Fix crash in method call in `ObjectSpace.each_object` block.

* Filter `MRB_TT_ENV` and `MRB_TT_ICLASS`.
* Set `mrb->string_class` in `mrb_init_exception` instead.

mrbgems/mruby-objectspace/src/mruby_objectspace.c

@@ -119,6 +119,13 @@ os_each_object_cb(mrb_state *mrb, struct RBasic *obj, void *ud)
     return;
   }
 
+  /* filter internal objects */
+  switch (obj->tt) {
+  case MRB_TT_ENV:
+  case MRB_TT_ICLASS:
+    return;
+  }
+
   /* filter class kind if target module defined */
   if (d->target_module && !mrb_obj_is_kind_of(mrb, mrb_obj_value(obj), d->target_module)) {
     return;

mrbgems/mruby-objectspace/test/objectspace.rb

@@ -54,3 +54,7 @@ assert('ObjectSpace.each_object') do
   assert_equal arys.length, arys_count
   assert_true arys.length < objs.length
 end
+
+assert 'Check class pointer of ObjectSpace.each_object.' do
+  ObjectSpace.each_object { |obj| !obj }
+end

src/error.c

@@ -91,15 +91,10 @@ static mrb_value
 exc_to_s(mrb_state *mrb, mrb_value exc)
 {
   mrb_value mesg = mrb_attr_get(mrb, exc, mrb_intern_lit(mrb, "mesg"));
-  struct RObject *p;
 
   if (!mrb_string_p(mesg)) {
     return mrb_str_new_cstr(mrb, mrb_obj_classname(mrb, exc));
   }
-  p = mrb_obj_ptr(mesg);
-  if (!p->c) {
-    p->c = mrb->string_class;
-  }
   return mesg;
 }
 
@@ -441,6 +436,9 @@ mrb_init_exception(mrb_state *mrb)
 {
   struct RClass *exception, *runtime_error, *script_error;
 
+  /* initialize mrb->string_class before creating RString object for nomem_err */
+  mrb->string_class = mrb_define_class(mrb, "String", mrb->object_class);
+
   mrb->eException_class = exception = mrb_define_class(mrb, "Exception", mrb->object_class); /* 15.2.22 */
   mrb_define_class_method(mrb, exception, "exception", mrb_instance_new,  MRB_ARGS_ANY());
   mrb_define_method(mrb, exception, "exception",       exc_exception,     MRB_ARGS_ANY());