From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 32143 invoked by alias); 3 Apr 2016 19:30:45 -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 32129 invoked by uid 89); 3 Apr 2016 19:30:44 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.9 required=5.0 tests=BAYES_00,RP_MATCHES_RCVD,SPF_HELO_PASS autolearn=ham version=3.3.2 spammy=admit, racy, async, Stop 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; Sun, 03 Apr 2016 19:30:43 +0000 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) (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 4751BC0005D8 for ; Sun, 3 Apr 2016 19:30:42 +0000 (UTC) Received: from host1.jankratochvil.net (ovpn-116-59.ams2.redhat.com [10.36.116.59]) by int-mx11.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u33JUcKA003250 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Sun, 3 Apr 2016 15:30:41 -0400 Date: Sun, 03 Apr 2016 19:30:00 -0000 From: Jan Kratochvil To: Pedro Alves Cc: gdb-patches@sourceware.org, Gary Benson Subject: Re: [patchv2 2/2] Workaround gdbserver<7.7 for setfs Message-ID: <20160403193038.GA28364@host1.jankratochvil.net> References: <20160319201842.GA16540@host1.jankratochvil.net> <56F13963.9040204@redhat.com> <20160322131604.GA24312@host1.jankratochvil.net> <56F14F1E.5010606@redhat.com> <20160323211547.GA17400@host1.jankratochvil.net> <20160324220933.GA27445@host1.jankratochvil.net> <20160324223241.GB2548@host1.jankratochvil.net> <56FBDFE7.90203@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56FBDFE7.90203@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-IsSubscribed: yes X-SW-Source: 2016-04/txt/msg00022.txt.bz2 On Wed, 30 Mar 2016 16:17:11 +0200, Pedro Alves wrote: > E.g., reading this I'm left wondering, did it always respond OK to > unknown vFile packets, or to all unknown packets? I think it was > actually the latter. Yes. > AFAICS from the commit you pointed at in v1, the "OK" was > gdbserver mistaking any unknown packet for a vStopped packet, > with vStopped being the notification ack for the "%Stop" RSP async > notification. So it could also happen that gdb sends the setfs > packet while gdbserver had a pending notification, and then > gdbserver replies back a stop reply instead of "OK"... OK, I did not realize this possible regression. > We may need to guarantee an early enough setfs is attempted. > Is that already the case? For linux targets it is because they read: /proc/29202/smaps Although you are right that does not need to be the case for non-linux targets. setfs packet seems to be implemented linux-independently. > If I'm right and gdbserver mishandled _any_ unknown packet, > then I wonder whether you fix this one, but will trip on another > when you get past initial connection and actually do any serious > debugging? That would mean gdbserver < 7.7 did not work for "any serious debugging". I have seen the regression only since "setfs" but I admit I did not do "any serious debugging". > If not, this may be sufficient. Otherwise, we may need to come up with > a different workaround, maybe based on sending an early probe packet, > like "MustReplyEmpty", to which well behaved stubs reply empty, just because > that's not a known packet to them. If a stub replies something other than > empty to that one, then maybe we should disable all other > auto-probed packets... That may force-disable too much functionality though... > > So in sum: The patch was fixing a common use case with RHEL<=7 targets. You have provided out a counterexample that it may hypothetically regress in a racy case of non-linux FSF gdbserver. Normally I would find this workaround applicable only for RHEL GDBs but now that everything needs to be upstream first the RHEL workaround needs to be implemented in FSF GDB first (where it does not belong much IMNSHO). I will therefore try to implement the "MustReplyEmpty" packet but I have no idea what effect will have your mentioned "disable all other auto-probed packets". Thanks, Jan