Re: Function tracing not working

[David Aldrich via lttng-dev <lttng-dev@lists.lttng.org>]

Hi Mathieu

I'd like to add some more detail.  I now run our app using this pattern:

LD_PRELOAD=liblttng-ust-cyg-profile.so ./app

On importing the trace into TraceCompass I see:

"null analysis for LTTng-UST CallStack"

Could the reason be the lttng commands I am using to capture UST and
Kernel events:

lttng enable-event --userspace 'lttng_ust_tracef:*'
lttng enable-channel --kernel --session app_trace kernel_channel
lttng enable-event --kernel --all --channel kernel_channel --session app_trace

Best regards
David

On Wed, Jun 4, 2025 at 5:22 PM David Aldrich
<david.aldrich.ntml@gmail.com> wrote:
>
> Hi Mathieu
>
> > > Any idea what I am doing wrong please?
> >
> > AFAIK, the "LD_PRELOAD" environment variable is cleared by
> > sudo when running its child process for security purposes.
>
> Thanks for your answer, that does help. However, I have now adjusted
> the code so that sudo is not required, but when I import the trace the
> UST-CallStacks are still strikethrough.
>
> Any thoughts why this is happening?
>
> I don't see any runtime errors whether or not I specify the prefix:
>
> LD_PRELOAD=liblttng-ust-cyg-profile.so
>
> Is that expected?
>
> Best regards, David