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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, MCP8xx and the IBM 4xx microprocessors. The PowerPC architecture defines 64-bit instructions, but they are not supported by any current processors.
Neither architecture is a subset of the other. However there is a large common subset of instructions supported by both. An MQ register is included in processors supporting the POWER architecture.
You use these options to specify which instructions are available on the processor you are using. The default value of these options is determined when configuring GNU CC. Specifying the ‘-mcpu=cpu_type’ overrides the specification of these options.
We recommend you use the ‘-mcpu=cpu_type’ option rather than any of these options.
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’, ‘620’, ‘power’, ‘power2’, ‘powerpc’, ‘403’, ‘505’, ‘821’, ‘860’ and ‘common’. The ‘-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 ‘-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; ‘-mcpu=602’, ‘-mcpu=603’, ‘-mcpu=603e’, ‘-mcpu=604’, ‘-mcpu=620’, ‘-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.
Exactly similarly, ‘-mcpu=403’, ‘-mcpu=505’, ‘-mcpu=821’, ‘-mcpu=860’ and ‘-mcpu=powerpc’ all 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 ‘-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’, ‘-mcpu=620’, ‘-mcpu=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 func-tions beyond the register save area (RSA) on the stack in addition to floating point register arguments. 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.

Warning:
Do not use -mstring on little endian PowerPC systems, since those instructions do not work when the processor is in little endian mode.

-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 ‘-mreloctable-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 trace-back 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 (ABI), 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 ‘-mnoeabi’ 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 operating 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 the standard C libraries are libsim.a and libc.a. This is default for ‘powerpc-*-eabisim’ configurations.

-mmvme
On embedded PowerPC systems, assume that the startup module is called mvme-crt0.o and the standard C libraries are ‘libmvme.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.