https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53037
--- Comment #20 from Martin Sebor <msebor at gcc dot gnu.org> ---
It would be useful to have the ability to trigger a warning when an object of a
type with an explicitly specified alignment (even if the alignment matches its
own native one) is defined in a way that would cause its alignment to be
reduced. The specific use case where it came up is defining a packed struct
that contains a member of type std::mutex (or some type that contains it.)
A test case for the warning I was asking about (with no warn_if_not_aligned
attribute) is simply:
struct __attribute___ ((aligned (8))) S8 { char a[8]; }; // explicitly
overaligned
struct __attribute__ ((packed)) S {
struct S8 s8; // warn here: alignment of 'struct A' reduced from 8 to 1
};
