From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 115010 invoked by alias); 26 Jun 2018 11:01:22 -0000 Mailing-List: contact gnu-gabi-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Post: List-Help: List-Subscribe: Sender: gnu-gabi-owner@sourceware.org Received: (qmail 114769 invoked by uid 89); 26 Jun 2018 11:01:10 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Checked: by ClamAV 0.99.4 on sourceware.org X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.3 required=5.0 tests=AWL,BAYES_00,KAM_LAZY_DOMAIN_SECURITY,SPF_HELO_PASS autolearn=no version=3.3.2 spammy=H*i:sk:7ada549, H*f:sk:7ada549, HContent-Transfer-Encoding:8bit X-Spam-Status: No, score=-1.3 required=5.0 tests=AWL,BAYES_00,KAM_LAZY_DOMAIN_SECURITY,SPF_HELO_PASS autolearn=no version=3.3.2 X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on sourceware.org X-Spam-Level: X-Spam-User: qpsmtpd, 3 recipients 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, 26 Jun 2018 11:01:09 +0000 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1A8FC87AC7; Tue, 26 Jun 2018 11:01:08 +0000 (UTC) Received: from oldenburg.str.redhat.com (ovpn-116-177.ams2.redhat.com [10.36.116.177]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2C799111762E; Tue, 26 Jun 2018 11:01:07 +0000 (UTC) Subject: Re: Invalid program counters and unwinding To: Nathan Sidwell , GCC , GNU C Library , Binutils , gnu-gabi@sourceware.org References: <7ada5491-f3f4-e048-dfec-6e51cd937163@acm.org> From: Florian Weimer Message-ID: <0c58f1bb-220c-d03d-7375-6066fb7d53e6@redhat.com> Date: Mon, 01 Jan 2018 00:00:00 -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: <7ada5491-f3f4-e048-dfec-6e51cd937163@acm.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Tue, 26 Jun 2018 11:01:08 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Tue, 26 Jun 2018 11:01:08 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'fweimer@redhat.com' RCPT:'' X-IsSubscribed: yes X-SW-Source: 2018-q2/txt/msg00016.txt.bz2 On 06/26/2018 12:56 PM, Nathan Sidwell wrote: > On 06/26/2018 05:26 AM, Florian Weimer wrote: > >> So it looks to me that the caller of _Unwind_Find_FDE needs to ensure >> that the PC is a valid element of the call stack.  Is this a correct >> assumption? > > I thought this was an (implicit?) requirement. You're unwinding a stack > to deliver an exception up it.  Are there use cases where that is not > the case? We have something approaching this scenario. pthread_cancel in glibc unwinds the stack using DWARF information until encounters a frame without unwind information, when it switches to longjmp to get past that obstacle. However, at the point of transition from a valid DWARF frame into the wilderness (without unwind data), we should still have accurate information on the caller's PC, so _Unwind_Find_FDE will reliably fail to find any unwind data for it. It's not a random pointer somewhere else, so I think even the pthread_cancel case is fully supported. Thanks, Florian