make kernel / make installworld failed - Signal 4

[Owen.G]

Hello all,

My PC is (or rather until Sunday, WAS) running 5.2.1#9.  I edited the 
kernel to reflect my installed hardware and add support for the PF 
firewall and then did a CVSup for sources - keeping to 5.2.1.  This 
isn't the first kernel edit and upgrade I've done but as far as I recall 
the only changes I made were the "pfi_hooks" (or something similar - for 
the PF firewall) and to disable the ata keyboard - I can use USB to a 
KVM switch.

Here's what happened . . .

# make buildworld - finished OK
# make kernel KERNCONF=EDEN - finished OK
* PC rebooted OK
# make installworld - failed with errors part way through.
* PC failed to reboot.  It gets part way through and then reboots.
. . .
So, at the boot loader prompt:
OK unload
OK load /boot/kernel.save/kernel
OK boot kernel.save -s
. . .
#mount -a
illegal instruction. Signal 4
#

Unloading the kernel and booting into single user mode seems to be OK 
and the PATH is correct.
No command except "cd" or "pwd" works, everything fails with "illegal 
instruction Signal 4"

e.g. "ls" or "df" or "mount -a" all fail with "illegal instruction Signal 4"

Any ideas please.

Thanks in anticipation,

Owen