[lttng-dev] "lttng enable-event" fails

[Thierry Bultel]

Hi,

I am using lttng (2.4.1), target is ARM Cortex A9; compiler is 
gcc-4.7.3, but I have the same issue with gcc-4.8.2
The kernel is Freescale's 3.0.35-4.1.0


lttng fails to start:

[root at buildroot ~]# lttng create
Session auto-19700319-135920 created.
Traces will be written in /root/lttng-traces/auto-19700319-135920
[root at buildroot~]# lttng enable-event --kernel --all
PERROR [5831/5915]: wait: Success (in run_as_clone() at runas.c:243)
Error: Trace directory creation error
Error: Events: Kernel create session failed (channel channel0, session
auto-19700319-135920)

My analysis show that lttng attempts to create the trace directory, when
"lttng enable-event" is called.
To do so, it uses a slave thread that performs a kind of "mkdir -p" ,
that thread is spawned via a call to "clone"
and the father waits for it via "waitpid".

When the slave returns, waitpid says it is not completed. Added a little
code to shows that the thread
is killed with SIGSEGV at the time it calls "return"

Changing it to call "exit" instead, makes it a little better, but other
numerous errors come when
calling "lttng start"

Did anyone encounter such an issue ?

Best regards
Thierry Bultel