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GNU CC Command Options

When you invoke GNU CC, it normally does preprocessing, compilation, assembly and linking. The "overall options" allow you to stop this process at an intermediate stage. For example, the `-c' option says not to run the linker. Then the output consists of object files output by the assembler.

Other options are passed on to one stage of processing. Some options control the preprocessor and others the compiler itself. Yet other options control the assembler and linker; most of these are not documented here, since you rarely need to use any of them.

Most of the command line options that you can use with GNU CC are useful for C programs; when an option is only useful with another language (usually C++), the explanation says so explicitly. If the description for a particular option does not mention a source language, you can use that option with all supported languages.

See section Compiling C++ Programs, for a summary of special options for compiling C++ programs.

The gcc program accepts options and file names as operands. Many options have multiletter names; therefore multiple single-letter options may not be grouped: `-dr' is very different from `-d -r'.

You can mix options and other arguments. For the most part, the order you use doesn't matter. Order does matter when you use several options of the same kind; for example, if you specify `-L' more than once, the directories are searched in the order specified.

Many options have long names starting with `-f' or with `-W'---for example, `-fforce-mem', `-fstrength-reduce', `-Wformat' and so on. Most of these have both positive and negative forms; the negative form of `-ffoo' would be `-fno-foo'. This manual documents only one of these two forms, whichever one is not the default.

Option Summary

Here is a summary of all the options, grouped by type. Explanations are in the following sections.

Overall Options
See section Options Controlling the Kind of Output. 
-c  -S  -E  -o file  -pipe  -v  -x language
C Language Options
See section Options Controlling C Dialect. 
-ansi  -fallow-single-precision -fcond-mismatch  -fno-asm
-fno-builtin  -fsigned-bitfields  -fsigned-char 
-funsigned-bitfields  -funsigned-char  -fwritable-strings
-traditional  -traditional-cpp  -trigraphs
C++ Language Options
See section Options Controlling C++ Dialect. 
-fall-virtual  -fdollars-in-identifiers  -felide-constructors
-fenum-int-equiv -fexternal-templates  -ffor-scope -fno-for-scope
-fhandle-signatures -fmemoize-lookups  -fno-default-inline -fno-gnu-keywords
-fnonnull-objects  -foperator-names  -fstrict-prototype
-fthis-is-variable -nostdinc++ -traditional  +en
Warning Options
See section Options to Request or Suppress Warnings. 
-fsyntax-only  -pedantic  -pedantic-errors
-w  -W  -Wall  -Waggregate-return  -Wbad-function-cast
-Wcast-align -Wcast-qual  -Wchar-subscript  -Wcomment
-Wconversion -Wenum-clash  -Werror  -Wformat
-Wid-clash-len  -Wimplicit  -Wimport  -Winline
-Wlarger-than-len  -Wmissing-declarations
-Wmissing-prototypes  -Wnested-externs
-Wno-import  -Woverloaded-virtual -Wparentheses
-Wpointer-arith  -Wredundant-decls -Wreorder -Wreturn-type -Wshadow
-Wstrict-prototypes  -Wswitch  -Wsynth  -Wtemplate-debugging
-Wtraditional  -Wtrigraphs -Wuninitialized  -Wunused
-Wwrite-strings
Debugging Options
See section Options for Debugging Your Program or GNU CC. 
-a  -dletters  -fpretend-float 
-g  -glevel -gcoff  -gdwarf  -gdwarf+
-ggdb  -gstabs  -gstabs+  -gxcoff  -gxcoff+
-p  -pg  -print-file-name=library  -print-libgcc-file-name
-print-prog-name=program  -print-search-dirs  -save-temps
Optimization Options
See section Options That Control Optimization. 
-fcaller-saves  -fcse-follow-jumps  -fcse-skip-blocks
-fdelayed-branch   -fexpensive-optimizations  
-ffast-math  -ffloat-store  -fforce-addr  -fforce-mem
-finline-functions  -fkeep-inline-functions  
-fno-default-inline  -fno-defer-pop  -fno-function-cse
-fno-inline  -fno-peephole  -fomit-frame-pointer  
-frerun-cse-after-loop  -fschedule-insns  
-fschedule-insns2  -fstrength-reduce  -fthread-jumps 
-funroll-all-loops  -funroll-loops
-O  -O0  -O1  -O2  -O3
Preprocessor Options
See section Options Controlling the Preprocessor. 
-Aquestion(answer)  -C  -dD  -dM  -dN
-Dmacro[=defn]  -E  -H
-idirafter dir
-include file  -imacros file
-iprefix file  -iwithprefix dir
-iwithprefixbefore dir  -isystem dir
-M  -MD  -MM  -MMD  -MG  -nostdinc  -P  -trigraphs
-undef  -Umacro  -Wp,option
Assembler Option
See section Passing Options to the Assembler. 
-Wa,option
Linker Options
See section Options for Linking. 
object-file-name  -llibrary
-nostartfiles  -nodefaultlibs  -nostdlib  
-s  -static  -shared  -symbolic  
-Wl,option  -Xlinker option
-u symbol
Directory Options
See section Options for Directory Search. 
-Bprefix  -Idir  -I-  -Ldir
Target Options
See section Specifying Target Machine and Compiler Version. 
-b machine  -V version
Machine Dependent Options
See section Hardware Models and Configurations. 
M680x0 Options
-m68000  -m68020  -m68020-40  -m68030  -m68040  -m68881  
-mbitfield  -mc68000  -mc68020  -mfpa  -mnobitfield  
-mrtd  -mshort  -msoft-float 

VAX Options
-mg  -mgnu  -munix

SPARC Options
-mapp-regs  -mcypress  -mepilogue  -mflat  -mfpu  -mhard-float
-mhard-quad-float  -mno-app-regs  -mno-flat  -mno-fpu
-mno-epilogue  -mno-unaligned-doubles
-msoft-float  -msoft-quad-float
-msparclite  -msupersparc  -munaligned-doubles  -mv8

SPARC V9 compilers support the following options
in addition to the above:

-mmedlow  -mmedany
-mint32  -mint64  -mlong32  -mlong64
-mno-stack-bias  -mstack-bias

Convex Options
-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
-mstorem-bug  -muser-registers

ARM Options
-mapcs -m2 -m3 -m6 -mbsd -mxopen -mno-symrename

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 
-mversion-03.00  -mwarn-passed-structs

RS/6000 and PowerPC Options
-mcpu=cpu  type
-mpower  -mno-power  -mpower2  -mno-power2
-mpowerpc  -mno-powerpc
-mpowerpc-gpopt  -mno-powerpc-gpopt
-mpowerpc-gfxopt  -mno-powerpc-gfxopt
-mnew-mnemonics  -mno-new-mnemonics
-mfull-toc   -mminimal-toc  -mno-fop-in-toc  -mno-sum-in-toc
-msoft-float  -mhard-float -mmultiple -mno-multiple
-mstring -mno-string -mbit-align -mno-bit-align
-mstrict-align -mno-strict-align -mrelocatable -mno-relocatable
-mtoc -mno-toc -mtraceback -mno-traceback
-mlittle -mlittle-endian -mbig -mbig-endian
-mcall-aix -mcall-sysv -mprototype

RT Options
-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  -mcpu=cpu  type  -membedded-data
-membedded-pic  -mfp32  -mfp64  -mgas  -mgp32  -mgp64
-mgpopt  -mhalf-pic  -mhard-float  -mint64 -mips1
-mips2 -mips3  -mlong64  -mlong-calls  -mmemcpy
-mmips-as  -mmips-tfile  -mno-abicalls
-mno-embedded-data  -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

i386 Options
-m486  -m386 -mieee-fp  -mno-fancy-math-387
-mno-fp-ret-in-387  -msoft-float  -msvr3-shlib  
-mno-wide-multiply -mrtd -malign-double
-mreg-alloc=list -mregparm=num
-malign-jumps=num -malign-loops=num
-malign-functions=num

HPPA Options
-mdisable-fpregs  -mdisable-indexing  -mfast-indirect-calls
-mgas  -mjump-in-delay -mlong-millicode-calls -mno-disable-fpregs
-mno-disable-indexing -mno-fast-indirect-calls -mno-gas
-mno-jump-in-delay -mno-millicode-long-calls
-mno-portable-runtime -mno-soft-float -msoft-float
-mpa-risc-1-0  -mpa-risc-1-1  -mportable-runtime -mschedule=list

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
-mtail-call

DEC Alpha Options
-mfp-regs  -mno-fp-regs  -mno-soft-float
-msoft-float

Clipper Options
-mc300 -mc400

H8/300 Options
-mrelax  -mh

System V Options
-Qy  -Qn  -YP,paths  -Ym,dir
Code Generation Options
See section Options for Code Generation Conventions. 
-fcall-saved-reg  -fcall-used-reg 
-ffixed-reg  -finhibit-size-directive 
-fno-common  -fno-ident  -fno-gnu-linker
-fpcc-struct-return  -fpic  -fPIC 
-freg-struct-return  -fshared-data  -fshort-enums
-fshort-double  -fvolatile  -fvolatile-global
-fverbose-asm -fpack-struct +e0  +e1

Options Controlling the Kind of Output

Compilation can involve up to four stages: preprocessing, compilation proper, assembly and linking, always in that order. The first three stages apply to an individual source file, and end by producing an object file; linking combines all the object files (those newly compiled, and those specified as input) into an executable file.

For any given input file, the file name suffix determines what kind of compilation is done:

file.c
C source code which must be preprocessed.
file.i
C source code which should not be preprocessed.
file.ii
C++ source code which should not be preprocessed.
file.m
Objective-C source code. Note that you must link with the library `libobjc.a' to make an Objective-C program work.
file.h
C header file (not to be compiled or linked).
file.cc
file.cxx
file.cpp
file.C
C++ source code which must be preprocessed. Note that in `.cxx', the last two letters must both be literally `x'. Likewise, `.C' refers to a literal capital C.
file.s
Assembler code.
file.S
Assembler code which must be preprocessed.
other
An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way.

You can specify the input language explicitly with the `-x' option:

-x language
Specify explicitly the language for the following input files (rather than letting the compiler choose a default based on the file name suffix). This option applies to all following input files until the next `-x' option. Possible values for language are: 
c  objective-c  c++
c-header  cpp-output  c++-cpp-output
assembler  assembler-with-cpp
-x none
Turn off any specification of a language, so that subsequent files are handled according to their file name suffixes (as they are if `-x' has not been used at all).

If you only want some of the stages of compilation, you can use `-x' (or filename suffixes) to tell gcc where to start, and one of the options `-c', `-S', or `-E' to say where gcc is to stop. Note that some combinations (for example, `-x cpp-output -E' instruct gcc to do nothing at all.

-c
Compile or assemble the source files, but do not link. The linking stage simply is not done. The ultimate output is in the form of an object file for each source file. By default, the object file name for a source file is made by replacing the suffix `.c', `.i', `.s', etc., with `.o'. Unrecognized input files, not requiring compilation or assembly, are ignored.
-S
Stop after the stage of compilation proper; do not assemble. The output is in the form of an assembler code file for each non-assembler input file specified. By default, the assembler file name for a source file is made by replacing the suffix `.c', `.i', etc., with `.s'. Input files that don't require compilation are ignored.
-E
Stop after the preprocessing stage; do not run the compiler proper. The output is in the form of preprocessed source code, which is sent to the standard output. Input files which don't require preprocessing are ignored.
-o file
Place output in file file. This applies regardless to whatever sort of output is being produced, whether it be an executable file, an object file, an assembler file or preprocessed C code. Since only one output file can be specified, it does not make sense to use `-o' when compiling more than one input file, unless you are producing an executable file as output. If `-o' is not specified, the default is to put an executable file in `a.out', the object file for `source.suffix' in `source.o', its assembler file in `source.s', and all preprocessed C source on standard output.
-v
Print (on standard error output) the commands executed to run the stages of compilation. Also print the version number of the compiler driver program and of the preprocessor and the compiler proper.
-pipe
Use pipes rather than temporary files for communication between the various stages of compilation. This fails to work on some systems where the assembler is unable to read from a pipe; but the GNU assembler has no trouble.

Compiling C++ Programs

C++ source files conventionally use one of the suffixes `.C', `.cc', `cpp', or `.cxx'; preprocessed C++ files use the suffix `.ii'. GNU CC recognizes files with these names and compiles them as C++ programs even if you call the compiler the same way as for compiling C programs (usually with the name gcc).

However, C++ programs often require class libraries as well as a compiler that understands the C++ language--and under some circumstances, you might want to compile programs from standard input, or otherwise without a suffix that flags them as C++ programs. g++ is a program that calls GNU CC with the default language set to C++, and automatically specifies linking against the GNU class library libg++. (1) On many systems, the script g++ is also installed with the name c++.

When you compile C++ programs, you may specify many of the same command-line options that you use for compiling programs in any language; or command-line options meaningful for C and related languages; or options that are meaningful only for C++ programs. See section Options Controlling C Dialect, for explanations of options for languages related to C. See section Options Controlling C++ Dialect, for explanations of options that are meaningful only for C++ programs.

Options Controlling C Dialect

The following options control the dialect of C (or languages derived from C, such as C++ and Objective C) that the compiler accepts:

-ansi
Support all ANSI standard C programs. This turns off certain features of GNU C that are incompatible with ANSI C, such as the asm, inline 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 ANSI trigraph feature, disallows `$' as part of identifiers, and disables recognition of C++ style `//' comments. The alternate keywords __asm__, __extension__, __inline__ and __typeof__ continue to work despite `-ansi'. You would not want to use them in an ANSI 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-ANSI programs to be rejected gratuitously. For that, `-pedantic' is required in addition to `-ansi'. See section Options to Request or Suppress Warnings. 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 ANSI standard doesn't call for; this is to avoid interfering with any programs that might use these names for other things. The functions alloca, abort, exit, and _exit are not builtin functions when `-ansi' is used.
-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, as it also disables the other, C++-specific, extension keywords such as headof.
-fno-builtin
Don't recognize builtin functions that do not begin with two leading underscores. Currently, the functions affected include abort, abs, alloca, cos, exit, fabs, ffs, labs, memcmp, memcpy, sin, sqrt, strcmp, strcpy, and strlen. GCC normally generates special code to handle certain builtin 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. The `-ansi' option prevents alloca and ffs from being builtin functions, since these functions do not have an ANSI standard meaning.
-trigraphs
Support ANSI C trigraphs. You don't want to know about this brain-damage. The `-ansi' option implies `-trigraphs'.
-traditional
Attempt to support some aspects of traditional C compilers. Specifically: You may wish to use `-fno-builtin' as well as `-traditional' if your program uses names that are normally GNU C builtin functions for other purposes of its own. You cannot use `-traditional' if you include any header files that rely on ANSI C features. Some vendors are starting to ship systems with ANSI C header files and you cannot use `-traditional' on such systems to compile files that include any system headers.
In the preprocessor, comments convert to nothing at all, rather than to a space. This allows traditional token concatenation.
In preprocessing directive, the `#' symbol must appear as the first character of a line.
In the preprocessor, macro arguments are recognized within string constants in a macro definition (and their values are stringified, though without additional quote marks, when they appear in such a context). The preprocessor always considers a string constant to end at a newline.
The predefined macro __STDC__ is not defined when you use `-traditional', but __GNUC__ is (since the GNU extensions which __GNUC__ indicates are not affected by `-traditional'). If you need to write header files that work differently depending on whether `-traditional' is in use, by testing both of these predefined macros you can distinguish four situations: GNU C, traditional GNU C, other ANSI C compilers, and other old C compilers. The predefined macro __STDC_VERSION__ is also not defined when you use `-traditional'. See section `Standard Predefined Macros' in The C Preprocessor, for more discussion of these and other predefined macros.
The preprocessor considers a string constant to end at a newline (unless the newline is escaped with `\'). (Without `-traditional', string constants can contain the newline character as typed.)
-traditional-cpp
Attempt to support some aspects of traditional C preprocessors. This includes the last five items in the table immediately above, but none of the other effects of `-traditional'.
-fcond-mismatch
Allow conditional expressions with mismatched types in the second and third arguments. The value of such an expression is void.
-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 bitfield is signed or unsigned, when the declaration does not use either signed or unsigned. By default, such a bitfield is signed, because this is consistent: the basic integer types such as int are signed types. However, when `-traditional' is used, bitfields 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 ANSI or GNU C conventions (the default).

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 -felide-constructors -O -c firstClass.C

In this example, only `-felide-constructors' is an option meant only for C++ programs; you can use the other options with any language supported by GNU CC.

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.
-fall-virtual
Treat all possible member functions as virtual, implicitly. All member functions (except for constructor functions and new or delete member operators) are treated as virtual functions of the class where they appear. This does not mean that all calls to these member functions will be made through the internal table of virtual functions. Under some circumstances, the compiler can determine that a call to a given virtual function can be made directly; in these cases the calls are direct in any case.
-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.
-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.
-fdollars-in-identifiers
Accept `$' in identifiers. You can also explicitly prohibit use of `$' with the option `-fno-dollars-in-identifiers'. (GNU C++ allows `$' by default on some target systems but not others.) Traditional C allowed the character `$' to form part of identifiers. However, ANSI C and C++ forbid `$' in identifiers.
-fenum-int-equiv
Anachronistically permit implicit conversion of int to enumeration types. Current C++ allows conversion of enum to int, but not the other way around.
-fexternal-templates
Cause template instantiations to obey `#pragma interface' and `implementation'; template instances are emitted or not according to the location of the template definition. See section Where's the Template?, for more information.
-falt-external-templates
Similar to -fexternal-templates, but template instances are emitted or not according to the place where they are first instantiated. See section Where's the Template?, for more information.
-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 draft 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 gcc, 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 classof, headof, signature, sigof or typeof as a keyword, so that code can use these words as identifiers. You can use the keywords __classof__, __headof__, __signature__, __sigof__, and __typeof__ instead. `-ansi' implies `-fno-gnu-keywords'.
-fno-implicit-templates
Never emit code for templates which are instantiated implicitly (i.e. by use); only emit code for explicit instantiations. See section Where's the Template?, for more information.
-fhandle-signatures
Recognize the signature and sigof keywords for specifying abstract types. The default (`-fno-handle-signatures') is not to recognize them. See section Type Abstraction using Signatures.
-fhuge-objects
Support virtual function calls for objects that exceed the size representable by a `short int'. Users should not use this flag by default; if you need to use it, the compiler will tell you so. If you compile any of your code with this flag, you must compile all of your code with this flag (including libg++, if you use it). This flag is not useful when compiling with -fvtable-thunks.
-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.
-fmemoize-lookups
-fsave-memoized
Use heuristics to compile faster. These heuristics are not enabled by default, since they are only effective for certain input files. Other input files compile more slowly. The first time the compiler must build a call to a member function (or reference to a data member), it must (1) determine whether the class implements member functions of that name; (2) resolve which member function to call (which involves figuring out what sorts of type conversions need to be made); and (3) check the visibility of the member function to the caller. All of this adds up to slower compilation. Normally, the second time a call is made to that member function (or reference to that data member), it must go through the same lengthy process again. This means that code like this: 
cout << "This " << p << " has " << n << " legs.\n";
makes six passes through all three steps. By using a software cache, a "hit" significantly reduces this cost. Unfortunately, using the cache introduces another layer of mechanisms which must be implemented, and so incurs its own overhead. `-fmemoize-lookups' enables the software cache. Because access privileges (visibility) to members and member functions may differ from one function context to the next, G++ may need to flush the cache. With the `-fmemoize-lookups' flag, the cache is flushed after every function that is compiled. The `-fsave-memoized' flag enables the same software cache, but when the compiler determines that the context of the last function compiled would yield the same access privileges of the next function to compile, it preserves the cache. This is most helpful when defining many member functions for the same class: with the exception of member functions which are friends of other classes, each member function has exactly the same access privileges as every other, and the cache need not be flushed. The code that implements these flags has rotted; you should probably avoid using them.
-fstrict-prototype
Within an `extern "C"' linkage specification, treat a function declaration with no arguments, such as `int foo ();', as declaring the function to take no arguments. Normally, such a declaration means that the function foo can take any combination of arguments, as in C. `-pedantic' implies `-fstrict-prototype' unless overridden with `-fno-strict-prototype'. This flag no longer affects declarations with C++ linkage.
-fno-nonnull-objects
Don't assume that a reference is initialized to refer to a valid object. Although the current C++ Working Paper prohibits null references, some old code may rely on them, and you can use `-fno-nonnull-objects' to turn on checking. At the moment, the compiler only does this checking for conversions to virtual base classes.
-foperator-names
Recognize the operator name keywords and, bitand, bitor, compl, not, or and xor as synonyms for the symbols they refer to. `-ansi' implies `-foperator-names'.
-fthis-is-variable
Permit assignment to this. The incorporation of user-defined free store management into C++ has made assignment to `this' an anachronism. Therefore, by default it is invalid to assign to this within a class member function; that is, GNU C++ treats `this' in a member function of class X as a non-lvalue of type `X *'. However, for backwards compatibility, you can make it valid with `-fthis-is-variable'.
-fvtable-thunks
Use `thunks' to implement the virtual function dispatch table (`vtable'). The traditional (cfront-style) approach to implementing vtables was to store a pointer to the function and two offsets for adjusting the `this' pointer at the call site. Newer implementations store a single pointer to a `thunk' function which does any necessary adjustment and then calls the target function. This option also enables a heuristic for controlling emission of vtables; if a class has any non-inline virtual functions, the vtable will be emitted in the translation unit containing the first one of those.
-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 libg++.)
-traditional
For C++ programs (in addition to the effects that apply to both C and C++), this has the same effect as `-fthis-is-variable'. See section Options Controlling C Dialect.

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. See section Options That Control Optimization.
-Wenum-clash
-Woverloaded-virtual
-Wtemplate-debugging
Warnings that apply only to C++ programs. See section Options to Request or Suppress Warnings.
+en
Control how virtual function definitions are used, in a fashion compatible with cfront 1.x. See section Options for Code Generation Conventions.

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.

These options control the amount and kinds of warnings produced by GNU CC:

-fsyntax-only
Check the code for syntax errors, but don't do anything beyond that.
-pedantic
Issue all the warnings demanded by strict ANSI standard C; reject all programs that use forbidden extensions. Valid ANSI standard C programs should compile properly with or without this option (though a rare few will require `-ansi'). However, without this option, certain GNU extensions and traditional 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. See section Alternate Keywords. This option is not intended to be useful; it exists only to satisfy pedants who would otherwise claim that GNU CC fails to support the ANSI standard. Some users try to use `-pedantic' to check programs for strict ANSI C conformance. They soon find that it does not do quite what they want: it finds some non-ANSI practices, but not all--only those for which ANSI C requires a diagnostic. A feature to report any failure to conform to ANSI C might be useful in some instances, but would require considerable additional work and would be quite different from `-pedantic'. We recommend, rather, that users take advantage of the extensions of GNU C and disregard the limitations of other compilers. Aside from certain supercomputers and obsolete small machines, there is less and less reason ever to use any other C compiler other than for bootstrapping GNU CC.
-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.
-Wformat
Check calls to printf and scanf, etc., to make sure that the arguments supplied have types appropriate to the format string specified.
-Wimplicit
Warn whenever a function or parameter is implicitly declared.
-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.
-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.
-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 (assuming they are enabled).
-Wunused
Warn whenever a variable is unused aside from its declaration, whenever a function is declared static but never defined, whenever a label is declared but not used, and whenever a statement computes a result that is explicitly not used. To suppress this warning for an expression, simply cast it to void. For unused variables and parameters, use the `unused' attribute (see section Specifying Attributes of Variables).
-Wuninitialized
An automatic variable is used without first being initialized. 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 GNU CC 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 GNU CC 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. Some spurious warnings can be avoided if you declare all the functions you use that never return as noreturn. See section Declaring Attributes of Functions.
-Wenum-clash
Warn about conversion between different enumeration types. (C++ only).
-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.
-Wtemplate-debugging
When using templates in a C++ program, warn if debugging is not yet fully available (C++ only).
-Wall
All of the above `-W' options combined. These are all the options which pertain to usage that we recommend avoiding and that we believe is easy to avoid, even in conjunction with macros.

The remaining `-W...' options are not implied by `-Wall' because they warn about constructions that we consider reasonable to use, on occasion, in clean programs.

-W
Print extra warning messages for these events:
-Wtraditional
Warn about certain constructs that behave differently in traditional and ANSI C.
-Wshadow
Warn whenever a local variable shadows another local variable.
-Wid-clash-len
Warn whenever two distinct identifiers match in the first len characters. This may help you prepare a program that will compile with certain obsolete, brain-damaged compilers.
-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
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
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. 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.
-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
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
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.
-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
Warn if an extern declaration is encountered within an function.
-Winline
Warn if a function can not be inlined, and either it was declared as inline, or else the `-finline-functions' option was given.
-Woverloaded-virtual
Warn when a derived class function declaration may be an error in defining a virtual function (C++ only). In a derived class, the definitions of virtual functions must match the type signature of a virtual function declared in the base class. With this option, the compiler warns when you define a function with the same name as a virtual function, but with a type signature that does not match any declarations from the base class.
-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 ='.
-Werror
Make all warnings into errors.

Options for Debugging Your Program or GNU CC

GNU CC 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+', or `-gdwarf' (see below). Unlike most other C compilers, GNU CC 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 GNU CC is generated with the capability for more than one debugging format.
-ggdb
Produce debugging information in the native format (if that is 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 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 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.
-glevel
-ggdblevel
-gstabslevel
-gcofflevel
-gxcofflevel
-gdwarflevel
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'.
-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.
-a
Generate extra code to write profile information for basic blocks, which will record the number of times each basic block is executed, the basic block start address, and the function name containing the basic block. If `-g' is used, the line number and filename of the start of the basic block will also be recorded. If not overridden by the machine description, the default action is to append to the text file `bb.out'. This data could be analyzed by a program like tcov. Note, however, that the format of the data is not what tcov expects. Eventually GNU gprof should be extended to process this data.
-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 word to the source file name (e.g. `foo.c.rtl' or `foo.c.jump'). Here are the possible letters for use in letters, and their meanings:
`M'
Dump all macro definitions, at the end of preprocessing, and write no output.
`N'
Dump all macro names, at the end of preprocessing.
`D'
Dump all macro definitions, at the end of preprocessing, in addition to normal output.
`y'
Dump debugging information during parsing, to standard error.
`r'
Dump after RTL generation, to `file.rtl'.
`x'
Just generate RTL for a function instead of compiling it. Usually used with `r'.
`j'
Dump after first jump optimization, to `file.jump'.
`s'
Dump after CSE (including the jump optimization that sometimes follows CSE), to `file.cse'.
`L'
Dump after loop optimization, to `file.loop'.
`t'
Dump after the second CSE pass (including the jump optimization that sometimes follows CSE), to `file.cse2'.
`f'
Dump after flow analysis, to `file.flow'.
`c'
Dump after instruction combination, to the file `file.combine'.
`S'
Dump after the first instruction scheduling pass, to `file.sched'.
`l'
Dump after local register allocation, to `file.lreg'.
`g'
Dump after global register allocation, to `file.greg'.
`R'
Dump after the second instruction scheduling pass, to `file.sched2'.
`J'
Dump after last jump optimization, to `file.jump2'.
`d'
Dump after delayed branch scheduling, to `file.dbr'.
`k'
Dump after conversion from registers to stack, to `file.stack'.
`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.
-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 GNU CC 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'.
-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, GNU CC does not compile or link anything; it just prints the file name.
-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 cpp: No such file or directory'. To resolve this you either need to put `cpp' 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 '/'. See section Environment Variables Affecting GNU CC.

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. Without `-O', the compiler only allocates variables declared register in registers. The resulting compiled code is a little worse than produced by PCC without `-O'. With `-O', the compiler tries to reduce code size and execution time. When you specify `-O', the compiler turns on `-fthread-jumps' and `-fdefer-pop' on all machines. The compiler turns on `-fdelayed-branch' on machines that have delay slots, and `-fomit-frame-pointer' on machines that can support debugging even without a frame pointer. On some machines the compiler also turns on other flags.
-O2
Optimize even more. GNU CC 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 and function inlining. 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.
-O3
Optimize yet more. `-O3' turns on all optimizations specified by `-O2' and also turns on the `inline-functions' option.
-O0
Do not optimize. 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. 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.
-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. See section Register Usage.
-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.
-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.
-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
This option allows GCC to violate some ANSI or IEEE rules and/or specifications in the interest of optimizing code for speed. For example, it allows the compiler to assume arguments to the sqrt function are non-negative numbers and that no floating-point values are NaNs. 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 ANSI rules/specifications for math functions.

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.

-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.
-fexpensive-optimizations
Perform a number of minor optimizations that are relatively expensive.
-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.
-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 enabled by default on certain machines, usually those which have no call-preserved registers to use instead.
-funroll-loops
Perform the optimization of loop unrolling. This is only done for loops whose number of iterations can be determined at compile time or run time. `-funroll-loop' implies both `-fstrength-reduce' and `-frerun-cse-after-loop'.
-funroll-all-loops
Perform the optimization of loop unrolling. This is done for all loops and usually makes programs run more slowly. `-funroll-all-loops' implies `-fstrength-reduce' as well as `-frerun-cse-after-loop'.
-fno-peephole
Disable any machine-specific peephole optimizations.

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.

-include file
Process file as input before processing the regular input file. In effect, the contents of file are compiled first. Any `-D' and `-U' options on the command line are always processed before `-include file', regardless of the order in which they are written. All the `-include' and `-imacros' options are processed in the order in which they are written.
-imacros file
Process file as input, discarding the resulting output, before processing the regular input file. Because the output generated from file is discarded, the only effect of `-imacros file' is to make the macros defined in file available for use in the main input. Any `-D' and `-U' options on the command line are always processed before `-imacros file', regardless of the order in which they are written. All the `-include' and `-imacros' options are processed in the order in which they are written.
-idirafter dir
Add the directory dir to the second include path. The directories on the second include path are searched when a header file is not found in any of the directories in the main include path (the one that `-I' adds to).
-iprefix prefix
Specify prefix as the prefix for subsequent `-iwithprefix' options.
-iwithprefix dir
Add a directory to the second include path. The directory's name is made by concatenating prefix and dir, where prefix was specified previously with `-iprefix'. If you have not specified a prefix yet, the directory containing the installed passes of the compiler is used as the default.
-iwithprefixbefore dir
Add a directory to the main include path. The directory's name is made by concatenating prefix and dir, as in the case of `-iwithprefix'.
-isystem dir
Add a directory to the beginning of the second include path, marking it as a system directory, so that it gets the same special treatment as is applied to the standard system directories.
-nostdinc
Do not search the standard system directories for header files. Only the directories you have specified with `-I' options (and the current directory, if appropriate) are searched. See section Options for Directory Search, for information on `-I'. By using both `-nostdinc' and `-I-', you can limit the include-file search path to only those directories you specify explicitly.
-undef
Do not predefine any nonstandard macros. (Including architecture flags).
-E
Run only the C preprocessor. Preprocess all the C source files specified and output the results to standard output or to the specified output file.
-C
Tell the preprocessor not to discard comments. Used with the `-E' option.
-P
Tell the preprocessor not to generate `#line' directives. Used with the `-E' option.
-M
Tell the preprocessor to output a rule suitable for make describing the dependencies of each object file. For each source file, the preprocessor outputs one make-rule whose target is the object file name for that source file and whose dependencies are all the #include header files it uses. This rule may be a single line or may be continued with `\'-newline if it is long. The list of rules is printed on standard output instead of the preprocessed C program. `-M' implies `-E'. Another way to specify output of a make rule is by setting the environment variable DEPENDENCIES_OUTPUT (see section Environment Variables Affecting GNU CC).
-MM
Like `-M' but the output mentions only the user header files included with `#include "file"'. System header files included with `#include <file>' are omitted.
-MD
Like `-M' but the dependency information is written to a file made by replacing ".c" with ".d" at the end of the input file names. This is in addition to compiling the file as specified---`-MD' does not inhibit ordinary compilation the way `-M' does. In Mach, you can use the utility md to merge multiple dependency files into a single dependency file suitable for using with the `make' command.
-MMD
Like `-MD' except mention only user header files, not system header files.
-MG
Treat missing header files as generated files and assume they live in the same directory as the source file. If you specify `-MG', you must also specify either `-M' or `-MM'. `-MG' is not supported with `-MD' or `-MMD'.
-H
Print the name of each header file used, in addition to other normal activities.
-Aquestion(answer)
Assert the answer answer for question, in case it is tested with a preprocessing conditional such as `#if #question(answer)'. `-A-' disables the standard assertions that normally describe the target machine.
-Dmacro
Define macro macro with the string `1' as its definition.
-Dmacro=defn
Define macro macro as defn. All instances of `-D' on the command line are processed before any `-U' options.
-Umacro
Undefine macro macro. `-U' options are evaluated after all `-D' options, but before any `-include' and `-imacros' options.
-dM
Tell the preprocessor to output only a list of the macro definitions that are in effect at the end of preprocessing. Used with the `-E' option.
-dD
Tell the preprocessing to pass all macro definitions into the output, in their proper sequence in the rest of the output.
-dN
Like `-dD' except that the macro arguments and contents are omitted. Only `#define name' is included in the output.
-trigraphs
Support ANSI C trigraphs. The `-ansi' option also has this effect.
-Wp,option
Pass option as an option to the preprocessor. If option contains commas, it is split into multiple options at the commas.

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.

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. See section Options Controlling the Kind of Output.
-llibrary
Search the library named library when linking. It makes a difference where in the command you write this option; the linker searches 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.
-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. One of the standard libraries bypassed by `-nostdlib' and `-nodefaultlibs' is `libgcc.a', a library of internal subroutines that GNU CC uses to overcome shortcomings of particular machines, or special needs for some languages. (See section Interfacing to GNU CC Output, 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 GNU CC library subroutines. (For example, `__main', used to ensure C++ constructors will be called; see section 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. Only a few systems support this option.
-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 GNU CC 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.

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 directory 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. If you use more than one `-I' option, the directories are scanned in left-to-right order; the standard system directories come after.
-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/' (see section Specifying Target Machine and Compiler Version). For each subprogram to be run, the compiler driver first tries the `-B' prefix, if any. If that name is not found, or if `-B' was not specified, the driver tries two standard prefixes, which are `/usr/lib/gcc/' and `/usr/local/lib/gcc-lib/'. If neither of those results in a file name that is found, the unmodified program name is searched for using the directories specified in your `PATH' environment variable. `-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. See section Environment Variables Affecting GNU CC.

Specifying Target Machine and Compiler Version

By default, GNU CC 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 GNU CC, 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 GNU CC 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 GNU CC as a cross-compiler. The value to use for machine is the same as was specified as the machine type when configuring GNU CC 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 GNU CC to run. This is useful when multiple versions are installed. For example, version might be `2.0', meaning to run GNU CC version 2.0. The default version, when you do not specify `-V', is the last version of GNU CC 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 GNU CC, 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 and version.

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 compiler version.

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.

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.

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.
-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. If your 68040 does not have code to emulate those instructions, use `-m68040'.
-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.
-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' option implies `-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 and 68020 processors, but not by the 68000.

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.

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 GNU CC, 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-epilogue
-mepilogue
With `-mepilogue' (the default), the compiler always emits code for function exit at the end of each function. Any function exit in the middle of the function (such as a return statement in C) will generate a jump to the exit code at the end of the function. With `-mno-epilogue', the compiler tries to emit exit code inline at every function exit.
-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 although debugger support is still incomplete. 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', GNU CC 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.
-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.
-mcypress
-msupersparc
These two options select the processor for which the code is optimised. 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.

In a future version of GCC, these options will very likely be renamed to `-mcpu=cypress' and `-mcpu=supersparc'.

These `-m' switches are supported in addition to the above on SPARC V9 processors:

-mmedlow
Generate code for the Medium/Low code model: assume a 32 bit address space. Programs are statically linked, PIC is not supported. Pointers are still 64 bits. It is very likely that a future version of GCC will rename this option.
-mmedany
Generate code for the Medium/Anywhere code model: assume a 32 bit text segment starting at offset 0, and a 32 bit data segment starting anywhere (determined at link time). Programs are statically linked, PIC is not supported. Pointers are still 64 bits. It is very likely that a future version of GCC will rename this option.
-mint64
Types long and int are 64 bits.
-mlong32
Types long and int are 32 bits.
-mlong64
-mint32
Type long is 64 bits, and type int is 32 bits.
-mstack-bias
-mno-stack-bias
With `-mstack-bias', GNU CC 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.

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.

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.
-msoft-float
Generate output containing library calls for floating point. Warning: the requisite libraries are not part of GNU CC. 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.

ARM Options

These `-m' options are defined for Advanced RISC Machines (ARM) architectures:

-m2
-m3
These options are identical. Generate code for the ARM2 and ARM3 processors. This option is the default. You should also use this option to generate code for ARM6 processors that are running with a 26-bit program counter.
-m6
Generate code for the ARM6 processor when running with a 32-bit program counter.
-mapcs
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.
-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.

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
-mno-optimize-arg-area
Control how function arguments are stored in stack frames. `-moptimize-arg-area' saves space by optimizing them, but this conflicts with the 88open specifications. The opposite alternative, `-mno-optimize-arg-area', agrees with 88open standards. By default GNU CC does not optimize the argument area.
-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, GNU C 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, GNU C generates the special instructions to guarantee consistency even when you use `-m88100', so that the code may be run on an MC88110 process