1. Java Bytecode for Discriminating Developers Anton Arhipov

2. whoami Anton Arhipov Java dev. / Product Lead JRebel http://arhipov.blogspot.com @antonarhipov @javarebel

3. Who-are-you?

4. The Master Plan 80%: Bytecode 101 20%: Examples

5. THE INTRO

6. 1 + 2

7. + 1 + 2 1 2

8. + 1 + 2 1 2 1 2 +

9. + 1 + 2 1 2 1 2 +

10. + 1 + 2 1 2 1 2 + 1 PUSH 1

11. + 1 + 2 1 2 1 2 + 2 PUSH 1 PUSH 2 1

12. + 1 + 2 1 2 1 2 + 3 PUSH 1 PUSH 2 ADD

13. + 1 + 2 1 2 1 2 + 3 ICONST_1 ICONST_2 IADD

14. ? = 1 + 2

15. TAXONOMY

16. Bytecode One-byte instructions 256 possible opcodes 200+ in use

17. Bytecode One-byte instructions 256 possible opcodes 200+ in use

18. TYPE OPERATION

19. TYPE OPERATION <TYPE> ::= b, s, c, i, l, f, d, a

20. TYPE OPERATION <TYPE> ::= b, s, c, i, l, f, d, a Operations with constant values (ldc, iconst_1)

21. TYPE OPERATION <TYPE> ::= b, s, c, i, l, f, d, a Operations with constant values (ldc, iconst_1) Local variables and stack interaction (load/store) Array operations (aload, astore) Math (add, sub, mul, div) Boolean/bitwise operations (iand, ixor) Comparisons (cmpg, cmpl, ifne, ifeq) Conversions (l2d, i2l)

22. Bytecode Taxonomy Stack Manipulation

23. Bytecode Taxonomy Stack Manipulation Flow Control

24. Bytecode Taxonomy Stack Manipulation Flow Control Object Model

25. Bytecode Taxonomy Stack Manipulation Flow Control Object Model Arithmetics

26. Bytecode Taxonomy Stack Manipulation Flow Control Object Model Arithmetics monitorenter monitorexit

27. TOOLING

28. javap Java class file disassembler Used with no options shows class structure only Methods, superclass, interfaces, etc -c shows the bytecode -private shows all methods and members -s prints internal signatures -l prints line numbers and local variable tables

29. HELLO WORLD!

31. C:orkeeconlasses>javap Hello -c

32. C:orkeeconlasses>javap Hello -c Compiled from "Hello.java" public class Hello extends java.lang.Object{ public Hello(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return

33. C:orkeeconlasses>javap Hello -c Compiled from "Hello.java" public class Hello extends java.lang.Object{ public Hello(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return the default constructor

34. C:orkeeconlasses>javap Hello -c Compiled from "Hello.java" public class Hello extends java.lang.Object{ public Hello(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return push this to stack

35. C:orkeeconlasses>javap Hello -c Compiled from "Hello.java" public class Hello extends java.lang.Object{ public Hello(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return invoke <init> on this

36. C:orkeeconlasses>javap Hello -c Compiled from "Hello.java" public class Hello extends java.lang.Object{ public Hello(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return

37. C:orkeeconlasses>javap Hello -c Compiled from "Hello.java" public class Hello extends java.lang.Object{ public Hello(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return public static void main(java.lang.String[]); Code: 0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream; 3: ldc #3; //String Hello, World! 5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V

38. C:orkeeconlasses>javap Hello -c Compiled from "Hello.java" public class Hello extends java.lang.Object{ public Hello(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return public static void main(java.lang.String[]); Code: 0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream; 3: ldc #3; //String Hello, World! 5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V get static field

39. C:orkeeconlasses>javap Hello -c Compiled from "Hello.java" public class Hello extends java.lang.Object{ public Hello(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return public static void main(java.lang.String[]); Code: 0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream; 3: ldc #3; //String Hello, World! 5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V load string to the stack

40. C:orkeeconlasses>javap Hello -c Compiled from "Hello.java" public class Hello extends java.lang.Object{ public Hello(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return public static void main(java.lang.String[]); Code: 0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream; 3: ldc #3; //String Hello, World! 5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V invoke method with parameter

41. C:orkeeconlasses>javap Hello -c Compiled from "Hello.java" public class Hello extends java.lang.Object{ public Hello(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return public static void main(java.lang.String[]); Code: 0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream; 3: ldc #3; //String Hello, World! 5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V

42. What’s #1,#2, etc ? C:orkeeconlasses>javap Hello -c Compiled from "Hello.java" public class Hello extends java.lang.Object{ public Hello(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return public static void main(java.lang.String[]); Code: 0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream; 3: ldc #3; //String Hello, World! 5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V

43. C:orkeeconlasses>javap Hello -c -verbose

44. C:orkeeconlasses>javap Hello -c -verbose

45. C:orkeeconlasses>javap Hello -c -verbose Compiled from "Hello.java“ public class Hello extends java.lang.Object SourceFile: "Hello.java" minor version: 0 major version: 50 Constant pool: const #1 = Method#6.#20; // java/lang/Object."<init>":()V const #2 = Field#21.#22; // java/lang/System.out:Ljava/io/PrintStream; const #3 = String#23; // Hello, World! const #4 = Method#24.#25; // java/io/PrintStream.println:(Ljava/lang/String;)V const #5 = class#26; // Hello const #6 = class#27; // java/lang/Object const #7 = Asciz<init>; const #8 = Asciz()V;

46. C:orkeeconlasses>javap Hello -c -verbose Compiled from "Hello.java“ public class Hello extends java.lang.Object SourceFile: "Hello.java" minor version: 0 major version: 50 Constant pool: const #1 = Method#6.#20; // java/lang/Object."<init>":()V const #2 = Field#21.#22; // java/lang/System.out:Ljava/io/PrintStream; const #3 = String#23; // Hello, World! const #4 = Method#24.#25; // java/io/PrintStream.println:(Ljava/lang/String;)V const #5 = class#26; // Hello const #6 = class#27; // java/lang/Object const #7 = Asciz<init>; const #8 = Asciz()V;

47. C:orkeeconlasses>javap Hello -c -verbose … public Hello(); Code: Stack=1, Locals=1, Args_size=1 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return LineNumberTable: line 1: 0 LocalVariableTable: Start Length Slot Name Signature 0 5 0 this LHello;

48. C:orkeeconlasses>javap Hello -c -verbose … public Hello(); Code: Stack=1, Locals=1, Args_size=1 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return LineNumberTable: line 1: 0 LocalVariableTable: Start Length Slot Name Signature 0 5 0 this LHello;

49. C:orkeeconlasses>javap Hello -c -verbose … public Hello(); Code: Stack=1, Locals=1, Args_size=1 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return LineNumberTable: line 1: 0 LocalVariableTable: Start Length Slot Name Signature 0 5 0 this LHello;

50. C:orkeeconlasses>javap Hello -c -verbose … public static void main(java.lang.String[]); Code: Stack=2, Locals=1, Args_size=1 0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream; 3: ldc #3; //String Hello, World! 5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V 8: return LineNumberTable: line 4: 0 line 5: 8 LocalVariableTable: Start Length Slot Name Signature 0 9 0 args [Ljava/lang/String;

51. STACK MACHINE

52. Stack Machine

53. Stack Machine JVM is a stack-based machine

54. Stack Machine JVM is a stack-based machine Each thread has a stack

55. Stack Machine JVM is a stack-based machine Each thread has a stack Stack stores frames

56. Stack Machine JVM is a stack-based machine Each thread has a stack Stack stores frames Frame is created on method invocation

57. Stack Machine JVM is a stack-based machine Each thread has a stack Stack stores frames Frame is created on method invocation Frame consists of: Operand stack Array of local variables

58. The Frame Local variables N 1 2 3 … Operand stack #1 Constant Pool

59. public java.lang.String getName(); Code: Stack=1, Locals=1, Args_size=1 0: aload_0 1: getfield #2; //Field name:Ljava/lang/String; 4: areturn LocalVariableTable: Start Length Slot Name Signature 0 5 0 this LGet;

60. 0 1 2 3 4 areturn aload_0 00 02 getfield public java.lang.String getName(); Code: Stack=1, Locals=1, Args_size=1 0: aload_0 1: getfield #2; //Field name:Ljava/lang/String; 4: areturn LocalVariableTable: Start Length Slot Name Signature 0 5 0 this LGet;

61. 0 1 2 3 4 B0 2A 00 02 B4 public java.lang.String getName(); Code: Stack=1, Locals=1, Args_size=1 0: aload_0 1: getfield #2; //Field name:Ljava/lang/String; 4: areturn LocalVariableTable: Start Length Slot Name Signature 0 5 0 this LGet;

62. public java.lang.String getName(); Code: Stack=1, Locals=1, Args_size=1 0: aload_0 1: getfield #2; //Field name:Ljava/lang/String; 4: areturn LocalVariableTable: Start Length Slot Name Signature 0 5 0 this LGet;

63. STACK CRUNCHING

64. A dup pop swap dup_x1 dup2_x2 B

65. A dup pop swap dup_x1 dup2_x2 A B

66. A dup pop swap dup_x1 dup2_x2 B

67. B dup pop swap dup_x1 dup2_x2 A

68. B dup pop swap dup_x1 dup2_x2 A B

69. B dup pop swap dup_x1 dup2_x2 A B B A

70. dup2_x2 How do you swap doubles?

71. dup2_x2

72. dup2_x2 dconst_0 0.0

73. dup2_x2 dconst_0 dconst_1 1.0 0.0

74. dup2_x2 dconst_0 dconst_1 swap 1.0 0.0

75. dup2_x2 dconst_0 dconst_1 swap 1.0 not allowed! 0.0

76. dup2_x2 dconst_0 dconst_1 swap2 1.0 0.0

77. dup2_x2 dconst_0 dconst_1 swap2 1.0 doesn’t exist 0.0

78. dup2_x2 dconst_0 dconst_1 dup2_x2 1.0 0.0 1.0

79. dup2_x2 dconst_0 dconst_1 dup2_x2 pop2 0.0 1.0

80. dup2_x2 dconst_0 dconst_1 dup2_x2 pop2 0.0 1.0 profit!

81. LOCAL VARIABLES

82. Local Variables

83. public int calculate(int); Code: Stack=2, Locals=2, Args_size=2 … LocalVariableTable: Start Length Slot Name Signature 0 5 0 this LLocalVariables; 0 5 1 value I Local Variables

84. public int calculate(int); Code: Stack=2, Locals=2, Args_size=2 … LocalVariableTable: Start Length Slot Name Signature 0 5 0 this LLocalVariables; 0 5 1 value I numbered from 0 Local Variables

85. public int calculate(int); Code: Stack=2, Locals=2, Args_size=2 … LocalVariableTable: Start Length Slot Name Signature 0 5 0 this LLocalVariables; 0 5 1 value I Local Variables instance methods have this at 0

86. The table maps numbers to names public int calculate(int); Code: Stack=2, Locals=2, Args_size=2 … LocalVariableTable: Start Length Slot Name Signature 0 5 0 this LLocalVariables; 0 5 1 value I Local Variables

87. Sized explicitly public int calculate(int); Code: Stack=2, Locals=2, Args_size=2 … LocalVariableTable: Start Length Slot Name Signature 0 5 0 this LLocalVariables; 0 5 1 value I Local Variables

88. Stack Local Variables value var value depth ldc"Hello" astore_0 iconst_1 astore_1 aload_0 0 0 1 1 2 2 3 3 4 4

89. Stack Local Variables value var value depth ldc"Hello" astore_0 iconst_1 astore_1 aload_0 0 0 "Hello" 1 1 2 2 3 3 4 4

90. Stack Local Variables value var value depth ldc"Hello" astore_0 iconst_1 astore_1 aload_0 "Hello" 0 0 1 1 2 2 3 3 4 4

91. Stack Local Variables value var value depth ldc"Hello" astore_0 iconst_1 astore_1 aload_0 "Hello" 0 0 1 1 1 2 2 3 3 4 4

92. Stack Local Variables value var value depth ldc"Hello" astore_0 iconst_1 astore_1 aload_0 "Hello" 0 0 1 1 1 2 2 3 3 4 4

93. Stack Local Variables value var value depth ldc"Hello" astore_0 iconst_1 astore_1 aload_0 "Hello" 0 0 "Hello" 1 1 1 2 2 3 3 4 4

94. load Stack Local Variables Table store

95. OBJECTS

96. new <init> <clinit> 0xBB Instance initialization method Class and interface initialization method Object Initialization

97. Object Initialization: static {} static {}; Code: 0: iconst_1 1: putstatic #2; //Field a:I 4: iconst_2 5: putstatic #3; //Field b:I 8: return

98. Object Initialization: static {} <clinit> static {}; Code: 0: iconst_1 1: putstatic #2; //Field a:I 4: iconst_2 5: putstatic #3; //Field b:I 8: return

99. Object Initialization: new

100. Object Initialization: new public Initializer(); Code:

101. Object Initialization: new public Initializer(); Code: 0: aload_0

102. Object Initialization: new public Initializer(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V

103. Object Initialization: new public Initializer(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: aload_0

104. Object Initialization: new public Initializer(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: aload_0 5: new#2; //class java/lang/Object 8: dup

105. Object Initialization: new public Initializer(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: aload_0 5: new#2; //class java/lang/Object 8: dup 9: invokespecial #1; //Method java/lang/Object."<init>":()V 12: putfield #3; //Field o:Ljava/lang/Object;

106. Object Initialization: new public Initializer(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: aload_0 5: new#2; //class java/lang/Object 8: dup 9: invokespecial #1; //Method java/lang/Object."<init>":()V 12: putfield #3; //Field o:Ljava/lang/Object; 15: return

107. Object Initialization: new public Initializer(); Code: 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: aload_0 5: new#2; //class java/lang/Object 8: dup 9: invokespecial #1; //Method java/lang/Object."<init>":()V 12: putfield #3; //Field o:Ljava/lang/Object; 15: return

108. Object Initialization: {}

109. Object Initialization: {} ?

110. Object Initialization: {} public Initializer(int); Code: 0:aload_0 1:invokespecial #1; // ..<init> 4:aload_0 5:iconst_1 6:putfield #2; //Field a:I 9:aload_0 10:iconst_2 11:putfield #3; //Field c:I 14:aload_0 15:iload_1 16:putfield #4; //Field b:I 19:return

112. There’s no initializer

113. METHOD INVOCATION&PARAMETER PASSING

114. Methods & Parameters invokestatic invokespecial invokevirtual invokeinterface invokedynamic Efficient Implementation of Java Interfaces: Invokeinterface Considered Harmless, Bowen Alpern, Anthony Cocchi, Stephen Fink, David Grove, and Derek Lieber, OOPSLA’01

115. Methods & Parameters invokestatic invokespecial invokevirtual invokeinterface invokedynamic Integer.valueOf(“42”) Efficient Implementation of Java Interfaces: Invokeinterface Considered Harmless, Bowen Alpern, Anthony Cocchi, Stephen Fink, David Grove, and Derek Lieber, OOPSLA’01

116. Methods & Parameters invokestatic invokespecial invokevirtual invokeinterface invokedynamic <init> private void foo(); super.method(); Efficient Implementation of Java Interfaces: Invokeinterface Considered Harmless, Bowen Alpern, Anthony Cocchi, Stephen Fink, David Grove, and Derek Lieber, OOPSLA’01

117. Methods & Parameters invokestatic invokespecial invokevirtual invokeinterface invokedynamic class A A/method1 A/method2 Efficient Implementation of Java Interfaces: Invokeinterface Considered Harmless, Bowen Alpern, Anthony Cocchi, Stephen Fink, David Grove, and Derek Lieber, OOPSLA’01

118. Methods & Parameters invokestatic invokespecial invokevirtual invokeinterface invokedynamic class A A/method1 A/method2 class B Efficient Implementation of Java Interfaces: Invokeinterface Considered Harmless, Bowen Alpern, Anthony Cocchi, Stephen Fink, David Grove, and Derek Lieber, OOPSLA’01

119. Methods & Parameters invokestatic invokespecial invokevirtual invokeinterface invokedynamic class A A/method1 A/method2 class B A/method1 B/method2 B/method3 Efficient Implementation of Java Interfaces: Invokeinterface Considered Harmless, Bowen Alpern, Anthony Cocchi, Stephen Fink, David Grove, and Derek Lieber, OOPSLA’01

120. Methods & Parameters invokestatic invokespecial invokevirtual invokeinterface invokedynamic class A A/method1 A/method2 class B impl X A/method1 B/method2 B/method3 X/methodX Efficient Implementation of Java Interfaces: Invokeinterface Considered Harmless, Bowen Alpern, Anthony Cocchi, Stephen Fink, David Grove, and Derek Lieber, OOPSLA’01

121. Methods & Parameters invokestatic invokespecial invokevirtual invokeinterface invokedynamic class A A/method1 A/method2 class B impl X A/method1 B/method2 B/method3 X/methodX class D impl X D/method1 X/methodX Efficient Implementation of Java Interfaces: Invokeinterface Considered Harmless, Bowen Alpern, Anthony Cocchi, Stephen Fink, David Grove, and Derek Lieber, OOPSLA’01

122. Methods & Parameters invokestatic invokespecial invokevirtual invokeinterface invokedynamic class A A/method1 A/method2 class B impl X A/method1 B/method2 B/method3 X/methodX class D impl X D/method1 X/methodX Efficient Implementation of Java Interfaces: Invokeinterface Considered Harmless, Bowen Alpern, Anthony Cocchi, Stephen Fink, David Grove, and Derek Lieber, OOPSLA’01

123. Methods & Parameters invokestatic invokespecial invokevirtual invokeinterface invokedynamic Efficient Implementation of Java Interfaces: Invokeinterface Considered Harmless, Bowen Alpern, Anthony Cocchi, Stephen Fink, David Grove, and Derek Lieber, OOPSLA’01

124. Method Invocation obj.method(param1, param2);

125. Method Invocation obj.method(param1, param2); push obj push param1 push param2 call method

126. Method Invocation obj.method(param1, param2); obj push obj push param1 push param2 call method

127. Method Invocation obj.method(param1, param2); param1 push obj push param1 push param2 call method obj

128. Method Invocation obj.method(param1, param2); param2 push obj push param1 push param2 call method param1 obj

129. Method Invocation obj.method(param1, param2); obj? push obj push param1 push param2 call method

130. Method Invocation this.add(1, 2); 0: aload_0 1: iconst_1 2: iconst_2 3: invokevirtual #2; //Method add:(II)I

131. INNER CLASSES

132. Inner Classes

133. Inner Classes

134. Inner Classes class Car$Engine extends j.l.Object{ final Car this$0; Car$Engine(Car); public void start(); Code: 0: aload_0 1: getfield #1; //Field this$0:LCar; 4: invokestatic #3; //Car.access$000:(LCar;)V 7: return }

135. Inner Classes public class Car extends j.l.Object{ public Car(); private void move(); static void access$000(Car); Code: 0: aload_0 1: invokespecial #1; // move: ()V; 4: return } class Car$Engine extends j.l.Object{ final Car this$0; Car$Engine(Car); public void start(); Code: 0: aload_0 1: getfield #1; //Field this$0:LCar; 4: invokestatic #3; //Car.access$000:(LCar;)V 7: return }

136. Inner Classes public class Car extends j.l.Object{ public Car(); private void move(); static void access$000(Car); Code: 0: aload_0 1: invokespecial #1; // move: ()V; 4: return } class Car$Engine extends j.l.Object{ final Car this$0; Car$Engine(Car); public void start(); Code: 0: aload_0 1: getfield #1; //Field this$0:LCar; 4: invokestatic #3; //Car.access$000:(LCar;)V 7: return }

137. “HOW DO THEY DO THAT?”

138. object Singleton { def test={} }

139. object Singleton { def test={} } $> scalacSingleton.scala Singleton.class Singleton$.class

140. public final class Singleton extends java.lang.Object{ public static final void test(); Code: 0: getstatic #11; //Field Singleton$.MODULE$:LSingleton$; 3: invokevirtual #13; //Method Singleton$.test:()V 6: return }

141. public final class Singleton extends java.lang.Object{ public static final void test(); Code: 0: getstatic #11; //Field Singleton$.MODULE$:LSingleton$; 3: invokevirtual #13; //Method Singleton$.test:()V 6: return }

142. public final class Singleton extends java.lang.Object{ public static final void test(); Code: 0: getstatic #11; //Field Singleton$.MODULE$:LSingleton$; 3: invokevirtual #13; //Method Singleton$.test:()V 6: return }

143. public final class Singleton extends java.lang.Object{ public static final void test(); Code: 0: getstatic #11; //Field Singleton$.MODULE$:LSingleton$; 3: invokevirtual #13; //Method Singleton$.test:()V 6: return } public final class Singleton$ extends java.lang.Object implements scala.ScalaObject{ public static final Singleton$ MODULE$; public static {}; Code: 0: new #9; //class Singleton$ 3: invokespecial #12; //Method "<init>":()V 6: return public void test(); private Singleton$(); }

144. public final class Singleton extends java.lang.Object{ public static final void test(); Code: 0: getstatic #11; //Field Singleton$.MODULE$:LSingleton$; 3: invokevirtual #13; //Method Singleton$.test:()V 6: return } public final class Singleton$ extends java.lang.Object implements scala.ScalaObject{ public static final Singleton$ MODULE$; public static {}; Code: 0: new #9; //class Singleton$ 3: invokespecial #12; //Method "<init>":()V 6: return public void test(); private Singleton$(); }

145. public final class Singleton extends java.lang.Object{ public static final void test(); Code: 0: getstatic #11; //Field Singleton$.MODULE$:LSingleton$; 3: invokevirtual #13; //Method Singleton$.test:()V 6: return } public final class Singleton$ extends java.lang.Object implements scala.ScalaObject{ public static final Singleton$ MODULE$; public static {}; Code: 0: new #9; //class Singleton$ 3: invokespecial #12; //Method "<init>":()V 6: return public void test(); private Singleton$(); }

146. public final class Singleton extends java.lang.Object{ public static final void test(); Code: 0: getstatic #11; //Field Singleton$.MODULE$:LSingleton$; 3: invokevirtual #13; //Method Singleton$.test:()V 6: return } public final class Singleton$ extends java.lang.Object implements scala.ScalaObject{ public static final Singleton$ MODULE$; public static {}; public void test(); private Singleton$(); Code: 0: aload_0 1: invokespecial#17; //Method java/lang/Object."<init>":()V 4: aload_0 5: putstatic#19; //Field MODULE$:LSingleton$; 8: return

147. object Singleton { def test={} }

148. publicclassSingleton { publicvoid test(){ Singleton$.MODULE$.test(); } } object Singleton { def test={} }

149. publicclassSingleton { publicvoid test(){ Singleton$.MODULE$.test(); } } public final class Singleton$ implements scala.ScalaObject{ public static final Singleton$ MODULE$; static { newSingleton$(); } private Singleton$(){ MODULE$ = this; } public void test() { } } object Singleton { def test={} }

150. classGroovy {}

151. classGroovy {} $> groovycGroovy.groovy $> javap –c –p Groovy

152. classGroovy {} $> groovycGroovy.groovy $> javap –c –p Groovy public class Test extends java.lang.Object implements groovy.lang.GroovyObject{ private static org.codehaus.groovy.reflection.ClassInfo $staticClassInfo; private transient groovy.lang.MetaClass metaClass; public static java.lang.Long __timeStamp; public static java.lang.Long __timeStamp__239_neverHappen1304807931117; private static java.lang.ref.SoftReference $callSiteArray; private static java.lang.Class $class$groovy$lang$MetaClass; private static java.lang.Class $class$Test; private static java.lang.Class $class$java$lang$String; public java.lang.Object this$dist$invoke$2(java.lang.String, java.lang.Object); public void this$dist$set$2(java.lang.String, java.lang.Object); public java.lang.Object this$dist$get$2(java.lang.String); protected groovy.lang.MetaClass $getStaticMetaClass(); public groovy.lang.MetaClass getMetaClass(); public void setMetaClass(groovy.lang.MetaClass); public java.lang.Object invokeMethod(java.lang.String, java.lang.Object); public java.lang.Object getProperty(java.lang.String); public void setProperty(java.lang.String, java.lang.Object);

153. CRASH! BOOM! BANG!

154. Javassist Bytecode manipulation made easy Source-level and bytecode-level API Uses the vocabulary of Java language On-the-fly compilation of the injected code http://www.jboss.org/javassist

155. for(inti = 0; i < 100; i++){ inta = 0; try { while (true) { a++; foo(a); if(a > 1) break; } } catch (Exception e) { } }

156. for(inti = 0; i < 100; i++){ inta = 0; try { while (true) { a++; foo(a); if(a > 1) break; } } catch (Exception e) { } }

157. for(inti = 0; i < 100; i++){ inta = 0; try{ while (true) { a++; foo(a); if(a > 1) break; } } catch (Exception e) { } }

158. for(inti = 0; i < 100; i++){ inta = 0; try{ while(true) { a++; foo(a); if(a > 1) break; } } catch (Exception e) { } }

159. for(inti = 0; i < 100; i++){ inta = 0; try{ while(true) { a++; foo(a); if(a > 1) break; } } catch (Exception e) { } }

160. Javassist CtMethod method = … method.setBody(“ for(inti = 0; i < 100; i++){ inta = 0; try { while (true) { a++; foo(a); if(a > 1) break; } } catch (Exception e) { } }”);

161. -noverify

162. # # A fatal error has been detected by the Java Runtime Environment: # # EXCEPTION_ACCESS_VIOLATION (0xc0000005) at # pc=0x01adff06, pid=7732, tid=868 # # JRE version: 6.0_21-b07 # Java VM: Java HotSpot(TM) Client VM (17.0-b17 mixed mode, # sharing windows-x86 ) # Problematic frame: # j zt.javassist.My.test()V+20 # # An error report file with more information is saved as: # C:orkuzzlerss_err_pid7732.log # # If you would like to submit a bug report, please visit: # http://java.sun.com/webapps/bugreport/crash.jsp # -noverify

163. Exception in thread "main" java.lang.VerifyError: (class: zt/javassist/My, method: test signature: ()V) Inconsistent stack height 0 != 1 -Xverify:all

164. public void test(); Code: Stack=2, Locals=4, Args_size=1 0: iconst_0 1: istore_1 2: iload_1 3: bipush 100 5: if_icmpge 42 8: iconst_0 9: istore_2 10: goto 29 13: iinc 2, 1 16: aload_0 17: iload_2 18: invokevirtual #23; //Method zt/javassist/My.foo:(I)V 21: iload_2 22: iconst_1 23: if_icmple 29 26: goto 32 29: goto 13 32: astore_3 33: goto 36 36: iinc 1, 1 39: goto 2 42: return Exception table: from to target type 10 32 32 Class java/lang/Exception

165. public void test(); Code: Stack=2, Locals=4, Args_size=1 0: iconst_0 1: istore_1 2: iload_1 3: bipush 100 5: if_icmpge 42 8: iconst_0 9: istore_2 10: goto 29 13: iinc 2, 1 16: aload_0 17: iload_2 18: invokevirtual #23; //Method zt/javassist/My.foo:(I)V 21: iload_2 22: iconst_1 23: if_icmple 29 26: goto 32 29: goto 13 32: astore_3 33: goto 36 36: iinc 1, 1 39: goto 2 42: return Exception table: from to target type 10 32 32 Class java/lang/Exception No local variables table

166. public void test(); Code: Stack=2, Locals=4, Args_size=1 0: iconst_0 1: istore_1 2: iload_1 3: bipush 100 5: if_icmpge 42 8: iconst_0 9: istore_2 10: goto 29 13: iinc 2, 1 16: aload_0 17: iload_2 18: invokevirtual #23; //Method zt/javassist/My.foo:(I)V 21: iload_2 22: iconst_1 23: if_icmple 29 26: goto 32 29: goto 13 32: astore_3 33: goto 36 36: iinc 1, 1 39: goto 2 42: return Exception table: from to target type 10 32 32 Class java/lang/Exception No local variables table

167. Q/A