Programming JVM Bytecode with Jitescript

Joe Kutner @codeﬁnger JVM Langs Owner @Heroku

$ cat Main.class ????3 <init>()VCodeLineNumberTablemain([Ljava/lang/ String;)V SourceFile Main.java java/util/ArrayListHello Mainjava/lang/Objectadd(Ljava/lang/Object;)Z! *?? *?Y??W?

class Main { public static void main(String[] args) { (new ArrayList<String>()).add("Hello"); } }

Compiled from "Main.java" public class Main { public Main(); Code: 0: aload_0 1: invokespecial #1 // Method java/lang/Object... 4: return public static void main(java.lang.String[]); Code: 0: new #2 // class java/util/ArrayList 3: dup 4: invokespecial #3 // Method java/util/ArrayList... 7: ldc #4 // String Hello 9: invokevirtual #5 // Method java/util/ArrayList... 12: pop 13: return } $ javac Main.java $ javap -c Main

0: new #2 3: dup 4: invokespecial #3 7: ldc #4 9: invokevirtual #5 12: pop 13: return

[POSITION]: [OPERATION] [OPERAND] 0: new #2

[POSITION]: [OPERATION] [OPERAND] Location of the instruction in the raw binary data 0: new #2

[POSITION]: [OPERATION] [OPERAND] A mnemonic that represents one of the 256 possible opcodes 0: new #2

[POSITION]: [OPERATION] [OPERAND] Arguments to the operation. The number and type of these depends on the operation in use. 0: new #2

... Constant pool: #1 = Methodref #7.#16 // java/lang/Object... #2 = Class #17 // java/util/ArrayList #3 = Methodref #2.#16 // java/util/ArrayList.”<init>” #4 = String #18 // Hello #5 = Methodref #2.#19 // java/util/ArrayList.add:(L... #6 = Class #20 // Main #7 = Class #21 // java/lang/Object #8 = Utf8 <init> #9 = Utf8 ()V #10 = Utf8 Code #11 = Utf8 LineNumberTable #12 = Utf8 main #13 = Utf8 ([Ljava/lang/String;)V #14 = Utf8 SourceFile #15 = Utf8 Main.java #16 = NameAndType #8:#9 // "<init>":()V #17 = Utf8 java/util/ArrayList $ javap -v -c Main

Stack-Based Model of Computation

Exception in thread "main" java.lang.NullPointerException at Printer.printString(Printer.java:13) at Printer.print(Printer.java:9) at Printer.main(Printer.java:19) Stack Frame Operand Stack Local Variable Array Constant Pool #1 = Methodref #2 = Class #3 = Methodref #4 = String #5 = Methodref ...

Stack Frame Operand StackLocal Vars Constant Pool #1 = Methodref #2 = Class #3 = Methodref #4 = String #5 = Methodref ... 0: new #2 3: dup 4: invokespecial #3 7: ldc #4 9: invokevirtual #5 12: pop 13: return

Stack Frame Operand StackLocal Vars Constant Pool <ArrayList> ArrayList #1 = Methodref #2 = Class #3 = Methodref #4 = String #5 = Methodref ... 0: new #2 3: dup 4: invokespecial #3 7: ldc #4 9: invokevirtual #5 12: pop 13: return

Stack Frame Operand StackLocal Vars Constant Pool <ArrayList> ArrayList #1 = Methodref #2 = Class #3 = Methodref #4 = String #5 = Methodref ... 0: new #2 3: dup 4: invokespecial #3 7: ldc #4 9: invokevirtual #5 12: pop 13: return <ArrayList>

invokespecial Used to invoke an initializer, private method, or superclass method invokeinterface Used to invoke an interface method invokestatic Used to invoke a class-level method (i.e. static methods) invokevirtual Used to invoke an instance method invokedynamic Used to invoke methods dynamically (new shiny)

Stack Frame Operand StackLocal Vars Constant Pool <ArrayList> ArrayList #1 = Methodref #2 = Class #3 = Methodref #4 = String #5 = Methodref ... 0: new #2 3: dup 4: invokespecial #3 7: ldc #4 9: invokevirtual #5 12: pop 13: return <ArrayList> Stack Frame Operand StackLocal Vars Constant Pool #1 = Methodref #2 = Class #3 = Methodref #4 = String #5 = Methodref ...

... Constant pool: #1 = Methodref #7.#16 // java/lang/Object... #2 = Class #17 // java/util/ArrayList #3 = Methodref #2.#16 // java/util/ArrayList.”<init>” #4 = String #18 // Hello #5 = Methodref #2.#19 // java/util/ArrayList.add:(L... #6 = Class #20 // Main #7 = Class #21 // java/lang/Object #8 = Utf8 <init> #9 = Utf8 ()V #10 = Utf8 Code #11 = Utf8 LineNumberTable #12 = Utf8 main #13 = Utf8 ([Ljava/lang/String;)V #14 = Utf8 SourceFile #15 = Utf8 Main.java #16 = NameAndType #8:#9 // "<init>":()V #17 = Utf8 java/util/ArrayList #18 = Utf8 Hello #19 = NameAndType #22:#23 // add:(Ljava/lang/Object;)Z $ javap -v -c Main

Stack Frame Operand StackLocal Vars Constant Pool <ArrayList> ArrayList #1 = Methodref #2 = Class #3 = Methodref #4 = String #5 = Methodref ... 0: new #2 3: dup 4: invokespecial #3 7: ldc #4 9: invokevirtual #5 12: pop 13: return <“Hello”>

java/util/ArrayList.add:(Ljava/lang/Object;)Z B - byte C - char S - short I - int J - long F - float D - double Z - boolean V - void L - object

Stack Frame Operand StackLocal Vars Constant Pool ArrayList ArrayList #1 = Methodref #2 = Class #3 = Methodref #4 = String #5 = Methodref ... 0: new #2 3: dup 4: invokespecial #3 7: ldc #4 9: invokevirtual #5 12: pop 13: return “Hello”

Object “Hello” ... Methodref Target Arguments Operand Stack

Stack Frame Operand StackLocal Vars Constant Pool ArrayList #1 = Methodref #2 = Class #3 = Methodref #4 = String #5 = Methodref ... 0: new #2 3: dup 4: invokespecial #3 7: ldc #4 9: invokevirtual #5 12: pop 13: return <ArrayList> <“Hello”> Stack Frame Operand StackLocal Vars Constant Pool #1 = Methodref #2 = Class #3 = Methodref #4 = String #5 = Methodref ... true

Stack Frame Operand StackLocal Vars Constant Pool ArrayList #1 = Methodref #2 = Class #3 = Methodref #4 = String #5 = Methodref ... 0: new #2 3: dup 4: invokespecial #3 7: ldc #4 9: invokevirtual #5 12: pop 13: return true

Stack Frame Operand StackLocal Vars Constant Pool ArrayList #1 = Methodref #2 = Class #3 = Methodref #4 = String #5 = Methodref ... 0: new #2 3: dup 4: invokespecial #3 7: ldc #4 9: invokevirtual #5 12: pop 13: return

Why Read Bytecode? • Diagnose performance problems • Reverse engineering • Security audit • Debug legacy code • FindBugs plugins that work across languages

000000B0: 73 01 00 0A 4C 43 6F 6D 70 69 6C 65 72 3B 01 00 000000C0: 07 63 6F 6D 70 69 6C 65 01 00 32 28 5B 4C 6A 61 000000D0: 76 61 2F 6C 61 6E 67 2F 53 74 72 69 6E 67 3B 29 000000E0: 4C 6D 65 2F 71 6D 78 2F 6A 69 74 65 73 63 72 69 000000F0: 70 74 2F 4A 69 74 65 43 6C 61 73 73 3B 01 00 06 00000100: 74 6F 6B 65 6E 73 01 00 13 5B 4C 6A 61 76 61 2F 00000110: 6C 61 6E 67 2F 53 74 72 69 6E 67 3B 01 00 04 6D 00000120: 61 69 6E 01 00 16 28 5B 4C 6A 61 76 61 2F 6C 61 00000130: 6E 67 2F 53 74 72 69 6E 67 3B 29 56 01 00 04 61 00000140: 72 67 73 01 00 09 6A 69 74 65 43 6C 61 73 73 01 00000150: 00 1D 4C 6D 65 2F 71 6D 78 2F 6A 69 74 65 73 63 00000160: 72 69 70 74 2F 4A 69 74 65 43 6C 61 73 73 3B 01 00000170: 00 06 6F 75 74 70 75 74 01 00 1A 4C 6A 61 76 61 00000180: 2F 69 6F 2F 46 69 6C 65 4F 75 74 70 75 74 53 74 00000190: 72 65 61 6D 3B 01 00 0A 45 78 63 65 70 74 69 6F 000001A0: 6E 73 07 00 3A 01 00 0A 53 6F 75 72 63 65 46 69 000001B0: 6C 65 01 00 0A 43 6F 6D 70 69 6C 65 72 2E 6A 61 000001C0: 76 61 0C 00 14 00 15 01 00 0A 43 6F 6D 70 69 6C 000001D0: 65 72 24 31 01 00 04 4D 61 69 6E 0C 00 14 00 3B 000001E0: 01 00 08 43 6F 6D 70 69 6C 65 72 0C 00 1B 00 1C

MethodVisitor mv = cv.visitMethod( Opcodes.ACC_PRIVATE, "setupLogger", "(Lorg/apache/maven/cli/MavenCli$CliRequest;)Lorg/codehaus/ plexus/logging/Logger;", null, null); mv.visitCode(); mv.visitTypeInsn( Opcodes.NEW, "com/github/jcgay/maven/color/logger/AnsiColorLogger"); https://github.com/jcgay/maven-color

Jitescript https://github.com/qmx/jitescript

An ECMAScript runtime for the JVM

JiteClass ➤ CodeBlock ➤ CodeBlock ➤ CodeBlock Compiled from "Main.java" public class Main { public Main(); Code: 0: aload_0 1: invokespecial #1 4: return public static void main... Code: 0: new #2 3: dup 4: invokespecial #3 7: ldc #4 9: invokevirtual #5 12: pop 13: return }

new JiteClass("Main") {{ defineMethod("main", ACC_PUBLIC | ACC_STATIC, sig(void.class, String[].class), new CodeBlock() {{ // ... }}); }};

new JiteClass("Main") {{ defineMethod("main", ACC_PUBLIC | ACC_STATIC, sig(void.class, String[].class), new CodeBlock() {{ new(p(ArrayList.class)); dup(); invokestatic( p(ArrayList.class), ”<init>”, sig(void.class)); ldc(“Hello”) invokevirtual( p(ArrayList.class), “add”, sig(boolean.class, Object.class)); pop(); voidreturn(); }}); }};

new JiteClass("Main") {{ defineMethod("main", ACC_PUBLIC | ACC_STATIC, sig(void.class, String[].class), new CodeBlock() {{ getstatic(p(System.class), "out", ci(PrintStream.class)); ldc(“42"); invokevirtual( p(PrintStream.class), "println", sig(void.class, Object.class)); voidreturn(); }}); }};

new JiteClass("Main") {{ defineMethod("main", ACC_PUBLIC | ACC_STATIC, sig(void.class, String[].class), new CodeBlock() {{ getstatic(p(System.class), "out", ci(PrintStream.class)); ldc(“42"); invokevirtual( p(PrintStream.class), "println", sig(void.class, Object.class)); voidreturn(); }}); }}; 0: getstatic #13 3: ldc #15 5: invokevirtual #21 8: return

Brainfu++ > > + + + + + + [ - s + + + + + + + s ] < p

p > < : print a variable : push a 0 onto the stack : pop the top value off of the stack + - [ : increment a variable : decrement a variable : start a loop ] : end a loop s : swap the top two values of the stack

This is our machine: An empty stack

> > + + + + + + [ - s + + + + + + + s ] < p

> > + + + + + + [ - s + + + + + + + s ] < p Push two zeros 0 0

> > + + + + + + [ - s + + + + + + + s ] < p Inc to 6 0 6

> > + + + + + + [ - s + + + + + + + s ] < p Loop 0 6

> > + + + + + + [ - s + + + + + + + s ] < p Loop 0 5 Decrement

> > + + + + + + [ - s + + + + + + + s ] < p Loop 5 0 Swap

> > + + + + + + [ - s + + + + + + + s ] < p Loop 5 7 Increment

> > + + + + + + [ - s + + + + + + + s ] < p Loop 7 5 Swap

> > + + + + + + [ - s + + + + + + + s ] < p Loop 7 5 End of loop

> > + + + + + + [ - s + + + + + + + s ] < p Loop 42 0 Repeat until 0

> > + + + + + + [ - s + + + + + + + s ] < p 42 Pop and Print

public JiteClass compile(final String program) { return new JiteClass("Main") {{ defineMethod("main", ACC_PUBLIC | ACC_STATIC, sig(void.class, String[].class), new CodeBlock() {{ // ... }}); }}; }

for (String cmd : program.split(“ “)) { if ("p".equals(cmd)) { } else if ("+".equals(cmd)) { } else if ("-".equals(cmd)) { } else if (">".equals(cmd)) { } else if ("<".equals(cmd)) { } else if ("s".equals(cmd)) { } else if ("[".equals(cmd)) { } else if ("]".equals(cmd)) { } }

if ("p".equals(cmd)) { dup(); invokestatic( p(String.class), "valueOf", sig(String.class, int.class)); getstatic(p(System.class), "out", ci(PrintStream.class)); swap(); invokevirtual( p(PrintStream.class), "print", sig(void.class, Object.class)); }

if ("p".equals(cmd)) { brainPrint(); }

else if ("+".equals(cmd)) { iconst_1(); iadd(); }

else if (“-".equals(cmd)) { iconst_1(); isub(); }

else if (“>".equals(cmd)) { iconst_0(); }

else if (“<".equals(cmd)) { pop(); }

else if (“s".equals(cmd)) { swap(); }

Stack<LabelNode[]> loopStack = new Stack<LabelNode[]>(); else if (“[“.equals(cmd)) { LabelNode begin = new LabelNode(); LabelNode end = new LabelNode(); label(begin); dup(); ifeq(end); loopStack.push(new LabelNode[] {begin, end}); }

else if (“]“.equals(cmd)) { LabelNode[] labelNodes = loopStack.pop(); LabelNode begin = labelNodes[0]; LabelNode end = labelNodes[1]; go_to(begin); label(end); }

14: dup 15: ifeq 39 ... 36: goto 14 39: pop

$ java Compiler “< < + + +” Generated Main.class $ java Main 42

Byteman http://byteman.jboss.org/

Javassist http://www.javassist.org/

class ThirdParty { public void run() { fetchData(); processData(); invokeService(); resolveConflicts(); finalize(); } }

ClassPool cp = ClassPool.getDefault(); CtClass cc = cp.get(“ThirdParty"); CtMethod m = cc.getDeclaredMethod(“fetchData"); m.addLocalVariable("t", CtClass.longType); m.insertBefore( "t = System.currentTimeMillis();"); m.insertAfter( “{“ + “ t = System.currentTimeMillis() - t;” + “ System.out.println("Time (ms): " + t);” + ”}"); byte[] byteCode = cc.toBytecode(); cc.detach(); http://www.tomsquest.com/blog/2014/01/intro-java-agent-and-bytecode-manipulation/

calling ThirdParty fetching data... Time (ms): 55 processing data... Time (ms): 6032

Brainfu** (Jipsy) List of JVM Bytecode Operations http://github.com/jkutner/jipsy http://docs.oracle.com/javase/specs/jvms/se8/html/ Jitescript https://github.com/qmx/jitescript

ASM Bytecode Outline ProGuard https://plugins.jetbrains.com/plugin/5918 http://proguard.sourceforge.net/ Dr. Garbage http://www.drgarbage.com/

The next time you compile… Run javap against the class ﬁle.

Thank You Joe Kutner @codeﬁnger http://www.slideshare.net/jkutner/programming-jvm-bytecode

Programming JVM Bytecode with Jitescript

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