Re: [RFA] mips-tdep.c: Add dwarf/dwarf2 regnum mapping functions

[Andrew Cagney <ac131313@redhat.com>]

>> mips_tdep could certainly gain a local tdep->fp0_regnum though.
> 
> 
> Did you notice the references to FP0_REGNUM in mips-linux-tdep.c and
> mips-nat.c?.  If we do as you suggest, an access method will need to
> be added to mips-tdep.h for getting at tdep->fp0_regnum (since you
> refuse to export the mips tdep struct).  Also, all occurrences of
> FP0_REGNUM in mips-linux-tdep.c and mips-nat.c will need to be
> rewritten to use this access method.

I ignored everything that wasn't core.
Such a rewrite goes on my to-do list.

> Certainly all of this could be done, but the need to know the first
> floating point register number is something that's shared among a
> number of ports.  Doesn't it makes sense to define (as has already
> been done) a common mechanism for determining this register number
> rather than letting each port develop ad hoc methods?

The problem is that FP0_REGNUM has no narrow and well defined meaning. 
  Same problem as with SP_REGNUM, PC_REGNUM, FP_REGNUM.

As a specific example.  Given an ISA with 64 bit FP registers that is 
running a 32 bit FP ABI (debug info refers to 32 bit FP registers). 
/proc assumes FP0_REGNUM designates the first 64 bit [raw] FP register, 
yet dwarf2 assumes that FP0_REGNUM designates the first 32 bit [cooked] 
FP register.

It doesn't work (well, ok the current mess involving register 
convertible kind of half sort of makes it appear to work).  Per previous 
  patches, that code needs an overhaul.

Andrew