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mccullsmcculls
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Updates j.l.ClassLoader to ensure superclasses and interfaces are loaded before classes that extend/implement them. (#6677)
1 parent aee3ca5 commit 1c33411

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‎dd-java-agent/agent-bootstrap/src/main/java/datadog/trace/bootstrap/instrumentation/classloading/ClassDefining.java‎

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package datadog.trace.bootstrap.instrumentation.classloading;
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/** Provides a way for a single optional observer to be notified before a class is defined. */
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public final class ClassDefining {
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private static volatile Observer OBSERVER = (loader, bytecode, offset, length) -> {};
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/** Registers the given observer to get notifications about class definitions. */
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public static void observe(Observer observer) {
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OBSERVER = observer;
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}
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/** Called from advice added to j.l.ClassLoader by DefineClassInstrumentation. */
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public static void begin(ClassLoader loader, byte[] bytecode, int offset, int length) {
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OBSERVER.beforeDefineClass(loader, bytecode, offset, length);
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}
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/** Observer of class definitions. */
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public interface Observer {
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void beforeDefineClass(ClassLoader loader, byte[] bytecode, int offset, int length);
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}
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}

‎dd-java-agent/agent-tooling/src/main/java/datadog/trace/agent/tooling/bytebuddy/memoize/MemoizedMatchers.java‎

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/** Supplies memoized matchers. */
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public final class MemoizedMatchers implements HierarchyMatchers.Supplier {
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public static void registerAsSupplier() {
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PreloadHierarchy.observeClassDefinitions();
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HierarchyMatchers.registerIfAbsent(new MemoizedMatchers());
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Memoizer.resetState();
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}

‎dd-java-agent/agent-tooling/src/main/java/datadog/trace/agent/tooling/bytebuddy/memoize/PreloadHierarchy.java‎

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package datadog.trace.agent.tooling.bytebuddy.memoize;
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import datadog.trace.bootstrap.instrumentation.classloading.ClassDefining;
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import net.bytebuddy.jar.asm.ClassReader;
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/** Ensures superclasses and interfaces are loaded before classes that extend/implement them. */
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final class PreloadHierarchy implements ClassDefining.Observer {
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private static final PreloadHierarchy PRELOADER = new PreloadHierarchy();
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static void observeClassDefinitions() {
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ClassDefining.observe(PRELOADER);
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}
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private static final int RECENTLY_CHECKED_MASK = (1 << 5) - 1;
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private final String[] recentlyChecked = new String[RECENTLY_CHECKED_MASK + 1];
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@Override
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public void beforeDefineClass(ClassLoader loader, byte[] bytecode, int offset, int length) {
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try {
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// check first byte matches the standard class header
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if (bytecode[offset] != (byte) 0xCA) {
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return; // ignore non-standard formats like J9 ROMs
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}
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// minimal parsing of bytecode to get name of superclass and any interfaces
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ClassReader cr = new ClassReader(bytecode, offset, length);
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String superName = cr.getSuperName();
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if (null != superName && !"java/lang/Object".equals(superName)) {
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preload(loader, superName);
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}
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for (String interfaceName : cr.getInterfaces()) {
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preload(loader, interfaceName);
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}
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} catch (Throwable ignore) {
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// stop preloading as soon as we encounter any issue
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}
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}
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/** Attempts to preload the named class using same class-loader as the original request. */
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private void preload(ClassLoader loader, String internalName) throws ClassNotFoundException {
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int slot = internalName.hashCode() & RECENTLY_CHECKED_MASK;
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if (!internalName.equals(recentlyChecked[slot])) {
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recentlyChecked[slot] = internalName;
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String name = internalName.replace('/', '.');
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// take advantage of no-match filter to avoid preloading known uninteresting classes
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if (!NoMatchFilter.contains(name)) {
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loader.loadClass(name);
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}
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}
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}
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}

‎dd-java-agent/agent-tooling/src/main/resources/datadog/trace/agent/tooling/bytebuddy/matcher/ignored_class_name.trie‎

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1 io.micronaut.tracing.*
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1 io.opentelemetry.javaagent.*
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1 java.*
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0 java.lang.ClassLoader
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# allow exception profiling instrumentation
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0 java.lang.Exception
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0 java.lang.Error

‎dd-java-agent/instrumentation/classloading/src/main/java/datadog/trace/instrumentation/classloading/DefineClassInstrumentation.java‎

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package datadog.trace.instrumentation.classloading;
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import static datadog.trace.agent.tooling.bytebuddy.matcher.NameMatchers.named;
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import static net.bytebuddy.matcher.ElementMatchers.isMethod;
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import static net.bytebuddy.matcher.ElementMatchers.takesArguments;
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import com.google.auto.service.AutoService;
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import datadog.trace.agent.tooling.Instrumenter;
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import datadog.trace.agent.tooling.InstrumenterModule;
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import datadog.trace.api.InstrumenterConfig;
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import datadog.trace.bootstrap.DatadogClassLoader;
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import datadog.trace.bootstrap.instrumentation.classloading.ClassDefining;
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import java.security.ProtectionDomain;
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import net.bytebuddy.asm.Advice;
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/** Updates j.l.ClassLoader to notify the tracer when classes are about to be defined. */
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@AutoService(Instrumenter.class)
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public final class DefineClassInstrumentation extends InstrumenterModule.Tracing
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implements Instrumenter.ForBootstrap, Instrumenter.ForSingleType {
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public DefineClassInstrumentation() {
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super("defineclass");
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}
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@Override
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public boolean isEnabled() {
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// only enable this when memoizing type hierarchies, where it provides the most ROI
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return super.isEnabled() && InstrumenterConfig.get().isResolverMemoizingEnabled();
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}
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@Override
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public String instrumentedType() {
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return "java.lang.ClassLoader";
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}
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@Override
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public void methodAdvice(MethodTransformer transformer) {
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transformer.applyAdvice(
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isMethod()
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.and(
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named("defineClass")
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.and(
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takesArguments(
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String.class,
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byte[].class,
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int.class,
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int.class,
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ProtectionDomain.class))),
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DefineClassInstrumentation.class.getName() + "$DefineClassAdvice");
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}
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public static class DefineClassAdvice {
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@Advice.OnMethodEnter(suppress = Throwable.class)
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public static void onEnter(
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@Advice.This ClassLoader loader,
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@Advice.Argument(1) byte[] bytecode,
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@Advice.Argument(2) int offset,
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@Advice.Argument(3) int length) {
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if (null != loader && loader.getClass() != DatadogClassLoader.class) {
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ClassDefining.begin(loader, bytecode, offset, length);
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}
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}
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}
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}

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