GNU bug report logs - #12745
crash in bidi_pop_it during (idle) redisplay

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From: Ami Fischman <ami <at> fischman.org>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 12745 <at> debbugs.gnu.org
Subject: bug#12745: crash in bidi_pop_it during (idle) redisplay
Date: Sun, 28 Oct 2012 21:26:55 -0700

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> If it loads the same .emacs, that is good enough.
>

Ok, attached.

> So this seems to say that there's at least one overlay string at
> > > buffer position 1295.  Is that reasonable?  What was the current
> > > buffer when this crashed?  You can find that out by typing this at GDB
> > > prompt:
> > >   (gdb) pp current_buffer->name_
> > (gdb) pp current_buffer->name_
> > Cannot access memory at address 0x8b6a00
> How about this:
>   (gdb) p current_buffer->name_
>   (gdb) xtype
> (Note: "p", not "pp".)
> If the last command says it's a Lisp string, display the contents of
> 'struct Lisp_String' whose address it shows.
>

(gdb) p current_buffer->name_
$22 = 101548849
(gdb) xtype
Lisp_String
(gdb) xstring current_buffer->name_
$23 = (struct Lisp_String *) 0x60d8330
  "cdm_wrapper.cc"


> > >   (gdb) p current_buffer->text->beg[1200]@100
> >  (gdb) p current_buffer->text->beg[1200]@100
> > $1 = "num to avoid later static_cast in\n// PluginInstance.\nenum
> > MediaKeyError {\n  kUnknownError = 1,\n  kCl"
> > which tells me the current buffer was an edited version of
> >
> http://src.chromium.org/viewvc/chrome/trunk/src/webkit/media/crypto/ppapi/cdm_wrapper.cc?view=markup(which
> Did that buffer have any minor mode or some other optional feature
> turned on, in addition to C++ Mode?


See attached b-g-e.txt, in which the current buffer is the same .cc file in
my HEAD session loading the same .emacs as the crashed one.

> Possibly interestingly, if I print p current_buffer->text->beg[0]@100000
> to
> > emit the entire buffer, I see this text starting at char 1675:
> > http://go", '\000' <repeats 2000 times>, "/b
> > Those 2000 NULs are definitely out of place (the URL should have started
> > with http://go/b) but I don't know if that's a debugging artifact, or
> what.
>
> This could be the gap, you should see its position and size like this:
>
>   (gdb) p current_buffer->text->gpt
>   (gdb) p current_buffer->text->gap_size


Yep, looks like it:
(gdb) p current_buffer->text->gpt
$24 = 1684
(gdb) p current_buffer->text->gap_size
$25 = 2000

> > (gdb) frame 6
> > > #6  0x0000000000447aa1 in pop_it (it=0x7fff2251f1e0) at xdisp.c:5769
> > > 5769          bidi_pop_it (&it->bidi_it);
> > > (gdb) pgrowx it->glyph_row
> > You can't do that without a process to debug.
> So are you debugging a core dump?
>

Yes.

-a

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[b-g-e.txt (text/plain, attachment)]

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