[PATCH] Backport PR47324 to gcc 4.5 branch

[Jack Howarth]

On Wed, Feb 16, 2011 at 09:32:33PM -0500, Jason Merrill wrote:
> I'm certainly sympathetic; this seems like a problem that is definitely  
> worth fixing, I'm just concerned about the potential for unforseen  
> consequences.  I think I'll defer to the release managers on this 
> question.
>
> Jason

Jason,
   Our main problem on darwin, since FSF gcc 4.5, is that we now use always
use the system unwinder (obtained from libgcc_s.10.4/10.5 for darwin8/9 or
from libSystem for darwin10). Unfortunately Apple doesn't ship debug versions
of those libraries so it is impossible to walk through the system unwinder
to debug issues. In theory one ought to be able to build the required debug
code from the darwin open source releses from Apple, however in practice this
apparently requires over 20 darwin open source packages to be built first in
an entirely undocumented procedure. So we should be esctatic to have found such
an obvious wrong code generation bug in the FSF gcc unwind code generation.
           Jack
ps While we could file a radar requesting that Apple provide these debug libraries, it
would be problematic since that would have to release new debug libraries with each
system update (which would either require a sister software update package from Apple
or bloat their current software updates).