[Bug gdb/18074] crash using "info frame"

["palves at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=18074

Pedro Alves <palves at redhat dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |palves at redhat dot com

--- Comment #1 from Pedro Alves <palves at redhat dot com> ---
Man, we _still_ haven't fixed this...  :-/

"frame ADDR" / "info frame ADDR" are very broken at several levels, IMO.  Even
though in your case, you explicitly wanted a frame at an address, the fact that
the user can typo a frame number and GDB ends up creating a new frame on the
spot is quite misleading.  It should be an explicit switch for "create frame if
you can't find it in the frame frame", IMO:

  https://sourceware.org/ml/gdb/2014-11/msg00028.html

In addition, I think I'd expect "bt" after "frame ADDR" to attempt to
backtracing starting at that created frame.

The crash in this case is a different bogosity: parse_frame_specification at
the tail end creates the new frame, but "current_frame" is not set to point at
it.  So, here:

3808          while (VALUE_LVAL (new_val) == lval_register && value_lazy
(new_val))
3809            {
3810              struct frame_id frame_id = VALUE_FRAME_ID (new_val);
3811
3812              frame = frame_find_by_id (frame_id);
3813              regnum = VALUE_REGNUM (new_val);

This looks up that frame that was created for ADDR in the frame chain, starting
at current_frame, and of course that never finds that hacked up frame...

Maybe parse_frame_specification should override current_frame.  But it isn't
that simple: we also need to handle the cases where gdb switches thread/frame
behind the user's back temporarily, and then restores them
(do_restore_current_thread_cleanup / restore_selected_frame use), in which case
we'd need to restore that cooked up frame.

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