問題解決ってわけでもないんだろうけど、とりあえず使えますよって感じ？

# /platform/sun4u/boot.conf
#
# name/value pairs used to augment boot(1M) policy.
#
# ALLOW_64BIT_KERNEL_ON_UltraSPARC_1_CPU
#
# On systems containing 200MHz or lower UltraSPARC-I processors,
# it is possible for a user to run a 64-bit program designed to exploit a
# problem that could cause the processor to stall. Since 64-bit programs
# cannot run on the 32-bit kernel, the 32-bit kernel is chosen as the
# default boot file on these systems.
#
# The code sequence that exploits the problem is very unusual and is not
# likely to be generated by a compiler. Assembler code had to be
# specifically written to demonstrate the problem. It is highly unlikely
# that a legitimate handwritten assembler routine would use this code sequence.
#
# Users willing to assume the risk that a user might accidentally or
# deliberately run a program designed to cause a processor to stall
# may choose to run the 64-bit kernel by uncommenting the following item:
#
ALLOW_64BIT_KERNEL_ON_UltraSPARC_1_CPU=true