--- old/src/hotspot/share/memory/filemap.cpp	2019-03-27 11:33:19.346006320 -0700
+++ new/src/hotspot/share/memory/filemap.cpp	2019-03-27 11:33:19.174000180 -0700
@@ -24,6 +24,7 @@
 
 #include "precompiled.hpp"
 #include "jvm.h"
+#include "classfile/classFileStream.hpp"
 #include "classfile/classLoader.inline.hpp"
 #include "classfile/classLoaderData.inline.hpp"
 #include "classfile/classLoaderExt.hpp"
@@ -1502,7 +1503,12 @@
   const char* const class_name = name->as_C_string();
   const char* const file_name = ClassLoader::file_name_for_class_name(class_name,
                                                                       name->utf8_length());
-  return cpe->open_stream_for_loader(file_name, ClassLoaderData::class_loader_data(class_loader()), THREAD);
+  ClassLoaderData* loader_data = ClassLoaderData::class_loader_data(class_loader());
+  ClassFileStream* cfs = cpe->open_stream_for_loader(file_name, loader_data, THREAD);
+  assert(cfs != NULL, "must be able to read the classfile data of shared classes for built-in loaders.");
+  log_debug(cds, jvmti)("classfile data for %s [%d: %s] = %d bytes", class_name, path_index,
+                        cfs->source(), cfs->length());
+  return cfs;
 }
 
 #endif