From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 65C6A385800C; Mon, 9 Aug 2021 18:07:19 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 65C6A385800C From: "kees at outflux dot net" To: gcc-bugs@gcc.gnu.org Subject: [Bug c/101832] __builtin_object_size(P->M, 1) where M ends with a flex-array behaves like sizeof() Date: Mon, 09 Aug 2021 18:07:19 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: c X-Bugzilla-Version: unknown X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: kees at outflux dot net X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Resolution: X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: gcc-bugs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-bugs mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 09 Aug 2021 18:07:19 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101832 --- Comment #5 from Kees Cook --- Perhaps the best question to ask is "given an arbitrary argument, how can c= ode detect the remaining bytes of a member, including if the member contains a flexible array?" Because right now, this does not work: #define __bytes_until_end_of_member(p) __builtin_object_size(p, 1) since this gives different answers, depending on the level of dereference: __bytes_until_end_of_member(wrap) =3D=3D -1 __bytes_until_end_of_member(&wrap->msg) =3D=3D 16 __bytes_until_end_of_member(&wrap->msg.nlmsg_content) =3D=3D -1 How can "wrap->msg" be 16 if "wrap" and "warp->msg.nlmsg_content" are -1?=