linux-kernel - [tip:perfcounters/urgent] perf_counter tools: Fix vmlinux fallback when running on a different kernel

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Message-ID: <tip-c1f47b454ce759d7b13604137a233cad4617e1e8@git.kernel.org>
Date:	Sun, 21 Jun 2009 13:09:35 GMT
From:	tip-bot for Ingo Molnar <mingo@...e.hu>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, acme@...hat.com, paulus@...ba.org,
	hpa@...or.com, mingo@...hat.com, a.p.zijlstra@...llo.nl,
	efault@....de, lucas.de.marchi@...il.com, tglx@...utronix.de,
	mingo@...e.hu
Subject: [tip:perfcounters/urgent] perf_counter tools: Fix vmlinux fallback when running on a different kernel

Commit-ID:  c1f47b454ce759d7b13604137a233cad4617e1e8
Gitweb:     http://git.kernel.org/tip/c1f47b454ce759d7b13604137a233cad4617e1e8
Author:     Ingo Molnar <mingo@...e.hu>
AuthorDate: Sun, 21 Jun 2009 13:58:51 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Sun, 21 Jun 2009 13:58:51 +0200

perf_counter tools: Fix vmlinux fallback when running on a different kernel

Lucas De Marchi reported that perf report and perf annotate
displays mismatching profile if a perf.data is analyzed on
an older kernel - even if the correct vmlinux is specified
via the -k option.

The reason is the fallback path in util/symbol.c:dso__load_kernel():

int dso__load_kernel(struct dso *self, const char *vmlinux,
                     symbol_filter_t filter, int verbose)
{
        int err = -1;

        if (vmlinux)
                err = dso__load_vmlinux(self, vmlinux, filter, verbose);

        if (err)
                err = dso__load_kallsyms(self, filter, verbose);

        return err;
}

dso__load_vmlinux() returns negative on error, but on success it
returns the number of symbols loaded - which confuses the function
to load the kallsyms.

This is normally harmless, as reporting is usually performed on the
same kernel that is analyzed - but if there's a mismatch then we
load the wrong kallsyms and create a non-sensical symbol tree.

The fix is to only fall back to kallsyms on errors.

Reported-by: Lucas De Marchi <lucas.de.marchi@...il.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Mike Galbraith <efault@....de>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@...e.hu>


---
 tools/perf/util/symbol.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 86e1437..01b62fa 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -629,7 +629,7 @@ int dso__load_kernel(struct dso *self, const char *vmlinux,
 	if (vmlinux)
 		err = dso__load_vmlinux(self, vmlinux, filter, verbose);
 
-	if (err)
+	if (err < 0)
 		err = dso__load_kallsyms(self, filter, verbose);
 
 	return err;
--
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