Fix missing write barrier on class fields

jhawthorn · jhawthorn · commit 912edb471626 · 2025-06-18T20:54:01.000-07:00
Found by wbcheck

    klass = Class.new
    200.times do |iv|
      klass.instance_variable_set("@_iv_#{iv}", Object.new)
    end
diff --git a/variable.c b/variable.c
@@ -4726,7 +4726,12 @@ class_fields_ivar_set(VALUE klass, VALUE fields_obj, ID id, VALUE val, bool conc
             // so that we're embedded as long as possible.
             fields_obj = rb_imemo_fields_new(rb_singleton_class(klass), next_capacity);
             if (original_fields_obj) {
-                MEMCPY(rb_imemo_fields_ptr(fields_obj), rb_imemo_fields_ptr(original_fields_obj), VALUE, RSHAPE_LEN(current_shape_id));
+                VALUE *fields = rb_imemo_fields_ptr(fields_obj);
+                attr_index_t fields_count = RSHAPE_LEN(current_shape_id);
+                MEMCPY(fields, rb_imemo_fields_ptr(original_fields_obj), VALUE, fields_count);
+                for (attr_index_t i = 0; i < fields_count; i++) {
+                    RB_OBJ_WRITTEN(fields_obj, Qundef, fields[i]);
+                }
             }
         }
 

Original file line number	Diff line number	Diff line change
`@@ -4726,7 +4726,12 @@ class_fields_ivar_set(VALUE klass, VALUE fields_obj, ID id, VALUE val, bool conc`
`4726`	`4726`	`// so that we're embedded as long as possible.`
`4727`	`4727`	`fields_obj = rb_imemo_fields_new(rb_singleton_class(klass), next_capacity);`
`4728`	`4728`	`if (original_fields_obj) {`
`4729`		`- MEMCPY(rb_imemo_fields_ptr(fields_obj), rb_imemo_fields_ptr(original_fields_obj), VALUE, RSHAPE_LEN(current_shape_id));`
	`4729`	`+ VALUE *fields = rb_imemo_fields_ptr(fields_obj);`
	`4730`	`+ attr_index_t fields_count = RSHAPE_LEN(current_shape_id);`
	`4731`	`+ MEMCPY(fields, rb_imemo_fields_ptr(original_fields_obj), VALUE, fields_count);`
	`4732`	`+ for (attr_index_t i = 0; i < fields_count; i++) {`
	`4733`	`+ RB_OBJ_WRITTEN(fields_obj, Qundef, fields[i]);`
	`4734`	`+ }`
`4730`	`4735`	`}`
`4731`	`4736`	`}`
`4732`	`4737`