pmap_virtual_space(v_start, v_end) vaddr_t *v_start; vaddr_t *v_end;
pmap_virtual_space(vaddr_t *v_start, vaddr_t *v_end)
pmap_virtual_space(v_start, v_end)        vaddr_t *v_start;        vaddr_t *v_end;{        *v_start = virtual_avail;        *v_end   = virtual_end;}