--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/hotspot/jtreg/vmTestbase/gc/g1/unloading/bytecode/BytecodeMutatorFactory.java	Thu May 17 14:52:47 2018 -0700
@@ -0,0 +1,125 @@
+/*
+ * Copyright (c) 2014, 2018, 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.
+ */
+package gc.g1.unloading.bytecode;
+
+import java.io.*;
+import java.nio.charset.*;
+import java.util.*;
+
+
+/**
+ * This BytecodeFactory produces bytecode that is golden bytecode with className substituted.
+ */
+public class BytecodeMutatorFactory implements BytecodeFactory {
+
+    private static final String FILLER_CHARACTER = "_";
+
+    /**
+     * Utility method in this class
+     */
+    public static String padName(String s, int length) {
+        int difference = length - s.length();
+        StringBuilder sb = new StringBuilder(s);
+        for (int i = 0; i < difference; i++) {
+            sb.append(FILLER_CHARACTER);
+        }
+        return sb.toString();
+    }
+
+    public String padName(String s) {
+        return padName(s, getNameLength());
+    }
+
+    private final Charset CHARACTER_SET = StandardCharsets.UTF_8;
+
+    private List<Integer> offsets = new LinkedList<>();
+
+    private byte[] templateBytecode;
+
+    private String templateClassName;
+
+    private byte[] templateClassNameAsBytes;
+
+    public BytecodeMutatorFactory() {
+        this(DefaultTemplateClass.class.getName());
+    }
+
+    public BytecodeMutatorFactory(String templateClassName) {
+        this.templateClassName = templateClassName;
+
+        // Read bytecode to array
+        InputStream is = ClassLoader.getSystemResourceAsStream(templateClassName.replace('.', '/').concat(".class"));
+        try {
+            templateBytecode = new byte[is.available()];
+            is.read(templateBytecode);
+            is.close();
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+
+        // Save offsets
+        templateClassNameAsBytes = templateClassName.replace('.', '/').getBytes(CHARACTER_SET);
+        for (int i = 0; i < templateBytecode.length; i++) {
+            boolean match = true;
+            for (int j = 0; j < templateClassNameAsBytes.length; j++) {
+                if (i + j >= templateBytecode.length || templateClassNameAsBytes[j] != templateBytecode[i + j]) {
+                    match = false;
+                    break;
+                }
+            }
+            if (match) {
+                offsets.add(i);
+            }
+        }
+    }
+
+    public byte[] getBytecode(String className) {
+
+        // Check size of name constraint
+        byte[] newClassNameAsBytes = className.replace('.', '/').getBytes(CHARACTER_SET);
+        if (newClassNameAsBytes.length != templateClassNameAsBytes.length) {
+            throw new RuntimeException("Can't produce bytecode with \"" + className + "\" substituted as class name. " +
+                    "Length of this name differs from length of \"" + templateClassName + "\" which equals to " + templateClassName.length() +
+                    ". Length of \"" + className + "\" is " + className.length() + ".");
+        }
+
+        // Prepare bytecode
+        byte[] result = Arrays.copyOf(templateBytecode, templateBytecode.length);
+        for (int offset : offsets) {
+            System.arraycopy(newClassNameAsBytes, 0, result, offset, newClassNameAsBytes.length);
+        }
+        return result;
+    }
+
+    public int getNameLength() {
+        return templateClassName.length();
+    }
+
+    @Override
+    public Bytecode createBytecode(String className) {
+        String finalClassName = padName(className);
+        byte[] bytecode = getBytecode(finalClassName);
+        return new Bytecode(finalClassName, bytecode);
+    }
+
+}