Re: RFA: Fix check for no-saved-pc

[Michael Snyder <msnyder at specifix dot com>]

Mark, is the 2nd form of the patch acceptable to you?

On Fri, 2007-11-30 at 17:37 -0800, Michael Snyder wrote:
> On Fri, 2007-11-30 at 18:00 -0500, Daniel Jacobowitz wrote:
> > On Fri, Nov 30, 2007 at 02:40:31PM -0800, Michael Snyder wrote:
> > > There's a check in get_prev_frame to see if the next saved pc
> > > is zero.  I think it has an off-by-one error, and is checking 
> > > for the pc of the wrong frame.
> > 
> > Mark K. and I have had roughly a month's worth of discussion on this
> > check over the last two years; it's where it is on purpose.  Here's
> > the last conversation:
> > 
> >   http://sourceware.org/ml/gdb-patches/2006-05/msg00196.html
> >   http://sourceware.org/ml/gdb-patches/2006-07/msg00296.html
> 
> All right.  Then let's leave that test alone, and add another
> test, much later on, to detect and report this situation.
> 
> Here's my revised patch.  Testsuites un-affected.
> 
> As before, the effect of this change is to have gdb print
> a more informative message instead of a meaningless zero-frame.
> 
> 2007-11-30  Michael Snyder  <msnyder@specifix.com>
> 
> 	* frame.c (get_prev_frame): Remove unused local variable.
> 	(get_prev_frame_1): Check for null saved pc in the calling 
> 	frame.  Set up stop_reason conditions for printing stop reason.
> 
> Index: frame.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/frame.c,v
> retrieving revision 1.235
> diff -u -p -r1.235 frame.c
> --- frame.c	2 Nov 2007 14:47:27 -0000	1.235
> +++ frame.c	1 Dec 2007 01:30:01 -0000
> @@ -1248,6 +1248,16 @@ get_prev_frame_1 (struct frame_info *thi
>  	  this_frame->prev = NULL;
>  	  return NULL;
>  	}
> +      /* Also check for a null saved_pc.  At this point it can 
> +	 only be a bad thing.  */
> +      if (frame_pc_unwind (this_frame) == 0)
> +	{
> +	  frame_debug_got_null_frame (gdb_stdlog, this_frame, 
> +				      "zero PC");
> +	  this_frame->stop_reason = UNWIND_NO_SAVED_PC;
> +	  this_frame->prev = NULL;
> +	  return NULL;
> +	}
>      }
>  
>    /* Allocate the new frame but do not wire it in to the frame chain.
> @@ -1355,8 +1365,6 @@ inside_entry_func (struct frame_info *th
>  struct frame_info *
>  get_prev_frame (struct frame_info *this_frame)
>  {
> -  struct frame_info *prev_frame;
> -
>    /* Return the inner-most frame, when the caller passes in NULL.  */
>    /* NOTE: cagney/2002-11-09: Not sure how this would happen.  The
>       caller should have previously obtained a valid frame using
> 
>