Re: perf cannot see call graph, visible in gdb

[David Ahern <dsahern@gmail.com>]

Adding Jiri.

On 9/9/13 5:59 AM, Mark Hills wrote:
> On Fri, 6 Sep 2013, Andi Kleen wrote:
>
>> Mark Hills <mark@pogo.org.uk> writes:
>>
>>> I have a pre-compiled .so library, which was given to me for profiling.
>>>
>>> gdb can see a complete call stack -- both the library and my own code,
>>> as expected.
>>>
>>> But in perf the callgraph for the library is not present. I'm using
>>> "perf record -g", and the callgraph for the other code is seen.
>>>
>>> In what cases could gdb see the stack, but perf cannot?
>>
>> No frame pointer.
>>
>> Recompile with -fno-omit-frame-pointer
>>
>> Or if you have a new enough perf, you can use -g dwarf to enable
>> dwarf backtracing, but it's very slow and also doesn't handle all
>> situations gdb handles.
>
> Thank you, much appreciated.
>
> A newer perf appears to need a newer kernel too, and it's not practical
> for me to break away from the RedHat kernel at the moment (currently on
> 2.6.32-358.14.1.el6)

Any updates to RHEL6 for dwarf callchains?

David

>
> Also I looked to cherry-pick the relevant patches, but it seems this is
> non-trivial.
>
> I'll speak to the author of the library in question but may have to
> re-visit the dwarf behaviour; omit-frame-pointer may have been used with
> performance in mind.
>
> Thanks
>