LTTng » LTTng-tools

Found this problem while investigating bug #598. It seems that applications that call "fork" are not traced.

See the following reproduction steps based on the lttng-tools/tests/regression/ust/fork/ test.

This patch must be applied to make sure the "fork" executable waits on "fork2".

[~/src/lttng-tools]$ ldd ./tests/regression/ust/fork/fork
    linux-vdso.so.1 (0x00007fff8beb2000)
    liblttng-ust-fork.so.0 => /usr/lib/liblttng-ust-fork.so.0 (0x00007f2c5cb4a000)
    liblttng-ust.so.0 => /usr/lib/liblttng-ust.so.0 (0x00007f2c5c900000)
    liblttng-ust-tracepoint.so.0 => /usr/lib/liblttng-ust-tracepoint.so.0 (0x00007f2c5c6e7000)
    librt.so.1 => /usr/lib/librt.so.1 (0x00007f2c5c4df000)
    liburcu-bp.so.3 => /usr/lib/liburcu-bp.so.3 (0x00007f2c5c2d8000)
    liburcu-cds.so.3 => /usr/lib/liburcu-cds.so.3 (0x00007f2c5c0d1000)
    liburcu-common.so.3 => /usr/lib/liburcu-common.so.3 (0x00007f2c5bece000)
    libdl.so.2 => /usr/lib/libdl.so.2 (0x00007f2c5bcca000)
    libpopt.so.0 => /usr/lib/libpopt.so.0 (0x00007f2c5babe000)
    libpthread.so.0 => /usr/lib/libpthread.so.0 (0x00007f2c5b8a1000)
    libc.so.6 => /usr/lib/libc.so.6 (0x00007f2c5b4f9000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f2c5cd4c000)

[~/src/lttng-tools]$ lttng create fork_test
Spawning a session daemon
Session fork_test created.
Traces will be written in /home/jgalar/lttng-traces/fork_test-20140226-110021

[~/src/lttng-tools]$ lttng enable-event -u -a
All UST events are enabled in channel channel0

[~/src/lttng-tools]$ lttng start
Tracing started for session fork_test

[~/src/lttng-tools]$ ./tests/regression/ust/fork/fork tests/regression/ust/fork/fork2
parent_pid 26641
child_pid 26673
IN FORK2

[~/src/lttng-tools]$ lttng stop
Waiting for data availability.
Tracing stopped for session fork_test

[~/src/lttng-tools]$ lttng destroy
Session fork_test destroyed

[~/src/lttng-tools]$ babeltrace ~/lttng-traces/fork_test-20140226-110021/

[~/src/lttng-tools]$ echo $?
0

The resulting trace is empty, yet the metadata contains all of fork and fork2's events.