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

[David Goulet]

On 24 Jun (08:47:21), Thierry Bultel wrote:
> 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 ?

Hrm, tbh I never tried lttng-tools on ARM but if a SIGSEGV is raised you
should be able to get a core dump and with gdb we can understand which
callsite failed badly.

Thanks!
David

> 
> Best regards
> Thierry Bultel
> 
> 
> 
> 
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> lttng-dev at lists.lttng.org
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