setjmp.asm

global setjmp

setjmp:
  push ebx
  mov ebx,[8 + esp]

  mov [0 + ebx],edi ; buf->edi == 0(ebx) == EDI
  mov [4 + ebx],esi ; buf->esi == 4(ebx) == ESI
  mov [8 + ebx],ebp ; buf->ebp == 8(ebx) == EBP

  mov [20 + ebx],edx  ; buf->edx == 20(ebx) == EDX
  mov [24 + ebx],ecx  ; buf->ecx == 24(ebx) == ECX
  mov [28 + ebx],eax  ; buf->eax == 28(ebx) == EAX

; use EBX value saved on stack; not the current value
  mov eax,[esp]
  mov [16 + ebx],eax  ; buf->ebx == 16(ebx) == EBX

; use ESP value after RET; not the current value
  lea eax,[8 + esp]
  mov [12 + ebx],eax  ; buf->esp == 32(ebx) == ESP

; use return address of this routine (EIP value saved on stack);
; not the current value
  mov eax,[4 + esp]
  mov [32 + ebx],eax  ; buf->eip == 36(ebx) == EIP

; none of the PUSH or MOV instructions changed EFLAGS!
  pushf
  pop dword [36 + ebx]  ; buf->eflags == 40(ebx) == EFLAGS
  pop ebx
  xor eax,eax
  ret