Bring back rb_mark_generic_ivar for mmtk compat

Author: byroot

gc.c

@@ -3087,10 +3087,7 @@ rb_gc_mark_children(void *objspace, VALUE obj)
     struct gc_mark_classext_foreach_arg foreach_args;
 
     if (rb_obj_exivar_p(obj)) {
-        VALUE fields_obj = rb_obj_fields_no_ractor_check(obj);
-        if (fields_obj) {
-            gc_mark_internal(fields_obj);
-        }
+        rb_mark_generic_ivar(obj);
     }
 
     switch (BUILTIN_TYPE(obj)) {

internal/variable.h

@@ -56,6 +56,7 @@ void rb_obj_field_set(VALUE obj, shape_id_t target_shape_id, ID field_name, VALU
 
 RUBY_SYMBOL_EXPORT_BEGIN
 /* variable.c (export) */
+void rb_mark_generic_ivar(VALUE obj);
 VALUE rb_const_missing(VALUE klass, VALUE name);
 bool rb_class_ivar_set(VALUE klass, ID vid, VALUE value);
 void rb_fields_tbl_copy(VALUE dst, VALUE src);

variable.c

@@ -1211,6 +1211,16 @@ rb_generic_fields_tbl_get(void)
     return generic_fields_tbl_;
 }
 
+void
+rb_mark_generic_ivar(VALUE obj)
+{
+    VALUE data;
+    // Bypass ASSERT_vm_locking() check because marking may happen concurrently with mmtk
+    if (st_lookup(generic_fields_tbl_, (st_data_t)obj, (st_data_t *)&data)) {
+        rb_gc_mark_movable(data);
+    }
+}
+
 VALUE
 rb_obj_fields(VALUE obj, ID field_name)
 {