From mboxrd@z Thu Jan 1 00:00:00 1970 From: Milian Wolff Subject: Re: PEBS level 2/3 breaks dwarf unwinding! [WAS: Re: Broken dwarf unwinding - wrong stack pointer register value?] Date: Thu, 15 Nov 2018 10:10:13 +0100 Message-ID: <6310843.N4ooJGWzKY@agathebauer> References: <2335309.gnWok9HYb4@agathebauer> <31474933.dcNFsqGoRn@agathebauer> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart1716263.NZ1ybqlvbz"; micalg="sha256"; protocol="application/pkcs7-signature" Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Travis Downs Cc: ak@linux.intel.com, jolsa@redhat.com, linux-kernel@vger.kernel.org, jolsa@kernel.org, namhyung@kernel.org, linux-perf-users@vger.kernel.org, acme@kernel.org List-Id: linux-perf-users.vger.kernel.org --nextPart1716263.NZ1ybqlvbz Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" On Donnerstag, 15. November 2018 03:05:32 CET Travis Downs wrote: > On Wed, Nov 14, 2018 at 8:20 AM Milian Wolff wrote: > > 3) I suggest we always keep the first frame and sample IP from the user > > regs, i.e. the accurate PEBS/IBS IP. Then we add the following frames > > from unwinding the ustack with the iregs. > > Does this mean that the displayed unwind will sometimes be > "impossible" to have actually be generated from a consistent execution > of the user program? Yes, that is exactly what I'm saying. > For example, the top frame (from PEBS) and second frame (from iregs) > may be inconsistent in that the latter function never calls the first. > At this point it would be good to have an indication at the top frame > is from a different source than the rest of the frames, lest the user > pull is hair out trying to determine how function X seems to call > function Y despite that not being the case in the source. I agree. I personally like your suggested approach - only add an indication when the IP differs so much that it points to a different function. What do others say to this? Cheers -- 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 --nextPart1716263.NZ1ybqlvbz 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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