Re: Building the igc branch on MS-Windows

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 27 Apr 2024 14:44:57 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: eller.helmut@gmail.com, emacs-devel@gnu.org
> 
> I added both ascii_font and extra to fix_face, but the segfault is
> still there.  What else can be done to dig into this crash?

Not sure if this helps, but what I see  when Emacs crashes is that it
happens when the display code needs to use a face that is cached under
index 22 in the frame's face cache.  That face seems to be clobbered,
but all the 22 faces before it in the face cache are valid.  The
cache's 'used' count is 57, so index 22 should be valid.  It sounds
like some part of the cache was released or relocated, but we weren't
told about that.

Looking at the related parts in igc.c, I'm confused by how we handle
frames, their face caches, and the faces themselves.  We have:

  . fix_face
  . fix_face_cache
  . IGC_OBJ_FACE and IGC_OBJ_FACE_CACHE cases in dflt_scanx
  . call to IGC_FIX12_RAW (ss, &f->face_cache) in fix_frame
  . igc_make_face_cache (which seems to treat a face cache as a PVEC??)

Can you explain what each one of these do (or is supposed to do) in
the context of this puzzle?