From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753320AbaIDOhx (ORCPT ); Thu, 4 Sep 2014 10:37:53 -0400 Received: from mail-oa0-f49.google.com ([209.85.219.49]:51676 "EHLO mail-oa0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751004AbaIDOhw (ORCPT ); Thu, 4 Sep 2014 10:37:52 -0400 MIME-Version: 1.0 In-Reply-To: <1409035119-24357-1-git-send-email-namhyung@kernel.org> References: <1409035119-24357-1-git-send-email-namhyung@kernel.org> Date: Thu, 4 Sep 2014 16:37:51 +0200 Message-ID: Subject: Re: [PATCH] perf tools: Fix build-id matching on vmlinux From: Stephane Eranian To: Namhyung Kim Cc: Arnaldo Carvalho de Melo , Peter Zijlstra , Ingo Molnar , Paul Mackerras , Namhyung Kim , LKML , Jiri Olsa , David Ahern , Adrian Hunter , Andi Kleen , stable@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 26, 2014 at 8:38 AM, Namhyung Kim wrote: > > There's a problem on finding correct kernel symbols when perf report > runs on a different kernel. Although a part of the problem was solved > by the prior commit 0a7e6d1b6844 ("perf tools: Check recorded kernel > version when finding vmlinux"), there's a remaining problem still. > > When perf records samples, it synthesizes the kernel map using > machine__mmap_name() and ref_reloc_sym like "[kernel.kallsyms]_text". > You can easily see it using 'perf report -D' command. > > After finishing record, it goes through the recorded events to find > maps/dsos actually used. And then record build-id info of them. > > During this process, it needs to load symbols in a dso and it'd call > dso__load_vmlinux() since the default value of the symbol_conf.try_ > vmlinux_path is true. However it changes dso->long_name to a real > path of the vmlinux file (e.g. /lib/modules/3.16.0-rc2+/build/vmlinux) > if one is running on a custom kernel. > > It resulted in that perf report reads the build-id of the vmlinux, but > cannot use it since it only knows about the [kernel.kallsyms] map. It > then falls back to possible vmlinux paths by using the recorded kernel > version (in case of a recent version) or a running kernel silently > (which might break the result). I think it's worth going to the > stable tree. > > I can think of a couple of ways to fix it. In this patch, I changed > to use the name of "[kernel.kallsyms]" for the kernel build-id event > instead of not trying vmlinux paths. This way we can provide maximum > info (like annotation) with minimum change IMHO. > > Before: > > $ perf record -a usleep 1 > > $ perf buildid-list > 00d5ff078efe1d30b8492854f259215fd877ce30 /lib/modules/3.16.0-rc2+/build/vmlinux > 78186287bba77069a056a5ccbeb14b7fd2ca3a4b /usr/lib64/libc-2.17.so > 4eadca6cb82e0a85edb87c15b5e3980742514501 /usr/lib64/ld-2.17.so > 1e272ca30081e81ef41935a630eb2f4c636798b4 /usr/lib64/dri/swrast_dri.so > > $ perf buildid-list -H > 0000000000000000000000000000000000000000 [kernel.kallsyms] > 78186287bba77069a056a5ccbeb14b7fd2ca3a4b /usr/lib64/libc-2.17.so > 4eadca6cb82e0a85edb87c15b5e3980742514501 /usr/lib64/ld-2.17.so > 1e272ca30081e81ef41935a630eb2f4c636798b4 /usr/lib64/dri/swrast_dri.so > 0000000000000000000000000000000000000000 /tmp/perf-2523.map > There is something I don't understand in your example above. The -H option shows only DSO with samples. So why do you get the buildid without -H and you get no buildid with -H? In other words, I don't connect the dots between what -H does on the buildid change for the kernel. Looks like you have the buildid in the perf.data file. > > After: > > $ perf record -a usleep 1 > > $ perf buildid-list > 00d5ff078efe1d30b8492854f259215fd877ce30 [kernel.kallsyms] > 78186287bba77069a056a5ccbeb14b7fd2ca3a4b /usr/lib64/libc-2.17.so > 4eadca6cb82e0a85edb87c15b5e3980742514501 /usr/lib64/ld-2.17.so > 1e272ca30081e81ef41935a630eb2f4c636798b4 /usr/lib64/dri/swrast_dri.so > > $ perf buildid-list -H > 00d5ff078efe1d30b8492854f259215fd877ce30 [kernel.kallsyms] > 78186287bba77069a056a5ccbeb14b7fd2ca3a4b /usr/lib64/libc-2.17.so > 4eadca6cb82e0a85edb87c15b5e3980742514501 /usr/lib64/ld-2.17.so > 1e272ca30081e81ef41935a630eb2f4c636798b4 /usr/lib64/dri/swrast_dri.so > 0000000000000000000000000000000000000000 /tmp/perf-2523.map > > Cc: stable@vger.kernel.org > Signed-off-by: Namhyung Kim > --- > tools/perf/util/header.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c > index 158c787ce0c4..5c4093dee467 100644 > --- a/tools/perf/util/header.c > +++ b/tools/perf/util/header.c > @@ -263,6 +263,9 @@ static int __dsos__write_buildid_table(struct list_head *head, > machine__mmap_name(machine, nm, sizeof(nm)); > name = nm; > name_len = strlen(nm) + 1; > + } else if (dso__is_vmlinux(pos)) { > + name = pos->name; > + name_len = strlen(pos->name) + 1; > } else { > name = pos->long_name; > name_len = pos->long_name_len + 1; > -- > 2.0.0 >