On Tue, 03 Nov 2020 23:17:09 +0100, Jiri Olsa wrote:
> When you compiled perf with libunwind, you get:
> 
>   $ make VF=1
>   $ perf report -i perf.data --stdio
> 
>   # Children      Self  Trace output
>   # ........  ........  ..............
>   #
>      100.00%   100.00%  (5640789cdf50)
>               |
>               |--98.85%--0x7fc8eca0f554
>               |          main
>               |          main_loop_wait
>               |          qemu_poll_ns
>               |
>                --1.15%--0x7fc8ecdc2ea4
>                          iothread_run
>                          aio_poll
>                          qemu_poll_ns
> 
> 
> When you compile perf with libdw, you get:
> 
>   $ make VF=1 NO_LIBUNWIND=1
>   $ perf report -i perf.data --stdio
> 
>   # Children      Self  Trace output
>   # ........  ........  ..............
>   #
>      100.00%   100.00%  (5640789cdf50)
>               |
>               |--98.85%--0x45260879
>               |          qemu_poll_ns
>               |
>                --1.15%--qemu_poll_ns

I get after the attached fix:

# Children      Self  Trace output  
# ........  ........  ..............
#
   100.00%   100.00%  (5640789cdf50)
            |          
            |--98.85%--main
            |          main_loop_wait
            |          qemu_poll_ns
            |          
             --1.15%--iothread_run
                       aio_poll
                       qemu_poll_ns


> any idea why libdw is doing that? ;-)

Because libdw was reporting separate debuginfo file as the main file:

(lldb) p thread->process->dwfl->modulelist->main.name
(char *) $1 = 0x0000000000b52490 "/home/jkratoch/.debug/.build-id/fc/d0111443729957fa8ef9511ff5dc3e9a5ccf9d/debug"
(lldb) p thread->process->dwfl->modulelist->debug.name
(char *) $2 = 0x0000000000000000

The correct way is to report the main ELF file as the main file:

(lldb) p thread->process->dwfl->modulelist->main.name
(char *) $1 = 0x0000000000b52490 "/home/jkratoch/.debug/.build-id/fc/d0111443729957fa8ef9511ff5dc3e9a5ccf9d/elf"
(lldb) p thread->process->dwfl->modulelist->debug.name
(char *) $2 = 0x0000000000000000

In some cases it may later fill-in even the ->debug.name with "/debug" filename.


Jan Kratochvil