| Register | APCS name | APCS role |
|---|---|---|
| r0 | a1 | argument 1/scratch register/result |
| r1 | a2 | argument 2/scratch register/result |
| r2 | a3 | argument 3/scratch register/result |
| r3 | a4 | argument 4/scratch register/result |
| r4 | v1 | register variable |
| r5 | v2 | register variable |
| r6 | v3 | register variable |
| r7 | v4 | register variable |
| r8 | v5 | register variable |
| r9 | sb/v6 | static base/register variable |
| r10 | sl/v7 | stack limit/stack chunk handle/register variable |
| r11 | fp/v8 | frame pointer/register variable |
| r12 | ip | scratch register/new -sb in inter-link-unit calls |
| r13 | sp | lower end of the current stack frame |
| r14 | lr | link register/scratch register |
| r15 | pc | program counter |
| Singles | Doubles | Quads | Volatile? | Role |
|---|---|---|---|---|
| s0-s3 | d0-d1 | q0 | Volatile | Parameters, result, scratch register |
| s4-s7 | d2-d3 | q1 | Volatile | Parameters, scratch register |
| s8-s11 | d4-d5 | q2 | Volatile | Parameters, scratch register |
| s12-s15 | d6-d7 | q3 | Volatile | Parameters, scratch register |
| s16-s19 | d8-d9 | q4 | Non-volatile | |
| s20-s23 | d10-d11 | q5 | Non-volatile | |
| s24-s27 | d12-d13 | q6 | Non-volatile | |
| s28-s31 | d14-d15 | q7 | Non-volatile | |
| d16-d31 | q8-q15 | Volatile |
-
Overview of ARM64 ABI conventions
-
Integer Registers:
- 32 64 bits: X0~X31
- 32 32 bits: W0~W31
-
Float Point and Vector Registers(Neon):
- 32 8 bits: B0~B31
- 32 16 bits: H0~H31
- 32 32 bits: S0~S31
- 32 64 bits: D0~D31
- 32 128 bits: Q0~Q31
-
SVE Registers
- 32 VL bits(128~2048 bits) data register: Z0~Z31
- 16 VL/8 bits mask register: P0~P15
- FFR(1 First Faulting Register)