think-o: dwarf2 CFA != frame->frame (x86-64)

[Andrew Cagney]

>> Please re-read what I wrote.
> 
> 
> You said " The problem is that this algorithm assumes that each frame uses 
> the same mechanism for locating register values.  With
>                        the introduction of dwarf2cfi, this is no longer 
> true.  Some frames may use the debug info while others may use the
>                        old prologue analysis technique.
> "
> 
> You are incorrect.

We're going to have to agree to disagree.

> It's an either-or case. Never is their a mixture of methods, unless you do 
> something illegal.

If GDB decides to do what you state, it will be incapable of unwinding 
through libraries (where there is no debug info).

I think that is a significant feature loss and one I don't consder 
acceptable.

I see no reason why GDB shouldn't act ``illegally'' and use the 
traditional prolog scanner as a fallback to debug info.

Andrew