Remove unportable assumption about struct layout (Bug#8884).

* buffer.c (clone_per_buffer_values): Don't assume that
sizeof (struct buffer) is a multiple of sizeof (Lisp_Object).
This isn't true in general, and it's particularly not true
if Emacs is configured with --with-wide-int.
* buffer.h (FIRST_FIELD_PER_BUFFER, LAST_FIELD_PER_BUFFER):
New macros, used in the buffer.c change.

src/ChangeLog

+2011-07-06  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Remove unportable assumption about struct layout (Bug#8884).
+	* buffer.c (clone_per_buffer_values): Don't assume that
+	sizeof (struct buffer) is a multiple of sizeof (Lisp_Object).
+	This isn't true in general, and it's particularly not true
+	if Emacs is configured with --with-wide-int.
+	* buffer.h (FIRST_FIELD_PER_BUFFER, LAST_FIELD_PER_BUFFER):
+	New macros, used in the buffer.c change.
+
 2011-07-05  Jan Djärv  <jan.h.d@swipnet.se>
 
 	* xsettings.c: Use both GConf and GSettings if both are available.

src/buffer.c

@@ -471,8 +471,8 @@ clone_per_buffer_values (struct buffer *from, struct buffer *to)
 
   /* buffer-local Lisp variables start at `undo_list',
      tho only the ones from `name' on are GC'd normally.  */
-  for (offset = PER_BUFFER_VAR_OFFSET (undo_list);
-       offset < sizeof *to;
+  for (offset = PER_BUFFER_VAR_OFFSET (FIRST_FIELD_PER_BUFFER);
+       offset <= PER_BUFFER_VAR_OFFSET (LAST_FIELD_PER_BUFFER);
        offset += sizeof (Lisp_Object))
     {
       Lisp_Object obj;

src/buffer.h

@@ -612,6 +612,7 @@ struct buffer
   /* Everything from here down must be a Lisp_Object.  */
   /* buffer-local Lisp variables start at `undo_list',
      tho only the ones from `name' on are GC'd normally.  */
+  #define FIRST_FIELD_PER_BUFFER undo_list
 
   /* Changes in the buffer are recorded here for undo.
      t means don't record anything.
@@ -846,6 +847,9 @@ struct buffer
      t means to use hollow box cursor.
      See `cursor-type' for other values.  */
   Lisp_Object BUFFER_INTERNAL_FIELD (cursor_in_non_selected_windows);
+
+  /* This must be the last field in the above list.  */
+  #define LAST_FIELD_PER_BUFFER cursor_in_non_selected_windows
 };