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From: "qing.zhao at oracle 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: Tue, 14 Jun 2022 16:02:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101836

--- Comment #27 from Qing Zhao <qing.zhao at oracle dot com> ---
> On Jun 14, 2022, at 11:39 AM, siddhesh at gcc dot gnu.org <gcc-bugzilla@g=
cc.gnu.org> wrote:
>=20
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101836
>=20
> --- Comment #26 from Siddhesh Poyarekar <siddhesh at gcc dot gnu.org> ---
> (In reply to qinzhao from comment #25)
>> So, based on all the discussion so far, how about the following:
>>=20
>> ** add the following gcc option:
>>=20
>> -fstrict-flex-arrays=3D[0|1|2|3]
>>=20
>> when -fstrict-flex-arrays=3D0:
>> treat all trailing arrays as flexible arrays. the default behavior;
>=20
> Wouldn't this be -fno-strict-flex-arrays, i.e. the current behaviour?

Yes, it=E2=80=99s the same.  =3D0 is aliased with -fno-strict-flex-arrays.

The point is, the larger the value of LEVEL, the stricter with treating the
flexing array.

i.e, 0 is the least strict, and 3 is the strictest mode.

But we can delete the level 0 if not necessary.
>=20
>> when -fstrict-flex-arrays=3D1:
>> Only treating [], [0], and [1] as flexible array;
>>=20
>> when -fstrict-flex-arrays=3D2:
>> Only treating [] and [0] as flexible array;
>>=20
>> when -fstrict-flex-arrays=3D3:
>> Only treating [] as flexible array; The strictest level.
>=20
> If yes, then you end up having:
>=20
> -fstrict-flex-arrays=3D[1|2|3]
>=20
> with, I suppose, 1 as the default based on Jakub's comment about maximum
> compatibility support.
Yes.  And 3 is the one Kees requested for kernel usage.=