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Message-ID: <87a96f9bci.fsf@sejong.aot.lge.com> Date: Fri, 05 Sep 2014 09:09:49 +0900 From: Namhyung Kim <namhyung@...nel.org> To: Arnaldo Carvalho de Melo <acme@...nel.org> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>, Ingo Molnar <mingo@...nel.org>, Paul Mackerras <paulus@...ba.org>, Namhyung Kim <namhyung.kim@....com>, LKML <linux-kernel@...r.kernel.org>, Jiri Olsa <jolsa@...hat.com>, David Ahern <dsahern@...il.com>, Adrian Hunter <adrian.hunter@...el.com>, Andi Kleen <andi@...stfloor.org>, Stephane Eranian <eranian@...gle.com>, stable@...r.kernel.org Subject: Re: [PATCH] perf tools: Fix build-id matching on vmlinux Hi Arnaldo, On Thu, 4 Sep 2014 11:18:45 -0300, Arnaldo Carvalho de Melo wrote: > Em Tue, Aug 26, 2014 at 03:38:39PM +0900, Namhyung Kim escreveu: >> 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 >> >> After: >> >> $ perf record -a usleep 1 >> >> $ perf buildid-list >> 00d5ff078efe1d30b8492854f259215fd877ce30 [kernel.kallsyms] > > We are losing information, namely the pathname for the kernel used, that > may be useful in analysis. Right. That's a problem. > > Why not make sure that if there is a build-id in the perf.data header, > then we completely refusing anything that doesn't match the build-id? > I.e. the name is irrelevant for this purpose, the contents, as keyed by > the build-id, is what matters. The perf report rebuilds machine states from the event records only. In this case, the kernel map was recorded in the name of [kernel.kallsyms] so it couldn't find the build-id from the table. Thanks, Namhyung > > - Arnaldo > >> 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@...r.kernel.org >> Signed-off-by: Namhyung Kim <namhyung@...nel.org> >> --- >> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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