81eb2c446b
The unmapped page separates the tip of the stack and possible adjanced segment, making some uses of stack overflow harder. The stack growing code refuses to expand the segment to the last page of the reseved region when sysctl security.bsd.stack_guard_page is set to 1. The default value for sysctl and accompanying tunable is 0. Please note that mmap(MAP_FIXED) still can place a mapping right up to the stack, making continuous region. Reviewed by: alc MFC after: 1 week