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Re: Fwd: Crash when buffer is edited while save-buffer asks for coding s

From: Kenichi Handa
Subject: Re: Fwd: Crash when buffer is edited while save-buffer asks for coding system
Date: Thu, 10 Jan 2008 10:31:19 +0900
User-agent: SEMI/1.14.3 (Ushinoya) FLIM/1.14.2 (Yagi-Nishiguchi) APEL/10.2 Emacs/23.0.60 (i686-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO)

In article <address@hidden>, Glenn Morris <address@hidden> writes:

> Does anyone have any ideas about this? It causes a reproducible crash
> (see very nice recipe below) with the current EMACS_22_BASE on
> Gnu/Linux, so it would be good to fix.

> It happens because when Fwrite_region calls
> Vselect_safe_coding_system_function, it opens a window for the user to
> modify the buffer mid-save. The abort in buf_charpos_to_bytepos in
> marker.c due to changed buffer size is what causes the actual crash.

> One easy solution is to for Fwrite_region to make the buffer read-only
> while Vselect_safe_coding_system_function is called. That will protect
> against accidental editing of the buffer at least, but of course a
> determined user could still make the buffer writable again.

> Ideally, I think one would want errors during write-region to abort
> the write, not Emacs.

I installed the following fix last year, but it was only to
the trunk.  Could someone who already has the working
directory of EMACS_22_BASE install it?

2007-12-27  Kenichi Handa  <address@hidden>

        * international/mule-cmds.el (select-safe-coding-system):
        When a buffer is modified, cancel the writing.

Index: mule-cmds.el
RCS file: /cvsroot/emacs/emacs/lisp/international/mule-cmds.el,v
retrieving revision 1.316
retrieving revision 1.317
diff -u -r1.316 -r1.317
--- mule-cmds.el        6 Dec 2007 00:46:17 -0000       1.316
+++ mule-cmds.el        27 Dec 2007 10:27:21 -0000      1.317
@@ -966,6 +966,7 @@
     (let ((codings (find-coding-systems-region from to))
          (coding-system nil)
+         (tick (if (not (stringp from)) (buffer-modified-tick)))
          safe rejected unsafe)
       (if (eq (car codings) 'undecided)
          ;; Any coding system is ok.
@@ -1030,6 +1031,8 @@
 %s specified by file contents.  Really save (else edit coding cookies \
 and try again)? " coding-system auto-cs))
              (error "Save aborted"))))
+      (when (and tick (/= tick (buffer-modified-tick)))
+       (error "Cancelled because the buffer was modified"))
 (setq select-safe-coding-system-function 'select-safe-coding-system)

Diffs between 1.316 and 1.317 end here.

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