From: Eli Zaretskii <eliz@gnu.org>
To: Dmitry Gutov <dgutov@yandex.ru>
Cc: 13743@debbugs.gnu.org
Subject: bug#13743: 24.2.93; Segmentation fault when trying to [s]teal a file opened elsewhere
Date: Mon, 25 Feb 2013 18:25:26 +0200 [thread overview]
Message-ID: <831uc4jr7t.fsf@gnu.org> (raw)
In-Reply-To: <512AFC18.4090504@yandex.ru>
> Date: Mon, 25 Feb 2013 09:52:24 +0400
> From: Dmitry Gutov <dgutov@yandex.ru>
> CC: monnier@iro.umontreal.ca, 13743@debbugs.gnu.org
>
> OTOH, the existing behavior in this area is rather messy anyway:
>
> a) If START equals to the beginning of the region with the same
> property, the buffer is marked modified anyway (even though nothing
> changes from the observer's point of view).
>
> So, the trivial example of repeating an `add-text-properties' call with
> the same arguments in a previously unpropertized buffer will mark it as
> modified every time.
>
> b) This probably has something to do with internal representation, but
> even having the same property span before START is not a safe bet:
That's a bug, actually, and a very old one at that (at least 17 years
old, IIUC). The code didn't handle correctly all the situations where
there's nothing to change, before it announced a change by calling
modify_region (and later called signal_after_change).
I installed on the trunk revision 111875 to fix this. Now all your
examples:
> 1. Create a new file with a line of text in it, preferably without
> spaces, to see face changes easily
> 2. Save it, disable font-lock-mode.
> 3. Evaluate:
>
> (add-text-properties 1 6 '(face font-lock-constant-face)) => modified
> save
> (add-text-properties 2 6 '(face font-lock-constant-face)) => unmodified
> (add-text-properties 2 7 '(face font-lock-constant-face)) => modified
> save
> (add-text-properties 2 6 '(face font-lock-constant-face)) => unmodified
> - optional step
> (add-text-properties 2 7 '(face font-lock-constant-face)) => modified(!)
> - even though 1 still has the same face
> - you can save and repeat this step indefinitely
work as expected.
Interestingly, this also fixes the original segfault which started
this discussion (not before I fixed similar bugs in
remove-text-properties and elsewhere in textprop.c, because making the
change only n add-text-properties still triggered a similar segfault
from remove-text-properties). So perhaps the fact that buffer
modifications were announced unnecessarily is the root cause for the
segfault.
I couldn't convince myself that, even after revision 111875, we could
not end up in a situation where redisplay triggered by modify_region
changes the intervals when it fontifies the buffer. So perhaps we
need a followup patch to plumb that potential hole, something along
the following:
=== modified file 'src/textprop.c'
--- src/textprop.c 2013-02-25 16:13:42 +0000
+++ src/textprop.c 2013-02-25 16:23:43 +0000
@@ -1134,6 +1134,7 @@ Return t if any property value actually
register int modified = 0;
struct gcpro gcpro1;
ptrdiff_t got;
+ int first_time = 1;
properties = validate_plist (properties);
if (NILP (properties))
@@ -1142,6 +1143,7 @@ Return t if any property value actually
if (NILP (object))
XSETBUFFER (object, current_buffer);
+ retry:
i = validate_interval_range (object, &start, &end, hard);
if (!i)
return Qnil;
@@ -1174,8 +1176,25 @@ Return t if any property value actually
copy_properties (unchanged, i);
}
- if (BUFFERP (object))
- modify_region (object, start, end);
+ if (BUFFERP (object) && first_time)
+ {
+ ptrdiff_t prev_total_length = TOTAL_LENGTH (i);
+ ptrdiff_t prev_pos = i->position;
+
+ modify_region (object, start, end);
+ /* If someone called us recursively as a side effect of
+ modify_region, and changed the intervals behind our back
+ (could happen if lock_file, called by prepare_to_modify_buffer,
+ triggers redisplay, and that calls add-text-properties again
+ in the same buffer), we cannot continue with I, because its
+ data changed. So we restart the interval analysis anew. */
+ if (TOTAL_LENGTH (i) != prev_total_length
+ || i->position != prev_pos)
+ {
+ first_time = 0;
+ goto retry;
+ }
+ }
/* We are at the beginning of interval I, with LEN chars to scan. */
for (;;)
next prev parent reply other threads:[~2013-02-25 16:25 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-18 6:41 bug#13743: 24.2.93; Segmentation fault when trying to [s]teal a file opened elsewhere Dmitry Gutov
2013-02-18 16:11 ` Eli Zaretskii
2013-02-19 0:52 ` Dmitry Gutov
2013-02-20 19:31 ` Eli Zaretskii
2013-02-21 8:30 ` Dmitry Gutov
2013-02-18 19:35 ` Glenn Morris
2013-02-19 0:55 ` Dmitry Gutov
2013-02-21 5:16 ` Paul Eggert
2013-02-21 7:03 ` Dmitry Gutov
2013-02-23 3:37 ` Dmitry Gutov
2013-02-23 15:10 ` Eli Zaretskii
2013-02-23 16:59 ` Stefan Monnier
2013-02-23 18:44 ` Eli Zaretskii
2013-02-24 15:28 ` Dmitry Gutov
2013-02-24 15:50 ` Eli Zaretskii
2013-02-25 5:52 ` Dmitry Gutov
2013-02-25 15:25 ` Stefan Monnier
2013-02-25 16:37 ` Eli Zaretskii
2013-02-25 18:29 ` Stefan Monnier
2013-02-25 18:56 ` Eli Zaretskii
2013-02-25 20:28 ` Stefan Monnier
2013-02-26 3:39 ` Eli Zaretskii
2013-02-26 4:35 ` Stefan Monnier
2013-03-02 9:30 ` Eli Zaretskii
2013-02-25 16:25 ` Eli Zaretskii [this message]
2013-02-25 18:27 ` Dmitry Gutov
2013-02-25 16:27 ` Eli Zaretskii
2013-02-25 19:08 ` Dmitry Gutov
2013-02-25 19:31 ` Eli Zaretskii
2013-02-25 23:23 ` Dmitry Gutov
2013-02-26 3:51 ` Eli Zaretskii
2013-02-26 3:59 ` Dmitry Gutov
2013-02-26 18:42 ` Eli Zaretskii
2013-02-27 17:46 ` Dmitry Gutov
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