--- a/src/hotspot/share/classfile/javaClasses.cpp	Fri Apr 05 07:10:07 2019 -0400
+++ b/src/hotspot/share/classfile/javaClasses.cpp	Fri Apr 05 10:01:09 2019 +0100
@@ -218,7 +218,7 @@
 
 void java_lang_String::set_compact_strings(bool value) {
   CompactStringsFixup fix(value);
-  InstanceKlass::cast(SystemDictionary::String_klass())->do_local_static_fields(&fix);
+  SystemDictionary::String_klass()->do_local_static_fields(&fix);
 }
 
 Handle java_lang_String::basic_create(int length, bool is_latin1, TRAPS) {
@@ -3991,6 +3991,48 @@
 int java_lang_System::out_offset_in_bytes() { return static_out_offset; }
 int java_lang_System::err_offset_in_bytes() { return static_err_offset; }
 
+// Support for jdk_internal_misc_UnsafeConstants
+//
+class UnsafeConstantsFixup : public FieldClosure {
+private:
+  int _address_size;
+  int _page_size;
+  bool _big_endian;
+  bool _use_unaligned_access;
+public:
+  UnsafeConstantsFixup() {
+    // round up values for all static final fields
+    _address_size = sizeof(void*);
+    _page_size = os::vm_page_size();
+    _big_endian = LITTLE_ENDIAN_ONLY(false) BIG_ENDIAN_ONLY(true);
+    _use_unaligned_access = UseUnalignedAccesses;
+  }
+
+  void do_field(fieldDescriptor* fd) {
+    oop mirror = fd->field_holder()->java_mirror();
+    assert(mirror != NULL, "UnsafeConstants must have mirror already");
+    assert(fd->field_holder() == SystemDictionary::UnsafeConstants_klass(), "Should be UnsafeConstants");
+    assert(fd->is_final(), "fields of UnsafeConstants must be final");
+    assert(fd->is_static(), "fields of UnsafeConstants must be static");
+    if (fd->name() == vmSymbols::address_size_name()) {
+      mirror->int_field_put(fd->offset(), _address_size);
+    } else if (fd->name() == vmSymbols::page_size_name()) {
+      mirror->int_field_put(fd->offset(), _page_size);
+    } else if (fd->name() == vmSymbols::big_endian_name()) {
+      mirror->bool_field_put(fd->offset(), _big_endian);
+    } else if (fd->name() == vmSymbols::use_unaligned_access_name()) {
+      mirror->bool_field_put(fd->offset(), _use_unaligned_access);
+    } else {
+      assert(false, "unexpected UnsafeConstants field");
+    }
+  }
+};
+
+void jdk_internal_misc_UnsafeConstants::set_unsafe_constants() {
+  UnsafeConstantsFixup fixup;
+  SystemDictionary::UnsafeConstants_klass()->do_local_static_fields(&fixup);
+}
+
 int java_lang_Class::_klass_offset;
 int java_lang_Class::_array_klass_offset;
 int java_lang_Class::_oop_size_offset;