add: top->dev_ino.st_dev = TYPE_MAXIMUM (dev_t); top->dev_ino.st_ino = TYPE_MAXIMUM (ino_t);
context: AD_push_initial (Dirstack_state *ds, struct saved_cwd const *cwd){  struct AD_ent *top;  /* Extend the stack.  */  obstack_blank (&ds->Active_dir, sizeof (struct AD_ent));  /* Fill in the new values.  */  top = AD_stack_top (ds);  top->u.saved_cwd = *cwd;  top->unremovable = NULL;}