[lttng-dev] Using lttng 2.11 and UST doesn't appear to work - getting empty trace files - Yitschak, Yehuda via lttng-dev

From: "Yitschak, Yehuda via lttng-dev" <lttng-dev@lists.lttng.org>
To: Brian Hutchinson <b.hutchman@gmail.com>,
	"lttng-dev@lists.lttng.org" <lttng-dev@lists.lttng.org>
Subject: [lttng-dev] Using lttng 2.11 and UST doesn't appear to work - getting empty trace files
Date: Tue, 25 Apr 2023 04:13:31 +0000	[thread overview]
Message-ID: <9b162e6a547c41b284327034a9749027@amazon.com> (raw)

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It might be related to the static linking of lttng-ust
https://lists.lttng.org/pipermail/lttng-dev/2018-January/027705.html

I also went down that path just to figure it’s not supported.
Perhaps lttng documentation should be updated to make a clear note static linking is not supported (or maybe I missed it)

Yehuda

Hi,

I'm on an embedded platform, i.MX8 using Lttng 2.11 with 5.6.69 kernel.

Tracing kernel events with lttng works fine but userspace (tracef and trace provider type tracing) appears to have an issue I can't figure out.

systemd is starting up my application ( a bunch of processes and threads on multiple cpu's) on boot.

I'm statically compiling and linking in lttng-ust.  If I use just tracef type tracing, when I do lttng list --userspace I get nothing.  If I add in a trace provider and a tracepoint, then I see my trace provider tracepoint and:

     lttng_ust_tracelog:TRACE_DEBUG (loglevel: TRACE_DEBUG (14)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_DEBUG_LINE (loglevel: TRACE_DEBUG_LINE (13)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_DEBUG_FUNCTION (loglevel: TRACE_DEBUG_FUNCTION (12)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_DEBUG_UNIT (loglevel: TRACE_DEBUG_UNIT (11)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_DEBUG_MODULE (loglevel: TRACE_DEBUG_MODULE (10)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_DEBUG_PROCESS (loglevel: TRACE_DEBUG_PROCESS (9)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_DEBUG_PROGRAM (loglevel: TRACE_DEBUG_PROGRAM (8)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_DEBUG_SYSTEM (loglevel: TRACE_DEBUG_SYSTEM (7)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_INFO (loglevel: TRACE_INFO (6)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_NOTICE (loglevel: TRACE_NOTICE (5)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_WARNING (loglevel: TRACE_WARNING (4)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_ERR (loglevel: TRACE_ERR (3)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_CRIT (loglevel: TRACE_CRIT (2)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_ALERT (loglevel: TRACE_ALERT (1)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_EMERG (loglevel: TRACE_EMERG (0)) (type: tracepoint)
     lttng_ust_tracef:event (loglevel: TRACE_DEBUG (14)) (type: tracepoint)
     lttng_ust_lib:unload (loglevel: TRACE_DEBUG_LINE (13)) (type: tracepoint)
     lttng_ust_lib:debug_link (loglevel: TRACE_DEBUG_LINE (13)) (type: tracepoint)
     lttng_ust_lib:build_id (loglevel: TRACE_DEBUG_LINE (13)) (type: tracepoint)
     lttng_ust_lib:load (loglevel: TRACE_DEBUG_LINE (13)) (type: tracepoint)
     lttng_ust_statedump:end (loglevel: TRACE_DEBUG_LINE (13)) (type: tracepoint)
     lttng_ust_statedump:debug_link (loglevel: TRACE_DEBUG_LINE (13)) (type: tracepoint)
     lttng_ust_statedump:build_id (loglevel: TRACE_DEBUG_LINE (13)) (type: tracepoint)
     lttng_ust_statedump:bin_info (loglevel: TRACE_DEBUG_LINE (13)) (type: tracepoint)
     lttng_ust_statedump:start (loglevel: TRACE_DEBUG_LINE (13)) (type: tracepoint)

When I do lttng start, I get a directory structure in the trace directory but the file sizes do not ever increase.  It's just a directory structure with files created and then that's it, no events being written to the files.  At first I thought things just weren't linked in right and not working but then discovered how to run lttng-sessiond in -vvv mode and then could see lots of things are going on, tracing appears to be trying to work as there is tons of activity being output by lttng-sessiond, but like I said the trace files aren't being added to.

I looked at the lttng-sessiond log I captured and can't quite make out the problem so attaching it.

I'm probably not doing something right but can't figure out what that is so any pointers appreciated.

Regards,

Brian

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