8359707: Add classfile modification code to RedefineClassHelper

Reviewed-by: lmesnik, dholmes, sspitsyn

Author: coleenp

test/hotspot/jtreg/serviceability/jvmti/RedefineClasses/ClassVersionAfterRedefine.java

@@ -32,68 +32,27 @@
  * @run main/othervm -javaagent:redefineagent.jar ClassVersionAfterRedefine
  */
 
-import java.io.InputStream;
 import java.lang.reflect.Method;
 
 import static jdk.test.lib.Asserts.assertTrue;
 
 public class ClassVersionAfterRedefine extends ClassLoader {
 
-    private static String myName = ClassVersionAfterRedefine.class.getName();
-
-    private static byte[] getBytecodes(String name) throws Exception {
-        InputStream is = ClassVersionAfterRedefine.class.getResourceAsStream(name + ".class");
-        byte[] buf = is.readAllBytes();
-        System.out.println("sizeof(" + name + ".class) == " + buf.length);
-        return buf;
-    }
-
-    private static int getStringIndex(String needle, byte[] buf) {
-        return getStringIndex(needle, buf, 0);
-    }
-
-    private static int getStringIndex(String needle, byte[] buf, int offset) {
-        outer:
-        for (int i = offset; i < buf.length - offset - needle.length(); i++) {
-            for (int j = 0; j < needle.length(); j++) {
-                if (buf[i + j] != (byte)needle.charAt(j)) continue outer;
-            }
-            return i;
-        }
-        return 0;
-    }
-
-    private static void replaceString(byte[] buf, String name, int index) {
-        for (int i = index; i < index + name.length(); i++) {
-            buf[i] = (byte)name.charAt(i - index);
-        }
-    }
-
-    private static void replaceAllStrings(byte[] buf, String oldString, String newString) throws Exception {
-        assertTrue(oldString.length() == newString.length(), "must have same length");
-        int index = -1;
-        while ((index = getStringIndex(oldString, buf, index + 1)) != 0) {
-            replaceString(buf, newString, index);
-        }
-    }
-
     public static void main(String[] s) throws Exception {
 
-        byte[] buf = getBytecodes("TestClassOld");
-        // Poor man's renaming of class "TestClassOld" to "TestClassXXX"
-        replaceAllStrings(buf, "TestClassOld", "TestClassXXX");
         ClassVersionAfterRedefine cvar = new ClassVersionAfterRedefine();
+
+        byte[] buf = RedefineClassHelper.replaceClassName(cvar, "TestClassOld", "TestClassXXX");
         Class<?> old = cvar.defineClass(null, buf, 0, buf.length);
         Method foo = old.getMethod("foo");
         Object result = foo.invoke(null);
         assertTrue("java-lang-String".equals(result));
         System.out.println(old.getSimpleName() + ".foo() = " + result);
 
-        buf = getBytecodes("TestClassNew");
         // Rename class "TestClassNew" to "TestClassXXX" so we can use it for
         // redefining the original version of "TestClassXXX" (i.e. "TestClassOld").
-        replaceAllStrings(buf, "TestClassNew", "TestClassXXX");
-        // Now redine the original version of "TestClassXXX" (i.e. "TestClassOld").
+        buf = RedefineClassHelper.replaceClassName(cvar, "TestClassNew", "TestClassXXX");
+        // Now redefine the original version of "TestClassXXX" (i.e. "TestClassOld").
         RedefineClassHelper.redefineClass(old, buf);
         result = foo.invoke(null);
         assertTrue("java.lang.String".equals(result));

test/lib/RedefineClassHelper.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2025, 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
@@ -21,8 +21,14 @@
  * questions.
  */
 
-import java.lang.instrument.Instrumentation;
+import java.io.InputStream;
+import java.lang.classfile.ClassElement;
+import java.lang.classfile.ClassFile;
+import java.lang.classfile.ClassModel;
+import java.lang.constant.ClassDesc;
+
 import java.lang.instrument.ClassDefinition;
+import java.lang.instrument.Instrumentation;
 import jdk.test.lib.compiler.InMemoryJavaCompiler;
 import jdk.test.lib.helpers.ClassFileInstaller;
 
@@ -33,6 +39,7 @@
  *
  * See sample test in test/testlibrary_tests/RedefineClassTest.java
  */
+
 public class RedefineClassHelper {
 
     public static Instrumentation instrumentation;
@@ -61,6 +68,41 @@ public static void redefineClass(Class<?> clazz, byte[] bytecode) throws Excepti
         instrumentation.redefineClasses(new ClassDefinition(clazz, bytecode));
     }
 
+    private static byte[] getBytecodes(ClassLoader loader, String name) throws Exception {
+        try (InputStream is = loader.getResourceAsStream(name + ".class")) {
+            byte[] buf = is.readAllBytes();
+            System.out.println("sizeof(" + name + ".class) == " + buf.length);
+            return buf;
+        }
+    }
+
+    /*
+     * Copy the class defined by `bytes`, replacing the name of the class with `newClassName`,
+     * so that both old and new classes can be compiled by jtreg for the test.
+     *
+     * @param bytes read from the original class file.
+     * @param newClassName new class name for the returned class representation
+     * @return a copy of the class represented by `bytes` but with the name `newClassName`
+     */
+    public static byte[] replaceClassName(byte[] bytes, String newClassName) throws Exception {
+        ClassModel classModel = ClassFile.of().parse(bytes);
+        return ClassFile.of().build(ClassDesc.of(newClassName), classModel::forEach);
+    }
+
+    /*
+     * Replace class name in bytecodes to the class we're trying to redefine, so that both
+     * old and new classes can be compiled with jtreg for the test.
+     *
+     * @param loader ClassLoader to find the bytes for the old class.
+     * @param oldClassName old class name.
+     * @param newClassName new class name to replace with old class name.
+     * @return a copy of the class represented by `bytes` but with the name `newClassName`
+     */
+    public static byte[] replaceClassName(ClassLoader loader, String oldClassName, String newClassName) throws Exception {
+        byte[] buf = getBytecodes(loader, oldClassName);
+        return replaceClassName(buf, newClassName);
+    }
+
     /**
      * Main method to be invoked before test to create the redefineagent.jar
      */