From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 7684A3858D33 for ; Tue, 28 Feb 2023 22:28:34 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 7684A3858D33 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1677623314; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding:resent-to: resent-from:resent-message-id:in-reply-to:in-reply-to: references:references; bh=OtWHCRKR+B253G/4e8pgst6eOwgGoMkw0yokcZnZ/8w=; b=EDowoLS2Gpl3/lR/iWnuqXIpFnP4yER80vtvfNtpnFnjfEEvKzGZHDmUy0zGa8JRMBnKmT qtUEvXb53+d2Nk8npqISoTjnFPgbTz+SPdt06pmnWjhFVjOMwqD0KNaJK9JDdv+tGccTCb dLCrG9LEj1cNy0QQBprOR7zLd0QP/CI= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-231-fVRkYLZ_PSW8ydtcErP2QQ-1; Tue, 28 Feb 2023 17:28:32 -0500 X-MC-Unique: fVRkYLZ_PSW8ydtcErP2QQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 063C8101157D; Tue, 28 Feb 2023 22:28:32 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.192.16]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 82D13422A9; Tue, 28 Feb 2023 22:28:31 +0000 (UTC) Received: from tucnak.zalov.cz (localhost [127.0.0.1]) by tucnak.zalov.cz (8.17.1/8.17.1) with ESMTPS id 31SMSSJo3510873 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Tue, 28 Feb 2023 23:28:29 +0100 Received: (from jakub@localhost) by tucnak.zalov.cz (8.17.1/8.17.1/Submit) id 31SMSSjW3510872; Tue, 28 Feb 2023 23:28:28 +0100 Resent-From: Jakub Jelinek Resent-Date: Tue, 28 Feb 2023 23:28:28 +0100 Resent-Message-ID: Resent-To: Richard Biener , "gcc-patches@gcc.gnu.org" Date: Tue, 28 Feb 2023 22:59:03 +0100 From: Jakub Jelinek To: Qing Zhao Cc: Richard Biener , "gcc-patches@gcc.gnu.org" Subject: Re: [PATCH] ubsan: Honor -fstrict-flex-arrays= in -fsanitize=bounds [PR108894] Message-ID: Reply-To: Jakub Jelinek References: <50C5DFA0-F8A5-4E1A-8353-FBF3CABF3F4B@oracle.com> <9B0A086B-0C48-4038-AD6F-BD18DFBCAEF3@oracle.com> MIME-Version: 1.0 In-Reply-To: <9B0A086B-0C48-4038-AD6F-BD18DFBCAEF3@oracle.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-3.3 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On Tue, Feb 28, 2023 at 07:19:40PM +0000, Qing Zhao wrote: > Understood. > So, your patch fixed this bug, and then [0] arrays are instrumented by default with this patch. > > > Well, it would complain about > > struct S { int a; int b[0]; int c; } s; > > ... &s.b[1] ... > > for C++, but not for C. > > A little confused here: [0] arrays were instrumented by default for C++ if it’s not a trailing array, but not for C? Given say struct S { int a; int b[0]; int c; } s; int main () { int *volatile p = &s.b[0]; p = &s.b[1]; int volatile q = s.b[0]; } both -fsanitize=bounds and -fsanitize=bounds-strict behaved the same way, in C nothing was reported, in C++ the p = &s.b[1]; statement. The reasons for s.b[0] not being reported in C++ was that for !ignore_off_by_one, bounds was ~(size_t)0, and so index > ~(size_t)0 is always false. While with the committed patch it is index >= (~(size_t)0)+1 and so always true. And in C additionally, we punted early because TYPE_MAX_VALUE (domain) was NULL. Jakub