AngheloAlf/MIPS eabi register convention.md

## MIPS eabi register convention.md

      
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              MIPS eabi register convention.md
            
          
    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


Floating point registers


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


References


https://sourceware.org/legacy-ml/binutils/2003-06/msg00436.html
https://gist.github.com/EllipticEllipsis/27eef11205c7a59d8ea85632bc49224d#file-mips_registers-md

Footnotes


Used as the second pair of a long long value in 32-bits mode ↩


Used as the second pair of a double value in 32-bits mode ↩
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`