[patch] Add support for single register window model on SPARC

[Mark Kettenis]

> From: Eric Botcazou <ebotcazou@adacore.com>
> Date: Tue, 21 Jun 2011 20:08:10 +0200
> 
> > Hmm, if full CFI for the explicit register saving code is emitted, I'd
> > expect backtraces to work.
> 
> Exceptions work well so the CFIs are very likely correct, at least
> in eh_frame.  A quick look didn't reveal differences between
> eh_frame and debug_frame so this is a little strange then.  Is GDB
> supposed to fall back to "manual" unwinding only when the DWARF
> unwinder gives up?

Typically, yes, but because of:

  /* FIXME: kettenis/20050423: Don't enable the unwinder until the
     StackGhost issues have been resolved.  */

we only install the DWARF unwinder for Linux, and I guess you tested
on some other platform.

> > StackGhost again.  Better leave this alone as well.
> 
> Yes, there is a bit of code duplication in these files. ;-)

Somewhat difficult to avoid though.

> Revised patch attached, will retest if approved.

No regression on OpenBSD/sparc64, so all fine with me.