Java Bytecode For Discriminating Developers - GeeCON 2011

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Java Bytecode for Discriminating Developers<br />Anton Arhipov<br />

whoami<br />Anton Arhipov<br />Java dev. / Product Lead<br />JRebel<br />http://arhipov.blogspot.com<br />@antonarhipov<br...

Who-are-you?<br />

The Master Plan<br />80%: Bytecode 101<br />20%: Examples<br />

THE INTRO<br />

1 + 2<br />

+<br />1 + 2<br />1<br />2<br />

+<br />1 + 2<br />1<br />2<br />1 2 + <br />

+<br />1 + 2<br />1<br />2<br />1 2 + <br />

+<br />1 + 2<br />1<br />2<br />1 2 + <br />1<br />PUSH 1<br />

+<br />1 + 2<br />1<br />2<br />1 2 + <br />2<br />PUSH 1<br />PUSH 2<br />1<br />

+<br />1 + 2<br />1<br />2<br />1 2 + <br />3<br />PUSH 1<br />PUSH 2<br />ADD<br />

+<br />1 + 2<br />1<br />2<br />1 2 + <br />3<br />ICONST_1<br />ICONST_2<br />IADD<br />

? = 1 + 2<br />

TAXONOMY<br />

Bytecode<br />One-byte instructions<br />256 possible opcodes<br />200+ in use<br />

Bytecode<br />One-byte instructions<br />256 possible opcodes<br />200+ in use<br />

TYPE<br />OPERATION<br />

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

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

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

Bytecode Taxonomy<br />Stack <br />Manipulation<br />

Bytecode Taxonomy<br />Stack <br />Manipulation<br />Flow<br />Control<br />

Bytecode Taxonomy<br />Stack <br />Manipulation<br />Flow<br />Control<br />Object <br />Model<br />

Bytecode Taxonomy<br />Stack <br />Manipulation<br />Flow<br />Control<br />Object <br />Model<br />Arithmetics<br />

Bytecode Taxonomy<br />Stack <br />Manipulation<br />Flow<br />Control<br />Object <br />Model<br />Arithmetics<br />monit...

TOOLING<br />

javap<br />Java class file disassembler<br />Used with no options shows class structure only<br />Methods, superclass, int...

HELLO WORLD!<br />

$C:\work\geecon\classes>javap Hello -c<br />$

$C:\work\geecon\classes>javap Hello -c<br />Compiled from "Hello.java"<br />public class Hello extends java.lang.Object{<br...$

$C:\work\geecon\classes>javap Hello -c<br />Compiled from "Hello.java"<br />public class Hello extends java.lang.Object{<br...$

$C:\work\geecon\classes>javap Hello -c<br />Compiled from "Hello.java"<br />public class Hello extends java.lang.Object{<br...$

$C:\work\geecon\classes>javap Hello -c<br />Compiled from "Hello.java"<br />public class Hello extends java.lang.Object{<br...$

$C:\work\geecon\classes>javap Hello -c<br />Compiled from "Hello.java"<br />public class Hello extends java.lang.Object{<br...$

$C:\work\geecon\classes>javap Hello -c<br />Compiled from "Hello.java"<br />public class Hello extends java.lang.Object{<br...$

$C:\work\geecon\classes>javap Hello -c<br />Compiled from "Hello.java"<br />public class Hello extends java.lang.Object{<br...$

$C:\work\geecon\classes>javap Hello -c<br />Compiled from "Hello.java"<br />public class Hello extends java.lang.Object{<br...$

$C:\work\geecon\classes>javap Hello -c<br />Compiled from "Hello.java"<br />public class Hello extends java.lang.Object{<br...$

$C:\work\geecon\classes>javap Hello -c<br />Compiled from "Hello.java"<br />public class Hello extends java.lang.Object{<br...$

$What’s #1,#2, etc ?<br />C:\work\geecon\classes>javap Hello -c<br />Compiled from "Hello.java"<br />public class Hello ext...$

$C:\work\geecon\classes>javap Hello -c -verbose<br />$

$C:\work\geecon\classes>javap Hello -c -verbose<br />$

$C:\work\geecon\classes>javap Hello -c -verbose<br />Compiled from "Hello.java“<br />public class Hello extends java.lang.O...$

$C:\work\geecon\classes>javap Hello -c -verbose<br />Compiled from "Hello.java“<br />public class Hello extends java.lang.O...$

$C:\work\geecon\classes>javap Hello -c -verbose<br />…<br />public Hello();<br />Code:<br /> Stack=1, Locals=1, Args_size...$

$C:\work\geecon\classes>javap Hello -c -verbose<br />…<br />public Hello();<br />Code:<br /> Stack=1, Locals=1, Args_size...$

$C:\work\geecon\classes>javap Hello -c -verbose<br />…<br />public Hello();<br />Code:<br /> Stack=1, Locals=1, Args_size...$

$C:\work\geecon\classes>javap Hello -c -verbose<br />…<br />public static void main(java.lang.String[]);<br /> Code:<br />...$

STACK MACHINE<br />

Stack Machine<br />

Stack Machine<br />JVM is a stack-based machine<br />

Stack Machine<br />JVM is a stack-based machine<br />Each thread has a stack<br />

Stack Machine<br />JVM is a stack-based machine<br />Each thread has a stack<br />Stack stores frames<br />

Stack Machine<br />JVM is a stack-based machine<br />Each thread has a stack<br />Stack stores frames<br />Frame is create...

Stack Machine<br />JVM is a stack-based machine<br />Each thread has a stack<br />Stack stores frames<br />Frame is create...

The Frame<br />Local variables<br />N<br />1<br />2<br />3<br />…<br />Operand stack<br />#1<br />Constant <br />Pool<br />

public java.lang.String getName();<br /> Code:<br /> Stack=1, Locals=1, Args_size=1<br /> 0: aload_0<br /> 1: g...

0 1 2 3 4<br />areturn<br />aload_0<br />00<br />02<br />getfield<br...

0 1 2 3 4<br />B0<br />2A<br />00<br />02<br />B4<br />public java.l...

public java.lang.String getName();<br /> Code:<br /> Stack=1, Locals=1, Args_size=1<br /> 0: aload_0<br /> 1: g...

STACK CRUNCHING<br />

A<br />dup<br />pop<br />swap<br />dup_x1<br />dup2_x2<br />B<br />

A<br />dup<br />pop<br />swap<br />dup_x1<br />dup2_x2<br />A<br />B<br />

A<br />dup<br />pop<br />swap<br />dup_x1<br />dup2_x2<br />B<br />

B<br />dup<br />pop<br />swap<br />dup_x1<br />dup2_x2<br />A<br />

B<br />dup<br />pop<br />swap<br />dup_x1<br />dup2_x2<br />A<br />B<br />

B<br />dup<br />pop<br />swap<br />dup_x1<br />dup2_x2<br />A<br />B<br />B<br />A<br />

dup2_x2<br />How do you <br />swap doubles?<br />

dup2_x2<br />

dup2_x2<br />dconst_0<br />0.0<br />

dup2_x2<br />dconst_0<br />dconst_1<br />1.0<br />0.0<br />

dup2_x2<br />dconst_0<br />dconst_1<br />swap<br />1.0<br />0.0<br />

dup2_x2<br />dconst_0<br />dconst_1<br />swap<br />1.0<br />not allowed!<br />0.0<br />

dup2_x2<br />dconst_0<br />dconst_1<br />swap2<br />1.0<br />0.0<br />

dup2_x2<br />dconst_0<br />dconst_1<br />swap2<br />1.0<br />doesn’t<br />exist<br />0.0<br />

dup2_x2<br />dconst_0<br />dconst_1<br />dup2_x2<br />1.0<br />0.0<br />1.0<br />

dup2_x2<br />dconst_0<br />dconst_1<br />dup2_x2<br />pop2<br />0.0<br />1.0<br />

dup2_x2<br />dconst_0<br />dconst_1<br />dup2_x2<br />pop2<br />0.0<br />1.0<br />profit!<br />

LOCAL VARIABLES<br />

Local Variables<br />

public int calculate(int);<br />Code:<br /> Stack=2, Locals=2, Args_size=2<br /> …<br /> LocalVariableTable:<br /> ...

public int calculate(int);<br />Code:<br /> Stack=2, Locals=2, Args_size=2<br /> …<br /> LocalVariableTable:<br /> ...

public int calculate(int);<br />Code:<br /> Stack=2, Locals=2, Args_size=2<br /> …<br /> LocalVariableTable:<br /> ...

The table maps numbers to names<br />public int calculate(int);<br />Code:<br /> Stack=2, Locals=2, Args_size=2<br /> ...

Sized explicitly<br />public int calculate(int);<br />Code:<br /> Stack=2, Locals=2, Args_size=2<br /> …<br /> Local...

Stack<br />Local Variables<br />value<br />var<br />value<br />depth<br />ldc"Hello"<br />astore_0<br />iconst_1<br />asto...

Stack<br />Local Variables<br />value<br />var<br />value<br />depth<br />ldc"Hello"<br />astore_0<br />iconst_1<br />asto...

Stack<br />Local Variables<br />value<br />var<br />value<br />depth<br />ldc"Hello"<br />astore_0<br />iconst_1<br />asto...

Stack<br />Local Variables<br />value<br />var<br />value<br />depth<br />ldc"Hello"<br />astore_0<br />iconst_1<br />asto...

Stack<br />Local Variables<br />value<br />var<br />value<br />depth<br />ldc"Hello"<br />astore_0<br />iconst_1<br />asto...

Stack<br />Local Variables<br />value<br />var<br />value<br />depth<br />ldc"Hello"<br />astore_0<br />iconst_1<br />asto...

load<br />Stack<br />Local Variables Table<br />store<br />

OBJECTS<br />

new<br /><init><br /><clinit><br />0xBB<br />Instance initialization method<br />Class and interface initialization method...

$Object Initialization: static {}<br />static {};<br /> Code:<br />0: iconst_1<br /> 1: putstatic #2; //Field ...$

$Object Initialization: static {}<br /><clinit><br />static {};<br /> Code:<br />0: iconst_1<br /> 1: putstatic ...$

Object Initialization: new<br />

Object Initialization: new<br />public Initializer();<br />Code:<br />

Object Initialization: new<br />public Initializer();<br />Code:<br /> 0: aload_0<br />

Object Initialization: new<br />public Initializer();<br />Code:<br /> 0: aload_0<br /> 1: invokespecial #1; //M...

Object Initialization: new<br />public Initializer();<br />Code:<br /> 0: aload_0<br /> 1: invokespecial #1; //M...

Object Initialization: new<br />public Initializer();<br />Code:<br /> 0: aload_0<br /> 1: invokespecial #1; //M...

Object Initialization: new<br />public Initializer();<br />Code:<br /> 0: aload_0<br /> 1: invokespecial #1; //M...

Object Initialization: new<br />public Initializer();<br />Code:<br /> 0: aload_0<br /> 1: invokespecial #1; //M...

Object Initialization: new<br />public Initializer();<br />Code:<br /> 0: aload_0<br /> 1: invokespecial #1; //M...

Object Initialization: {}<br />

Object Initialization: {}<br />?<br />

$Object Initialization: {}<br />public Initializer(int);<br /> Code:<br />0:aload_0<br /> 1:invokespecial #1; // ..<in...$

There’s no initializer<br />

METHOD INVOCATION&PARAMETER PASSING<br />

Methods & Parameters<br />invokestatic<br />invokespecial<br />invokevirtual<br />invokeinterface<br />invokedynamic<br />...

Methods & Parameters<br />invokestatic<br />invokespecial<br />invokevirtual<br />invokeinterface<br />invokedynamic<br />...

Methods & Parameters<br />invokestatic<br />invokespecial<br />invokevirtual<br />invokeinterface<br />invokedynamic<br />...

Methods & Parameters<br />invokestatic<br />invokespecial<br />invokevirtual<br />invokeinterface<br />invokedynamic<br />...

Methods & Parameters<br />invokestatic<br />invokespecial<br />invokevirtual<br />invokeinterface<br />invokedynamic<br />...

Methods & Parameters<br />invokestatic<br />invokespecial<br />invokevirtual<br />invokeinterface<br />invokedynamic<br />...

Methods & Parameters<br />invokestatic<br />invokespecial<br />invokevirtual<br />invokeinterface<br />invokedynamic<br />...

Methods & Parameters<br />invokestatic<br />invokespecial<br />invokevirtual<br />invokeinterface<br />invokedynamic<br />...

Methods & Parameters<br />invokestatic<br />invokespecial<br />invokevirtual<br />invokeinterface<br />invokedynamic<br />...

Methods & Parameters<br />invokestatic<br />invokespecial<br />invokevirtual<br />invokeinterface<br />invokedynamic<br />...

Method Invocation<br />obj.method(param1, param2);<br />

Method Invocation<br />obj.method(param1, param2);<br />push obj<br />push param1<br />push param2<br />call method<br />

Method Invocation<br />obj.method(param1, param2);<br />obj<br />push obj<br />push param1<br />push param2<br />call meth...

Method Invocation<br />obj.method(param1, param2);<br />param1<br />push obj<br />push param1<br />push param2<br />call m...

Method Invocation<br />obj.method(param1, param2);<br />param2<br />push obj<br />push param1<br />push param2<br />call m...

Method Invocation<br />obj.method(param1, param2);<br />obj?<br />push obj<br />push param1<br />push param2<br />call met...

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

INNER CLASSES<br />

Inner Classes<br />

Inner Classes<br />

Inner Classes<br />class Car$Engine extends j.l.Object{<br />final Car this$0;<br />Car$Engine(Car);<br />public void star...

Inner Classes<br />public class Car extends j.l.Object{<br />public Car();<br />private void move();<br />static void acce...

Inner Classes<br />public class Car extends j.l.Object{<br />public Car();<br />private void move();<br />static void acce...

“HOW DO THEY DO THAT?” <br />

object Singleton {<br />def test={}<br />}<br />

object Singleton {<br />def test={}<br />}<br />$> scalacSingleton.scala<br />Singleton.class<br />Singleton$.class<br />

public final class Singleton extends java.lang.Object{<br />public static final void test();<br />Code:<br />0: getstati...

public final class Singleton extends java.lang.Object{<br />public static final void test();<br />Code:<br />0: getstati...

public final class Singleton extends java.lang.Object{<br />public static final void test();<br />Code:<br />0: getstati...

public final class Singleton extends java.lang.Object{<br />public static final void test();<br />Code:<br />0: getstati...

public final class Singleton extends java.lang.Object{<br />public static final void test();<br />Code:<br />0: getstati...

public final class Singleton extends java.lang.Object{<br />public static final void test();<br />Code:<br />0: getstati...

public final class Singleton extends java.lang.Object{<br />public static final void test();<br />Code:<br />0: getstati...

object Singleton {<br />def test={}<br />}<br />

publicclassSingleton {<br />publicvoid test(){<br />Singleton$.MODULE$.test();<br /> }<br />}<br />object Singleton {<br ...

publicclassSingleton {<br />publicvoid test(){<br />Singleton$.MODULE$.test();<br /> }<br />}<br />public final class Sin...

classGroovy {}<br />

classGroovy {}<br />$> groovycGroovy.groovy<br />$> javap –c –p Groovy<br />

classGroovy {}<br />$> groovycGroovy.groovy<br />$> javap –c –p Groovy<br />public class Test extends java.lang.Object imp...

CRASH! BOOM! BANG!<br />

Javassist<br />Bytecode manipulation made easy<br />Source-level and bytecode-level API<br />Uses the vocabulary of Java l...

for(inti = 0; i < 100; i++){ <br />inta = 0;<br /> try { <br /> while (true) {<br /> a++;<br /> foo(a);<br /> ...

for(inti = 0; i < 100; i++){ <br />inta = 0;<br />try { <br /> while (true) {<br /> a++;<br /> foo(a);<br /> ...

for(inti = 0; i < 100; i++){ <br />inta = 0;<br />try{ <br />while (true) {<br /> a++;<br /> foo(a);<br /> if...

for(inti = 0; i < 100; i++){ <br />inta = 0;<br />try{ <br />while(true) {<br />a++;<br /> foo(a);<br /> if(a > 1...

for(inti = 0; i < 100; i++){ <br />inta = 0;<br />try{ <br />while(true) {<br /> a++;<br />foo(a);<br /> if(a > 1...

Javassist<br />CtMethod method = …<br />method.setBody(“<br />for(inti = 0; i < 100; i++){ <br />inta = 0;<br /> try { <b...

-noverify<br />

#<br /># A fatal error has been detected by the Java Runtime Environment:<br />#<br /># EXCEPTION_ACCESS_VIOLATION (0xc00...

Exception in thread "main" java.lang.VerifyError: (class: zt/javassist/My, method: test signature: ()V) Inconsistent stack...

public void test();<br /> Code:<br /> Stack=2, Locals=4, Args_size=1<br /> 0: iconst_0<br /> 1: istore_1<br /> ...

public void test();<br /> Code:<br /> Stack=2, Locals=4, Args_size=1<br /> 0: iconst_0<br /> 1: istore_1<br /> ...

public void test();<br /> Code:<br /> Stack=2, Locals=4, Args_size=1<br /> 0: iconst_0<br /> 1: istore_1<br /> ...

Q/A<br />