Remove more assumptions re struct layout (Bug#8884).

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
+	* alloc.c (mark_buffer):
+	* buffer.c (reset_buffer_local_variables, Fbuffer_local_variables)
+	(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.

src/alloc.c

@@ -5619,7 +5619,8 @@ mark_buffer (Lisp_Object buf)
   /* buffer-local Lisp variables start at `undo_list',
      tho only the ones from `name' on are GC'd normally.  */
   for (ptr = &buffer->BUFFER_INTERNAL_FIELD (name);
-       (char *)ptr < (char *)buffer + sizeof (struct buffer);
+       ptr <= &PER_BUFFER_VALUE (buffer,
+				 PER_BUFFER_VAR_OFFSET (LAST_FIELD_PER_BUFFER));
        ptr++)
     mark_object (*ptr);
 

src/buffer.c

@@ -830,8 +830,8 @@ reset_buffer_local_variables (register struct buffer *b, int permanent_too)
 
   /* 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 *b;
+  for (offset = PER_BUFFER_VAR_OFFSET (FIRST_FIELD_PER_BUFFER);
+       offset <= PER_BUFFER_VAR_OFFSET (LAST_FIELD_PER_BUFFER);
        offset += sizeof (Lisp_Object))
     {
       int idx = PER_BUFFER_IDX (offset);
@@ -1055,8 +1055,8 @@ No argument or nil as argument means use current buffer as BUFFER.  */)
 
     /* 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 (struct buffer);
+    for (offset = PER_BUFFER_VAR_OFFSET (FIRST_FIELD_PER_BUFFER);
+	 offset <= PER_BUFFER_VAR_OFFSET (LAST_FIELD_PER_BUFFER);
 	 /* sizeof EMACS_INT == sizeof Lisp_Object */
 	 offset += (sizeof (EMACS_INT)))
       {