Well, I rebuilt the kernel with makeoptions DEBUG="-g" and tried again.
After booting up, I logged in and typed `startx'.  It responded with the
standard "screen 0...." message, cleared the screen, and then gave me two
of those "Data modified on freelist" messages.  Then, it gave me an
"Illegal instruction - core dumped" message and (apparently) exitted - I
got a block cursor back, but no shell prompt.  So, I typed a return and
got my shell prompt.  

Then, while I wqas sitting there trying to figure out what to try next, I
got the MMU fault!  (Total delay, about 4 or 5 seconds.)

	vm_fault(116000, bbbbb000, 3, 0) -> 1
	    type 8, code [mmu,,ssw]: 401070d
	trap type 8, code = 401070d, v = bbbbbbc3
	Kernel: MMU fault trap
	pid = 157, pc = 0004FCA8, ps = 2104, sfc = 0001, dfc = 0001

	Registers:
	dreg:    0000007E 00000000 00000000 00000000 00000000 00002104 00000020 00000011
	areg:    BBBBBBBB 00000000 06BF1800 06BF1880 06BEE000 0000000D 00840E28 FFFFC7D8

	Kernel stack (I didn't really want to write all this down! )

	Traceback:
	_Debugger
	_panic
	_trap
	faultstkadj
	_udp_usrreq
	_soclose
	_soo_close
	_closef
	_fdfree
	_exit1
	_sigexit
	_postsig
	_trap
	fault

My guess is there's something somewhere stomping on a dangling pointer,
and managing to screw something else up royally.

BTW, are you sure about the DEBUG="-g" makeoptions?  The resulting kernel
is the same size as it was without that line...

On Sun, 25 May 1997, Jason Thorpe wrote:

> On Sun, 25 May 1997 17:27:14 -0700 (PDT) 
>  Paul Goyette <paul@whooppee.com> wrote:
> 
>  > Well, that helped out a little bit - at least it gets the right address
>  > and attaches the ite0!  But I guess there's still something else that's
>  > very fundamentally wrong, since as soon as I start up X (xdm, actually) it
>  > clears the display to all white (_not_ the pseudo-gray background) and
>  > then gets an MMU fault.
>  > 
>  > Oh, and on its way to MMU fault, I got a couple of those "freelist data
>  > modified" messages that someone else mentioned the other day...
> 
> ...stray pointers... what does the MMU fault tell you?  I would
> recommend building your kernel with full debugging symbols
> (makeoptions DEBUG="-g" in your kernel config file, then rebuild
> from scratch) so that you can more easily use gdb after the crash.
> 
> Jason R. Thorpe                                       thorpej@nas.nasa.gov
> NASA Ames Research Center                               Home: 408.866.1912
> NAS: M/S 258-6                                          Work: 415.604.0935
> Moffett Field, CA 94035                                Pager: 415.428.6939
> 

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