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 X-Spam-Level: X-Spam-Status: No, score=-0.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2308AC43331 for ; Tue, 31 Mar 2020 14:44:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DBC5920784 for ; Tue, 31 Mar 2020 14:44:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kdab.com header.i=@kdab.com header.b="HoURdjF7" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730286AbgCaOo3 (ORCPT ); Tue, 31 Mar 2020 10:44:29 -0400 Received: from mail.kdab.com ([176.9.126.58]:9271 "EHLO mail.kdab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726595AbgCaOo3 (ORCPT ); Tue, 31 Mar 2020 10:44:29 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kdab.com; h= content-type:content-type:mime-version:references:in-reply-to :organization:message-id:date:date:subject:subject:from:from; s= dkim; t=1585665862; x=1586529863; bh=RBuxnHHB8dHz+9ksDb4Ran1j1C0 aboaDPX1FUsAiy90=; b=HoURdjF7kPofpE0imhQKKA1uRxm7a/v1YbqA6HYmL7l w15412Ez3xDnnZVt67g4dUCpzeKq8y0mHwNP1FrBDnl1tNsuNxmK6OtLK2CIHgm5 Q6UukNlcNFBMDtYjzoZJ7Cw8o4VGPmJKRtSd8npfiCxeUYCBDgQF1sRyyBCjzLUA = X-Virus-Scanned: amavisd-new at kdab.com From: Milian Wolff To: Jiri Olsa , ahmadkhorrami Cc: Steven Rostedt , Arnaldo Carvalho de Melo , Linux-trace Users , Peter Zijlstra , linux-trace-users-owner@vger.kernel.org, Jin Yao , Namhyung Kim , Andi Kleen Subject: Re: Wrong Perf Backtraces Date: Tue, 31 Mar 2020 16:44:18 +0200 Message-ID: <8573002.CDJkKcVGEf@agathebauer> Organization: KDAB In-Reply-To: <08bf52eda6e699ee6b3070c75eac9123@ut.ac.ir> References: <821540886fc57d7749edee585a50602f@ut.ac.ir> <20200331132052.GD2518490@krava> <08bf52eda6e699ee6b3070c75eac9123@ut.ac.ir> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart2976818.5fSG56mABF"; micalg="sha256"; protocol="application/pkcs7-signature" Sender: linux-trace-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-trace-users@vger.kernel.org --nextPart2976818.5fSG56mABF Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="iso-8859-1" On Dienstag, 31. M=E4rz 2020 15:39:18 CEST ahmadkhorrami wrote: > But the addresses do not match. Do you confirm this as a bug in > libdwarf,...? >=20 > So I will ignore addresses without a matching symbol. But they do not > seem reliable! >=20 > Could you tell me the name of the library that generates the raw > addresses, so that I can try to debug it? This is a platform specific question. There are multiple ways to unwind a=20 stack. If you are on x86 then by default the .eh_frame section is available= =20 which holds the information necessary for unwinding. It doesn't depend on=20 debug symbols, that's only used for symbolization and inline-frame resoluti= on=20 as Jiri indicated. That said, in the context of perf, there are multiple scenarios that can le= ad=20 to broken unwinding: a) perf record --call-graph dwarf: unwinding can overflow the stack copy=20 associated with every sample, so the upper end of the stack will be broken b) perf record --call-graph $any: when you are sampling on a precise event,= =20 such as cycles:P which is the default afaik, then on Intel with PEBS e.g. t= he=20 stack copy may be "wrong". See e.g. https://lkml.org/lkml/2018/11/6/257 and= =20 the overall thread. This is not solved yet afaik and after my initial attem= pt=20 at workarounding this issue I stopped looking into it and instead opted for= =20 explicitly sampling on the non-precise events when I record call graphs... = You=20 could try that too: do you see the issue when you run e.g.: `perf record --call-graph dwarf -e cycles` This should take the non-precise version for sampling but then at least the= =20 call stacks are correct. I.e. you trade the accuracy of the instruction=20 pointer to which a sample points with reduced call stack breakage. c) bugs :) =2D-=20 Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer KDAB (Deutschland) GmbH, a KDAB Group company Tel: +49-30-521325470 KDAB - The Qt, C++ and OpenGL Experts --nextPart2976818.5fSG56mABF Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCDEIw ggXmMIIDzqADAgECAhBqm+E4O/8ra58B1dm4p1JWMA0GCSqGSIb3DQEBDAUAMIGFMQswCQYDVQQG EwJHQjEbMBkGA1UECBMSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYDVQQHEwdTYWxmb3JkMRowGAYD VQQKExFDT01PRE8gQ0EgTGltaXRlZDErMCkGA1UEAxMiQ09NT0RPIFJTQSBDZXJ0aWZpY2F0aW9u IEF1dGhvcml0eTAeFw0xMzAxMTAwMDAwMDBaFw0yODAxMDkyMzU5NTlaMIGXMQswCQYDVQQGEwJH QjEbMBkGA1UECBMSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYDVQQHEwdTYWxmb3JkMRowGAYDVQQK 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