patch for printing 64-bit values in i386 registers; STABS format

[Andrew Cagney]

>  - stabs would have to be modified (if we did this fixup in each and
> every debug reader, instead of in read_var_value and friends; I see
> good arguments both ways)

It would hopefully be a shared function that those debug readers could 
call.  The important thing is that the core code only knows about one 
mechanism.

>> >This is one of the intended purposes of this mechanism, and as I 
> 
>> >>indicated, is needed by MIPS.  Being able to project an arbitrary [debug 
>> >>info] view of the registers onto the raw register buffer.
>> >>
>> >>BTW, what happens when there is an attempt to write a long long value? 
>> >>GDB again assumes that it can write to contigious registers - the reason 
>> >>why REGISTER_BYTE can't be killed.
> 
>> >
>> >
>> >That ugliness could go away too with Mark's introduced method.  GDB
>> >could be fixed to find the next register properly.
> 
>> 
>> GDB also uses it to encode offsets into a register.  It also does not 
>> help the MIPS where the debug register does need to be projected into 
>> the raw registers.   Why have add more mechanisms when the existing one 
>> is sufficient.  Focus the effort on fixing the real problem.
>> 
>> BTW, my comment about no names was wrong.  They can be named, that 
>> restriction should have been removed by the introduction of reggroups.
> 
> 
> Well, in that case I guess it would work.  Let's do it?
> 
> It still feels much more like a hack to me than Mark's approach; I'll
> just quietly disagree I suppose.

Hmm, I think it will be needed anyway, what happens when the user is 
debugging an i386 mode function (with 32 bit register based long long 
debug info) on an x86-64 target?  That's the MIPS problem, and it needs 
that projection(1).

Also, the next_regnum method assumes that all debug infos use the same 
register sequencing.

A word of caution though, the projection, at the register level works. 
Frame's might need tweaking.  The alternative is to start out with 
deprecated_next_regnum so that it is clear where this stands.

Andrew

(1) dwarf2 debug info makes certain assumptions about the size of registers