From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 49D4EC433EF for ; Wed, 6 Apr 2022 13:56:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234127AbiDFN52 (ORCPT ); Wed, 6 Apr 2022 09:57:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47826 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233934AbiDFN5M (ORCPT ); Wed, 6 Apr 2022 09:57:12 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 7AC6A35770F; Wed, 6 Apr 2022 02:08:45 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 449E323A; Wed, 6 Apr 2022 02:08:45 -0700 (PDT) Received: from [10.57.10.15] (unknown [10.57.10.15]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 41F193F718; Wed, 6 Apr 2022 02:08:44 -0700 (PDT) Message-ID: <2dc4266f-02b1-0937-a884-dfa037cc7ffd@arm.com> Date: Wed, 6 Apr 2022 10:08:42 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: perf tool: About "perf arm64: Inject missing frames when using 'perf record --call-graph=fp'" Content-Language: en-US To: John Garry , alexandre.truong@arm.com Cc: linux-perf-users@vger.kernel.org, "jolsa@kernel.org >> Jiri Olsa" , german.gomez@arm.com, Linux Kernel Mailing List , Arnaldo Carvalho de Melo References: <5f1d8b3f-0afa-2724-4ff1-f061939c68c5@huawei.com> From: James Clark In-Reply-To: <5f1d8b3f-0afa-2724-4ff1-f061939c68c5@huawei.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/04/2022 15:04, John Garry wrote: > Hi Alexandre, > > I notice that with commit b9f6fbb3b2c2 ("perf arm64: Inject missing frames when using 'perf record --call-graph=fp'") that I get messages spewing the console when running perf record+report, as below: > > john@ubuntu:~/linux$sudo tools/perf/perf record -ag fio null12.fio > john@ubuntu:~/linux$sudo tools/perf/perf report > report > unwind: can't read reg 29 > unwind: can't read reg 29 > unwind: can't read reg 29 > unwind: can't read reg 29 > ... > > Do you know the possible cause? I haven't checked... Hi John, I'm going to look into this today. I expect the cause is because we only record the link register for this change and then do a best effort unwind to see if we can get the return address just from that. So I don't think this is a major issue, probably the outcome will be that I mask any of these errors just for this call to libunwind that we added. The other main call to libunwind should still print these errors. One thing that is interesting is why we didn't see this when we were testing the patch before, and we've also found it a little bit difficult to reproduce here. So there might be more to it than just masking the error, but I'm not sure yet. Either way, I don't expect that any unwinding is broken, just that it's printing an annoying message. James > > Thanks, > john