[lttng-dev] Crash on first run of target using liblttng-ust-cyg-profile.so, but subsequent runs succeed

[Sean Heelan]

Hi Michael/everyone else,

Indeed the above does seem to resolve the issue. Thanks for looking into
this!

Cheers,
Sean


On Wed, Mar 2, 2016 at 5:45 PM, Michael Jeanson <mjeanson at efficios.com>
wrote:

> Hi Sean,
>
> As mentioned by Mathieu this is caused by the docker default seccomp
> profile
> blocking the "restart_syscall" syscall. This problem only happens on host
> systems where docker 0.10.2 and up was built against libseccomp 2.2.1 and
> up.
>
> Hopefully docker will add this syscall to their default whitelist but in
> the
> meantime, you can simply get the json profile [1] from git and add this :
>
>   {
>     "name": "restart_syscall",
>     "action": "SCMP_ACT_ALLOW",
>      "args": []
>   }
>
> Then start your container with "--security-opt
> seccomp:/path/to/myprofile.json".
>
> Hope it helps,
>
> Michael
>
>
> [1]
> https://github.com/docker/docker/blob/master/profiles/seccomp/default.json
>
>
> ----- On Feb 11, 2016, at 9:01 AM, Sean Heelan seanheelan at gmail.com wrote:
>
> > Hi all,
> >
> > I am running a target within a Docker instance, and tracing function
> execution
> > using the latest LTTng release (2.7). The commands I am issuing look as
> > follows:
> >
> > ----
> > lttng create cc_session -o bla
> > lttng enable-event --userspace lttng_ust_cyg_profile:func_entry
> > lttng start
> >
> > LD_PRELOAD=liblttng-ust-cyg-profile.so target
> >
> > lttng stop
> > lttng destroy
> > ----
> >
> > When the target is executed it aborts with the following error:
> >
> > ----
> > php: lttng-ust-comm.c:1582: lttng_ust_init: Assertion `!ret' failed.
> > ----
> >
> > If I rerun the command it then works fine. In fact, simply doing the
> following
> > within the Docker container demonstrates the issue:
> >
> > ----
> > LD_PRELOAD=liblttng-ust-cyg-profile.so ls
> > LD_PRELOAD=liblttng-ust-cyg-profile.so ls
> > ----
> >
> > The first 'ls' will fail at the same point mentioned above, while the
> second
> > will succeed. Off the top of my head I'm struggling to come up with an
> > explanation as to what impact the first execution using LD_PRELOAD would
> have
> > on the second. Does it impact a shared lib cache in some way, which I'm
> unaware
> > of?
> >
> > Any assistance would be appreciated!
> >
> > Sean
> >
> >
> >
> > _______________________________________________
> > lttng-dev mailing list
> > lttng-dev at lists.lttng.org
> > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
>
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