early panic and dump

Hi!

I tried to install both RELENG-6 and CURRENT, and both kernels behaved
the same way: panicked quite early (before init) with a page fault. Has
anyone met with this phenomena?

I'd like to show you some fancy backtracks, but as it all happened before
starting init, rc.conf settings won't help me in getting the dump.

What I've read: 

"the dump device can be hard-coded via the dump clause in the config(5)
line of a kernel configuration file."

But putting 

dump /dev/ad0s4

into the config file is considered a syntax error, and the man page
of config doesn't contain anything about dumping.

Another thing which I found on the net suggests setting the dumpdev
variable in the loader(8). I can do that, but it doesn't make a difference,
and again, the man page doesn't mention dumping.

How to get that wacky dump these days?

TIA.

Cheers,
Csaba