ABI Cheat Sheet

The following are ABI register usage notes accumulated with development and porting of musl to various archs:

aarch64

x30 lr
x31 zr or pc

arm

r0-r3 args/ret
r4-r11 saved
r12 temp (ip scratch)
r13 sp
r14 lr
r15 pc

microblaze

r0 zero
r1 sp
r2 ro sda
r3-r4 ret
r5-r10 args
r11-12 temp
r13 rw sda
r14 syscall ret addr
r15 function ret addr
r16 break ret addr
r17 exception ret addr
r18 assembler temp
r19-r20 saved
r21 thread pointer
r21-r31 saved

mips

$0 zero
$1 at (assembler temp)
$2-$3 ret (aka v0-v1)
$4-$7 args (aka a0-a3)
$8-$15 temp (aka t0-t7)
$16-$23 saved (aka s0-s7)
$24 temp (aka t8)
$25 function call addr (aka t9)
$26-$27 kernel use
$28 gp, call-clobbered
$29 sp
$30 fp
$31 ra

Source: http://www.inf.ed.ac.uk/teaching/courses/car/Notes/slide03.pdf

or1k (OpenRISC)

r0 zero
r1 sp
r2 fp
r3-r8 args
r9 lr
r11,r12 retval (lo,hi)
r10 thread pointer
r14-r30(even) saved
r13-r31(odd) temp

Source: openrisc-arch-1.1-rev0.pdf, p.335

powerpc

0 temp
1 sp
2 toc (thread pointer)
3 ret, arg0
4-10 args
11-12 temp
13-31 saved
lr (not gpr; use mtlr/mflr)
30 got
11 plt temp
ctr plt temp

Sources: http://www.csd.uwo.ca/~mburrel/stuff/ppc-asm.html, http://devpit.org/wiki/Debugging_PowerPC_ELF_Binaries

sh (SuperH)

r0-r3 ret
r2 struct ret addr
r4-r7 args
r8-r13 saved
r12 gp (saved)
r14 fp (saved)
r15 sp
pr lr
gbr thread ptr

Source: http://www.st.com/st-web-ui/static/active/en/resource/technical/document/reference_manual/CD17839242.pdf, p.9