From: Namhyung Kim <namhy...@kernel.org>
There's a problem on finding correct kernel symbols when perf report
runs on a different kernel. Although a part of the problem was solved
by the prior commit 0a7e6d1b6844 ("perf tools: Check recorded kernel
version when finding vmlinux"), there's a remaining problem still.
When perf records samples, it synthesizes the kernel map using
machine__mmap_name() and ref_reloc_sym like "[kernel.kallsyms]_text".
You can easily see it using 'perf report -D' command.
After finishing record, it goes through the recorded events to find
maps/dsos actually used. And then record build-id info of them.
During this process, it needs to load symbols in a dso and it'd call
dso__load_vmlinux_path() since the default value of the symbol_conf.
try_vmlinux_path is true. However it changes dso->long_name to a real
path of the vmlinux file (e.g. /lib/modules/3.16.4/build/vmlinux) if one
is running on a custom kernel.
It resulted in that perf report reads the build-id of the vmlinux, but
cannot use it since it only knows about the [kernel.kallsyms] map. It
then falls back to possible vmlinux paths by using the recorded kernel
version (in case of a recent version) or a running kernel silently.
Even with the recent tools, this still has a possibility of breaking
the result. As the build directory is a symbolic link, if one built a
new kernel in the same directory with different source/config, the old
link to vmlinux will point the new file. So it's absolutely needed to
use build-id when finding a kernel image.
In this patch, it's now changed to try to search a kernel dso in the
existing dso list which was constructed during build-id table parsing
so it'll always have a build-id. If not found, search "[kernel.kallsyms]".
Before:
$ perf report
# Children Self Command Shared Object Symbol
# ........ ........ ....... .................
...............................
#
72.15% 0.00% swapper [kernel.kallsyms] [k] set_curr_task_rt
72.15% 0.00% swapper [kernel.kallsyms] [k] native_calibrate_tsc
72.15% 0.00% swapper [kernel.kallsyms] [k]
tsc_refine_calibration_work
71.87% 71.87% swapper [kernel.kallsyms] [k] module_finalize
...
After (for the same perf.data):
72.15% 0.00% swapper vmlinux [k] cpu_startup_entry
72.15% 0.00% swapper vmlinux [k] arch_cpu_idle
72.15% 0.00% swapper vmlinux [k] default_idle
71.87% 71.87% swapper vmlinux [k] native_safe_halt
...
Signed-off-by: Namhyung Kim <namhy...@kernel.org>
Acked-by: Ingo Molnar <mi...@kernel.org>
Link: http://lkml.kernel.org/r/20140924073356.gb1...@gmail.com
Cc: Adrian Hunter <adrian.hun...@intel.com>
Cc: David Ahern <dsah...@gmail.com>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Jiri Olsa <jo...@redhat.com>
Cc: Namhyung Kim <namhyung....@lge.com>
Cc: Paul Mackerras <pau...@samba.org>
Cc: Peter Zijlstra <a.p.zijls...@chello.nl>
Cc: Stephane Eranian <eran...@google.com>
Link:
http://lkml.kernel.org/r/1415063674-17206-8-git-send-email-namhy...@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <a...@redhat.com>
---
tools/perf/util/header.c | 2 +-
tools/perf/util/machine.c | 16 ++++++++++++++--
2 files changed, 15 insertions(+), 3 deletions(-)
diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 3e2c156d9c64..76442caca37e 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -1269,7 +1269,7 @@ static int __event_process_build_id(struct build_id_event
*bev,
dso__set_build_id(dso, &bev->build_id);
- if (filename[0] == '[')
+ if (!is_kernel_module(filename, NULL))
dso->kernel = dso_type;
build_id__sprintf(dso->build_id, sizeof(dso->build_id),
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 946c7d62cb6e..53f90e9c65fe 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1085,8 +1085,20 @@ static int machine__process_kernel_mmap_event(struct
machine *machine,
* Should be there already, from the build-id table in
* the header.
*/
- struct dso *kernel = __dsos__findnew(&machine->kernel_dsos,
- kmmap_prefix);
+ struct dso *kernel = NULL;
+ struct dso *dso;
+
+ list_for_each_entry(dso, &machine->kernel_dsos.head, node) {
+ if (is_kernel_module(dso->long_name, NULL))
+ continue;
+
+ kernel = dso;
+ break;
+ }
+
+ if (kernel == NULL)
+ kernel = __dsos__findnew(&machine->kernel_dsos,
+ kmmap_prefix);
if (kernel == NULL)
goto out_problem;
--
1.9.3
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