Re: RFA: handle missing fpregs

[Jim Blandy <jimb at redhat dot com>]

Jason Thorpe <thorpej@wasabisystems.com> writes:

> On May 10, 2004, at 3:15 PM, Jim Blandy wrote:
> 
> > Thanks for looking at this.
> >
> > How about changing the comment to this:
> >
> >   /* FIXME: jimb/2004-05-05: Some PPC variants don't have floating
> >      point registers.  Traditionally, GDB's register set has still
> >      listed the floating point registers for such machines, so this
> >      code is harmless.  However, the new E500 port actually omits the
> >      floating point registers entirely from the register set --- they
> >      don't even have register numbers assigned to them.
> >
> >      It's not clear to me how best to update this code, so this assert
> >      will alert the first person to encounter the NetBSD/E500
> >      combination to the problem.  */
> 
> Ah, this clarifies the situation greatly.  I didn't realize that we
> were in E500 land with this change.

That is the storied and mysterious terrain I tenant for the time
being.  :)

> > How is the change to the code itself?  The present code, if run when
> > the current architecture is the E500, will just inappropriate numbers
> > for the floating-point registers and hit the assert in
> > regcache_raw_supply, if you're lucky.  So the change is an improvement
> > over the current state of affairs.
> 
> If I am to understand correctly, the assert won't trip on e.g. 405 or
> 440... if that is true (i.e. does not break NetBSD FPU-less PowerPC
> support that currently works), then it's OK with me.

That's right.  The patch changes ppc_floating_point_p to return true
unless fp0 or fpscr do not have register numbers, and it arranges for
that to occur only on the E500.  So it shouldn't affect the behavior
of anything unless you're running on an E500.

I've (re-)committed this change.