https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96293
--- Comment #9 from Long Deng <ldeng at mail dot ustc.edu.cn> ---
I take your point, although there seems to be a slight problem with your
example. In your code, `&a->record.data[0]` is not a well-aligned access,
because `struct attribute` is defined as packed, so compiler has no any
information about where `a` itself is aligned to. `a` could start at any
address so `a->record.data` might not well-aligned.
Maybe a better example is defining `struct record` as `((packed))` and `struct
attribute` as `((packed, aligned(2))`, which ensure `a` is well-aligned. Even
in this case, gcc still issue the warning.
Full example:
```
#include <stdio.h>
#include <stddef.h>
#include <stdint.h>
#include <assert.h>
struct Unaligned {
uint8_t b;
uint32_t c;
uint16_t d;
}__attribute__((packed));
struct Aligned {
uint8_t d;
struct Unaligned u;
}__attribute__((packed, aligned(8)));
static_assert(sizeof(struct Aligned) == 8);
void fun(uint16_t* addr) {
*addr = 1234;
}
int main() {
struct Aligned a;
printf("addr of a: %p\n", &a);
printf("offsetof d: %zu\n",offsetof(struct Aligned, u.d));
fun(&a.u.d);
return 0;
}
```
