From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 104342 invoked by alias); 11 Mar 2016 11:09:12 -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 104321 invoked by uid 89); 11 Mar 2016 11:09:11 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-0.9 required=5.0 tests=BAYES_00,KAM_LAZY_DOMAIN_SECURITY,RP_MATCHES_RCVD,SPF_HELO_PASS autolearn=no version=3.3.2 spammy= X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES256-GCM-SHA384 encrypted) ESMTPS; Fri, 11 Mar 2016 11:09:10 +0000 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (Postfix) with ESMTPS id DFEFC326918; Fri, 11 Mar 2016 11:09:08 +0000 (UTC) Received: from [127.0.0.1] (ovpn01.gateway.prod.ext.phx2.redhat.com [10.5.9.1]) by int-mx13.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u2BB97jJ002193; Fri, 11 Mar 2016 06:09:08 -0500 Subject: Re: [PATCH 3/8] Deliver signal in hardware single step To: Yao Qi , gdb-patches@sourceware.org References: <1457088276-1170-1-git-send-email-yao.qi@linaro.org> <1457088276-1170-4-git-send-email-yao.qi@linaro.org> <56E2A685.2080602@redhat.com> From: Pedro Alves Message-ID: <56E2A753.9060805@redhat.com> Date: Fri, 11 Mar 2016 11:09:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <56E2A685.2080602@redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-SW-Source: 2016-03/txt/msg00179.txt.bz2 On 03/11/2016 11:05 AM, Pedro Alves wrote: > On 03/04/2016 10:44 AM, Yao Qi wrote: >> GDBserver doesn't deliver signal when stepping over a breakpoint even >> hardware single step is used. When GDBserver started to step over >> (thread creation) breakpoint for mutlit-threaded debugging in 2002 [1], >> GDBserver behaves this way. >> >> This behaviour gets trouble on conditional breakpoints on branch to >> self instruction like this, >> >> 0x00000000004005b6 <+29>: jmp 0x4005b6 >> >> and I set breakpoint >> >> $(gdb) break branch-to-self.c:43 if counter > 3 >> >> and the variable counter will be set to 5 in SIGALRM signal handler. >> Since GDBserver keeps stepping over breakpoint, the SIGALRM can never >> be dequeued and delivered to the inferior, so the program can't stop. >> The test can be found in gdb.base/branch-to-self.exp. >> >> I can understand why does GDBserver queue signal for software single >> step, but I can't figure out a reason we should queue signal for >> hardware single step. With this patch applied, GDBserver forward the >> signal to inferior and the program can stop correctly. >> >> [1] PATCH: Multithreaded debugging for gdbserver >> https://sourceware.org/ml/gdb-patches/2002-06/msg00157.html >> > > Because the signal handler might recurse and call the same code > that had the breakpoint (or some other removed breakpoint), and thus > we'd miss a breakpoint hit in the signal handler. Hmm, no, I got confused. We'll stop in first instruction in the signal handler. Let me go back and take a fresh look. Thanks, Pedro Alves