Re: [patch/rfc,rfa:ppc64] Add osabi wildcard support

[Daniel Jacobowitz <drow@mvista.com>]

On Fri, Oct 24, 2003 at 10:31:11AM -0400, Andrew Cagney wrote:
> >and the second is to explicitly register both of these architecture 
> >variants vis:
> >
> >  gdbarch_register_osabi (bfd_arch_powerpc, bfd_mach_ppc, ...
> >  gdbarch_register_osabi (bfd_arch_powerpc, bfd_mach_ppc64, ...
> 
> plus, I believe, either
> + gdbarch_register_osabi (bfd_arch_rs6000, bfd_mach_rs6k);
> or:
> + gdbarch_register_osabi (bfd_arch_powerpc, bfd_mach_rs6k);
> 
> Per this post:
> http://sources.redhat.com/ml/binutils/2003-10/msg00543.html
> rs6000:6000 isn't considered compatible with the generic PPC, and hence 
> the OSABI code couldn't find a match.  That lead to the warning.

Excuse the rambling.  I always have to type this out to figure out
which way it goes.

From bfd/cpu-powerpc.c, I see:
    case bfd_arch_rs6000:
      if (a->mach == bfd_mach_ppc)
        return a;

Let's take:
  ppc = {bfd_arch_powerpc, bfd_mach_ppc};
  ppcrs6k = {bfd_arch_powerpc, bfd_mach_rs6k};
  rs6k = {bfd_arch_rs6000, bfd_mach_rs6k};

We call default_arch->compatible (default_arch, handler_arch).  That's
"can the default architecture run code for the architecture being
handled".

We call rs6k->compatible(rs6k, ppc).  That's "an rs6k can run code
written for a generic powerpc", which returns false.  The only true one
is rs6k->compatible(rs6k, rs6k) or rs6k->compatible(rs6k, ppcrs6k): an
rs6k can not run generic ppc code but it can run ppc/rs6k code.  So
your suggestion seems right.

Confusingly, a generic ppc can run code for any rs6k according to the
compatible function.  That threw me a loop.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer