When the following lines are commented out of the kernel
compile, it results in the following undefined symbols.  I would
assume that this should be circumventable by not including the SUN4C
or SUN4M options, but this doesn't work as described in an earlier
message.  At least I should be getting a new kernel to try today...

# Bus types found on SPARC systems.
sbus0	at mainbus0				# sun4c
iommu0	at mainbus0				# sun4m
sbus0	at iommu0				# sun4m

obio.o: Undefined symbol `_sbus_translate' referenced from text segment
obio.o: Undefined symbol `_sbus_translate' referenced from text segment
bwtwo.o: Undefined symbol `_sbus_establish' referenced from text segment
vm_machdep.o: Undefined symbol `_has_iocache' referenced from text segment
vm_machdep.o: Undefined symbol `_has_iocache' referenced from text segment
vm_machdep.o: Undefined symbol `_iommu_enter' referenced from text segment
vm_machdep.o: Undefined symbol `_iommu_remove' referenced from text segment