| %rax |
Temporary register; with variable arguments passes information about the number of vector registers used; 1st return register |
No |
| %rbx |
Callee-saved register; optionally used as base pointer |
Yes |
| %rcx |
Used to pass 4th integer argument to functions |
No |
| %rdx |
Used to pass 3rd argument to functions; 2nd return register |
No |
| %rsp |
Stack pointer |
Yes |
| %rbp |
Callee-saved register; optionally used as frame pointer |
Yes |
| %rsi |
Used to pass 2nd argument to functions |
No |
| %rdi |
Used to pass 1st argument to functions |
No |
| %r8 |
Used to pass 5th argument to functions |
No |
| %r9 |
Used to pass 6th argument to functions |
No |
| %r10 |
Temporary register, used for passing a function’s static chain pointer |
No |
| %r11 |
Temporary register |
No |
| %r12–%r15 |
Callee-saved registers |
Yes |
| %xmm0–%xmm1 |
Used to pass and return floating point arguments |
No |
| %xmm2–%xmm7 |
Used to pass floating point arguments |
No |
| %xmm8–%xmm15 |
Temporary registers |
No |
| %mmx0–%mmx7 |
Temporary registers |
No |
| %st0, %st1 |
Temporary registers; used to return long double arguments |
No |
| %st2–%st7 |
Temporary registers |
No |
| %fs |
Reserved for system (as thread specific data register) |
No |
| mxcsr |
SSE2 control and status word |
Partial |
| x87 SW |
x87 status word |
No |
| x87 CW |
x87 control word |
Yes |
