On Sun, May 05 2024, Gerd Möllmann wrote:

>> Would something like this also be needed for glyph matrices?  
>
> Probably. Either we make the matrices roots, or objects, I guess. For
> correctness. We can't easily realloc when they are objects, but I don't
> think that's a big problem.
>
>> Or in general, can we scan anything other than the block that
>> dflt_scan was called with? 
>
> Let's say we shouldn't :-). MPS lets us scan memory it doesn't manage,
> but with multi-threading it's not really safe.

So fix_glyph_matrix currently doesn't things exactly by the book.  Hm.

Anyway, I have a patch that prevents my Emacs from sporadically crashing
at startup.