Java Bytecode for Discriminating Developers - JavaZone 2011
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The document discusses Java bytecode and provides examples of decompiling a simple "Hello World" Java program to bytecode using the javap tool. It summarizes the structure of bytecode, including one-byte instructions, opcode taxonomy involving stack manipulation, flow control, and object models. The document demonstrates how javap can be used to disassemble a class file into bytecode instructions and interpret the constant pool references.
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
}](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-31-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>javap Hello -c
}](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-32-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>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](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-33-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>javap Hello -c
} Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();
Code: the default constructor
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-34-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>javap Hello -c
} Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();
Code: push this to stack
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-35-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>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](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-36-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>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](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-37-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>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](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-38-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>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
get static field
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](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-39-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>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](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-40-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>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](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-41-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>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](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-42-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>javap Hello -c
What’s #1,#2, etc ?
} 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](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-43-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>javap Hello -c -verbose
}](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-44-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>javap Hello -c -verbose
}](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-45-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>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;](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-46-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>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;](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-47-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>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;](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-48-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>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;](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-49-320.jpg)
![public class Hello {
public static void main(String[] args) {
System.out.println ( “Hello, World!” );
}
C:workgeeconclasses>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;](https://image.slidesharecdn.com/javazone-antonarhipov-javabytecodefordiscriminatingdevelopers-110908045212-phpapp01/85/Java-Bytecode-for-Discriminating-Developers-JavaZone-2011-50-320.jpg)
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Java Bytecode for Discriminating Developers - JavaZone 2011
- 1. Java Bytecode for Discriminating Developers JavaZone’11, Oslo
- 2. whoami Anton Arhipov Java dev. / Product Lead JRebel http://arhipov.blogspot.com @antonarhipov @javarebel
- 3. Java… Do you speak it!?
- 4. Java… Do you speak it!?
- 5. The Master Plan Examples Bytecode 101
- 6. THE INTRO
- 7. 1+2
- 8. + 1+2 1 2
- 9. + 1+2 1 2 12+
- 10. + 1+2 1 2 12+
- 11. + 1+2 1 2 12+ PUSH 1 1
- 12. + 1+2 1 2 12+ PUSH 1 PUSH 2 2 1
- 13. + 1+2 1 2 12+ PUSH 1 PUSH 2 3 ADD
- 14. + 1+2 1 2 12+ ICONST_1 ICONST_2 3 IADD
- 15. ?=1+2
- 16. TAXONOMY
- 17. Bytecode One-byte instructions 256 possible opcodes 200+ in use
- 18. Bytecode One-byte instructions 256 possible opcodes 200+ in use
- 19. TYPE OPERATION
- 20. TYPE OPERATION <TYPE> ::= b, s, c, i, l, f, d, a
- 21. TYPE OPERATION <TYPE> ::= b, s, c, i, l, f, d, a Operations with constant values (ldc, iconst_1)
- 22. 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)
- 23. Bytecode Taxonomy Stack Manipulation
- 24. Bytecode Taxonomy Stack Flow Manipulation Control
- 25. Bytecode Taxonomy Stack Flow Manipulation Control Object Model
- 26. Bytecode Taxonomy Stack Flow Manipulation Control Object Arithmetics Model
- 27. Bytecode Taxonomy Stack Flow Manipulation Control monitorenter monitorexit Object Arithmetics Model
- 28. TOOLING
- 29. javap -c -verbose Clazz
- 30. HELLO, WORLD!
- 31. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } }
- 32. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>javap Hello -c }
- 33. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>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
- 34. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>javap Hello -c } Compiled from "Hello.java" public class Hello extends java.lang.Object{ public Hello(); Code: the default constructor 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return
- 35. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>javap Hello -c } Compiled from "Hello.java" public class Hello extends java.lang.Object{ public Hello(); Code: push this to stack 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return
- 36. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>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
- 37. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>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
- 38. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>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
- 39. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>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 get static field 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
- 40. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>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
- 41. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>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
- 42. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>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. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>javap Hello -c What’s #1,#2, etc ? } 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
- 44. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>javap Hello -c -verbose }
- 45. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>javap Hello -c -verbose }
- 46. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>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. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>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;
- 48. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>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. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>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. public class Hello { public static void main(String[] args) { System.out.println ( “Hello, World!” ); } C:workgeeconclasses>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;
- 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. Local variables 0 1 2 … N Operand stack #1 Constant Pool
- 59. public class Get { String name; public String getName() { return name; } } 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. public class Get { String name; public String getName() { return name; } } 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 aload_0 getfield 00 02 areturn 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. 0 1 2 3 4 2A B4 00 02 B0 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;
- 64. STACK JUGGLING
- 65. dup A pop B swap dup_x1 dup2_x1
- 66. dup A pop A swap B dup_x1 dup2_x1
- 67. dup A pop B swap dup_x1 dup2_x1
- 68. dup B pop A swap dup_x1 dup2_x1
- 69. dup B pop A swap B dup_x1 dup2_x1
- 70. dup B pop A swap B dup_x1 B dup2_x1 A
- 71. How do you swap doubles?
- 72. dup2_x2
- 73. dup2_x2 dconst_0 0.0
- 74. dup2_x2 dconst_0 dconst_1 1.0 0.0
- 75. dup2_x2 dconst_0 dconst_1 1.0 swap 0.0
- 76. dup2_x2 dconst_0 dconst_1 1.0 swap not allowed! 0.0
- 77. dup2_x2 dconst_0 dconst_1 1.0 swap2 0.0
- 78. dup2_x2 dconst_0 dconst_1 1.0 doesn’t swap2 exist 0.0
- 79. dup2_x2 dconst_0 dconst_1 1.0 dup2_x2 0.0 1.0
- 80. dup2_x2 dconst_0 dconst_1 0.0 dup2_x2 pop2 1.0
- 81. dup2_x2 dconst_0 dconst_1 0.0 dup2_x2 pop2 1.0 profit!
- 82. LOCAL VARIABLES
- 83. Local Variables public int calculate(int value) { return value + 42; }
- 84. Local Variables public int calculate(int value) { return value + 42; } 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
- 85. Local Variables public int calculate(int value) { return value + 42; } 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
- 86. Local Variables public int calculate(int value) { return value + 42; } 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
- 87. Local Variables public int calculate(int value) { return value + 42; } The table public int calculate(int); Code: maps Stack=2, Locals=2, Args_size=2 numbers to … names LocalVariableTable: Start Length Slot Name Signature 0 5 0 this LLocalVariables; 0 5 1 value I
- 88. Local Variables public int calculate(int value) { return value + 42; } public int calculate(int); Code: Stack=2, Locals=2, Args_size=2 Sized explicitly … LocalVariableTable: Start Length Slot Name Signature 0 5 0 this LLocalVariables; 0 5 1 value I
- 89. Local Variables Stack var value depth value ldc "Hello" 0 0 astore_0 1 iconst_1 1 astore_1 2 aload_0 2 3 3 4 4
- 90. Local Variables Stack var value depth value ldc "Hello" 0 0 "Hello" astore_0 1 iconst_1 1 astore_1 2 aload_0 2 3 3 4 4
- 91. Local Variables Stack var value depth value ldc "Hello" 0 "Hello" 0 astore_0 1 iconst_1 1 astore_1 2 aload_0 2 3 3 4 4
- 92. Local Variables Stack var value depth value ldc "Hello" 0 "Hello" 0 1 astore_0 1 iconst_1 1 astore_1 2 aload_0 2 3 3 4 4
- 93. Local Variables Stack var value depth value ldc "Hello" 0 "Hello" 0 astore_0 1 1 iconst_1 1 astore_1 2 aload_0 2 3 3 4 4
- 94. Local Variables Stack var value depth value ldc "Hello" 0 "Hello" 0 "Hello" astore_0 1 1 iconst_1 1 astore_1 2 aload_0 2 3 3 4 4
- 95. load Local Variables Stack Table store
- 96. OBJECTS
- 97. Object Initialization new 0xBB <init> Instance initialization method <clinit> Class and interface initialization method
- 98. Object Initialization: static {} public class Initializer { static int a; static int b; static { a = 1; } static { b = 2; } 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: static {} public class Initializer { static int a; static int b; <clinit> static { a = 1; } static { b = 2; } static {}; Code: } 0: iconst_1 1: putstatic #2; //Field a:I 4: iconst_2 5: putstatic #3; //Field b:I 8: return
- 100. Object Initialization: new public class Initializer { Object o; public Initializer() { o = new Object(); } }
- 101. Object Initialization: new public class Initializer { Object o; public Initializer() { o = new Object(); public Initializer(); } Code: }
- 102. Object Initialization: new public class Initializer { Object o; public Initializer() { o = new Object(); public Initializer(); } Code: 0: aload_0 }
- 103. Object Initialization: new public class Initializer { Object o; public Initializer() { o = new Object(); public Initializer(); } Code: 0: aload_0 } 1: invokespecial #1; //Method java/lang/Object."<init>":()V
- 104. Object Initialization: new public class Initializer { Object o; public Initializer() { o = new Object(); public Initializer(); } Code: 0: aload_0 } 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: aload_0
- 105. Object Initialization: new public class Initializer { Object o; public Initializer() { o = new Object(); 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
- 106. Object Initialization: new public class Initializer { Object o; public Initializer() { o = new Object(); 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;
- 107. Object Initialization: new public class Initializer { Object o; public Initializer() { o = new Object(); 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: new public class Initializer { Object o; public Initializer() { o = new Object(); 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
- 109. Object Initialization: {} public class Initializer { int a; int b; int c; { a = 1; } public Initializer(int b) { this.b = b; } { c = 2; } }
- 110. Object Initialization: {} public class Initializer { int a; int b; int c; { a = 1; } public Initializer(int b) { this.b = b; } { c = 2; } }
- 111. Object Initialization: {} public class Initializer { int a; int b; int c; { a = 1; } public Initializer(int b) { this.b = b; } { c = 2; } }
- 112. Object Initialization: {} public class Initializer { int a; int b; int c; { a = 1; } public Initializer(int b) { this.b = b; } { c = 2; } }
- 113. Object Initialization: {} public class Initializer { int a; public Initializer(int); int b; Code: int c; 0: aload_0 1: invokespecial #1; // ..<init> 4: aload_0 { a = 1; } 5: iconst_1 6: putfield #2; //Field a:I public Initializer(int b) { 9: aload_0 this.b = b; 10: iconst_2 } 11: putfield #3; //Field c:I 14: aload_0 { c = 2; } 15: iload_1 } 16: putfield #4; //Field b:I 19: return
- 117. METHOD INVOCATION & PARAMETER PASSING METHOD INVOCATION
- 119. Java Method Invocation invokestatic invokespecial invokevirtual invokeinterface invokedynamic
- 120. Java Method Invocation invokestatic invokespecial invokevirtual invokeinterface Integer.valueOf(“42”) invokedynamic
- 121. Java Method Invocation invokestatic invokespecial <init> invokevirtual invokeinterface invokedynamic private void foo(); super.method();
- 122. Java Method Invocation invokestatic class A invokespecial A/method1 A/method2 invokevirtual invokeinterface invokedynamic
- 123. Java Method Invocation invokestatic class A invokespecial A/method1 A/method2 invokevirtual invokeinterface class B invokedynamic
- 124. Java Method Invocation invokestatic class A invokespecial A/method1 A/method2 invokevirtual invokeinterface class B A/method1 invokedynamic B/method2 B/method3
- 125. Java Method Invocation invokestatic class A invokespecial A/method1 A/method2 invokevirtual invokeinterface class B impl X A/method1 invokedynamic B/method2 B/method3 X/methodX
- 126. Java Method Invocation invokestatic class A invokespecial A/method1 A/method2 invokevirtual invokeinterface class B impl X A/method1 invokedynamic B/method2 B/method3 X/methodX class D impl X D/method1 X/methodX
- 127. Java Method Invocation invokestatic class A invokespecial A/method1 A/method2 invokevirtual invokeinterface class B impl X A/method1 invokedynamic B/method2 B/method3 X/methodX class D impl X D/method1 X/methodX
- 128. Java Method Invocation 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
- 130. Method Invocation obj.method(param1, param2); push obj push param1 push param2 call method
- 131. Method Invocation obj.method(param1, param2); obj push obj push param1 push param2 call method
- 132. Method Invocation obj.method(param1, param2); param1 push obj obj push param1 push param2 call method
- 133. Method Invocation obj.method(param1, param2); param2 push obj param1 push param1 obj push param2 call method
- 134. Method Invocation obj.method(param1, param2); obj? push obj push param1 push param2 call method
- 135. INNER CLASSES
- 136. Inner Classes public class Car { class Engine { public void start() { move(); } } private void move() { } }
- 137. 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$000:(LCar;)V 7: return }
- 138. Inner Classes public class Car extends j.l.Object{ public Car(); private void move(); class Car$Engine extends j.l.Object{ static void access$000(Car); final Car this$0; Code: 0: aload_0 Car$Engine(Car); 1: invokespecial #1; // move: ()V; 4: return public void start(); } Code: 0: aload_0 1: getfield #1; //Field this$0:LCar; 4: invokestatic #3; // Car.access$000:(LCar;)V 7: return }
- 139. Inner Classes public class Car extends j.l.Object{ public Car(); private void move(); class Car$Engine extends j.l.Object{ static void access$000(Car); final Car this$0; Code: 0: aload_0 Car$Engine(Car); 1: invokespecial #1; // move: ()V; 4: return public void start(); } Code: 0: aload_0 1: getfield #1; //Field this$0:LCar; 4: invokestatic #3; // Car.access$000:(LCar;)V 7: return }
- 140. “HOW DO THEY DO THAT?”
- 141. object Singleton { def test={} }
- 142. object Singleton { def test={} } $> scalac Singleton.scala Singleton.class Singleton$.class
- 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 }
- 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 }
- 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 }
- 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$; public static {}; Code: 0: new #9; //class Singleton$ 3: invokespecial #12; //Method "<init>":()V 6: return public void test(); private Singleton$(); }
- 147. public final class Singleton extends java.lang.Object { public static final void test(); Code: 0: getstatic #11; //Field Singleton$.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$(); }
- 148. public final class Singleton extends java.lang.Object { public static final void test(); Code: 0: getstatic #11; //Field Singleton$.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$(); }
- 149. public final class Singleton extends java.lang.Object { public static final void test(); Code: 0: getstatic #11; //Field Singleton$.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
- 150. object Singleton { def test={} }
- 151. public class Singleton { public void test(){ Singleton$.MODULE$.test(); } } object Singleton { def test={} }
- 152. public class Singleton { public void test(){ Singleton$.MODULE$.test(); } } public final class Singleton$ object Singleton { implements scala.ScalaObject { def test={} public static final Singleton$ MODULE$; } static { new Singleton$(); } private Singleton$(){ MODULE$ = this; } public void test() { } }
- 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(int i = 0; i < 100; i++){ int a = 0; try { while (true) { a++; foo(a); if(a > 1) break; } } catch (Exception e) { } }
- 156. Javassist CtMethod method = … method.setBody(“ for(int i = 0; i < 100; i++){ int a = 0; try { while (true) { a++; foo(a); if(a > 1) break; } } catch (Exception e) { } }”);
- 157. -Xverify:all Exception in thread "main" java.lang.VerifyError: (class: zt/javassist/My, method: test signature: ()V) Inconsistent stack height 0 != 1
- 158. 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
- 159. 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 No local 22: iconst_1 23: if_icmple 29 variables table 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
- 160. 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 No local 22: iconst_1 23: if_icmple 29 variables table 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
- 161. Bytecode is fun! Know your platform! Maybe, you can build your own language? You may need to read bytecode someday.
- 162. http://arhipov.blogspot.com [email protected] @antonarhipov @javarebel