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From: "kees at outflux dot net" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/101836] __builtin_object_size(P->M, 1) where M is an
 array and the last member of a struct fails
Date: Wed, 06 Jul 2022 16:49:46 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101836

--- Comment #34 from Kees Cook <kees at outflux dot net> ---
-fstrict-flex-arrays=3D3 is still needed. (E.g. for proper FORTIFY coverage,
etc.) I don't have an opinion about the -W options, though.(In reply to Jam=
es Y
Knight from comment #33)
> (In reply to qinzhao from comment #32)
> > there is a Bugzilla that has been filed for GCC to request the same war=
ning
> > for GCC:
> > https://gcc.gnu.org/bugzilla//show_bug.cgi?id=3D94428
> >=20
> > -Wzero-length-array
>=20
> Great. Adding that flag, and eliminating the -fstrict-flex-arrays=3D3 opt=
ion
> from this proposal would be good.

Hmm? No, -fstrict-flex-arrays=3D3 is still needed (because it changes compi=
ler
_behavior_, e.g. for proper FORTIFY coverage or trailing arrays, etc).

I don't have a strong opinion about the -W options; but they can't warn if =
they
just see a struct declaration with a 0 or 1 element array: userspace will h=
ave
those for years to come. Maybe it would warn if such a struct member is ever
actually used in the code? That kind of behavior would be useful for the Li=
nux
kernel at least.=