[Bug c/51628] __attribute__((packed)) is unsafe in some cases

[alexey.salmin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51628

Alexey Salmin <alexey.salmin at gmail dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |alexey.salmin at gmail dot com

--- Comment #36 from Alexey Salmin <alexey.salmin at gmail dot com> ---
FYI a test case that actually triggers SIGSEGV on x86 with gcc 7.2:
https://godbolt.org/g/kPw6NJ

Compiler emits a movaps instruction which is alignment-sensitive. A warning
would be helpful.

struct pair_t {
    char c;
    __int128_t i;
} __attribute__((packed));

struct pair_t p = {0, 1};
__int128_t *addr = &p.i;

int main() {
    *addr = ~(__int128_t)0;
    return (p.i != 1) ? 0 : 1;
}