From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.polymtl.ca (smtp.polymtl.ca [132.207.4.11]) by sourceware.org (Postfix) with ESMTPS id 9BEC93858D34 for ; Thu, 26 Aug 2021 02:55:41 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 9BEC93858D34 Received: from simark.ca (simark.ca [158.69.221.121]) (authenticated bits=0) by smtp.polymtl.ca (8.14.7/8.14.7) with ESMTP id 17Q2tYrZ031802 (version=TLSv1/SSLv3 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 25 Aug 2021 22:55:38 -0400 DKIM-Filter: OpenDKIM Filter v2.11.0 smtp.polymtl.ca 17Q2tYrZ031802 Received: from [10.0.0.11] (192-222-157-6.qc.cable.ebox.net [192.222.157.6]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by simark.ca (Postfix) with ESMTPSA id F24231EDF5; Wed, 25 Aug 2021 22:55:33 -0400 (EDT) Subject: Re: [RFC][gdb/doc] Document non-stop attach behaviour To: Tom de Vries , gdb-patches@sourceware.org Cc: Pedro Alves References: <20210607132127.GA10588@delia.home> From: Simon Marchi Message-ID: <413e84be-8827-53fb-cd6f-e2ecc66a4af2@polymtl.ca> Date: Wed, 25 Aug 2021 22:55:33 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20210607132127.GA10588@delia.home> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Poly-FromMTA: (simark.ca [158.69.221.121]) at Thu, 26 Aug 2021 02:55:34 +0000 X-Spam-Status: No, score=-11.2 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, NICE_REPLY_A, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_PASS, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 26 Aug 2021 02:55:52 -0000 On 2021-06-07 9:21 a.m., Tom de Vries wrote: > Hi, > > While investigating PR27908, I got confused about what the proper behaviour > is when attaching to a multi-threaded program in non-stop mode. > > In particular, when running a script that issues an "info threads" after an > attach in non-stop mode, it can show a non-current thread as still running: > ... > $ ./a.out & pid=$!; \ > gdb -q \ > -iex "set trace-commands on" \ > -iex "set pagination off" \ > -iex "set non-stop on" \ > -p $pid \ > -ex "info threads" > [2] 10038 > +set pagination off > +set non-stop on > Attaching to process 10038 > [New LWP 10040] > main () at test.c:37 > 37 while (1) > +info threads > Id Target Id Frame > * 1 Thread 0x7f63547a8740 (LWP 10038) "a.out" main () at t.c:37 > 2 Thread 0x7f6353fd7700 (LWP 10040) "a.out" (running) > (gdb) > Thread 2 "a.out" stopped. > thread_func (p=0x0) at test.c:13 > 13 while (1) > ... > > An "info threads" after the 'Thread 2 "a.out" stopped' message will show it as > stopped though: > ... > info threads > +info threads > Id Target Id Frame > * 1 Thread 0x7f63547a8740 (LWP 10038) "a.out" main () at t.c:37 > 2 Thread 0x7f6353fd7700 (LWP 10040) "a.out" thread_func (p=0x0) at t.c:13 > (gdb) > ... > > In conclusion, it seems that attaching in non-stop mode stops all threads, > just like in all-stop mode. But the stopping of non-current threads is > visible to the user. > > Update the non-stop documentation to describe the attach behaviour in some > detail. > > Any comments? > > Thanks, > - Tom > > [gdb/doc] Document non-stop attach behaviour > > gdb/doc/ChangeLog: > > 2021-06-07 Tom de Vries > > * gdb.texinfo (Non-Stop Mode): Describe non-stop attach behaviour. > > --- > gdb/doc/gdb.texinfo | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo > index d09b86cda95..0fd7ab16150 100644 > --- a/gdb/doc/gdb.texinfo > +++ b/gdb/doc/gdb.texinfo > @@ -6957,6 +6957,13 @@ one thread while allowing others to run freely, stepping > one thread while holding all others stopped, or stepping several threads > independently and simultaneously. > > +Note that attaching in non-stop mode stops all threads, just as in > +all-stop mode. However, while in all-stop mode the attach command is > +finished only once all threads are stopped, in non-stop mode it's > +finished once the current thread is stopped. Consequently, it's > +briefly possible to observe non-current threads still running after an > +attach. > + > To enter non-stop mode, use this sequence of commands before you run > or attach to your program: > > I think your patch describes well the current behaviour of GDB, so that's good. I think the behavior could be a bit more user friendly, we could wait for all the attached program's threads to have reported their stop before showing the prompt. Same with the interrupt (with and without "-a") command, we know which threads we expect to become stopped, we could wait for them to be stopped before giving back the prompt. That would make it easier for scripts: when the attach / interrupt command returns, you know the attached / interrupted threads are stopped and can be inspected. Simon