bug#41321: 27.0.91; Emacs aborts due to invalid pseudovector objects

[Eli Zaretskii]

> From: Pip Cet <pipcet@gmail.com>
> Date: Sat, 30 May 2020 16:36:31 +0000
> Cc: eggert@cs.ucla.edu, 41321@debbugs.gnu.org, 
>       Stefan Monnier <monnier@iro.umontreal.ca>
> 
> On Sat, May 30, 2020 at 4:32 PM Eli Zaretskii <eliz@gnu.org> wrote:
> > > From: Pip Cet <pipcet@gmail.com>
> > > Date: Sat, 30 May 2020 13:29:33 +0000
> > > Cc: eggert@cs.ucla.edu, 41321@debbugs.gnu.org,
> > >       Stefan Monnier <monnier@iro.umontreal.ca>
> > > (The runtime stack isn't relevant, as far as I can tell, since we walk
> > > that in 4-byte steps on such systems anyway.)
> >
> > I think it might be relevant for stack-based Lisp objects (if we keep
> > requiring that Lisp objects are 8-byte aligned on 32-bit platforms).
> 
> We should never mark stack-based Lisp objects, no matter how
> well-aligned they are!

But we do require them to be aligned, at least in the current
codebase.  We actually had crashes in the past when the Windows build
didn't force GCC to align stack on 8-byte boundary in callback
functions.  I don't remember if this was related to GC or not, but the
requirement is definitely there.