Historical netbsd-5 domUs now panic

[Stephen Borrill <netbsd%precedence.co.uk@localhost>]

I've recently updated our XenServers with the latest 
security patches and had to set pv-linear-pt=true to get NetBSD domUs to 
boot. For historical reasons, I have a couple of netbsd-5/i386 VMs which 
are now frequently panicking:

xpq_flush_queue: 3 entries
0x000000060481bfe0: 0x0000000604819001
0x00000007eac9fd40: 0x0000000604819001
0x00000007eab73d40: 0x0000000604819001
panic: HYPERVISOR_mmu_update failed

fatal breakpoint trap in supervisor mode
trap type 1 code 0 eip c039e374 cs 9 eflags 246 cr2 bb75b1a0 ilevel 6
Stopped in pid 15.1 (fsck_ffs) at       0xc039e374:     popl    %ebp

Kernel is pretty old and also has no symbols:
NetBSD 5.2_STABLE (XEN3PAE_DOMU) #37: Fri Nov 27 12:02:02 UTC 2015

Does anyone have an idea of a quick way to fix this (yes, I know I could 
use a newer kernel with the old userland)? If I build a kernel with 
symbols, would a backtrace help?

--
Stephen