the compiler's built-in specs--and don't do anything else.
+ (This is used when GCC itself is being built.) *Note Spec Files::.
+
+\1f
+File: gcc.info, Node: Optimize Options, Next: Preprocessor Options, Prev: Debugging Options, Up: Invoking GCC
+
+3.10 Options That Control Optimization
+======================================
+
+These options control various sorts of optimizations:
+
+`-O'
+`-O1'
+ Optimize. Optimizing compilation takes somewhat more time, and a
+ lot more memory for a large function.
+
+ Without `-O', 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.
+
+ With `-O', the compiler tries to reduce code size and execution
+ time, without performing any optimizations that take a great deal
+ of compilation time.
+
+`-O2'
+ Optimize even more. GCC performs nearly all supported
+ optimizations that do not involve a space-speed tradeoff. The
+ compiler does not perform loop unrolling or function inlining when
+ you specify `-O2'. As compared to `-O', this option increases
+ both compilation time and the performance of the generated code.
+
+ `-O2' turns on all optional optimizations except for loop
+ unrolling, function inlining, and register renaming. It also
+ turns on the `-fforce-mem' option on all machines and frame
+ pointer elimination on machines where doing so does not interfere
+ with debugging.
+
+ Please note the warning under `-fgcse' about invoking `-O2' on
+ programs that use computed gotos.
+
+`-O3'
+ Optimize yet more. `-O3' turns on all optimizations specified by
+ `-O2' and also turns on the `-finline-functions' and
+ `-frename-registers' options.
+
+`-O0'
+ Do not optimize.
+
+`-Os'
+ Optimize for size. `-Os' enables all `-O2' optimizations that do
+ not typically increase code size. It also performs further
+ optimizations designed to reduce code size.
+
+ 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 which is not the default. You can figure out the
+other form by either removing `no-' or adding it.
+
+`-ffloat-store'
+ Do not store floating point variables in registers, and inhibit
+ other options that might change whether a floating point value is
+ taken from a register or memory.
+
+ This option prevents undesirable excess precision on machines such
+ as the 68000 where the floating registers (of the 68881) keep more
+ precision than a `double' is supposed to have. Similarly for the
+ x86 architecture. For most programs, the excess precision does
+ only good, but a few programs rely on the precise definition of
+ IEEE floating point. Use `-ffloat-store' for such programs, after
+ modifying them to store all pertinent intermediate computations
+ into variables.
+
+`-fno-default-inline'
+ Do not make member functions inline by default merely because they
+ are defined inside the class scope (C++ only). Otherwise, when
+ you specify `-O', member functions defined inside class scope are
+ compiled inline by default; i.e., you don't need to add `inline'
+ in front of the member function name.
+
+`-fno-defer-pop'
+ Always pop the arguments to each function call as soon as that
+ function returns. For machines which must pop arguments after a
+ function call, the compiler normally lets arguments accumulate on
+ the stack for several function calls and pops them all at once.
+
+`-fforce-mem'
+ Force memory operands to be copied into registers before doing
+ arithmetic on them. This produces better code by making all memory
+ references potential common subexpressions. When they are not
+ common subexpressions, instruction combination should eliminate
+ the separate register-load. The `-O2' option turns on this option.
+
+`-fforce-addr'
+ Force memory address constants to be copied into registers before
+ doing arithmetic on them. This may produce better code just as
+ `-fforce-mem' may.
+
+`-fomit-frame-pointer'
+ Don't keep the frame pointer in a register for functions that
+ don't need one. This avoids the instructions to save, set up and
+ restore frame pointers; it also makes an extra register available
+ in many functions. *It also makes debugging impossible on some
+ machines.*
+
+ On some machines, such as the VAX, this flag has no effect, because
+ the standard calling sequence automatically handles the frame
+ pointer and nothing is saved by pretending it doesn't exist. The
+ machine-description macro `FRAME_POINTER_REQUIRED' controls
+ whether a target machine supports this flag. *Note Register
+ Usage: (gccint)Registers.
+
+`-foptimize-sibling-calls'
+ Optimize sibling and tail recursive calls.
+
+`-ftrapv'
+ This option generates traps for signed overflow on addition,
+ subtraction, multiplication operations.
+
+`-fno-inline'
+ Don't pay attention to the `inline' keyword. Normally this option
+ is used to keep the compiler from expanding any functions inline.
+ Note that if you are not optimizing, no functions can be expanded
+ inline.
+
+`-finline-functions'
+ Integrate all simple functions into their callers. The compiler
+ heuristically decides which functions are simple enough to be worth
+ integrating in this way.
+
+ If all calls to a given function are integrated, and the function
+ is declared `static', then the function is normally not output as
+ assembler code in its own right.
+
+`-finline-limit=N'
+ By default, gcc limits the size of functions that can be inlined.
+ This flag allows the control of this limit for functions that are
+ explicitly marked as inline (ie 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++.
+
+ _Note:_ pseudo instruction represents, in this particular context,
+ an abstract measurement of function's size. In no way, it
+ represents a count of assembly instructions and as such its exact
+ meaning might change from one release to an another.
+
+`-fkeep-inline-functions'
+ Even if all calls to a given function are integrated, and the
+ function is declared `static', nevertheless output a separate
+ run-time callable version of the function. This switch does not
+ affect `extern inline' functions.
+
+`-fkeep-static-consts'
+ Emit variables declared `static const' when optimization isn't
+ turned on, even if the variables aren't referenced.
+
+ GCC enables this option by default. If you want to force the
+ compiler to check if the variable was referenced, regardless of
+ whether or not optimization is turned on, use the
+ `-fno-keep-static-consts' option.
+
+`-fmerge-constants'
+ Attempt to merge identical constants (string constants and
+ floating point constants) accross compilation units.
+
+ This option is default for optimized compilation if assembler and
+ linker support it. Use `-fno-merge-constants' to inhibit this
+ behavior.
+
+`-fmerge-all-constants'
+ Attempt to merge identical constants and identical variables.
+
+ This option implies `-fmerge-constants'. In addition to
+ `-fmerge-constants' this considers e.g. even constant initialized
+ arrays or initialized constant variables with integral or floating
+ point types. Languages like C or C++ require each non-automatic
+ variable to have distinct location, so using this option will
+ result in non-conforming behavior.
+
+`-fno-branch-count-reg'
+ Do not use "decrement and branch" instructions on a count register,
+ but instead generate a sequence of instructions that decrement a
+ register, compare it against zero, then branch based upon the
+ result. This option is only meaningful on architectures that
+ support such instructions, which include x86, PowerPC, IA-64 and
+ S/390.
+
+`-fno-function-cse'
+ Do not put function addresses in registers; make each instruction
+ that calls a constant function contain the function's address
+ explicitly.
+
+ This option results in less efficient code, but some strange hacks
+ that alter the assembler output may be confused by the
+ optimizations performed when this option is not used.
+
+`-ffast-math'
+ Sets `-fno-math-errno', `-funsafe-math-optimizations', and
+ `-fno-trapping-math'.
+
+ This option causes the preprocessor macro `__FAST_MATH__' to be
+ defined.
+
+ This option should never be turned on by any `-O' option since it
+ can result in incorrect output for programs which depend on an
+ exact implementation of IEEE or ISO rules/specifications for math
+ functions.
+
+`-fno-math-errno'
+ Do not set ERRNO after calling math functions that are executed
+ with a single instruction, e.g., sqrt. A program that relies on
+ IEEE exceptions for math error handling may want to use this flag
+ for speed while maintaining IEEE arithmetic compatibility.
+
+ This option should never be turned on by any `-O' option since it
+ can result in incorrect output for programs which depend on an
+ exact implementation of IEEE or ISO rules/specifications for math
+ functions.
+
+ The default is `-fmath-errno'.
+
+`-funsafe-math-optimizations'
+ Allow optimizations for floating-point arithmetic that (a) assume
+ that arguments and results are valid and (b) may violate IEEE or
+ ANSI standards. When used at link-time, it may include libraries
+ or startup files that change the default FPU control word or other
+ similar optimizations.
+
+ This option should never be turned on by any `-O' option since it
+ can result in incorrect output for programs which depend on an
+ exact implementation of IEEE or ISO rules/specifications for math
+ functions.
+
+ The default is `-fno-unsafe-math-optimizations'.
+
+`-fno-trapping-math'
+ Compile code assuming that floating-point operations cannot
+ generate user-visible traps. Setting this option may allow faster
+ code if one relies on "non-stop" IEEE arithmetic, for example.
+
+ This option should never be turned on by any `-O' option since it
+ can result in incorrect output for programs which depend on an
+ exact implementation of IEEE or ISO rules/specifications for math
+ functions.
+
+ The default is `-ftrapping-math'.
+
+`-fbounds-check'
+ For front-ends that support it, generate additional code to check
+ that indices used to access arrays are within the declared range.
+ This is currenly only supported by the Java and Fortran 77
+ front-ends, where this option defaults to true and false
+ respectively.
+
+
+ The following options control specific optimizations. The `-O2'
+option turns on all of these optimizations except `-funroll-loops' and
+`-funroll-all-loops'. On most machines, the `-O' option turns on the
+`-fthread-jumps' and `-fdelayed-branch' options, but specific machines
+may handle it differently.
+
+ You can use the following flags in the rare cases when "fine-tuning"
+of optimizations to be performed is desired.
+
+ Not all of the optimizations performed by GCC have `-f' options to
+control them.
+
+`-fstrength-reduce'
+ Perform the optimizations of loop strength reduction and
+ elimination of iteration variables.
+
+`-fthread-jumps'
+ Perform optimizations where we check to see if a jump branches to a
+ location where another comparison subsumed by the first is found.
+ If so, the first branch is redirected to either the destination of
+ the second branch or a point immediately following it, depending
+ on whether the condition is known to be true or false.
+
+`-fcse-follow-jumps'
+ In common subexpression elimination, scan through jump instructions
+ when the target of the jump is not reached by any other path. For
+ example, when CSE encounters an `if' statement with an `else'
+ clause, CSE will follow the jump when the condition tested is
+ false.
+
+`-fcse-skip-blocks'
+ This is similar to `-fcse-follow-jumps', but causes CSE to follow
+ jumps which conditionally skip over blocks. When CSE encounters a
+ simple `if' statement with no else clause, `-fcse-skip-blocks'
+ causes CSE to follow the jump around the body of the `if'.
+
+`-frerun-cse-after-loop'
+ Re-run common subexpression elimination after loop optimizations
+ has been performed.
+
+`-frerun-loop-opt'
+ Run the loop optimizer twice.
+
+`-fgcse'
+ Perform a global common subexpression elimination pass. This pass
+ also performs global constant and copy propagation.
+
+ _Note:_ When compiling a program using computed gotos, a GCC
+ extension, you may get better runtime performance if you disable
+ the global common subexpression elmination pass by adding
+ `-fno-gcse' to the command line.
+
+`-fgcse-lm'
+ When `-fgcse-lm' is enabled, global common subexpression
+ elimination will attempt to move loads which are only killed by
+ stores into themselves. This allows a loop containing a
+ load/store sequence to be changed to a load outside the loop, and
+ a copy/store within the loop.
+
+`-fgcse-sm'
+ When `-fgcse-sm' is enabled, A store motion pass is run after
+ global common subexpression elimination. This pass will attempt
+ to move stores out of loops. When used in conjunction with
+ `-fgcse-lm', loops containing a load/store sequence can be changed
+ to a load before the loop and a store after the loop.
+
+`-fdelete-null-pointer-checks'
+ Use global dataflow analysis to identify and eliminate useless
+ checks for null pointers. The compiler assumes that dereferencing
+ a null pointer would have halted the program. If a pointer is
+ checked after it has already been dereferenced, it cannot be null.
+
+ In some environments, this assumption is not true, and programs can
+ safely dereference null pointers. Use
+ `-fno-delete-null-pointer-checks' to disable this optimization for
+ programs which depend on that behavior.
+
+`-fexpensive-optimizations'
+ Perform a number of minor optimizations that are relatively
+ expensive.
+
+`-foptimize-register-move'
+`-fregmove'
+ Attempt to reassign register numbers in move instructions and as
+ operands of other simple instructions in order to maximize the
+ amount of register tying. This is especially helpful on machines
+ with two-operand instructions. GCC enables this optimization by
+ default with `-O2' or higher.
+
+ Note `-fregmove' and `-foptimize-register-move' are the same
+ optimization.
+
+`-fdelayed-branch'
+ If supported for the target machine, attempt to reorder
+ instructions to exploit instruction slots available after delayed
+ branch instructions.
+
+`-fschedule-insns'
+ If supported for the target machine, attempt to reorder
+ instructions to eliminate execution stalls due to required data
+ being unavailable. This helps machines that have slow floating
+ point or memory load instructions by allowing other instructions
+ to be issued until the result of the load or floating point
+ instruction is required.
+
+`-fschedule-insns2'
+ Similar to `-fschedule-insns', but requests an additional pass of
+ instruction scheduling after register allocation has been done.
+ This is especially useful on machines with a relatively small
+ number of registers and where memory load instructions take more
+ than one cycle.
+
+`-fno-sched-interblock'
+ Don't schedule instructions across basic blocks. This is normally
+ enabled by default when scheduling before register allocation, i.e.
+ with `-fschedule-insns' or at `-O2' or higher.
+
+`-fno-sched-spec'
+ Don't allow speculative motion of non-load instructions. This is
+ normally enabled by default when scheduling before register
+ allocation, i.e. with `-fschedule-insns' or at `-O2' or higher.
+
+`-fsched-spec-load'
+ Allow speculative motion of some load instructions. This only
+ makes sense when scheduling before register allocation, i.e. with
+ `-fschedule-insns' or at `-O2' or higher.
+
+`-fsched-spec-load-dangerous'
+ Allow speculative motion of more load instructions. This only
+ makes sense when scheduling before register allocation, i.e. with
+ `-fschedule-insns' or at `-O2' or higher.
+
+`-ffunction-sections'
+`-fdata-sections'
+ Place each function or data item into its own section in the output
+ file if the target supports arbitrary sections. The name of the
+ function or the name of the data item determines the section's name
+ in the output file.
+
+ Use these options on systems where the linker can perform
+ optimizations 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'.
+
+`-fcaller-saves'
+ Enable values to be allocated in registers that will be clobbered
+ by function calls, by emitting extra instructions to save and
+ restore the registers around such calls. Such allocation is done
+ only when it seems to result in better code than would otherwise
+ be produced.
+
+ This option is always enabled by default on certain machines,
+ usually those which have no call-preserved registers to use
+ instead.
+
+ For all machines, optimization level 2 and higher enables this
+ flag by default.
+
+`-funroll-loops'
+ Unroll loops whose number of iterations can be determined at
+ compile time or upon entry to the loop. `-funroll-loops' implies
+ both `-fstrength-reduce' and `-frerun-cse-after-loop'. This
+ option makes code larger, and may or may not make it run faster.
+
+`-funroll-all-loops'
+ Unroll all loops, even if their number of iterations is uncertain
+ when the loop is entered. This usually makes programs run more
+ slowly. `-funroll-all-loops' implies the same options as
+ `-funroll-loops',
+
+`-fprefetch-loop-arrays'
+ If supported by the target machine, generate instructions to
+ prefetch memory to improve the performance of loops that access
+ large arrays.
+
+`-fmove-all-movables'
+ Forces all invariant computations in loops to be moved outside the
+ loop.
+
+`-freduce-all-givs'
+ Forces all general-induction variables in loops to be
+ strength-reduced.
+
+ _Note:_ When compiling programs written in Fortran,
+ `-fmove-all-movables' and `-freduce-all-givs' are enabled by
+ default when you use the optimizer.
+
+ These options may generate better or worse code; results are highly
+ dependent on the structure of loops within the source code.
+
+ These two options are intended to be removed someday, once they
+ have helped determine the efficacy of various approaches to
+ improving loop optimizations.
+
+ Please let us (<gcc@gcc.gnu.org> and <fortran@gnu.org>) know how
+ use of these options affects the performance of your production
+ code. We're very interested in code that runs _slower_ when these
+ options are _enabled_.
+
+`-fno-peephole'
+`-fno-peephole2'
+ Disable any machine-specific peephole optimizations. The
+ difference 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.
+
+`-fbranch-probabilities'
+ After running a program compiled with `-fprofile-arcs' (*note
+ Options for Debugging Your Program or `gcc': Debugging Options.),
+ you can compile 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_EXEC_COUNT' note on
+ the first instruction of each basic block, and a `REG_BR_PROB'
+ note on each `JUMP_INSN' and `CALL_INSN'. These can be used to
+ improve optimization. Currently, they are only used in one place:
+ in `reorg.c', 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.
+
+`-fno-guess-branch-probability'
+ Do not guess branch probabilities using a randomized model.
+
+ Sometimes gcc will opt to use a randomized model to guess branch
+ probabilities, when none are available from either profiling
+ feedback (`-fprofile-arcs') or `__builtin_expect'. This means that
+ different runs of the compiler on the same program may produce
+ different object code.
+
+ In a hard real-time system, people don't want different runs of the
+ compiler to produce code that has different behavior; minimizing
+ non-determinism is of paramount import. This switch allows users
+ to reduce non-determinism, possibly at the expense of inferior
+ optimization.
+
+`-fstrict-aliasing'
+ Allows the compiler to assume the strictest aliasing rules
+ applicable to the language being compiled. For C (and C++), this
+ activates optimizations based on the type of expressions. In
+ particular, an object of one type is assumed never to reside at
+ the same address as an object of a different type, unless the
+ types are almost the same. For example, an `unsigned int' can
+ 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
+ memory 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
+ analysis should define a function that computes, given an `tree'
+ node, an alias set for the node. Nodes in different alias sets
+ are not allowed to alias. For an example, see the C front-end
+ function `c_get_alias_set'.
+
+`-falign-functions'
+`-falign-functions=N'
+ Align the start of functions to the next power-of-two greater than
+ N, skipping up to N bytes. For instance, `-falign-functions=32'
+ aligns functions to the next 32-byte boundary, but
+ `-falign-functions=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.
+
+`-falign-labels'
+`-falign-labels=N'
+ Align all branch targets to a power-of-two boundary, skipping up to
+ N bytes like `-falign-functions'. This option can easily make
+ code slower, because it must insert dummy operations for when the
+ branch target is reached in the usual flow of the code.
+
+ If `-falign-loops' or `-falign-jumps' are applicable and are
+ greater than this value, then their values are used instead.
+
+ If N is not specified, use a machine-dependent default which is
+ very likely to be `1', meaning no alignment.
+
+`-falign-loops'
+`-falign-loops=N'
+ Align loops to a power-of-two boundary, skipping up to N bytes
+ like `-falign-functions'. The hope is that the loop will be
+ executed many times, which will make up for any execution of the
+ dummy operations.
+
+ If N is not specified, use a machine-dependent default.
+
+`-falign-jumps'
+`-falign-jumps=N'
+ Align branch targets to a power-of-two boundary, for branch targets
+ where the targets can only be reached by jumping, skipping up to N
+ bytes like `-falign-functions'. In this case, no dummy operations
+ need be executed.
+
+ If N is not specified, use a machine-dependent default.
+
+`-fssa'
+ Perform optimizations in static single assignment form. Each
+ function's flow graph is translated into SSA form, optimizations
+ are performed, and the flow graph is translated back from SSA
+ form. Users should not specify this option, since it is not yet
+ ready for production use.
+
+`-fssa-ccp'
+ Perform Sparse Conditional Constant Propagation in SSA form.
+ Requires `-fssa'. Like `-fssa', this is an experimental feature.
+
+`-fssa-dce'
+ Perform aggressive dead-code elimination in SSA form. Requires
+ `-fssa'. Like `-fssa', this is an experimental feature.
+
+`-fsingle-precision-constant'
+ Treat floating point constant as single precision constant instead
+ of implicitly converting it to double precision constant.
+
+`-frename-registers'
+ Attempt to avoid false dependencies in scheduled code by making use
+ of registers left over after register allocation. This
+ optimization will most benefit processors with lots of registers.
+ It can, however, make debugging impossible, since variables will
+ no longer stay in a "home register".
+
+`-fno-cprop-registers'
+ After register allocation and post-register allocation instruction
+ splitting, we perform a copy-propagation pass to try to reduce
+ scheduling dependencies and occasionally eliminate the copy.
+
+`--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
+ functions that contain more that a certain number of instructions.
+ You can control some of these constants on the command-line using
+ the `--param' option.
+
+ In each case, the VALUE is an integer. The allowable choices for
+ NAME are given in the following table:
+
+ `max-delay-slot-insn-search'
+ The maximum number of instructions to consider when looking
+ for an instruction to fill a delay slot. If more than this
+ arbitrary 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 executable run time.
+
+ `max-delay-slot-live-search'
+ When trying to fill delay slots, the maximum number of
+ instructions to consider when searching for a block with
+ valid live register information. Increasing this arbitrarily
+ chosen value means more aggressive optimization, increasing
+ the compile time. This parameter should be removed when the
+ delay slot code is rewritten to maintain the control-flow
+ graph.
+
+ `max-gcse-memory'
+ The approximate maximum amount of memory that will be
+ allocated in order to perform the global common subexpression
+ elimination optimization. If more memory than specified is
+ required, the optimization will not be done.
+
+ `max-gcse-passes'
+ The maximum number of passes of GCSE to run.
+
+ `max-pending-list-length'
+ The maximum number of pending dependencies scheduling will
+ allow before flushing the current state and starting over.
+ Large functions with few branches or calls can create
+ excessively large lists which needlessly consume memory and
+ resources.
+
+ `max-inline-insns'
+ If an function contains more than this many instructions, it
+ will not be inlined. This option is precisely equivalent to
+ `-finline-limit'.
+
+
+\1f
+File: gcc.info, Node: Preprocessor Options, Next: Assembler Options, Prev: Optimize Options, Up: Invoking GCC
+
+3.11 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 handle 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 processed after all `-D' and `-U' options.
+
+`-U NAME'
+ Cancel any previous definition of NAME, either built in or
+ provided with a `-D' option.
+
+`-undef'
+ Do not predefine any system-specific macros. The common predefined
+ macros remain defined.
+
+`-I DIR'
+ Add the directory DIR to the list of directories to be searched
+ for header files. Directories named by `-I' are searched before
+ the standard system include directories.
+
+ It is dangerous to specify a standard system include directory in
+ an `-I' option. This defeats the special treatment of system
+ headers . It can also defeat the repairs to buggy system headers
+ which GCC makes when it is installed.
+
+`-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
+ interpretation of a second non-option argument, so you must use
+ `-o' to specify the output file.
+
+`-Wall'
+ Turns on all optional warnings which are desirable for normal
+ code. At present this is `-Wcomment' and `-Wtrigraphs'. Note that
+ many of the preprocessor's warnings are on by default and have no
+ options to control them.
+
+`-Wcomment'
+`-Wcomments'
+ Warn whenever a comment-start sequence `/*' appears in a `/*'
+ comment, or whenever a backslash-newline appears in a `//' comment.
+ (Both forms have the same effect.)
+
+`-Wtrigraphs'
+ Warn if any trigraphs are encountered. This option used to take
+ effect only if `-trigraphs' was also specified, but now works
+ independently. Warnings are not given for trigraphs within
+ comments, as they do not affect the meaning of the program.
+
+`-Wtraditional'
+ Warn about certain constructs that behave differently in
+ traditional and ISO C. Also warn about ISO C constructs that have
+ no traditional C equivalent, and problematic constructs which
+ should be avoided.
+
+`-Wimport'
+ Warn the first time `#import' is used.
+
+`-Wundef'
+ Warn whenever an identifier which is not a macro is encountered in
+ an `#if' directive, outside of `defined'. Such identifiers are
+ replaced with zero.
+
+`-Werror'
+ Make all warnings into hard errors. Source code which triggers
+ warnings will be rejected.
+
+`-Wsystem-headers'
+ Issue warnings for code in system headers. These are normally
+ unhelpful in finding bugs in your own code, therefore suppressed.
+ If you are responsible for the system library, you may want to see
+ them.
+
+`-w'
+ Suppress all warnings, including those which GNU CPP issues by
+ default.
+
+`-pedantic'
+ Issue all the mandatory diagnostics listed in the C standard.
+ Some of them are left out by default, since they trigger
+ frequently on harmless code.
+
+`-pedantic-errors'
+ Issue all the mandatory diagnostics, and make all mandatory
+ diagnostics 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' (*note DEPENDENCIES_OUTPUT::). Debug output
+ will still be sent to the regular output stream as normal.
+
+ Passing `-M' to the driver implies `-E'.
+
+`-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'
+ When used with `-M' or `-MM', specifies a file to write the
+ dependencies to. If no `-MF' switch is given the preprocessor
+ sends the rules to the same place it would have sent preprocessed
+ output.
+
+ When used with the driver options `-MD' or `-MMD', `-MF' overrides
+ the default dependency output file.
+
+`-MG'
+ When used with `-M' or `-MM', `-MG' says to treat missing header
+ files as generated files and assume they live in the same
+ directory as the source file. It suppresses preprocessed output,
+ as a missing header file is ordinarily an error.
+
+ This feature is used in automatic updating of makefiles.
+
+`-MP'
+ This option instructs CPP to add a phony target for each dependency
+ other than the main file, causing each to depend on nothing. These
+ dummy rules work around errors `make' gives if you remove header
+ files without updating the `Makefile' to match.
+
+ This is typical output:
+
+ test.o: test.c test.h
+
+ test.h:
+
+`-MT TARGET'
+ Change the target of the rule emitted by dependency generation. By
+ default CPP takes the name of the main input file, including any
+ path, deletes any file suffix such as `.c', and appends the
+ platform's usual object suffix. The result is the target.
+
+ An `-MT' option will set the target to be exactly the string you
+ specify. If you want multiple targets, you can specify them as a
+ single argument to `-MT', or use multiple `-MT' options.
+
+ For example, `-MT '$(objpfx)foo.o'' might give
+
+ $(objpfx)foo.o: foo.c
+
+`-MQ TARGET'
+ Same as `-MT', but it quotes any characters which are special to
+ Make. `-MQ '$(objpfx)foo.o'' gives
+
+ $$(objpfx)foo.o: foo.c
+
+ The default target is automatically quoted, as if it were given
+ with `-MQ'.
+
+`-MD'
+ `-MD' is equivalent to `-M -MF FILE', except that `-E' is not
+ implied. The driver determines FILE based on whether an `-o'
+ option is given. If it is, the driver uses its argument but with
+ a suffix of `.d', otherwise it take the basename of the input file
+ and applies a `.d' suffix.
+
+ If `-MD' is used in conjunction with `-E', any `-o' switch is
+ understood to specify the dependency output file (but *note
+ -MF::), but if used without `-E', each `-o' is understood to
+ specify a target object file.
+
+ Since `-E' is not implied, `-MD' can be used to generate a
+ dependency output file as a side-effect of the compilation process.
+
+`-MMD'
+ Like `-MD' except mention only user header files, not system
+ -header files.
+
+`-x c'
+`-x c++'
+`-x objective-c'
+`-x assembler-with-cpp'
+ Specify the source language: C, C++, Objective-C, or assembly.
+ This has nothing to do with standards conformance or extensions;
+ it merely selects which base syntax to expect. If you give none
+ of these options, cpp will deduce the language from the extension
+ of the source file: `.c', `.cc', `.m', or `.S'. Some other common
+ extensions for C++ and assembly are also recognized. If cpp does
+ not recognize the extension, it will treat the file as C; this is
+ the most generic mode.
+
+ *Note_* Previous versions of cpp accepted a `-lang' option which
+ selected both the language and the standards conformance level.
+ This option has been removed, because it conflicts with the `-l'
+ option.
+
+`-std=STANDARD'
+`-ansi'
+ Specify the standard to which the code should conform. Currently
+ cpp only knows about the standards for C; other language standards
+ will be added in the future.
+
+ STANDARD may be one of:
+ `iso9899:1990'
+ `c89'
+ The ISO C standard from 1990. `c89' is the customary
+ shorthand for this version of the standard.
+
+ The `-ansi' option is equivalent to `-std=c89'.
+
+ `iso9899:199409'
+ The 1990 C standard, as amended in 1994.
+
+ `iso9899:1999'
+ `c99'
+ `iso9899:199x'
+ `c9x'
+ The revised ISO C standard, published in December 1999.
+ Before publication, this was known as C9X.
+
+ `gnu89'
+ The 1990 C standard plus GNU extensions. This is the default.
+
+ `gnu99'
+ `gnu9x'
+ The 1999 C standard plus GNU extensions.
+
+`-I-'
+ Split the include path. Any directories specified with `-I'
+ options before `-I-' are searched only for headers requested with
+ `#include "FILE"'; they are not searched for `#include <FILE>'.
+ If additional directories are specified with `-I' options after
+ the `-I-', those directories are searched for all `#include'
+ directives.
+
+ In addition, `-I-' inhibits the use of the directory of the current
+ file directory as the first search directory for `#include "FILE"'.
+
+`-nostdinc'
+ Do not search the standard system directories for header files.
+ Only the directories you have specified with `-I' options (and the
+ directory of the current file, if appropriate) are searched.
+
+`-nostdinc++'
+ Do not search for header files in the C++-specific standard
+ directories, 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
+ directory 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
+ specified 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.
+ `-iwithprefixbefore' puts it in the same place `-I' would;
+ `-iwithprefix' puts it where `-idirafter' would.
+
+ Use of these options is discouraged.
+
+`-isystem DIR'
+ Search DIR for header files, after all directories specified by
+ `-I' but before the standard system directories. Mark it as a
+ system directory, so that it gets the same special treatment as is
+ applied to the standard system directories.
+
+`-fpreprocessed'
+ Indicate to the preprocessor that the input file has already been
+ preprocessed. This suppresses things like macro expansion,
+ trigraph conversion, escaped newline splicing, and processing of
+ most directives. The preprocessor still recognizes and removes
+ comments, so that you can pass a file preprocessed with `-C' to
+ the compiler without problems. In this mode the integrated
+ preprocessor is little more than a tokenizer for the front ends.
+
+ `-fpreprocessed' is implicit if the input file has one of the
+ extensions `.i', `.ii' or `.mi'. These are the extensions that
+ GCC uses for preprocessed files created by `-save-temps'.
+
+`-ftabstop=WIDTH'
+ Set the distance between tab stops. This helps the preprocessor
+ report correct column numbers in warnings or errors, even if tabs
+ appear on the line. If the value is less than 1 or greater than
+ 100, the option is ignored. The default is 8.
+
+`-fno-show-column'
+ Do not print column numbers in diagnostics. This may be necessary
+ if diagnostics are being scanned by a program that does not
+ understand the column numbers, such as `dejagnu'.
+
+`-A PREDICATE=ANSWER'
+ Make an assertion with the predicate PREDICATE and answer ANSWER.
+ This form is preferred to the older form `-A PREDICATE(ANSWER)',
+ which is still supported, because it does not use shell special
+ characters.
+
+`-A -PREDICATE=ANSWER'
+ Cancel an assertion with the predicate PREDICATE and answer ANSWER.
+
+`-A-'
+ Cancel all predefined assertions and all assertions preceding it on
+ the command line. Also, undefine all predefined macros and all
+ macros preceding it on the command line. (This is a historical
+ wart and may change in the future.)
+
+`-dCHARS'
+ CHARS is a sequence of one or more of the following characters,
+ and must not be preceded by a space. Other characters are
+ interpreted by the compiler proper, or reserved for future
+ versions of GCC, and so are silently ignored. If you specify
+ characters whose behavior conflicts, the result is undefined.
+
+ `M'
+ Instead of the normal output, generate a list of `#define'
+ directives 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
+ predefined 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
+ preprocessing.
+
+`-P'
+ Inhibit generation of linemarkers in the output from the
+ preprocessor. This might be useful when running the preprocessor
+ on something that is not C code, and will be sent to a program
+ 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
+ ordinary source line, since the first token on the line is no
+ longer a `#'.
+
+`-gcc'
+ Define the macros __GNUC__, __GNUC_MINOR__ and
+ __GNUC_PATCHLEVEL__. These are defined automatically when you use
+ `gcc -E'; you can turn them off in that case with `-no-gcc'.
+
+`-traditional'
+ Try to imitate the behavior of old-fashioned C, as opposed to ISO
+ C.
+
+`-trigraphs'
+ Process trigraph sequences. These are three-character sequences,
+ all starting with `??', that are defined by ISO C to stand for
+ single characters. For example, `??/' stands for `\', so `'??/n''
+ is a character constant for a newline. By default, GCC ignores
+ trigraphs, but in standard-conforming modes it converts them. See
+ the `-std' and `-ansi' options.
+
+ The nine trigraphs and their replacements are
+
+ Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??-
+ Replacement: [ ] { } # \ ^ | ~
+
+`-remap'
+ Enable special code to work around file systems which only permit
+ very short file names, such as MS-DOS.
+
+`-$'
+ Forbid the use of `$' in identifiers. The C standard allows
+ implementations to define extra characters that can appear in
+ identifiers. By default GNU CPP permits `$', a common extension.
+
+`-h'
+`--help'
+`--target-help'
+ Print text describing all the command line options instead of
+ preprocessing 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
+ normal activities. Each name is indented to show how deep in the
+ `#include' stack it is.
+
+`-version'
+`--version'
+ Print out GNU CPP's version number. With one dash, proceed to
+ preprocess as normal. With two dashes, exit immediately.
+
+\1f
+File: gcc.info, Node: Assembler Options, Next: Link Options, Prev: Preprocessor Options, Up: Invoking GCC
+
+3.12 Passing Options to the Assembler
+=====================================
+
+You can pass options to the assembler.
+
+`-Wa,OPTION'
+ Pass OPTION as an option to the assembler. If OPTION contains
+ commas, it is split into multiple options at the commas.
+
+\1f
+File: gcc.info, Node: Link Options, Next: Directory Options, Prev: Assembler Options, Up: Invoking GCC
+
+3.13 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.
+
+`OBJECT-FILE-NAME'
+ A file name that does not end in a special recognized suffix is
+ considered to name an object file or library. (Object files are
+ distinguished from libraries by the linker according to the file
+ contents.) If linking is done, these object files are used as
+ input to the linker.
+
+`-c'
+`-S'
+`-E'
+ If any of these options is used, then the linker is not run, and
+ object file names should not be used as arguments. *Note Overall
+ Options::.
+
+`-lLIBRARY'
+`-l LIBRARY'
+ Search the library named LIBRARY when linking. (The second
+ alternative with the library as a separate argument is only for
+ POSIX compliance and is not recommended.)
+
+ 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
+ directories 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
+ fashion. The only difference between using an `-l' option and
+ specifying a file name is that `-l' surrounds LIBRARY with `lib'
+ and `.a' and searches several directories.
+
+`-lobjc'
+ You need this special case of the `-l' option in order to link an
+ Objective-C program.
+
+`-nostartfiles'
+ Do not use the standard system startup files when linking. The
+ standard system libraries are used normally, unless `-nostdlib' or
+ `-nodefaultlibs' is used.
+
+`-nodefaultlibs'
+ Do not use the standard system libraries when linking. Only the
+ libraries you specify will be passed to the linker. The standard
+ startup files are used normally, unless `-nostartfiles' is used.
+ The compiler may generate calls to memcmp, memset, and memcpy for
+ 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.
+
+`-nostdlib'
+ Do not use the standard system startup files or libraries when
+ linking. No startup files and only the libraries you specify will
+ be passed to the linker. The compiler may generate calls to
+ memcmp, 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.
+
+ One of the standard libraries bypassed by `-nostdlib' and
+ `-nodefaultlibs' is `libgcc.a', a library of internal subroutines
+ that GCC uses to overcome shortcomings of particular machines, or
+ special needs for some languages. (*Note Interfacing to GCC
+ Output: (gccint)Interface, for more discussion of `libgcc.a'.) 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++
+ constructors will be called; *note `collect2': (gccint)Collect2.)
+
+`-s'
+ Remove all symbol table and relocation information from the
+ executable.
+
+`-static'
+ On systems that support dynamic linking, this prevents linking
+ with the shared libraries. On other systems, this option has no
+ effect.
+
+`-shared'
+ Produce a shared object which can then be linked with other
+ objects to form an executable. Not all systems support this
+ option. For predictable results, you must also specify the same
+ set of options that were used to generate code (`-fpic', `-fPIC',
+ or model suboptions) when you specify this option.(1)
+
+`-shared-libgcc'
+`-static-libgcc'
+ On systems that provide `libgcc' as a shared library, these options
+ force the use of either the shared or static version respectively.
+ If no shared version of `libgcc' was built when the compiler was
+ configured, these options have no effect.
+
+ There are several situations in which an application should use the
+ shared `libgcc' instead of the static version. The most common of
+ these is when the application wishes to throw and catch exceptions
+ across different shared libraries. In that case, each of the
+ libraries as well as the application itself should use the shared
+ `libgcc'.
+
+ Therefore, the G++ and GCJ drivers automatically add
+ `-shared-libgcc' whenever you build a shared library or a main
+ executable, because C++ and Java programs typically use
+ exceptions, so this is the right thing to do.
+
+ If, instead, you use the GCC driver to create shared libraries,
+ you may find that they will not always be linked with the shared
+ `libgcc'. If GCC finds, at its configuration time, that you have
+ a GNU linker that does not support option `--eh-frame-hdr', it
+ will link the shared version of `libgcc' into shared libraries by
+ default. Otherwise, it will take advantage of the linker and
+ optimize away the linking with the shared version of `libgcc',
+ linking with the static version of libgcc by default. This allows
+ exceptions to propagate through such shared libraries, without
+ incurring relocation costs at library load time.
+
+ However, if a library or main executable is supposed to throw or
+ catch exceptions, you must link it using the G++ or GCJ driver, as
+ appropriate for the languages used in the program, or using the
+ option `-shared-libgcc', such that it is linked with the shared
+ `libgcc'.
+
+`-symbolic'
+ Bind references to global symbols when building a shared object.
+ Warn about any unresolved references (unless overridden by the
+ link editor option `-Xlinker -z -Xlinker defs'). Only a few
+ systems support 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 recognize.
+
+ If you want to pass an option that takes an argument, you must use
+ `-Xlinker' twice, once for the option and once for the argument.
+ For example, to pass `-assert definitions', you must write
+ `-Xlinker -assert -Xlinker definitions'. It does not work to write
+ `-Xlinker "-assert definitions"', because this passes the entire
+ string as a single argument, which is not what the linker expects.
+
+`-Wl,OPTION'
+ Pass OPTION as an option to the linker. If OPTION contains
+ commas, it is split into multiple options at the commas.
+
+`-u SYMBOL'
+ Pretend the symbol SYMBOL is undefined, to force linking of
+ library modules to define it. You can use `-u' multiple times with
+ different symbols to force loading of additional library modules.
+
+ ---------- Footnotes ----------
+
+ (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.
+
+\1f
+File: gcc.info, Node: Directory Options, Next: Spec Files, Prev: Link Options, Up: Invoking GCC
+
+3.14 Options for Directory Search
+=================================
+
+These options specify directories to search for header files, for
+libraries and for parts of the compiler:
+
+`-IDIR'
+ Add the directory DIR to the head of the list of directories to be
+ searched for header files. This can be used to override a system
+ header file, substituting your own version, since these
+ directories are searched before the system header file
+ directories. However, you should not use this option to add
+ directories that contain vendor-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
+ inadvertantly 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
+ directory (where the current input file came from) as the first
+ search directory for `#include "FILE"'. There is no way to
+ override this effect of `-I-'. With `-I.' you can specify
+ searching the directory which was current when the compiler was
+ invoked. That is not exactly the same as what the preprocessor
+ does by default, but it is often satisfactory.
+
+ `-I-' does not inhibit the use of the standard system directories
+ for header files. Thus, `-I-' and `-nostdinc' are independent.
+
+`-LDIR'
+ Add directory DIR to the list of directories to be searched for
+ `-l'.
+
+`-BPREFIX'
+ This option specifies where to find the executables, libraries,
+ include files, and data files of the compiler itself.
+
+ The compiler driver program runs one or more of the subprograms
+ `cpp', `cc1', `as' and `ld'. It tries PREFIX as a prefix for each
+ program it tries to run, both with and without `MACHINE/VERSION/'
+ (*note Target Options::).
+
+ 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' environment 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
+ standard 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'. *Note Environment
+ Variables::.
+
+ 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 compiler.
+
+`-specs=FILE'
+ Process FILE after the compiler reads in the standard `specs'
+ file, in order to override the defaults that the `gcc' driver
+ program uses when determining what switches to pass to `cc1',
+ `cc1plus', `as', `ld', etc. More than one `-specs=FILE' can be
+ specified on the command line, and they are processed in order,
+ from left to right.
+
+\1f
+File: gcc.info, Node: Spec Files, Next: Target Options, Prev: Directory Options, Up: Invoking GCC
+
+3.15 Specifying subprocesses and the switches to pass to them
+=============================================================
+
+`gcc' is a driver program. It performs its job by invoking a sequence
+of other programs to do the work of compiling, assembling and linking.
+GCC interprets its command-line parameters and uses these to deduce
+which programs it should invoke, and which command-line options it
+ought to place on their command lines. This behavior is controlled by
+"spec strings". In most cases there is one spec string for each
+program that GCC can invoke, but a few programs have multiple spec
+strings to control their behavior. The spec strings built into GCC can
+be overridden by using the `-specs=' command-line switch to specify a
+spec file.
+
+ "Spec files" are plaintext files that are used to construct spec
+strings. They consist of a sequence of directives separated by blank
+lines. The type of directive is determined by the first non-whitespace
+character on the line and it can be one of the following:
+
+`%COMMAND'
+ Issues a COMMAND to the spec file processor. The commands that can
+ appear here are:
+
+ `%include <FILE>'
+ Search for FILE and insert its text at the current point in
+ the specs file.
+
+ `%include_noerr <FILE>'
+ Just like `%include', but do not generate an error message if
+ the include file cannot be found.
+
+ `%rename OLD_NAME NEW_NAME'
+ Rename the spec string OLD_NAME to NEW_NAME.
+
+
+`*[SPEC_NAME]:'
+ This tells the compiler to create, override or delete the named
+ spec string. All lines after this directive up to the next
+ directive or blank line are considered to be the text for the spec
+ string. If this results in an empty string then the spec will be
+ deleted. (Or, if the spec did not exist, then nothing will
+ happened.) Otherwise, if the spec does not currently exist a new
+ spec will be created. If the spec does exist then its contents
+ will be overridden by the text of this directive, unless the first
+ character of that text is the `+' character, in which case the
+ text will be appended to the spec.
+
+`[SUFFIX]:'
+ Creates a new `[SUFFIX] spec' pair. All lines after this directive
+ and up to the next directive or blank line are considered to make
+ up the spec string for the indicated suffix. When the compiler
+ encounters an input file with the named suffix, it will processes
+ the spec string in order to work out how to compile that file.
+ For example:
+
+ .ZZ:
+ z-compile -input %i
+
+ This says that any input file whose name ends in `.ZZ' should be
+ passed to the program `z-compile', which should be invoked with the
+ command-line switch `-input' and with the result of performing the
+ `%i' substitution. (See below.)
+
+ As an alternative to providing a spec string, the text that
+ follows a suffix directive can be one of the following:
+
+ `@LANGUAGE'
+ This says that the suffix is an alias for a known LANGUAGE.
+ This is similar to using the `-x' command-line switch to GCC
+ to specify a language explicitly. For example:
+
+ .ZZ:
+ @c++
+
+ Says that .ZZ files are, in fact, C++ source files.
+
+ `#NAME'
+ This causes an error messages saying:
+
+ NAME compiler not installed on this system.
+
+ GCC already has an extensive list of suffixes built into it. This
+ directive will add an entry to the end of the list of suffixes, but
+ since the list is searched from the end backwards, it is
+ effectively possible to override earlier entries using this
+ technique.
+
+
+ GCC has the following spec strings built into it. Spec files can
+override these strings or create their own. Note that individual
+targets can also add their own spec strings to this list.
+
+ asm Options to pass to the assembler
+ asm_final Options to pass to the assembler post-processor
+ cpp Options to pass to the C preprocessor
+ cc1 Options to pass to the C compiler
+ cc1plus Options to pass to the C++ compiler
+ endfile Object files to include at the end of the link
+ link Options to pass to the linker
+ lib Libraries to include on the command line to the linker
+ libgcc Decides which GCC support library to pass to the linker
+ linker Sets the name of the linker
+ predefines Defines to be passed to the C preprocessor
+ signed_char Defines to pass to CPP to say whether `char' is signed
+ by default
+ startfile Object files to include at the start of the link
+
+ Here is a small example of a spec file:
+
+ %rename lib old_lib
+
+ *lib:
+ --start-group -lgcc -lc -leval1 --end-group %(old_lib)
+
+ This example renames the spec called `lib' to `old_lib' and then
+overrides the previous definition of `lib' with a new one. The new
+definition adds in some extra command-line options before including the
+text of the old definition.
+
+ "Spec strings" are a list of command-line options to be passed to
+their corresponding program. In addition, the spec strings can contain
+`%'-prefixed sequences to substitute variable text or to conditionally
+insert text into the command line. Using these constructs it is
+possible to generate quite complex command lines.
+
+ Here is a table of all defined `%'-sequences for spec strings. Note
+that spaces are not generated automatically around the results of
+expanding these sequences. Therefore you can concatenate them together
+or combine them with constant text in a single argument.
+
+`%%'
+ Substitute one `%' into the program name or argument.
+
+`%i'
+ Substitute the name of the input file being processed.
+
+`%b'
+ Substitute the basename of the input file being processed. This
+ is the substring up to (and not including) the last period and not
+ including the directory.
+
+`%B'
+ This is the same as `%b', but include the file suffix (text after
+ the last period).
+
+`%d'
+ Marks the argument containing or following the `%d' as a temporary
+ file name, so that that file will be deleted if GCC exits
+ successfully. Unlike `%g', this contributes no text to the
+ argument.
+
+`%gSUFFIX'
+ Substitute a file name that has suffix SUFFIX and is chosen once
+ per compilation, and mark the argument in the same way as `%d'.
+ To reduce exposure to denial-of-service attacks, the file name is
+ now chosen in a way that is hard to predict even when previously
+ chosen file names are known. For example, `%g.s ... %g.o ... %g.s'
+ might turn into `ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s'. SUFFIX
+ matches the regexp `[.A-Za-z]*' or the special string `%O', which
+ is treated exactly as if `%O' had been preprocessed. Previously,
+ `%g' was simply substituted with a file name chosen once per
+ compilation, without regard to any appended suffix (which was
+ therefore treated just like ordinary text), making such attacks
+ more likely to succeed.
+
+`%uSUFFIX'
+ Like `%g', but generates a new temporary file name even if
+ `%uSUFFIX' was already seen.
+
+`%USUFFIX'
+ Substitutes the last file name generated with `%uSUFFIX',
+ generating a new one if there is no such last file name. In the
+ absence of any `%uSUFFIX', this is just like `%gSUFFIX', except
+ they don't share the same suffix _space_, so `%g.s ... %U.s ...
+ %g.s ... %U.s' would involve the generation of two distinct file
+ names, one for each `%g.s' and another for each `%U.s'.
+ Previously, `%U' was simply substituted with a file name chosen
+ for the previous `%u', without regard to any appended suffix.
+
+`%jSUFFIX'
+ Substitutes the name of the `HOST_BIT_BUCKET', if any, and if it is
+ writable, and if save-temps is off; otherwise, substitute the name
+ of a temporary file, just like `%u'. This temporary file is not
+ meant for communication between processes, but rather as a junk
+ disposal mechanism.
+
+`%.SUFFIX'
+ Substitutes .SUFFIX for the suffixes of a matched switch's args
+ when it is subsequently output with `%*'. SUFFIX is terminated by
+ the next space or %.
+
+`%w'
+ Marks the argument containing or following the `%w' as the
+ designated output file of this compilation. This puts the argument
+ into the sequence of arguments that `%o' will substitute later.
+
+`%o'
+ Substitutes the names of all the output files, with spaces
+ automatically placed around them. You should write spaces around
+ the `%o' as well or the results are undefined. `%o' is for use in
+ the specs for running the linker. Input files whose names have no
+ recognized suffix are not compiled at all, but they are included
+ among the output files, so they will be linked.
+
+`%O'
+ Substitutes the suffix for object files. Note that this is
+ handled specially when it immediately follows `%g, %u, or %U',
+ because of the need for those to form complete file names. The
+ handling is such that `%O' is treated exactly as if it had already
+ been substituted, except that `%g, %u, and %U' do not currently
+ support additional SUFFIX characters following `%O' as they would
+ following, for example, `.o'.
+
+`%p'
+ Substitutes the standard macro predefinitions for the current
+ target machine. Use this when running `cpp'.
+
+`%P'
+ Like `%p', but puts `__' before and after the name of each
+ predefined macro, except for macros that start with `__' or with
+ `_L', where L is an uppercase letter. This is for ISO C.
+
+`%I'
+ Substitute a `-iprefix' option made from `GCC_EXEC_PREFIX'.
+
+`%s'
+ Current argument is the name of a library or startup file of some
+ sort. Search for that file in a standard list of directories and
+ substitute the full name found.
+
+`%eSTR'
+ Print STR as an error message. STR is terminated by a newline.
+ Use this when inconsistent options are detected.
+
+`%|'
+ Output `-' if the input for the current command is coming from a
+ pipe.
+
+`%(NAME)'
+ Substitute the contents of spec string NAME at this point.
+
+`%[NAME]'
+ Like `%(...)' but put `__' around `-D' arguments.
+
+`%x{OPTION}'
+ Accumulate an option for `%X'.
+
+`%X'
+ Output the accumulated linker options specified by `-Wl' or a `%x'
+ spec string.
+
+`%Y'
+ Output the accumulated assembler options specified by `-Wa'.
+
+`%Z'
+ Output the accumulated preprocessor options specified by `-Wp'.
+
+`%v1'
+ Substitute the major version number of GCC. (For version 2.9.5,
+ this is 2.)
+
+`%v2'
+ Substitute the minor version number of GCC. (For version 2.9.5,
+ this is 9.)
+
+`%v3'
+ Substitute the patch level number of GCC. (For version 2.9.5,
+ this is 5.)
+
+`%a'
+ Process the `asm' spec. This is used to compute the switches to
+ be passed to the assembler.
+
+`%A'
+ Process the `asm_final' spec. This is a spec string for passing
+ switches to an assembler post-processor, if such a program is
+ needed.
+
+`%l'
+ Process the `link' spec. This is the spec for computing the
+ command line passed to the linker. Typically it will make use of
+ the `%L %G %S %D and %E' sequences.
+
+`%D'
+ Dump out a `-L' option for each directory that GCC believes might
+ contain startup files. If the target supports multilibs then the
+ current multilib directory will be prepended to each of these
+ paths.
+
+`%M'
+ Output the multilib directory with directory separators replaced
+ with `_'. If multilib directories are not set, or the multilib
+ directory is `.' then this option emits nothing.
+
+`%L'
+ Process the `lib' spec. This is a spec string for deciding which
+ libraries should be included on the command line to the linker.
+
+`%G'
+ Process the `libgcc' spec. This is a spec string for deciding
+ which GCC support library should be included on the command line
+ to the linker.
+
+`%S'
+ Process the `startfile' spec. This is a spec for deciding which
+ object files should be the first ones passed to the linker.
+ Typically this might be a file named `crt0.o'.
+
+`%E'
+ Process the `endfile' spec. This is a spec string that specifies
+ the last object files that will be passed to the linker.
+
+`%C'
+ Process the `cpp' spec. This is used to construct the arguments
+ to be passed to the C preprocessor.
+
+`%c'
+ Process the `signed_char' spec. This is intended to be used to
+ tell cpp whether a char is signed. It typically has the
+ definition:
+ %{funsigned-char:-D__CHAR_UNSIGNED__}
+
+`%1'
+ Process the `cc1' spec. This is used to construct the options to
+ be passed to the actual C compiler (`cc1').
+
+`%2'
+ Process the `cc1plus' spec. This is used to construct the options
+ to be passed to the actual C++ compiler (`cc1plus').
+
+`%*'
+ Substitute the variable part of a matched option. See below.
+ Note that each comma in the substituted string is replaced by a
+ single space.
+
+`%{`S'}'
+ Substitutes the `-S' switch, if that switch was given to GCC. If
+ that switch was not specified, this substitutes nothing. Note that
+ the leading dash is omitted when specifying this option, and it is
+ automatically inserted if the substitution is performed. Thus the
+ spec string `%{foo}' would match the command-line option `-foo'
+ and would output the command line option `-foo'.
+
+`%W{`S'}'
+ Like %{`S'} but mark last argument supplied within as a file to be
+ deleted on failure.
+
+`%{`S'*}'
+ Substitutes all the switches specified to GCC whose names start
+ with `-S', but which also take an argument. This is used for
+ switches like `-o', `-D', `-I', etc. GCC considers `-o foo' as
+ being one switch whose names starts with `o'. %{o*} would
+ substitute this text, including the space. Thus two arguments
+ would be generated.
+
+`%{^`S'*}'
+ Like %{`S'*}, but don't put a blank between a switch and its
+ argument. Thus %{^o*} would only generate one argument, not two.
+
+`%{`S'*&`T'*}'
+ Like %{`S'*}, but preserve order of `S' and `T' options (the order
+ of `S' and `T' in the spec is not significant). There can be any
+ number of ampersand-separated variables; for each the wild card is
+ optional. Useful for CPP as `%{D*&U*&A*}'.
+
+`%{<`S'}'
+ Remove all occurrences of `-S' from the command line. Note--this
+ command is position dependent. `%' commands in the spec string
+ before this option will see `-S', `%' commands in the spec string
+ after this option will not.
+
+`%{`S'*:`X'}'
+ Substitutes `X' if one or more switches whose names start with
+ `-S' are specified to GCC. Note that the tail part of the `-S'
+ option (i.e. the part matched by the `*') will be substituted for
+ each occurrence of `%*' within `X'.
+
+`%{`S':`X'}'
+ Substitutes `X', but only if the `-S' switch was given to GCC.
+
+`%{!`S':`X'}'
+ Substitutes `X', but only if the `-S' switch was _not_ given to
+ GCC.
+
+`%{|`S':`X'}'
+ Like %{`S':`X'}, but if no `S' switch, substitute `-'.
+
+`%{|!`S':`X'}'
+ Like %{!`S':`X'}, but if there is an `S' switch, substitute `-'.
+
+`%{.`S':`X'}'
+ Substitutes `X', but only if processing a file with suffix `S'.
+
+`%{!.`S':`X'}'
+ Substitutes `X', but only if _not_ processing a file with suffix
+ `S'.
+
+`%{`S'|`P':`X'}'
+ Substitutes `X' if either `-S' or `-P' was given to GCC. This may
+ be combined with `!' and `.' sequences as well, although they have
+ a stronger binding than the `|'. For example a spec string like
+ this:
+
+ %{.c:-foo} %{!.c:-bar} %{.c|d:-baz} %{!.c|d:-boggle}
+
+ will output the following command-line options from the following
+ input command-line options:
+
+ fred.c -foo -baz
+ jim.d -bar -boggle
+ -d fred.c -foo -baz -boggle
+ -d jim.d -bar -baz -boggle
+
+
+ The conditional text `X' in a %{`S':`X'} or %{!`S':`X'} construct
+may contain other nested `%' constructs or spaces, or even newlines.
+They are processed as usual, as described above.
+
+ The `-O', `-f', `-m', and `-W' switches are handled specifically in
+these constructs. If another value of `-O' or the negated form of a
+`-f', `-m', or `-W' switch is found later in the command line, the
+earlier switch value is ignored, except with {`S'*} where `S' is just
+one letter, which passes all matching options.
+
+ The character `|' at the beginning of the predicate text is used to
+indicate that a command should be piped to the following command, but
+only if `-pipe' is specified.
+
+ It is built into GCC which switches take arguments and which do not.
+(You might think it would be useful to generalize this to allow each
+compiler's spec to say which switches take arguments. But this cannot
+be done in a consistent fashion. GCC cannot even decide which input
+files have been specified without knowing which switches take arguments,
+and it must know which input files to compile in order to tell which
+compilers to run).
+
+ GCC also knows implicitly that arguments starting in `-l' are to be
+treated as compiler output files, and passed to the linker in their
+proper position among the other output files.
+
+\1f
+File: gcc.info, Node: Target Options, Next: Submodel Options, Prev: Spec Files, Up: Invoking GCC
+
+3.16 Specifying Target Machine and Compiler Version
+===================================================
+
+By default, GCC compiles code for the same type of machine that you are
+using. However, it can also be installed as a cross-compiler, to
+compile for some other type of machine. In fact, several different
+configurations of GCC, for different target machines, can be installed
+side by side. Then you specify which one to use with the `-b' option.
+
+ In addition, older and newer versions of GCC can be installed side
+by side. One of them (probably the newest) will be the default, but
+you may sometimes wish to use another.
+
+`-b MACHINE'
+ The argument MACHINE specifies the target machine for compilation.
+ This is useful when you have installed GCC as a cross-compiler.
+
+ The value to use for MACHINE is the same as was specified as the
+ machine type when configuring GCC as a cross-compiler. For
+ example, if a cross-compiler was configured with `configure
+ i386v', meaning to compile for an 80386 running System V, then you
+ would specify `-b i386v' to run that cross compiler.
+
+ When you do not specify `-b', it normally means to compile for the
+ same type of machine that you are using.
+
+`-V VERSION'
+ The argument VERSION specifies which version of GCC to run. This
+ is useful when multiple versions are installed. For example,
+ VERSION might be `2.0', meaning to run GCC version 2.0.
+
+ The default version, when you do not specify `-V', is the last
+ version of GCC that you installed.
+
+ The `-b' and `-V' options actually work by controlling part of the
+file name used for the executable files and libraries used for
+compilation. A given version of GCC, for a given target machine, is
+normally kept in the directory `/usr/local/lib/gcc-lib/MACHINE/VERSION'.
+
+ Thus, sites can customize the effect of `-b' or `-V' either by
+changing the names of these directories or adding alternate names (or
+symbolic links). If in directory `/usr/local/lib/gcc-lib/' the file
+`80386' is a link to the file `i386v', then `-b 80386' becomes an alias
+for `-b i386v'.
+
+ In one respect, the `-b' or `-V' do not completely change to a
+different compiler: the top-level driver program `gcc' that you
+originally invoked continues to run and invoke the other executables
+(preprocessor, compiler per se, assembler and linker) that do the real
+work. However, since no real work is done in the driver program, it
+usually does not matter that the driver program in use is not the one
+for the specified target. It is common for the interface to the other
+executables to change incompatibly between compiler versions, so unless
+the version specified is very close to that of the driver (for example,
+`-V 3.0' with a driver program from GCC version 3.0.1), use of `-V' may
+not work; for example, using `-V 2.95.2' will not work with a driver
+program from GCC 3.0.
+
+ The only way that the driver program depends on the target machine is
+in the parsing and handling of special machine-specific options.
+However, this is controlled by a file which is found, along with the
+other executables, in the directory for the specified version and
+target machine. As a result, a single installed driver program adapts
+to any specified target machine, and sufficiently similar compiler
+versions.
+
+ The driver program executable does control one significant thing,
+however: the default version and target machine. Therefore, you can
+install different instances of the driver program, compiled for
+different targets or versions, under different names.
+
+ For example, if the driver for version 2.0 is installed as `ogcc'
+and that for version 2.1 is installed as `gcc', then the command `gcc'
+will use version 2.1 by default, while `ogcc' will use 2.0 by default.
+However, you can choose either version with either command with the
+`-V' option.
+
+\1f
+File: gcc.info, Node: Submodel Options, Next: Code Gen Options, Prev: Target Options, Up: Invoking GCC
+
+3.17 Hardware Models and Configurations
+=======================================
+
+Earlier we discussed the standard option `-b' which chooses among
+different 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
+special options, starting with `-m', to choose among various hardware
+models or configurations--for example, 68010 vs 68020, floating
+coprocessor or none. A single installed version of the compiler can
+compile for any model or configuration, according to the options
+specified.
+
+ Some configurations of the compiler also support additional special
+options, usually for compatibility with other compilers on the same
+platform.
+
+ These options are defined by the macro `TARGET_SWITCHES' in the
+machine description. The default for the options is also defined by
+that macro, which enables you to change the defaults.
+
+* Menu:
+
+* M680x0 Options::
+* M68hc1x Options::
+* VAX Options::
+* SPARC Options::
+* Convex Options::
+* AMD29K Options::
+* ARM Options::
+* MN10200 Options::
+* MN10300 Options::
+* M32R/D Options::
+* M88K Options::
+* RS/6000 and PowerPC Options::
+* RT Options::
+* MIPS Options::
+* i386 and x86-64 Options::
+* HPPA Options::
+* Intel 960 Options::
+* DEC Alpha Options::
+* DEC Alpha/VMS Options::
+* Clipper Options::
+* H8/300 Options::
+* SH Options::
+* System V Options::
+* TMS320C3x/C4x Options::
+* V850 Options::
+* ARC Options::
+* NS32K Options::
+* AVR Options::
+* MCore Options::
+* IA-64 Options::
+* D30V Options::
+* S/390 and zSeries Options::
+* CRIS Options::
+* MMIX Options::
+* PDP-11 Options::
+* Xstormy16 Options::
+* Xtensa Options::
+
+\1f
+File: gcc.info, Node: M680x0 Options, Next: M68hc1x Options, Up: Submodel Options
+
+3.17.1 M680x0 Options
+---------------------
+
+These are the `-m' options defined for the 68000 series. The default
+values for these options depends on which style of 68000 was selected
+when the compiler was configured; the defaults for the most common
+choices are given below.
+
+`-m68000'
+`-mc68000'
+ Generate output for a 68000. This is the default when the
+ compiler is configured for 68000-based systems.
+
+ Use this option for microcontrollers with a 68000 or EC000 core,
+ including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
+
+`-m68020'
+`-mc68020'
+ Generate output for a 68020. This is the default when the
+ compiler is configured for 68020-based systems.
+
+`-m68881'
+ Generate output containing 68881 instructions for floating point.
+ This is the default for most 68020 systems unless `--nfp' was
+ specified when the compiler was configured.
+
+`-m68030'
+ Generate output for a 68030. This is the default when the
+ compiler is configured for 68030-based systems.
+
+`-m68040'
+ Generate output for a 68040. This is the default when the
+ compiler is configured for 68040-based systems.
+
+ This option inhibits the use of 68881/68882 instructions that have
+ to be emulated by software on the 68040. Use this option if your
+ 68040 does not have code to emulate those instructions.
+
+`-m68060'
+ Generate output for a 68060. This is the default when the
+ compiler is configured for 68060-based systems.
+
+ This option inhibits the use of 68020 and 68881/68882 instructions
+ that have to be emulated by software on the 68060. Use this
+ option if your 68060 does not have code to emulate those
+ instructions.
+
+`-mcpu32'
+ Generate output for a CPU32. This is the default when the
+ compiler is configured for CPU32-based systems.
+
+ Use this option for microcontrollers with a CPU32 or CPU32+ core,
+ including the 68330, 68331, 68332, 68333, 68334, 68336, 68340,
+ 68341, 68349 and 68360.
+
+`-m5200'
+ Generate output for a 520X "coldfire" family cpu. This is the
+ default when the compiler is configured for 520X-based systems.
+
+ Use this option for microcontroller with a 5200 core, including
+ the MCF5202, MCF5203, MCF5204 and MCF5202.
+
+`-m68020-40'
+ Generate output for a 68040, without using any of the new
+ instructions. This results in code which can run relatively
+ efficiently on either a 68020/68881 or a 68030 or a 68040. The
+ generated code does use the 68881 instructions that are emulated
+ on the 68040.
+
+`-m68020-60'
+ Generate output for a 68060, without using any of the new
+ instructions. This results in code which can run relatively
+ efficiently on either a 68020/68881 or a 68030 or a 68040. The
+ generated code does use the 68881 instructions that are emulated
+ on the 68060.
+
+`-mfpa'
+ Generate output containing Sun FPA instructions for floating point.
+
+`-msoft-float'
+ Generate output containing library calls for floating point.
+ *Warning:* the requisite libraries are not available for all m68k
+ targets. Normally the facilities of the machine's usual C
+ compiler are used, but this can't be done directly in
+ cross-compilation. You must make your own arrangements to provide
+ suitable library functions for cross-compilation. The embedded
+ targets `m68k-*-aout' and `m68k-*-coff' do provide software
+ floating point support.
+
+`-mshort'
+ Consider type `int' to be 16 bits wide, like `short int'.
+
+`-mnobitfield'
+ Do not use the bit-field instructions. The `-m68000', `-mcpu32'
+ and `-m5200' options imply `-mnobitfield'.
+
+`-mbitfield'
+ Do use the bit-field instructions. The `-m68020' option implies
+ `-mbitfield'. This is the default if you use a configuration
+ designed for a 68020.
+
+`-mrtd'
+ Use a different function-calling convention, in which functions
+ that take a fixed number of arguments return with the `rtd'
+ instruction, which pops their arguments while returning. This
+ saves one instruction in the caller since there is no need to pop
+ the arguments there.
+
+ This calling convention is incompatible with the one normally used
+ on Unix, so you cannot use it if you need to call libraries
+ compiled with the Unix compiler.
+
+ 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.)
+
+ The `rtd' instruction is supported by the 68010, 68020, 68030,
+ 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
+
+`-malign-int'
+`-mno-align-int'
+ Control whether GCC aligns `int', `long', `long long', `float',
+ `double', and `long double' variables on a 32-bit boundary
+ (`-malign-int') or a 16-bit boundary (`-mno-align-int'). Aligning
+ variables on 32-bit boundaries produces code that runs somewhat
+ faster on processors with 32-bit busses at the expense of more
+ memory.
+
+ *Warning:* if you use the `-malign-int' switch, GCC will align
+ structures containing the above types differently than most
+ published application binary interface specifications for the m68k.
+
+`-mpcrel'
+ Use the pc-relative addressing mode of the 68000 directly, instead
+ of using a global offset table. At present, this option implies
+ `-fpic', allowing at most a 16-bit offset for pc-relative
+ addressing. `-fPIC' is not presently supported with `-mpcrel',
+ though this could be supported for 68020 and higher processors.
+
+`-mno-strict-align'
+`-mstrict-align'
+ Do not (do) assume that unaligned memory references will be
+ handled by the system.
+
+
+\1f
+File: gcc.info, Node: M68hc1x Options, Next: VAX Options, Prev: M680x0 Options, Up: Submodel Options
+
+3.17.2 M68hc1x Options
+----------------------
+
+These are the `-m' options defined for the 68hc11 and 68hc12
+microcontrollers. The default values for these options depends on
+which style of microcontroller was selected when the compiler was
+configured; the defaults for the most common choices are given below.
+
+`-m6811'
+`-m68hc11'
+ Generate output for a 68HC11. This is the default when the
+ compiler is configured for 68HC11-based systems.
+
+`-m6812'
+`-m68hc12'
+ Generate output for a 68HC12. This is the default when the
+ compiler is configured for 68HC12-based systems.
+
+`-mauto-incdec'
+ Enable the use of 68HC12 pre and post auto-increment and
+ auto-decrement addressing modes.
+
+`-mshort'
+ Consider type `int' to be 16 bits wide, like `short int'.
+
+`-msoft-reg-count=COUNT'
+ Specify the number of pseudo-soft registers which are used for the
+ code generation. The maximum number is 32. Using more pseudo-soft
+ register may or may not result in better code depending on the
+ program. The default is 4 for 68HC11 and 2 for 68HC12.
+
+
+\1f
+File: gcc.info, Node: VAX Options, Next: SPARC Options, Prev: M68hc1x Options, Up: Submodel Options
+
+3.17.3 VAX Options
+------------------
+
+These `-m' options are defined for the VAX:
+
+`-munix'
+ Do not output certain jump instructions (`aobleq' and so on) that
+ the Unix assembler for the VAX cannot handle across long ranges.
+
+`-mgnu'
+ Do output those jump instructions, on the assumption that you will
+ assemble with the GNU assembler.
+
+`-mg'
+ Output code for g-format floating point numbers instead of
+ d-format.
+
+\1f
+File: gcc.info, Node: SPARC Options, Next: Convex Options, Prev: VAX Options, Up: Submodel Options
+
+3.17.4 SPARC Options
+--------------------
+
+These `-m' switches are supported on the SPARC:
+
+`-mno-app-regs'
+`-mapp-regs'
+ Specify `-mapp-regs' to generate output using the global registers
+ 2 through 4, which the SPARC SVR4 ABI reserves for applications.
+ This is the default.
+
+ To be fully SVR4 ABI compliant at the cost of some performance
+ loss, specify `-mno-app-regs'. You should compile libraries and
+ system software with this option.
+
+`-mfpu'
+`-mhard-float'
+ Generate output containing floating point instructions. This is
+ the default.
+
+`-mno-fpu'
+`-msoft-float'
+ Generate output containing library calls for floating point.
+ *Warning:* the requisite libraries are not available for all SPARC
+ targets. Normally the facilities of the machine's usual C
+ compiler are used, but this cannot be done directly in
+ cross-compilation. You must make your own arrangements to provide
+ suitable library functions for cross-compilation. The embedded
+ targets `sparc-*-aout' and `sparclite-*-*' do provide software
+ floating point support.
+
+ `-msoft-float' changes the calling convention in the output file;
+ therefore, it is only useful if you compile _all_ of a program with
+ this option. In particular, you need to compile `libgcc.a', the
+ library that comes with GCC, with `-msoft-float' in order for this
+ to work.
+
+`-mhard-quad-float'
+ Generate output containing quad-word (long double) floating point
+ instructions.
+
+`-msoft-quad-float'
+ Generate output containing library calls for quad-word (long
+ double) floating point instructions. The functions called are
+ those specified in the SPARC ABI. This is the default.
+
+ As of this writing, there are no sparc implementations that have
+ hardware support for the quad-word floating point instructions.
+ They all invoke a trap handler for one of these instructions, and
+ then the trap handler emulates the effect of the instruction.
+ Because of the trap handler overhead, this is much slower than
+ calling the ABI library routines. Thus the `-msoft-quad-float'
+ option is the default.
+
+`-mno-flat'
+`-mflat'
+ With `-mflat', the compiler does not generate save/restore
+ instructions and will use a "flat" or single register window
+ calling convention. This model uses %i7 as the frame pointer and
+ is compatible with the normal register window model. Code from
+ either may be intermixed. The local registers and the input
+ registers (0-5) are still treated as "call saved" registers and
+ will be saved on the stack as necessary.
+
+ With `-mno-flat' (the default), the compiler emits save/restore
+ instructions (except for leaf functions) and is the normal mode of
+ operation.
+
+`-mno-unaligned-doubles'
+`-munaligned-doubles'
+ Assume that doubles have 8 byte alignment. This is the default.
+
+ With `-munaligned-doubles', GCC assumes that doubles have 8 byte
+ alignment only if they are contained in another type, or if they
+ have an absolute address. Otherwise, it assumes they have 4 byte
+ alignment. Specifying this option avoids some rare compatibility
+ problems with code generated by other compilers. It is not the
+ default because it results in a performance loss, especially for
+ floating point code.
+
+`-mno-faster-structs'
+`-mfaster-structs'
+ With `-mfaster-structs', the compiler assumes that structures
+ should have 8 byte alignment. This enables the use of pairs of
+ `ldd' and `std' instructions for copies in structure assignment,
+ in place of twice as many `ld' and `st' pairs. However, the use
+ of this changed alignment directly violates the Sparc ABI. Thus,
+ it's intended only for use on targets where the developer
+ acknowledges that their resulting code will not be directly in
+ line with the rules of the ABI.
+
+`-mv8'
+`-msparclite'
+ These two options select variations on the SPARC architecture.
+
+ By default (unless specifically configured for the Fujitsu
+ SPARClite), GCC generates code for the v7 variant of the SPARC
+ architecture.
+
+ `-mv8' will give you SPARC v8 code. The only difference from v7
+ code is that the compiler emits the integer multiply and integer
+ divide instructions which exist in SPARC v8 but not in SPARC v7.
+
+ `-msparclite' will give you SPARClite code. This adds the integer
+ multiply, integer divide step and scan (`ffs') instructions which
+ exist in SPARClite but not in SPARC v7.
+
+ These options are deprecated and will be deleted in a future GCC
+ release. They have been replaced with `-mcpu=xxx'.
+
+`-mcypress'
+`-msupersparc'
+ These two options select the processor for which the code is
+ optimized.
+
+ With `-mcypress' (the default), the compiler optimizes code for the
+ Cypress CY7C602 chip, as used in the SparcStation/SparcServer 3xx
+ series. This is also appropriate for the older SparcStation 1, 2,
+ IPX etc.
+
+ With `-msupersparc' the compiler optimizes code for the SuperSparc
+ cpu, as used in the SparcStation 10, 1000 and 2000 series. This
+ flag also enables use of the full SPARC v8 instruction set.
+
+ These options are deprecated and will be deleted in a future GCC
+ release. They have been replaced with `-mcpu=xxx'.
+
+`-mcpu=CPU_TYPE'
+ Set the instruction set, register set, and instruction scheduling
+ parameters for machine type CPU_TYPE. Supported values for
+ CPU_TYPE are `v7', `cypress', `v8', `supersparc', `sparclite',
+ `hypersparc', `sparclite86x', `f930', `f934', `sparclet',
+ `tsc701', `v9', and `ultrasparc'.
+
+ Default instruction scheduling parameters are used for values that
+ select an architecture and not an implementation. These are `v7',
+ `v8', `sparclite', `sparclet', `v9'.
+
+ Here is a list of each supported architecture and their supported
+ implementations.
+
+ v7: cypress
+ v8: supersparc, hypersparc
+ sparclite: f930, f934, sparclite86x
+ sparclet: tsc701
+ v9: ultrasparc
+
+`-mtune=CPU_TYPE'
+ Set the instruction scheduling parameters for machine type
+ CPU_TYPE, but do not set the instruction set or register set that
+ the option `-mcpu=CPU_TYPE' would.
+
+ The same values for `-mcpu=CPU_TYPE' can be used for
+ `-mtune=CPU_TYPE', but the only useful values are those that
+ select a particular cpu implementation. Those are `cypress',
+ `supersparc', `hypersparc', `f930', `f934', `sparclite86x',
+ `tsc701', and `ultrasparc'.
+
+
+ These `-m' switches are supported in addition to the above on the
+SPARCLET processor.
+
+`-mlittle-endian'
+ Generate code for a processor running in little-endian mode.
+
+`-mlive-g0'
+ Treat register `%g0' as a normal register. GCC will continue to
+ clobber it as necessary but will not assume it always reads as 0.
+
+`-mbroken-saverestore'
+ Generate code that does not use non-trivial forms of the `save' and
+ `restore' instructions. Early versions of the SPARCLET processor
+ do not correctly handle `save' and `restore' instructions used with
+ arguments. They correctly handle them used without arguments. A
+ `save' instruction used without arguments increments the current
+ window pointer but does not allocate a new stack frame. It is
+ assumed that the window overflow trap handler will properly handle
+ this case as will interrupt handlers.
+
+ These `-m' switches are supported in addition to the above on SPARC
+V9 processors in 64-bit environments.
+
+`-mlittle-endian'
+ Generate code for a processor running in little-endian mode.
+
+`-m32'
+`-m64'
+ Generate code for a 32-bit or 64-bit environment. The 32-bit
+ environment sets int, long and pointer to 32 bits. The 64-bit
+ environment sets int to 32 bits and long and pointer to 64 bits.
+
+`-mcmodel=medlow'
+ Generate code for the Medium/Low code model: the program must be
+ linked in the low 32 bits of the address space. Pointers are 64
+ bits. Programs can be statically or dynamically linked.
+
+`-mcmodel=medmid'
+ Generate code for the Medium/Middle code model: the program must
+ be linked in the low 44 bits of the address space, the text
+ segment must be less than 2G bytes, and data segment must be
+ within 2G of the text segment. Pointers are 64 bits.
+
+`-mcmodel=medany'
+ Generate code for the Medium/Anywhere code model: the program may
+ be linked anywhere in the address space, the text segment must be
+ less than 2G bytes, and data segment must be within 2G of the text
+ segment. Pointers are 64 bits.
+
+`-mcmodel=embmedany'
+ Generate code for the Medium/Anywhere code model for embedded
+ systems: assume a 32-bit text and a 32-bit data segment, both
+ starting anywhere (determined at link time). Register %g4 points
+ to the base of the data segment. Pointers are still 64 bits.
+ Programs are statically linked, PIC is not supported.
+
+`-mstack-bias'
+`-mno-stack-bias'
+ With `-mstack-bias', GCC assumes that the stack pointer, and frame
+ pointer if present, are offset by -2047 which must be added back
+ when making stack frame references. Otherwise, assume no such
+ offset is present.
+
+\1f
+File: gcc.info, Node: Convex Options, Next: AMD29K Options, Prev: SPARC Options, Up: Submodel Options
+
+3.17.5 Convex Options
+---------------------
+
+These `-m' options are defined for Convex:
+
+`-mc1'
+ Generate output for C1. The code will run on any Convex machine.
+ The preprocessor symbol `__convex__c1__' is defined.
+
+`-mc2'
+ Generate output for C2. Uses instructions not available on C1.
+ Scheduling and other optimizations are chosen for max performance
+ on C2. The preprocessor symbol `__convex_c2__' is defined.
+
+`-mc32'
+ Generate output for C32xx. Uses instructions not available on C1.
+ Scheduling and other optimizations are chosen for max performance
+ on C32. The preprocessor symbol `__convex_c32__' is defined.
+
+`-mc34'
+ Generate output for C34xx. Uses instructions not available on C1.
+ Scheduling and other optimizations are chosen for max performance
+ on C34. The preprocessor symbol `__convex_c34__' is defined.
+
+`-mc38'
+ Generate output for C38xx. Uses instructions not available on C1.
+ Scheduling and other optimizations are chosen for max performance
+ on C38. The preprocessor symbol `__convex_c38__' is defined.
+
+`-margcount'
+ Generate code which puts an argument count in the word preceding
+ each argument list. This is compatible with regular CC, and a few
+ programs may need the argument count word. GDB and other
+ source-level debuggers do not need it; this info is in the symbol
+ table.
+
+`-mnoargcount'
+ Omit the argument count word. This is the default.
+
+`-mvolatile-cache'
+ Allow volatile references to be cached. This is the default.
+
+`-mvolatile-nocache'
+ Volatile references bypass the data cache, going all the way to
+ memory. This is only needed for multi-processor code that does
+ not use standard synchronization instructions. Making
+ non-volatile references to volatile locations will not necessarily
+ work.
+
+`-mlong32'
+ Type long is 32 bits, the same as type int. This is the default.
+
+`-mlong64'
+ Type long is 64 bits, the same as type long long. This option is
+ useless, because no library support exists for it.
+
+\1f
+File: gcc.info, Node: AMD29K Options, Next: ARM Options, Prev: Convex Options, Up: Submodel Options
+
+3.17.6 AMD29K Options
+---------------------
+
+These `-m' options are defined for the AMD Am29000:
+
+`-mdw'
+ Generate code that assumes the `DW' bit is set, i.e., that byte and
+ halfword operations are directly supported by the hardware. This
+ is the default.
+
+`-mndw'
+ Generate code that assumes the `DW' bit is not set.
+
+`-mbw'
+ Generate code that assumes the system supports byte and halfword
+ write operations. This is the default.
+
+`-mnbw'
+ Generate code that assumes the systems does not support byte and
+ halfword write operations. `-mnbw' implies `-mndw'.
+
+`-msmall'
+ Use a small memory model that assumes that all function addresses
+ are either within a single 256 KB segment or at an absolute
+ address of less than 256k. This allows the `call' instruction to
+ be used instead of a `const', `consth', `calli' sequence.
+
+`-mnormal'
+ Use the normal memory model: Generate `call' instructions only when
+ calling functions in the same file and `calli' instructions
+ otherwise. This works if each file occupies less than 256 KB but
+ allows the entire executable to be larger than 256 KB. This is
+ the default.
+
+`-mlarge'
+ Always use `calli' instructions. Specify this option if you expect
+ a single file to compile into more than 256 KB of code.
+
+`-m29050'
+ Generate code for the Am29050.
+
+`-m29000'
+ Generate code for the Am29000. This is the default.
+
+`-mkernel-registers'
+ Generate references to registers `gr64-gr95' instead of to
+ registers `gr96-gr127'. This option can be used when compiling
+ kernel code that wants a set of global registers disjoint from
+ that used by user-mode code.
+
+ Note that when this option is used, register names in `-f' flags
+ must use the normal, user-mode, names.
+
+`-muser-registers'
+ Use the normal set of global registers, `gr96-gr127'. This is the
+ default.
+
+`-mstack-check'
+`-mno-stack-check'
+ Insert (or do not insert) a call to `__msp_check' after each stack
+ adjustment. This is often used for kernel code.
+
+`-mstorem-bug'
+`-mno-storem-bug'
+ `-mstorem-bug' handles 29k processors which cannot handle the
+ separation of a mtsrim insn and a storem instruction (most 29000
+ chips to date, but not the 29050).
+
+`-mno-reuse-arg-regs'
+`-mreuse-arg-regs'
+ `-mno-reuse-arg-regs' tells the compiler to only use incoming
+ argument registers for copying out arguments. This helps detect
+ calling a function with fewer arguments than it was declared with.
+
+`-mno-impure-text'
+`-mimpure-text'
+ `-mimpure-text', used in addition to `-shared', tells the compiler
+ to not pass `-assert pure-text' to the linker when linking a
+ shared object.
+
+`-msoft-float'
+ Generate output containing library calls for floating point.
+ *Warning:* the requisite libraries are not part of GCC. Normally
+ the facilities of the machine's usual C compiler are used, but
+ this can't be done directly in cross-compilation. You must make
+ your own arrangements to provide suitable library functions for
+ cross-compilation.
+
+`-mno-multm'
+ Do not generate multm or multmu instructions. This is useful for
+ some embedded systems which do not have trap handlers for these
+ instructions.
+
+\1f
+File: gcc.info, Node: ARM Options, Next: MN10200 Options, Prev: AMD29K Options, Up: Submodel Options
+
+3.17.7 ARM Options
+------------------
+
+These `-m' options are defined for Advanced RISC Machines (ARM)
+architectures:
+
+`-mapcs-frame'
+ Generate a stack frame that is compliant with the ARM Procedure
+ Call Standard for all functions, even if this is not strictly
+ necessary for correct execution of the code. Specifying
+ `-fomit-frame-pointer' with this option will cause the stack
+ frames not to be generated for leaf functions. The default is
+ `-mno-apcs-frame'.
+
+`-mapcs'
+ This is a synonym for `-mapcs-frame'.
+
+`-mapcs-26'
+ Generate code for a processor running with a 26-bit program
+ counter, and conforming to the function calling standards for the
+ APCS 26-bit option. This option replaces the `-m2' and `-m3'
+ options of previous releases of the compiler.
+
+`-mapcs-32'
+ Generate code for a processor running with a 32-bit program
+ counter, and conforming to the function calling standards for the
+ APCS 32-bit option. This option replaces the `-m6' option of
+ previous releases of the compiler.
+
+`-mthumb-interwork'
+ Generate code which supports calling between the ARM and Thumb
+ instruction sets. Without this option the two instruction sets
+ cannot be reliably used inside one program. The default is
+ `-mno-thumb-interwork', since slightly larger code is generated
+ when `-mthumb-interwork' is specified.
+
+`-mno-sched-prolog'
+ Prevent the reordering of instructions in the function prolog, or
+ the merging of those instruction with the instructions in the
+ function's body. This means that all functions will start with a
+ recognizable set of instructions (or in fact one of a choice from
+ a small set of different function prologues), and this information
+ can be used to locate the start if functions inside an executable
+ piece of code. The default is `-msched-prolog'.
+
+`-mhard-float'
+ Generate output containing floating point instructions. This is
+ the default.
+
+`-msoft-float'
+ Generate output containing library calls for floating point.
+ *Warning:* the requisite libraries are not available for all ARM
+ targets. Normally the facilities of the machine's usual C
+ compiler are used, but this cannot be done directly in
+ cross-compilation. You must make your own arrangements to provide
+ suitable library functions for cross-compilation.
+
+ `-msoft-float' changes the calling convention in the output file;
+ therefore, it is only useful if you compile _all_ of a program with
+ this option. In particular, you need to compile `libgcc.a', the
+ library that comes with GCC, with `-msoft-float' in order for this
+ to work.
+
+`-mlittle-endian'
+ Generate code for a processor running in little-endian mode. This
+ is the default for all standard configurations.
+
+`-mbig-endian'
+ Generate code for a processor running in big-endian mode; the
+ default is to compile code for a little-endian processor.
+
+`-mwords-little-endian'
+ This option only applies when generating code for big-endian
+ processors. Generate code for a little-endian word order but a
+ big-endian byte order. That is, a byte order of the form
+ `32107654'. Note: this option should only be used if you require
+ compatibility with code for big-endian ARM processors generated by
+ versions of the compiler prior to 2.8.
+
+`-malignment-traps'
+ Generate code that will not trap if the MMU has alignment traps
+ enabled. On ARM architectures prior to ARMv4, there were no
+ instructions to access half-word objects stored in memory.
+ However, when reading from memory a feature of the ARM
+ architecture allows a word load to be used, even if the address is
+ unaligned, and the processor core will rotate the data as it is
+ being loaded. This option tells the compiler that such misaligned
+ accesses will cause a MMU trap and that it should instead
+ synthesise the access as a series of byte accesses. The compiler
+ can still use word accesses to load half-word data if it knows
+ that the address is aligned to a word boundary.
+
+ This option is ignored when compiling for ARM architecture 4 or
+ later, since these processors have instructions to directly access
+ half-word objects in memory.
+
+`-mno-alignment-traps'
+ Generate code that assumes that the MMU will not trap unaligned
+ accesses. This produces better code when the target instruction
+ set does not have half-word memory operations (i.e.
+ implementations prior to ARMv4).
+
+ Note that you cannot use this option to access unaligned word
+ objects, since the processor will only fetch one 32-bit aligned
+ object from memory.
+
+ The default setting for most targets is `-mno-alignment-traps',
+ since this produces better code when there are no half-word memory
+ instructions available.
+
+`-mshort-load-bytes'
+`-mno-short-load-words'
+ These are deprecated aliases for `-malignment-traps'.
+
+`-mno-short-load-bytes'
+`-mshort-load-words'
+ This are deprecated aliases for `-mno-alignment-traps'.
+
+`-mbsd'
+ This option only applies to RISC iX. Emulate the native BSD-mode
+ compiler. This is the default if `-ansi' is not specified.
+
+`-mxopen'
+ This option only applies to RISC iX. Emulate the native
+ X/Open-mode compiler.
+
+`-mno-symrename'
+ This option only applies to RISC iX. Do not run the assembler
+ post-processor, `symrename', after code has been assembled.
+ Normally it is necessary to modify some of the standard symbols in
+ preparation for linking with the RISC iX C library; this option
+ suppresses this pass. The post-processor is never run when the
+ compiler is built for cross-compilation.
+
+`-mcpu=NAME'
+ This specifies the name of the target ARM processor. GCC uses
+ this name to determine what kind of instructions it can emit when
+ generating assembly code. Permissible names are: `arm2', `arm250',
+ `arm3', `arm6', `arm60', `arm600', `arm610', `arm620', `arm7',
+ `arm7m', `arm7d', `arm7dm', `arm7di', `arm7dmi', `arm70', `arm700',
+ `arm700i', `arm710', `arm710c', `arm7100', `arm7500', `arm7500fe',
+ `arm7tdmi', `arm8', `strongarm', `strongarm110', `strongarm1100',
+ `arm8', `arm810', `arm9', `arm9e', `arm920', `arm920t', `arm940t',
+ `arm9tdmi', `arm10tdmi', `arm1020t', `xscale'.
+
+`-mtune=NAME'
+ This option is very similar to the `-mcpu=' option, except that
+ instead of specifying the actual target processor type, and hence
+ restricting which instructions can be used, it specifies that GCC
+ should tune the performance of the code as if the target were of
+ the type specified in this option, but still choosing the
+ instructions that it will generate based on the cpu specified by a
+ `-mcpu=' option. For some ARM implementations better performance
+ can be obtained by using this option.
+
+`-march=NAME'
+ This specifies the name of the target ARM architecture. GCC uses
+ this name to determine what kind of instructions it can emit when
+ generating assembly code. This option can be used in conjunction
+ with or instead of the `-mcpu=' option. Permissible names are:
+ `armv2', `armv2a', `armv3', `armv3m', `armv4', `armv4t', `armv5',
+ `armv5t', `armv5te'.
+
+`-mfpe=NUMBER'
+`-mfp=NUMBER'
+ This specifies the version of the floating point emulation
+ available on the target. Permissible values are 2 and 3. `-mfp='
+ is a synonym for `-mfpe=', for compatibility with older versions
+ of GCC.
+
+`-mstructure-size-boundary=N'
+ The size of all structures and unions will be rounded up to a
+ multiple of the number of bits set by this option. Permissible
+ values are 8 and 32. The default value varies for different
+ toolchains. For the COFF targeted toolchain the default value is
+ 8. Specifying the larger number can produce faster, more
+ efficient code, but can also increase the size of the program.
+ The two values are potentially incompatible. Code compiled with
+ one value cannot necessarily expect to work with code or libraries
+ compiled with the other value, if they exchange information using
+ structures or unions.
+
+`-mabort-on-noreturn'
+ Generate a call to the function `abort' at the end of a `noreturn'
+ function. It will be executed if the function tries to return.
+
+`-mlong-calls'
+`-mno-long-calls'
+ Tells the compiler to perform function calls by first loading the
+ address of the function into a register and then performing a
+ subroutine call on this register. This switch is needed if the
+ target function will lie outside of the 64 megabyte addressing
+ range of the offset based version of subroutine call instruction.
+
+ Even if this switch is enabled, not all function calls will be
+ turned into long calls. The heuristic is that static functions,
+ functions which have the `short-call' attribute, functions that
+ are inside the scope of a `#pragma no_long_calls' directive and
+ functions whose definitions have already been compiled within the
+ current compilation unit, will not be turned into long calls. The
+ exception to this rule is that weak function definitions,
+ functions with the `long-call' attribute or the `section'
+ attribute, and functions that are within the scope of a `#pragma
+ long_calls' directive, will always be turned into long calls.
+
+ This feature is not enabled by default. Specifying
+ `-mno-long-calls' will restore the default behavior, as will
+ placing the function calls within the scope of a `#pragma
+ long_calls_off' directive. Note these switches have no effect on
+ how the compiler generates code to handle function calls via
+ function pointers.
+
+`-mnop-fun-dllimport'
+ Disable support for the `dllimport' attribute.
+
+`-msingle-pic-base'
+ Treat the register used for PIC addressing as read-only, rather
+ than loading it in the prologue for each function. The run-time
+ system is responsible for initializing this register with an
+ appropriate value before execution begins.
+
+`-mpic-register=REG'
+ Specify the register to be used for PIC addressing. The default
+ is R10 unless stack-checking is enabled, when R9 is used.
+
+`-mpoke-function-name'
+ Write the name of each function into the text section, directly
+ preceding the function prologue. The generated code is similar to
+ this:
+
+ t0
+ .ascii "arm_poke_function_name", 0
+ .align
+ t1
+ .word 0xff000000 + (t1 - t0)
+ arm_poke_function_name
+ mov ip, sp
+ stmfd sp!, {fp, ip, lr, pc}
+ sub fp, ip, #4
+
+ When performing a stack backtrace, code can inspect the value of
+ `pc' stored at `fp + 0'. If the trace function then looks at
+ location `pc - 12' and the top 8 bits are set, then we know that
+ there is a function name embedded immediately preceding this
+ location and has length `((pc[-3]) & 0xff000000)'.
+
+`-mthumb'
+ Generate code for the 16-bit Thumb instruction set. The default
+ is to use the 32-bit ARM instruction set.
+
+`-mtpcs-frame'
+ Generate a stack frame that is compliant with the Thumb Procedure
+ Call Standard for all non-leaf functions. (A leaf function is one
+ that does not call any other functions.) The default is
+ `-mno-tpcs-frame'.
+
+`-mtpcs-leaf-frame'
+ Generate a stack frame that is compliant with the Thumb Procedure
+ Call Standard for all leaf functions. (A leaf function is one
+ that does not call any other functions.) The default is
+ `-mno-apcs-leaf-frame'.
+
+`-mcallee-super-interworking'
+ Gives all externally visible functions in the file being compiled
+ an ARM instruction set header which switches to Thumb mode before
+ executing the rest of the function. This allows these functions
+ to be called from non-interworking code.
+
+`-mcaller-super-interworking'
+ Allows calls via function pointers (including virtual functions) to
+ execute correctly regardless of whether the target code has been
+ compiled for interworking or not. There is a small overhead in
+ the cost of executing a function pointer if this option is enabled.
+
+
+\1f
+File: gcc.info, Node: MN10200 Options, Next: MN10300 Options, Prev: ARM Options, Up: Submodel Options
+
+3.17.8 MN10200 Options
+----------------------
+
+These `-m' options are defined for Matsushita MN10200 architectures:
+`-mrelax'
+ Indicate to the linker that it should perform a relaxation
+ optimization pass to shorten branches, calls and absolute memory
+ addresses. This option only has an effect when used on the
+ command line for the final link step.
+
+ This option makes symbolic debugging impossible.
+
+\1f
+File: gcc.info, Node: MN10300 Options, Next: M32R/D Options, Prev: MN10200 Options, Up: Submodel Options
+
+3.17.9 MN10300 Options
+----------------------
+
+These `-m' options are defined for Matsushita MN10300 architectures:
+
+`-mmult-bug'
+ Generate code to avoid bugs in the multiply instructions for the
+ MN10300 processors. This is the default.
+
+`-mno-mult-bug'
+ Do not generate code to avoid bugs in the multiply instructions
+ for the MN10300 processors.
+
+`-mam33'
+ Generate code which uses features specific to the AM33 processor.
+
+`-mno-am33'
+ Do not generate code which uses features specific to the AM33
+ processor. This is the default.
+
+`-mno-crt0'
+ Do not link in the C run-time initialization object file.
+
+`-mrelax'
+ Indicate to the linker that it should perform a relaxation
+ optimization pass to shorten branches, calls and absolute memory
+ addresses. This option only has an effect when used on the
+ command line for the final link step.
+
+ This option makes symbolic debugging impossible.
+
+\1f
+File: gcc.info, Node: M32R/D Options, Next: M88K Options, Prev: MN10300 Options, Up: Submodel Options
+
+3.17.10 M32R/D Options
+----------------------
+
+These `-m' options are defined for Mitsubishi M32R/D architectures:
+
+`-m32rx'
+ Generate code for the M32R/X.
+
+`-m32r'
+ Generate code for the M32R. This is the default.
+
+`-mcode-model=small'
+ Assume all objects live in the lower 16MB of memory (so that their
+ addresses can be loaded with the `ld24' instruction), and assume
+ all subroutines are reachable with the `bl' instruction. This is
+ the default.
+
+ The addressability of a particular object can be set with the
+ `model' attribute.
+
+`-mcode-model=medium'
+ Assume objects may be anywhere in the 32-bit address space (the
+ compiler will generate `seth/add3' instructions to load their
+ addresses), and assume all subroutines are reachable with the `bl'
+ instruction.
+
+`-mcode-model=large'
+ Assume objects may be anywhere in the 32-bit address space (the
+ compiler will generate `seth/add3' instructions to load their
+ addresses), and assume subroutines may not be reachable with the
+ `bl' instruction (the compiler will generate the much slower
+ `seth/add3/jl' instruction sequence).
+
+`-msdata=none'
+ Disable use of the small data area. Variables will be put into
+ one of `.data', `bss', or `.rodata' (unless the `section'
+ attribute has been specified). This is the default.
+
+ The small data area consists of sections `.sdata' and `.sbss'.
+ Objects may be explicitly put in the small data area with the
+ `section' attribute using one of these sections.
+
+`-msdata=sdata'
+ Put small global and static data in the small data area, but do not
+ generate special code to reference them.
+
+`-msdata=use'
+ Put small global and static data in the small data area, and
+ generate special instructions to reference them.
+
+`-G NUM'
+ Put global and static objects less than or equal to NUM bytes into
+ the small data or bss sections instead of the normal data or bss
+ sections. The default value of NUM is 8. The `-msdata' option
+ must be set to one of `sdata' or `use' for this option to have any
+ effect.
+
+ All modules should be compiled with the same `-G NUM' value.
+ Compiling with different values of NUM may or may not work; if it
+ doesn't the linker will give an error message--incorrect code will
+ not be generated.
+
+
+\1f
+File: gcc.info, Node: M88K Options, Next: RS/6000 and PowerPC Options, Prev: M32R/D Options, Up: Submodel Options
+
+3.17.11 M88K Options
+--------------------
+
+These `-m' options are defined for Motorola 88k architectures:
+
+`-m88000'
+ Generate code that works well on both the m88100 and the m88110.
+
+`-m88100'
+ Generate code that works best for the m88100, but that also runs
+ on the m88110.
+
+`-m88110'
+ Generate code that works best for the m88110, and may not run on
+ the m88100.
+
+`-mbig-pic'
+ Obsolete option to be removed from the next revision. Use `-fPIC'.
+
+`-midentify-revision'
+ Include an `ident' directive in the assembler output recording the
+ source file name, compiler name and version, timestamp, and
+ compilation flags used.
+
+`-mno-underscores'
+ In assembler output, emit symbol names without adding an underscore
+ character at the beginning of each name. The default is to use an
+ underscore as prefix on each name.
+
+`-mocs-debug-info'
+`-mno-ocs-debug-info'
+ Include (or omit) additional debugging information (about
+ registers used in each stack frame) as specified in the 88open
+ Object Compatibility Standard, "OCS". This extra information
+ allows debugging of code that has had the frame pointer
+ eliminated. The default for DG/UX, SVr4, and Delta 88 SVr3.2 is
+ to include this information; other 88k configurations omit this
+ information by default.
+
+`-mocs-frame-position'
+ When emitting COFF debugging information for automatic variables
+ and parameters stored on the stack, use the offset from the
+ canonical frame address, which is the stack pointer (register 31)
+ on entry to the function. The DG/UX, SVr4, Delta88 SVr3.2, and
+ BCS configurations use `-mocs-frame-position'; other 88k
+ configurations have the default `-mno-ocs-frame-position'.
+
+`-mno-ocs-frame-position'
+ When emitting COFF debugging information for automatic variables
+ and parameters stored on the stack, use the offset from the frame
+ pointer register (register 30). When this option is in effect,
+ the frame pointer is not eliminated when debugging information is
+ selected by the -g switch.
+
+`-moptimize-arg-area'
+ Save space by reorganizing the stack frame. This option generates
+ code that does not agree with the 88open specifications, but uses
+ less memory.
+
+`-mno-optimize-arg-area'
+ Do not reorganize the stack frame to save space. This is the
+ default. The generated conforms to the specification, but uses
+ more memory.
+
+`-mshort-data-NUM'
+ Generate smaller data references by making them relative to `r0',
+ which allows loading a value using a single instruction (rather
+ than the usual two). You control which data references are
+ affected by specifying NUM with this option. For example, if you
+ specify `-mshort-data-512', then the data references affected are
+ those involving displacements of less than 512 bytes.
+ `-mshort-data-NUM' is not effective for NUM greater than 64k.
+
+`-mserialize-volatile'
+`-mno-serialize-volatile'
+ Do, or don't, generate code to guarantee sequential consistency of
+ volatile memory references. By default, consistency is guaranteed.
+
+ The order of memory references made by the MC88110 processor does
+ not always match the order of the instructions requesting those
+ references. In particular, a load instruction may execute before
+ a preceding store instruction. Such reordering violates
+ sequential consistency of volatile memory references, when there
+ are multiple processors. When consistency must be guaranteed,
+ GCC generates special instructions, as needed, to force execution
+ in the proper order.
+
+ The MC88100 processor does not reorder memory references and so
+ always provides sequential consistency. However, by default, GCC
+ generates the special instructions to guarantee consistency even
+ when you use `-m88100', so that the code may be run on an MC88110
+ processor. If you intend to run your code only on the MC88100
+ processor, you may use `-mno-serialize-volatile'.
+
+ The extra code generated to guarantee consistency may affect the
+ performance of your application. If you know that you can safely
+ forgo this guarantee, you may use `-mno-serialize-volatile'.
+
+`-msvr4'
+`-msvr3'
+ Turn on (`-msvr4') or off (`-msvr3') compiler extensions related
+ to System V release 4 (SVr4). This controls the following:
+
+ 1. Which variant of the assembler syntax to emit.
+
+ 2. `-msvr4' makes the C preprocessor recognize `#pragma weak'
+ that is used on System V release 4.
+
+ 3. `-msvr4' makes GCC issue additional declaration directives
+ used in SVr4.
+
+ `-msvr4' is the default for the m88k-motorola-sysv4 and
+ m88k-dg-dgux m88k configurations. `-msvr3' is the default for all
+ other m88k configurations.
+
+`-mversion-03.00'
+ This option is obsolete, and is ignored.
+
+`-mno-check-zero-division'
+`-mcheck-zero-division'
+ Do, or don't, generate code to guarantee that integer division by
+ zero will be detected. By default, detection is guaranteed.
+
+ Some models of the MC88100 processor fail to trap upon integer
+ division by zero under certain conditions. By default, when
+ compiling code that might be run on such a processor, GCC
+ generates code that explicitly checks for zero-valued divisors and
+ traps with exception number 503 when one is detected. Use of
+ `-mno-check-zero-division' suppresses such checking for code
+ generated to run on an MC88100 processor.
+
+ GCC assumes that the MC88110 processor correctly detects all
+ instances of integer division by zero. When `-m88110' is
+ specified, no explicit checks for zero-valued divisors are
+ generated, and both `-mcheck-zero-division' and
+ `-mno-check-zero-division' are ignored.
+
+`-muse-div-instruction'
+ Use the div instruction for signed integer division on the MC88100
+ processor. By default, the div instruction is not used.
+
+ On the MC88100 processor the signed integer division instruction
+ div) traps to the operating system on a negative operand. The
+ operating system transparently completes the operation, but at a
+ large cost in execution time. By default, when compiling code
+ that might be run on an MC88100 processor, GCC emulates signed
+ integer division using the unsigned integer division instruction
+ divu), thereby avoiding the large penalty of a trap to the
+ operating system. Such emulation has its own, smaller, execution
+ cost in both time and space. To the extent that your code's
+ important signed integer division operations are performed on two
+ nonnegative operands, it may be desirable to use the div
+ instruction directly.
+
+ On the MC88110 processor the div instruction (also known as the
+ divs instruction) processes negative operands without trapping to
+ the operating system. When `-m88110' is specified,
+ `-muse-div-instruction' is ignored, and the div instruction is used
+ for signed integer division.
+
+ Note that the result of dividing `INT_MIN' by -1 is undefined. In
+ particular, the behavior of such a division with and without
+ `-muse-div-instruction' may differ.
+
+`-mtrap-large-shift'
+`-mhandle-large-shift'
+ Include code to detect bit-shifts of more than 31 bits;
+ respectively, trap such shifts or emit code to handle them
+ properly. By default GCC makes no special provision for large bit
+ shifts.
+
+`-mwarn-passed-structs'
+ Warn when a function passes a struct as an argument or result.
+ Structure-passing conventions have changed during the evolution of
+ the C language, and are often the source of portability problems.
+ By default, GCC issues no such warning.
+
+\1f
+File: gcc.info, Node: RS/6000 and PowerPC Options, Next: RT Options, Prev: M88K Options, Up: Submodel Options
+
+3.17.12 IBM RS/6000 and PowerPC Options
+---------------------------------------
+
+These `-m' options are defined for the IBM RS/6000 and PowerPC:
+`-mpower'
+`-mno-power'
+`-mpower2'
+`-mno-power2'
+`-mpowerpc'
+`-mno-powerpc'
+`-mpowerpc-gpopt'
+`-mno-powerpc-gpopt'
+`-mpowerpc-gfxopt'
+`-mno-powerpc-gfxopt'
+`-mpowerpc64'
+`-mno-powerpc64'
+ GCC supports two related instruction set architectures for the
+ RS/6000 and PowerPC. The "POWER" instruction set are those
+ instructions supported by the `rios' chip set used in the original
+ RS/6000 systems and the "PowerPC" instruction set is the
+ architecture of the Motorola MPC5xx, MPC6xx, MPC8xx
+ microprocessors, and the IBM 4xx microprocessors.
+
+ Neither architecture is a subset of the other. However there is a
+ large common subset of instructions supported by both. An MQ
+ register 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.
+ Specifying `-mpowerpc-gpopt' implies `-mpowerpc' and also allows
+ GCC to use the optional PowerPC architecture instructions in the
+ General Purpose group, including floating-point square root.
+ Specifying `-mpowerpc-gfxopt' implies `-mpowerpc' and also allows
+ GCC to use the optional PowerPC architecture instructions in the
+ Graphics group, including floating-point select.
+
+ The `-mpowerpc64' option allows GCC to generate the additional
+ 64-bit instructions that are found in the full PowerPC64
+ architecture and to treat GPRs as 64-bit, doubleword quantities.
+ GCC defaults to `-mno-powerpc64'.
+
+ If you specify both `-mno-power' and `-mno-powerpc', GCC will use
+ only the instructions in the common subset of both architectures
+ plus some special AIX common-mode calls, and will not use the MQ
+ register. Specifying both `-mpower' and `-mpowerpc' permits GCC
+ to use any instruction from either architecture and to allow use
+ of the MQ register; specify this for the Motorola MPC601.
+
+`-mnew-mnemonics'
+`-mold-mnemonics'
+ Select which mnemonics to use in the generated assembler code.
+ With `-mnew-mnemonics', GCC uses the assembler mnemonics defined
+ for the PowerPC architecture. With `-mold-mnemonics' it uses the
+ assembler mnemonics defined for the POWER architecture.
+ Instructions defined in only one architecture have only one
+ mnemonic; GCC uses that mnemonic irrespective of which of these
+ options is specified.
+
+ GCC defaults to the mnemonics appropriate for the architecture in
+ use. Specifying `-mcpu=CPU_TYPE' sometimes overrides the value of
+ these option. Unless you are building a cross-compiler, you
+ should normally not specify either `-mnew-mnemonics' or
+ `-mold-mnemonics', but should instead accept the default.
+
+`-mcpu=CPU_TYPE'
+ Set architecture type, register usage, choice of mnemonics, and
+ instruction scheduling parameters for machine type CPU_TYPE.
+ Supported 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
+ generated 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' specify generic POWER, POWER2, pure 32-bit
+ PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
+ types, with an appropriate, generic processor model assumed for
+ scheduling purposes.
+
+ The other options specify a specific processor. Code generated
+ under those options will run best on that processor, and may not
+ run at all on others.
+
+ The `-mcpu' options automatically enable or disable other `-m'
+ options as follows:
+
+ `common'
+ `-mno-power', `-mno-powerc'
+
+ `power'
+ `power2'
+ `rios1'
+ `rios2'
+ `rsc'
+ `-mpower', `-mno-powerpc', `-mno-new-mnemonics'
+
+ `powerpc'
+ `rs64a'
+ `602'
+ `603'
+ `603e'
+ `604'
+ `620'
+ `630'
+ `740'
+ `7400'
+ `7450'
+ `750'
+ `505'
+ `-mno-power', `-mpowerpc', `-mnew-mnemonics'
+
+ `601'
+ `-mpower', `-mpowerpc', `-mnew-mnemonics'
+
+ `403'
+ `821'
+ `860'
+ `-mno-power', `-mpowerpc', `-mnew-mnemonics', `-msoft-float'
+
+`-mtune=CPU_TYPE'
+ Set the instruction scheduling parameters for machine type
+ CPU_TYPE, but do not set the architecture type, register usage, or
+ choice of mnemonics, as `-mcpu=CPU_TYPE' would. The same values
+ for CPU_TYPE are used for `-mtune' as for `-mcpu'. If both are
+ specified, the code generated will use the architecture,
+ registers, and mnemonics set by `-mcpu', but the scheduling
+ parameters set by `-mtune'.
+
+`-maltivec'
+`-mno-altivec'
+ These switches enable or disable the use of built-in functions that
+ allow access to the AltiVec instruction set. You may also need to
+ set `-mabi=altivec' to adjust the current ABI with AltiVec ABI
+ enhancements.
+
+`-mfull-toc'
+`-mno-fp-in-toc'
+`-mno-sum-in-toc'
+`-mminimal-toc'
+ Modify generation of the TOC (Table Of Contents), which is created
+ for every executable file. The `-mfull-toc' option is selected by
+ default. In that case, GCC will allocate at least one TOC entry
+ for each unique non-automatic variable reference in your program.
+ GCC will also place floating-point constants in the TOC. However,
+ only 16,384 entries are available in the TOC.
+
+ If you receive a linker error message that saying you have
+ overflowed the available TOC space, you can reduce the amount of
+ TOC space used with the `-mno-fp-in-toc' and `-mno-sum-in-toc'
+ options. `-mno-fp-in-toc' prevents GCC from putting floating-point
+ constants in the TOC and `-mno-sum-in-toc' forces GCC to generate
+ code to calculate the sum of an address and a constant at run-time
+ instead of putting that sum into the TOC. You may specify one or
+ both of these options. Each causes GCC to produce very slightly
+ slower and larger code at the expense of conserving TOC space.
+
+ If you still run out of space in the TOC even when you specify
+ both of these options, specify `-mminimal-toc' instead. This
+ option causes GCC to make only one TOC entry for every file. When
+ you specify this option, GCC will produce code that is slower and
+ larger but which uses extremely little TOC space. You may wish to
+ use this option only on files that contain less frequently
+ executed code.
+
+`-maix64'
+`-maix32'
+ Enable 64-bit AIX ABI and calling convention: 64-bit pointers,
+ 64-bit `long' type, and the infrastructure needed to support them.
+ Specifying `-maix64' implies `-mpowerpc64' and `-mpowerpc', while
+ `-maix32' disables the 64-bit ABI and implies `-mno-powerpc64'.
+ GCC defaults to `-maix32'.
+
+`-mxl-call'
+`-mno-xl-call'
+ On AIX, pass floating-point arguments to prototyped functions
+ beyond the register save area (RSA) on the stack in addition to
+ argument FPRs. The AIX calling convention was extended but not
+ initially documented to handle an obscure K&R C case of calling a
+ function that takes the address of its arguments with fewer
+ arguments than declared. AIX XL compilers access floating point
+ arguments which do not fit in the RSA from the stack when a
+ subroutine is compiled without optimization. Because always
+ storing floating-point arguments on the stack is inefficient and
+ rarely needed, this option is not enabled by default and only is
+ necessary when calling subroutines compiled by AIX XL compilers
+ without optimization.
+
+`-mpe'
+ Support "IBM RS/6000 SP" "Parallel Environment" (PE). Link an
+ application 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 appropriate directory location. The Parallel
+ Environment does not support threads, so the `-mpe' option and the
+ `-pthread' option are incompatible.
+
+`-msoft-float'
+`-mhard-float'
+ Generate code that does not use (uses) the floating-point register
+ set. Software floating point emulation is provided if you use the
+ `-msoft-float' option, and pass the option to GCC when linking.
+
+`-mmultiple'
+`-mno-multiple'
+ Generate code that uses (does not use) the load multiple word
+ instructions and the store multiple word instructions. These
+ instructions are generated by default on POWER systems, and not
+ generated on PowerPC systems. Do not use `-mmultiple' on little
+ endian PowerPC systems, since those instructions do not work when
+ the processor is in little endian mode. The exceptions are PPC740
+ and PPC750 which permit the instructions usage in little endian
+ mode.
+
+`-mstring'
+`-mno-string'
+ Generate code that uses (does not use) the load string instructions
+ and the store string word instructions to save multiple registers
+ and do small block moves. These instructions are generated by
+ default on POWER systems, and not generated on PowerPC systems.
+ Do not use `-mstring' on little endian PowerPC systems, since those
+ instructions do not work when the processor is in little endian
+ mode. The exceptions are PPC740 and PPC750 which permit the
+ instructions usage in little endian mode.
+
+`-mupdate'
+`-mno-update'
+ Generate code that uses (does not use) the load or store
+ instructions that update the base register to the address of the
+ calculated memory location. These instructions are generated by
+ default. If you use `-mno-update', there is a small window
+ between the time that the stack pointer is updated and the address
+ of the previous frame is stored, which means code that walks the
+ stack frame across interrupts or signals may get corrupted data.
+
+`-mfused-madd'
+`-mno-fused-madd'
+ Generate code that uses (does not use) the floating point multiply
+ and accumulate instructions. These instructions are generated by
+ default if hardware floating is used.
+
+`-mno-bit-align'
+`-mbit-align'
+ On System V.4 and embedded PowerPC systems do not (do) force
+ structures and unions that contain bit-fields to be aligned to the
+ base type of the bit-field.
+
+ For example, by default a structure containing nothing but 8
+ `unsigned' bit-fields of length 1 would be aligned to a 4 byte
+ boundary and have a size of 4 bytes. By using `-mno-bit-align',
+ the structure would be aligned to a 1 byte boundary and be one
+ byte in size.
+
+`-mno-strict-align'
+`-mstrict-align'
+ On System V.4 and embedded PowerPC systems do not (do) assume that
+ unaligned memory references will be handled by the system.
+
+`-mrelocatable'
+`-mno-relocatable'
+ On embedded PowerPC systems generate code that allows (does not
+ allow) the program to be relocated to a different address at
+ runtime. If you use `-mrelocatable' on any module, all objects
+ linked together must be compiled with `-mrelocatable' or
+ `-mrelocatable-lib'.
+
+`-mrelocatable-lib'
+`-mno-relocatable-lib'
+ On embedded PowerPC systems generate code that allows (does not
+ allow) the program to be relocated to a different address at
+ runtime. Modules compiled with `-mrelocatable-lib' can be linked
+ with either modules compiled without `-mrelocatable' and
+ `-mrelocatable-lib' or with modules compiled with the
+ `-mrelocatable' options.
+
+`-mno-toc'
+`-mtoc'
+ On System V.4 and embedded PowerPC systems do not (do) assume that
+ register 2 contains a pointer to a global area pointing to the
+ addresses used in the program.
+
+`-mlittle'
+`-mlittle-endian'
+ On System V.4 and embedded PowerPC systems compile code for the
+ processor in little endian mode. The `-mlittle-endian' option is
+ the same as `-mlittle'.
+
+`-mbig'
+`-mbig-endian'
+ On System V.4 and embedded PowerPC systems compile code for the
+ processor in big endian mode. The `-mbig-endian' option is the
+ same as `-mbig'.
+
+`-mcall-sysv'
+ On System V.4 and embedded PowerPC systems compile code using
+ calling conventions that adheres to the March 1995 draft of the
+ System V Application Binary Interface, PowerPC processor
+ supplement. This is the default unless you configured GCC using
+ `powerpc-*-eabiaix'.
+
+`-mcall-sysv-eabi'
+ Specify both `-mcall-sysv' and `-meabi' options.
+
+`-mcall-sysv-noeabi'
+ Specify both `-mcall-sysv' and `-mno-eabi' options.
+
+`-mcall-aix'
+ On System V.4 and embedded PowerPC systems compile code using
+ calling conventions that are similar to those used on AIX. This
+ is the default if you configured GCC using `powerpc-*-eabiaix'.
+
+`-mcall-solaris'
+ On System V.4 and embedded PowerPC systems compile code for the
+ Solaris operating system.
+
+`-mcall-linux'
+ On System V.4 and embedded PowerPC systems compile code for the
+ Linux-based GNU system.
+
+`-mcall-gnu'
+ On System V.4 and embedded PowerPC systems compile code for the
+ Hurd-based GNU system.
+
+`-mcall-netbsd'
+ On System V.4 and embedded PowerPC systems compile code for the
+ NetBSD operating system.
+
+`-maix-struct-return'
+ Return all structures in memory (as specified by the AIX ABI).
+
+`-msvr4-struct-return'
+ Return structures smaller than 8 bytes in registers (as specified
+ by the SVR4 ABI).
+
+`-mabi=altivec'
+ Extend the current ABI with AltiVec ABI extensions. This does not
+ change the default ABI, instead it adds the AltiVec ABI extensions
+ to the current ABI.
+
+`-mabi=no-altivec'
+ Disable AltiVec ABI extensions for the current ABI.
+
+`-mprototype'
+`-mno-prototype'
+ On System V.4 and embedded PowerPC systems assume that all calls to
+ variable argument functions are properly prototyped. Otherwise,
+ the compiler must insert an instruction before every non
+ prototyped call to set or clear bit 6 of the condition code
+ register (CR) to indicate whether floating point values were
+ passed in the floating point registers in case the function takes
+ a variable arguments. With `-mprototype', only calls to
+ prototyped variable argument functions will set or clear the bit.
+
+`-msim'
+ On embedded PowerPC systems, assume that the startup module is
+ called `sim-crt0.o' and that the standard C libraries are
+ `libsim.a' and `libc.a'. This is the default for
+ `powerpc-*-eabisim'. configurations.
+
+`-mmvme'
+ On embedded PowerPC systems, assume that the startup module is
+ called `crt0.o' and the standard C libraries are `libmvme.a' and
+ `libc.a'.
+
+`-mads'
+ On embedded PowerPC systems, assume that the startup module is
+ called `crt0.o' and the standard C libraries are `libads.a' and
+ `libc.a'.
+
+`-myellowknife'
+ On embedded PowerPC systems, assume that the startup module is
+ called `crt0.o' and the standard C libraries are `libyk.a' and
+ `libc.a'.
+
+`-mvxworks'
+ On System V.4 and embedded PowerPC systems, specify that you are
+ compiling for a VxWorks system.
+
+`-memb'
+ On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags
+ header to indicate that `eabi' extended relocations are used.
+
+`-meabi'
+`-mno-eabi'
+ On System V.4 and embedded PowerPC systems do (do not) adhere to
+ the Embedded Applications Binary Interface (eabi) which is a set of
+ modifications to the System V.4 specifications. Selecting `-meabi'
+ means that the stack is aligned to an 8 byte boundary, a function
+ `__eabi' is called to from `main' to set up the eabi environment,
+ and the `-msdata' option can use both `r2' and `r13' to point to
+ two separate small data areas. Selecting `-mno-eabi' means that
+ the stack is aligned to a 16 byte boundary, do not call an
+ initialization 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
+ `powerpc*-*-eabi*' options.
+
+`-msdata=eabi'
+ On System V.4 and embedded PowerPC systems, put small initialized
+ `const' global and static data in the `.sdata2' section, which is
+ pointed to by register `r2'. Put small initialized non-`const'
+ global and static data in the `.sdata' section, which is pointed
+ to by register `r13'. Put small uninitialized global and static
+ data in the `.sbss' section, which is adjacent to the `.sdata'
+ section. The `-msdata=eabi' option is incompatible with the
+ `-mrelocatable' option. The `-msdata=eabi' option also sets the
+ `-memb' option.
+
+`-msdata=sysv'
+ On System V.4 and embedded PowerPC systems, put small global and
+ static data in the `.sdata' section, which is pointed to by
+ register `r13'. Put small uninitialized global and static data in
+ the `.sbss' section, which is adjacent to the `.sdata' section.
+ The `-msdata=sysv' option is incompatible with the `-mrelocatable'
+ option.
+
+`-msdata=default'
+`-msdata'
+ On System V.4 and embedded PowerPC systems, if `-meabi' is used,
+ compile code the same as `-msdata=eabi', otherwise compile code the
+ same as `-msdata=sysv'.
+
+`-msdata-data'
+ On System V.4 and embedded PowerPC systems, put small global and
+ static data in the `.sdata' section. Put small uninitialized
+ global and static data in the `.sbss' section. Do not use
+ register `r13' to address small data however. This is the default
+ behavior unless other `-msdata' options are used.
+
+`-msdata=none'
+`-mno-sdata'
+ On embedded PowerPC systems, put all initialized global and static
+ data in the `.data' section, and all uninitialized data in the
+ `.bss' section.
+
+`-G NUM'
+ On embedded PowerPC systems, put global and static items less than
+ or equal to NUM bytes into the small data or bss sections instead
+ of the normal data or bss section. By default, NUM is 8. The `-G
+ NUM' switch is also passed to the linker. All modules should be
+ compiled with the same `-G NUM' value.
+
+`-mregnames'
+`-mno-regnames'
+ On System V.4 and embedded PowerPC systems do (do not) emit
+ register names in the assembly language output using symbolic
+ forms.
+
+`-pthread'
+ Adds support for multithreading with the "pthreads" library. This
+ option sets flags for both the preprocessor and linker.
+
+
+\1f
+File: gcc.info, Node: RT Options, Next: MIPS Options, Prev: RS/6000 and PowerPC Options, Up: Submodel Options
+
+3.17.13 IBM RT Options
+----------------------
+
+These `-m' options are defined for the IBM RT PC:
+
+`-min-line-mul'
+ Use an in-line code sequence for integer multiplies. This is the
+ default.
+
+`-mcall-lib-mul'
+ Call `lmul$$' for integer multiples.
+
+`-mfull-fp-blocks'
+ Generate full-size floating point data blocks, including the
+ minimum amount of scratch space recommended by IBM. This is the
+ default.
+
+`-mminimum-fp-blocks'
+ Do not include extra scratch space in floating point data blocks.
+ This results in smaller code, but slower execution, since scratch
+ space must be allocated dynamically.
+
+`-mfp-arg-in-fpregs'
+ Use a calling sequence incompatible with the IBM calling
+ convention in which floating point arguments are passed in
+ floating point registers. Note that `varargs.h' and `stdarg.h'
+ will not work with floating point operands if this option is
+ specified.
+
+`-mfp-arg-in-gregs'
+ Use the normal calling convention for floating point arguments.
+ This is the default.
+
+`-mhc-struct-return'
+ Return structures of more than one word in memory, rather than in a
+ register. This provides compatibility with the MetaWare HighC (hc)
+ compiler. Use the option `-fpcc-struct-return' for compatibility
+ with the Portable C Compiler (pcc).
+
+`-mnohc-struct-return'
+ Return some structures of more than one word in registers, when
+ convenient. This is the default. For compatibility with the
+ IBM-supplied compilers, use the option `-fpcc-struct-return' or the
+ option `-mhc-struct-return'.
+
+\1f
+File: gcc.info, Node: MIPS Options, Next: i386 and x86-64 Options, Prev: RT Options, Up: Submodel Options
+
+3.17.14 MIPS Options
+--------------------
+
+These `-m' options are defined for the MIPS family of computers:
+
+`-march=CPU-TYPE'
+ Assume the defaults for the machine type CPU-TYPE when generating
+ instructions. The choices for CPU-TYPE are `r2000', `r3000',
+ `r3900', `r4000', `r4100', `r4300', `r4400', `r4600', `r4650',
+ `r5000', `r6000', `r8000', and `orion'. Additionally, the
+ `r2000', `r3000', `r4000', `r5000', and `r6000' can be abbreviated
+ as `r2k' (or `r2K'), `r3k', etc.
+
+`-mtune=CPU-TYPE'
+ Assume the defaults for the machine type CPU-TYPE when scheduling
+ instructions. The choices for CPU-TYPE are `r2000', `r3000',
+ `r3900', `r4000', `r4100', `r4300', `r4400', `r4600', `r4650',
+ `r5000', `r6000', `r8000', and `orion'. Additionally, the
+ `r2000', `r3000', `r4000', `r5000', and `r6000' can be abbreviated
+ as `r2k' (or `r2K'), `r3k', etc. While picking a specific
+ CPU-TYPE will schedule things appropriately for that particular
+ chip, the compiler will not generate any code that does not meet
+ level 1 of the MIPS ISA (instruction set architecture) without a
+ `-mipsX' or `-mabi' switch being used.
+
+`-mcpu=CPU-TYPE'
+ This is identical to specifying both `-march' and `-mtune'.
+
+`-mips1'
+ Issue instructions from level 1 of the MIPS ISA. This is the
+ default. `r3000' is the default CPU-TYPE at this ISA level.
+
+`-mips2'
+ Issue instructions from level 2 of the MIPS ISA (branch likely,
+ square root instructions). `r6000' is the default CPU-TYPE at this
+ ISA level.
+
+`-mips3'
+ Issue instructions from level 3 of the MIPS ISA (64-bit
+ instructions). `r4000' is the default CPU-TYPE at this ISA level.
+
+`-mips4'
+ Issue instructions from level 4 of the MIPS ISA (conditional move,
+ prefetch, enhanced FPU instructions). `r8000' is the default
+ CPU-TYPE at this ISA level.
+
+`-mfp32'
+ Assume that 32 32-bit floating point registers are available.
+ This is the default.
+
+`-mfp64'
+ Assume that 32 64-bit floating point registers are available.
+ This is the default when the `-mips3' option is used.
+
+`-mfused-madd'
+`-mno-fused-madd'
+ Generate code that uses (does not use) the floating point multiply
+ and accumulate instructions, when they are available. These
+ instructions are generated by default if they are available, but
+ this may be undesirable if the extra precision causes problems or
+ on certain chips in the mode where denormals are rounded to zero
+ where denormals generated by multiply and accumulate instructions
+ cause exceptions anyway.
+
+`-mgp32'
+ Assume that 32 32-bit general purpose registers are available.
+ This is the default.
+
+`-mgp64'
+ Assume that 32 64-bit general purpose registers are available.
+ This is the default when the `-mips3' option is used.
+
+`-mint64'
+ Force int and long types to be 64 bits wide. See `-mlong32' for an
+ explanation of the default, and the width of pointers.
+
+`-mlong64'
+ Force long types to be 64 bits wide. See `-mlong32' for an
+ explanation of the default, and the width of pointers.
+
+`-mlong32'
+ Force long, int, and pointer types to be 32 bits wide.
+
+ If none of `-mlong32', `-mlong64', or `-mint64' are set, the size
+ of ints, longs, and pointers depends on the ABI and ISA chosen.
+ For `-mabi=32', and `-mabi=n32', ints and longs are 32 bits wide.
+ For `-mabi=64', ints are 32 bits, and longs are 64 bits wide. For
+ `-mabi=eabi' and either `-mips1' or `-mips2', ints and longs are
+ 32 bits wide. For `-mabi=eabi' and higher ISAs, ints are 32 bits,
+ and longs are 64 bits wide. The width of pointer types is the
+ smaller of the width of longs or the width of general purpose
+ registers (which in turn depends on the ISA).
+
+`-mabi=32'
+`-mabi=o64'
+`-mabi=n32'
+`-mabi=64'
+`-mabi=eabi'
+ Generate code for the indicated ABI. The default instruction
+ level is `-mips1' for `32', `-mips3' for `n32', and `-mips4'
+ otherwise. Conversely, with `-mips1' or `-mips2', the default ABI
+ is `32'; otherwise, the default ABI is `64'.
+
+`-mmips-as'
+ Generate code for the MIPS assembler, and invoke `mips-tfile' to
+ add normal debug information. This is the default for all
+ platforms except for the OSF/1 reference platform, using the
+ OSF/rose object format. If the either of the `-gstabs' or
+ `-gstabs+' switches are used, the `mips-tfile' program will
+ encapsulate the stabs within MIPS ECOFF.
+
+`-mgas'
+ Generate code for the GNU assembler. This is the default on the
+ OSF/1 reference platform, using the OSF/rose object format. Also,
+ this is the default if the configure option `--with-gnu-as' is
+ used.
+
+`-msplit-addresses'
+`-mno-split-addresses'
+ Generate code to load the high and low parts of address constants
+ separately. This allows GCC to optimize away redundant loads of
+ the high order bits of addresses. This optimization requires GNU
+ as and GNU ld. This optimization is enabled by default for some
+ embedded targets where GNU as and GNU ld are standard.
+
+`-mrnames'
+`-mno-rnames'
+ The `-mrnames' switch says to output code using the MIPS software
+ names for the registers, instead of the hardware names (ie, A0
+ instead of $4). The only known assembler that supports this option
+ is the Algorithmics assembler.
+
+`-mgpopt'
+`-mno-gpopt'
+ The `-mgpopt' switch says to write all of the data declarations
+ before the instructions in the text section, this allows the MIPS
+ assembler to generate one word memory references instead of using
+ two words for short global or static data items. This is on by
+ default if optimization is selected.
+
+`-mstats'
+`-mno-stats'
+ For each non-inline function processed, the `-mstats' switch
+ causes the compiler to emit one line to the standard error file to
+ print statistics about the program (number of registers saved,
+ stack size, etc.).
+
+`-mmemcpy'
+`-mno-memcpy'
+ The `-mmemcpy' switch makes all block moves call the appropriate
+ string function (`memcpy' or `bcopy') instead of possibly
+ generating inline code.
+
+`-mmips-tfile'
+`-mno-mips-tfile'
+ The `-mno-mips-tfile' switch causes the compiler not postprocess
+ the object file with the `mips-tfile' program, after the MIPS
+ assembler has generated it to add debug support. If `mips-tfile'
+ is not run, then no local variables will be available to the
+ debugger. In addition, `stage2' and `stage3' objects will have
+ the temporary file names passed to the assembler embedded in the
+ object file, which means the objects will not compare the same.
+ The `-mno-mips-tfile' switch should only be used when there are
+ bugs in the `mips-tfile' program that prevents compilation.
+
+`-msoft-float'
+ Generate output containing library calls for floating point.
+ *Warning:* the requisite libraries are not part of GCC. Normally
+ the facilities of the machine's usual C compiler are used, but
+ this can't be done directly in cross-compilation. You must make
+ your own arrangements to provide suitable library functions for
+ cross-compilation.
+
+`-mhard-float'
+ Generate output containing floating point instructions. This is
+ the default if you use the unmodified sources.
+
+`-mabicalls'
+`-mno-abicalls'
+ Emit (or do not emit) the pseudo operations `.abicalls',
+ `.cpload', and `.cprestore' that some System V.4 ports use for
+ position independent code.
+
+`-mlong-calls'
+`-mno-long-calls'
+ Do all calls with the `JALR' instruction, which requires loading
+ up a function's address into a register before the call. You need
+ to use this switch, if you call outside of the current 512
+ megabyte segment to functions that are not through pointers.
+
+`-mhalf-pic'
+`-mno-half-pic'
+ Put pointers to extern references into the data section and load
+ them up, rather than put the references in the text section.
+
+`-membedded-pic'
+`-mno-embedded-pic'
+ Generate PIC code suitable for some embedded systems. All calls
+ are made using PC relative address, and all data is addressed
+ using the $gp register. No more than 65536 bytes of global data
+ may be used. This requires GNU as and GNU ld which do most of the
+ work. This currently only works on targets which use ECOFF; it
+ does not work with ELF.
+
+`-membedded-data'
+`-mno-embedded-data'
+ Allocate variables to the read-only data section first if
+ possible, then next in the small data section if possible,
+ otherwise in data. This gives slightly slower code than the
+ default, but reduces the amount of RAM required when executing,
+ and thus may be preferred for some embedded systems.
+
+`-muninit-const-in-rodata'
+`-mno-uninit-const-in-rodata'
+ When used together with `-membedded-data', it will always store
+ uninitialized const variables in the read-only data section.
+
+`-msingle-float'
+`-mdouble-float'
+ The `-msingle-float' switch tells gcc to assume that the floating
+ point coprocessor only supports single precision operations, as on
+ the `r4650' chip. The `-mdouble-float' switch permits gcc to use
+ double precision operations. This is the default.
+
+`-mmad'
+`-mno-mad'
+ Permit use of the `mad', `madu' and `mul' instructions, as on the
+ `r4650' chip.
+
+`-m4650'
+ Turns on `-msingle-float', `-mmad', and, at least for now,
+ `-mcpu=r4650'.
+
+`-mips16'
+`-mno-mips16'
+ Enable 16-bit instructions.
+
+`-mentry'
+ Use the entry and exit pseudo ops. This option can only be used
+ with `-mips16'.
+
+`-EL'
+ Compile code for the processor in little endian mode. The
+ requisite libraries are assumed to exist.
+
+`-EB'
+ Compile code for the processor in big endian mode. The requisite
+ libraries are assumed to exist.
+
+`-G NUM'
+ 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. This allows the assembler to emit one word memory
+ reference instructions based on the global pointer (GP or $28),
+ instead of the normal two words used. By default, NUM is 8 when
+ the MIPS assembler is used, and 0 when the GNU assembler is used.
+ The `-G NUM' switch is also passed to the assembler and linker.
+ All modules should be compiled with the same `-G NUM' value.
+
+`-nocpp'
+ Tell the MIPS assembler to not run its preprocessor over user
+ assembler files (with a `.s' suffix) when assembling them.
+
+`-mfix7000'
+ Pass an option to gas which will cause nops to be inserted if the
+ read of the destination register of an mfhi or mflo instruction
+ occurs in the following two instructions.
+
+`-no-crt0'
+ Do not include the default crt0.
+
+`-mflush-func=FUNC'
+`-mno-flush-func'
+ Specifies the function to call to flush the I and D caches, or to
+ not call any such function. If called, the function must take the
+ same arguments as the common `_flush_func()', that is, the address
+ of the memory range for which the cache is being flushed, the size
+ of the memory range, and the number 3 (to flush both caches). The
+ default depends on the target gcc was configured for, but commonly
+ is either `_flush_func' or `__cpu_flush'.
+
+ 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.
+
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