Re: i386 register numbering

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

   Date: Sat, 28 Jul 2001 11:13:15 -0400
   From: Andrew Cagney <ac131313@cygnus.com>

   They map a stab/dwarf/... reg onto a cooked regnum (not to be confused 
   with a raw reg found in the register cache).  Because the i386 
   implements its registers using the old PSUEDO / CONVERT stuff, the 
   importance of differentiating between the two may not be obvious.

For most of the registers on the i386, the raw and the cooked regnum
will probably be the same.  MMX will probably end up as a cooked
registers some day (since they provide a different view on the
standard FP registers).  I cannot see how I can get rid of the convert
stuff for the FP registers though.  On the i386 the FP registers can
contain a `float', `double' or `long double' but the internal
representation in the FP register is identical.  Turning every FP
register into three cooked registers won't work since in the debug
info they will all have the same register number :-(.

   There is something here I don't get either.

   At present it is assumed that, for a given ISA/ABI, there is only one 
   mapping from a DEBUG reg to a REGNUM.  I take it, Mark, that you're 
   saying that in reality, the mapping depends on all of:

   {compiler, object format, debug format, ISA/ABI} (debug reg) -> REGNUM

   True? Ulgh!

That's another way to put it.  Note that GDB allows for different
mappings for each debug format.  When we go multi-arch, we can easily
differentiate by object format too just like for ISA/ABI.  The only
compiler that I have access to is GCC, so I don't know whether there
are other compilers out there that use different numbering schemes.
However, since there doesn't seem to be any standard, I suspect that
they will, at least for the FP, SSE and MMX registers.

We can probably deal with all these differences.  It just means a bit
more work :-(.

Mark