From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 98803 invoked by alias); 22 Jan 2016 18:30:28 -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 98759 invoked by uid 89); 22 Jan 2016 18:30:27 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=BAYES_00,RP_MATCHES_RCVD,SPF_HELO_PASS autolearn=ham version=3.3.2 spammy=vCont, vcont 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, 22 Jan 2016 18:30:26 +0000 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) by mx1.redhat.com (Postfix) with ESMTPS id 75010C07584A; Fri, 22 Jan 2016 18:30:23 +0000 (UTC) Received: from [127.0.0.1] (ovpn01.gateway.prod.ext.phx2.redhat.com [10.5.9.1]) by int-mx11.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u0MIUMSr012310; Fri, 22 Jan 2016 13:30:22 -0500 Message-ID: <56A2753E.4030208@redhat.com> Date: Fri, 22 Jan 2016 18:30:00 -0000 From: Pedro Alves User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Yao Qi CC: gdb-patches@sourceware.org Subject: Re: [PATCH] Fix fail in gdb.base/interrupt-noterm.exp References: <1453480183-5131-1-git-send-email-yao.qi@linaro.org> <56A25D13.2080608@redhat.com> <86twm5r0yp.fsf@gmail.com> <56A26849.9070206@redhat.com> In-Reply-To: <56A26849.9070206@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-SW-Source: 2016-01/txt/msg00581.txt.bz2 On 01/22/2016 05:35 PM, Pedro Alves wrote: > On 01/22/2016 05:14 PM, Yao Qi wrote: >> Pedro Alves writes: >> >>> Can you expand the rationale some more? >>> >>> E.g., why is this not a gdbserver bug? Instintively I'd say it is. >> >> The interaction between GDB and GDBserver is like this, >> >> 1. GDB sends vCont;c and doesn't wait for the stop reply because >> "continue &" is background command, >> 2. GDBserver receives vCont;c, enables the async i/o (by >> enable_async_io) and resumes the inferior. >> 3. GDB sends interrupt packet, >> >> #1 happens before #2 and #3, but the order of #2 and #3 is not >> determined. If #2 happens before #3, it is fine, otherwise, the >> GDBserver doesn't know the interrupt from GDB. > > If 1. is followed by 3., then the \\003 is always read by gdb > after the vCont;c. We call enable_async_io before reaching > mywait. Since we're in all-stop, that means we'll block > inside mywait -> waitpid, all the while \\003 is already available to > read in the socket. Since we're blocked in waitpid, we won't see > the \\003 until after the next time the program happens to stop. > > Agree? > > It still seems to me like a gdbserver bug. > > I think that after calling enable_async_io, we need to check whether > input is already pending from GDB, and if so, process it immediately -- we > know the only input coming from GDB at this point is a \\003. IOW, I think > we need to call input_interrupt after calling enable_async_io. input_interrupt > already uses select before reading, so it handles the case of there > being no input available without blocking. > > However, we need to be careful, because a SIGIO can race with calling > input_interrupt from mainline code... Might be simpler to always have the SIGIO handler installed (install it early), and change enable_async_io/disable_async_io to use sigprocmask to block/unblock the signal. That way, if input comes before the signal is unblocked, the handler is called immediately when enable_async_io is called. Thanks, Pedro Alves