Make sure we mark reachable killed buffers during GC

* src/alloc.c (live_buffer_holding): Add ALL_BUFFERS argument for
returning killed buffers.
(mark_maybe_object, mark_maybe_pointer): Use the additional
argument.  (Bug#39962)

Author: pipcet

src/alloc.c

@@ -4597,20 +4597,22 @@ live_vector_p (struct mem_node *m, void *p)
 }
 
 /* If P is a pointer into a live buffer, return the buffer.
-   Otherwise, return nil.  M is a pointer to the mem_block for P.  */
+   Otherwise, return nil.  M is a pointer to the mem_block for P.
+   Also return killed buffers if ALL-BUFFERS is true.  */
 
 static Lisp_Object
-live_buffer_holding (struct mem_node *m, void *p)
+live_buffer_holding (struct mem_node *m, void *p, bool all_buffers)
 {
-  /* P must point into the block, and the buffer
-     must not have been killed.  */
+  /* P must point into the block, and the buffer must not
+     have been killed unless ALL-BUFFERS is true.  */
   if (m->type == MEM_TYPE_BUFFER)
     {
       struct buffer *b = m->start;
       char *cb = m->start;
       char *cp = p;
       ptrdiff_t offset = cp - cb;
-      if (0 <= offset && offset < sizeof *b && !NILP (b->name_))
+      if (0 <= offset && offset < sizeof *b
+	  && (all_buffers || !NILP (b->name_)))
 	{
 	  Lisp_Object obj;
 	  XSETBUFFER (obj, b);
@@ -4623,7 +4625,7 @@ live_buffer_holding (struct mem_node *m, void *p)
 static bool
 live_buffer_p (struct mem_node *m, void *p)
 {
-  return !NILP (live_buffer_holding (m, p));
+  return !NILP (live_buffer_holding (m, p, false));
 }
 
 /* Mark OBJ if we can prove it's a Lisp_Object.  */
@@ -4681,7 +4683,7 @@ mark_maybe_object (Lisp_Object obj)
 
 	case Lisp_Vectorlike:
 	  mark_p = (EQ (obj, live_vector_holding (m, po))
-		    || EQ (obj, live_buffer_holding (m, po)));
+		    || EQ (obj, live_buffer_holding (m, po, true)));
 	  break;
 
 	default:
@@ -4751,7 +4753,7 @@ mark_maybe_pointer (void *p)
 	  break;
 
 	case MEM_TYPE_BUFFER:
-	  obj = live_buffer_holding (m, p);
+	  obj = live_buffer_holding (m, p, true);
 	  break;
 
 	case MEM_TYPE_CONS: