[lttng-dev] I'm still getting empty ust traces using tracef

Brian Hutchinson b.hutchman at gmail.com
Thu May 11 12:36:19 EDT 2023

... more background.  I've always used ltt in the kernel so I don't
have much experience with the user side of it and especially
multi-threaded, multi-core so I'm probably missing some fundamental
concepts that I need to understand.



On Thu, May 11, 2023 at 11:53 AM Brian Hutchinson <b.hutchman at gmail.com> wrote:
> Hi,
> I posted a while ago (thread - Using lttng 2.11 and UST doesn't appear
> to work - getting empty trace files) about this problem I'm having
> with getting empty trace logs.
> I've since upgraded to lttng v2.13 and while I can do a simple hello
> world program with tracef and get events in the log files, my more
> complicated large multi-threaded app I'm trying to debug is still
> getting empty log file traces.
> I can list the user space events in my app.
> Next I do:
> lttng enable-event --userspace 'lttng_ust_tracef:*'
> ... to enable the events, start lttng, start my app, .... and I get a
> trace directory structure that's empty.
> I feel like I've read every thread in the archives about people having
> the same problem.
> I did try using LD_PRELOAD with various libs thinking that was the
> problem but so far I'm still getting empty traces.
> So far I've tried:
> LD_PRELOAD=liblttng-ust-libc-wrapper.so.1:liblttng-ust-pthread-wrapper.so.1:liblttng-ust-dl.so.1:liblttng-ust-fork.so.1:liblttng-ust-fd.so.1
> /usr/local/bin/my_app
> I guess one question I have is how do I determine which "helper libs"
> I need to preload?
> The application I'm working on is made up of a bunch of smaller static
> libs linked together into one big executable and that is linked with
> -llttng-ust and -ldl.
> I'm pretty stuck at the moment.  Anyone have any wisdom on what I
> might be doing wrong or how I can tell why I'm not getting events in
> the logs?
> Thanks,
> Brian

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