[lttng-dev] tracing program flow

Mathieu Desnoyers mathieu.desnoyers at efficios.com
Mon May 7 10:53:22 EDT 2012

* Oestman, Fredrik (Fredrik_Oestman at mentor.com) wrote:
> Alexandre Montplaisir wrote:
> > There's a feature on the wishlist to use GCC hooks to automatically
> > generate those probes [1]. The end result would be the same, but it
> > would be much less tedious to do the instrumentation part. A Clang
> > plugin was also mentioned previously [2], but I don't think anybody has
> > tried it yet.
> Providing functions to GCC containing LTTng tracepoints isn't that
> much of a problem. We found it useful to add the thread ID to the
> trace data provided by GCC so we could keep the threads apart. As far
> as I know, this has to be made in application code at the moment,
> since LTTng can add context trace information only to kernel events at
> the moment.

The "vtid" context is also available in user-space traces. The list of
user-space contexts currently available:

vtid, vpid, pthread_id, procname.

> We also have used the dynamic linker to add LTTng tracepoints to
> memory allocation and de-allocation functions as well as to the
> functions in the ptreads library. It can be done, but overhead is
> significant.
> Any road-map information for the ability of LTTng to add context
> information to user-space events?

Already available :)



> Cheers,
> Fredrik Östman
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Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.

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