From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 81526 invoked by alias); 28 Aug 2018 18:39:56 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 81509 invoked by uid 89); 28 Aug 2018 18:39:55 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=AWL,BAYES_00,KAM_LAZY_DOMAIN_SECURITY,SPF_HELO_PASS autolearn=no version=3.3.2 spammy= X-HELO: mx1.redhat.com Received: from mx3-rdu2.redhat.com (HELO mx1.redhat.com) (66.187.233.73) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Tue, 28 Aug 2018 18:39:54 +0000 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 46D72807689C; Tue, 28 Aug 2018 18:39:53 +0000 (UTC) Received: from [127.0.0.1] (ovpn04.gateway.prod.ext.ams2.redhat.com [10.39.146.4]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4929A2166B41; Tue, 28 Aug 2018 18:39:52 +0000 (UTC) Subject: Re: [PATCH 3/9] Avoid undefined behavior in extract_integer To: Tom Tromey , gdb-patches@sourceware.org References: <20180827145620.11055-1-tom@tromey.com> <20180827145620.11055-4-tom@tromey.com> From: Pedro Alves Message-ID: <9e249cb4-8c92-30d4-b887-b3de97916eb4@redhat.com> Date: Tue, 28 Aug 2018 18:39:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20180827145620.11055-4-tom@tromey.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-SW-Source: 2018-08/txt/msg00705.txt.bz2 On 08/27/2018 03:56 PM, Tom Tromey wrote: > -fsanitize=undefined showed that extract_integer could left-shift a > negative value, which is undefined. This patch fixes the problem by > doing all the work in an unsigned type, and then using a static_cast > at the end of the function. This relies on implementation-defined > behavior, but I tend to think we are on safe ground there. (Also, if > need be, violations of this could probably be detected, either by > configure or by a static_assert.) > > ChangeLog > 2018-08-27 Tom Tromey > > * findvar.c (extract_integer): Do work in an unsigned type and > cast at the end. LGTM. I suspect we assume two's complement in a good number of places, and I don't think it's worth it to bother with anything else. There's even been discussion in the C++ committee about baking the the assumption into the language. Is the cast really necessary, though? What error do you get? Thanks, Pedro Alves