vm: update callback stub machine code at the end of compaction to prevent it from seeing an inconsistent data stack

vm/callbacks.cpp

@@ -62,6 +62,23 @@ code_block *callback_heap::add(cell owner)
 	return stub;
 }
 
+struct callback_updater {
+	callback_heap *callbacks;
+
+	explicit callback_updater(callback_heap *callbacks_) : callbacks(callbacks_) {}
+
+	void operator()(code_block *stub)
+	{
+		callbacks->update(stub);
+	}
+};
+
+void callback_heap::update()
+{
+	callback_updater updater(this);
+	each_callback(updater);
+}
+
 void factor_vm::primitive_callback()
 {
 	tagged<word> w(dpop());

vm/callbacks.hpp

@@ -41,6 +41,8 @@ struct callback_heap {
 	void update(code_block *stub);
 	code_block *add(cell owner);
 
+	void update();
+
 	code_block *next(code_block *stub)
 	{
 		return (code_block *)((cell)stub + stub->size());

vm/compaction.cpp

@@ -206,6 +206,7 @@ void factor_vm::collect_compact_impl(bool trace_contexts_p)
 	}
 
 	update_code_roots_for_compaction();
+	callbacks->update();
 
 	current_gc->event->ended_compaction();
 }
@@ -252,6 +253,7 @@ void factor_vm::collect_compact_code_impl(bool trace_contexts_p)
 	code->allocator->compact(code_block_updater,code_block_sizer);
 
 	update_code_roots_for_compaction();
+	callbacks->update();
 }
 
 void factor_vm::collect_compact(bool trace_contexts_p)

vm/slot_visitor.hpp

@@ -120,7 +120,6 @@ struct callback_slot_visitor {
 	void operator()(code_block *stub)
 	{
 		visitor->visit_handle(&stub->owner);
-		callbacks->update(stub);
 	}
 };