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

[Daniel Berlin <dan@dberlin.org>]

On Tue, 9 Apr 2002, Andrew Cagney wrote:

> 
> >> 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.
> 
Okeydokey.

> > 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).

Libraries have debug info as well.

Even those without debug info, can still have dwarf2 frame info.
Most do these days.
You just don't realize it.
The default libc that came with my ppc linux distribution contains unwind 
info for all routines, fer instance. It's glibc 2.2.4 based, for the 
curious.  I installed this distribution a *while* ago, so it's not a 
recent happening.
All the libraries have unwind info as well.
No debug info, just unwind info.
> 
> I think that is a significant feature loss and one I don't consder 
> acceptable.
Who says you have lost a feature?
> 
> I see no reason why GDB shouldn't act ``illegally'' and use the 
> traditional prolog scanner as a fallback to debug info.
Now you've twisted my words.
I said it would be illegal to attempt to use .eh_frame under the 
assumption it contains unwind info for all routines. It might, it might 
not.
I said nothing about prolog scanning, besides that it is unnecessary when 
the dwarf2 unwind info is present.
 > 
> Andrew
>