write（）的包装函数无法正常工作

Question

给定系统调用write的包装函数：

ssize_t my_write(int fd, const void *buf, size_t count)
{
    long __res;
    __asm__ volatile
        ("int $0x80"
                : "=a" (__res)
                : "0" (4),"D" ((long)(fd)),"S" ((long)(buf)), "d" ((long)(count))
                : "ebx","memory");

      if (-125 <= __res && __res < 0)
      {
        errno = -__res;
        __res   = -1;
      }

      return __res;
}

我已经尝试了代码（来自int main（））：

int main() {


     my_write(2,"an read error occured\n",26);


     return 0;
 }

但是它不起作用。 知道为什么吗？

谢谢

Answer 1

您的约束已关闭，文件描述符需要放入EBX，ECX中的缓冲区（而不是像您分别的EDI / ESI）。

尝试：

__asm__ volatile
    ("int $0x80"
            : "=a" (__res)
            : "0" (4),"b" ((long)(fd)),"c" ((long)(buf)), "d" ((long)(count))
            : "memory");