8048353: jstack -l crashes VM when a Java mirror for a primitive type is locked

Reviewed-by: coleenp, dcubed

src/share/vm/classfile/javaClasses.cpp

@@ -782,6 +782,22 @@ Symbol* java_lang_Class::as_signature(oop java_class, bool intern_if_not_found,
   return name;
 }
 
+// Returns the Java name for this Java mirror (Resource allocated)
+// See Klass::external_name().
+// For primitive type Java mirrors, its type name is returned.
+const char* java_lang_Class::as_external_name(oop java_class) {
+  assert(java_lang_Class::is_instance(java_class), "must be a Class object");
+  const char* name = NULL;
+  if (is_primitive(java_class)) {
+    name = type2name(primitive_type(java_class));
+  } else {
+    name = as_Klass(java_class)->external_name();
+  }
+  if (name == NULL) {
+    name = "<null>";
+  }
+  return name;
+}
 
 Klass* java_lang_Class::array_klass(oop java_class) {
   Klass* k = ((Klass*)java_class->metadata_field(_array_klass_offset));

src/share/vm/classfile/javaClasses.hpp

@@ -270,6 +270,7 @@ class java_lang_Class : AllStatic {
   }
   static Symbol* as_signature(oop java_class, bool intern_if_not_found, TRAPS);
   static void print_signature(oop java_class, outputStream *st);
+  static const char* as_external_name(oop java_class);
   // Testing
   static bool is_instance(oop obj) {
     return obj != NULL && obj->klass() == SystemDictionary::Class_klass();

src/share/vm/runtime/vframe.cpp

@@ -148,8 +148,7 @@ static void print_locked_object_class_name(outputStream* st, Handle obj, const c
   if (obj.not_null()) {
     st->print("\t- %s <" INTPTR_FORMAT "> ", lock_state, (address)obj());
     if (obj->klass() == SystemDictionary::Class_klass()) {
-      Klass* target_klass = java_lang_Class::as_Klass(obj());
-      st->print_cr("(a java.lang.Class for %s)", InstanceKlass::cast(target_klass)->external_name());
+      st->print_cr("(a java.lang.Class for %s)", java_lang_Class::as_external_name(obj()));
     } else {
       Klass* k = obj->klass();
       st->print_cr("(a %s)", k->external_name());