java bytecode for discriminating developers - javazone 2011

Java Bytecode for

Discriminating Developers

JavaZone’11, Oslo

whoami

http://arhipov.blogspot.com

@antonarhipov

@javarebel

Anton Arhipov Java dev. / Product Lead

JRebel

http://arhipov.blogspot.com/

Java… Do you speak it!?

The Master Plan

Bytecode 101

Examples

THE INTRO

1 + 2 1 2

+

1 + 2

1 2 +

1 2

+

1 + 2

1 2 + PUSH 1 1

1 2

+

1 + 2

1 2 + PUSH 1

PUSH 2 2 1

1 2

+

1 + 2

1 2 + PUSH 1

PUSH 2

ADD

3

1 2

+

1 + 2

1 2 + ICONST_1

ICONST_2

IADD

3

1 2

+

? = 1 + 2

TAXONOMY

Bytecode

One-byte instructions

256 possible opcodes

200+ in use

TYPE OPERATION

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

TYPE OPERATION

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

Operations with constant values (ldc, iconst_1)

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)

TYPE OPERATION

Bytecode Taxonomy

Stack

Manipulation

Bytecode Taxonomy

Stack

Manipulation

Flow

Control

Bytecode Taxonomy

Stack

Manipulation

Flow

Control

Object

Model

Bytecode Taxonomy

Stack

Manipulation

Flow

Control

Arithmetics Object

Model

Arithmetics

Bytecode Taxonomy

Stack

Manipulation

Flow

Control

Object

Model

monitorenter

monitorexit

TOOLING

javap -c -verbose Clazz

HELLO, WORLD!

public class Hello {

public static void main(String[] args) {

System.out.println ( “Hello, World!” );

}

}

C:\work\geecon\classes>javap Hello -c




}

}

C:\work\geecon\classes>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 Hello();

Code:

0: aload_0


4: return

the default constructor




}

}



public Hello();

Code:

0: aload_0


4: return

push this to stack




}

}



public Hello();

Code:

0: aload_0


4: return

invoke <init> on this




}

}



public Hello();

Code:

0: aload_0


4: return




}

}



public Hello();

Code:

0: aload_0


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




}

}



public Hello();

Code:

0: aload_0


4: return


Code:




get static field




}

}



public Hello();

Code:

0: aload_0


4: return


Code:




load string to the stack




}

}



public Hello();

Code:

0: aload_0


4: return


Code:




invoke method with parameter




}

}



public Hello();

Code:

0: aload_0


4: return


Code:







}

}



public Hello();

Code:

0: aload_0


4: return


Code:




What’s #1,#2, etc ?




}

}

C:\work\geecon\classes>javap Hello -c -verbose




}

}

C:\work\geecon\classes>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;




}

}

C:\work\geecon\classes>javap Hello -c -verbose …

public Hello();

Code:

Stack=1, Locals=1, Args_size=1

0: aload_0


4: return

LineNumberTable:

line 1: 0

LocalVariableTable:

Start Length Slot Name Signature

0 5 0 this LHello;




}

}

STACK

MACHINE

Stack Machine

Stack Machine

JVM is a stack-based machine

Stack Machine


Each thread has a stack

Stack Machine



Stack stores frames

Stack Machine



Stack stores frames

Frame is created on method

invocation

Stack Machine



Stack stores frames

Frame is created on method

invocation

Frame consists of: Operand stack

Array of local variables

Operand stack

Local variables

2 0 1 N …

Constant

Pool

#1

public java.lang.String getName();

Code:


0: aload_0

1: getfield #2; //Field name:Ljava/lang/String;

4: areturn

LocalVariableTable:


0 5 0 this LGet;

public class Get {

String name;

public String getName() {

return name;

}

}

aload_0 getfield 00 02 areturn


Code:


0: aload_0


4: areturn

LocalVariableTable:


0 5 0 this LGet;

0 1 2 3 4


Code:


0: aload_0


4: areturn

LocalVariableTable:


0 5 0 this LGet;

2A B4 00 02 B0

0 1 2 3 4

STACK

JUGGLING

A B

dup

pop

swap

dup_x1

dup2_x1

A

B

dup

pop

swap

dup_x1

dup2_x1

A

dup

pop

swap

dup_x1

dup2_x1

A B

dup

pop

swap

dup_x1

dup2_x1

A B

B

dup

pop

swap

dup_x1

dup2_x1

A B

B B A

How do you

swap doubles?

dup2_x2

dup2_x2

dconst_0 0.0

dup2_x2

dconst_0

dconst_1 1.0

0.0

dup2_x2

dconst_0

dconst_1

swap

1.0

0.0

dup2_x2

dconst_0

dconst_1

swap

1.0

0.0

not allowed!

dup2_x2

dconst_0

dconst_1

swap2

1.0

0.0

dup2_x2

dconst_0

dconst_1

swap2

1.0

0.0

doesn’t

exist

dup2_x2

dconst_0

dconst_1

dup2_x2

1.0

0.0

1.0

dup2_x2

dconst_0

dconst_1

dup2_x2

pop2

0.0

1.0

dup2_x2

dconst_0

dconst_1

dup2_x2

pop2

0.0

1.0

profit!

LOCAL

VARIABLES

Local Variables

public int calculate(int value) {

return value + 42;

}

public int calculate(int);

Code:


…

LocalVariableTable:


0 5 0 this LLocalVariables;

0 5 1 value I

Local Variables


return value + 42;

}


Code:


…

LocalVariableTable:



0 5 1 value I

The table

maps

numbers to

names

Local Variables


return value + 42;

}


Code:


…

LocalVariableTable:



0 5 1 value I

Sized explicitly

Local Variables


return value + 42;

}

ldc "Hello"

astore_0

iconst_1

astore_1

aload_0

depth value

Stack

var value

Local Variables

0

1

2

3

4

0

1

2

3

4

ldc "Hello"

astore_0

iconst_1

astore_1

aload_0

depth value

Stack

var value

Local Variables

"Hello" 0

1

2

3

4

0

1

2

3

4

ldc "Hello"

astore_0

iconst_1

astore_1

aload_0

depth value var value

Local Variables

"Hello" 0

1

2

3

4

0

1

2

3

4

Stack

ldc "Hello"

astore_0

iconst_1

astore_1

aload_0

depth value

Stack

var value

Local Variables

"Hello" 0

1

2

3

4

0

1

2

3

4

1

ldc "Hello"

astore_0

iconst_1

astore_1

aload_0

depth value

Stack

var value

Local Variables

"Hello" 0

1

2

3

4

0

1

2

3

4

1

"Hello"

Stack Local

Variables

Table

store

load

OBJECTS

new

<init>

<clinit> Instance initialization method

Class and interface

initialization method

Object Initialization

0xBB

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

public class Initializer {

static int a;

static int b;

static { a = 1; }

static { b = 2; }

}

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

<clinit>


static int a;

static int b;

static { a = 1; }

static { b = 2; }

}

Object Initialization: new


Object o;

public Initializer() {

o = new Object();

}

}


public Initializer();

Code:


Object o;


o = new Object();

}

}



Code:

0: aload_0


Object o;


o = new Object();

}

}



Code:

0: aload_0



Object o;


o = new Object();

}

}



Code:

0: aload_0


4: aload_0


Object o;


o = new Object();

}

}



Code:

0: aload_0


4: aload_0

5: new #2; //class java/lang/Object

8: dup


Object o;


o = new Object();

}

}



Code:

0: aload_0


4: aload_0


8: dup


12: putfield #3; //Field o:Ljava/lang/Object;


Object o;


o = new Object();

}

}



Code:

0: aload_0


4: aload_0


8: dup


12: putfield #3; //Field o:Ljava/lang/Object;

15: return


Object o;


o = new Object();

}

}

Object Initialization: {}


int a;

int b;

int c;

{ a = 1; }

public Initializer(int b) {

this.b = b;

}

{ c = 2; }

}

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


int a;

int b;

int c;

{ a = 1; }

public Initializer(int b) {

this.b = b;

}

{ c = 2; }

}

There’s no initializer

METHOD INVOCATION

&

PARAMETER PASSING

METHOD

INVOCATION

Java Method Invocation


invokestatic

invokespecial

invokevirtual

invokeinterface

invokedynamic


invokestatic

invokespecial

invokevirtual

invokeinterface

invokedynamic Integer.valueOf(“42”)


invokestatic

invokespecial

invokevirtual

invokeinterface

invokedynamic

<init>

private void foo();

super.method();


invokestatic

invokespecial

invokevirtual

invokeinterface

invokedynamic

class A A/method1

A/method2


invokestatic

invokespecial

invokevirtual

invokeinterface

invokedynamic

class A

class B

A/method1

A/method2


invokestatic

invokespecial

invokevirtual

invokeinterface

invokedynamic

class A

class B

A/method1

A/method2

A/method1

B/method2

B/method3


invokestatic

invokespecial

invokevirtual

invokeinterface

invokedynamic

class A

class B impl X

A/method1

A/method2

A/method1

B/method2

B/method3

X/methodX


invokestatic

invokespecial

invokevirtual

invokeinterface

invokedynamic

class A

class B impl X

A/method1

A/method2

A/method1

B/method2

B/method3

X/methodX class D impl X

D/method1

X/methodX


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

Method Invocation

obj.method(param1, param2);

Method Invocation


push obj

push param1

push param2

call method

Method Invocation

obj.method(param1, param2); obj

push obj

push param1

push param2

call method

Method Invocation


obj

param1 push obj

push param1

push param2

call method

Method Invocation


obj

param1

param2 push obj

push param1

push param2

call method

Method Invocation

obj.method(param1, param2); obj?

push obj

push param1

push param2

call method

INNER

CLASSES

Inner Classes

public class Car {

class Engine {

public void start() {

move();

}

}

private void move() {

}

}

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

}

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

}

“HOW DO THEY DO THAT?”

object Singleton {

def test={}

}

object Singleton {

def test={}

}

$> scalac Singleton.scala

Singleton.class Singleton$.class

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

}



Code:



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$();

}



Code:



6: return

}

public final class Singleton$ extends java.lang.Object implements

scala.ScalaObject {


public static {};

public void test();

private Singleton$();

Code:

0: aload_0


4: aload_0

5: putstatic #19; //Field MODULE$:LSingleton$;

8: return

object Singleton {

def test={}

}

object Singleton {

def test={}

}

public class Singleton {

public void test(){

Singleton$.MODULE$.test();

}

}

object Singleton {

def test={}

}

public class Singleton {

public void test(){

Singleton$.MODULE$.test();

}

}

public final class Singleton$

implements scala.ScalaObject {


static { new Singleton$(); }

private Singleton$(){

MODULE$ = this;

}

public void test() {

}

}

CRASH!

BOOM!

BANG!

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

for(int i = 0; i < 100; i++){

int a = 0;

try {

while (true) {

a++;

foo(a);

if(a > 1) break;

}

} catch (Exception e) {

}

}

Javassist

for(int i = 0; i < 100; i++){

int a = 0;

try {

while (true) {

a++;

foo(a);

if(a > 1) break;

}

} catch (Exception e) {

}

}”);

method.setBody(“

CtMethod method = …

Exception in thread "main" java.lang.VerifyError:

(class: zt/javassist/My, method: test signature:

()V) Inconsistent stack height 0 != 1

-Xverify:all

public void test();

Code:


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

public void test();

Code:


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

Bytecode is fun!

Know your platform!

Maybe, you can build your own language?

You may need to read bytecode someday.

http://arhipov.blogspot.com

[email protected]

@antonarhipov

@javarebel

http://arhipov.blogspot.com/

java bytecode for discriminating developers - javazone 2011

Technology

public class hello

public hello code

println hello

string hello

javap c

string code

method javalangobject

method javaioprintstream