[PATCH roland/arm-avoid-pc] ARM: Support avoiding pc as destination register.

[Roland McGrath]

> I expect these various patches will need updating after Richard's changes 

Yes.  I've updated all my branches after those went in.  I'm completing the
re-testing today and will post new versions of each when they're verified.

> ... also, is there an ABI document explaining the exact restrictions 
> involved, especially as regards pc-avoidance?

I don't think there is anything that is either up to date or concise.
https://sites.google.com/a/chromium.org/dev/nativeclient/reference/arm-overview
is something you might find informative.

For the particular issue at hand, it's enough to know that the platform
prohibits all operations using pc as a destination register.  Only the
various explicit branch operations are allowed.  The platform also requires
ARMv7-A as its baseline, so "bx" is always available.


Thanks,
Roland