perf report: Include partial stacks unwound with libdw

perf report: Include partial stacks unwound with libdw

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@amazon.com>
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: Sasha Levin <sashal@kernel.org>