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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,PLING_QUERY, SPF_PASS autolearn=ham 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 4B4DCC0044C for ; Wed, 7 Nov 2018 22:41:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EBF4F20862 for ; Wed, 7 Nov 2018 22:41:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kdab.com header.i=@kdab.com header.b="VULOifAt" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EBF4F20862 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=kdab.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728201AbeKHIOL (ORCPT ); Thu, 8 Nov 2018 03:14:11 -0500 Received: from mail.kdab.com ([176.9.126.58]:63758 "EHLO mail.kdab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727760AbeKHIOL (ORCPT ); Thu, 8 Nov 2018 03:14:11 -0500 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=1541630498; x=1542494499; bh=Bp5/0rEBHLYpNdxrT1eHAGx9dQn 0Jua5dTCJ5SDl0E0=; b=VULOifAtHa7HBvy+t2fCtcU9Kw93LVhxLdC3Ziy53J5 peG95RIiLAwZxFhyPYcB1yA4546jfxcWlHyYr9nRs8lU8NcMEqrSLgCq3f8fzVlq SqjfmpBgm1d9OwkWIzUymZMmKdWE0MVX2Y6Zk0X0MvwBSRQQG53cNxpuS3Oyl7jo = X-Virus-Scanned: amavisd-new at kdab.com From: Milian Wolff To: Andi Kleen Cc: Jiri Olsa , linux-kernel@vger.kernel.org, Jiri Olsa , namhyung@kernel.org, linux-perf-users@vger.kernel.org, Arnaldo Carvalho Subject: Re: PEBS level 2/3 breaks dwarf unwinding! [WAS: Re: Broken dwarf unwinding - wrong stack pointer register value?] Date: Wed, 07 Nov 2018 23:41:31 +0100 Message-ID: <1584560.aXQ729uQp3@agathebauer> Organization: KDAB In-Reply-To: <20181106202411.GU6218@tassilo.jf.intel.com> References: <2335309.gnWok9HYb4@agathebauer> <2102566.fCj8pZGm78@agathebauer> <20181106202411.GU6218@tassilo.jf.intel.com> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart2604735.gXIAmy9HsQ"; micalg="sha256"; protocol="application/pkcs7-signature" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --nextPart2604735.gXIAmy9HsQ Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" On Dienstag, 6. November 2018 21:24:11 CET Andi Kleen wrote: > > Where would I look for the source to change here? So far, I only > > concentrated on the userspace side of perf in tools/perf. > > Kind of similar to > > a405bad5ad20 perf/x86: Add Haswell specific transaction flag reporting > fdfbbd07e91f perf: Add generic transaction flags > > Report the original (not overwritten) regs->ip and regs->sp Thanks a lot Andi! With your help, I have managed to find the exact issue for my scenario. Turns out, it really is "just" the instruction pointer that is wrong. I.e. originally we have IP = 0x7feda32ca68c, but with PEBS we correct that to IP = 7feda32ca688. The SP register value stays the same according to my printk output. Using the original IP value, we can unwind correctly since we point to the correct place in the .eh_frame section. The PEBS IP points to a different position in the .eh_frame section, which is "too early". That brings up some questions: - I noticed `perf record --intr-regs`, but the values recorded in the perf.data file are always the same. I.e. comparing uregs and iregs, I always see the same values printed by `perf script`. This smells like a bug to me, but so far I haven't figured out why this happens... - Independently, when I add a custom printk manually in `arch/x86/events/ intel/ds.c` at the end of `setup_pebs_sample_data`, then I'm never seeing any differences between SP in iregs/pebs/regs. Shouldn't it also be recorded via PEBS? Or is it just chance that I'm never seeing any difference in setup_pebs_sample_data between iregs->sp and regs->sp? - Generally, how do we want to handle this bug? If `--intr-regs` would actually record a different IP than stored in uregs in the perf.data file, then we could use that as a fallback for unwinding, when it fails the first time. Or should we always unwind from that IP? How do we mark the "actual" frame/IP then, if that differs? Thanks -- 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 --nextPart2604735.gXIAmy9HsQ 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 ExFDT01PRE8gQ0EgTGltaXRlZDE9MDsGA1UEAxM0Q09NT0RPIFJTQSBDbGllbnQgQXV0aGVudGlj YXRpb24gYW5kIFNlY3VyZSBFbWFpbCBDQTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEB 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