Now, one can print the call chain for every encountered sys_exit event,
e.g.:

    $ perf trace -e nanosleep --call-graph dwarf path/to/ex_sleep
    1005.757 (1000.090 ms): ex_sleep/13167 nanosleep(...) = 0
                                             syscall_slow_exit_work ([kernel.kallsyms])
                                             syscall_return_slowpath ([kernel.kallsyms])
                                             int_ret_from_sys_call ([kernel.kallsyms])
                                             __nanosleep (/usr/lib/libc-2.23.so)
                                             [unknown] (/usr/lib/libQt5Core.so.5.6.0)
                                             QThread::sleep (/usr/lib/libQt5Core.so.5.6.0)
                                             main (path/to/ex_sleep)
                                             __libc_start_main (/usr/lib/libc-2.23.so)
                                             _start (path/to/ex_sleep)

Note that it is advised to increase the number of mmap pages to prevent
event losses when using this new feature. Often, adding `-m 10M` to the
`perf trace` invocation is enough.

This feature is also available in strace when built with libunwind via
`strace -k`. Performance wise, this solution is much better:

    $ time find path/to/linux &> /dev/null

    real    0m0.051s
    user    0m0.013s
    sys     0m0.037s

    $ time perf trace -m 800M --call-graph dwarf find path/to/linux &> /dev/null

    real    0m2.624s
    user    0m1.203s
    sys     0m1.333s

    $ time strace -k find path/to/linux  &> /dev/null

    real    0m35.398s
    user    0m10.403s
    sys     0m23.173s

Note that it is currently not possible to configure the print output.
Adding such a feature, similar to what is available in `perf script` via
its `--fields` knob can be added later on.
Signed-off-by: Milian Wolff <milian.wolff@kdab.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
LPU-Reference: 1460115255-17648-1-git-send-email-milian.wolff@kdab.com
[ Split from a larger patch, do not print the IP, left align,
  remove dup call symbol__init(), added man page entry ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>