>> The largest storage consuming system call
>> is mmap, which would occupy eight 32bit registers and r9 should be
>> free for it.  The change was neccessiated by off_t change, I guess.
>
> I think it makes sense, then, to provide r10-r12 as some room for
> expansion and to use r13 for the syscall number,

It's questionable extention to have 9,10,11th arguments in registers
(no NetBSD syscall has them, and syscall() in various ports assumes
args[8]).  If ever, such values on user stack should be accessed by
copyin() in an appropriate way.  It seems not a good practice to load
values blindly from sp(32),sp(36),sp(40) for any system calls all the
time.

Tohru Nishimura
Nara Institute of Science and Technology