绕过“cast增加所需的对齐顺序”消息

Question

我有一些类似于以下内容的代码：

void somefunc(uint64_t val) {
    uint8_t *p;
    uint8_t *s;

    s = calloc( (max_sa_len + sizeof(uint64_t) - 1) / sizeof(uint64_t), sizeof(uint64_t));
    // s must be 8 byte aligned here
    p = (s + sizeof(uint64_t)); 
    // p must be 8 byte aligned here

    *(uint64_t)*p = hton64(val & 0xffff);
...
}

当我编译时，我得到：

file.c:400:10: error: cast increases required alignment of target type [-Werror=cast-align]

有没有一种干净的方法来解决这个警告？ s，因此p 必须与 64 位地址对齐，这不是真正的错误。我尝试p=__builtin_assume_alinged(p,8);在代码中添加一个，但它没有修复错误。我在使用 arm32 (v7) gcc 交叉编译器 v 4.7.0 时遇到此错误

Answer 1

uint64_t *s_u64 = calloc( (max_sa_len + sizeof(uint64_t) - 1) / sizeof(uint64_t), 
    sizeof(uint64_t));
s = s_u64; // if you need to address by byte as well 
...
s_u64[1] = hton64(val & 0xffff);