Re: Function tracing not working

[Mathieu Desnoyers via lttng-dev <lttng-dev@lists.lttng.org>]

On 2025-06-02 10:37, David Aldrich via lttng-dev wrote:
> Hi,
> 
> I am trying to use lttng-ust-cyg-profile.
> 
> Our application is large so, so far, I only compile main.cpp with
> compiler option '-finstrument-functions' (I don't specify option
> '-pg').
> 
> Our app must be run as root so I run it, and capture with lttng, like this:
> 
> lttng create app_trace
> 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
> export LD_PRELOAD=liblttng-ust-cyg-profile.so
> lttng start
> sudo -E ./myapp
> lttng stop
> 
> I notice that many events get discarded:
> 
> Warning: 198522 events were discarded, please refer to the
> documentation on channel configuration.
> 
> I then import into TraceCompass.  I see the traces in the Resources
> View, but when I expand Experiment > Views, all 3 'LTTng-UST
> CallStack' entries are striked through so I can't select them. So I
> can't visualise the function calls.
> 
> 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,

Mathieu

> 
> Best regards, David


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com