MIPS __asm Statement Registers

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The following table gives MIPS macro names and associated register descriptions.

MIPS16 macro name MIPSII macro name Associated Register Description
zero zero $0 Always zero; writes to this register are ignored.
N/A AT $1 Assembler temporary.
v0 v0 $2 Used to hold return value.
v1 v1 $3 Used to hold return value.
a0 a0 $4 Argument registers; used to pass first four words of integer arguments.
a1 a1 $5 Argument registers; used to pass first four words of integer arguments.
a2 a2 $6 Argument registers; used to pass first four words of integer arguments.
a3 a3 $7 Argument registers; used to pass first four words of integer arguments.
N/A t0 $8 Temporary registers; may be freely changed.
N/A t1 $9 Temporary registers; may be freely changed.
N/A t2 $10 Temporary registers; may be freely changed.
N/A t3 $11 Temporary registers; may be freely changed.
N/A t4 $12 Temporary registers; may be freely changed.
N/A t5 $13 Temporary registers; may be freely changed.
N/A t6 $14 Temporary registers; may be freely changed.
N/A t7 $15 Temporary registers; may be freely changed.
N/A s0 $16 Saved registers; must be preserved across function calls.
N/A s1 $17 Saved registers; must be preserved across function calls.
N/A s2 $18 Saved registers; must be preserved across function calls.
N/A s3 $19 Saved registers; must be preserved across function calls.
N/A s4 $20 Saved registers; must be preserved across function calls.
N/A s5 $21 Saved registers; must be preserved across function calls.
N/A s6 $22 Saved registers; must be preserved across function calls.
N/A s7 $23 Saved registers; must be preserved across function calls.
t8 t8 $24 Additional temporary registers.
N/A t9 $25 Additional temporary registers.
N/A k0 $26 Kernel reserved registers.
N/A k1 $27 Kernel reserved registers.
N/A gp $28 Global pointer.
sp sp $29 Stack pointer.
N/A s8 $30 Additional saved register.
ra ra $31 Return address register.

The register macro names are interchangeable with their numeric names using a dollar sign prefix. For example, the following two statements are equivalent:

__asm("add v0, a0, $16");
__asm("add $2, $4, s0");

See Also

The _asm Keyword in MIPS Inline Assembly | C or C++ References in MIPS Inline Assembly | Restrictions to MIPS __asm Statements

 Last updated on Thursday, April 08, 2004

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