• Compiling for PowerPC targets
• Floating-point subroutines for PowerPC targets
• Preprocessor macro for PowerPC targets
• Assembler options for PowerPC targets
• Debugging PowerPC targets
• The stack frame
• Argument passing
• Function return values

-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 IBM 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, 604e, 620, power, power2, powerpc, 403, 505, 801, 821, 823, 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.
IBM AIX versions 4 or greater selects -mcpu=common by default, so that code will operate on all members of the IBM 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.
-msoft-float
-mhard-float
Generate code that does not use or does use 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.
-mupdate
-mno-update
Generate code that uses (or 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 and do force structures and unions containing bit fields 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, 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.
-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 ` libyk.a and ` libc.a are the standard C libraries.
-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.

• Software implementations of the basic functions (floating-point multiply, divide, add, subtract), for use when there is no hardware floating-point support.
• General-purpose mathematical subroutines, included with implementation of the standard C mathematical subroutine library. See Mathematical functions (math.h) in GNUPro Math Library in GNUPro Libraries.

Assembler options for PowerPC targets

-mgas
Compile using the GNU assembler, gas, to assemble GCC output.
-Wa
If you invoke the GNU assembler through the GNU C compiler (version 2), you can use the -Wa option to pass arguments through to the assembler. One common use of this option is to exploit the assembler s listing features.
Assembler arguments that you specify with GCC, -Wa must be separated from each other (and the -Wa) by commas, like the options, -alh and -L, in the following example input, separate from -Wa.

powerpc-eabi-gcc -c -g -O -Wa,-alh, -L file.c

-L
The additional assembler option, -L, preserves local labels, which may make the listing output more intelligible to humans.
For example, in the following commandline, the assembler option, -ahl, requests a listing with interspersed high-level language and assembly language.

powerpc-eabi-gcc -c -g -O -Wa,-alh,-L file.c

-L preserves local labels, while the compiler debugging option, -g, gives the assembler the necessary debugging information.
Use the following options to enable listing output from the assembler. The letters after -a may be combined into one option, such as -al .
-a
By itself, -a requests listings of high-level language source, assembly language, and symbols.
-ah
Requests a high-level language listing.
-al
Request an output-program assembly listing.
 

-as

Requests a symbol table listing.
-ad
Omits debugging directives from listing. High-level listings require a compiler debugging option like -g, and assembly listings (such as -al) requested.

.list
Turn on listings for further input.
.nolist
Turn off listings for further input.
.psize linecount, columnwidth
Describe the page size for your output (the default is 60, 200). gas generates form feeds after printing each group of linecount lines. To avoid these automatic form feeds, specify 0 as linecount. The variable input for columnwidth uses the same descriptive option.
.eject
Skip to a new page (issue a form feed).
.title
Use as the title (this is the second line of the listing output, directly after the source file name and page number) when generating assembly listings.
.sbttl
Use as the subtitle (this is the third line of the listing output, directly after the title line) when generating assembly listings.
-an
Turn off all forms processing.

• Specifications for what you want to use one, such as target remote, gdb s generic debugging protocol.
• Specifications for what serial device connects your PowerPC board (the first serial device available on your host is the default).
• Specifications for what speed to use over the serial device.

target powerpc serial-device
To run a program on the board, start up GDB with the name of your program as the argument. To connect to the board, use the command, target interface serial-device, where interface is an interface from the previous list of specifications and serial-device is the name of the serial port connected to the board. If the program has not already been downloaded to the board, you may use the load command to download it. You can then use all the usual gdb commands. For example, the following sequence connects to the target board through a serial port, and loads and runs programs, designated here as prog, through the debugger.

(gdb) target powerpc com1 

... 

breakinst () ../sparc-stub.c:975 

975     } 

(gdb) s 

main    ()   hello.c:50 

50       writer(1,    "Got to here\n"); 

(gdb) 

target powerpc hostname : portnumber

You can specify a TCP/IP connection instead of a serial port, using the syntax, hostname : portnumber (assuming your board, designated here as hostname, is connected, for instance, to use a serial line, designated by portnumber, managed by a terminal concentrator).

GDB also supports set remotedebug n. You can see some debugging information about communications with the board by setting the variable, remotedebug.

• The stack grows downwards from high addresses to low addresses.
• A leaf function need not allocate a stack frame if it does not need one.
• A frame pointer need not be allocated.
• The stack pointer shall always be aligned to 4 byte boundaries.
• The register save area shall be aligned to a 4 byte boundary.