early panic and dump

[Csaba Henk]

I sent the following post to freebsd-current, but maybe it's better to
be sent to questions -- the problem of dumping as such is not a
current-specific question...

> 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

Note that the above quote is from Developers Handbook and the full quote
is:

Alternatively, the dump device can be hard-coded via the dump clause in
the config(5) line of a kernel configuration file. This approach is
deprecated and should be used only if a kernel is crashing before
dumpon(8) can be executed.

And that I fall into the "only if" case.

Thanks.

Csaba