Chapter 29.

MIPS Dependent Features

gnu

as

for mips architectures supports several different mips processors, and MIPS ISA levels I

through V, MIPS32, and MIPS64. For information about the mips instruction set, see [MIPS RISC

Architecture], by Kane and Heindrich (Prentice Hall). For an overview of mips assembly conventions,

see "Appendix D: Assembly Language Programming" in the same work.

29.1. Assembler options

The mips configurations of gnu

as

support these special options:

 G num

This option sets the largest size of an object that can be referenced implicitly with the

gp

register.

It is only accepted for targets that use ecoff format. The default value is 8.

 EB

 EL

Any mips configuration of

as

can select big endian or little endian output at run time (unlike the

other gnu development tools, which must be configured for one or the other). Use

 EB

to select

big endian output, and

 EL

for little endian.

 mips1

 mips2

 mips3

 mips4

 mips5

 mips32

 mips32r2

 mips64

 mips64r2

Generate code for a particular MIPS Instruction Set Architecture level.

 mips1

corresponds to

the r2000 and r3000 processors,

 mips2

to the r6000 processor,

 mips3

to the r4000 processor,

and

 mips4

to the r8000 and r10000 processors.

 mips5

,

 mips32

,

 mips32r2

,

 mips64

, and

 mips64r2

correspond to generic MIPS V, MIPS32, MIPS32 Release 2, MIPS64, and MIPS64

Release 2 ISA processors, respectively. You can also switch instruction sets during the assembly;

see Directives to override the ISA level.

 mgp32

 mfp32

Some macros have different expansions for 32 bit and 64 bit registers. The register sizes are

normally inferred from the ISA and ABI, but these flags force a certain group of registers to be

treated as 32 bits wide at all times.

 mgp32

controls the size of general purpose registers and

 mfp32

controls the size of floating point registers.

On some MIPS variants there is a 32 bit mode flag; when this flag is set, 64 bit instructions

generate a trap. Also, some 32 bit OSes only save the 32 bit registers on a context switch, so it

is essential never to use the 64 bit registers.