number of args in a syscall

I'm faced with porting some code that has patched the 8.0 kernel
to accept up to 16 args in a syscall.
It makes my skin crawl a bit but if I can't give a good reason to
suggest that they do things differently in 10 (pass a pointer to a 
struct maybe)
then I'll just take the easy path and s/8/16/ in
the appropriate line in amd64/include/proc.h and get on with life.

I initially thought it may confuse things like ktrace or truss but I 
haven't seen any problems..
allocating more space on the stack is another thing but you only ever 
do one syscall at a time.

Julian