Debugging kernel panics

[Michael Reynolds]

I've recently cvsup'd from 4.8-STABLE to 4.9-PRERELEASE.  After a 
reboot, my machine's kernel panics at the initialization of the xl1 
device (a 3com nic).  I've checked out the FAQ on the site, under 
advanced topics, regarding kernel panics, and read the relevant man 
pages.  I have 2 swap partitions, ad0s1b, and ad2s1b.  I have set 
dumpdev to "ad2s1b" in /etc/rc.conf and /boot/loader.conf.  I've also 
built a debug kernel.  However, it appears a kernel core is not being 
dumped on panic.  I've manually executed savecore, with force option, 
and it wrote a 0 byte vmcore.  Is there anywhere else I need to specify 
the dump device?  Do I need to specify the full path instead of just the 
device?  I've not had a kernel panic before, so I'm pretty much a newbie 
when it comes to that aspect.  I have no custom code added to the 
kernel.  Any help will be *greatly* appreciated.

-Mike