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

[Mathieu Desnoyers]

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.

Which are the exact versions of LTTng-UST and LTTng-Tools you are using 
now ? (2.13.N or which git commit ?)

Thanks,

Mathieu

> 
> Regards,
> 
> Brian
> 
> 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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-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com