[coyotos-dev] SPAM-LOW: FCRB concept is broken

[Sandro Magi]

Jonathan S. Shapiro wrote:
> I am feeling very cranky this morning, because I have just realized (I
> think) that FCRBs are broken. This means that the entire Coyotos message
> system is a bad design that should be abandoned. More precisely:
> [...]
> Two weeks ago, I added a "c0" slot to FCRBs to permit one capability to
> be delivered in a short message (aside: we need a c1 as well). This is
> necessary in order for the reply capability to be transmitted. The
> assumption was that c0 would be delivered to a capability register when
> the FCRB was delivered to the activation handler. Obviously, this
> overwrites the destination register.
> 
> Unfortunately, the activation/de-activation mechanism does not provide
> any way to move/save that register, which means that we are going to
> clobber valid and important state.

I must be missing something. Why can't fcrb.c0 be updated while the
preemption handler is running, or on preemption return?

Sandro