SlideShare a Scribd company logo

Mastering java bytecode with ASM - GeeCON 2012

Download as PPTX, PDF
Anton Arhipov, profile picture
Anton Arhipov

The document provides an overview of using the ASM bytecode manipulation framework. It discusses constructing a ClassWriter to output bytecode, visiting classes and methods, and generating simple bytecode instructions like loading constants, invoking methods, and control flow instructions like if/goto. The goal is to demonstrate how to generate and modify Java bytecode programmatically using ASM.

TechnologyEducation
1 of 119
Downloaded 276 times
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
Mastering Java Bytecode with ASM Learn some bytecode to yourself!
whoami Anton Arhipov Java Dev / Product Lead ZeroTurnaround, JRebel Messing with bytecode since 2010 anton@zeroturnaround.com @antonarhipov @javarebel
whoami Anton Arhipov Java Dev / Product Lead ZeroTurnaround, JRebel Messing with bytecode since 2010 anton@zeroturnaround.com @antonarhipov @javarebel
Why Bytecode? • Know your platform! • Build your own JVM language? • Programming models (AOP, ORM) • Awesome tools (like JRebel ) ... just bored?
Bytecode 101 Instrumentation API javap ObjectWeb ASM
Bytecode 101 Gentle introduction
Adding Two Values A+B
Adding Two Values A+B AB+
Adding Two Values A+B AB+
Adding Two Values A+B PUSH A A AB+
Adding Two Values A+B PUSH 1 PUSH 2 B AB+ A
Adding Two Values A+B PUSH 1 PUSH 2 15 AB+ ADD
Adding Two Values A+B ICONST_1 ICONST_2 15 AB+ IADD
TYPE OPERATION • <TYPE> ::= b, s, c, i, l, f, d, a • 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 & branching (cmpl, ifeq, jsr, tableswitch) • Conversions (l2d, i2l)
Model of Execution
Enter JVM JVM process
Enter Threads Thread A Thread B Thread C Thread D
Enter Frames
The Frame Local variables 0 1 2 … N Operand stack #1 Constant Pool
Juggling The Stack
Juggling The Stack dup A pop B swap dup_x1 dup2_x1
Juggling The Stack dup A pop A swap B dup_x1 dup2_x1
Juggling The Stack dup A pop B swap dup_x1 dup2_x1
Juggling The Stack dup B pop A swap dup_x1 dup2_x1
Juggling The Stack dup B pop A swap B dup_x1 dup2_x1
Juggling The Stack dup B pop A swap B dup_x1 B dup2_x1 A
Local Variables
Local Variables Stack var value depth value 0 ldc "Hello" 0 astore_0 1 1 iconst_1 2 astore_1 2 3 aload_0 3 4 4
Local Variables Stack var value depth value 0 ldc "Hello" 0 "Hello" astore_0 1 1 iconst_1 2 astore_1 2 3 aload_0 3 4 4
Local Variables Stack var value depth value 0 ldc "Hello" 0 "Hello" astore_0 1 1 iconst_1 2 astore_1 2 3 aload_0 3 4 4
Local Variables Stack var value depth value 0 ldc "Hello" 0 "Hello" 1 astore_0 1 1 iconst_1 2 astore_1 2 3 aload_0 3 4 4
Local Variables Stack var value depth value 0 ldc "Hello" 0 "Hello" astore_0 1 1 1 iconst_1 2 astore_1 2 3 aload_0 3 4 4
Local Variables Stack var value depth value 0 ldc "Hello" 0 "Hello" "Hello" astore_0 1 1 1 iconst_1 2 astore_1 2 3 aload_0 3 4 4
load Local Variables Stack Table store
Method Invoсation
Method Invocation obj.method(param1, param2);
Method Invocation obj.method(param1, param2); push obj push param1 push param2 invoke method
Method Invocation obj.method(param1, param2); obj push obj push param1 push param2 invoke method
Method Invocation obj.method(param1, param2); param1 push obj obj push param1 push param2 invoke method
Method Invocation obj.method(param1, param2); param2 push obj param1 push param1 obj push param2 invoke method
Method Invocation obj.method(param1, param2); obj? push obj push param1 push param2 invoke method
Operator Overloading
Operator Overloading [int] A + B [Foo] A.plus(B)
Operator Overloading [int] A + B [Foo] A.plus(B) push A push A push B push B iadd invokevirtual plus
Operator Overloading [int] A + B [Foo] A + B push A push A push B push B iadd invokevirtual plus
pop push Stack
pop push load Local Variables Stack Table store
pop push load Local Variables Stack Table store
pop push load Local Variables Stack invoke Table store pop push load Local Variables Stack Table store
javap The disassembler
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 • -verbose for verbosity 
Mastering java bytecode with ASM - GeeCON 2012
C:workgeeconclasses>javap Hello -c
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
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
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
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 super() 4: return
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
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
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
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
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
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
What’s #1,#2, etc ? 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
SLIDES GOTO: IDE SLIDES IDE: JAVAP DEMO
ASM The de facto standard for bytecode manipulation
ASM • “All purpose bytecode manipulation and analysis framework” • De facto standard bytecode library • http://asm.ow2.org
Basic Process • Construct ClassWriter • Stack up the visitors for: • annotations, methods, fields, etc • Write out bytes
Hello.java
ClassWriter ClassWriter cw = new ClassWriter( ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES);
COMPUTE_*** • COMPUTE_MAXS –ASM will calculate max stack/local vars • COMPUTE_FRAMES –ASM will calculate Java 6 stack map
Visit Class cv.visit(V1_6, ACC_PUBLIC, "X", null, "java/lang/Object", null);
Opcodes • Interface full of constants –Bytecodes –Visibility modifiers –Java versions –Other stuff
ACC_*** • Some you know –ACC_PUBLIC, ACC_ABSTRACT, etc • Some you (probably) don’t –ACC_BRIDGE, ACC_SYNTHETIC
Class Names "java/lang/Object" packageClass.replaceAll('.', '/')
Type Descriptors
Type Descriptors B byte C char S string I int J long F float D double Z boolean V void
Type Descriptors Lsome/Class;
Type Descriptors [Lsome/Class;
Method Signatures ()V void foo() (Ljava/lang/Object;)I int foo(Object) ([Ljava/lang/String;)V void main(String[])
Visit Method MethodVisitor constructor = cv.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null); MethodVisitor mv = cv.visitMethod( ACC_PUBLIC + ACC_STATIC, "main", "([Ljava/lang/String;)V", null, null);
Visit Method MethodVisitor constructor = cv.visitMethod(ACC_PUBLIC, "<init>", Wat!? o_O "()V", null, null); MethodVisitor mv = cv.visitMethod( ACC_PUBLIC + ACC_STATIC, "main", "([Ljava/lang/String;)V", null, null);
Special Methods • <init> –Constructor • <clinit> –Static initializer
MethodVisitor • Visit annotations • Visit code – Bytecodes, local variables, line numbers, etc • Visit maxs – Pass bogus values if COMPUTE_MAX
Constructor c.visitVarInsn(ALOAD, 0); c.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V"); c.visitInsn(RETURN); c.visitMaxs(0, 0);
Constructor c.visitVarInsn(ALOAD, 0); c.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V"); c.visitInsn(RETURN); c.visitMaxs(0, 0); aload_0 invokespecial return
public static void main()
public static void main() mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;"); mv.visitLdcInsn("Hello"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V"); mv.visitInsn(RETURN);
public static void main() mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", getstatic "Ljava/io/PrintStream;"); ldc “Hello” invokevirtual mv.visitLdcInsn("Hello"); return mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V"); mv.visitInsn(RETURN);
Enter Loops
Enter Loops start: int i = 0 loop: print "Hello" i=i+1 if i < 10 goto loop end: return
Enter Loops start: int i = 0 GOTO isn’t harmful ;) loop: print "Hello" i=i+1 if i < 10 goto loop end: return
Enter Loops 0: iconst_0 1: istore_1 2: iload_1 3: bipush 10 5: if_icmpge 22 System.out.println(“Hello”) 16: iinc 1, 1 19: goto 2 22: return
Enter Loops start: iconst_0 1: istore_1 loop: iload_1 3: bipush 10 5: if_icmpge end System.out.println(“Hello”) 16: iinc 1, 1 19: goto loop end: return
Enter Loops start: iconst_0 1: istore_1 int i = 0 loop: iload_1 3: bipush 10 5: if_icmpge end System.out.println(“Hello”) 16: iinc 1, 1 19: goto loop end: return
Enter Loops start: iconst_0 1: istore_1 loop: iload_1 3: bipush 10 i < 10 5: if_icmpge end System.out.println(“Hello”) 16: iinc 1, 1 19: goto loop end: return
Enter Loops start: iconst_0 1: istore_1 loop: iload_1 3: bipush 10 5: if_icmpge end System.out.println(“Hello”) 16: iinc 1, 1 i++ 19: goto loop end: return
Enter Loops start: iconst_0 1: istore_1 loop: iload_1 3: bipush 10 5: if_icmpge end System.out.println(“Hello”) 16: iinc 1, 1 19: goto loop end: return
Enter ASM Loops Label start = new Label(); Label loop = new Label(); Label end = new Label(); // i = 0 mv.visitLabel(start); mv.visitInsn(ICONST_0); mv.visitVarInsn(ISTORE, 1);
Enter ASM Loops Label start = new Label(); Label loop = new Label(); Label end = new Label(); // i = 0 mv.visitLabel(start); mv.visitInsn(ICONST_0); mv.visitVarInsn(ISTORE, 1); // i < 10 mv.visitLabel(loop); mv.visitVarInsn(ILOAD, 1); mv.visitLdcInsn(10); mv.visitJumpInsn(IF_ICMPGE, end);
Enter ASM Loops Label start = new Label(); Label loop = new Label(); Label end = new Label(); //increment & continue the loop mv.visitIincInsn(1, 1); // i = 0 mv.visitJumpInsn(GOTO, loop); mv.visitLabel(start); mv.visitLabel(end); mv.visitInsn(ICONST_0); mv.visitVarInsn(ISTORE, 1); // i < 10 mv.visitLabel(loop); mv.visitVarInsn(ILOAD, 1); mv.visitLdcInsn(10); mv.visitJumpInsn(IF_ICMPGE, end);
Mastering java bytecode with ASM - GeeCON 2012
ClassWriter
geecon$ java Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello Hello
ASMified ASMifierClassVisitor mv = cw.visitMethod(ACC_PUBLIC, "getId", "(I)I", null, null); mv.visitCode(); Label l0 = new Label(); mv.visitLabel(l0); mv.visitLineNumber(16, l0); mv.visitVarInsn(ALOAD, 0); mv.visitFieldInsn(GETFIELD, "zt/asm/Items", "ids", "Ljava/util/List;"); java -cp asm-all-3.3.1.jar:asm-util-3.3.1.jar mv.visitVarInsn(ILOAD, 1); org.objectweb.asm.util.ASMifierClassVisitor mv.visitMethodInsn(INVOKEINTERFACE, "java/util/List", "get", "(I)Ljava/lang/Object;"); Hello.class mv.visitTypeInsn(CHECKCAST, "java/lang/Integer"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Integer", "intValue", "()I"); mv.visitInsn(IRETURN); Label l1 = new Label(); mv.visitLabel(l1); mv.visitLocalVariable("this", "Lzt/asm/Items;", null, l0, l1, 0); mv.visitLocalVariable("i", "I", null, l0, l1, 1); mv.visitMaxs(2, 2); mv.visitEnd();
Bytecode instrumentation Some magic for your own good
WAT!? Ninja.class Ninja.class’ 10101010101 10101010101 11000101010 11100001010 10101010001 10101010001 00010001110 00010001110 11011101011 11011101110
Who? Containers (Java EE, Spring) Terracotta JRebel Tapestry Byteman
How? • Add –javaagent to hook into class loading process • Implement ClassFileTransformer • Use bytecode manipulation libraries (Javassist, cglib, asm) to add any custom logic java.lang.instrument
How ? (2) • Use custom ClassLoader – Override ClassLoader#findClass – Use ClassReader(String) to read the class in and transform it via visitor chain – Call ClassLoader#defineClass explicitly with the result from the transformation step
java.lang.instrument import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.Instrumentation; public class Agent { public static void premain(String args, Instrumentation inst) { inst.addTransformer(new ClassFileTransformer(), true); } public static void agentmain(String args, Instrumentation inst) { premain(args,inst); } }
java.lang.instrument import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.Instrumentation; public class Agent { public static void premain(String args, Instrumentation inst) { inst.addTransformer(new ClassFileTransformer(), true); } public static void agentmain(String args, Instrumentation inst) { premain(args,inst); } }
java.lang.instrument import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.Instrumentation; public class Agent { public static void premain(String args, Instrumentation inst) { inst.addTransformer(new ClassFileTransformer(), true); } public static void agentmain(String args, Instrumentation inst) { premain(args,inst); } } META-INF/MANIFEST.MF Premain-Class: Agent java –javaagent:agent.jar … Agent-Class: Agent
j.l.instrument.ClassFileTransformer new ClassFileTransformer() { public byte[] transform(ClassLoader loader, String className, Class<?>classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer){ ClassReader cr = new ClassReader(classfileBuffer); ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES); MyAdapter ca = new MyAdapter(cw); cr.accept(ca, ClassReader.EXPAND_FRAMES); return cw.toByteArray(); }
j.l.instrument.ClassFileTransformer new ClassFileTransformer() { public byte[] transform(ClassLoader loader, String className, Class<?>classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer){ ClassReader cr = new ClassReader(classfileBuffer); ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES); MyAdapter ca = new MyAdapter(cw); cr.accept(ca, ClassReader.EXPAND_FRAMES); return cw.toByteArray(); }
j.l.instrument.ClassFileTransformer new ClassFileTransformer() { public byte[] transform(ClassLoader loader, String className, Class<?>classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer){ ClassReader cr = new ClassReader(classfileBuffer); ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES); MyAdapter ca = new MyAdapter(cw); cr.accept(ca, ClassReader.EXPAND_FRAMES); return cw.toByteArray(); }
public class MyClassLoader extends ClassLoader { protected Class findClass(String name) throws ClassNotFoundException { ClassReader cr = new ClassReader(name); ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES); MyClassAdapter ca = new MyClassAdapter(cw); cr.accept(ca, ClassReader.EXPAND_FRAMES); byte b[] = cw.toByteArray(); return defineClass(name, b, 0, b.length); }
SLIDES GOTO: IDE SLIDES IDE: ASM DEMO
@antonarhipov anton@zeroturnaround.com https://github.com/antonarhipov/asmdemo

More Related Content

PPTX
Mastering Java Bytecode With ASM - 33rd degree, 2012
Anton Arhipov
 
PPTX
All you need to know about the JavaScript event loop
Saša Tatar
 
PPTX
java memory management & gc
exsuns
 
KEY
JavaOne 2011 - JVM Bytecode for Dummies
Charles Nutter
 
PDF
Svelte JS introduction
Mikhail Kuznetcov
 
KEY
2장. Runtime Data Areas
김 한도
 
PPT
JDBC – Java Database Connectivity
Information Technology
 
PDF
[수정본] 우아한 객체지향
Young-Ho Cho
 
Mastering Java Bytecode With ASM - 33rd degree, 2012
Anton Arhipov
 
All you need to know about the JavaScript event loop
Saša Tatar
 
java memory management & gc
exsuns
 
JavaOne 2011 - JVM Bytecode for Dummies
Charles Nutter
 
Svelte JS introduction
Mikhail Kuznetcov
 
2장. Runtime Data Areas
김 한도
 
JDBC – Java Database Connectivity
Information Technology
 
[수정본] 우아한 객체지향
Young-Ho Cho
 

What's hot (20)

PPTX
cours javascript.pptx
YaminaGh1
 
PPT
CSS
Sunil OS
 
PPTX
JavaScript Event Loop
Designveloper
 
PPTX
Express js
Manav Prasad
 
PPT
JavaScript
Sunil OS
 
PPT
Collections Framework
Sunil OS
 
PDF
Object Oriented Programming in JavaScript
zand3rs
 
PPT
C++ oop
Sunil OS
 
PPTX
Introduction Dart
Eric Zile Kouassi
 
PDF
NodeJS for Beginner
Apaichon Punopas
 
PPTX
Java Virtual Machine, Call stack, Java Byte Code
Javajigi Jaesung
 
PPT
Java EE and Spring Side-by-Side
Reza Rahman
 
KEY
HTML CSS & Javascript
David Lindkvist
 
PDF
Spring Boot
HongSeong Jeon
 
PPT
Java Script ppt
Priya Goyal
 
PPTX
Introduction to NodeJS
Cere Labs Pvt. Ltd
 
PDF
ES6 presentation
ritika1
 
PPTX
Spring Boot
Jiayun Zhou
 
PDF
Introduction to SQLAlchemy ORM
Jason Myers
 
PPTX
Java packages
Shreyans Pathak
 
cours javascript.pptx
YaminaGh1
 
CSS
Sunil OS
 
JavaScript Event Loop
Designveloper
 
Express js
Manav Prasad
 
JavaScript
Sunil OS
 
Collections Framework
Sunil OS
 
Object Oriented Programming in JavaScript
zand3rs
 
C++ oop
Sunil OS
 
Introduction Dart
Eric Zile Kouassi
 
NodeJS for Beginner
Apaichon Punopas
 
Java Virtual Machine, Call stack, Java Byte Code
Javajigi Jaesung
 
Java EE and Spring Side-by-Side
Reza Rahman
 
HTML CSS & Javascript
David Lindkvist
 
Spring Boot
HongSeong Jeon
 
Java Script ppt
Priya Goyal
 
Introduction to NodeJS
Cere Labs Pvt. Ltd
 
ES6 presentation
ritika1
 
Spring Boot
Jiayun Zhou
 
Introduction to SQLAlchemy ORM
Jason Myers
 
Java packages
Shreyans Pathak
 
Ad

Similar to Mastering java bytecode with ASM - GeeCON 2012 (18)

PDF
LatJUG. Java Bytecode Fundamentals
denis Udod
 
PDF
tutorial5
tutorialsruby
 
PDF
tutorial5
tutorialsruby
 
PDF
Distributed Search in Riak - Integrating Search in a NoSQL Database: Presente...
Lucidworks
 
PDF
Javascript engine performance
Duoyi Wu
 
PDF
Scala introduction
vito jeng
 
PPT
Yokozuna
PDX Web & Design
 
PPTX
Java Bytecode Fundamentals - JUG.lv
Anton Arhipov
 
PDF
NoSQL - how it works (@pavlobaron)
Pavlo Baron
 
KEY
2011.06.20 stratified-btree
Acunu
 
KEY
Charles nutter star techconf 2011 - jvm languages
StarTech Conference
 
PDF
From Hand To Mouth (@pavlobaron)
Pavlo Baron
 
KEY
High Performance Ruby - Golden Gate RubyConf 2012
Charles Nutter
 
PPTX
Java Bytecode: Passing Parameters
Anton Arhipov
 
PDF
The Gremlin in the Graph
Marko Rodriguez
 
PDF
Virtual machine and javascript engine
Duoyi Wu
 
PDF
A Guide to the Post Relational Revolution
Theo Hultberg
 
PDF
Yapc asia 2011_zigorou
Toru Yamaguchi
 
LatJUG. Java Bytecode Fundamentals
denis Udod
 
tutorial5
tutorialsruby
 
tutorial5
tutorialsruby
 
Distributed Search in Riak - Integrating Search in a NoSQL Database: Presente...
Lucidworks
 
Javascript engine performance
Duoyi Wu
 
Scala introduction
vito jeng
 
Yokozuna
PDX Web & Design
 
Java Bytecode Fundamentals - JUG.lv
Anton Arhipov
 
NoSQL - how it works (@pavlobaron)
Pavlo Baron
 
2011.06.20 stratified-btree
Acunu
 
Charles nutter star techconf 2011 - jvm languages
StarTech Conference
 
From Hand To Mouth (@pavlobaron)
Pavlo Baron
 
High Performance Ruby - Golden Gate RubyConf 2012
Charles Nutter
 
Java Bytecode: Passing Parameters
Anton Arhipov
 
The Gremlin in the Graph
Marko Rodriguez
 
Virtual machine and javascript engine
Duoyi Wu
 
A Guide to the Post Relational Revolution
Theo Hultberg
 
Yapc asia 2011_zigorou
Toru Yamaguchi
 
Ad

More from Anton Arhipov (20)

PDF
JavaZone 2022 - Building Kotlin DSL.pdf
Anton Arhipov
 
PDF
Idiomatic kotlin
Anton Arhipov
 
PDF
TechTrain 2019 - (Не)адекватное техническое интервью
Anton Arhipov
 
PDF
Build pipelines with TeamCity
Anton Arhipov
 
PDF
Build pipelines with TeamCity
Anton Arhipov
 
PDF
Devoxx Ukraine 2018 - Kotlin DSL in under an hour
Anton Arhipov
 
PDF
GeeCON Prague 2018 - Kotlin DSL in under an hour
Anton Arhipov
 
PDF
Build pipelines with TeamCity and Kotlin DSL
Anton Arhipov
 
PDF
Build pipelines with TeamCity
Anton Arhipov
 
PDF
JavaDay Kiev 2017 - Integration testing with TestContainers
Anton Arhipov
 
PDF
GeeCON Prague 2017 - TestContainers
Anton Arhipov
 
PDF
JavaOne 2017 - The hitchhiker’s guide to Java class reloading
Anton Arhipov
 
PDF
JavaOne 2017 - TestContainers: integration testing without the hassle
Anton Arhipov
 
PDF
JavaOne 2017 - The hitchhiker’s guide to Java class reloading
Anton Arhipov
 
PDF
JavaZone 2017 - The Hitchhiker’s guide to Java class reloading
Anton Arhipov
 
PDF
JUG.ua 20170225 - Java bytecode instrumentation
Anton Arhipov
 
PDF
Riga DevDays 2017 - The hitchhiker’s guide to Java class reloading
Anton Arhipov
 
PDF
GeeCON 2017 - TestContainers. Integration testing without the hassle
Anton Arhipov
 
PDF
JEEConf 2017 - The hitchhiker’s guide to Java class reloading
Anton Arhipov
 
PDF
JEEConf 2017 - Having fun with Javassist
Anton Arhipov
 
JavaZone 2022 - Building Kotlin DSL.pdf
Anton Arhipov
 
Idiomatic kotlin
Anton Arhipov
 
TechTrain 2019 - (Не)адекватное техническое интервью
Anton Arhipov
 
Build pipelines with TeamCity
Anton Arhipov
 
Build pipelines with TeamCity
Anton Arhipov
 
Devoxx Ukraine 2018 - Kotlin DSL in under an hour
Anton Arhipov
 
GeeCON Prague 2018 - Kotlin DSL in under an hour
Anton Arhipov
 
Build pipelines with TeamCity and Kotlin DSL
Anton Arhipov
 
Build pipelines with TeamCity
Anton Arhipov
 
JavaDay Kiev 2017 - Integration testing with TestContainers
Anton Arhipov
 
GeeCON Prague 2017 - TestContainers
Anton Arhipov
 
JavaOne 2017 - The hitchhiker’s guide to Java class reloading
Anton Arhipov
 
JavaOne 2017 - TestContainers: integration testing without the hassle
Anton Arhipov
 
JavaOne 2017 - The hitchhiker’s guide to Java class reloading
Anton Arhipov
 
JavaZone 2017 - The Hitchhiker’s guide to Java class reloading
Anton Arhipov
 
JUG.ua 20170225 - Java bytecode instrumentation
Anton Arhipov
 
Riga DevDays 2017 - The hitchhiker’s guide to Java class reloading
Anton Arhipov
 
GeeCON 2017 - TestContainers. Integration testing without the hassle
Anton Arhipov
 
JEEConf 2017 - The hitchhiker’s guide to Java class reloading
Anton Arhipov
 
JEEConf 2017 - Having fun with Javassist
Anton Arhipov
 

Recently uploaded (20)

PDF
Architecting across the Boundaries of two Complex Domains - Healthcare & Tech...
Peter Tan
 
PDF
KodekX | Application Modernization Development
KodekX
 
PDF
Peak of Data & AI Encore- AI for Metadata and Smarter Workflows
Safe Software
 
PPT
Teaching material agriculture food technology
LiaRayya
 
PDF
Shreyas Phanse Resume: Experienced Backend Engineer | Java • Spring Boot • Ka...
SHREYAS PHANSE
 
PPTX
Detection-First SIEM: Rule Types, Dashboards, and Threat-Informed Strategy
ReZa AdineH
 
PDF
Chapter 3 Spatial Domain Image Processing.pdf
Getnet Tigabie Askale -(GM)
 
PDF
Building Integrated photovoltaic BIPV_UPV.pdf
SandeepSingh286037
 
PDF
NewMind AI Weekly Chronicles - August'25 Week I
NewMind AI
 
PDF
Bridging biosciences and deep learning for revolutionary discoveries: a compr...
IAESIJAI
 
PDF
Reach Out and Touch Someone: Haptics and Empathic Computing
Mark Billinghurst
 
PDF
CIFDAQ's Market Insight: SEC Turns Pro Crypto
CIFDAQ
 
PDF
Blue Purple Modern Animated Computer Science Presentation.pdf.pdf
Akar16
 
PDF
Unlocking AI with Model Context Protocol (MCP)
Brian McKeiver
 
PDF
Spectral efficient network and resource selection model in 5G networks
IAESIJAI
 
PDF
Mobile App Security Testing_ A Comprehensive Guide.pdf
flufftailshop
 
PDF
Build a system with the filesystem maintained by OSTree @ COSCUP 2025
Jian-Hong Pan
 
PDF
Diabetes mellitus diagnosis method based random forest with bat algorithm
IAESIJAI
 
PDF
TokAI - TikTok AI Agent : The First AI Application That Analyzes 10,000+ Vira...
SOFTTECHHUB
 
PPTX
Effective Security Operations Center (SOC) A Modern, Strategic, and Threat-In...
ReZa AdineH
 
Architecting across the Boundaries of two Complex Domains - Healthcare & Tech...
Peter Tan
 
KodekX | Application Modernization Development
KodekX
 
Peak of Data & AI Encore- AI for Metadata and Smarter Workflows
Safe Software
 
Teaching material agriculture food technology
LiaRayya
 
Shreyas Phanse Resume: Experienced Backend Engineer | Java • Spring Boot • Ka...
SHREYAS PHANSE
 
Detection-First SIEM: Rule Types, Dashboards, and Threat-Informed Strategy
ReZa AdineH
 
Chapter 3 Spatial Domain Image Processing.pdf
Getnet Tigabie Askale -(GM)
 
Building Integrated photovoltaic BIPV_UPV.pdf
SandeepSingh286037
 
NewMind AI Weekly Chronicles - August'25 Week I
NewMind AI
 
Bridging biosciences and deep learning for revolutionary discoveries: a compr...
IAESIJAI
 
Reach Out and Touch Someone: Haptics and Empathic Computing
Mark Billinghurst
 
CIFDAQ's Market Insight: SEC Turns Pro Crypto
CIFDAQ
 
Blue Purple Modern Animated Computer Science Presentation.pdf.pdf
Akar16
 
Unlocking AI with Model Context Protocol (MCP)
Brian McKeiver
 
Spectral efficient network and resource selection model in 5G networks
IAESIJAI
 
Mobile App Security Testing_ A Comprehensive Guide.pdf
flufftailshop
 
Build a system with the filesystem maintained by OSTree @ COSCUP 2025
Jian-Hong Pan
 
Diabetes mellitus diagnosis method based random forest with bat algorithm
IAESIJAI
 
TokAI - TikTok AI Agent : The First AI Application That Analyzes 10,000+ Vira...
SOFTTECHHUB
 
Effective Security Operations Center (SOC) A Modern, Strategic, and Threat-In...
ReZa AdineH
 

Mastering java bytecode with ASM - GeeCON 2012

  • 1. Mastering Java Bytecode with ASM Learn some bytecode to yourself!
  • 2. whoami Anton Arhipov Java Dev / Product Lead ZeroTurnaround, JRebel Messing with bytecode since 2010 [email protected] @antonarhipov @javarebel
  • 3. whoami Anton Arhipov Java Dev / Product Lead ZeroTurnaround, JRebel Messing with bytecode since 2010 [email protected] @antonarhipov @javarebel
  • 4. Why Bytecode? • Know your platform! • Build your own JVM language? • Programming models (AOP, ORM) • Awesome tools (like JRebel ) ... just bored?
  • 5. Bytecode 101 Instrumentation API javap ObjectWeb ASM
  • 6. Bytecode 101 Gentle introduction
  • 10. Adding Two Values A+B PUSH A A AB+
  • 11. Adding Two Values A+B PUSH 1 PUSH 2 B AB+ A
  • 12. Adding Two Values A+B PUSH 1 PUSH 2 15 AB+ ADD
  • 13. Adding Two Values A+B ICONST_1 ICONST_2 15 AB+ IADD
  • 14. TYPE OPERATION • <TYPE> ::= b, s, c, i, l, f, d, a • 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 & branching (cmpl, ifeq, jsr, tableswitch) • Conversions (l2d, i2l)
  • 17. Enter Threads Thread A Thread B Thread C Thread D
  • 19. The Frame Local variables 0 1 2 … N Operand stack #1 Constant Pool
  • 21. Juggling The Stack dup A pop B swap dup_x1 dup2_x1
  • 22. Juggling The Stack dup A pop A swap B dup_x1 dup2_x1
  • 23. Juggling The Stack dup A pop B swap dup_x1 dup2_x1
  • 24. Juggling The Stack dup B pop A swap dup_x1 dup2_x1
  • 25. Juggling The Stack dup B pop A swap B dup_x1 dup2_x1
  • 26. Juggling The Stack dup B pop A swap B dup_x1 B dup2_x1 A
  • 28. Local Variables Stack var value depth value 0 ldc "Hello" 0 astore_0 1 1 iconst_1 2 astore_1 2 3 aload_0 3 4 4
  • 29. Local Variables Stack var value depth value 0 ldc "Hello" 0 "Hello" astore_0 1 1 iconst_1 2 astore_1 2 3 aload_0 3 4 4
  • 30. Local Variables Stack var value depth value 0 ldc "Hello" 0 "Hello" astore_0 1 1 iconst_1 2 astore_1 2 3 aload_0 3 4 4
  • 31. Local Variables Stack var value depth value 0 ldc "Hello" 0 "Hello" 1 astore_0 1 1 iconst_1 2 astore_1 2 3 aload_0 3 4 4
  • 32. Local Variables Stack var value depth value 0 ldc "Hello" 0 "Hello" astore_0 1 1 1 iconst_1 2 astore_1 2 3 aload_0 3 4 4
  • 33. Local Variables Stack var value depth value 0 ldc "Hello" 0 "Hello" "Hello" astore_0 1 1 1 iconst_1 2 astore_1 2 3 aload_0 3 4 4
  • 34. load Local Variables Stack Table store
  • 37. Method Invocation obj.method(param1, param2); push obj push param1 push param2 invoke method
  • 38. Method Invocation obj.method(param1, param2); obj push obj push param1 push param2 invoke method
  • 39. Method Invocation obj.method(param1, param2); param1 push obj obj push param1 push param2 invoke method
  • 40. Method Invocation obj.method(param1, param2); param2 push obj param1 push param1 obj push param2 invoke method
  • 41. Method Invocation obj.method(param1, param2); obj? push obj push param1 push param2 invoke method
  • 43. Operator Overloading [int] A + B [Foo] A.plus(B)
  • 44. Operator Overloading [int] A + B [Foo] A.plus(B) push A push A push B push B iadd invokevirtual plus
  • 45. Operator Overloading [int] A + B [Foo] A + B push A push A push B push B iadd invokevirtual plus
  • 46. pop push Stack
  • 47. pop push load Local Variables Stack Table store
  • 48. pop push load Local Variables Stack Table store
  • 49. pop push load Local Variables Stack invoke Table store pop push load Local Variables Stack Table store
  • 51. 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 • -verbose for verbosity 
  • 54. 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
  • 55. 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
  • 56. 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
  • 57. 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 super() 4: return
  • 58. 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
  • 59. 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
  • 60. 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
  • 61. 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
  • 62. 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
  • 63. 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
  • 64. What’s #1,#2, etc ? 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
  • 66. ASM The de facto standard for bytecode manipulation
  • 67. ASM • “All purpose bytecode manipulation and analysis framework” • De facto standard bytecode library • http://asm.ow2.org
  • 68. Basic Process • Construct ClassWriter • Stack up the visitors for: • annotations, methods, fields, etc • Write out bytes
  • 70. ClassWriter ClassWriter cw = new ClassWriter( ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES);
  • 71. COMPUTE_*** • COMPUTE_MAXS –ASM will calculate max stack/local vars • COMPUTE_FRAMES –ASM will calculate Java 6 stack map
  • 72. Visit Class cv.visit(V1_6, ACC_PUBLIC, "X", null, "java/lang/Object", null);
  • 73. Opcodes • Interface full of constants –Bytecodes –Visibility modifiers –Java versions –Other stuff
  • 74. ACC_*** • Some you know –ACC_PUBLIC, ACC_ABSTRACT, etc • Some you (probably) don’t –ACC_BRIDGE, ACC_SYNTHETIC
  • 75. Class Names "java/lang/Object" packageClass.replaceAll('.', '/')
  • 77. Type Descriptors B byte C char S string I int J long F float D double Z boolean V void
  • 80. Method Signatures ()V void foo() (Ljava/lang/Object;)I int foo(Object) ([Ljava/lang/String;)V void main(String[])
  • 81. Visit Method MethodVisitor constructor = cv.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null); MethodVisitor mv = cv.visitMethod( ACC_PUBLIC + ACC_STATIC, "main", "([Ljava/lang/String;)V", null, null);
  • 82. Visit Method MethodVisitor constructor = cv.visitMethod(ACC_PUBLIC, "<init>", Wat!? o_O "()V", null, null); MethodVisitor mv = cv.visitMethod( ACC_PUBLIC + ACC_STATIC, "main", "([Ljava/lang/String;)V", null, null);
  • 83. Special Methods • <init> –Constructor • <clinit> –Static initializer
  • 84. MethodVisitor • Visit annotations • Visit code – Bytecodes, local variables, line numbers, etc • Visit maxs – Pass bogus values if COMPUTE_MAX
  • 85. Constructor c.visitVarInsn(ALOAD, 0); c.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V"); c.visitInsn(RETURN); c.visitMaxs(0, 0);
  • 86. Constructor c.visitVarInsn(ALOAD, 0); c.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V"); c.visitInsn(RETURN); c.visitMaxs(0, 0); aload_0 invokespecial return
  • 88. public static void main() mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;"); mv.visitLdcInsn("Hello"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V"); mv.visitInsn(RETURN);
  • 89. public static void main() mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", getstatic "Ljava/io/PrintStream;"); ldc “Hello” invokevirtual mv.visitLdcInsn("Hello"); return mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V"); mv.visitInsn(RETURN);
  • 91. Enter Loops start: int i = 0 loop: print "Hello" i=i+1 if i < 10 goto loop end: return
  • 92. Enter Loops start: int i = 0 GOTO isn’t harmful ;) loop: print "Hello" i=i+1 if i < 10 goto loop end: return
  • 93. Enter Loops 0: iconst_0 1: istore_1 2: iload_1 3: bipush 10 5: if_icmpge 22 System.out.println(“Hello”) 16: iinc 1, 1 19: goto 2 22: return
  • 94. Enter Loops start: iconst_0 1: istore_1 loop: iload_1 3: bipush 10 5: if_icmpge end System.out.println(“Hello”) 16: iinc 1, 1 19: goto loop end: return
  • 95. Enter Loops start: iconst_0 1: istore_1 int i = 0 loop: iload_1 3: bipush 10 5: if_icmpge end System.out.println(“Hello”) 16: iinc 1, 1 19: goto loop end: return
  • 96. Enter Loops start: iconst_0 1: istore_1 loop: iload_1 3: bipush 10 i < 10 5: if_icmpge end System.out.println(“Hello”) 16: iinc 1, 1 19: goto loop end: return
  • 97. Enter Loops start: iconst_0 1: istore_1 loop: iload_1 3: bipush 10 5: if_icmpge end System.out.println(“Hello”) 16: iinc 1, 1 i++ 19: goto loop end: return
  • 98. Enter Loops start: iconst_0 1: istore_1 loop: iload_1 3: bipush 10 5: if_icmpge end System.out.println(“Hello”) 16: iinc 1, 1 19: goto loop end: return
  • 99. Enter ASM Loops Label start = new Label(); Label loop = new Label(); Label end = new Label(); // i = 0 mv.visitLabel(start); mv.visitInsn(ICONST_0); mv.visitVarInsn(ISTORE, 1);
  • 100. Enter ASM Loops Label start = new Label(); Label loop = new Label(); Label end = new Label(); // i = 0 mv.visitLabel(start); mv.visitInsn(ICONST_0); mv.visitVarInsn(ISTORE, 1); // i < 10 mv.visitLabel(loop); mv.visitVarInsn(ILOAD, 1); mv.visitLdcInsn(10); mv.visitJumpInsn(IF_ICMPGE, end);
  • 101. Enter ASM Loops Label start = new Label(); Label loop = new Label(); Label end = new Label(); //increment & continue the loop mv.visitIincInsn(1, 1); // i = 0 mv.visitJumpInsn(GOTO, loop); mv.visitLabel(start); mv.visitLabel(end); mv.visitInsn(ICONST_0); mv.visitVarInsn(ISTORE, 1); // i < 10 mv.visitLabel(loop); mv.visitVarInsn(ILOAD, 1); mv.visitLdcInsn(10); mv.visitJumpInsn(IF_ICMPGE, end);
  • 105. ASMified ASMifierClassVisitor mv = cw.visitMethod(ACC_PUBLIC, "getId", "(I)I", null, null); mv.visitCode(); Label l0 = new Label(); mv.visitLabel(l0); mv.visitLineNumber(16, l0); mv.visitVarInsn(ALOAD, 0); mv.visitFieldInsn(GETFIELD, "zt/asm/Items", "ids", "Ljava/util/List;"); java -cp asm-all-3.3.1.jar:asm-util-3.3.1.jar mv.visitVarInsn(ILOAD, 1); org.objectweb.asm.util.ASMifierClassVisitor mv.visitMethodInsn(INVOKEINTERFACE, "java/util/List", "get", "(I)Ljava/lang/Object;"); Hello.class mv.visitTypeInsn(CHECKCAST, "java/lang/Integer"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Integer", "intValue", "()I"); mv.visitInsn(IRETURN); Label l1 = new Label(); mv.visitLabel(l1); mv.visitLocalVariable("this", "Lzt/asm/Items;", null, l0, l1, 0); mv.visitLocalVariable("i", "I", null, l0, l1, 1); mv.visitMaxs(2, 2); mv.visitEnd();
  • 107. WAT!? Ninja.class Ninja.class’ 10101010101 10101010101 11000101010 11100001010 10101010001 10101010001 00010001110 00010001110 11011101011 11011101110
  • 108. Who? Containers (Java EE, Spring) Terracotta JRebel Tapestry Byteman
  • 109. How? • Add –javaagent to hook into class loading process • Implement ClassFileTransformer • Use bytecode manipulation libraries (Javassist, cglib, asm) to add any custom logic java.lang.instrument
  • 110. How ? (2) • Use custom ClassLoader – Override ClassLoader#findClass – Use ClassReader(String) to read the class in and transform it via visitor chain – Call ClassLoader#defineClass explicitly with the result from the transformation step
  • 111. java.lang.instrument import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.Instrumentation; public class Agent { public static void premain(String args, Instrumentation inst) { inst.addTransformer(new ClassFileTransformer(), true); } public static void agentmain(String args, Instrumentation inst) { premain(args,inst); } }
  • 112. java.lang.instrument import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.Instrumentation; public class Agent { public static void premain(String args, Instrumentation inst) { inst.addTransformer(new ClassFileTransformer(), true); } public static void agentmain(String args, Instrumentation inst) { premain(args,inst); } }
  • 113. java.lang.instrument import java.lang.instrument.ClassFileTransformer; import java.lang.instrument.Instrumentation; public class Agent { public static void premain(String args, Instrumentation inst) { inst.addTransformer(new ClassFileTransformer(), true); } public static void agentmain(String args, Instrumentation inst) { premain(args,inst); } } META-INF/MANIFEST.MF Premain-Class: Agent java –javaagent:agent.jar … Agent-Class: Agent
  • 114. j.l.instrument.ClassFileTransformer new ClassFileTransformer() { public byte[] transform(ClassLoader loader, String className, Class<?>classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer){ ClassReader cr = new ClassReader(classfileBuffer); ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES); MyAdapter ca = new MyAdapter(cw); cr.accept(ca, ClassReader.EXPAND_FRAMES); return cw.toByteArray(); }
  • 115. j.l.instrument.ClassFileTransformer new ClassFileTransformer() { public byte[] transform(ClassLoader loader, String className, Class<?>classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer){ ClassReader cr = new ClassReader(classfileBuffer); ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES); MyAdapter ca = new MyAdapter(cw); cr.accept(ca, ClassReader.EXPAND_FRAMES); return cw.toByteArray(); }
  • 116. j.l.instrument.ClassFileTransformer new ClassFileTransformer() { public byte[] transform(ClassLoader loader, String className, Class<?>classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer){ ClassReader cr = new ClassReader(classfileBuffer); ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES); MyAdapter ca = new MyAdapter(cw); cr.accept(ca, ClassReader.EXPAND_FRAMES); return cw.toByteArray(); }
  • 117. public class MyClassLoader extends ClassLoader { protected Class findClass(String name) throws ClassNotFoundException { ClassReader cr = new ClassReader(name); ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES); MyClassAdapter ca = new MyClassAdapter(cw); cr.accept(ca, ClassReader.EXPAND_FRAMES); byte b[] = cw.toByteArray(); return defineClass(name, b, 0, b.length); }
  • 119. @antonarhipov [email protected] https://github.com/antonarhipov/asmdemo

Editor's Notes

  • #5: Why would learn Java bytecode and ASM at all?Well, creating a brand new JVM language might be a good idea  This is what all the cool kids are doing, right?Secondly – programming model that is exposed by many frameworks is backed with bytecode generation or instrumentation. AspectJ, for instance uses bytecode instrumentation extensively.Also, there are some many awesome tools that do awesome stuff, like …. JRebel for instance 
  • #6: This presentation provides some pointers to the subject
  • #51: Actually, before going further, let’s mention javap– the Java class disassembler. The output of javap command isn’t particularly useful as there’s no way to modify it and compile back to the executable code. However, it is much more easier to read the bytecodes produced by javap, rather than the code that is written using ASM API. So, javap is good for reference when studying the bytecode.
  • #69: The most common scenario to generate bytecode that corresponds to the example source, is to create ClassWriter, visit the structure – fields, methods, etc, and after the job is done, write out the final bytes.
  • #71: Let’s go on and construct a ClassWriter.. The constructor takes anint which is composed of different flags.COMPUTE_MAXS says that the sizes of local variables and operand stack parts will be computed automatically. Still have to call visitMaxs with any argumentsCOMPUTE_FRAMES – everything is computed automatically. ASM will compute the stack map, still have to call visitMaxs
  • #106: ... using ASMifierClassVisitor (ASMifier in ASM4). The output is rather noisy, with all the labels,but the noise is easy to remove.