[rfc] 'union' handling for Fortran (in GDB)

[Steve Kargl]

On Sun, Jul 01, 2007 at 06:15:50PM -0400, Daniel Jacobowitz wrote:
> I can't make a sensible decision about this; I know roughly nothing
> of what Fortran programmers would expect.  So I'm copying your message
> to the GCC Fortran list, and I hope someone there has a suggestion.
> 
> For fortran@, the context starts here:
>   http://sourceware.org/ml/gdb-patches/2007-06/msg00131.html
> 
> The SPU has a number of vector registers.  Their type is represented
> in GDB as a union of useful views.  When you're in Fortran mode,
> there's no way to handle unions, and it's hard to see the registers.
> 
> I think that we could add union handling if someone familiar with
> Fortran wants to pick a fake syntax, suitably unlikely to mean
> something in a later revision of Fortran, or something equivalent from
> the current Fortran.  Equivalences don't seem to be quite the same
> thing.
> 
> Or we could come up with an entirely different way to represent vector
> registers in GDB.  The current representation is not very helpful
> sometimes.  Maybe we should display the register in only one type
> by default, as a giant hex string, and provide built-in functions
> to convert it to other types.
> 
> I'm open to ideas :-)
> 

Hi Daniel,

Technically, this is outside the scope of the Fortran language
in that the language has no concept of register.  If these registers
are accessed through a union, then the nearest construct in the Fortran
language is EQUIVALENCE.  But as you said, EQUIVALENCE does feel
quite right.  Unfortunately, I suspect most gfortran contributors
know very little about gdb internals.

I personally like your idea of printing registers as a hex string.
The verbose syntax could be 'print register 1'.  It someone wanted
all the registers, then 'print registers' or 'print register all'.
One could sub 'show' for 'print'.

-- 
Steve