segfault in xl create for HVM with PCI passthrough

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

Hi guys,
I have used XEN for quiet some time and after a steep learning curve I 
have always been a very happy user! XEN is really a great product. 
Unfortunately I am now facing a problem that leaves me at loss:

Using gentoo as a rolling distribution I recently I upgraded to XEN 
4.3.3 (from 4.3.1) and also upgraded the gcc compiler to 4.8.3 (from 
4.7.3). Both packages are the latest stable versions available under gentoo.

After emerging (that is the re-compilation and installation of XEN 4.3.3 
on my machine) following a toolchain upgrade to the new gcc I can't 
start my two HVM FreeBSD virtual machines anymore. Both use PCI 
passthrough devices and both the motherboard and the processor support 
VT-d. XEN PV gentoo domUs (without passed through PCI devices) still 
start up (but are useless for me at the moment as they depend on the 
services provided by the tow HVM domus).

The error when starting manifests itself as follows:
# xl create -c pfsense
Parsing config from 01:pfsense.1
xc: info: VIRTUAL MEMORY ARRANGEMENT:
   Loader:        0000000000100000->00000000001c12a4
   Modules:       0000000000000000->0000000000000000
   TOTAL:         0000000000000000->000000001f800000
   ENTRY ADDRESS: 0000000000100000
xc: info: PHYSICAL MEMORY ALLOCATION:
   4KB PAGES: 0x0000000000000200
   2MB PAGES: 0x00000000000000fb
   1GB PAGES: 0x0000000000000000
Segmentation fault
#

The domU is in a state of paused for reasons unknown to me and does not 
use any CPU cycles:
# xl list
Name                              ID   Mem VCPUs      State   Time(s)
Domain-0                           0  4094     8     r-----      41.7
pfsense                            1   512     1     --p---       0.0
#

The expected output is actually the boot-menu from FreeBSD (I do use a 
serial console in FreeBSD and that worked for month without any hickup 
before the recent update). It also never entered a paused state ...

/var/log/messages shows the following line related to the segfault:
Oct 27 20:16:22 vm-host kernel: [  458.354314] xl[2906]: segfault at 
7fbc56b93eb0 ip 00007fbc54430b64 sp 00007fbc56b93eb0 error 6 in 
libgcc_s.so.1[7fbc54422000+16000]

If I destroy the paused domU by issuing
# xl destroy pfsense
Segmentation fault
#

An error is again logged in /var/log/messages similar to the start error 
messages as follows:
Oct 27 22:06:59 vm-host kernel: [ 7095.794688] xl[3218]: segfault at 
7f22ced42eb0 ip 00007f22cc5cfb64 sp 00007f22ced42eb0 error 6 in 
libgcc_s.so.1[7f22cc5c1000+16000]

The pfsense config file is pretty simple/basic, nothing fancy in there:
builder       = 'hvm'
cpus          = '2-7'
vcpus         = 1
cpu_weight    = 512
memory        = 512
name          = 'pfsense'
disk          = [ 'phy:/etc/xen/guests/disk.d/pfsense.disk,sda,w' ]
vif           = [ 'mac=00:16:3e:a1:64:01,bridge=xenbr0,model=e1000' ]
on_poweroff  = 'destroy'
on_reboot    = 'restart'
on_crash     = 'restart'
localtime    = 0
boot         = 'c'
vnc          = 0
nographic    = 1
serial       = 'pty'
nx           = 1
pci          = [ '04:00.0', '0a:08.0', '0a:0b.0' ]


In order to rule out any inconsistency after the gcc update I have today 
also emerged the complete world set (including kernel re-compilation) - 
unfortunately to no avail: The error persists. Other than this xl/XEN 
problem the machine operates without any issues.

I'd very much appreciate if somebody could shed some light on this 
issue. In case you require any more information, I am more than happy to 
provide it.

Many thanks in advance and best regards

Atom2