Okay, I just built a new kernel from sources up-to-date as of about an hour ago.
After booting it, I logged in, and ran startx & exit. The kernel paniced with
a fatal uvm fault. I did not have DEBUG/DDB/makeoptions DEBUG="-g" in the kernel
at the time.

I rebooted, and (without starting X) rebuilt the kernel with all the debug
options.
Now, startx&exit works just like it did before, no panic.

Is there any reason anyone can think of for this to happen? The only changes in
kernel config between the kernel that paniced on startx and the kernel that
doesn't are:
options DEBUG
options DDB
makeoptions DEBUG="-g"

in the currently working fine kernel.
Any suggestions?

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