如下代码计算地址并16字节对齐：

    char* buffer = (char*)malloc(a3 + 0x1000);
    unsigned long long tmp = (((unsigned long long)buffer + 0x10) & 0xffffffffffffff00);
    char* buf = (char*)tmp;

假如把地址当作整数，加减程序运算，直接转换是不行的，gcc会提示各种错误：

error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]

恼人的地方在于，无论你怎么改，除非将buffer 类型改为uintptr_t，或者unsigned long，其他类型都无效！

唯一可行、有效的方法如下：

    char* buffer = (char*)malloc(a3 + 0x1000);
    uintptr_t tmp = ((( uintptr_t )buffer + 0x10) & 0xffffffffffffff00);
    char* buf = (char*)tmp;