RE: [Xen-ia64-devel] Floating-point software assist (FPSWA)

["Luck, Tony" <tony.luck@xxxxxxxxx>]

> To minic native behavior, can we provide a single physical copy of FPSWA
> for whole system without copying for each new domain created?

I'm not sure how easy it is for you to figure out the start/end of
the FPSWA code.  The EFI interface just provides the entry point
and revision number of the handler, not a start,end (or start,len)
pair.  You might be able to deduce the bounds by looking at the
efi memory map and picking the entire block that contains the
entry point ... but that may be more than you need (or conceivably
in some bizarre situation might be less if the EFI loader did separate
allocations for text/data of the fpswa.efi code).

Your original idea of fixing the FPSWA faults in Xen, and providing
the illusion of a fully implemented FPU to the guest sounds like a
better idea.  It does mean that the guest will see different behaivour
from a native implementation ... but I can't immediately see why this
would cause any problems[1] ... but there might be some code complexity
in making sure that exceptions that should be raised by the fpswa
code get mapped correctly to the guest so that the right signals are
sent to the process.

-Tony

[1] Unless there is some application that relies on seeing the
"floating point assist fault" messages in the console log of the
guest, but this seems highly improbable.

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