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

Matthew Khouzam matthew.khouzam at ericsson.com
Tue Sep 10 11:26:12 EDT 2013

Alex brought up an excellent point,
these locations should be events since there can be address collisions.

A default event for location with a payload of address and name would be
sufficient I think. DlOpen will create many events then.

On 13-09-10 11:15 AM, Matthew Khouzam wrote:
> Hi Alex and Mathieu,
> A year ago we discussed this and said iirc: "the addresses are a good
> first step, we'll do more later." and "It would be nice to dump the
> stabs into the metadata of the ctf trace"
> I would still maintain that this seems to be the way to go.
> A technical hurdle that is probably trivial to our high level tracing
> vanguards would be to handle dlopens and libs that replace other libs.
> I would suggest something like this in TSDL:
> location {
>     address = 0xdeadbeef;
>     name = "get_actual_lost_events";
> }
> location {
>     address = 0xf00ff00f;
>     name = "get_pretend_lost_events";
>     // optional
>     timestart = 123456;
>     timeend = 123457;
> }
> The metadata will get big and dynamic though.
> On 13-09-09 07:44 PM, 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
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