he is telling you what ELF_START_MMAP is all about. it is the base
address that the linux kernel for that architecture will start giving
out addresses. so when running Linux on an x86 system, the first
mmap() a process does will start at 0x80000000 and move up.
although looking at the elfload code quickly, it doesnt seem that this
is really used anymore. so it probably can be ignored.
Uhmm that makes sense and explains many things like why they can
simply consider always possible that the target is allocated at
elf_ppnt->p_vaddr, without risking it to clash with qemu-user
code..