Re: [patch/rfc] Add a sentinel frame

Daniel Jacobowitz
2003-02-19T16:56:27Z

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