(mark_object): Ignore Lisp_Misc_Free objects.

Such objects may be freed markers which still exist on an undo list.

1 files changed, 10 insertions, 1 deletions

diff --git a/src/alloc.c b/src/alloc.c
index b5a96953adb..dd4823bd9e3 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -844,7 +844,7 @@ lisp_align_free (block)
   free_ablock = ablock;
   /* Update busy count.  */
   ABLOCKS_BUSY (abase) = (struct ablocks *) (-2 + (long) ABLOCKS_BUSY (abase));
-  
+
   if (2 > (long) ABLOCKS_BUSY (abase))
     { /* All the blocks are free.  */
       int i = 0, aligned = (long) ABLOCKS_BUSY (abase);
@@ -4976,6 +4976,15 @@ mark_object (arg)
       break;
 
     case Lisp_Misc:
+      if (XMISCTYPE (obj) == Lisp_Misc_Free)
+        {
+          /* This is (probably) a freed marker which may still exist on
+             a buffer undo list, so accept it here.  */
+          /* If we reuse the marker, and it still exists on the undo
+             list, and we do undo, behaviour is unpredictable --
+             but at least we don't crash here.  KFS 2004-05-17 */
+          break;
+        }
       CHECK_ALLOCATED_AND_LIVE (live_misc_p);
       if (XMARKER (obj)->gcmarkbit)
         break;