bug#17771: 24.3.91; SIGSEGV in cleanup_vector

[Eli Zaretskii <eliz@gnu.org>]

> From: Stephen Berman <stephen.berman@gmx.net>
> Cc: 17771@debbugs.gnu.org
> Date: Fri, 13 Jun 2014 16:13:42 +0200
> 
> > I installed a trivial workaround for that in r117235 on the emacs-24
> > branch.  The diffs are below.  Can you try this and see if the problem
> > is solved?  It's possible that the real problem is somewhere else, in
> > which case you will probably see it when you apply the patch.
> 
> With the patch, Emacs still crashes with the same recipe, but the first
> frame of backtrace is different (looks like not in Emacs):

I think it's just a bogus pointer to the font driver, and somehow
valid_font_driver doesn't catch it in time.

> Program received signal SIGSEGV, Segmentation fault.
> 0x0000000000c260b2 in ?? ()
> (gdb) bt full
> #0  0x0000000000c260b2 in ?? ()
> No symbol table info available.
> #1  0x00000000005aa580 in cleanup_vector (vector=0x3dd52c8)
>     at ../../../../bzr/emacs/emacs-24/src/alloc.c:2935
>         drv = 0x3dd5130
> #2  0x00000000005aa686 in sweep_vectors ()
>     at ../../../../bzr/emacs/emacs-24/src/alloc.c:2974
>         total_bytes = 140737488344592
>         free_this_block = false
>         nbytes = 1048
>         block = 0x3dd4680
>         bprev = 0xbf1060
>         lv = 0x6282a3 <balance_intervals+31>
>         lvprev = 0xbf2070
>         vector = 0x3dd52c8
>         next = 0x3dd52c8
> #3  0x00000000005b0141 in gc_sweep () at ../../../../bzr/emacs/emacs-24/src/alloc.c:6721

So Dmitry, I think Stephen here just found you a perfect recipe to
reproduce bug #16140, something that I failed to do.  Could you please
look into this?

Thanks.