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From: "isanbard at gmail dot com" <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: Fri, 22 Jul 2022 22:33:55 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101836

Bill Wendling <isanbard at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |isanbard at gmail dot com

--- Comment #40 from Bill Wendling <isanbard at gmail dot com> ---
(In reply to James Y Knight from comment #36)
> (In reply to Kees Cook from comment #34)
> > > Great. Adding that flag, and eliminating the -fstrict-flex-arrays=3D3=
 option
> > > from this proposal would be good.
> >=20
> > Hmm? No, -fstrict-flex-arrays=3D3 is still needed (because it changes c=
ompiler
> > _behavior_, e.g. for proper FORTIFY coverage or trailing arrays, etc).
>=20
> There is no purpose served by writing a struct member `int x[0];` other t=
han
> to create a FAM. Zero-length arrays are not permitted by the C standard, =
but
> are a GCC compiler extension explicitly for the purpose of creating a FAM.
> This is entirely unlike `int x[1];` or `int x[10];` which of course have a
> primary meaning as a concrete array size...
>=20
> If the linux kernel doesn't want to allow `int x[0];` FAMs, then prohibit
> them entirely using -Werror=3Dzero-length-array (once it's implemented).

[Kees, correct me if I'm wrong.]

I don't think this satisfies what Kees initially asked for. The GCC extensi=
on
that a trailing `[0]' array in a structure is causing FORTIFY to fail. It w=
ould
be great to remove them all, but that's more-or-less a separate issue from
making FORTIFY work in all instances. (From what I understand, removing the
trailing `[0]' from Linux is an ongoing project.)

The question then is if `-fstrict-flex-arrays=3D3' is used, what does a `[0=
]' at
the end of a struct represent (assuming GCC no longer treats it as an FAM)?=