From: Milian Wolff milian.wolff@kdab.com
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: Milian Wolff milian.wolff@kdab.com Cc: Jiri Olsa jolsa@redhat.com Cc: Namhyung Kim namhyung@kernel.org Link: http://lkml.kernel.org/r/20170601210021.20046-1-milian.wolff@kdab.com Signed-off-by: Arnaldo Carvalho de Melo acme@redhat.com Cc: Amit Shah aams@amazon.de Cc: David Woodhouse dwmw@amazon.co.uk Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: stable@vger.kernel.org # 4.9 Signed-off-by: Nikson Kanti Paul nikson@amazon.com --- 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;
/*