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Living in the Matrix with Bytecode Manipulation QCon NY 2014 Wednesday, June 11, 14 Ashley Puls Senior Software Engineer New Relic, Inc. Wednesday, June 11, 14 Follow Along http://slidesha.re/1kZwCXr Wednesday, June 11, 14 Outline

  1. lets code Manifest: Premain-Class: com.example.qcon.agent.Agent package com.example.qcon.agent; public class Agent { public static void premain(String agentArgs, Instrumentation inst) { System.out.println("Starting the agent"); inst.addTransformer(new ImportantLogClassTransformer()); } } Wednesday, June 11, 14

  2. lets code package com.example.qcon.agent; import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.IllegalClassFormatException; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException { //TODO return null; } } Wednesday, June 11, 14

  3. lets code package com.example.qcon.agent; import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.IllegalClassFormatException; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException { //TODO return null; } } Wednesday, June 11, 14

  4. lets code package com.example.qcon.agent; import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.IllegalClassFormatException; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException { System.out.println(" Loading class: " + className); return null; } } Wednesday, June 11, 14

  5. lets code Starting the agent Loading class: java/lang/invoke/MethodHandleImpl Loading class: java/lang/invoke/MemberName$Factory Loading class: java/lang/invoke/LambdaForm$NamedFunction Loading class: java/lang/invoke/MethodType$ConcurrentWeakInternSet Loading class: java/lang/invoke/MethodHandleStatics Loading class: java/lang/invoke/MethodHandleStatics$1 Loading class: java/lang/invoke/MethodTypeForm Loading class: java/lang/invoke/Invokers Loading class: java/lang/invoke/MethodType$ConcurrentWeakInternSet$WeakEntry Loading class: java/lang/Void Loading class: java/lang/IllegalAccessException Loading class: sun/misc/PostVMInitHook Loading class: sun/launcher/LauncherHelper Loading class: java/util/concurrent/ConcurrentHashMap$ForwardingNode Loading class: sun/misc/URLClassPath$FileLoader$1 Loading class: com/example/qcon/mains/BankTransactions Loading class: sun/launcher/LauncherHelper$FXHelper Wednesday, June 11, 14

  6. lets code package com.example.qcon.agent; import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.IllegalClassFormatException; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException { System.out.println(" Loading class: " + className); return null; } } Wednesday, June 11, 14

  7. lets code package com.example.qcon.agent; import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.IllegalClassFormatException; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException { // manipulate the bytes here and then return them return null; } } Wednesday, June 11, 14

  8. Bytecode Manipulation Frameworks • ASM: http://asm.ow2.org/ • BCEL: http://commons.apache.org/proper/commons-bcel/ • CGLib: https://github.com/cglib/cglib • Javassist: http://www.csg.ci.i.u-tokyo.ac.jp/~chiba/javassist/ • Serp: http://serp.sourceforge.net/ • Cojen: https://github.com/cojen/Cojen/wiki • Soot: http://www.sable.mcgill.ca/soot/ Wednesday, June 11, 14

  9. Bytecode Manipulation Frameworks • ASM: http://asm.ow2.org/ • BCEL: http://commons.apache.org/proper/commons-bcel/ • CGLib: https://github.com/cglib/cglib • Javassist: http://www.csg.ci.i.u-tokyo.ac.jp/~chiba/javassist/ • Serp: http://serp.sourceforge.net/ • Cojen: https://github.com/cojen/Cojen/wiki • Soot: http://www.sable.mcgill.ca/soot/ Wednesday, June 11, 14

  10. Javassist • Java Programming Assistant • Subproject of JBoss • Actively updated • Version 3.18.2 released May 2014 • Source code: https://github.com/jboss-javassist/ javassist • Documentation: http://www.csg.ci.i.u-tokyo.ac.jp/ ~chiba/javassist/tutorial/tutorial.html Wednesday, June 11, 14

  11. Javassist CtClass: represents a compile time class ArrayList HashMap Wednesday, June 11, 14

  12. Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ArrayList HashMap Wednesday, June 11, 14

  13. Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ArrayList ArrayList HashMap HashMap Wednesday, June 11, 14

  14. Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ArrayList ArrayList HashMap HashMap BankTrans Wednesday, June 11, 14

  15. Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ByteArrayClassPath: converts a byte[] to a CtClass ArrayList ArrayList HashMap HashMap BankTrans Wednesday, June 11, 14

  16. Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ByteArrayClassPath: converts a byte[] to a CtClass Classpool.getDefault().insertClassPath(new ByteArrayClassPath(“BankTrans”, classBytes); ArrayList ArrayList HashMap HashMap BankTrans Wednesday, June 11, 14

  17. Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ByteArrayClassPath: converts a byte[] to a CtClass Classpool.getDefault().insertClassPath(new ByteArrayClassPath(“BankTrans”, classBytes); ArrayList ArrayList HashMap HashMap BankTrans BankTrans Wednesday, June 11, 14

  18. Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ByteArrayClassPath: converts a byte[] to a CtClass Classpool.getDefault().insertClassPath(new ByteArrayClassPath(“BankTrans”, classBytes); CtClass bank = Classpool.getDefault().get(“BankTrans”); ArrayList ArrayList HashMap HashMap BankTrans BankTrans Wednesday, June 11, 14

  19. Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ByteArrayClassPath: converts a byte[] to a CtClass Classpool.getDefault().insertClassPath(new ByteArrayClassPath(“BankTrans”, classBytes); CtClass bank = Classpool.getDefault().get(“BankTrans”); ArrayList ArrayList HashMap BankTrans HashMap BankTrans BankTrans Wednesday, June 11, 14

  20. Javassist CtClass: represents a compile time class BankTrans Wednesday, June 11, 14

  21. Javassist CtClass: represents a compile time class CtConstructor: represents a compile time constructor BankTrans init Wednesday, June 11, 14

  22. Javassist CtClass: represents a compile time class CtConstructor: represents a compile time constructor CtMethod: represents a compile time class BankTrans init login process Wednesday, June 11, 14

  23. Javassist CtClass: represents a compile time class CtConstructor: represents a compile time constructor CtMethod: represents a compile time method CtMethod loginMethod = loginCtClass.getDeclaredMethod(“login”); BankTrans init login process Wednesday, June 11, 14

  24. Javassist CtClass: represents a compile time class CtConstructor: represents a compile time constructor CtMethod: represents a compile time method CtMethod loginMethod = loginCtClass.getDeclaredMethod(“login”); BankTrans init login process login Wednesday, June 11, 14

  25. Javassist CtMethod: represents a compile time method login Wednesday, June 11, 14

  26. Javassist CtMethod: represents a compile time method Modifications: login Wednesday, June 11, 14

  27. Javassist CtMethod: represents a compile time method Modifications: putMethod.insertBefore(“System.out.println(\“before method\”);”); putMethod.insertAfter(“System.out.println(\”after method\”);”); login Wednesday, June 11, 14

  28. Javassist CtMethod: represents a compile time method Modifications: putMethod.insertBefore(“System.out.println(\“before method\”);”); putMethod.insertAfter(“System.out.println(\”after method\”);”); System.out.println(“before method”); login System.out.println(“after method”); Wednesday, June 11, 14

  29. Javassist CtMethod: represents a compile time method Modifications: CtClass exceptionType = classpool.get(“java.io.IOException”); putMethod.addCatch(“{System.out.println($e); throw $e}”, exceptionType); login Wednesday, June 11, 14

  30. Javassist CtMethod: represents a compile time method Modifications: CtClass exceptionType = classpool.get(“java.io.IOException”); putMethod.addCatch(“{System.out.println($e); throw $e}”, exceptionType); login System.out.println(“exception”); throw exception; Wednesday, June 11, 14

  31. Javassist CtMethod: represents a compile time method Modifications: putMethod.insertAt(5, true, “System.out.println(\“hello\”);”); login Wednesday, June 11, 14

  32. Javassist CtMethod: represents a compile time method Modifications: putMethod.insertAt(5, true, “System.out.println(\“hello\”);”); login System.out.println(“hello”); Wednesday, June 11, 14

  33. Javassist CtMethod: represents a compile time method Modifications: insertBefore insertAfter insertAt addCatch System.out.println(“before method”); login System.out.println(“hello”); System.out.println(“exception”); throw exception; System.out.println(“after method”); Wednesday, June 11, 14

  34. Javassist CtMethod: represents a compile time method Modifications: insertBefore insertAfter insertAt addCatch Freeze Class: System.out.println(“before method”); login System.out.println(“hello”); System.out.println(“exception”); throw exception; System.out.println(“after method”); Wednesday, June 11, 14

  35. Javassist CtMethod: represents a compile time method Modifications: insertBefore insertAfter insertAt addCatch Freeze Class: writeFile() toClass() toBytecode() System.out.println(“before method”); login System.out.println(“hello”); System.out.println(“exception”); throw exception; System.out.println(“after method”); Wednesday, June 11, 14

  36. lets code Wednesday, June 11, 14

  37. lets code package com.example.qcon.agent; import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.IllegalClassFormatException; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException { //TODO return null; } } Wednesday, June 11, 14

  38. lets code package com.example.qcon.agent; import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.IllegalClassFormatException; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException { //TODO return null; } } Wednesday, June 11, 14

  39. lets code public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] cfbuffer) throws IllegalClassFormatException { 1. convert byte array to a ct class object 2. check each method of ct class for annotation @ImportantLog 3. if @ImportantLog annotation present on method, then a. get important method parameter indexes b. add logging statement to beginning of the method return null; } Wednesday, June 11, 14

  40. lets code public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertClassPath(new ByteArrayClassPath(className, classfileBuffer)); CtClass cclass = pool.get(className.replaceAll("/", ".")); 2. check each method of ct class for annotation @ImportantLog 3. if @ImportantLog annotation present on method, then a. get important method parameter indexes b. add logging statement to beginning of the method return null; } Wednesday, June 11, 14

  41. lets code public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertClassPath(new ByteArrayClassPath(className, classfileBuffer)); CtClass cclass = pool.get(className.replaceAll("/", ".")); if (!cclass.isFrozen()) { for (CtMethod currentMethod : cclass.getDeclaredMethods()) { Annotation annotation = getAnnotation(currentMethod); 3. if @ImportantLog annotation present on method, then a. get important method parameter indexes b. add logging statement to beginning of the method } } return null; } Wednesday, June 11, 14

  42. lets code public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertClassPath(new ByteArrayClassPath(className, classfileBuffer)); CtClass cclass = pool.get(className.replaceAll("/", ".")); if (!cclass.isFrozen()) { for (CtMethod currentMethod : cclass.getDeclaredMethods()) { Annotation annotation = getAnnotation(currentMethod); if (annotation != null) { List<String> parameterIndexes = getParamIndexes(annotation); b. add logging statement to beginning of the method } } } return null; } Wednesday, June 11, 14

  43. lets code public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertClassPath(new ByteArrayClassPath(className, classfileBuffer)); CtClass cclass = pool.get(className.replaceAll("/", ".")); if (!cclass.isFrozen()) { for (CtMethod currentMethod : cclass.getDeclaredMethods()) { Annotation annotation = getAnnotation(currentMethod); if (annotation != null) { List<String> parameterIndexes = getParamIndexes(annotation); currentMethod.insertBefore(createJavaString( currentMethod, className, parameterIndexes)); } } return cclass.toBytecode(); } return null; } Wednesday, June 11, 14

  44. lets code public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertClassPath(new ByteArrayClassPath(className, classfileBuffer)); CtClass cclass = pool.get(className.replaceAll("/", ".")); if (!cclass.isFrozen()) { for (CtMethod currentMethod : cclass.getDeclaredMethods()) { Annotation annotation = getAnnotation(currentMethod); if (annotation != null) { List<String> parameterIndexes = getParamIndexes(annotation); currentMethod.insertBefore(createJavaString( currentMethod, className, parameterIndexes)); } } return cclass.toBytecode(); } return null; } Wednesday, June 11, 14

  45. lets code private Annotation getAnnotation(CtMethod method) { MethodInfo mInfo = method.getMethodInfo(); // the attribute we are looking for is a runtime invisible attribute // use Retention(RetentionPolicy.RUNTIME) on the annotation to make it // visible at runtime AnnotationsAttribute attInfo = (AnnotationsAttribute) mInfo .getAttribute(AnnotationsAttribute.invisibleTag); if (attInfo != null) { // this is the type name meaning use dots instead of slashes return attInfo.getAnnotation("com.example.qcon.mains.ImportantLog"); } return null; } Wednesday, June 11, 14

  46. lets code public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertClassPath(new ByteArrayClassPath(className, classfileBuffer)); CtClass cclass = pool.get(className.replaceAll("/", ".")); if (!cclass.isFrozen()) { for (CtMethod currentMethod : cclass.getDeclaredMethods()) { Annotation annotation = getAnnotation(currentMethod); if (annotation != null) { List<String> parameterIndexes = getParamIndexes(annotation); currentMethod.insertBefore(createJavaString( currentMethod, className, parameterIndexes)); } } return cclass.toBytecode(); } return null; } Wednesday, June 11, 14

  47. lets code private List<String> getParamIndexes(Annotation annotation) { ArrayMemberValue fields = (ArrayMemberValue) annotation .getMemberValue(“fields”); if (fields != null) { MemberValue[] values = (MemberValue[]) fields.getValue(); List<String> parameterIndexes = new ArrayList<String>(); for (MemberValue val : values) { parameterIndexes.add(((StringMemberValue) val).getValue()); } return parameterIndexes; } return Collections.emptyList(); } Wednesday, June 11, 14

  48. lets code public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertClassPath(new ByteArrayClassPath(className, classfileBuffer)); CtClass cclass = pool.get(className.replaceAll("/", ".")); if (!cclass.isFrozen()) { for (CtMethod currentMethod : cclass.getDeclaredMethods()) { Annotation annotation = getAnnotation(currentMethod); if (annotation != null) { List<String> parameterIndexes = getParamIndexes(annotation); currentMethod.insertBefore(createJavaString( currentMethod, className, parameterIndexes)); } } return cclass.toBytecode(); } return null; } Wednesday, June 11, 14

  49. lets code private String createJavaString(CtMethod currentMethod, String className, List<String> indexParameters) { StringBuilder sb = new StringBuilder(); sb.append("{StringBuilder sb = new StringBuilder"); sb.append("(\"A call was made to method '\");"); sb.append("sb.append(\""); sb.append(currentMethod.getName()); sb.append("\");sb.append(\"' on class '\");"); sb.append("sb.append(\""); sb.append(className); sb.append("\");sb.append(\"'.\");"); sb.append("sb.append(\"\\n Important params:\");"); . . . Wednesday, June 11, 14

  50. lets code private String createJavaString(CtMethod currentMethod, String className, List<String> indexParameters) { StringBuilder sb = new StringBuilder(); sb.append("{StringBuilder sb = new StringBuilder"); sb.append("(\"A call was made to method '\");"); sb.append("sb.append(\""); sb.append(currentMethod.getName()); sb.append("\");sb.append(\"' on class '\");"); sb.append("sb.append(\""); sb.append(className); sb.append("\");sb.append(\"'.\");"); sb.append("sb.append(\"\\n Important params:\");"); . . . Put multiple statements inside brackets {} Wednesday, June 11, 14

  51. lets code private String createJavaString(CtMethod currentMethod, String className, List<String> indexParameters) { . . . for (String index : indexParameters) { try { int localVar = Integer.parseInt(index) + 1; sb.append("sb.append(\"\\n Index: \");"); sb.append("sb.append(\""); sb.append(index); sb.append("\");sb.append(\" value: \");"); sb.append("sb.append($" + localVar + ");"); } catch (NumberFormatException e) { e.printStackTrace(); } } sb.append("System.out.println(sb.toString());}"); return sb.toString(); } Wednesday, June 11, 14

  52. lets code private String createJavaString(CtMethod currentMethod, String className, List<String> indexParameters) { . . . for (String index : indexParameters) { try { int localVar = Integer.parseInt(index) + 1; sb.append("sb.append(\"\\n Index: \");"); sb.append("sb.append(\""); sb.append(index); sb.append("\");sb.append(\" value: \");"); sb.append("sb.append($" + localVar + ");"); } catch (NumberFormatException e) { e.printStackTrace(); } } sb.append("System.out.println(sb.toString());}"); return sb.toString(); $0, $1, $2, ... can be used to access } “this” and the actual method parameters Wednesday, June 11, 14

  53. lets code public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertClassPath(new ByteArrayClassPath(className, classfileBuffer)); CtClass cclass = pool.get(className.replaceAll("/", ".")); if (!cclass.isFrozen()) { for (CtMethod currentMethod : cclass.getDeclaredMethods()) { Annotation annotation = getAnnotation(currentMethod); if (annotation != null) { List<String> parameterIndexes = getParamIndexes(annotation); currentMethod.insertBefore(createJavaString( currentMethod, className, parameterIndexes)); } } return cclass.toBytecode(); } return null; } Wednesday, June 11, 14

  54. Javassist • Positives • Simplicity • Do not have to write actual bytecode • Decent documentation • Negatives • Generally slower than ASM • Less functionality Wednesday, June 11, 14

  55. ASM • Released in Open Source in 2002 • Actively updated • Version 5.0.3 released May 2014 • Two ASM libraries • Event based (SAX like) • Visitor design pattern • Object based (DOM like) • Documentation: http://download.forge.objectweb.org/ asm/asm4-guide.pdf Wednesday, June 11, 14

  56. ASM Source: http://download.forge.objectweb.org/asm/asm4-guide.pdf Wednesday, June 11, 14

  57. ASM Source: http://download.forge.objectweb.org/asm/asm4-guide.pdf Wednesday, June 11, 14

  58. ASM Source: http://download.forge.objectweb.org/asm/asm4-guide.pdf Wednesday, June 11, 14

  59. ASM ClassReader: given a byte[], parses a compiled class ClassReader: ClassVisitor: ClassWriter: event producer event filter event consumer BankTrans Wednesday, June 11, 14

  60. ASM ClassReader: given a byte[], parses a compiled class ClassReader: ClassVisitor: ClassWriter: event producer event filter event consumer BankTrans visitField visitMethod Wednesday, June 11, 14

  61. ASM ClassReader: given a byte[], parses a compiled class ClassVisitor: delegates class events, event filter visitAttribute visitField visitMethod visitInnerClass visitEnd ClassReader: ClassVisitor: ClassWriter: event producer event filter event consumer BankTrans visitField visitMethod Wednesday, June 11, 14

  62. ASM ClassReader: given a byte[], parses a compiled class ClassVisitor: delegates class events, event filter visitAttribute visitField visitMethod visitInnerClass visitEnd ClassWriter: produces output byte[] ClassReader: ClassVisitor: ClassWriter: event producer event filter event consumer BankTrans BankTrans visitField visitMethod Wednesday, June 11, 14

  63. lets code package com.example.qcon.agent; import java.lang.instrument.Instrumentation; public class Agent { public static void premain(String agentArgs, Instrumentation inst) { System.out.println("Starting the agent"); inst.addTransformer(new ImportantLogClassTransformer()); } } Wednesday, June 11, 14

  64. lets code package com.example.qcon.agent; import java.lang.instrument.Instrumentation; public class Agent { public static void premain(String agentArgs, Instrumentation inst) { System.out.println("Starting the agent"); inst.addTransformer(new ImportantLogClassTransformer()); } } Wednesday, June 11, 14

  65. lets code package com.example.qcon.agent; import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.IllegalClassFormatException; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException { //TODO return null; } } Wednesday, June 11, 14

  66. lets code package com.example.qcon.agent; import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.IllegalClassFormatException; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException { //TODO return null; } } Wednesday, June 11, 14

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