GNU bug report logs - #79116
31.0.50; Crash on IGC build

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From: Helmut Eller <eller.helmut <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: spd <at> toadstyle.org, pipcet <at> protonmail.com, 79116 <at> debbugs.gnu.org
Subject: bug#79116: 31.0.50; Crash on IGC build
Date: Wed, 30 Jul 2025 18:31:39 +0200

On Wed, Jul 30 2025, Eli Zaretskii wrote:

> You seem to be talking about the data structures manipulated by the
> display engine, but the thread which got hit with SIGABRT was not the
> main thread (which indeed was in redisplay), it's some other thread.
> And I wonder how come that other thread called MPS.

I think that's the usual way how page faults are handled on MacOS:

  1. the main thread hits a memory barrier (in this case in redisplay)

  2. the Mach kernel stops the main thread and sends an message to
     process' exception port

  3. there is a dedicated thread that reads the message from the
     exception port.  It's this thread that calls into MPS and
     copies/scans objects as needed.  In this case that triggered the
     assertion.

I'm not sure when or how the main thread is resumed. Gerd would
certainly know.

Helmut

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