[lttng-dev] Getting function names with lttng-ust-cyg-profile.so

[Amit Margalit]

+1 on that.

I think we should have a way for UST to store the function names in the 
metadata, so the trace remains valid for any viewer that correctly 
supports CTF.

I think Mathieu Desnoyers said once that this requires a modification to 
the CTF spec, so let's start raising out voice for this...

As Paul mentioned, he has a solution, and I have a somewhat different 
solution (which I will share sometime in the near future), but I still 
think that having the function names in the metadata is better.

Amit Margalit
IBM XIV - Storage Reinvented
XIV-NAS Development Team
Tel. 03-689-7774
Fax. 03-689-7230



From:   "Woegerer, Paul" <Paul_Woegerer at mentor.com>
To:     <alexmonthy at voxpopuli.im>, Mathieu Desnoyers 
<mathieu.desnoyers at efficios.com>
Cc:     lttng-dev <lttng-dev at lists.lttng.org>
Date:   09/10/2013 10:01 AM
Subject:        Re: [lttng-dev] Getting function names with 
lttng-ust-cyg-profile.so



Hi Alexandre,

For trivial examples you can go with 'nm -CS' (or the like), but when
you start to use liblttng-ust-cyg-profile.so in combination with shared
objects you will need to record base address information as well (to
allow you map a virtual memory address at a given point in time to
offset and path of a shared object (or executable)).

That is one of the reasons why I have submitted:
http://lists.lttng.org/pipermail/lttng-dev/2013-August/021264.html

Thanks,
Paul

On 09/10/2013 01:44 AM, Mathieu Desnoyers wrote:
> We might want to investigate doing a side-program that gathers the
> executables on the system, and lookup the symbols from the ELF. We could
> save those in a bin/ subdirectory of a CTF trace. All we need is
> instrumentation of the dynamic linker, and to know the executable names
> associated with PIDs. There is a UST feature request for dynamic linker
> instrumentation.
>
> Thanks,
>
> Mathieu
>
> * Alexandre Montplaisir (alexmonthy at voxpopuli.im) wrote:
>> Hi all,
>>
>> I've recently started playing with liblttng-ust-cyg-profile.so (aka,
>> getting UST events from -finstrument-functions), and I have to say it's
>> pretty nifty! I haven't done any benchmarks, but it's certainly faster
>> than the typical printf() that people use with it...
>>
>> However, in the resulting trace, one only gets the addresses of the
>> functions. I understand how it's relatively "easy" for the seasoned 
user
>> to use nm or addr2line to get the actual function names, but would it
>> possible - and how hard would it be - to have this information 
(function
>> names) directly in the trace?
>>
>>
>> I'm trying to leverage this feature in Eclipse TMF to display a call
>> stack for such UST traces. And to be honest, displaying a call stack
>> with only the function addresses is completely useless, we need the
>> function names.
>>
>> We could have the user import a text file (which he can generate with
>> "nm appname > file.txt" for example). But then he needs the original
>> binary, which he might not have. And that binary needs to be compiled
>> with debugging symbols. If the function name information was already in
>> the trace, it would make the user experience much better, and our job
>> much easier! ;)
>>
>>
>> Thoughts?
>>
>> Thanks,
>> Alex
>>
>> _______________________________________________
>> lttng-dev mailing list
>> lttng-dev at lists.lttng.org
>> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev


-- 
Paul Woegerer, SW Development Engineer
Sourcery Analyzer <http://go.mentor.com/sourceryanalyzer>
Mentor Graphics, Embedded Software Division


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