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From: Eli Zaretskii <eliz@gnu.org>
Newsgroups: gmane.emacs.devel
Subject: Re: (select-window nil) crash with gcc-8.2.0
Date: Sun, 07 Apr 2019 19:16:30 +0300
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To: Andreas Schwab <schwab@linux-m68k.org>
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> From: Andreas Schwab <schwab@linux-m68k.org>
> Date: Sun, 07 Apr 2019 09:13:44 +0200
> Cc: emacs-devel@gnu.org
> 
> On Apr 07 2019, Madhu <enometh@meer.net> wrote:
> 
> > the problem is that if gcc is producing the wrong code then the
> > backtrace is unreliable.  This is not the backtrace one would expect
> > from calling (select-window nil).
> 
> Step through select_window to see where it goes wrong.

Right.  And I'm afraid the stepping will need to be done on machine
instruction level, i.e. "stepi", not "step".  The backtrace looks
completely bogus, it doesn't even show the file names correctly, let
alone line numbers.

The main issue here is why CHECK_LIVE_WINDOW doesn't do its job in
that case.  It does here, and signals an error because nil is not a
live window.