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From: "siddhesh at gcc dot gnu.org" <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 05:09:48 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101836

--- Comment #22 from Siddhesh Poyarekar <siddhesh at gcc dot gnu.org> ---
(In reply to Kees Cook from comment #21)
> How about "-fnot-flex-arrays=3DN" to mean "trailing arrays with N or more
> elements will NOT be treated like a flex array"?
>=20
> Then code with sockaddr can use "-fnot-flex-arrays=3D15", code with "[1]"
> arrays can use "-fnot-flex-arrays=3D2", code with only "[0]" arrays can u=
se
> "-fnot-flex-arrays=3D1", and "-fstrict-flex-arrays" can be an alias for
> "-fnot-flex-arrays=3D0", which Linux would use.

An arbitrary N will only make it abuse-friendly and potentially mask bugs. =
 IMO
if we choose to make multiple levels here it should only be
-fstrict-flex-arrays=3D{1,2} where 1 (the default) only allows "[]" and 2 a=
llows
"[0]", disabling all other size values.  For anything else,
-fno-strict-flex-arrays.  My opinion on the default is not strong FWIW.=