nasm aat函数 x86

xxx.asm:

%define p1 ebp+8
%define p2 ebp+12
%define p3 ebp+16

section .text
	global dllmain

dllmain:
	mov eax,1
	ret 12

aat:
	push ebp
	mov ebp,esp

	; 函数必须保留所有寄存器，但eax，ecx和edx除外
	; esp则必须根据调用约定进行更新
	mov ecx,[p1]  	 ; array ptr
	mov edx,[p2]     ; index
	mov eax,[p3] 	 ; size
	mul edx			 ; eax=eax*edx
	lea eax,[ecx+eax]

	mov esp,ebp
	pop ebp
	ret 12

c++:

#include <iostream>
#include <Windows.h>

typedef PVOID (CALLBACK* aat_t)(PVOID pArray, size_t index, size_t size);

aat_t aat;

struct Player
{
  size_t id;
  DWORD hp;
  DWORD mp;
};

int main()
{
  HMODULE myDLL = LoadLibraryA("xxx.dll");
  aat = (aat_t)GetProcAddress(myDLL, "aat");

  int a[] = { 1,2,3 };
  printf("%d\n", *(int*)aat(a, 2, sizeof(int))); // 3

  Player b[] = {
    Player{1, 10, 20},
    Player{2, 50, 60},
    Player{3, 90, 20},
  };

  Player* it = (Player*)aat(b, 0, sizeof(Player));
  printf("[%d]: %d %d\n", it->id, it->hp, it->mp); // [1]: 10 20

  it = (Player*)aat(b, 1, sizeof(Player));
  printf("[%d]: %d %d\n", it->id, it->hp, it->mp); // [2]: 50 60

  it = (Player*)aat(b, 2, sizeof(Player));
  printf("[%d]: %d %d\n", it->id, it->hp, it->mp); // [3]: 90 20

  return 0;
}