[lttng-dev] some troubles having lttgng-ust actually log something on a shared library

[Mathieu Desnoyers]

* Sébastien Barthélémy (barthelemy at crans.org) wrote:
> Hi Mathieu,
> 
> thank you for you help, it is much appreciated.
> 
> 2011/12/16 Mathieu Desnoyers <compudj at krystal.dyndns.org>:
> > * Sébastien Barthélémy (barthelemy at crans.org) wrote:
> >>
> >> using ust debug mode, I noticed this error message:
> >>   libust[30999/31001]: Error: futex: Bad address (in
> >> wait_for_sessiond() at lttng-ust-comm.c:571)
> >
> > I changed this so it only shows up if "LTTNG_UST_DEBUG" env var is set
> 
> I set that var.
> 
> >> a shared library. I probably have missed some obvious step.
> 
> > This diff to the makefile makes it work here (you forgot to add
> > ust_motion.o to your .so).
> 
> That was indeed an obvious step to miss! Indeed it fixes the example
> here too, thank you.
> 
> Alas, that does not solve my original problem: I'm trying to add
> tracing to a bigger application,
> for which tracing does not really work yet.
> 
> The example I sent was just a attempt to reproduce my problems on a
> simpler application.
> I guess I was just too happy to reproduce it on such a simple program, that I
> sent it to the ML without double checking. Sorry for that (and thank you again).
> 
> Back to my original problem now: the application I'd like to add
> tracing to loads plugins
> (dlopened shared libraries I guess). Tracepoints added to these
> plugins are never logged
> anywhere. However, traces added to the main executable show up in
> babeltrace. I probably
> have some link problem again, what do you think?

Please try to reproduce this problem in a simple application that uses
dlopen to load libs.

> 
> A better understanding of the way probes are enabled would probably
> help me debug it.
> Is it documented somewhere? Or could you point me to the right source file?

liblttng-ust/tracepoint.c
liblttng-ust/ltt-probe.c
include/lttng/tracepoint.h include/lttng/ust-tracepoint-event.h

would be a good start,

Best regards,

Mathieu

> 
> Thank you again.
> 
> Regards
> -- Sebastian
> 
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-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com