Component(s) involved:

• LTTng-modules (kernel tracing)

• LTTng-tools

---

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