[PATCH] perf tools: Fix not finding kcore in buildid cache

[PATCH] perf tools: Fix not finding kcore in buildid cache

[Adrian Hunter]

The logic was not looking in the buildid cache for kcore
if the host kernel buildid did not match the recorded
kernel buildid.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
 tools/perf/util/symbol.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index ce9ce10..360eefe 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -1526,14 +1526,15 @@ static char *dso__find_kallsyms(struct dso *dso, struct map *map)
 
 	build_id__sprintf(dso->build_id, sizeof(dso->build_id), sbuild_id);
 
+	scnprintf(path, sizeof(path), "%s/[kernel.kcore]/%s", buildid_dir,
+		  sbuild_id);
+
 	/* Use /proc/kallsyms if possible */
 	if (is_host) {
 		DIR *d;
 		int fd;
 
 		/* If no cached kcore go with /proc/kallsyms */
-		scnprintf(path, sizeof(path), "%s/[kernel.kcore]/%s",
-			  buildid_dir, sbuild_id);
 		d = opendir(path);
 		if (!d)
 			goto proc_kallsyms;
@@ -1558,6 +1559,10 @@ static char *dso__find_kallsyms(struct dso *dso, struct map *map)
 		goto proc_kallsyms;
 	}
 
+	/* Find kallsyms in build-id cache with kcore */
+	if (!find_matching_kcore(map, path, sizeof(path)))
+		return strdup(path);
+
 	scnprintf(path, sizeof(path), "%s/[kernel.kallsyms]/%s",
 		  buildid_dir, sbuild_id);
 
-- 
1.7.11.7

Re: [PATCH] perf tools: Fix not finding kcore in buildid cache

[Ingo Molnar]

* Adrian Hunter <adrian.hunter@intel.com> wrote:

> The logic was not looking in the buildid cache for kcore
> if the host kernel buildid did not match the recorded
> kernel buildid.

It would be nice to also include the specific failure mode in the 
changelog: exactly how can users run into this. That will be more 
useful to most people reading these changelogs than a more abstract 
bug description.

Thanks,

	Ingo

Re: [PATCH] perf tools: Fix not finding kcore in buildid cache

[Adrian Hunter]

On 26/11/13 18:15, Ingo Molnar wrote:
> 
> * Adrian Hunter <adrian.hunter@intel.com> wrote:
> 
>> The logic was not looking in the buildid cache for kcore
>> if the host kernel buildid did not match the recorded
>> kernel buildid.
> 
> It would be nice to also include the specific failure mode in the 
> changelog: exactly how can users run into this. That will be more 
> useful to most people reading these changelogs than a more abstract 
> bug description.

The preconditions for the problem are that kcore is in the buildid
cache and that the running kernel has a different buildid e.g.

$ perf buildid-list | grep kernel.kallsyms
b18fbe769dea12513028a4287dae02efc1582c29 [kernel.kallsyms]

$ perf record -o /tmp/junk true >/dev/null 2>&1 ; perf buildid-list -i /tmp/junk | grep kernel.kallsyms
504f9fd9328c40714995ce76fe1354c6e90136ce [kernel.kallsyms]



Before the patch:


$ perf script -v >out.txt
build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
<SNIP>
Using /home/ahunter/.debug/[kernel.kallsyms]/b18fbe769dea12513028a4287dae02efc1582c29 for symbols

perf script stopped


After the patch:


$ perf script -v >out.txt
build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
<SNIP>
Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kcore for kernel object code
Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kallsyms for symbols

perf script stopped

Re: [PATCH] perf tools: Fix not finding kcore in buildid cache

[Ingo Molnar]

* Adrian Hunter <adrian.hunter@intel.com> wrote:

> On 26/11/13 18:15, Ingo Molnar wrote:
> > 
> > * Adrian Hunter <adrian.hunter@intel.com> wrote:
> > 
> >> The logic was not looking in the buildid cache for kcore
> >> if the host kernel buildid did not match the recorded
> >> kernel buildid.
> > 
> > It would be nice to also include the specific failure mode in the 
> > changelog: exactly how can users run into this. That will be more 
> > useful to most people reading these changelogs than a more abstract 
> > bug description.
> 
> The preconditions for the problem are that kcore is in the buildid
> cache and that the running kernel has a different buildid e.g.
> 
> $ perf buildid-list | grep kernel.kallsyms
> b18fbe769dea12513028a4287dae02efc1582c29 [kernel.kallsyms]
> 
> $ perf record -o /tmp/junk true >/dev/null 2>&1 ; perf buildid-list -i /tmp/junk | grep kernel.kallsyms
> 504f9fd9328c40714995ce76fe1354c6e90136ce [kernel.kallsyms]
> 
> 
> 
> Before the patch:
> 
> 
> $ perf script -v >out.txt
> build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
> <SNIP>
> Using /home/ahunter/.debug/[kernel.kallsyms]/b18fbe769dea12513028a4287dae02efc1582c29 for symbols
> 
> perf script stopped
> 
> 
> After the patch:
> 
> 
> $ perf script -v >out.txt
> build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
> <SNIP>
> Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kcore for kernel object code
> Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kallsyms for symbols
> 
> perf script stopped

So the result of the patch is that kernel symbols get 
resolved/annotated correctly, as expected from the live kcore feature, 
right?

Thanks,

	Ingo

Re: [PATCH] perf tools: Fix not finding kcore in buildid cache

[Adrian Hunter]

On 27/11/13 13:32, Ingo Molnar wrote:
> 
> * Adrian Hunter <adrian.hunter@intel.com> wrote:
> 
>> On 26/11/13 18:15, Ingo Molnar wrote:
>>>
>>> * Adrian Hunter <adrian.hunter@intel.com> wrote:
>>>
>>>> The logic was not looking in the buildid cache for kcore
>>>> if the host kernel buildid did not match the recorded
>>>> kernel buildid.
>>>
>>> It would be nice to also include the specific failure mode in the 
>>> changelog: exactly how can users run into this. That will be more 
>>> useful to most people reading these changelogs than a more abstract 
>>> bug description.
>>
>> The preconditions for the problem are that kcore is in the buildid
>> cache and that the running kernel has a different buildid e.g.
>>
>> $ perf buildid-list | grep kernel.kallsyms
>> b18fbe769dea12513028a4287dae02efc1582c29 [kernel.kallsyms]
>>
>> $ perf record -o /tmp/junk true >/dev/null 2>&1 ; perf buildid-list -i /tmp/junk | grep kernel.kallsyms
>> 504f9fd9328c40714995ce76fe1354c6e90136ce [kernel.kallsyms]
>>
>>
>>
>> Before the patch:
>>
>>
>> $ perf script -v >out.txt
>> build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
>> <SNIP>
>> Using /home/ahunter/.debug/[kernel.kallsyms]/b18fbe769dea12513028a4287dae02efc1582c29 for symbols
>>
>> perf script stopped
>>
>>
>> After the patch:
>>
>>
>> $ perf script -v >out.txt
>> build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
>> <SNIP>
>> Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kcore for kernel object code
>> Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kallsyms for symbols
>>
>> perf script stopped
> 
> So the result of the patch is that kernel symbols get 
> resolved/annotated correctly, as expected from the live kcore feature, 
> right?

Yes but this is the non-live case i.e. the kernel has changed and we are
looking at a special copy of kcore that we placed in the buildid cache
(using "perf buildid-cache -v -k /proc/kcore") when the data was recorded.

Re: [PATCH] perf tools: Fix not finding kcore in buildid cache

[Ingo Molnar]

* Adrian Hunter <adrian.hunter@intel.com> wrote:

> On 27/11/13 13:32, Ingo Molnar wrote:
> > 
> > * Adrian Hunter <adrian.hunter@intel.com> wrote:
> > 
> >> On 26/11/13 18:15, Ingo Molnar wrote:
> >>>
> >>> * Adrian Hunter <adrian.hunter@intel.com> wrote:
> >>>
> >>>> The logic was not looking in the buildid cache for kcore
> >>>> if the host kernel buildid did not match the recorded
> >>>> kernel buildid.
> >>>
> >>> It would be nice to also include the specific failure mode in the 
> >>> changelog: exactly how can users run into this. That will be more 
> >>> useful to most people reading these changelogs than a more abstract 
> >>> bug description.
> >>
> >> The preconditions for the problem are that kcore is in the buildid
> >> cache and that the running kernel has a different buildid e.g.
> >>
> >> $ perf buildid-list | grep kernel.kallsyms
> >> b18fbe769dea12513028a4287dae02efc1582c29 [kernel.kallsyms]
> >>
> >> $ perf record -o /tmp/junk true >/dev/null 2>&1 ; perf buildid-list -i /tmp/junk | grep kernel.kallsyms
> >> 504f9fd9328c40714995ce76fe1354c6e90136ce [kernel.kallsyms]
> >>
> >>
> >>
> >> Before the patch:
> >>
> >>
> >> $ perf script -v >out.txt
> >> build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
> >> <SNIP>
> >> Using /home/ahunter/.debug/[kernel.kallsyms]/b18fbe769dea12513028a4287dae02efc1582c29 for symbols
> >>
> >> perf script stopped
> >>
> >>
> >> After the patch:
> >>
> >>
> >> $ perf script -v >out.txt
> >> build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
> >> <SNIP>
> >> Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kcore for kernel object code
> >> Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kallsyms for symbols
> >>
> >> perf script stopped
> > 
> > So the result of the patch is that kernel symbols get 
> > resolved/annotated correctly, as expected from the live kcore feature, 
> > right?
> 
> Yes but this is the non-live case i.e. the kernel has changed and we are
> looking at a special copy of kcore that we placed in the buildid cache
> (using "perf buildid-cache -v -k /proc/kcore") when the data was recorded.

Okay.

Thanks,

	Ingo

Re: [PATCH] perf tools: Fix not finding kcore in buildid cache

[Arnaldo Carvalho de Melo]

Em Wed, Nov 27, 2013 at 12:52:47PM +0100, Ingo Molnar escreveu:
> 
> * Adrian Hunter <adrian.hunter@intel.com> wrote:
> 
> > On 27/11/13 13:32, Ingo Molnar wrote:
> > > 
> > > * Adrian Hunter <adrian.hunter@intel.com> wrote:
> > > 
> > >> On 26/11/13 18:15, Ingo Molnar wrote:
> > >>>
> > >>> * Adrian Hunter <adrian.hunter@intel.com> wrote:
> > >>>
> > >>>> The logic was not looking in the buildid cache for kcore
> > >>>> if the host kernel buildid did not match the recorded
> > >>>> kernel buildid.
> > >>>
> > >>> It would be nice to also include the specific failure mode in the 
> > >>> changelog: exactly how can users run into this. That will be more 
> > >>> useful to most people reading these changelogs than a more abstract 
> > >>> bug description.
> > >>
> > >> The preconditions for the problem are that kcore is in the buildid
> > >> cache and that the running kernel has a different buildid e.g.
> > >>
> > >> $ perf buildid-list | grep kernel.kallsyms
> > >> b18fbe769dea12513028a4287dae02efc1582c29 [kernel.kallsyms]
> > >>
> > >> $ perf record -o /tmp/junk true >/dev/null 2>&1 ; perf buildid-list -i /tmp/junk | grep kernel.kallsyms
> > >> 504f9fd9328c40714995ce76fe1354c6e90136ce [kernel.kallsyms]
> > >>
> > >>
> > >>
> > >> Before the patch:
> > >>
> > >>
> > >> $ perf script -v >out.txt
> > >> build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
> > >> <SNIP>
> > >> Using /home/ahunter/.debug/[kernel.kallsyms]/b18fbe769dea12513028a4287dae02efc1582c29 for symbols
> > >>
> > >> perf script stopped
> > >>
> > >>
> > >> After the patch:
> > >>
> > >>
> > >> $ perf script -v >out.txt
> > >> build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
> > >> <SNIP>
> > >> Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kcore for kernel object code
> > >> Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kallsyms for symbols
> > >>
> > >> perf script stopped
> > > 
> > > So the result of the patch is that kernel symbols get 
> > > resolved/annotated correctly, as expected from the live kcore feature, 
> > > right?
> > 
> > Yes but this is the non-live case i.e. the kernel has changed and we are
> > looking at a special copy of kcore that we placed in the buildid cache
> > (using "perf buildid-cache -v -k /proc/kcore") when the data was recorded.
> 
> Okay.

Thanks for the questions and answers, I'll edit it and add to the patch.

- Arnaldo

[tip:perf/core] perf symbols: Fix not finding kcore in buildid cache

[tip-bot for Adrian Hunter]

Commit-ID:  449867e346bfd52c5df6bba5b706a795c35e78d4
Gitweb:     http://git.kernel.org/tip/449867e346bfd52c5df6bba5b706a795c35e78d4
Author:     Adrian Hunter <adrian.hunter@intel.com>
AuthorDate: Tue, 26 Nov 2013 15:19:24 +0200
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Wed, 27 Nov 2013 14:58:38 -0300

perf symbols: Fix not finding kcore in buildid cache

The logic was not looking in the buildid cache for kcore if the host
kernel buildid did not match the recorded kernel buildid.

This affects the non-live case i.e. the kernel has changed and we are
looking at a special copy of kcore that we placed in the buildid cache
(using "perf buildid-cache -v -k /proc/kcore") when the data was
recorded.

After this fix kernel symbols get resolved/annotated correctly.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1385471964-4037-1-git-send-email-adrian.hunter@intel.com
[ Added further explanation extracted from conversation between Ingo & Adrian on lkml ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/symbol.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index ce9ce10..360eefe 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -1526,14 +1526,15 @@ static char *dso__find_kallsyms(struct dso *dso, struct map *map)
 
 	build_id__sprintf(dso->build_id, sizeof(dso->build_id), sbuild_id);
 
+	scnprintf(path, sizeof(path), "%s/[kernel.kcore]/%s", buildid_dir,
+		  sbuild_id);
+
 	/* Use /proc/kallsyms if possible */
 	if (is_host) {
 		DIR *d;
 		int fd;
 
 		/* If no cached kcore go with /proc/kallsyms */
-		scnprintf(path, sizeof(path), "%s/[kernel.kcore]/%s",
-			  buildid_dir, sbuild_id);
 		d = opendir(path);
 		if (!d)
 			goto proc_kallsyms;
@@ -1558,6 +1559,10 @@ static char *dso__find_kallsyms(struct dso *dso, struct map *map)
 		goto proc_kallsyms;
 	}
 
+	/* Find kallsyms in build-id cache with kcore */
+	if (!find_matching_kcore(map, path, sizeof(path)))
+		return strdup(path);
+
 	scnprintf(path, sizeof(path), "%s/[kernel.kallsyms]/%s",
 		  buildid_dir, sbuild_id);