bug#71929: 30.0.60; crash in mark_image_cache

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

>> Cc: 71929@debbugs.gnu.org
>> Date: Thu, 04 Jul 2024 08:53:41 +0300
>> From: Eli Zaretskii <eliz@gnu.org>
>> 
>> > From: Sean Whitton <spwhitton@spwhitton.name>
>> > Date: Thu, 04 Jul 2024 10:44:04 +0800
>> > 
>> > Hello,
>> > 
>> > On Thu 04 Jul 2024 at 10:33am +08, Sean Whitton wrote:
>> > 
>> > > My pgtk Emacs keeps crashing.  This time I think I caught it.
>> > > I see there was a recent commit to code around here; if this backtrace
>> > > is not sufficient, I can try bisecting, but I cannot currently reproduce
>> > > the crash reliably.
>> > >
>> > > Thread 1 "emacs" received signal SIGSEGV, Segmentation fault.
>> > > 0x00005555557a2c51 in mark_image_cache (c=0x55555729fc70) at image.c:3775
>> > > 3775             if (c->images[i])
>> > > (gdb)
>> > 
>> > ... and i was 0, i.e. it crashes on the first iteration.
>> 
>> What is the value of c->images?  IOW, why did this line segfault?
>
> Also, what is the value of c->refcount?

Please answer these questions, yes.