In several places, entry start and end field are checked, after excluding the possibility that the entry is map->header. By assigning max and min values to the start and end fields of map->header in vm_map_init, the explicit map->header checks become unnecessary.
I have addressed the comments (made offline) from alc. He has stated that he has no objections to the resulting patch, but that I will have to rely on someone else to give it final approval and checkin. I'd appreciate that help from somebody, please.