8033735: make Throwable.backtrace visible to Class.getDeclaredField again

Removed old hack to workaround an old crash.

Reviewed-by: hseigel, twisti, mchung

hotspot/src/share/vm/prims/jvm.cpp

@@ -1818,9 +1818,6 @@ JVM_ENTRY(jobjectArray, JVM_GetClassDeclaredFields(JNIEnv *env, jclass ofClass,
   // Ensure class is linked
   k->link_class(CHECK_NULL);
 
-  // 4496456 We need to filter out java.lang.Throwable.backtrace
-  bool skip_backtrace = false;
-
   // Allocate result
   int num_fields;
 
@@ -1831,11 +1828,6 @@ JVM_ENTRY(jobjectArray, JVM_GetClassDeclaredFields(JNIEnv *env, jclass ofClass,
     }
   } else {
     num_fields = k->java_fields_count();
-
-    if (k() == SystemDictionary::Throwable_klass()) {
-      num_fields--;
-      skip_backtrace = true;
-    }
   }
 
   objArrayOop r = oopFactory::new_objArray(SystemDictionary::reflect_Field_klass(), num_fields, CHECK_NULL);
@@ -1844,12 +1836,6 @@ JVM_ENTRY(jobjectArray, JVM_GetClassDeclaredFields(JNIEnv *env, jclass ofClass,
   int out_idx = 0;
   fieldDescriptor fd;
   for (JavaFieldStream fs(k); !fs.done(); fs.next()) {
-    if (skip_backtrace) {
-      // 4496456 skip java.lang.Throwable.backtrace
-      int offset = fs.offset();
-      if (offset == java_lang_Throwable::get_backtrace_offset()) continue;
-    }
-
     if (!publicOnly || fs.access_flags().is_public()) {
       fd.reinitialize(k(), fs.index());
       oop field = Reflection::new_field(&fd, CHECK_NULL);

hotspot/test/runtime/Throwable/ThrowableIntrospectionSegfault.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.    See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8033735
+ * @summary check backtrace field introspection
+ * @library /testlibrary
+ * @run main ThrowableIntrospectionSegfault
+ */
+
+import java.lang.reflect.*;
+
+public class ThrowableIntrospectionSegfault {
+    public static void main(java.lang.String[] unused) {
+        // Construct a throwable object.
+        Throwable throwable = new Throwable();
+        throwable.fillInStackTrace();
+
+        // Retrieve a reflection handle to the private backtrace field.
+        Class class1 = throwable.getClass();
+        Field field;
+        try {
+            field = class1.getDeclaredField("backtrace");
+        }
+        catch (NoSuchFieldException e) {
+            System.err.println("Can't retrieve field handle Throwable.backtrace: " + e.toString());
+            return;
+        }
+        field.setAccessible(true);
+
+        // Retrieve the value of the backtrace field.
+        Object backtrace;
+        try {
+            backtrace = field.get(throwable);
+        }
+        catch (IllegalAccessException e) {
+            System.err.println( "Can't retrieve field value for Throwable.backtrace: " + e.toString());
+            return;
+        }
+
+        try {
+
+            // Retrieve the class of throwable.backtrace[0][0].
+            Class class2 = ((Object[]) ((Object[]) backtrace)[2])[0].getClass();
+
+            // Segfault occurs while executing this line, to retrieve the name of
+            // this class.
+            String class2Name = class2.getName();
+
+            System.err.println("class2Name=" + class2Name);
+            return;  // pass!   Passes if it doesn't crash.
+        } catch (ClassCastException e) {
+            // Passes if it doesn't crash. Also if the backtrace changes this test might get
+            // ClassCastException and that's ok too.
+            System.out.println("Catch exception " + e);
+            return;  // pass!   Passes if it doesn't crash.
+        }
+    }
+}