1 Register Usage 2 rax temporary register; with variable arguments passes information 3 about the number of SSE registers used; 1st return register 4 5 rbx* callee-saved register; optionally used as base pointer 6 7 rcx used to pass 4th integer argument to functions 8 9 rdx used to pass 3rd argument to functions 2nd return register 10 11 rsp* stack pointer 12 13 rbp* callee-saved register; optionally used as frame pointer 14 15 rsi used to pass 2nd argument to functions 16 17 rdi used to pass 1st argument to functions 18 19 r8 used to pass 5th argument to functions 20 21 r9 used to pass 6th argument to functions 22 23 r10 temporary register, used for passing a function's static chain pointer 24 25 r11 temporary register 26 27 r12-15* callee-saved registers 28 29 xmm01 used to pass and return floating point arguments 30 31 xmm27 used to pass floating point arguments 32 33 xmm815 temporary registers 34 35 mmx07 temporary registers 36 37 st0 temporary register; used to return long double arguments 38 39 st1 temporary registers; used to return long double arguments 40 41 st27 temporary registers 42 43 fs Reserved for system use (as thread specific data register) 44 45 46 47 *) must be preserved across function calls 48 49 Integer arguments from list: rdi,rsi,rdx,rcx,r8,r9,stack 50 Floating point arguments from list: xmm0-xmm7
