Well, I finally got around to building a kernel after the recent addition 
of the obio stuff in the configuration files.  I got the following errors 
from the link step:

ld -n -Ttext 0 -e start -x -o netbsd ${SYSTEM_OBJ} vers.o
am7990.o: Undefined symbol `_ether_ifattach' referenced from text segment
am7990.o: Undefined symbol `_ether_sprintf' referenced from text segment
am7990.o: Undefined symbol `_ether_input' referenced from text segment
am7990.o: Undefined symbol `_arp_ifinit' referenced from text segment
am7990.o: Undefined symbol `_ether_addmulti' referenced from text segment
am7990.o: Undefined symbol `_ether_delmulti' referenced from text segment
*** Error code 1

Stop.

And, here's the relevant section of my config file:

config		netbsd	root on sd1	swap on sd1 and sd2 and sd0 and vnd0	dumps on sd1b

grf0		at obio0

nubus0		at mainbus0

#ae*	at nubus0	slot -1   id ?   claimed 0

grf*		at nubus0

ncrscsi0	at obio0		# SCSI NCR 5380
#ncr96scsi0	at obio?		# SCSI NCR 53C96

scsibus0	at scsi0


Note that I _don't_ have an Ethernet of any sort, so why did it bother 
with the am7990 module?  And just what is this thing, anyway?  I don't 
remember having seen it before...