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3.17.24 IBM RS/6000 and PowerPC Options
These ‘-m’ options are defined for the IBM RS/6000 and PowerPC:
- @gcctabopt -mpower
- @gcctabopt -mno-power
- @gcctabopt -mpower2
- @gcctabopt -mno-power2
- @gcctabopt -mpowerpc
- @gcctabopt -mno-powerpc
- @gcctabopt -mpowerpc-gpopt
- @gcctabopt -mno-powerpc-gpopt
- @gcctabopt -mpowerpc-gfxopt
- @gcctabopt -mno-powerpc-gfxopt
- @gcctabopt -mpowerpc64
- @gcctabopt -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.
- @gcctabopt -mnew-mnemonics
- @gcctabopt -mold-mnemonics
Select which mnemonics to use in the generated assembler code. With ‘-mnew-mnemonics’, GCC uses the assembler mnemonics defined for the PowerPC architecture. With ‘-mold-mnemonics’ it uses 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.
- @gcctabopt -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 ‘401’, ‘403’, ‘405’, ‘405fp’, ‘440’, ‘440fp’, ‘505’, ‘601’, ‘602’, ‘603’, ‘603e’, ‘604’, ‘604e’, ‘620’, ‘630’, ‘740’, ‘7400’, ‘7450’, ‘750’, ‘801’, ‘821’, ‘823’, ‘860’, ‘970’, ‘8540’, ‘common’, ‘ec603e’, ‘G3’, ‘G4’, ‘G5’, ‘power’, ‘power2’, ‘power3’, ‘power4’, ‘power5’, ‘powerpc’, ‘powerpc64’, ‘rios’, ‘rios1’, ‘rios2’, ‘rsc’, and ‘rs64a’.
‘-mcpu=common’ selects a completely generic processor. Code generated under this option will run on any POWER or PowerPC processor. GCC will use only the instructions in the common subset of both architectures, and will not use the MQ register. GCC assumes a generic processor model for scheduling purposes.
‘-mcpu=power’, ‘-mcpu=power2’, ‘-mcpu=powerpc’, and ‘-mcpu=powerpc64’ specify generic POWER, POWER2, pure 32-bit PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine types, with an appropriate, generic processor model assumed for scheduling purposes.
The other options specify a specific processor. Code generated under those options will run best on that processor, and may not run at all on others.
The ‘-mcpu’ options automatically enable or disable the following options: ‘-maltivec’, ‘-mhard-float’, ‘-mmfcrf’, ‘-mmultiple’, ‘-mnew-mnemonics’, ‘-mpower’, ‘-mpower2’, ‘-mpowerpc64’, ‘-mpowerpc-gpopt’, ‘-mpowerpc-gfxopt’, ‘-mstring’. The particular options set for any particular CPU will vary between compiler versions, depending on what setting seems to produce optimal code for that CPU; it doesn't necessarily reflect the actual hardware's capabilities. If you wish to set an individual option to a particular value, you may specify it after the ‘-mcpu’ option, like ‘-mcpu=970 -mno-altivec’.
On AIX, the ‘-maltivec’ and ‘-mpowerpc64’ options are not enabled or disabled by the ‘-mcpu’ option at present, since AIX does not have full support for these options. You may still enable or disable them individually if you're sure it'll work in your environment.
- @gcctabopt -mtune=cpu_type
Set the instruction scheduling parameters for machine type cpu_type, but do not set the architecture type, register usage, or choice of mnemonics, as ‘-mcpu=cpu_type’ would. The same values for cpu_type are used for ‘-mtune’ as for ‘-mcpu’. If both are specified, the code generated will use the architecture, registers, and mnemonics set by ‘-mcpu’, but the scheduling parameters set by ‘-mtune’.
- @gcctabopt -maltivec
- @gcctabopt -mno-altivec
Generate code that uses (does not use) AltiVec instructions, and also enable the use of built-in functions that allow more direct access to the AltiVec instruction set. You may also need to set ‘-mabi=altivec’ to adjust the current ABI with AltiVec ABI enhancements.
- @gcctabopt -mabi=spe
Extend the current ABI with SPE ABI extensions. This does not change the default ABI, instead it adds the SPE ABI extensions to the current ABI.
- @gcctabopt -mabi=no-spe
Disable Booke SPE ABI extensions for the current ABI.
- @gcctabopt -misel=yes/no
- @gcctabopt -misel
This switch enables or disables the generation of ISEL instructions.
- @gcctabopt -mspe=yes/no
- @gcctabopt -mspe
This switch enables or disables the generation of SPE simd instructions.
- @gcctabopt -mfloat-gprs=yes/single/double/no
- @gcctabopt -mfloat-gprs
This switch enables or disables the generation of floating point operations on the general purpose registers for architectures that support it.
The argument yes or single enables the use of single-precision floating point operations.
The argument double enables the use of single and double-precision floating point operations.
The argument no disables floating point operations on the general purpose registers.
This option is currently only available on the MPC854x.
- @gcctabopt -m32
- @gcctabopt -m64
Generate code for 32-bit or 64-bit environments of Darwin and SVR4 targets (including GNU/Linux). The 32-bit environment sets int, long and pointer to 32 bits and generates code that runs on any PowerPC variant. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits, and generates code for PowerPC64, as for ‘-mpowerpc64’.
- @gcctabopt -mfull-toc
- @gcctabopt -mno-fp-in-toc
- @gcctabopt -mno-sum-in-toc
- @gcctabopt -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.
- @gcctabopt -maix64
- @gcctabopt -maix32
Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
longtype, 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’.
- @gcctabopt -mxl-compat
- @gcctabopt -mno-xl-compat
Produce code that conforms more closely to IBM XLC semantics when using AIX-compatible ABI. Pass floating-point arguments to prototyped functions beyond the register save area (RSA) on the stack in addition to argument FPRs. Do not assume that most significant double in 128 bit long double value is properly rounded when comparing values.
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.
- @gcctabopt -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 ‘-pthread’ option are incompatible.
- @gcctabopt -malign-natural
- @gcctabopt -malign-power
On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option ‘-malign-natural’ overrides the ABI-defined alignment of larger types, such as floating-point doubles, on their natural size-based boundary. The option ‘-malign-power’ instructs GCC to follow the ABI-specified alignment rules. GCC defaults to the standard alignment defined in the ABI.
On 64-bit Darwin, natural alignment is the default, and ‘-malign-power’ is not supported.
- @gcctabopt -msoft-float
- @gcctabopt -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.
- @gcctabopt -mmultiple
- @gcctabopt -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.
- @gcctabopt -mstring
- @gcctabopt -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.
- @gcctabopt -mupdate
- @gcctabopt -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.
- @gcctabopt -mfused-madd
- @gcctabopt -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.
- @gcctabopt -mno-bit-align
- @gcctabopt -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
unsignedbit-fields 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.
- @gcctabopt -mno-strict-align
- @gcctabopt -mstrict-align
On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory references will be handled by the system.
- @gcctabopt -mrelocatable
- @gcctabopt -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’.
- @gcctabopt -mrelocatable-lib
- @gcctabopt -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.
- @gcctabopt -mno-toc
- @gcctabopt -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.
- @gcctabopt -mlittle
- @gcctabopt -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’.
- @gcctabopt -mbig
- @gcctabopt -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’.
- @gcctabopt -mdynamic-no-pic
On Darwin and Mac OS X systems, compile code so that it is not relocatable, but that its external references are relocatable. The resulting code is suitable for applications, but not shared libraries.
- @gcctabopt -mprioritize-restricted-insns=priority
This option controls the priority that is assigned to dispatch-slot restricted instructions during the second scheduling pass. The argument priority takes the value 0/1/2 to assign no/highest/second-highest priority to dispatch slot restricted instructions.
- @gcctabopt -msched-costly-dep=dependence_type
This option controls which dependences are considered costly by the target during instruction scheduling. The argument dependence_type takes one of the following values: no: no dependence is costly, all: all dependences are costly, true_store_to_load: a true dependence from store to load is costly, store_to_load: any dependence from store to load is costly, number: any dependence which latency >= number is costly.
- @gcctabopt -minsert-sched-nops=scheme
This option controls which nop insertion scheme will be used during the second scheduling pass. The argument scheme takes one of the following values: no: Don't insert nops. pad: Pad with nops any dispatch group which has vacant issue slots, according to the scheduler's grouping. regroup_exact: Insert nops to force costly dependent insns into separate groups. Insert exactly as many nops as needed to force an insn to a new group, according to the estimated processor grouping. number: Insert nops to force costly dependent insns into separate groups. Insert number nops to force an insn to a new group.
- @gcctabopt -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’.
- @gcctabopt -mcall-sysv-eabi
Specify both ‘-mcall-sysv’ and ‘-meabi’ options.
- @gcctabopt -mcall-sysv-noeabi
Specify both ‘-mcall-sysv’ and ‘-mno-eabi’ options.
- @gcctabopt -mcall-solaris
On System V.4 and embedded PowerPC systems compile code for the Solaris operating system.
- @gcctabopt -mcall-linux
On System V.4 and embedded PowerPC systems compile code for the Linux-based GNU system.
- @gcctabopt -mcall-gnu
On System V.4 and embedded PowerPC systems compile code for the Hurd-based GNU system.
- @gcctabopt -mcall-netbsd
On System V.4 and embedded PowerPC systems compile code for the NetBSD operating system.
- @gcctabopt -maix-struct-return
Return all structures in memory (as specified by the AIX ABI).
- @gcctabopt -msvr4-struct-return
Return structures smaller than 8 bytes in registers (as specified by the SVR4 ABI).
- @gcctabopt -mabi=altivec
Extend the current ABI with AltiVec ABI extensions. This does not change the default ABI, instead it adds the AltiVec ABI extensions to the current ABI.
- @gcctabopt -mabi=no-altivec
Disable AltiVec ABI extensions for the current ABI.
- @gcctabopt -mprototype
- @gcctabopt -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.
- @gcctabopt -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.
- @gcctabopt -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’.
- @gcctabopt -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’.
- @gcctabopt -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’.
- @gcctabopt -mvxworks
On System V.4 and embedded PowerPC systems, specify that you are compiling for a VxWorks system.
- @gcctabopt -mwindiss
Specify that you are compiling for the WindISS simulation environment.
- @gcctabopt -memb
On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags header to indicate that ‘eabi’ extended relocations are used.
- @gcctabopt -meabi
- @gcctabopt -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
__eabiis called to from
mainto set up the eabi environment, and the ‘-msdata’ option can use both
r13to 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
r13to 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.
- @gcctabopt -msdata=eabi
On System V.4 and embedded PowerPC systems, put small initialized
constglobal and static data in the ‘.sdata2’ section, which is pointed to by register
r2. Put small initialized non-
constglobal 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.
- @gcctabopt -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.
- @gcctabopt -msdata=default
- @gcctabopt -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’.
- @gcctabopt -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
r13to address small data however. This is the default behavior unless other ‘-msdata’ options are used.
- @gcctabopt -msdata=none
- @gcctabopt -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.
- @gcctabopt -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.
- @gcctabopt -mregnames
- @gcctabopt -mno-regnames
On System V.4 and embedded PowerPC systems do (do not) emit register names in the assembly language output using symbolic forms.
- @gcctabopt -mlongcall
- @gcctabopt -mno-longcall
Default to making all function calls indirectly, using a register, so that functions which reside further than 32 megabytes (33,554,432 bytes) from the current location can be called. This setting can be overridden by the
shortcallfunction attribute, or by
Some linkers are capable of detecting out-of-range calls and generating glue code on the fly. On these systems, long calls are unnecessary and generate slower code. As of this writing, the AIX linker can do this, as can the GNU linker for PowerPC/64. It is planned to add this feature to the GNU linker for 32-bit PowerPC systems as well.
On Darwin/PPC systems,
#pragma longcallwill generate “jbsr callee, L42”, plus a “branch island” (glue code). The two target addresses represent the callee and the “branch island”. The Darwin/PPC linker will prefer the first address and generate a “bl callee” if the PPC “bl” instruction will reach the callee directly; otherwise, the linker will generate “bl L42” to call the “branch island”. The “branch island” is appended to the body of the calling function; it computes the full 32-bit address of the callee and jumps to it.
On Mach-O (Darwin) systems, this option directs the compiler emit to the glue for every direct call, and the Darwin linker decides whether to use or discard it.
In the future, we may cause GCC to ignore all longcall specifications when the linker is known to generate glue.
- @gcctabopt -pthread
Adds support for multithreading with the pthreads library. This option sets flags for both the preprocessor and linker.
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