Re: [patch/rfc] Add a sentinel frame

[Daniel Jacobowitz <drow@mvista.com>]

On Wed, Feb 19, 2003 at 11:51:40AM -0500, Andrew Cagney wrote:
> >On Wed, Feb 19, 2003 at 08:32:32AM -0500, Andrew Cagney wrote:
> >
> >>So I think it is one of these tests going awall:
> >>
> >>  if (next_frame->level >= 0
> >>      && !backtrace_below_main
> >>      && inside_main_func (get_frame_pc (next_frame)))
> >>    /* Don't unwind past main(), bug always unwind the sentinel frame.
> >>       Note, this is done _before_ the frame has been marked as
> >>       previously unwound.  That way if the user later decides to
> >>       allow unwinds past main(), that just happens.  */
> >>    return NULL;
> >>
> >>  /* If we're inside the entry file, it isn't valid.  */
> >>  /* NOTE: drow/2002-12-25: should there be a way to disable this
> >>     check?  It assumes a single small entry file, and the way some
> >>     debug readers (e.g.  dbxread) figure out which object is the
> >>     entry file is somewhat hokey.  */
> >>  /* NOTE: cagney/2003-01-10: If there is a way of disabling this test
> >>     then it should probably be moved to before the ->prev_p test,
> >>     above.  */
> >>  if (inside_entry_file (get_frame_pc (next_frame)))
> >>      return NULL;
> >>
> >>The second looks worrying (the dummy frame breakpoint lives in the entry 
> >>file ...).  Perhaphs something like:
> >>
> >>if (dummy_frame_p (get_frame_pc (next_frame) != NULL
> >>    && inside_entry_file (get_frame_pc (next_frame))
> >>  return NULL;
> >
> >
> >Hrm, shouldn't we have already detected the dummy frame at this point? 
> 
> No.  GDB is trying to perform:
> 
> 	pop_frame (get_current_frame())
> 
> with the assumption that it has a dummy frame and get_current_frame() 
> will return it.
> 
> >That's what happens on i386 IIRC...

I thought that we wouldn't reach frame_chain_valid if the next frame
was a dummy frame.  Hmm, that only seems to happen for deprecated
generic dummy frames:

  if (DEPRECATED_USE_GENERIC_DUMMY_FRAMES
      && DEPRECATED_PC_IN_CALL_DUMMY (get_frame_pc (fi), 0, 0))
    return 1;

Oh I didn't realize the contents of frame_chain_valid had ended up
repeated in get_prev_frame, I've been looking at the wrong function.
That's why I didn't understand you.  Should the check above exist in
get_prev_frame also?

[Why does this logic need to be in more than one place?]

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer