RTEMS GNU Tools On-Line Library

Using and Porting the GNU Compiler Collection (GCC)

2.14.12: IBM RS/6000 and PowerPC Options

These `-m' options are defined for the IBM RS/6000 and PowerPC:

-mpower

-mno-power

-mpower2

-mno-power2

-mpowerpc

-mno-powerpc

-mpowerpc-gpopt

-mno-powerpc-gpopt

-mpowerpc-gfxopt

-mno-powerpc-gfxopt

-mpowerpc64

-mno-powerpc64

GCC supports two related instruction set architectures for the RS/6000 and PowerPC. The POWER instruction set are those instructions supported by the `rios' chip set used in the original RS/6000 systems and the PowerPC instruction set is the architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and the IBM 4xx microprocessors.

Neither architecture is a subset of the other. However there is a large common subset of instructions supported by both. An MQ register is included in processors supporting the POWER architecture.

You use these options to specify which instructions are available on the processor you are using. The default value of these options is determined when configuring GCC. Specifying the `-mcpu=cpu_type' overrides the specification of these options. We recommend you use the `-mcpu=cpu_type' option rather than the options listed above.

The `-mpower' option allows GCC to generate instructions that are found only in the POWER architecture and to use the MQ register. Specifying `-mpower2' implies `-power' and also allows GCC to generate instructions that are present in the POWER2 architecture but not the original POWER architecture.

The `-mpowerpc' option allows GCC to generate instructions that are found only in the 32-bit subset of the PowerPC architecture. Specifying `-mpowerpc-gpopt' implies `-mpowerpc' and also allows GCC to use the optional PowerPC architecture instructions in the General Purpose group, including floating-point square root. Specifying `-mpowerpc-gfxopt' implies `-mpowerpc' and also allows GCC to use the optional PowerPC architecture instructions in the Graphics group, including floating-point select.

The `-mpowerpc64' option allows GCC to generate the additional 64-bit instructions that are found in the full PowerPC64 architecture and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to `-mno-powerpc64'.

If you specify both `-mno-power' and `-mno-powerpc', GCC will use only the instructions in the common subset of both architectures plus some special AIX common-mode calls, and will not use the MQ register. Specifying both `-mpower' and `-mpowerpc' permits GCC to use any instruction from either architecture and to allow use of the MQ register; specify this for the Motorola MPC601.

-mnew-mnemonics

-mold-mnemonics

Select which mnemonics to use in the generated assembler code. `-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; GCC uses that mnemonic irrespective of which of these options is specified.

GCC defaults to the mnemonics appropriate for the architecture in use. Specifying `-mcpu=cpu_type' sometimes overrides the value of these option. Unless you are building a cross-compiler, you should normally not specify either `-mnew-mnemonics' or `-mold-mnemonics', but should instead accept the default.

-mcpu=cpu_type

Set architecture type, register usage, choice of mnemonics, and instruction scheduling parameters for machine type cpu_type. Supported values for cpu_type are `rs6000', `rios1', `rios2', `rsc', `601', `602', `603', `603e', `604', `604e', `620', `740', `750', `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, GCC will use only the instructions in the common subset of both architectures plus some special AIX common-mode calls, and will not use the MQ register. GCC 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, GCC will allocate at least one TOC entry for each unique non-automatic variable reference in your program. GCC will also place floating-point constants in the TOC. However, only 16,384 entries are available in the TOC.

If you receive a linker error message that saying you have overflowed the available TOC space, you can reduce the amount of TOC space used with the `-mno-fp-in-toc' and `-mno-sum-in-toc' options. `-mno-fp-in-toc' prevents GCC from putting floating-point constants in the TOC and `-mno-sum-in-toc' forces GCC to generate code to calculate the sum of an address and a constant at run-time instead of putting that sum into the TOC. You may specify one or both of these options. Each causes GCC to produce very slightly slower and larger code at the expense of conserving TOC space.

If you still run out of space in the TOC even when you specify both of these options, specify `-mminimal-toc' instead. This option causes GCC to make only one TOC entry for every file. When you specify this option, GCC will produce code that is slower and larger but which uses extremely little TOC space. You may wish to use this option only on files that contain less frequently executed code.

-maix64

-maix32

Enable AIX 64-bit ABI and calling convention: 64-bit pointers, 64-bit long type, and the infrastructure needed to support them. Specifying `-maix64' implies `-mpowerpc64' and `-mpowerpc', while `-maix32' disables the 64-bit ABI and implies `-mno-powerpc64'. GCC defaults to `-maix32'.

-mxl-call

-mno-xl-call

On AIX, pass floating-point arguments to prototyped functions beyond the register save area (RSA) on the stack in addition to argument FPRs. The AIX calling convention was extended but not initially documented to handle an obscure K&R C case of calling a function that takes the address of its arguments with fewer arguments than declared. AIX XL compilers access floating point arguments which do not fit in the RSA from the stack when a subroutine is compiled without optimization. Because always storing floating-point arguments on the stack is inefficient and rarely needed, this option is not enabled by default and only is necessary when calling subroutines compiled by AIX XL compilers without optimization.

-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 GCC when linking.

-mmultiple

-mno-multiple

Generate code that uses (does not use) the load multiple word instructions and the store multiple word instructions. These instructions are generated by default on POWER systems, and not generated on PowerPC systems. Do not use `-mmultiple' on little endian PowerPC systems, since those instructions do not work when the processor is in little endian mode. The exceptions are PPC740 and PPC750 which permit the instructions usage in little endian mode.

-mstring

-mno-string

Generate code that uses (does not use) the load string instructions and the store string word instructions to save multiple registers and do small block moves. These instructions are generated by default on POWER systems, and not generated on PowerPC systems. Do not use `-mstring' on little endian PowerPC systems, since those instructions do not work when the processor is in little endian mode. The exceptions are PPC740 and PPC750 which permit the instructions usage in little endian mode.

-mupdate

-mno-update

Generate code that uses (does not use) the load or store instructions that update the base register to the address of the calculated memory location. These instructions are generated by default. If you use `-mno-update', there is a small window between the time that the stack pointer is updated and the address of the previous frame is stored, which means code that walks the stack frame across interrupts or signals may get corrupted data.

-mfused-madd

-mno-fused-madd

Generate code that uses (does not use) the floating point multiply and accumulate instructions. These instructions are generated by default if hardware floating is used.

-mno-bit-align

-mbit-align

On System V.4 and embedded PowerPC systems do not (do) force structures and unions that contain bit fields to be aligned to the base type of the bit field.

For example, by default a structure containing nothing but 8 unsigned 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.

-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.

Using and Porting the GNU Compiler Collection (GCC)

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