On Thu, May 10, 2001 at 09:04:03PM -0000, eeh@netbsd.org wrote:
> 
> 	I got my DEBUG enabled kernel crashed with the attached test,
> 	first it breaks system to ddb and an attempt to continue
> 	ends up in ofw 'ok' prompt. Commenting out lines below helps.
> 	locore.s:4795
> 	#ifdef DEBUG
> 		tst	%g2
> 		tz	1		! tpc NULL? Panic
> 		tst	%i6
> 		tz	1		! %fp NULL? Panic
> 	#endif
> 
> That check is there to make sure the cpu is not trying to return from a
> trap with either a NULL pc or stack pointer.  The machine is unlikely to
> recover in that event, and this the trap lets you determine what the problem
> is.
> 
That's what I started with. If I change DEBUG to DEBUG_NOTDEF
then the same test doesn't cause any of the problems, i.e even
%g2 is still 0 it doesn't lead to crash.

I concluded that %g2 at this point not necessarily will become tpc
and that trap to debugger won't return normally.

	Andrey