From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 87186394D891; Mon, 8 Mar 2021 10:14:01 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 87186394D891 From: "jakub at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug sanitizer/99418] sanitizer checks for accessing multidimentional VLA-array Date: Mon, 08 Mar 2021 10:14:00 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: sanitizer X-Bugzilla-Version: 10.2.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: jakub at gcc dot gnu.org X-Bugzilla-Status: WAITING 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, 08 Mar 2021 10:14:01 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99418 --- Comment #4 from Jakub Jelinek --- Asan can't by design detect neither #c0 nor #c1, only ubsan can. The reason why ubsan has that off by one stuff is that in C/C++, &mas[n - 1][m] is not undefined behavior, only mas[n - 1][m] is. And with classes, it actually means calling some method with &mas[n - 1][m] argument. For #c1, the big question is what exactly is UB in C++, whether already bin= ding a reference to the object after the end of the array or only actually acces= sing that reference. If the former, ubsan could treat REFERENCE_TYPE differentl= y, if the latter, then I'm afraid it can't do that, and ubsan by design has to= be done early before all the optimizations change the IL so much that it is completely lost what were the user errors in it. For the method calls, there really isn't a reference in the IL either, this argument is a pointer, but .UBSAN_BOUNDS calls are added in the FE and so perhaps it could know it is a method call and treat it as a reference. So, something can be done but we need answers on where the UB in C++ exactly happens.=