perf header: Set proper module name when build-id event found

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>

1 files changed, 10 insertions, 2 deletions

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 314a07151fb7..c40a4d8acf8b 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -1469,8 +1469,16 @@ 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);