> Alas... I could figure out 'args-on-stack' case only happens 'indirect
> mmap'.   All other cases comfortably fit in 'args-in-trapframe' case.
> Tentative sketch of syscall() would look like;

Looks good to me.  I can certainly understand your concern with changing
the argument passing semantics to use r10-r12.  I had forgotten about
the SYS_[_]syscall cases.

> 			error = copyin(
> 				(void *)(frame->r31 + 8 * sizeof(register_t)),
> 				(void *)((caddr_t)args + argsize),
> 				callp->sy_argsize - argsize);

What are the 8 words that you are passing over here?  I followed the
rest, with appropriate variable name changes...  (uargsused/nargsused,
in particular)

Thank you for your patience with me.

-allen