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

Michael Jeanson mjeanson at efficios.com
Thu May 11 14:14:31 EDT 2023

On 2023-05-11 12:36, Brian Hutchinson via lttng-dev wrote:
> ... 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.
> Regards,
> Brian


If you are static linking 'liblttng-ust' then the library constructor won't be 
executed and you'll get no traces. While this setup is untested and 
unsupported, you could call the UST constructor from your application early 
initialisation but that would require patching lttng-ust to export the 
'lttng_ust_ctor' symbol.

And the first thing to do to start diagnosing UST tracing issues is to run 
your application with hte LTTNG_UST_DEBUG environment variable set, see [1] 
for details.



[1] https://lttng.org/man/3/lttng-ust/v2.13/#doc-_environment_variables

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