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GNU Info File | 1993-10-21 | 41KB | 772 lines

This is Info file gcc.info, produced by Makeinfo-1.54 from the input
file gcc.texi.
   This file documents the use and the internals of the GNU compiler.
   Published by the Free Software Foundation 675 Massachusetts Avenue
Cambridge, MA 02139 USA
   Copyright (C) 1988, 1989, 1992, 1993 Free Software Foundation, Inc.
   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the sections entitled "GNU General Public License" and "Protect
Your Freedom--Fight `Look And Feel'" are included exactly as in the
original, and provided that the entire resulting derived work is
distributed under the terms of a permission notice identical to this
   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that the sections entitled "GNU General Public
License" and "Protect Your Freedom--Fight `Look And Feel'", and this
permission notice, may be included in translations approved by the Free
Software Foundation instead of in the original English.
File: gcc.info,  Node: RS/6000 and PowerPC Options,  Next: RT Options,  Prev: M88K Options,  Up: Submodel Options
IBM RS/6000 and PowerPC Options
-------------------------------
   These `-m' options are defined for the IBM RS/6000 and PowerPC:
`-mpower'
`-mno-power'
`-mpower2'
`-mno-power2'
`-mpowerpc'
`-mno-powerpc'
`-mpowerpcsqr'
`-mno-powerpcsqr'
`-mpowerpc64'
`-mno-powerpc64'
     GNU CC supports two related instruction set architectures for the
     RS/6000 and PowerPC.  The "POWER" instruction set are those
     instructions supported by the `rios' chip set used in the original
     RS/6000 systems and the "PowerPC" instruction set is the
     architecture of the Motorola MPC6xx microprocessors.  The PowerPC
     architecture defines 64-bit instructions, but they are not
     supported by any current processors.
     Neither architecture is a subset of the other.  However there is a
     large common subset of instructions supported by both.  An MQ
     register is included in processors supporting the POWER
     architecture.
     You use these options to specify which instructions are available
     on the processor you are using.  The default value of these
     options is determined when configuring GNU CC.  Specifying the
     `-mcpu=CPU_TYPE' overrides the specification of these options.  We
     recommend you use that option rather than these.
     The `-mpower' option allows GNU CC to generate instructions that
     are found only in the POWER architecture and to use the MQ
     register.  Specifying `-mpower2' implies `-power' and also allows
     GNU CC to generate instructions that are present in the POWER2
     architecture but not the original POWER architecture.
     The `-mpowerpc' option allows GNU CC to generate instructions that
     are found only in the 32-bit subset of the PowerPC architecture.
     Specifying `-mpowerpcsqr' implies `-mpowerpc' and also allows GNU
     CC to use the floating point square root instructions in the
     PowerPC architecture but not in its first implementation.
     Likewise, specifying `-mpowerpc64' implies `-mpowerpc' and also
     allows GNU CC to use the 64-bit instructions in the PowerPC
     architecture.
     If you specify both `-mno-power' and `-mno-powerpc', GNU CC will
     use only the instructions in the common subset of both
     architectures and will not use the MQ register.  Specifying both
     `-mpower' and `-mpowerpc' permits GNU CC to use any instruction
     from either architecture and to allow use of the MQ register;
     specify this for the Motorola MPC601.
`-mnew-mnemonics'
`-mold-mnemonics'
     Select the mnemonics for GNU CC to use in the generated assembler
     code.  `-mnew-mnemonics' requests GNU CC to produce output that
     uses the assembler mnemonics defined for the PowerPC architecture
     and the `-mold-mnemonics' requests GNU CC to use the assembler
     mnemonics defined for the POWER architecture.  Instructions
     defined in only one architecture have only one mnemonic; GNU CC
     uses that mnemonic irrespective of which of thse options is
     specified.
     PowerPC assemblers support both the old and new mnemonics, as will
     later POWER assemblers.  Current POWER assemblers only support the
     old mnemonics.  Specify `-mnew-mnemonics' if you have an assembler
     that sypports them, otherwise specify `-mold-mnemonics'.
     The default value of these options depends on how GNU CC was
     configured.  Specifing `-mcpu=CPU_TYPE' sometimes overrides the
     value of these option.  Unless you are building a cross-compiled,
     you should normally not specify either `-mnew-mnemonics' or
     `-mold-mnemonics', but should instead accept the default.
`-mcpu=CPU_TYPE'
     Set architecture type, register usage, choice of mnemonics, and
     instruction scheduling parameters for machine type CPU_TYPE.  By
     default, CPU_TYPE is the target system defined when GNU CC was
     configured.  Supported values for CPU_TYPE are `rios1', `rios2',
     `601', `603', `604', `620' and `all'.
     Specifying `-mcpu=rios1' or `-mcpu=rios2' enables the `-mpower'
     option and disables the `-mpowerpc' option, `-mcpu=601' enables
     both the `-mpower' and `-mpowerpc' options, `-mcpu=603' and
     `-mcpu=604' enable the `-mpowerpc' option and disables the
     `-mpower' option, and `-mcpu=620' enables both the `-mpowerpc' and
     `-mpowerpc64' options and also disables the `-mpower' option.
     To generate code that will operate on all members of the RS/6000
     and PowerPC family, specify `-mcpu=all'.  In that case, GNU CC will
     only use instructions in the common subset and will not use the MQ
     register.  The instruction scheduling parameters and choice of
     mnemonics are not affected.
     Specifying `-mcpu=601', `-mcpu=603', `-mcpu=604', or `-mcpu=620'
     also enables the `new-mnemonics' option.
`-mnormal-toc'
`-mno-fp-in-toc'
`-mminimal-toc'
     Modify generation of the TOC (Table Of Contents), which is created
     for every executable file.  The `-mnormal-toc' option is selected
     by default.  In that case, GNU CC will allocate at least one TOC
     entry for each unique non-automatic variable reference in your
     program.  GNU CC will also place floating-point constants in the
     TOC.  However, only 16K entries are available in the TOC.
     If you receive a linker error message that says you have
     overflowed the available TOC space, recompile your files with
     either the `-mno-fp-in-toc' or `-mminimal-toc' options.
     `-mno-fp-in-toc' prevents GNU CC from putting floating-point
     constants in the TOC.  `-mminimal-toc' causes GNU CC to make only
     one TOC entry for every file.  Using the `-minimal-toc' option
     produces slightly slower and larger code than the `-mnormal-toc' or
     `-mno-fp-in-toc' options.  If you use floating-point, try the
     `-mno-fp-in-toc' option before you specify `-mminimal-toc'.
File: gcc.info,  Node: RT Options,  Next: MIPS Options,  Prev: RS/6000 and PowerPC Options,  Up: Submodel Options
IBM RT Options
--------------
   These `-m' options are defined for the IBM RT PC:
`-min-line-mul'
     Use an in-line code sequence for integer multiplies.  This is the
     default.
`-mcall-lib-mul'
     Call `lmul$$' for integer multiples.
`-mfull-fp-blocks'
     Generate full-size floating point data blocks, including the
     minimum amount of scratch space recommended by IBM.  This is the
     default.
`-mminimum-fp-blocks'
     Do not include extra scratch space in floating point data blocks.
     This results in smaller code, but slower execution, since scratch
     space must be allocated dynamically.
`-mfp-arg-in-fpregs'
     Use a calling sequence incompatible with the IBM calling
     convention in which floating point arguments are passed in
     floating point registers.  Note that `varargs.h' and `stdargs.h'
     will not work with floating point operands if this option is
     specified.
`-mfp-arg-in-gregs'
     Use the normal calling convention for floating point arguments.
     This is the default.
`-mhc-struct-return'
     Return structures of more than one word in memory, rather than in a
     register.  This provides compatibility with the MetaWare HighC (hc)
     compiler.  Use the option `-fpcc-struct-return' for compatibility
     with the Portable C Compiler (pcc).
`-mnohc-struct-return'
     Return some structures of more than one word in registers, when
     convenient.  This is the default.  For compatibility with the
     IBM-supplied compilers, use the option `-fpcc-struct-return' or the
     option `-mhc-struct-return'.
File: gcc.info,  Node: MIPS Options,  Next: i386 Options,  Prev: RT Options,  Up: Submodel Options
MIPS Options
------------
   These `-m' options are defined for the MIPS family of computers:
`-mcpu=CPU TYPE'
     Assume the defaults for the machine type CPU TYPE when scheduling
     instructions.  The default CPU TYPE is `default', which picks the
     longest cycles times for any of the machines, in order that the
     code run at reasonable rates on all MIPS cpu's.  Other choices for
     CPU TYPE are `r2000', `r3000', `r4000', and `r6000'.  While
     picking a specific CPU TYPE will schedule things appropriately for
     that particular chip, the compiler will not generate any code that
     does not meet level 1 of the MIPS ISA (instruction set
     architecture) without the `-mips2' or `-mips3' switches being used.
`-mips2'
     Issue instructions from level 2 of the MIPS ISA (branch likely,
     square root instructions).  The `-mcpu=r4000' or `-mcpu=r6000'
     switch must be used in conjunction with `-mips2'.
`-mips3'
     Issue instructions from level 3 of the MIPS ISA (64 bit
     instructions).  You must use the `-mcpu=r4000' switch along with
     `-mips3'.
`-mint64'
`-mlong64'
`-mlonglong128'
     These options don't work at present.
`-mmips-as'
     Generate code for the MIPS assembler, and invoke `mips-tfile' to
     add normal debug information.  This is the default for all
     platforms except for the OSF/1 reference platform, using the
     OSF/rose object format.  If the either of the `-gstabs' or
     `-gstabs+' switches are used, the `mips-tfile' program will
     encapsulate the stabs within MIPS ECOFF.
`-mgas'
     Generate code for the GNU assembler.  This is the default on the
     OSF/1 reference platform, using the OSF/rose object format.
`-mrnames'
`-mno-rnames'
     The `-mrnames' switch says to output code using the MIPS software
     names for the registers, instead of the hardware names (ie, A0
     instead of $4).  The GNU assembler does not support the `-mrnames'
     switch, and the MIPS assembler will be instructed to run the MIPS
     C preprocessor over the source file.  The `-mno-rnames' switch is
     default.
`-mgpopt'
`-mno-gpopt'
     The `-mgpopt' switch says to write all of the data declarations
     before the instructions in the text section, this allows the MIPS
     assembler to generate one word memory references instead of using
     two words for short global or static data items.  This is on by
     default if optimization is selected.
`-mstats'
`-mno-stats'
     For each non-inline function processed, the `-mstats' switch
     causes the compiler to emit one line to the standard error file to
     print statistics about the program (number of registers saved,
     stack size, etc.).
`-mmemcpy'
`-mno-memcpy'
     The `-mmemcpy' switch makes all block moves call the appropriate
     string function (`memcpy' or `bcopy') instead of possibly
     generating inline code.
`-mmips-tfile'
`-mno-mips-tfile'
     The `-mno-mips-tfile' switch causes the compiler not postprocess
     the object file with the `mips-tfile' program, after the MIPS
     assembler has generated it to add debug support.  If `mips-tfile'
     is not run, then no local variables will be available to the
     debugger.  In addition, `stage2' and `stage3' objects will have
     the temporary file names passed to the assembler embedded in the
     object file, which means the objects will not compare the same.
     The `-mno-mips-tfile' switch should only be used when there are
     bugs in the `mips-tfile' program that prevents compilation.
`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not part of 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.
`-mhard-float'
     Generate output containing floating point instructions.  This is
     the default if you use the unmodified sources.
`-mfp64'
     Assume that the FR bit in the status word is on, and that there
     are 32 64-bit floating point registers, instead of 32 32-bit
     floating point registers.  You must also specify the `-mcpu=r4000'
     and `-mips3' switches.
`-mfp32'
     Assume that there are 32 32-bit floating point registers.  This is
     the default.
`-mabicalls'
`-mno-abicalls'
     Emit (or do not emit) the pseudo operations `.abicalls',
     `.cpload', and `.cprestore' that some System V.4 ports use for
     position independent code.
`-mlong-calls'
`-mlong-calls'
     Do all calls with the `JALR' instruction, which requires loading
     up a function's address into a register before the call.  You need
     to use this switch, if you call outside of the current 512
     megabyte segment to functions that are not through pointers.
`-mhalf-pic'
`-mno-half-pic'
     Put pointers to extern references into the data section and load
     them up, rather than put the references in the text section.
`-G NUM'
     Put global and static items less than or equal to NUM bytes into
     the small data or bss sections instead of the normal data or bss
     section.  This allows the assembler to emit one word memory
     reference instructions based on the global pointer (GP or $28),
     instead of the normal two words used.  By default, NUM is 8 when
     the MIPS assembler is used, and 0 when the GNU assembler is used.
     The `-G NUM' switch is also passed to the assembler and linker.
     All modules should be compiled with the same `-G NUM' value.
`-nocpp'
     Tell the MIPS assembler to not run it's preprocessor over user
     assembler files (with a `.s' suffix) when assembling them.
   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.
File: gcc.info,  Node: i386 Options,  Next: HPPA Options,  Prev: MIPS Options,  Up: Submodel Options
Intel 386 Options
-----------------
   These `-m' options are defined for the i386 family of computers:
`-m486'
`-mno-486'
     Control whether or not code is optimized for a 486 instead of an
     386.  Code generated for an 486 will run on a 386 and vice versa.
`-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.
     On machines where a function returns floating point results in the
     80387 register stack, some floating point opcodes may be emitted
     even if `-msoft-float' is used.
`-mno-fp-ret-in-387'
     Do not use the FPU registers for return values of functions.
     The usual calling convention has functions return values of types
     `float' and `double' in an FPU register, even if there is no FPU.
     The idea is that the operating system should emulate an FPU.
     The option `-mno-fp-ret-in-387' causes such values to be returned
     in ordinary CPU registers instead.
File: gcc.info,  Node: HPPA Options,  Next: Intel 960 Options,  Prev: i386 Options,  Up: Submodel Options
HPPA Options
------------
   These `-m' options are defined for the HPPA family of computers:
`-mpa-risc-1-0'
     Generate code for a PA 1.0 processor.
`-mpa-risc-1-1'
     Generate code for a PA 1.1 processor.
`-mlong-calls'
     Generate code which allows calls to functions greater than 256k
     away from the caller when the caller and callee are in the same
     source file.  Do not turn this option on unless code refuses to
     link with "branch out of range errors" from the linker.
`-mdisable-fpregs'
     Prevent floating point registers from being used in any manner.
     This is necessary for compiling kernels which perform lazy context
     switching of floating point registers.  If you use this option and
     attempt to perform floating point operations, the compiler will
     abort.
`-mdisable-indexing'
     Prevent the compiler from using indexing address modes.  This
     avoids some rather obscure problems when compiling MIG generated
     code under MACH.
`-mtrailing-colon'
     Add a colon to the end of label definitions (for ELF assemblers).
File: gcc.info,  Node: Intel 960 Options,  Next: DEC Alpha Options,  Prev: HPPA Options,  Up: Submodel Options
Intel 960 Options
-----------------
   These `-m' options are defined for the Intel 960 implementations:
`-mCPU TYPE'
     Assume the defaults for the machine type CPU TYPE for some of the
     other options, including instruction scheduling, floating point
     support, and addressing modes.  The choices for CPU TYPE are `ka',
     `kb', `mc', `ca', `cf', `sa', and `sb'.  The default is `kb'.
`-mnumerics'
`-msoft-float'
     The `-mnumerics' option indicates that the processor does support
     floating-point instructions.  The `-msoft-float' option indicates
     that floating-point support should not be assumed.
`-mleaf-procedures'
`-mno-leaf-procedures'
     Do (or do not) attempt to alter leaf procedures to be callable
     with the `bal' instruction as well as `call'.  This will result in
     more efficient code for explicit calls when the `bal' instruction
     can be substituted by the assembler or linker, but less efficient
     code in other cases, such as calls via function pointers, or using
     a linker that doesn't support this optimization.
`-mtail-call'
`-mno-tail-call'
     Do (or do not) make additional attempts (beyond those of the
     machine-independent portions of the compiler) to optimize
     tail-recursive calls into branches.  You may not want to do this
     because the detection of cases where this is not valid is not
     totally complete.  The default is `-mno-tail-call'.
`-mcomplex-addr'
`-mno-complex-addr'
     Assume (or do not assume) that the use of a complex addressing
     mode is a win on this implementation of the i960.  Complex
     addressing modes may not be worthwhile on the K-series, but they
     definitely are on the C-series.  The default is currently
     `-mcomplex-addr' for all processors except the CB and CC.
`-mcode-align'
`-mno-code-align'
     Align code to 8-byte boundaries for faster fetching (or don't
     bother).  Currently turned on by default for C-series
     implementations only.
`-mic-compat'
`-mic2.0-compat'
`-mic3.0-compat'
     Enable compatibility with iC960 v2.0 or v3.0.
`-masm-compat'
`-mintel-asm'
     Enable compatibility with the iC960 assembler.
`-mstrict-align'
`-mno-strict-align'
     Do not permit (do permit) unaligned accesses.
`-mold-align'
     Enable structure-alignment compatibility with Intel's gcc release
     version 1.3 (based on gcc 1.37).  Currently this is buggy in that
     `#pragma align 1' is always assumed as well, and cannot be turned
     off.
File: gcc.info,  Node: DEC Alpha Options,  Next: Clipper Options,  Prev: Intel 960 Options,  Up: Submodel Options
DEC Alpha Options
-----------------
   These `-m' options are defined for the DEC Alpha implementations:
`-mno-soft-float'
`-msoft-float'
     Use (do not use) the hardware floating-point instructions for
     floating-point operations.  When `-msoft-float' is specified,
     functions in `libgcc1.c' will be used to perform floating-point
     operations.  Unless they are replaced by routines that emulate the
     floating-point operations, or compiled in such a way as to call
     such emulations routines, these routines will issue floating-point
     operations.   If you are compiling for an Alpha without
     floating-point operations, you must ensure that the library is
     built so as not to call them.
     Note that Alpha implementations without floating-point operations
     are required to have floating-point registers.
`-mfp-reg'
`-mno-fp-regs'
     Generate code that uses (does not use) the floating-point register
     set.  `-mno-fp-regs' implies `-msoft-float'.  If the floating-point
     register set is not used, floating point operands are passed in
     integer registers as if they were integers and floating-point
     results are passed in $0 instead of $f0.  This is a non-standard
     calling sequence, so any function with a floating-point argument
     or return value called by code compiled with `-mno-fp-regs' must
     also be compiled with that option.
     A typical use of this option is building a kernel that does not
     use, and hence need not save and restore, any floating-point
     registers.
File: gcc.info,  Node: Clipper Options,  Next: System V Options,  Prev: DEC Alpha Options,  Up: Submodel Options
Clipper Options
---------------
   These `-m' options are defined for the Clipper implementations:
`-mc300'
     Produce code for a C300 Clipper processor. This is the default.
`-mc400'
     Produce code for a C400 Clipper processor i.e. use floting point
     registers f8..f15.
File: gcc.info,  Node: System V Options,  Prev: Clipper Options,  Up: Submodel Options
Options for System V
--------------------
   These additional options are available on System V Release 4 for
compatibility with other compilers on those systems:
`-Qy'
     Identify the versions of each tool used by the compiler, in a
     `.ident' assembler directive in the output.
`-Qn'
     Refrain from adding `.ident' directives to the output file (this is
     the default).
`-YP,DIRS'
     Search the directories DIRS, and no others, for libraries
     specified with `-l'.
`-Ym,DIR'
     Look in the directory DIR to find the M4 preprocessor.  The
     assembler uses this option.
File: gcc.info,  Node: Code Gen Options,  Next: Environment Variables,  Prev: Submodel Options,  Up: Invoking GCC
Options for Code Generation Conventions
=======================================
   These machine-independent options control the interface conventions
used in code generation.
   Most of them have both positive and negative forms; the negative form
of `-ffoo' would be `-fno-foo'.  In the table below, only one of the
forms is listed--the one which is not the default.  You can figure out
the other form by either removing `no-' or adding it.
`-fpcc-struct-return'
     Return "short" `struct' and `union' values in memory like longer
     ones, rather than in registers.  This convention is less
     efficient, but it has the advantage of allowing intercallability
     between GNU CC-compiled files and files compiled with other
     compilers.
     The precise convention for returning structures in memory depends
     on the target configuration macros.
     Short structures and unions are those whose size and alignment
     match that of some integer type.
`-freg-struct-return'
     Use the convention that `struct' and `union' values are returned
     in registers when possible.  This is more efficient for small
     structures than `-fpcc-struct-return'.
     If you specify neither `-fpcc-struct-return' nor its contrary
     `-freg-struct-return', GNU CC defaults to whichever convention is
     standard for the target.  If there is no standard convention, GNU
     CC defaults to `-fpcc-struct-return', except on targets where GNU
     CC is the principal compiler.  In those cases, we can choose the
     standard, and we chose the more efficient register return
     alternative.
`-fshort-enums'
     Allocate to an `enum' type only as many bytes as it needs for the
     declared range of possible values.  Specifically, the `enum' type
     will be equivalent to the smallest integer type which has enough
     room.
`-fshort-double'
     Use the same size for `double' as for `float'.
`-fshared-data'
     Requests that the data and non-`const' variables of this
     compilation be shared data rather than private data.  The
     distinction makes sense only on certain operating systems, where
     shared data is shared between processes running the same program,
     while private data exists in one copy per process.
`-fno-common'
     Allocate even uninitialized global variables in the bss section of
     the object file, rather than generating them as common blocks.
     This has the effect that if the same variable is declared (without
     `extern') in two different compilations, you will get an error
     when you link them.  The only reason this might be useful is if
     you wish to verify that the program will work on other systems
     which always work this way.
`-fno-ident'
     Ignore the `#ident' directive.
`-fno-gnu-linker'
     Do not output global initializations (such as C++ constructors and
     destructors) in the form used by the GNU linker (on systems where
     the GNU linker is the standard method of handling them).  Use this
     option when you want to use a non-GNU linker, which also requires
     using the `collect2' program to make sure the system linker
     includes constructors and destructors.  (`collect2' is included in
     the GNU CC distribution.)  For systems which *must* use
     `collect2', the compiler driver `gcc' is configured to do this
     automatically.
`-finhibit-size-directive'
     Don't output a `.size' assembler directive, or anything else that
     would cause trouble if the function is split in the middle, and the
     two halves are placed at locations far apart in memory.  This
     option is used when compiling `crtstuff.c'; you should not need to
     use it for anything else.
`-fverbose-asm'
     Put extra commentary information in the generated assembly code to
     make it more readable.  This option is generally only of use to
     those who actually need to read the generated assembly code
     (perhaps while debugging the compiler itself).
`-fvolatile'
     Consider all memory references through pointers to be volatile.
`-fvolatile-global'
     Consider all memory references to extern and global data items to
     be volatile.
`-fpic'
     Generate position-independent code (PIC) suitable for use in a
     shared library, if supported for the target machine.  Such code
     accesses all constant addresses through a global offset table
     (GOT).  If the GOT size for the linked executable exceeds a
     machine-specific maximum size, you get an error message from the
     linker indicating that `-fpic' does not work; in that case,
     recompile with `-fPIC' instead.  (These maximums are 16k on the
     m88k, 8k on the Sparc, and 32k on the m68k and RS/6000.  The 386
     has no such limit.)
     Position-independent code requires special support, and therefore
     works only on certain machines.  For the 386, GNU CC supports PIC
     for System V but not for the Sun 386i.  Code generated for the IBM
     RS/6000 is always position-independent.
     The GNU assembler does not fully support PIC.  Currently, you must
     use some other assembler in order for PIC to work.  We would
     welcome volunteers to upgrade GAS to handle this; the first part
     of the job is to figure out what the assembler must do differently.
`-fPIC'
     If supported for the target machine, emit position-independent
     code, suitable for dynamic linking and avoiding any limit on the
     size of the global offset table.  This option makes a difference
     on the m68k, m88k and the Sparc.
     Position-independent code requires special support, and therefore
     works only on certain machines.
`-ffixed-REG'
     Treat the register named REG as a fixed register; generated code
     should never refer to it (except perhaps as a stack pointer, frame
     pointer or in some other fixed role).
     REG must be the name of a register.  The register names accepted
     are machine-specific and are defined in the `REGISTER_NAMES' macro
     in the machine description macro file.
     This flag does not have a negative form, because it specifies a
     three-way choice.
`-fcall-used-REG'
     Treat the register named REG as an allocatable register that is
     clobbered by function calls.  It may be allocated for temporaries
     or variables that do not live across a call.  Functions compiled
     this way will not save and restore the register REG.
     Use of this flag for a register that has a fixed pervasive role in
     the machine's execution model, such as the stack pointer or frame
     pointer, will produce disastrous results.
     This flag does not have a negative form, because it specifies a
     three-way choice.
`-fcall-saved-REG'
     Treat the register named REG as an allocatable register saved by
     functions.  It may be allocated even for temporaries or variables
     that live across a call.  Functions compiled this way will save
     and restore the register REG if they use it.
     Use of this flag for a register that has a fixed pervasive role in
     the machine's execution model, such as the stack pointer or frame
     pointer, will produce disastrous results.
     A different sort of disaster will result from the use of this flag
     for a register in which function values may be returned.
     This flag does not have a negative form, because it specifies a
     three-way choice.
`+e0'
`+e1'
     Control whether virtual function definitions in classes are used to
     generate code, or only to define interfaces for their callers.
     (C++ only).
     These options are provided for compatibility with `cfront' 1.x
     usage; the recommended alternative GNU C++ usage is in flux.
     *Note Declarations and Definitions in One Header: C++ Interface.
     With `+e0', virtual function definitions in classes are declared
     `extern'; the declaration is used only as an interface
     specification, not to generate code for the virtual functions (in
     this compilation).
     With `+e1', G++ actually generates the code implementing virtual
     functions defined in the code, and makes them publicly visible.
File: gcc.info,  Node: Environment Variables,  Next: Running Protoize,  Prev: Code Gen Options,  Up: Invoking GCC
Environment Variables Affecting GNU CC
======================================
   This section describes several environment variables that affect how
GNU CC operates.  They work by specifying directories or prefixes to use
when searching for various kinds of files.
   Note that you can also specify places to search using options such as
`-B', `-I' and `-L' (*note Directory Options::.).  These take
precedence over places specified using environment variables, which in
turn take precedence over those specified by the configuration of GNU
CC.  *Note Driver::.
`TMPDIR'
     If `TMPDIR' is set, it specifies the directory to use for temporary
     files.  GNU CC uses temporary files to hold the output of one
     stage of compilation which is to be used as input to the next
     stage: for example, the output of the preprocessor, which is the
     input to the compiler proper.
`GCC_EXEC_PREFIX'
     If `GCC_EXEC_PREFIX' is set, it specifies a prefix to use in the
     names of the subprograms executed by the compiler.  No slash is
     added when this prefix is combined with the name of a subprogram,
     but you can specify a prefix that ends with a slash if you wish.
     If GNU CC cannot find the subprogram using the specified prefix, it
     tries looking in the usual places for the subprogram.
     Other prefixes specified with `-B' take precedence over this
     prefix.
     This prefix is also used for finding files such as `crt0.o' that
     are used for linking.
     In addition, the prefix is used in an unusual way in finding the
     directories to search for header files.  For each of the standard
     directories whose name normally begins with
     `/usr/local/lib/gcc-lib' (more precisely, with the value of
     `GCC_INCLUDE_DIR'), GNU CC tries replacing that beginning with the
     specified prefix to produce an alternate directory name.  Thus,
     with `-Bfoo/', GNU CC will search `foo/bar' where it would
     normally search `/usr/local/lib/bar'.  These alternate directories
     are searched first; the standard directories come next.
`COMPILER_PATH'
     The value of `COMPILER_PATH' is a colon-separated list of
     directories, much like `PATH'.  GNU CC tries the directories thus
     specified when searching for subprograms, if it can't find the
     subprograms using `GCC_EXEC_PREFIX'.
`LIBRARY_PATH'
     The value of `LIBRARY_PATH' is a colon-separated list of
     directories, much like `PATH'.  GNU CC tries the directories thus
     specified when searching for special linker files, if it can't
     find them using `GCC_EXEC_PREFIX'.  Linking using GNU CC also uses
     these directories when searching for ordinary libraries for the
     `-l' option (but directories specified with `-L' come first).
`C_INCLUDE_PATH'
`CPLUS_INCLUDE_PATH'
`OBJC_INCLUDE_PATH'
     These environment variables pertain to particular languages.  Each
     variable's value is a colon-separated list of directories, much
     like `PATH'.  When GNU CC searches for header files, it tries the
     directories listed in the variable for the language you are using,
     after the directories specified with `-I' but before the standard
     header file directories.
`DEPENDENCIES_OUTPUT'
     If this variable is set, its value specifies how to output
     dependencies for Make based on the header files processed by the
     compiler.  This output looks much like the output from the `-M'
     option (*note Preprocessor Options::.), but it goes to a separate
     file, and is in addition to the usual results of compilation.
     The value of `DEPENDENCIES_OUTPUT' can be just a file name, in
     which case the Make rules are written to that file, guessing the
     target name from the source file name.  Or the value can have the
     form `FILE TARGET', in which case the rules are written to file
     FILE using TARGET as the target name.
File: gcc.info,  Node: Running Protoize,  Prev: Environment Variables,  Up: Invoking GCC
Running Protoize
================
   The program `protoize' is an optional part of GNU C.  You can use it
to add prototypes to a program, thus converting the program to ANSI C
in one respect.  The companion program `unprotoize' does the reverse:
it removes argument types from any prototypes that are found.
   When you run these programs, you must specify a set of source files
as command line arguments.  The conversion programs start out by
compiling these files to see what functions they define.  The
information gathered about a file FOO is saved in a file named `FOO.X'.
   After scanning comes actual conversion.  The specified files are all
eligible to be converted; any files they include (whether sources or
just headers) are eligible as well.
   But not all the eligible files are converted.  By default,
`protoize' and `unprotoize' convert only source and header files in the
current directory.  You can specify additional directories whose files
should be converted with the `-d DIRECTORY' option.  You can also
specify particular files to exclude with the `-x FILE' option.  A file
is converted if it is eligible, its directory name matches one of the
specified directory names, and its name within the directory has not
been excluded.
   Basic conversion with `protoize' consists of rewriting most function
definitions and function declarations to specify the types of the
arguments.  The only ones not rewritten are those for varargs functions.
   `protoize' optionally inserts prototype declarations at the
beginning of the source file, to make them available for any calls that
precede the function's definition.  Or it can insert prototype
declarations with block scope in the blocks where undeclared functions
are called.
   Basic conversion with `unprotoize' consists of rewriting most
function declarations to remove any argument types, and rewriting
function definitions to the old-style pre-ANSI form.
   Both conversion programs print a warning for any function
declaration or definition that they can't convert.  You can suppress
these warnings with `-q'.
   The output from `protoize' or `unprotoize' replaces the original
source file.  The original file is renamed to a name ending with
`.save'.  If the `.save' file already exists, then the source file is
simply discarded.
   `protoize' and `unprotoize' both depend on GNU CC itself to scan the
program and collect information about the functions it uses.  So
neither of these programs will work until GNU CC is installed.
   Here is a table of the options you can use with `protoize' and
`unprotoize'.  Each option works with both programs unless otherwise
stated.
`-B DIRECTORY'
     Look for the file `SYSCALLS.c.X' in DIRECTORY, instead of the
     usual directory (normally `/usr/local/lib').  This file contains
     prototype information about standard system functions.  This option
     applies only to `protoize'.
`-c COMPILATION-OPTIONS'
     Use  COMPILATION-OPTIONS as the options when running `gcc' to
     produce the `.X' files.  The special option `-aux-info' is always
     passed in addition, to tell `gcc' to write a `.X' file.
     Note that the compilation options must be given as a single
     argument to `protoize' or `unprotoize'.  If you want to specify
     several `gcc' options, you must quote the entire set of
     compilation options to make them a single word in the shell.
     There are certain `gcc' arguments that you cannot use, because they
     would produce the wrong kind of output.  These include `-g', `-O',
     `-c', `-S', and `-o' If you include these in the
     COMPILATION-OPTIONS, they are ignored.
     Rename files to end in `.C' instead of `.c'.  This is convenient
     if you are converting a C program to C++.  This option applies
     only to `protoize'.
     Add explicit global declarations.  This means inserting explicit
     declarations at the beginning of each source file for each function
     that is called in the file and was not declared.  These
     declarations precede the first function definition that contains a
     call to an undeclared function.  This option applies only to
     `protoize'.
`-i STRING'
     Indent old-style parameter declarations with the string STRING.
     This option applies only to `protoize'.
     `unprotoize' converts prototyped function definitions to old-style
     function definitions, where the arguments are declared between the
     argument list and the initial `{'.  By default, `unprotoize' uses
     five spaces as the indentation.  If you want to indent with just
     one space instead, use `-i " "'.
     Keep the `.X' files.  Normally, they are deleted after conversion
     is finished.
     Add explicit local declarations.  `protoize' with `-l' inserts a
     prototype declaration for each function in each block which calls
     the function without any declaration.  This option applies only to
     `protoize'.
     Make no real changes.  This mode just prints information about the
     conversions that would have been done without `-n'.
     Make no `.save' files.  The original files are simply deleted.
     Use this option with caution.
`-p PROGRAM'
     Use the program PROGRAM as the compiler.  Normally, the name `gcc'
     is used.
     Work quietly.  Most warnings are suppressed.
     Print the version number, just like `-v' for `gcc'.
   If you need special compiler options to compile one of your program's
source files, then you should generate that file's `.X' file specially,
by running `gcc' on that source file with the appropriate options and
the option `-aux-info'.  Then run `protoize' on the entire set of
files.  `protoize' will use the existing `.X' file because it is newer
than the source file.  For example:
     gcc -Dfoo=bar file1.c -aux-info
     protoize *.c
You need to include the special files along with the rest in the
`protoize' command, even though their `.X' files already exist, because
otherwise they won't get converted.
   *Note Protoize Caveats::, for more information on how to use
`protoize' successfully.