Allocation of PASM registers (in PASM mode)

[Leopold Toetsch]

Am Sonntag, 11. Januar 2009 18:13 schrieb Geoffrey Broadwell:

First, I'm reciting Coke's argument here:

"If P42 in PASM acts the same way as $P42 in PIR, why do we have two
different ways to say the same thing?"

Seconded.

And last time I checked, you could use P42 in PIR too.

> It feels like there is a stability/security question here.  If someone
> can ask for register 42 or 999, what's to stop them for asking for
> register 1000000000 and allocating all of main mem?

You'll get out of memory error in that case.

> Whatever solution chosen to catch this during the compile, we still have
> to do bytecode validation anyway.  An argument can be made to leave the
> problem entirely to bytecode validation (and runtime checks for e.g.
> memory allocation failures), as long as the bytecode annotations allow
> us to report errors nicely.

Yep.

> It is of course always nice to report insanity as early as possible, but
> since the PASM compile and bytecode execution can be done on separate
> machines, it may not be clear at compile time that a register allocation
> is insane ....

Indeed. Runtime checks are needed _as well_. You might warn on insane 
allocation and die on totally insane allocation according to some percentage 
and a given amount for insaneness.

Don't forget the debugging issues, when PBC register != PASM register.

> -'f

leo