On Thu, Jun 04, 2026 at 10:32:16PM +0100, David Laight wrote:

Talking of broken compilers, had you noticed that:
struct foo {
    int a;
    char c[32];
};

int b(struct foo *f)
{
    return __builtin_object_size(f->c, 1);
}
returns -1 (size unknown/indefinite).
You can't use __builtin_object_size() to stop code running off the end
of anything referenced by address - even when the size is constant.

That is the entire point of using '-fstrict-flex-arrays=3' in the
kernel:

  df8fc4e934c1 ("kbuild: Enable -fstrict-flex-arrays=3")
  https://godbolt.org/z/bvfrh7W58

Without it, all trailing arrays in structures are treated as flexible
arrays, even those with fixed sizes.

-- 
Cheers,
Nathan