Re: perf probe dwarf on shared libraries

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Thu, Sep 04, 2014 at 03:11:31PM -0500, david lerner escreveu:
> Has perf probe for userspace shared libraries been modified to use dwarf info?
> The first commit to provide this useful functionality...
>    fb7345bbf7fad9  perf probe: Support basic dwarf-based operations on
> uprobe events,
> shows examples only with the executable perf, but not with a shared library.
 
> With version 3.14 I'm able to set probes in application executable,
> for example for the test application 'libunwind-test.out' I see the
> usual args to main():
>    root@qemu0:~# perf probe -x ./libunwind-test.out --vars main
>    Available variables at main
>         @<main+0>
>                 char**  a
>                 int     c
> But I can't access the variables in a library that has embedded (not
> split out) dwarf debug info...
>    root@qemu0:~# perf probe -x /usr/lib64/libunwind.so --vars unw_backtrace
>    Failed to find symbol at 0x33c38039cd
>    Failed to find variables at unw_backtrace (-2)
>    Error: Failed to show vars. (-2)
> I've used gdb to confirm that perf found the correct function address
> for unw_backtrace(), and that gdb knows the symbolic names of the
> arguments.
 
> Is using dwarf debuginfo with shared libraries for perf uprobes on the
> to-do list?
> Or is this capability incomplete in version 3.14 and I need to pick up
> other patches?

Have to check this, but perhaps Masami has this working already?

- Arnaldo