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This is Info file gcc.info, produced by Makeinfo version 1.67 from the input file gcc.texi. This file documents the use and the internals of the GNU compiler. Published by the Free Software Foundation 59 Temple Place - Suite 330 Boston, MA 02111-1307 USA Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995 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," "Funding for Free Software," 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 one. 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," "Funding for Free Software," 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: 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 choices for CPU TYPE are `r2000', `r3000', `r4000', `r4400', `r4600', 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. `-mips1' Issue instructions from level 1 of the MIPS ISA. This is the default. `r3000' is the default CPU TYPE at this ISA level. `-mips2' Issue instructions from level 2 of the MIPS ISA (branch likely, square root instructions). `r6000' is the default CPU TYPE at this ISA level. `-mips3' Issue instructions from level 3 of the MIPS ISA (64 bit instructions). `r4000' is the default CPU TYPE at this ISA level. This option does not change the sizes of any of the C data types. `-mfp32' Assume that 32 32-bit floating point registers are available. This is the default. `-mfp64' Assume that 32 64-bit floating point registers are available. This is the default when the `-mips3' option is used. `-mgp32' Assume that 32 32-bit general purpose registers are available. This is the default. `-mgp64' Assume that 32 64-bit general purpose registers are available. This is the default when the `-mips3' option is used. `-mint64' Types long, int, and pointer are 64 bits. This works only if `-mips3' is also specified. `-mlong64' Types long and pointer are 64 bits, and type int is 32 bits. This works only if `-mips3' is also specified. `-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 only known assembler that supports this option is the Algorithmics assembler. `-mgpopt' `-mno-gpopt' The `-mgpopt' switch says to write all of the data declarations before the instructions in the text section, this allows the MIPS assembler to generate one word memory references instead of using two words for short global or static data items. This is on by default if optimization is selected. `-mstats' `-mno-stats' For each non-inline function processed, the `-mstats' switch causes the compiler to emit one line to the standard error file to print statistics about the program (number of registers saved, stack size, etc.). `-mmemcpy' `-mno-memcpy' The `-mmemcpy' switch makes all block moves call the appropriate string function (`memcpy' or `bcopy') instead of possibly generating inline code. `-mmips-tfile' `-mno-mips-tfile' The `-mno-mips-tfile' switch causes the compiler not postprocess the object file with the `mips-tfile' program, after the MIPS assembler has generated it to add debug support. If `mips-tfile' is not run, then no local variables will be available to the debugger. In addition, `stage2' and `stage3' objects will have the temporary file names passed to the assembler embedded in the object file, which means the objects will not compare the same. The `-mno-mips-tfile' switch should only be used when there are bugs in the `mips-tfile' program that prevents compilation. `-msoft-float' Generate output containing library calls for floating point. *Warning:* the requisite libraries are not part of 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. `-mabicalls' `-mno-abicalls' Emit (or do not emit) the pseudo operations `.abicalls', `.cpload', and `.cprestore' that some System V.4 ports use for position independent code. `-mlong-calls' `-mno-long-calls' Do all calls with the `JALR' instruction, which requires loading up a function's address into a register before the call. You need to use this switch, if you call outside of the current 512 megabyte segment to functions that are not through pointers. `-mhalf-pic' `-mno-half-pic' Put pointers to extern references into the data section and load them up, rather than put the references in the text section. `-membedded-pic' `-mno-embedded-pic' Generate PIC code suitable for some embedded systems. All calls are made using PC relative address, and all data is addressed using the $gp register. This requires GNU as and GNU ld which do most of the work. `-membedded-data' `-mno-embedded-data' Allocate variables to the read-only data section first if possible, then next in the small data section if possible, otherwise in data. This gives slightly slower code than the default, but reduces the amount of RAM required when executing, and thus may be preferred for some embedded systems. `-msingle-float' `-mdouble-float' The `-msingle-float' switch tells gcc to assume that the floating point coprocessor only supports single precision operations, as on the `r4650' chip. The `-mdouble-float' switch permits gcc to use double precision operations. This is the default. `-mmad' `-mno-mad' Permit use of the `mad', `madu' and `mul' instructions, as on the `r4650' chip. `-m4650' Turns on `-msingle-float', `-mmad', and, at least for now, `-mcpu=r4650'. `-EL' Compile code for the processor in little endian mode. The requisite libraries are assumed to exist. `-EB' Compile code for the processor in big endian mode. The requisite libraries are assumed to exist. `-G NUM' Put global and static items less than or equal to NUM bytes into the small data or bss sections instead of the normal data or bss section. This allows the assembler to emit one word memory reference instructions based on the global pointer (GP or $28), instead of the normal two words used. By default, NUM is 8 when the MIPS assembler is used, and 0 when the GNU assembler is used. The `-G NUM' switch is also passed to the assembler and linker. All modules should be compiled with the same `-G NUM' value. `-nocpp' Tell the MIPS assembler to not run 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' `-m386' 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. `-mieee-fp' `-mno-ieee-fp' Control whether or not the compiler uses IEEE floating point comparisons. These handle correctly the case where the result of a comparison is unordered. `-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. `-mno-fancy-math-387' Some 387 emulators do not support the `sin', `cos' and `sqrt' instructions for the 387. Specify this option to avoid generating those instructions. This option is the default on FreeBSD. As of revision 2.6.1, these instructions are not generated unless you also use the `-ffast-math' switch. `-malign-double' `-mno-align-double' Control whether GNU CC aligns `double', `long double', and `long long' variables on a two word boundary or a one word boundary. Aligning `double' variables on a two word boundary will produce code that runs somewhat faster on a `Pentium' at the expense of more memory. *Warning:* if you use the `-malign-double' switch, structures containing the above types will be aligned differently than the published application binary interface specifications for the 386. `-msvr3-shlib' `-mno-svr3-shlib' Control whether GNU CC places uninitialized locals into `bss' or `data'. `-msvr3-shlib' places these locals into `bss'. These options are meaningful only on System V Release 3. `-mno-wide-multiply' `-mwide-multiply' Control whether GNU CC uses the `mul' and `imul' that produce 64 bit results in `eax:edx' from 32 bit operands to do `long long' multiplies and 32-bit division by constants. `-mrtd' Use a different function-calling convention, in which functions that take a fixed number of arguments return with the `ret' NUM instruction, which pops their arguments while returning. This saves one instruction in the caller since there is no need to pop the arguments there. You can specify that an individual function is called with this calling sequence with the function attribute `stdcall'. You can also override the `-mrtd' option by using the function attribute `cdecl'. *Note Function Attributes:: *Warning:* 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.) `-mreg-alloc=REGS' Control the default allocation order of integer registers. The string REGS is a series of letters specifying a register. The supported letters are: `a' allocate EAX; `b' allocate EBX; `c' allocate ECX; `d' allocate EDX; `S' allocate ESI; `D' allocate EDI; `B' allocate EBP. `-mregparm=NUM' Control how many registers are used to pass integer arguments. By default, no registers are used to pass arguments, and at most 3 registers can be used. You can control this behavior for a specific function by using the function attribute `regparm'. *Note Function Attributes:: *Warning:* if you use this switch, and NUM is nonzero, then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules. `-malign-loops=NUM' Align loops to a 2 raised to a NUM byte boundary. If `-malign-loops' is not specified, the default is 2. `-malign-jumps=NUM' Align instructions that are only jumped to to a 2 raised to a NUM byte boundary. If `-malign-jumps' is not specified, the default is 2 if optimizing for a 386, and 4 if optimizing for a 486. `-malign-functions=NUM' Align the start of functions to a 2 raised to NUM byte boundary. If `-malign-jumps' is not specified, the default is 2 if optimizing for a 386, and 4 if optimizing for a 486. 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. `-mjump-in-delay' Fill delay slots of function calls with unconditional jump instructions by modifying the return pointer for the function call to be the target of the conditional jump. `-mmillicode-long-calls' Generate code which assumes millicode routines can not be reached by the standard millicode call sequence, linker-generated long-calls, or linker-modified millicode calls. In practice this should only be needed for dynamicly linked executables with extremely large SHLIB_INFO sections. `-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. `-mfast-indirect-calls' Generate code which performs faster indirect calls. Such code is suitable for kernels and for static linking. The fast indirect call code will fail miserably if it's part of a dynamically linked executable and in the presense of nested functions. `-mportable-runtime' Use the portable calling conventions proposed by HP for ELF systems. `-mgas' Enable the use of assembler directives only GAS understands. `-mschedule=CPU TYPE' Schedule code according to the constraints for the machine type CPU TYPE. The choices for CPU TYPE are `700' for 7N0 machines, `7100' for 7N5 machines, and `7100' for 7N2 machines. `700' is the default for CPU TYPE. Note the `7100LC' scheduling information is incomplete and using `7100LC' often leads to bad schedules. For now it's probably best to use `7100' instead of `7100LC' for the 7N2 machines. `-msoft-float' Generate output containing library calls for floating point. *Warning:* the requisite libraries are not available for all HPPA 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 target `hppa1.1-*-pro' does 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. 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: H8/300 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 floating point registers f8..f15. File: gcc.info, Node: H8/300 Options, Next: System V Options, Prev: Clipper Options, Up: Submodel Options H8/300 Options -------------- These `-m' options are defined for the H8/300 implementations: `-mrelax' Shorten some address references at link time, when possible; uses the linker option `-relax'. *Note `ld' and the H8/300: (ld.info)H8/300, for a fuller description. `-mh' Generate code for the H8/300H. File: gcc.info, Node: System V Options, Prev: H8/300 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. `-fpack-struct' Pack all structure members together without holes. Usually you would not want to use this option, since it makes the code suboptimal, and the offsets of structure members won't agree with system libraries. `-fstack-check' Generate code to verify that you do not go beyond the boundary of the stack. You should specify this flag if you are running in an environment with multiple threads, but only rarely need to specify it in a single-threaded environment since stack overflow is automatically detected on nearly all systems if there is only one stack. `+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. `-fargument-alias' `-fargument-noalias' `-fargument-noalias-global' Specify the possible relationships among parameters and between parameters and global data. `-fargument-alias' specifies that arguments (parameters) may alias each other and may alias global storage. `-fargument-noalias' specifies that arguments do not alias each other, but may alias global storage. `-fargument-noalias-global' specifies that arguments do not alias each other and do not alias global storage. For code written in C, C++, and Objective-C, `-fargument-alias' is the default. For code written in Fortran, `-fargument-noalias-global' is the default, though this is pertinent only on systems where `g77' is installed. (See the documentation for other compilers for information on the defaults for their respective languages.) Normally, `gcc' assumes that a write through a pointer passed as a parameter to the current function might modify a value pointed to by another pointer passed as a parameter, or in global storage. For example, consider this code: void x(int *i, int *j) { extern int k; ++*i; ++*j; ++k; } When compiling the above function, `gcc' assumes that `i' might be a pointer to the same variable as `j', and that either `i', `j', or both might be a pointer to `k'. Therefore, `gcc' does not assume it can generate code to read `*i', `*j', and `k' into separate registers, increment each register, then write the incremented values back out. Instead, `gcc' must generate code that reads `*i', increments it, and writes it back before reading `*j', in case `i' and `j' are aliased, and, similarly, that writes `*j' before reading `k'. The result is code that, on many systems, takes longer to execute, due to the way many processors schedule instruction execution. Compiling the above code with the `-fargument-noalias' option allows `gcc' to assume that `i' and `j' do not alias each other, but either might alias `k'. Compiling the above code with the `-fargument-noalias-global' option allows `gcc' to assume that no combination of `i', `j', and `k' are aliases for each other. *Note:* Use the `-fargument-noalias' and `-fargument-noalias-global' options with care. While they can result in faster executables, they can also result in executables with subtle bugs, bugs that show up only when compiled for specific target systems, or bugs that show up only when compiled by specific versions of `g77'. 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. The default value of `GCC_EXEC_PREFIX' is `PREFIX/lib/gcc-lib/' where PREFIX is the value of `prefix' when you ran the `configure' script. Other prefixes specified with `-B' take precedence over this prefix. This prefix is also used for finding files such as `crt0.o' that are used for linking. In addition, the prefix is used in an unusual way in finding the directories to search for header files. For each of the standard directories whose name normally begins with `/usr/local/lib/gcc-lib' (more precisely, with the value of `GCC_INCLUDE_DIR'), 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'. When configured as a native compiler, 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. `-C' 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'. `-g' 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 " "'. `-k' Keep the `.X' files. Normally, they are deleted after conversion is finished. `-l' 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'. `-n' Make no real changes. This mode just prints information about the conversions that would have been done without `-n'. `-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. `-q' Work quietly. Most warnings are suppressed. `-v' 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.