Component(s) involved:
* LTTng-modules (kernel tracing)
* LTTng-tools
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Component version:
* lttng-tools: 2.13.15 (lttng --version)
* lttng-modules-dkms: 2.13.18 (modinfo lttng_tracer | grep version)
* Babeltrace2: 2.0.4 (babeltrace2 --version)
________________________________
System information:
* Architecture: x86_64, 4 CPUs
* OS: Ubuntu 22.04.4 LTS
* Kernel:
* Linux shrtripathi-vm 5.15.0-140-generic #150-Ubuntu SMP Sat Apr 12
06:00:09 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
* Also tested: 5.15.0-141-generic
* Distribution: Ubuntu 22.04.4 LTS
Expected results: After running a kernel trace session, the file
/tmp/my-kernel-trace/kernel/metadata should be plain text, starting with /* CTF
1.8 */, and be readable by Babeltrace2 and the Python bt2 bindings.
________________________________
Actual results:
* The metadata file is written in "packetized" (binary) format, as detected
by the file command:
text
Apply
/tmp/my-kernel-trace/kernel/metadata: Common Trace Format (CTF) packetized
metadata (LE), v1.8
* The first line is binary garbage, not /* CTF 1.8 */.
* Babeltrace2 and the Python bt2 bindings cannot parse the trace, reporting
errors about invalid metadata.
* Example of the first lines of the metadata file:
W�u�kzM�W{L����^l�typealias integer { size = 8; align = 8; signed = false; }
:= uint8_t;
typealias integer { size = 16; align = 8; signed = false; } := uint16_t;
...
Logs and context:
* Babeltrace2 error:
At line 146 in metadata stream: Invalid character: char="", val=0x1d
At line 146 in metadata stream: syntax error, unexpected CTF_ERROR, expecting
CTF_TYPEASSIGN or CTF_EQUAL: token=""
* All LTTng kernel modules and user-space tools are version 2.13.18.
* All modules are loaded from /lib/modules/5.15.0-140-generic/updates/dkms/
and match the running kernel.
* No old or mismatched modules are present.
Loaded kernel modules:
lsmod | grep lttng
lttng_clock 16384 0
lttng_kretprobes 16384 0
lttng_kprobes 16384 0
lttng_uprobes 16384 0
lttng_statedump 749568 0
lttng_wrapper 16384 1 lttng_statedump
...
Additional context:
* The issue persists across multiple kernel versions (5.15.0-140-generic,
5.15.0-141-generic).
* User-space tracing works as expected (metadata is plain text).
* The issue is not fixable by editing the file, as the format is
fundamentally binary.
________________________________
What should happen:
The kernel tracer should write plain text CTF metadata, starting with /* CTF
1.8 */, so that Babeltrace2 and the Python bt2 bindings can parse the
trace.What happens:The kernel tracer writes packetized (binary) metadata, which
is not usable for analysis.
________________________________
Thank you for your help! Please let me know if you need any more logs or
information.
Regards
Shreya Tripathi
