Re: [Emacs-diffs] master 8ba156f: Attempt to avoid crashes in plist-member

[Eli Zaretskii <eliz@gnu.org>]

> Cc: emacs-devel@gnu.org
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Mon, 12 Oct 2015 20:36:06 -0700
> 
>     QUIT could call some Lisp.
>
> Sure, but Lisp cannot affect the value of CONSP (plist).

Not the value of CONSP, the list itself.  We follow the CONSP test
with XCAR, which crashed.  The only way I could imagine that happening
is that the list got modified between the test and the XCAR call.  Is
there any other way to explain that?

>     How else would you explain a segfault in that loop?
> 
> It's not clear the code is in that loop.

The address clearly points to Fplist_member at fns.c:2879.

> It could merely be RtlCaptureStackBackTrace misbehaving, no?

I don't think so.  It could be something else, though: the segfault
could have happened in another thread while the Lisp thread was in
plist-member.

But the change I made cannot do any harm, and it tried to use the only
evidence I had from the report.  The alternative was to do nothing at
all.