Mastering Java Bytecode - JAX.de 2012

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Ad

Mastering Java Bytecode
Anton Arhipov | ZeroTurnaround

whoami
• Anton Arhipov
• Java Dev / Product Lead
• ZeroTurnaround, JRebel

• @antonarhipov @javarebel

Today – Java Core
• Mastering Java Bytecode

• The Future of Java on Multi-
Core, Lambdas, Spliterators and
Methods

•...

Why Bytecode?
• Know your platform!
• Create your own compiler?
• Programming model (AOP, ORM)
• Awesome tools (JR...

THE INTRO

1+2

1+2

12+

1+2

12+

1+2

12+ PUSH 1
1

1+2

12+ PUSH 1
PUSH 2
2
1

1+2

12+ PUSH 1
PUSH 2
3
ADD

1+2

12+ ICONST_1
ICONST_2
3
IADD

?=1+2

TAXONOMY

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

TYPE OPERATION

TYPE OPERATION

• <TYPE> ::= b, s, c, i, l, f, d, a

TYPE OPERATION

• <TYPE> ::= b, s, c, i, l, f, d, a
• constant values (ldc, iconst_1)

TYPE OPERATION

• <TYPE> ::= b, s, c, i, l, f, d, a
• constant values (ldc, iconst_1)
• Local variables and stack intera...

Bytecode Taxonomy

Bytecode Taxonomy

Stack
Manipulation

Bytecode Taxonomy

Stack Flow
Manipulation Control

Bytecode Taxonomy

Stack Flow
Manipulation Control

Object
Model

Bytecode Taxonomy

Stack Flow
Manipulation Control

Object
Arithmetics
Model

Bytecode Taxonomy

Stack Flow
Manipulation Control

monitorenter
monit...

TOOLING

javap
• Java class file disassembler
• Used with no options shows class structure
only
– Methods, superclass, interfa...

HELLO WORLD!

C:workgeeconclasses>javap Hello -c

C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();...

C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();...

C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();...

C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();...

C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();...

C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();...

C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();...

C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();...

C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();...

C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();...

What’s #1,#2, etc ?
C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Obj...

C:workgeeconclasses>javap Hello -c -verbose

C:workgeeconclasses>javap Hello -c -verbose

C:workgeeconclasses>javap Hello -c -verbose
Compiled from "Hello.java“
public class Hello extends java.lang.Object
Source...

C:workgeeconclasses>javap Hello -c -verbose
Compiled from "Hello.java“
public class Hello extends java.lang.Object
Source...

C:workgeeconclasses>javap Hello -c -verbose
…
public Hello();
Code:
Stack=1, Locals=1, Args_size=1
0: aload_0
1: invok...

C:workgeeconclasses>javap Hello -c -verbose
…
public Hello();
Code:
Stack=1, Locals=1, Args_size=1
0: aload_0
1: invok...

C:workgeeconclasses>javap Hello -c -verbose
…
public Hello();
Code:
Stack=1, Locals=1, Args_size=1
0: aload_0
1: invok...

C:workgeeconclasses>javap Hello -c -verbose
…
public static void main(java.lang.String[]);
Code:
Stack=2, Locals=1, Args...

MODEL OF
COMPUTATION

Stack Machine

Stack Machine
• JVM is a stack-based machine

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

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

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

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

The Frame
Local variables
0 1 2 … N
Operand stack

#1
Constant
...

public java.lang.String getName();
Code:
Stack=1, Locals=1, Args_size=1
0: aload_0
1: getfield #2; //Field name:L...

0 1 2 3 4

aload_0 getfield 00 02 areturn

public java.lang.String ge...

0 1 2 3 4

2A B4 00 02 B0

public java.lang.String getN...

public java.lang.String getName();
Code:
Stack=1, Locals=1, Args_size=1
0: aload_0
1: getfield #2; //Field name:L...

STACK CRUNCHING

dup A
pop B
swap
dup_x1
dup2_x1

dup A
pop A
swap B
dup_x1
dup2_x1

dup A
pop B
swap
dup_x1
dup2_x1

dup B
pop A
swap
dup_x1
dup2_x1

dup B
pop A
swap B
dup_x1
dup2_x1

dup B
pop A
swap B
dup_x1 B
dup2_x1 A

dup2_x2

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 1.0
swap
0.0

dup2_x2
dconst_0
dconst_1 1.0
swap not allowed!

0.0

dup2_x2
dconst_0
dconst_1 1.0
swap2
0.0

dup2_x2
dconst_0
dconst_1 1.0
doesn’t
swap2 exist
0.0

dup2_x2
dconst_0
dconst_1 1.0
dup2_x2
0.0

1.0

dup2_x2
dconst_0
dconst_1 0.0
dup2_x2
pop2 1.0

dup2_x2
dconst_0
dconst_1 0.0
dup2_x2
pop2 1.0

profit! 

LOCAL VARIABLES

Local Variables

Local Variables

public int calculate(int);
Code:
Stack=2, Locals=2, Args_size=2
…

LocalVariableTable:
Start Leng...

Local Variables

public int calculate(int);
Code:
Stack=2, Locals=2, Args_size=2
…

LocalVariableTable:
Start Leng...

Local Variables

public int calculate(int);
Code:
Stack=2, Locals=2, Args_size=2
…

LocalVariableTable:
Start Leng...

Local Variables

The table
public int calculate(int);
Code: ...

Local Variables

public int calculate(int);
Code:
Stack=2, Locals=2, Args_size=2 Sized explicitly
…

L...

Local Variables Stack

var value depth value
...

Local Variables Stack

var value depth value
...

Local Variables Stack

var value depth value
...

Local Variables Stack

var value depth value
...

Local Variables Stack

var value depth value
...

Local Variables Stack

var value depth value
...

load
Local
Variables Stack
Table

store

OBJECTS

Object Initialization
new
0xBB

<init>
Instance initialization method

<clinit>
...

$Object Initialization: static {} static {}; Code: 0: iconst_1 ...$

Object Initialization: static {}

<clinit>

static {};
...

Object Initialization: new

Object Initialization: new

Object Initialization: new

public Initializer();
Code:

Object Initialization: new

public Initializer();
Code:
0: aload_0

Object Initialization: new

public Initializer();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<in...

Object Initialization: new

public Initializer();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<in...

Object Initialization: new

public Initializer();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<in...

Object Initialization: new

public Initializer();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<in...

Object Initialization: new

public Initializer();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<in...

Object Initialization: new

public Initializer();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<in...

Object Initialization: {}

Object Initialization: {}

$Object Initialization: {} public Initializer(int); Code: 0:aload_0 ...$

There’s no initializer

METHOD
INVOCATION

invokeXXX
• invokestatic
• invokespecial
• invokevirtual
• invokeinterface
• invokedynamic

invokestatic
• invokestatic
• invokespecial
• invokevirtual Integer.valueOf(“42”)
• invokeinterface
• invoke...

invokespecial
• invokestatic <init>
• invokespecial
• invokevirtual private void foo();
• invokeint...

invokevirtual
class A
• invokestatic A/method1
A/method2
• in...

invokevirtual
class A
• invokestatic A/method1
A/metho...

invokevirtual
class A
• invokestatic A/method1
...

invokeinterface
class A
• invokestatic A/method1
...

invokeinterface
class A
• invokestatic A/method1
...

invokeinterface
class A
• invokestatic A/method1
...

invokeinterface
class A
• invokestatic A/met...

Method Invocation

Method Invocation
obj.method(param1, param2);

Method Invocation
obj.method(param1, param2);

Method Invocation
obj.method(param1, param2);

push obj
push param1
push param2
call method

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

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

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

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

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

INNER CLASSES

Inner Classes

Inner Classes

Inner Classes

class Car$Engine extends j.l.Object{
final Car this$0;

Car$Engine(Car);

public void start();
Code:
0: a...

Inner Classes
public class Car extends j.l.Object{
...

Inner Classes
public class Car extends j.l.Object{
...

“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; ...

public final class Singleton extends java.lang.Object {
public static final void test();
Code:
0: getstatic #11; ...

public final class Singleton extends java.lang.Object {
public static final void test();
Code:
0: getstatic #11; ...

public final class Singleton extends java.lang.Object {
public static final void test();
Code:
0: getstatic #11; ...

public final class Singleton extends java.lang.Object {
public static final void test();
Code:
0: getstatic #11; ...

public final class Singleton extends java.lang.Object {
public static final void test();
Code:
0: getstatic #11; ...

public final class Singleton extends java.lang.Object {
public static final void test();
Code:
0: getstatic #11; ...

object Singleton {
def test={}
}

public class Singleton {
public void test(){
Singleton$.MODULE$.test();
...

public class Singleton {
public void test(){
Singleton$.MODULE$.test();
...

class Groovy { }

class Groovy { }
$> groovyc Groovy.groovy
$> javap –c –p Groovy

class Groovy { }
$> groovyc Groovy.groovy
$> javap –c –p Groovy
public class Test extends java.lang.Object implements groo...

OBJECTWEB ASM

SLIDES
GOTO IDE
SLIDES
IDE: DEMO

https://github.com/antonarhipov

@antonarhipov

anton@zeroturnaround.com