bug#38748: 28.0.50; crash on MacOS 10.15.2

[Eli Zaretskii]

> From: Pip Cet <pipcet@gmail.com>
> Date: Wed, 8 Jan 2020 20:39:43 +0000
> Cc: rpluim@gmail.com, alan@idiocy.org, jguenther@gmail.com, 
>       andreyk.mad@gmail.com, 38748@debbugs.gnu.org
> 
> > No, GC is known to take many thousands of recursive calls to
> > mark_object.  9000 is not a particularly high number, and doesn't
> > necessarily signal infinite recursion.
> 
> In general, you're absolutely correct. But in this case, it still
> sounds very likely: infinite recursion of a properly tail-recursive
> function would loop rather than cause a stack overflow, which would
> explain everything, except for why it's not actually an infinite loop;
> I suspect the macOS code somewhere does modify things asynchronously.

The backtrace shows a very recursive GC, it doesn't show any other
function being deeply recursive.  So I'm not sure I understand what
tail-recursive function did you have in mind.  Can you elaborate?