Re: [BUG] XEN 4.3.3 - segfault in xl create for HVM with PCI passthrough

[Atom2 <ariel.atom2@web2web.at>]

Am 05.11.14 um 13:39 schrieb Ian Campbell:
> On Wed, 2014-11-05 at 13:01 +0100, Atom2 wrote:
>
> Thanks for all that, sadly it's not giving me any clues what is going
> wrong :-/
>
> So unless "-v --leak-check=full" tells me something (which I'm doubtful
> of at this stage) I think we're back to bisecting the changes since
> 4.3.1, sorry.
Things are getting very strange at the moment.
After much work an research I have been able to download the source and 
compile the old version which has worked before (which incidentally was 
not 4.3.1 but rather 4.3.2-r5 - sorry for any confusion that might have 
caused). I initially thought that's good news because there are less 
changes between 4.3.2 and 4.3.3 but after re-ompiling 4.3.2-r5 I am now 
experiencing the same segfault as with 4.3.3.

So my next step was trying to figure out what else had changed since the 
problems started on 26.10.14 by working through log files and those are 
the relevant events that had happened. The sequence of events was as 
follows:

11.10.14 04:13:	Last system reboot with working version (xen 4.3.2-r5)
		(xen-4.3.2-r5 was in use since 21.08.14)
18.10.14 22:50:	Last successful creation of HVM with PCI passthrough
		(that domU run up to 26.10.14 as did another HVM)

Updates and new package installs since last reboot:
22.10.14:	app-misc/pax-utils-0.8.1 (update)
24.10.14:	dev-libs/libaio-0.3.110 (update)
		dev-libs/popt-1.16-r2 (update)
		sys-libs/libcap-ng-0.7.3 (new)
		dev-libs/libgcrypt-1.5.4-r1 (update)
		net-analyzer/tcpdump-4.6.2 (update)
25.10.14:	sys-devel/gcc-4.8.3 (update from 4.7.3-r1)
26.10.14:	app-emulation/xen-tools-4.3.3-r1 (update from 4.3.2-r5)
		app-emulation/xen-4.3.3-r1 (update from 4.3.2-r5)

26.10.14:	reboot - 1st segfault msg in syslog at shutdown time
		system reboots, can't start HVM PCI passthrough domUs
		segfault messages in syslog referring to libgcc_s.so.1
		problems since despite world/kernel/system recompile

If I read this correctly I would come to the conclusion that the only 
package that is a dependency for both 4.3.2-r5 (the previously working, 
but now also non-working version) and 4.3.3-r1 (which never worked) is 
gcc which is required to compile the binaries from source. I don't think 
any of the other packages should have any influence.

Also the error message referring to libgcc_s.so.1 might hint towards a 
problme with gcc. It's probably worth mentioning that the system apart 
from XEN runs without any hickups and is still rock solid. At the moment 
it looks as if xen and gcc-4.8.3 don't co-operate well.

It's probably also worth mentioning that gcc is (and also was with the 
older gcc-4.7.3) the hardened gcc version of gentoo which forces 
position-independent executables (PIE), stack smashing protection (SPP) 
and compile time buffer checks (see 
http://wiki.gentoo.org/wiki/Hardened_Gentoo). The rest of hardend (PAX, 
grSecurity, SELinux is not (and never was) in use (so far). I don't know 
whether any of this might have contributed to the problems I am 
currently being faced with.

Now going back to to an older version of gcc from a newer version is not 
recommened and (according to my research on google) might create 
numerous other issues - so there seems to be no easy route to get back 
to gcc-4.7.3 and therefore getting back the binaries for 4.3.2-r5 in the 
state they were before the problems started seems impossible.

I am still at loss and hope for the combined intelligence of the list to 
again get my system up and running.

Many thanks Atom2