>
> In general, Emacs can only prevent GTK from handling certain events. 
> If it handles an event that it must handle (in this case, 
> XI_HierarchyChange) incorrectly, and that causes GTK to later 
> dereference NULL, there is nothing that Emacs can do.  Just like what 
> happens when GTK calls _exit under our nose.
>

I sent a short demo that shows how one can escape from an _exit a few 
weeks ago in bug#56967; I attach it here again.  The same kind of things 
can be done to circumvent segfaults in library functions.