Jan Kiszka wrote:
> Gilles Chanteperdrix wrote:
>> Philippe Gerum wrote:
>> > Jan Kiszka wrote:
>> > > Philippe,
>> > >
>> > > you recently said there is a bug in the x86_64 support when syscall
>> > > tracing is enabled. Now I think I stepped on it as well: In order to
>> > > validate my APIC frequency patches for that arch, I wanted to use LTTng
>> > > there. But as soon as I start the trace, the latency test fails to run,
>> > > prematurely exiting due to a segfault.
>> > Exactly what Gilles sees on his box too, latency segfaulting at startup.
>> > On mine, the kernel does not even boot.
>> > Gdb and the kernel say that user
>> > > land jumped to address 0, I just yet failed to find out where they come
>> > > from. I strongly assume LTTng enables syscall tracing, because its
>> > > entry/exit instrumentations are inside the hook function
>> > > (syscall_trace_entry/leave).
>> > >
>> > > Do you have any further details on your tracing issue? Does may
>> > > observation correlates with yours?
>> > Quite frankly, I did not dig the issue that far yet, but yes, my first
>> > impression is that something is broken in the syscall return path (or
>> > entry?), and it shows when the return path to user-space is diverted in
>> > some way, either for security auditing, or likely for tracing like
>> > you've just reported.
>> From what I have read in some comments, the syscall auditing function
>> kmallocs some memory that is kfreed on syscall return. Obviously, this
>> can not work with Xenomai.
> Just a short update on this: Right before going mad over this bug, I
> recalled some posting on ltt-dev by Mathieu Desnoyers about x86_64 and
> some syscall tracing race. With this patch  applied, things work
> again as they should! Then I followed his thread on LKML and tried the
> second version of the patch , but that one does not work for us. Now
> I wonder (but didn't analyse yet) if the first patch just moves some
> race window around or actually fixes the bug for us?
I just once again ran into this issue - this time without any LTTng
patch applied. Sigh.
Philippe, we need  in the x86-64 Adeos patch to allow for
CONFIG_AUDITSYSCALL. In my case, leaving out --enable-sep during Xenomai
user land build worked around this, but that's no solution.
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