nasm astrchr函数 x86

xxx.asm:

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

section .text
  global dllmain
  export astrchr

dllmain:
  mov eax,1
  ret 12

astrchr:
  push ebp
  mov ebp,esp

  mov eax,[p1]	; char ptr
  mov ecx,[p2]	; char

  .for:
  ;-------------------------------------------;
  ;   找到后返回第一次出现的指针
  ;-------------------------------------------;
  cmp [eax],cl
  je .return
  inc eax

  ;-------------------------------------------;
  ;   如果找不到该字符，则该函数返回空指针
  ;-------------------------------------------;
  cmp byte [eax],0
  je .error
  jmp .for

  .error:
  xor eax,eax

  .return:
  mov esp,ebp
  pop ebp
  ret 8

c++:

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

typedef char*(CALLBACK* astrchr_t)(const char* str, int character);

astrchr_t astrchr;

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

  char str[] = "hello world";

  char* pch = strchr(str, 'l');
  printf("%s\n", pch); // llo world

  char* pch2 = astrchr(str, 'l');
  printf("%s\n", pch2); // llo world

  //==============================//

  char* pch3 = strchr(str, 'b');
  printf("%s\n", pch3); // (null)

  char* pch4 = astrchr(str, 'b');
  printf("%s\n", pch4); // (null)
  return 0;
}