Stack Example
- include <stdio.h>
void __declspec(naked) swap(int *a, int *b) { __asm { push ebp ; Preserve ebp. mov ebp, esp ; Set up the frame pointer. sub esp, 8 ; Make room for two local variables. push esi ; Preserve esi on the stack. push edi ; Preserve edi on the stack.
mov ecx, [ebp+8] ; Put the first parameter (a pointer) into ecx. mov edx, [ebp+12] ; Put the second parameter (a pointer) into edx.
mov esi, [ecx] ; Dereference the pointer to get the first parameter. mov edi, [edx] ; Dereference the pointer to get the second parameter.
mov [ebp-4], esi ; Store the first as a local variable mov [ebp-8], edi ; Store the second as a local variable
mov esi, [ebp-8] ; Retrieve them in reverse mov edi, [ebp-4]
mov [ecx], esi ; Put the second value into the first address. mov [edx], edi ; Put the first value into the second address.
pop edi ; Restore the edi register pop esi ; Restore the esi register add esp, 8 ; Remove the local variables from the stack pop ebp ; Restore ebp ret ; Return (eax isn't set, so there's no return value) } }
int main(int argc, char* argv[]) { int a = 3; int b = 4;
printf("a = %d, b = %d\n", a, b); swap(&a, &b); printf("a = %d, b = %d\n", a, b);
while(1) ;
return 0; }