Re: [PATCH] Fix frame ID comparison problem on s390

[Andrew Cagney <cagney at gnu dot org>]

> Daniel Jacobowitz wrote:
>
>
> > > Rather than cheat in the backend - most other backends will probably
> > > have the same issue - I'd like to know what's actually using the code
> > > wildcard.
>
>
> I have no idea -- maybe this is obsolete by now?
>
> The following patch simply removes the wild card feature, and it works
> for s390 without test suite regressions (and fixes the signull failure
> as well).
>
> I've tried to look at the other platforms, but they appear not to be
> using the wild card feature either ...

Symbol table code often returns 0 to indicate a failed lookup (here a 
search for the function containing pc).  That zero can end up in the 
frame ID.  Look at calls to get_frame_func / frame_func_unwind (which 
I've proposed eliminating).

From memory architectures that do not implement dummy ID unwind also 
end up with wild-card IDs (fortunatly the dummy-frame code works around 
this).

Broken tramp unwinders often leave the .code address zero (see paragraph 
#1 for why).

Andrew