From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 90727 invoked by alias); 1 Jul 2016 17:01:21 -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 90700 invoked by uid 89); 1 Jul 2016 17:01:19 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-3.2 required=5.0 tests=BAYES_00,RP_MATCHES_RCVD,SPF_HELO_PASS autolearn=ham version=3.3.2 spammy=Hx-languages-length:1837, H*M:9209, queued 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, 01 Jul 2016 17:01:17 +0000 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 7DC707F6B6; Fri, 1 Jul 2016 17:01:16 +0000 (UTC) Received: from [127.0.0.1] (ovpn01.gateway.prod.ext.ams2.redhat.com [10.39.146.11]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u61H1F9v020854; Fri, 1 Jul 2016 13:01:15 -0400 Subject: Re: [PATCH 7/9] Enqueue signal even when resuming threads To: Yao Qi References: <1467295765-3457-1-git-send-email-yao.qi@linaro.org> <1467295765-3457-8-git-send-email-yao.qi@linaro.org> <4a3c91d8-85bb-31f2-7f9e-bc0fe0de0ff6@redhat.com> <4b9dce0a-023f-964c-77e4-85154d7087f2@redhat.com> Cc: "gdb-patches@sourceware.org" From: Pedro Alves Message-ID: Date: Fri, 01 Jul 2016 17:01:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: <4b9dce0a-023f-964c-77e4-85154d7087f2@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-SW-Source: 2016-07/txt/msg00017.txt.bz2 On 07/01/2016 05:55 PM, Pedro Alves wrote: > On 07/01/2016 05:45 PM, Yao Qi wrote: > >> You meant "after resuming it" rather than "before resuming it", right? We have >> two pending signals, so we resume the lwp and deliver the first signal. After >> resuming, we need to immediately deliver the second signal, so we call >> send_sigstop. > > No, I really meant "before resuming it". We'd queue a SIGSTOP > in the kernel, and then resume the thread with > PTRACE_CONTINUE/STEP + signal. The idea being that the thread would > continue out of the signal delivery path in the kernel side with > the signal we resume it with, so if there's a signal handler, > it's what the kernel makes the thread execute as soon as it reaches > userspace. But given we had _also_ queued a SIGSTOP, the thread would > immediately report the SIGSTOP before it had a chance of executing the > first instruction of the handler. IOW, it'd report the SIGSTOP in > the first instruction of the handler, or where it was already > stopped before, if the signal signal passed to PTRACE_CONTINUE > is SIG_IGN. Eh, actually, if this works, looks like I just come up with a way to step into a signal handler on software single-step targets. Thanks, Pedro Alves > > Seeing the thread stop for a SIGSTOP that gdbserver had itself > sent, gdbserver would immediately re-resume the thread, this time, > with the other pending signal. This latter part probably already > works without any change. See tail end of linux_low_filter_event, > where we have: > > if (WIFSTOPPED (wstat) && WSTOPSIG (wstat) == SIGSTOP > && child->stop_expected) > { > if (debug_threads) > debug_printf ("Expected stop.\n"); > child->stop_expected = 0; > >> IIUC, this patch is OK as-is, right? >> > > Yes. > > Thanks, > Pedro Alves >