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, 1996, 1997, 1998 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: M88K Options, Next: RS/6000 and PowerPC Options, Prev: M32R/D Options, Up: Submodel Options 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 processor. If you intend to run your code only on the MC88100 processor, you may use `-mno-serialize-volatile'. The extra code generated to guarantee consistency may affect the performance of your application. If you know that you can safely forgo this guarantee, you may use `-mno-serialize-volatile'. `-msvr4' `-msvr3' Turn on (`-msvr4') or off (`-msvr3') compiler extensions related to System V release 4 (SVr4). This controls the following: 1. Which variant of the assembler syntax to emit. 2. `-msvr4' makes the C preprocessor recognize `#pragma weak' that is used on System V release 4. 3. `-msvr4' makes GNU CC issue additional declaration directives used in SVr4. `-msvr4' is the default for the m88k-motorola-sysv4 and m88k-dg-dgux m88k configurations. `-msvr3' is the default for all other m88k configurations. `-mversion-03.00' This option is obsolete, and is ignored. `-mno-check-zero-division' `-mcheck-zero-division' Do, or don't, generate code to guarantee that integer division by zero will be detected. By default, detection is guaranteed. Some models of the MC88100 processor fail to trap upon integer division by zero under certain conditions. By default, when compiling code that might be run on such a processor, GNU C generates code that explicitly checks for zero-valued divisors and traps with exception number 503 when one is detected. Use of mno-check-zero-division suppresses such checking for code generated to run on an MC88100 processor. GNU C assumes that the MC88110 processor correctly detects all instances of integer division by zero. When `-m88110' is specified, both `-mcheck-zero-division' and `-mno-check-zero-division' are ignored, and no explicit checks for zero-valued divisors are generated. `-muse-div-instruction' Use the div instruction for signed integer division on the MC88100 processor. By default, the div instruction is not used. On the MC88100 processor the signed integer division instruction div) traps to the operating system on a negative operand. The operating system transparently completes the operation, but at a large cost in execution time. By default, when compiling code that might be run on an MC88100 processor, GNU C emulates signed integer division using the unsigned integer division instruction divu), thereby avoiding the large penalty of a trap to the operating system. Such emulation has its own, smaller, execution cost in both time and space. To the extent that your code's important signed integer division operations are performed on two nonnegative operands, it may be desirable to use the div instruction directly. On the MC88110 processor the div instruction (also known as the divs instruction) processes negative operands without trapping to the operating system. When `-m88110' is specified, `-muse-div-instruction' is ignored, and the div instruction is used for signed integer division. Note that the result of dividing INT_MIN by -1 is undefined. In particular, the behavior of such a division with and without `-muse-div-instruction' may differ. `-mtrap-large-shift' `-mhandle-large-shift' Include code to detect bit-shifts of more than 31 bits; respectively, trap such shifts or emit code to handle them properly. By default GNU CC makes no special provision for large bit shifts. `-mwarn-passed-structs' Warn when a function passes a struct as an argument or result. Structure-passing conventions have changed during the evolution of the C language, and are often the source of portability problems. By default, GNU CC issues no such warning.  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' `-mpowerpc-gpopt' `-mno-powerpc-gpopt' `-mpowerpc-gfxopt' `-mno-powerpc-gfxopt' 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 MPC5xx, MPC6xx, MPC8xx microprocessors, and the IBM 4xx microprocessors. Neither architecture is a subset of the other. However there is a large common subset of instructions supported by both. An MQ register is included in processors supporting the POWER architecture. You use these options to specify which instructions are available on the processor you are using. The default value of these options is determined when configuring GNU CC. Specifying the `-mcpu=CPU_TYPE' overrides the specification of these options. We recommend you use the `-mcpu=CPU_TYPE' option rather than the options listed above. The `-mpower' option allows 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 `-mpowerpc-gpopt' implies `-mpowerpc' and also allows GNU CC to use the optional PowerPC architecture instructions in the General Purpose group, including floating-point square root. Specifying `-mpowerpc-gfxopt' implies `-mpowerpc' and also allows GNU CC to use the optional PowerPC architecture instructions in the Graphics group, including floating-point select. If you specify both `-mno-power' and `-mno-powerpc', GNU CC will use only the instructions in the common subset of both architectures plus some special AIX common-mode calls, and will not use the MQ register. Specifying both `-mpower' and `-mpowerpc' permits 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 which mnemonics to use in the generated assembler code. `-mnew-mnemonics' requests output that uses the assembler mnemonics defined for the PowerPC architecture, while `-mold-mnemonics' requests 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 these 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 supports them, otherwise specify `-mold-mnemonics'. The default value of these options depends on how GNU CC was configured. Specifying `-mcpu=CPU_TYPE' sometimes overrides the value of these option. Unless you are building a cross-compiler, you should normally not specify either `-mnew-mnemonics' or `-mold-mnemonics', but should instead accept the default. `-mcpu=CPU_TYPE' Set architecture type, register usage, choice of mnemonics, and instruction scheduling parameters for machine type CPU_TYPE. Supported values for CPU_TYPE are `rs6000', `rios1', `rios2', `rsc', `601', `602', `603', `603e', `604', `604e', `620', `power', `power2', `powerpc', `403', `505', `801', `821', `823', and `860' and `common'. `-mcpu=power', `-mcpu=power2', and `-mcpu=powerpc' specify generic POWER, POWER2 and pure PowerPC (i.e., not MPC601) architecture machine types, with an appropriate, generic processor model assumed for scheduling purposes. Specifying any of the following options: `-mcpu=rios1', `-mcpu=rios2', `-mcpu=rsc', `-mcpu=power', or `-mcpu=power2' enables the `-mpower' option and disables the `-mpowerpc' option; `-mcpu=601' enables both the `-mpower' and `-mpowerpc' options. All of `-mcpu=602', `-mcpu=603', `-mcpu=603e', `-mcpu=604', `-mcpu=620', enable the `-mpowerpc' option and disable the `-mpower' option. Exactly similarly, all of `-mcpu=403', `-mcpu=505', `-mcpu=821', `-mcpu=860' and `-mcpu=powerpc' enable the `-mpowerpc' option and disable the `-mpower' option. `-mcpu=common' disables both the `-mpower' and `-mpowerpc' options. AIX versions 4 or greater selects `-mcpu=common' by default, so that code will operate on all members of the RS/6000 and PowerPC families. In that case, GNU CC will use only the instructions in the common subset of both architectures plus some special AIX common-mode calls, and will not use the MQ register. GNU CC assumes a generic processor model for scheduling purposes. Specifying any of the options `-mcpu=rios1', `-mcpu=rios2', `-mcpu=rsc', `-mcpu=power', or `-mcpu=power2' also disables the `new-mnemonics' option. Specifying `-mcpu=601', `-mcpu=602', `-mcpu=603', `-mcpu=603e', `-mcpu=604', `620', `403', or `-mcpu=powerpc' also enables the `new-mnemonics' option. Specifying `-mcpu=403', `-mcpu=821', or `-mcpu=860' also enables the `-msoft-float' option. `-mtune=CPU_TYPE' Set the instruction scheduling parameters for machine type CPU_TYPE, but do not set the architecture type, register usage, choice of mnemonics like `-mcpu='CPU_TYPE would. The same values for CPU_TYPE are used for `-mtune='CPU_TYPE as for `-mcpu='CPU_TYPE. The `-mtune='CPU_TYPE option overrides the `-mcpu='CPU_TYPE option in terms of instruction scheduling parameters. `-mfull-toc' `-mno-fp-in-toc' `-mno-sum-in-toc' `-mminimal-toc' Modify generation of the TOC (Table Of Contents), which is created for every executable file. The `-mfull-toc' option is selected by default. In that case, 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 16,384 entries are available in the TOC. If you receive a linker error message that saying you have overflowed the available TOC space, you can reduce the amount of TOC space used with the `-mno-fp-in-toc' and `-mno-sum-in-toc' options. `-mno-fp-in-toc' prevents GNU CC from putting floating-point constants in the TOC and `-mno-sum-in-toc' forces GNU CC to generate code to calculate the sum of an address and a constant at run-time instead of putting that sum into the TOC. You may specify one or both of these options. Each causes GNU CC to produce very slightly slower and larger code at the expense of conserving TOC space. If you still run out of space in the TOC even when you specify both of these options, specify `-mminimal-toc' instead. This option causes GNU CC to make only one TOC entry for every file. When you specify this option, GNU CC will produce code that is slower and larger but which uses extremely little TOC space. You may wish to use this option only on files that contain less frequently executed code. `-mxl-call' `-mno-xl-call' On AIX, pass floating-point arguments to prototyped functions beyond the register save area (RSA) on the stack in addition to argument FPRs. The AIX calling convention was extended but not initially documented to handle an obscure K&R C case of calling a function that takes the address of its arguments with fewer arguments than declared. AIX XL compilers assume that floating point arguments which do not fit in the RSA are on the stack when they compile a subroutine without optimization. Because always storing floating-point arguments on the stack is inefficient and rarely needed, this option is not enabled by default and only is necessary when calling subroutines compiled by AIX XL compilers without optimization. `-mthreads' Support "AIX Threads". Link an application written to use "pthreads" with special libraries and startup code to enable the application to run. `-mpe' Support "IBM RS/6000 SP" "Parallel Environment" (PE). Link an application written to use message passing with special startup code to enable the application to run. The system must have PE installed in the standard location (`/usr/lpp/ppe.poe/'), or the `specs' file must be overridden with the `-specs=' option to specify the appropriate directory location. The Parallel Environment does not support threads, so the `-mpe' option and the `-mthreads' option are incompatible. `-msoft-float' `-mhard-float' Generate code that does not use (uses) the floating-point register set. Software floating point emulation is provided if you use the `-msoft-float' option, and pass the option to GNU CC when linking. `-mmultiple' `-mno-multiple' Generate code that uses (does not use) the load multiple word instructions and the store multiple word instructions. These instructions are generated by default on POWER systems, and not generated on PowerPC systems. Do not use `-mmultiple' on little endian PowerPC systems, since those instructions do not work when the processor is in little endian mode. `-mstring' `-mno-string' Generate code that uses (does not use) the load string instructions and the store string word instructions to save multiple registers and do small block moves. These instructions are generated by default on POWER systems, and not generated on PowerPC systems. Do not use `-mstring' on little endian PowerPC systems, since those instructions do not work when the processor is in little endian mode. `-mupdate' `-mno-update' Generate code that uses (does not use) the load or store instructions that update the base register to the address of the calculated memory location. These instructions are generated by default. If you use `-mno-update', there is a small window between the time that the stack pointer is updated and the address of the previous frame is stored, which means code that walks the stack frame across interrupts or signals may get corrupted data. `-mfused-madd' `-mno-fused-madd' Generate code that uses (does not use) the floating point multiply and accumulate instructions. These instructions are generated by default if hardware floating is used. `-mno-bit-align' `-mbit-align' On System V.4 and embedded PowerPC systems do not (do) force structures and unions that contain bit fields to be aligned to the base type of the bit field. For example, by default a structure containing nothing but 8 `unsigned' bitfields of length 1 would be aligned to a 4 byte boundary and have a size of 4 bytes. By using `-mno-bit-align', the structure would be aligned to a 1 byte boundary and be one byte in size. `-mno-strict-align' `-mstrict-align' On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory references will be handled by the system. `-mrelocatable' `-mno-relocatable' On embedded PowerPC systems generate code that allows (does not allow) the program to be relocated to a different address at runtime. If you use `-mrelocatable' on any module, all objects linked together must be compiled with `-mrelocatable' or `-mrelocatable-lib'. `-mrelocatable-lib' `-mno-relocatable-lib' On embedded PowerPC systems generate code that allows (does not allow) the program to be relocated to a different address at runtime. Modules compiled with `-mrelocatable-lib' can be linked with either modules compiled without `-mrelocatable' and `-mrelocatable-lib' or with modules compiled with the `-mrelocatable' options. `-mno-toc' `-mtoc' On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains a pointer to a global area pointing to the addresses used in the program. `-mno-traceback' `-mtraceback' On embedded PowerPC systems do not (do) generate a traceback tag before the start of the function. This tag can be used by the debugger to identify where the start of a function is. `-mlittle' `-mlittle-endian' On System V.4 and embedded PowerPC systems compile code for the processor in little endian mode. The `-mlittle-endian' option is the same as `-mlittle'. `-mbig' `-mbig-endian' On System V.4 and embedded PowerPC systems compile code for the processor in big endian mode. The `-mbig-endian' option is the same as `-mbig'. `-mcall-sysv' On System V.4 and embedded PowerPC systems compile code using calling conventions that adheres to the March 1995 draft of the System V Application Binary Interface, PowerPC processor supplement. This is the default unless you configured GCC using `powerpc-*-eabiaix'. `-mcall-sysv-eabi' Specify both `-mcall-sysv' and `-meabi' options. `-mcall-sysv-noeabi' Specify both `-mcall-sysv' and `-mno-eabi' options. `-mcall-aix' On System V.4 and embedded PowerPC systems compile code using calling conventions that are similar to those used on AIX. This is the default if you configured GCC using `powerpc-*-eabiaix'. `-mcall-solaris' On System V.4 and embedded PowerPC systems compile code for the Solaris operating system. `-mcall-linux' On System V.4 and embedded PowerPC systems compile code for the Linux-based GNU system. `-mprototype' `-mno-prototype' On System V.4 and embedded PowerPC systems assume that all calls to variable argument functions are properly prototyped. Otherwise, the compiler must insert an instruction before every non prototyped call to set or clear bit 6 of the condition code register (CR) to indicate whether floating point values were passed in the floating point registers in case the function takes a variable arguments. With `-mprototype', only calls to prototyped variable argument functions will set or clear the bit. `-msim' On embedded PowerPC systems, assume that the startup module is called `sim-crt0.o' and that the standard C libraries are `libsim.a' and `libc.a'. This is the default for `powerpc-*-eabisim'. configurations. `-mmvme' On embedded PowerPC systems, assume that the startup module is called `crt0.o' and the standard C libraries are `libmvme.a' and `libc.a'. `-mads' On embedded PowerPC systems, assume that the startup module is called `crt0.o' and the standard C libraries are `libads.a' and `libc.a'. `-myellowknife' On embedded PowerPC systems, assume that the startup module is called `crt0.o' and the standard C libraries are `libyk.a' and `libc.a'. `-memb' On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags header to indicate that `eabi' extended relocations are used. `-meabi' `-mno-eabi' On System V.4 and embedded PowerPC systems do (do not) adhere to the Embedded Applications Binary Interface (eabi) which is a set of modifications to the System V.4 specifications. Selecting `-meabi' means that the stack is aligned to an 8 byte boundary, a function `__eabi' is called to from `main' to set up the eabi environment, and the `-msdata' option can use both `r2' and `r13' to point to two separate small data areas. Selecting `-mno-eabi' means that the stack is aligned to a 16 byte boundary, do not call an initialization function from `main', and the `-msdata' option will only use `r13' to point to a single small data area. The `-meabi' option is on by default if you configured GCC using one of the `powerpc*-*-eabi*' options. `-msdata=eabi' On System V.4 and embedded PowerPC systems, put small initialized `const' global and static data in the `.sdata2' section, which is pointed to by register `r2'. Put small initialized non-`const' global and static data in the `.sdata' section, which is pointed to by register `r13'. Put small uninitialized global and static data in the `.sbss' section, which is adjacent to the `.sdata' section. The `-msdata=eabi' option is incompatible with the `-mrelocatable' option. The `-msdata=eabi' option also sets the `-memb' option. `-msdata=sysv' On System V.4 and embedded PowerPC systems, put small global and static data in the `.sdata' section, which is pointed to by register `r13'. Put small uninitialized global and static data in the `.sbss' section, which is adjacent to the `.sdata' section. The `-msdata=sysv' option is incompatible with the `-mrelocatable' option. `-msdata=default' `-msdata' On System V.4 and embedded PowerPC systems, if `-meabi' is used, compile code the same as `-msdata=eabi', otherwise compile code the same as `-msdata=sysv'. `-msdata-data' On System V.4 and embedded PowerPC systems, put small global and static data in the `.sdata' section. Put small uninitialized global and static data in the `.sbss' section. Do not use register `r13' to address small data however. This is the default behavior unless other `-msdata' options are used. `-msdata=none' `-mno-sdata' On embedded PowerPC systems, put all initialized global and static data in the `.data' section, and all uninitialized data in the `.bss' section. `-G NUM' On embedded PowerPC systems, put global and static items less than or equal to NUM bytes into the small data or bss sections instead of the normal data or bss section. By default, NUM is 8. The `-G NUM' switch is also passed to the linker. All modules should be compiled with the same `-G NUM' value. `-mregnames' `-mno-regnames' On System V.4 and embedded PowerPC systems do (do not) emit register names in the assembly language output using symbolic forms.  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. Also, this is the default if the configure option `--with-gnu-as' is used. `-msplit-addresses' `-mno-split-addresses' Generate code to load the high and low parts of address constants separately. This allows `gcc' to optimize away redundant loads of the high order bits of addresses. This optimization requires GNU as and GNU ld. This optimization is enabled by default for some embedded targets where GNU as and GNU ld are standard. `-mrnames' `-mno-rnames' The `-mrnames' switch says to output code using the MIPS software names for the registers, instead of the hardware names (ie, A0 instead of $4). The only known assembler that supports this option is the Algorithmics assembler. `-mgpopt' `-mno-gpopt' The `-mgpopt' switch says to write all of the data declarations before the instructions in the text section, this allows the MIPS assembler to generate one word memory references instead of using two words for short global or static data items. This is on by default if optimization is selected. `-mstats' `-mno-stats' For each non-inline function processed, the `-mstats' switch causes the compiler to emit one line to the standard error file to print statistics about the program (number of registers saved, stack size, etc.). `-mmemcpy' `-mno-memcpy' The `-mmemcpy' switch makes all block moves call the appropriate string function (`memcpy' or `bcopy') instead of possibly generating inline code. `-mmips-tfile' `-mno-mips-tfile' The `-mno-mips-tfile' switch causes the compiler not postprocess the object file with the `mips-tfile' program, after the MIPS assembler has generated it to add debug support. If `mips-tfile' is not run, then no local variables will be available to the debugger. In addition, `stage2' and `stage3' objects will have the temporary file names passed to the assembler embedded in the object file, which means the objects will not compare the same. The `-mno-mips-tfile' switch should only be used when there are bugs in the `mips-tfile' program that prevents compilation. `-msoft-float' Generate output containing library calls for floating point. *Warning:* the requisite libraries are not part of 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: `-mcpu=CPU TYPE' Assume the defaults for the machine type CPU TYPE when scheduling instructions. The choices for CPU TYPE are: `i386', `i486', `i586' (`pentium'), `pentium', `i686' (`pentiumpro') and `pentiumpro'. While picking a specific CPU TYPE will schedule things appropriately for that particular chip, the compiler will not generate any code that does not run on the i386 without the `-march=CPU TYPE' option being used. `-march=CPU TYPE' Generate instructions for the machine type CPU TYPE. The choices for CPU TYPE are: `i386', `i486', `pentium', and `pentiumpro'. Specifying `-march=CPU TYPE' implies `-mcpu=CPU TYPE'. `-m386' `-m486' `-mpentium' `-mpentiumpro' Synonyms for -mcpu=i386, -mcpu=i486, -mcpu=pentium, and -mcpu=pentiumpro respectively. `-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-functions' 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. `-mbig-switch' Generate code suitable for big switch tables. Use this option only if the assembler/linker complain about out of range branches within a switch table. `-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. `-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. `-mno-space-regs' Generate code that assumes the target has no space registers. This allows GCC to generate faster indirect calls and use unscaled index address modes. Such code is suitable for level 0 PA systems and kernels. `-mfast-indirect-calls' Generate code that assumes calls never cross space boundaries. This allows GCC to emit code which performs faster indirect calls. This option will not work in the presense of shared libraries or nested functions. `-mspace' Optimize for space rather than execution time. Currently this only enables out of line function prologues and epilogues. This option is incompatible with PIC code generation and profiling. `-mlong-load-store' Generate 3-instruction load and store sequences as sometimes required by the HP-UX 10 linker. This is equivalent to the `+k' option to the HP compilers. `-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. `7100' 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. `-mlinker-opt' Enable the optimization pass in the HPUX linker. Note this makes symbolic debugging impossible. It also triggers a bug in the HPUX 8 and HPUX 9 linkers in which they give bogus error messages when linking some programs. `-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). This option implies `-mstrict-align'.