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JIT debug agent using ASM
-This agent creates the hook needed to inject the code for running the debug agent tool Signed-off-by: Shane Killoran <shanegkilloran@gmail.com>
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‎jit-debug-agent/DebugAgent.mf‎

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Manifest-Version: 1.0
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Premain-Class: DebugAgent
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Agent-Class: DebugAgent
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Class-path: asm-9.2.jar junit-4.12.jar
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Can-Redefine-Classes: true
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Can-Retransform-Classes: true

‎jit-debug-agent/README.md‎

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# OpenJ9 JIT Debug Agent
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This tool automatically obtains a limited JIT trace log for a miscompiled method. It works by using preexistence
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and a hooked internal API to repeatedly run a test by sequentially reverting JIT methods to be executed in the interpreter.
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By repeatedly executing a test in a controlled environment we are able to devertmine which JIT method needs to be interpreted
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for the test to start passing. This is how the tool determines which JIT method _may_ be responsible for the test case failure.
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Once the JIT method is identified the tool performs a `lastOptIndex` search by recompiling the JIT method at different
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optimization levels. Once again, when the test starts passing we have determined the minimal `lastOptIndex` which causes the
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failure. At that point the tool gather a _"good"_ and _"bad"_ JIT trace log with the optimization included and excluded for
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JIT developers to investigate.
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# When to use this tool
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This tool should be used for highly intermittent JIT defects from automated testing environments where we are either not able
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to determine the JIT method responsible for the failure, or we are unable to trace the suspect JIT method due to a Heisenbug.
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# How to use this tool
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1. Using maven and running the command `$ mvn install` in this directory will package the agent into a jar file, you will find it in the `target` directory.
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2. add the java agent option to your `java` execution which would look like this: `-javaagent: jit-debug-agent-1.0.jar`
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3. Run the test by forcing preexistence.
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Currently the tool is not robust enough to enable this automatically, so we have to force every JIT method compilation to use
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preexistence. This is to ensure that we have a _revert to interpreter_ stub inserted in the preprologue of every method.
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Inserting this stub happens at binary encoding and should not affect the semantics of the method itself.
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```
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java -Xdump:none -Xnoaot -Xcheck:jni -Xjit:forceUsePreexistence -javaagent: jit-debug-agent-1.0.jar <test>

‎jit-debug-agent/pom.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>org.openj9</groupId>
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<artifactId>jit-debug-agent</artifactId>
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<version>1.0</version>
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<dependencies>
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<dependency>
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<groupId>org.ow2.asm</groupId>
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<artifactId>asm</artifactId>
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<version>9.2</version>
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</dependency>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<version>4.12</version>
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<scope>compile</scope>
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</dependency>
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</dependencies>
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<properties>
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<maven.compiler.source>11</maven.compiler.source>
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<maven.compiler.target>11</maven.compiler.target>
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</properties>
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<build>
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<plugins>
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<plugin>
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<artifactId>maven-assembly-plugin</artifactId>
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<configuration>
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<archive>
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<manifestEntries>
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<Premain-Class>
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DebugAgent
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</Premain-Class>
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<Can-Retransform-Classes>
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true
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</Can-Retransform-Classes>
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<Can-Redefine-Classes>
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true
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</Can-Redefine-Classes>
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</manifestEntries>
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</archive>
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<descriptorRefs>
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<descriptorRef>jar-with-dependencies</descriptorRef>
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</descriptorRefs>
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<appendAssemblyId>false</appendAssemblyId>
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</configuration>
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<executions>
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<execution>
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<id>make-assembly</id>
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<phase>package</phase>
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<goals>
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<goal>single</goal>
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</goals>
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</execution>
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</executions>
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</plugin>
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</plugins>
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</build>
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</project>

‎jit-debug-agent/src/main/java/DebugAgent.java‎

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{{- /*******************************************************************************
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* Copyright (c) 2021, 2021 IBM Corp. and others
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*
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* This program and the accompanying materials are made available under
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* the terms of the Eclipse Public License 2.0 which accompanies this
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* distribution and is available at https://www.eclipse.org/legal/epl-2.0/
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* or the Apache License, Version 2.0 which accompanies this distribution and
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* is available at https://www.apache.org/licenses/LICENSE-2.0.
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*
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* This Source Code may also be made available under the following
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* Secondary Licenses when the conditions for such availability set
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* forth in the Eclipse Public License, v. 2.0 are satisfied: GNU
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* General Public License, version 2 with the GNU Classpath
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* Exception [1] and GNU General Public License, version 2 with the
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* OpenJDK Assembly Exception [2].
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*
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* [1] https://www.gnu.org/software/classpath/license.html
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* [2] http://openjdk.java.net/legal/assembly-exception.html
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*
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* SPDX-License-Identifier: EPL-2.0 OR Apache-2.0 OR GPL-2.0 WITH Classpath-exception-2.0 OR LicenseRef-GPL-2.0 WITH Assembly-exception
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*******************************************************************************/ -}}
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import java.lang.instrument.*;
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import java.security.ProtectionDomain;
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import java.io.IOException;
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public class DebugAgent {
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private static String REFLECT_METHOD_NAME = "java/lang/reflect/Method";
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private static String EXPECT_EXCEPTION_NAME = "org/junit/internal/runners/statements/ExpectException";
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private static Class REFLECT_METHOD_CLASS = java.lang.reflect.Method.class;
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private static Class EXPECT_EXCEPTION_CLASS = org.junit.internal.runners.statements.ExpectException.class;
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private static String INVOKE = "invoke";
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private static String EVALUATE = "evaluate";
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public static void premain(String args, Instrumentation inst) throws Exception {
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inst.addTransformer(new ClassFileTransformer(){
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@Override
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public byte[] transform(
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ClassLoader l,
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String name,
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Class c,
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ProtectionDomain d,
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byte[] b
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) throws IllegalClassFormatException {
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if(name.equals(REFLECT_METHOD_NAME)) {
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try {
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DebugClassWriter writer = new DebugClassWriter(c.getName());
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return writer.applyDebugger(INVOKE);
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} catch (IOException e) {
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System.out.println(e);
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}
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}
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if(name.equals(EXPECT_EXCEPTION_NAME)) {
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try{
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DebugClassWriter writer = new DebugClassWriter(c.getName());
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return writer.applyDebugger(EVALUATE);
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} catch (IOException e) {
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System.out.println(e);
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}
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}
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return b;
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}
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}, true);
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Class[] classesToTransform = {EXPECT_EXCEPTION_CLASS, REFLECT_METHOD_CLASS};
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inst.retransformClasses(classesToTransform);
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}
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}

‎jit-debug-agent/src/main/java/DebugClassWriter.java‎

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{{- /*******************************************************************************
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* Copyright (c) 2021, 2021 IBM Corp. and others
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*
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* This program and the accompanying materials are made available under
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* the terms of the Eclipse Public License 2.0 which accompanies this
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* distribution and is available at https://www.eclipse.org/legal/epl-2.0/
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* or the Apache License, Version 2.0 which accompanies this distribution and
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* is available at https://www.apache.org/licenses/LICENSE-2.0.
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*
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* This Source Code may also be made available under the following
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* Secondary Licenses when the conditions for such availability set
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* forth in the Eclipse Public License, v. 2.0 are satisfied: GNU
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* General Public License, version 2 with the GNU Classpath
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* Exception [1] and GNU General Public License, version 2 with the
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* OpenJDK Assembly Exception [2].
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*
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* [1] https://www.gnu.org/software/classpath/license.html
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* [2] http://openjdk.java.net/legal/assembly-exception.html
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*
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* SPDX-License-Identifier: EPL-2.0 OR Apache-2.0 OR GPL-2.0 WITH Classpath-exception-2.0 OR LicenseRef-GPL-2.0 WITH Assembly-exception
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*******************************************************************************/ -}}
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import org.objectweb.asm.*;
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import java.io.IOException;
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public class DebugClassWriter {
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private ClassReader reader;
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private ClassWriter writer;
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private static String INVOKE = "invoke";
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public DebugClassWriter(String className) throws IOException {
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reader = new ClassReader(className);
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writer = new ClassWriter(reader, ClassWriter.COMPUTE_FRAMES);
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}
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public byte[] applyDebugger(String methodName){
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if (methodName == INVOKE) {
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MethodDebugAdapter methodDebugAdapter = new MethodDebugAdapter(methodName, writer);
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reader.accept(methodDebugAdapter, 0);
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} else {
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ExpectDebugAdapter expectDebugAdapter = new ExpectDebugAdapter(methodName, writer);
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reader.accept(expectDebugAdapter, 0);
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}
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return writer.toByteArray();
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}
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}

‎jit-debug-agent/src/main/java/EvaluateDebugAdapter.java‎

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{{- /*******************************************************************************
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* Copyright (c) 2021, 2021 IBM Corp. and others
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*
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* This program and the accompanying materials are made available under
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* the terms of the Eclipse Public License 2.0 which accompanies this
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* distribution and is available at https://www.eclipse.org/legal/epl-2.0/
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* or the Apache License, Version 2.0 which accompanies this distribution and
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* is available at https://www.apache.org/licenses/LICENSE-2.0.
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*
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* This Source Code may also be made available under the following
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* Secondary Licenses when the conditions for such availability set
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* forth in the Eclipse Public License, v. 2.0 are satisfied: GNU
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* General Public License, version 2 with the GNU Classpath
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* Exception [1] and GNU General Public License, version 2 with the
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* OpenJDK Assembly Exception [2].
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*
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* [1] https://www.gnu.org/software/classpath/license.html
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* [2] http://openjdk.java.net/legal/assembly-exception.html
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*
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* SPDX-License-Identifier: EPL-2.0 OR Apache-2.0 OR GPL-2.0 WITH Classpath-exception-2.0 OR LicenseRef-GPL-2.0 WITH Assembly-exception
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*******************************************************************************/ -}}
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import org.objectweb.asm.*;
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public class EvaluateDebugAdapter extends MethodVisitor {
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public EvaluateDebugAdapter(MethodVisitor mv) {
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super(Opcodes.ASM9, mv);
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this.mv = mv;
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}
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@Override
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public void visitCode() {
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mv.visitCode();
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mv.visitVarInsn(Opcodes.ALOAD, 0);
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mv.visitFieldInsn(Opcodes.GETFIELD, "org/junit/internal/runners/statements/ExpectException", "expected", "Ljava/lang/Class;");
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mv.visitMethodInsn(Opcodes.INVOKESTATIC, "com/ibm/jit/JITHelpers", "setExpectedException", "(Ljava/lang/Class;)V", false);
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}
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@Override
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public void visitLineNumber(int line, Label start){
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mv.visitLineNumber(line, start);
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if (line == 31) {
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mv.visitInsn(Opcodes.ACONST_NULL);
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mv.visitMethodInsn(Opcodes.INVOKESTATIC, "com/ibm/jit/JITHelpers", "setExpectedException", "(Ljava/lang/Class;)V", false);
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}
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}
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}

‎jit-debug-agent/src/main/java/ExpectDebugAdapter.java‎

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{{- /*******************************************************************************
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* Copyright (c) 2021, 2021 IBM Corp. and others
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*
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* This program and the accompanying materials are made available under
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* the terms of the Eclipse Public License 2.0 which accompanies this
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* distribution and is available at https://www.eclipse.org/legal/epl-2.0/
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* or the Apache License, Version 2.0 which accompanies this distribution and
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* is available at https://www.apache.org/licenses/LICENSE-2.0.
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*
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* This Source Code may also be made available under the following
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* Secondary Licenses when the conditions for such availability set
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* forth in the Eclipse Public License, v. 2.0 are satisfied: GNU
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* General Public License, version 2 with the GNU Classpath
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* Exception [1] and GNU General Public License, version 2 with the
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* OpenJDK Assembly Exception [2].
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*
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* [1] https://www.gnu.org/software/classpath/license.html
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* [2] http://openjdk.java.net/legal/assembly-exception.html
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*
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* SPDX-License-Identifier: EPL-2.0 OR Apache-2.0 OR GPL-2.0 WITH Classpath-exception-2.0 OR LicenseRef-GPL-2.0 WITH Assembly-exception
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*******************************************************************************/ -}}
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import org.objectweb.asm.*;
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public class ExpectDebugAdapter extends ClassVisitor {
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private String methodName;
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private int access = org.objectweb.asm.Opcodes.ACC_PUBLIC;
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public ExpectDebugAdapter(String methodName, ClassVisitor cv) {
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super(org.objectweb.asm.Opcodes.ASM9, cv);
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this.cv = cv;
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this.methodName = methodName;
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}
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@Override
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public MethodVisitor visitMethod(
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int access,
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String name,
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String desc,
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String signature,
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String[] exceptions) {
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MethodVisitor mv;
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mv = cv.visitMethod(
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access,
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name,
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desc,
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signature,
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exceptions);
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if (name.equals(methodName) && mv != null) {
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return new EvaluateDebugAdapter(mv);
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}
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return mv;
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}
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}

‎jit-debug-agent/src/main/java/InvokeDebugAdapter.java‎

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{{- /*******************************************************************************
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* Copyright (c) 2021, 2021 IBM Corp. and others
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*
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* This program and the accompanying materials are made available under
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* the terms of the Eclipse Public License 2.0 which accompanies this
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* distribution and is available at https://www.eclipse.org/legal/epl-2.0/
7+
* or the Apache License, Version 2.0 which accompanies this distribution and
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* is available at https://www.apache.org/licenses/LICENSE-2.0.
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*
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* This Source Code may also be made available under the following
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* Secondary Licenses when the conditions for such availability set
12+
* forth in the Eclipse Public License, v. 2.0 are satisfied: GNU
13+
* General Public License, version 2 with the GNU Classpath
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* Exception [1] and GNU General Public License, version 2 with the
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* OpenJDK Assembly Exception [2].
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*
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* [1] https://www.gnu.org/software/classpath/license.html
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* [2] http://openjdk.java.net/legal/assembly-exception.html
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*
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* SPDX-License-Identifier: EPL-2.0 OR Apache-2.0 OR GPL-2.0 WITH Classpath-exception-2.0 OR LicenseRef-GPL-2.0 WITH Assembly-exception
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*******************************************************************************/ -}}
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import org.objectweb.asm.*;
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public class InvokeDebugAdapter extends MethodVisitor {
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public InvokeDebugAdapter(MethodVisitor mv) {
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super(Opcodes.ASM9, mv);
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}
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@Override
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public void visitMethodInsn(int opcode, java.lang.String owner, java.lang.String name, java.lang.String descriptor, boolean isInterface) {
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if(opcode==Opcodes.INVOKEINTERFACE){
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mv.visitMethodInsn(
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Opcodes.INVOKESTATIC,
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"com/ibm/jit/JITHelpers",
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"invoke",
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"(Ljdk/internal/reflect/MethodAccessor;Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;",
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false);
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} else {
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mv.visitMethodInsn(opcode, owner, name, descriptor, isInterface);
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}
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}
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}

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