From: Milian Wolff <milian.wolff@xxxxxxxx>
commit 5ea0416f51cc93436bbe497c62ab49fd9cb245b6 upstream.
So far the whole stack was thrown away when any error occurred before
the maximum stack depth was unwound. This is actually a very common
scenario though. The stacks that got unwound so far are still
interesting. This removes a large chunk of differences when comparing
perf script output for libunwind and libdw perf unwinding.
E.g. with libunwind:
~~~~~
heaptrack_gui 2228 135073.388524: 479408 cycles:
ffffffff811749ed perf_iterate_ctx ([kernel.kallsyms])
ffffffff81181662 perf_event_mmap ([kernel.kallsyms])
ffffffff811cf5ed mmap_region ([kernel.kallsyms])
ffffffff811cfe6b do_mmap ([kernel.kallsyms])
ffffffff811b0dca vm_mmap_pgoff ([kernel.kallsyms])
ffffffff811cdb0c sys_mmap_pgoff ([kernel.kallsyms])
ffffffff81033acb sys_mmap ([kernel.kallsyms])
ffffffff81631d37 entry_SYSCALL_64_fastpath ([kernel.kallsyms])
192ca mmap64 (/usr/lib/ld-2.25.so)
59a9 _dl_map_object_from_fd (/usr/lib/ld-2.25.so)
83d0 _dl_map_object (/usr/lib/ld-2.25.so)
cda1 openaux (/usr/lib/ld-2.25.so)
1834f _dl_catch_error (/usr/lib/ld-2.25.so)
cfe2 _dl_map_object_deps (/usr/lib/ld-2.25.so)
3481 dl_main (/usr/lib/ld-2.25.so)
17387 _dl_sysdep_start (/usr/lib/ld-2.25.so)
4d37 _dl_start (/usr/lib/ld-2.25.so)
d87 _start (/usr/lib/ld-2.25.so)
heaptrack_gui 2228 135073.388677: 611329 cycles:
1a3e0 strcmp (/usr/lib/ld-2.25.so)
82b2 _dl_map_object (/usr/lib/ld-2.25.so)
cda1 openaux (/usr/lib/ld-2.25.so)
1834f _dl_catch_error (/usr/lib/ld-2.25.so)
cfe2 _dl_map_object_deps (/usr/lib/ld-2.25.so)
3481 dl_main (/usr/lib/ld-2.25.so)
17387 _dl_sysdep_start (/usr/lib/ld-2.25.so)
4d37 _dl_start (/usr/lib/ld-2.25.so)
d87 _start (/usr/lib/ld-2.25.so)
~~~~~
With libdw without this patch:
~~~~~
heaptrack_gui 2228 135073.388524: 479408 cycles:
ffffffff811749ed perf_iterate_ctx ([kernel.kallsyms])
ffffffff81181662 perf_event_mmap ([kernel.kallsyms])
ffffffff811cf5ed mmap_region ([kernel.kallsyms])
ffffffff811cfe6b do_mmap ([kernel.kallsyms])
ffffffff811b0dca vm_mmap_pgoff ([kernel.kallsyms])
ffffffff811cdb0c sys_mmap_pgoff ([kernel.kallsyms])
ffffffff81033acb sys_mmap ([kernel.kallsyms])
ffffffff81631d37 entry_SYSCALL_64_fastpath ([kernel.kallsyms])
heaptrack_gui 2228 135073.388677: 611329 cycles:
~~~~~
With this patch applied, the libdw unwinder will produce the same
output as the libunwind unwinder.
Signed-off-by: Nikson Kanti Paul <nikson@xxxxxxxxxx>
Signed-off-by: Milian Wolff <milian.wolff@xxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/20170601210021.20046-1-milian.wolff@xxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Amit Shah <aams@xxxxxxxxx>
Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 4.9
---
tools/perf/util/unwind-libdw.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/perf/util/unwind-libdw.c b/tools/perf/util/unwind-libdw.c
index b46e1cf347e5..b632048baf18 100644
--- a/tools/perf/util/unwind-libdw.c
+++ b/tools/perf/util/unwind-libdw.c
@@ -231,7 +231,7 @@ int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
err = dwfl_getthread_frames(ui->dwfl, thread->tid, frame_callback, ui);
- if (err && !ui->max_stack)
+ if (err && ui->max_stack != max_stack)
err = 0;
/*
--
2.16.5
