From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <476BAE70.5080600@domain.hid> Date: Fri, 21 Dec 2007 13:15:44 +0100 From: Jan Kiszka MIME-Version: 1.0 References: <47373B12.7020808@domain.hid> <47373CB9.2010104@domain.hid> <18231.25399.331189.714344@domain.hid> <47381AC0.6020502@domain.hid> In-Reply-To: <47381AC0.6020502@domain.hid> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-core] x86_64: problems with syscall tracing? List-Id: "Xenomai life and development \(bug reports, patches, discussions\)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Philippe Gerum Cc: xenomai-core 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 [1] applied, things work > again as they should! Then I followed his thread on LKML and tried the > second version of the patch [2], 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? > > Jan > > [1]http://listserv.shafik.org/pipermail/ltt-dev/2007-October/002519.html > [2]http://lkml.org/lkml/2007/10/28/160 I just once again ran into this issue - this time without any LTTng patch applied. Sigh. Philippe, we need [2] 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. Jan -- Siemens AG, Corporate Technology, CT SE 2 Corporate Competence Center Embedded Linux