Otherwise the initial call to set_top_of_stack(), which occurs before fpuinit() sets the correct value for cpu_max_ext_state_size, leaves the stack base at an incorrect location. Then, when the full area is zeroed, we end up erroneously zeroing part of the following page. Reviewed by: kib MFC after: 1 week Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D24754