From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from outbound-ss-761.bluehost.com (outbound-ss-761.bluehost.com [74.220.211.250]) by sourceware.org (Postfix) with ESMTPS id C30DD3854171 for ; Fri, 21 Oct 2022 18:02:58 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org C30DD3854171 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=tromey.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=tromey.com Received: from cmgw14.mail.unifiedlayer.com (unknown [10.0.90.129]) by progateway8.mail.pro1.eigbox.com (Postfix) with ESMTP id 437E510047D65 for ; Fri, 21 Oct 2022 18:02:46 +0000 (UTC) Received: from box5379.bluehost.com ([162.241.216.53]) by cmsmtp with ESMTP id lwM1o2wdyoMaxlwM1o7SC3; Fri, 21 Oct 2022 18:02:46 +0000 X-Authority-Reason: nr=8 X-Authority-Analysis: v=2.4 cv=X4CXlEfe c=1 sm=1 tr=0 ts=6352dec6 a=ApxJNpeYhEAb1aAlGBBbmA==:117 a=ApxJNpeYhEAb1aAlGBBbmA==:17 a=dLZJa+xiwSxG16/P+YVxDGlgEgI=:19 a=Qawa6l4ZSaYA:10:nop_rcvd_month_year a=Qbun_eYptAEA:10:endurance_base64_authed_username_1 a=CCpqsmhAAAAA:8 a=6npAA9dYgSkQ-lpkVFAA:9 a=ul9cdbp4aOFLsgKbc677:22 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=tromey.com; s=default; h=Content-Type:MIME-Version:Message-ID:In-Reply-To:Date:References :Subject:Cc:To:From:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=QxYgymQQoAAHsi1FAxjGqn/i4hjR1MynsNFjmz6Kksk=; b=e3EDTOJdxyWvauoignBTeRDZuu JnSDiu1+XQuBGVfv2pa1/cVNx0Ov3qPNwsVmfMXPH2nIdcWx0EZWzol561zdpOTwK/oNjNmpvvLQc bgvOvi6J7JjbQ5HWzGj12sziN; Received: from 97-122-76-186.hlrn.qwest.net ([97.122.76.186]:56748 helo=murgatroyd) by box5379.bluehost.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1olwM0-0001nn-TI; Fri, 21 Oct 2022 12:02:45 -0600 From: Tom Tromey To: Simon Marchi via Gdb-patches Cc: Tom Tromey , Simon Marchi Subject: Re: [PATCH 1/2] gdb: check for empty offsets vector in inherit_abstract_dies References: <20221021132104.1772565-1-simon.marchi@polymtl.ca> <87czalchpi.fsf@tromey.com> X-Attribution: Tom Date: Fri, 21 Oct 2022 12:02:41 -0600 In-Reply-To: (Simon Marchi via Gdb-patches's message of "Fri, 21 Oct 2022 11:46:51 -0400") Message-ID: <87k04tawce.fsf@tromey.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - box5379.bluehost.com X-AntiAbuse: Original Domain - sourceware.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - tromey.com X-BWhitelist: no X-Source-IP: 97.122.76.186 X-Source-L: No X-Exim-ID: 1olwM0-0001nn-TI X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: 97-122-76-186.hlrn.qwest.net (murgatroyd) [97.122.76.186]:56748 X-Source-Auth: tom+tromey.com X-Email-Count: 1 X-Source-Cap: ZWx5bnJvYmk7ZWx5bnJvYmk7Ym94NTM3OS5ibHVlaG9zdC5jb20= X-Local-Domain: yes X-Spam-Status: No, score=-3022.3 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, JMQ_SPF_NEUTRAL, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 21 Oct 2022 18:03:02 -0000 >>>>> "Simon" == Simon Marchi via Gdb-patches writes: >> This subsequent loop does stuff like: >> >> while (offsetp < offsets_end >> && *offsetp < origin_child_die->sect_off) >> offsetp++; >> >> which in this scenario would be comparing null pointers using "<"? Simon> Is it undefined behavior to compre two null pointers (both offsetp and Simon> offset_end would be nullptr or both wouldn't be nullptr)? At least Simon> clang's UB sanitizer doesn't panic. I don't know but it's certainly weird. >> I'm guessing this whole loop should be hoisted into the 'if'. Simon> I don't understand enough what the code does to be convinced this would Simon> be a correct change. Any real work done in the loop is conditional on checking 'offsetp', which will always be NULL in this scenario. The loop also updates origin_child_die, but that's not used after the loop completes. So while I also think the code is super obscure, it also seems correct to do this hoisting. Simon> Note that the following patch changes this to use iterators, so it makes Simon> the worry about comparing null pointers being undefined behavior go Simon> away. It becomes comparing offsets.end() with offsets.end(). Yeah. Tom