1 files changed, 73 insertions, 0 deletions

diff --git a/src/alloc.c b/src/alloc.c
index 47fa6820102..be4c82d0a1e 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -1816,6 +1816,46 @@ Garbage collection happens automatically if you cons more than\n\
     }  
   mark_kboards ();
 
+  /* Look thru every buffer's undo list
+     for elements that update markers that were not marked,
+     and delete them.  */
+  {
+    register struct buffer *nextb = all_buffers;
+
+    while (nextb)
+      {
+        /* If a buffer's undo list is Qt, that means that undo is
+           turned off in that buffer.  Calling truncate_undo_list on
+           Qt tends to return NULL, which effectively turns undo back on.
+           So don't call truncate_undo_list if undo_list is Qt.  */
+        if (! EQ (nextb->undo_list, Qt))
+          {
+            Lisp_Object tail, prev;
+            tail = nextb->undo_list;
+            prev = Qnil;
+            while (CONSP (tail))
+              {
+                if (GC_CONSP (XCONS (tail)->car)
+                    && GC_MARKERP (XCONS (XCONS (tail)->car)->car)
+                    && ! XMARKBIT (XMARKER (XCONS (XCONS (tail)->car)->car)->chain))
+                  {
+                    if (NILP (prev))
+                      nextb->undo_list = tail = XCONS (tail)->cdr;
+                    else
+                      tail = XCONS (prev)->cdr = XCONS (tail)->cdr;
+                  }
+                else
+                  {
+                    prev = tail;
+                    tail = XCONS (tail)->cdr;
+                  }
+              }
+          }
+
+        nextb = nextb->next;
+      }
+  }
+
   gc_sweep ();
 
   /* Clear the mark bits that we set in certain root slots.  */
@@ -2228,6 +2268,39 @@ mark_buffer (buf)
 
   MARK_INTERVAL_TREE (BUF_INTERVALS (buffer));
 
+  if (CONSP (buffer->undo_list))
+    {
+      Lisp_Object tail;
+      tail = buffer->undo_list;
+
+      while (CONSP (tail))
+        {
+          register struct Lisp_Cons *ptr = XCONS (tail);
+
+          if (XMARKBIT (ptr->car))
+            break;
+          XMARK (ptr->car);
+          if (GC_CONSP (ptr->car)
+              && ! XMARKBIT (XCONS (ptr->car)->car)
+              && GC_MARKERP (XCONS (ptr->car)->car))
+            {
+              XMARK (XCONS (ptr->car)->car);
+              mark_object (&XCONS (ptr->car)->cdr);
+            }
+          else
+            mark_object (&ptr->car);
+
+          if (CONSP (ptr->cdr))
+            tail = ptr->cdr;
+          else
+            break;
+        }
+
+      mark_object (&XCONS (tail)->cdr);
+    }
+  else
+    mark_object (&buffer->undo_list);
+
 #if 0
   mark_object (buffer->syntax_table);