[PATCH AUTOSEL for 4.4 125/167] perf header: Set proper module name when build-id event found

Sasha Levin
2018-03-19T17:09:53Z

From: Namhyung Kim <namhyung@kernel.org>

[ Upstream commit 1deec1bd96ccd8beb04d2112a6d12fe20505c3a6 ]

When perf processes build-id event, it creates DSOs with the build-id.
But it didn't set the module short name (like '[module-name]') so when
processing a kernel mmap event of the module, it cannot found the DSO as
it only checks the short names.

That leads for perf to create a same DSO without the build-id info and
it'll lookup the system path even if the DSO is already in the build-id
cache. After kernel was updated, perf cannot find the DSO and cannot
show symbols in it anymore.

You can see this if you have an old data file (w/ old kernel version):

$ perf report -i perf.data.old -v |& grep scsi_mod
build id event received for /lib/modules/3.19.2-1-ARCH/kernel/drivers/scsi/scsi_mod.ko.gz : cafe1ce6ca13a98a5d9ed3425cde249e57a27fc1
Failed to open /lib/modules/3.19.2-1-ARCH/kernel/drivers/scsi/scsi_mod.ko.gz, continuing without symbols
...

The second message didn't show the build-id. With this patch:

$ perf report -i perf.data.old -v |& grep scsi_mod
build id event received for /lib/modules/3.19.2-1-ARCH/kernel/drivers/scsi/scsi_mod.ko.gz: cafe1ce6ca13a98a5d9ed3425cde249e57a27fc1
/lib/modules/3.19.2-1-ARCH/kernel/drivers/scsi/scsi_mod.ko.gz with build id cafe1ce6ca13a98a5d9ed3425cde249e57a27fc1 not found, continuing without symbols
...

Now it shows the build-id but still cannot load the symbol table. This
is a different problem which will be fixed in the next patch.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: kernel-team@lge.com
Link: http://lkml.kernel.org/r/20170531120105.21731-1-namhyung@kernel.org
[ Fix the build on older compilers (debian <= 8, fedora <= 21, etc) wrt kmod_path var init ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
tools/perf/util/header.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 43838003c1a1..304f5d710143 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -1258,8 +1258,16 @@ static int __event_process_build_id(struct build_id_event *bev,

dso__set_build_id(dso, &bev->build_id);

- if (!is_kernel_module(filename, cpumode))
- dso->kernel = dso_type;
+ if (dso_type != DSO_TYPE_USER) {
+ struct kmod_path m = { .name = NULL, };
+
+ if (!kmod_path__parse_name(&m, filename) && m.kmod)
+ dso__set_short_name(dso, strdup(m.name), true);
+ else
+ dso->kernel = dso_type;
+
+ free(m.name);
+ }

build_id__sprintf(dso->build_id, sizeof(dso->build_id),
sbuild_id);
--
2.14.1