Re: Unifying the x86 FPU register sets

[Mark Kettenis <kettenis at wins dot uva dot nl>]

   From: Jim Blandy <jimb@cygnus.com>
   Date: 15 Oct 1999 18:57:31 -0500

   It would certainly be possible to allow the register sizes vary from
   one platform to the next, and make sure i387-tdep.c relies entirely on
   the macros and tables to do its job.  But to do that, we would need to
   design the macros more carefully than I have --- I don't think they're
   sufficient for the job right now.  I'd rather have them be fixed.

Actually I think they are fine, since I no longer see a reason for
different register sizes on different i386 platforms.

   We could make the control registers (except $fdoff and $fcoff)
   sixteen-bit values.  But that makes more work for platforms that do
   use FSAVE's 32-bit format; I assume those are the majority.

Although initially I thought I needed to use different register sizes
to implement things for exactly that format, I now see that I don't
need that.  The reserved bits are exactly in the right place to treat
it as an array of 32-bit values.  Only the code segment and opcode
registers need to be treated in a different way, as you did on the
Linux side.

A remaining issue is what we do with the reserved bits?  From looking
at your code, it seems that you allow the user to modify the reserved
bits (except for the reserved bit in the opcode word).  Is that a
sensible thing to do?

Mark