Anyone around here still familiar with Alpha assembler (and the Alpha kernel in general) willing to point me in the right direction?

Supposing one wanted to implement instruction emulation for the BWX extensions, etc, like Tru64 and OpenVMS do, so that you can run the same binaries on EV4 and EV5, where would be the best place to hook in?  illegal0 in /sys/src/9/alphapc/l.s or illegal in /sys/src/9/alphapc/trap.c?  

Furthermore, how would one obtain the faulting instruction?  Best I can tell, it's the Ureg *ur passed to illegal in trap.c or 8(R30) from illegal0.

Thanks in advance!

-Ben