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

[Pip Cet]

On Sun, May 24, 2020 at 6:40 PM Eli Zaretskii <eliz@gnu.org> wrote:
> > From: Pip Cet <pipcet@gmail.com>
> > Date: Sun, 24 May 2020 18:03:57 +0000
> > Cc: 41321@debbugs.gnu.org, Stefan Monnier <monnier@iro.umontreal.ca>
> >
> > > If you still claim that I didn't demonstrate that the buffer's overlay
> > > chain got corrupted
> >
> > I do, of course. The message GDB prints simply does not say anything
> > problematic about the buffer's overlay chain.
> >
> > > as part of the bug that caused the segfault,
> > > please point out what I missed here.
> >
> > You omitted the third call to xtype, which was even more clearly
> > nonsensical: xtype was misbehaving. We don't know in which way it was
> > misbehaving. So there's no evidence either way.
> >
> > FWIW, running into gdb bugs is something that happens to me almost on
> > a regular basis. There's no point reporting those, as there's
> > generally no response. In your case, you're in an unusual environment
> > with a rather large and complicated .gdbinit file which does very
> > strange things to avoid running into GDB bugs that we know about. All
> > that increases the likelihood of your encountering a gdb bug that no
> > one else has, or that has been reported but never responded to.
>
> I don't buy this, sorry.

So you think there's a second bug, located in Emacs, which causes GDB,
which isn't supposed to be broken by anything the debuggee does, to be
broken and respond in nonsensical ways?

> I use GDB every day in this very "unusual
> environment", both when debugging Emacs and other programs.

And you've never run into GDB bugs?

> The
> probability of these being due to some bug in GDB or in .gdbinit
> commands is very low, as I and others use them all the time.

I'm perfectly willing to help you trace down this bug (in GDB or
.gdbinit; we've already found the bug in mingw and the one in Emacs)
if it serves any purpose, but I suspect you don't have the time.

But I can't conceive of an explanation in which a bug in Emacs could
cause a bug-free GDB to respond in the nonsensical way your last
invocation of xtype did.

> It is much more probable that the commands I've shown are signs of a real
> trouble in Emacs and not in GDB.

Are you saying the bug I've found isn't "a real trouble"? I'm curious
as to what trouble you're imagining.

> I'm not willing to disregard what
> those commands show me because they don't match your theory.

What they show you is that memory at a certain address, which they
helpfully specify, isn't mapped.

You conclude that memory at a totally different address isn't mapped,
even though GDB quite explicitly never says so.

That conclusion is invalid.