Using and Porting GNU CC

3.14.3: SPARC Options

These `-m' switches are supported on the SPARC:

-mno-app-regs

-mapp-regs

Specify `-mapp-regs' to generate output using the global registers 2 through 4, which the SPARC SVR4 ABI reserves for applications. This is the default.

To be fully SVR4 ABI compliant at the cost of some performance loss, specify `-mno-app-regs'. You should compile libraries and system software with this option.

-mfpu

-mhard-float

Generate output containing floating point instructions. This is the default.

-mno-fpu

-msoft-float

Generate output containing library calls for floating point. Warning: there is no GNU floating-point library for SPARC. 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.

`-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.

-mhard-quad-float

Generate output containing quad-word (long double) floating point instructions.

-msoft-quad-float

Generate output containing library calls for quad-word (long double) floating point instructions. The functions called are those specified in the SPARC ABI. This is the default.

As of this writing, there are no sparc implementations that have hardware support for the quad-word floating point instructions. They all invoke a trap handler for one of these instructions, and then the trap handler emulates the effect of the instruction. Because of the trap handler overhead, this is much slower than calling the ABI library routines. Thus the `-msoft-quad-float' option is the default.

-mno-epilogue

-mepilogue

With `-mepilogue' (the default), the compiler always emits code for function exit at the end of each function. Any function exit in the middle of the function (such as a return statement in C) will generate a jump to the exit code at the end of the function.

With `-mno-epilogue', the compiler tries to emit exit code inline at every function exit.

-mno-flat

-mflat

With `-mflat', the compiler does not generate save/restore instructions and will use a "flat" or single register window calling convention. This model uses %i7 as the frame pointer and is compatible with the normal register window model. Code from either may be intermixed although debugger support is still incomplete. The local registers and the input registers (0-5) are still treated as "call saved" registers and will be saved on the stack as necessary.

With `-mno-flat' (the default), the compiler emits save/restore instructions (except for leaf functions) and is the normal mode of operation.

-mno-unaligned-doubles

-munaligned-doubles

Assume that doubles have 8 byte alignment. This is the default.

With `-munaligned-doubles', GNU CC assumes that doubles have 8 byte alignment only if they are contained in another type, or if they have an absolute address. Otherwise, it assumes they have 4 byte alignment. Specifying this option avoids some rare compatibility problems with code generated by other compilers. It is not the default because it results in a performance loss, especially for floating point code.

-mv8

-msparclite

These two options select variations on the SPARC architecture.

By default (unless specifically configured for the Fujitsu SPARClite), GCC generates code for the v7 variant of the SPARC architecture.

`-mv8' will give you SPARC v8 code. The only difference from v7 code is that the compiler emits the integer multiply and integer divide instructions which exist in SPARC v8 but not in SPARC v7.

`-msparclite' will give you SPARClite code. This adds the integer multiply, integer divide step and scan (ffs) instructions which exist in SPARClite but not in SPARC v7.

-mcypress

-msupersparc

These two options select the processor for which the code is optimised.

With `-mcypress' (the default), the compiler optimizes code for the Cypress CY7C602 chip, as used in the SparcStation/SparcSever 3xx series. This is also apropriate for the older SparcStation 1, 2, IPX etc.

With `-msupersparc' the compiler optimizes code for the SuperSparc cpu, as used in the SparcStation 10, 1000 and 2000 series. This flag also enables use of the full SPARC v8 instruction set.

In a future version of GCC, these options will very likely be renamed to `-mcpu=cypress' and `-mcpu=supersparc'.

These `-m' switches are supported in addition to the above on SPARC V9 processors:

-mcode-model=medium-low

Generate code for the Medium/Low code model: assume a 32 bit address space. Programs are statically linked, PIC is not supported. Pointers are still 64 bits.

-mcode-model=medium-anywhere

Generate code for the Medium/Anywhere code model: assume a 32 bit text segment starting at offset 0, and a 32 bit data segment starting anywhere (determined at link time). Programs are statically linked, PIC is not supported. Pointers are still 64 bits.

-mint64

Types long and int are 64 bits.

-mlong32

Types long and int are 32 bits.

-mlong64

-mint32

Type long is 64 bits, and type int is 32 bits.

-mstack-bias

-mno-stack-bias

With `-mstack-bias', GNU CC assumes that the stack pointer, and frame pointer if present, are offset by -2047 which must be added back when making stack frame references. Otherwise, assume no such offset is present.