Quoting Tom I Helbekkmo,

> Possibly related: Since I upgraded from a November 11th snapshot to a
> January 1st one, my i386 has been dropping into the kernel debugger
> whenever I attempt to go from multiuser mode to single user mode.  The
> crash is always the same, and occurs at the point where I'm expecting
> to be asked whether I want /bin/sh or another shell:

> 	kernel: page fault trap, code=0
> 	Stopped at _gdt_compact+0x30: movl 0x68(%ecx),%edx

I filed a bugreport on that one, see PR port-i386/1964. The problem is
that the user area was made pageable, but gdt_compact touches
the user area of all processes, which may lead to page faults at a bad
time.

- Frank