MIPS eabi register convention

This document tries to specify how the registers are used on the eabi MIPS ABI.

This ABI does not have any official register names, so names from other ABIs are left as references.

General purpose registers

N°	Usage	O32 name	N32 name
0	Zero	`$zero`	`$zero`
1	Volatile	`$at`	`$at`
2	Volatile / Return val	`$v0`	`$v0`
3	Volatile / Return val ¹	`$v1`	`$v1`
4	Volatile / Arg	`$a0`	`$a0`
5	Volatile / Arg	`$a1`	`$a1`
6	Volatile / Arg	`$a2`	`$a2`
7	Volatile / Arg	`$a3`	`$a3`
8	Volatile / Arg	`$t0`	`$a4`
9	Volatile / Arg	`$t1`	`$a5`
10	Volatile / Arg	`$t2`	`$a6`
11	Volatile / Arg	`$t3`	`$a7`
12	Volatile	`$t4`	`$t0`
13	Volatile	`$t5`	`$t1`
14	Volatile	`$t6`	`$t2`
15	Volatile	`$t7`	`$t3`
16	Non-volatile	`$s0`	`$s0`
17	Non-volatile	`$s1`	`$s1`
18	Non-volatile	`$s2`	`$s2`
19	Non-volatile	`$s3`	`$s3`
20	Non-volatile	`$s4`	`$s4`
21	Non-volatile	`$s5`	`$s5`
22	Non-volatile	`$s6`	`$s6`
23	Non-volatile	`$s7`	`$s7`
24	Volatile	`$t8`	`$t8`
25	Volatile	`$t9`	`$t9`
26	Kernel	`$k0`	`$k0`
27	Kernel	`$k1`	`$k1`
28	gp	`$gp`	`$gp`
29	stack pointer	`$sp`	`$sp`
30	Non-volatile	`$fp`/`$s8`	`$fp`/`$s8`
31	Return address	`$ra`	`$ra`

N°	Usage	O32 name	N32 name	N64 name
`$f0`	Return value	`$fv0`	`$fv0`	`$fv0`
`$f1`	Return value ²	`$fv0f`	`$ft14`	`$ft12`
`$f2`		`$fv1`	`$fv1`	`$fv1`
`$f3`		`$fv1f`	`$ft15`	`$ft13`
`$f4`		`$ft0`	`$ft0`	`$ft0`
`$f5`		`$ft0f`	`$ft1`	`$ft1`
`$f6`		`$ft1`	`$ft2`	`$ft2`
`$f7`		`$ft1f`	`$ft3`	`$ft3`
`$f8`		`$ft2`	`$ft4`	`$ft4`
`$f9`		`$ft2f`	`$ft5`	`$ft5`
`$f10`		`$ft3`	`$ft6`	`$ft6`
`$f11`		`$ft3f`	`$ft7`	`$ft7`
`$f12`	Arg	`$fa0`	`$fa0`	`$fa0`
`$f13`	Arg	`$fa0f`	`$fa1`	`$fa1`
`$f14`	Arg	`$fa1`	`$fa2`	`$fa2`
`$f15`	Arg	`$fa1f`	`$fa3`	`$fa3`
`$f16`	Arg	`$ft4`	`$fa4`	`$fa4`
`$f17`	Arg	`$ft4f`	`$fa5`	`$fa5`
`$f18`	Arg	`$ft5`	`$fa6`	`$fa6`
`$f19`	Arg	`$ft5f`	`$fa7`	`$fa7`
`$f20`		`$fs0`	`$fs0`	`$ft8`
`$f21`		`$fs0f`	`$ft8`	`$ft9`
`$f22`		`$fs1`	`$fs1`	`$ft10`
`$f23`		`$fs1f`	`$ft9`	`$ft11`
`$f24`		`$fs2`	`$fs2`	`$fs0`
`$f25`		`$fs2f`	`$ft10`	`$fs1`
`$f26`		`$fs3`	`$fs3`	`$fs2`
`$f27`		`$fs3f`	`$ft11`	`$fs3`
`$f28`		`$fs4`	`$fs4`	`$fs4`
`$f29`		`$fs4f`	`$ft12`	`$fs5`
`$f30`		`$fs5`	`$fs5`	`$fs6`
`$f31`		`$fs5f`	`$ft13`	`$fs7`