linux-kernel - [PATCH 3/3] perf tools: Use correct filename for compressed modules in build-id cache

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Date:   Wed, 31 May 2017 21:01:05 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Jiri Olsa <jolsa@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, kernel-team@....com,
        David Ahern <dsahern@...il.com>,
        Andi Kleen <andi@...stfloor.org>
Subject: [PATCH 3/3] perf tools: Use correct filename for compressed modules in build-id cache

The decompress_kmodule() is to decompress kernel module in order to load
symbols from it.  In DSO_BINARY_TYPE__BUILD_ID_CACHE case, it needs full
file path to extract the file extension to determine decompress method.
But overwriting 'name' will fail to decompress since it might point to a
non-existing old file.

Instead, use dso->long_name for extension and use real filename to
decompress.  In DSO_BINARY_TYPE__SYSTEM_PATH_KMODULE_COMP case, both
name should be same.  This can show symbols in the old modules.

Before:

  $ perf report -i perf.data.old | grep scsi_mod
     0.00%  cc1      [scsi_mod]    [k] 0x0000000000004aa6
     0.00%  as       [scsi_mod]    [k] 0x00000000000099e1
     0.00%  cc1      [scsi_mod]    [k] 0x0000000000009830
     0.00%  cc1      [scsi_mod]    [k] 0x0000000000001b8f

After:

     0.00%  cc1      [scsi_mod]    [k] scsi_handle_queue_ramp_up
     0.00%  as       [scsi_mod]    [k] scsi_sg_alloc
     0.00%  cc1      [scsi_mod]    [k] scsi_setup_cmnd
     0.00%  cc1      [scsi_mod]    [k] scsi_get_command

Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 tools/perf/util/symbol-elf.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index e7ee47f7377a..1fb2efae4f02 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -649,10 +649,7 @@ static int decompress_kmodule(struct dso *dso, const char *name,
 	    type != DSO_BINARY_TYPE__BUILD_ID_CACHE)
 		return -1;
 
-	if (type == DSO_BINARY_TYPE__BUILD_ID_CACHE)
-		name = dso->long_name;
-
-	if (kmod_path__parse_ext(&m, name) || !m.comp)
+	if (kmod_path__parse_ext(&m, dso->long_name) || !m.comp)
 		return -1;
 
 	fd = mkstemp(tmpbuf);
-- 
2.13.0