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


From: Glenn Morris
Subject: Fwd: Crash when buffer is edited while save-buffer asks for coding system
Date: Wed, 09 Jan 2008 19:45:15 -0500
User-agent: Gnus (www.gnus.org), GNU Emacs (www.gnu.org/software/emacs/)

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.


--- Begin Message --- Subject: Crash when buffer is edited while save-buffer asks for coding system Date: Tue, 25 Dec 2007 01:34:00 +0100 User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; de; rv:1.8.1.6) Gecko/20070728 Thunderbird/2.0.0.6 Mnenhy/0.7.5.0
Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:


Manual way:
- emacs -Q
- Create a new text file
- C-x RET f windows-1252 RET
- insert "Hi"
- M-x ucs-insert RET 2122 RET (inserts a trademark symbol)
- C-x C-s
- C-x RET f latin-1 RET C-x C-s
- Emacs will ask for a coding system, since latin-1 does not contain the
  trademark symbol.
- C-x C-o until point is in your file with the trademark
- C-a C-d to delete the first character
- C-x C-o until point is back at minibuffer
- RET
- "Would you like to attach a debugger?" I guess you will select Yes
  here :)

Automatic way:

(progn
  (with-current-buffer (find-file-noselect (make-temp-file
                                            "charsetbug"))
    (set-buffer-file-coding-system 'windows-1252)
    (insert "Hi")
    (ucs-insert 8482) ;; trademark sign
    (save-buffer 0)
    (setq buf (current-buffer))
    (pop-to-buffer buf))
  (set-buffer buf)
  (set-buffer-file-coding-system 'latin-1)
  (defun abcd () (interactive)
    (let ((wnd (selected-window)))
    (select-window (get-buffer-window buf))
    (goto-char (point-min))
    (delete-char 1)
    (select-window wnd)
    (execute-kbd-macro "\r")))
  (global-set-key "\C-cq" 'abcd)
  (execute-kbd-macro "\C-x\C-s\C-cq"))

Merry Christmas! :)



In GNU Emacs 22.1.1 (i386-mingw-nt5.1.2600)
 of 2007-06-02 on RELEASE
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4) --cflags -Ic:/gnuwin32/include'

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: DEU
  locale-coding-system: cp1252
  default-enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  encoded-kbd-mode: t
  tooltip-mode: t
  tool-bar-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  unify-8859-on-encoding-mode: t
  utf-translate-cjk-mode: t
  auto-compression-mode: t
  line-number-mode: t

Recent input:
M-x r e p o r t - e m a c s - b u g <return>

Recent messages:
("D:\\Progs\\emacs\\bin\\emacs.exe" "-q")
Loading encoded-kb...done
For information about the GNU Project and its goals, type C-h C-p. [2 times]
Loading emacsbug...
Loading regexp-opt...done
Loading emacsbug...done

--- End Message ---

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