Charles Nutter, profile picture
Uploaded byCharles Nutter
KEY, PPTX8,082 views

JavaOne 2011 - JVM Bytecode for Dummies

This document provides an introduction to JVM bytecode, including how to inspect, generate, and understand bytecode. It discusses two main parts - JVM bytecode itself such as basic instructions and stack operations, and the JVM JIT compiler which compiles bytecode to machine code. Various tools for working with bytecode like javap and ASM are also introduced. The document is intended to help readers gain a better understanding of how the Java platform works from the lowest level.

Embed presentation

Download as KEY, PPTX
1 / 141
2 / 141
3 / 141
4 / 141
5 / 141
6 / 141
7 / 141
8 / 141
9 / 141
10 / 141
11 / 141
12 / 141
13 / 141
14 / 141
15 / 141
16 / 141
17 / 141
18 / 141
19 / 141
20 / 141
21 / 141
22 / 141
23 / 141
24 / 141
25 / 141
26 / 141
27 / 141
28 / 141
29 / 141
30 / 141
31 / 141
32 / 141
33 / 141
34 / 141
35 / 141
36 / 141
37 / 141
38 / 141
39 / 141
40 / 141
41 / 141
42 / 141
43 / 141
44 / 141
45 / 141
46 / 141
47 / 141
48 / 141
49 / 141
50 / 141
51 / 141
52 / 141
53 / 141
54 / 141
55 / 141
56 / 141
57 / 141
58 / 141
59 / 141
60 / 141
61 / 141
62 / 141
63 / 141
64 / 141
65 / 141
66 / 141
67 / 141
68 / 141
69 / 141
70 / 141
71 / 141
72 / 141
73 / 141
74 / 141
75 / 141
76 / 141
77 / 141
78 / 141
79 / 141
80 / 141
81 / 141
82 / 141
83 / 141
84 / 141
85 / 141
86 / 141
87 / 141
88 / 141
89 / 141
90 / 141
91 / 141
92 / 141
93 / 141
94 / 141
95 / 141
96 / 141
97 / 141
98 / 141
99 / 141
100 / 141
101 / 141
102 / 141
103 / 141
104 / 141
105 / 141
106 / 141
107 / 141
108 / 141
109 / 141
110 / 141
111 / 141
112 / 141
113 / 141
114 / 141
115 / 141
116 / 141
117 / 141
118 / 141
119 / 141
120 / 141
121 / 141
122 / 141
123 / 141
124 / 141
125 / 141
126 / 141
127 / 141
128 / 141
129 / 141
130 / 141
131 / 141
132 / 141
133 / 141
134 / 141
135 / 141
136 / 141
137 / 141
138 / 141
139 / 141
140 / 141
141 / 141
JVM Bytecode for Dummies (and for the rest of you, as well)
Intro • Charles Oliver Nutter • “JRuby Guy” • Sun Microsystems 2006-2009 • Engine Yard 2009- • Primarily responsible for compiler, perf • Lots of bytecode generation
Two Parts • JVM Bytecode • Inspection • Generation • How it works • JVM JIT • How it works • Monitoring • Assembly (don’t be scared!)
Two Parts } • JVM Bytecode • Inspection Today • Generation • How it works } • JVM JIT • How it works Session 25141 Hilton Yosemite ABC • Monitoring Wednesday 10AM • Assembly (don’t be scared!)
Bytecode Definition • “... instruction sets designed for efficient execution by a software interpreter ...” • “... suitable for further compilation into machine code.
Byte Code • One-byte instructions • 256 possible “opcodes” • 200 in use on current JVMs • Room for more :-) • Little variation since Java 1.0
Microsoft’s CLR • Stack-based, but not interpreted • Two-byte “Wordcodes” • Similar operations to JVM
Why Learn It • Know your platform • Full understanding from top to bottom • Bytecode generation is fun and easy • Build your own language? • May need to read bytecode someday • Many libraries generate bytecode
Hello World public class HelloWorld { public static void main(String[] args) { System.out.println("Hello, world"); } }
javap • Java class file disassembler • Basic operation shows class structure • Methods, superclasses, interface, etc • -c flag includes bytecode • -public, -private, -protected • -verbose for stack size, locals, args
javap ~/projects/bytecode_for_dummies ➔ javap HelloWorld Compiled from "HelloWorld.java" public class HelloWorld extends java.lang.Object{ public HelloWorld(); public static void main(java.lang.String[]); }
javap -c ~/projects/bytecode_for_dummies ➔ javap -c HelloWorld Compiled from "HelloWorld.java" public class HelloWorld extends java.lang.Object{ public HelloWorld(); 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 8:! return }
javap -verbose ~/projects/bytecode_for_dummies ➔ javap -c -verbose HelloWorld Compiled from "HelloWorld.java" public class HelloWorld extends java.lang.Object SourceFile: "HelloWorld.java" minor version: 0 major version: 50 Constant pool: const #1 = Method! #6.#15;!// java/lang/Object."<init>":()V const #2 = Field!#16.#17;! / java/lang/System.out:Ljava/io/PrintStream; / const #3 = String! #18;! / Hello, world / const #4 = Method! #19.#20;! / java/io/PrintStream.println:(Ljava/lang/String;)V / const #5 = class!#21;! / HelloWorld / ... {
javap -verbose ... public HelloWorld(); Code: Stack=1, Locals=1, Args_size=1 0:!aload_0 1:!invokespecial! #1; //Method java/lang/Object."<init>":()V 4:!return LineNumberTable: line 1: 0
javap -verbose public static void main(java.lang.String[]); Code: Stack=2, Locals=1, Args_size=1 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 8:! return LineNumberTable: line 3: 0 line 4: 8 }
TraceClassVisitor $ java -cp <ASM stuff> org.objectweb.asm.util.TraceClassVisitor HelloWorld.class // class version 50.0 (50) // access flags 33 public class HelloWorld { // access flags 1 public <init>()V ALOAD 0 INVOKESPECIAL java/lang/Object.<init> ()V RETURN MAXSTACK = 1 MAXLOCALS = 1 // access flags 9 public static main([Ljava/lang/String;)V GETSTATIC java/lang/System.out : Ljava/io/PrintStream; LDC "Hello, world" INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V RETURN MAXSTACK = 2 MAXLOCALS = 1 }
ASMifierClassVisitor $ java -cp <ASM stuff> org.objectweb.asm.util.ASMifierClassVisitor HelloWorld.class import java.util.*; import org.objectweb.asm.*; import org.objectweb.asm.attrs.*; public class HelloWorldDump implements Opcodes { public static byte[] dump () throws Exception { ClassWriter cw = new ClassWriter(0); FieldVisitor fv; MethodVisitor mv; AnnotationVisitor av0; cw.visit(V1_6, ACC_PUBLIC + ACC_SUPER, "HelloWorld", null, "java/lang/Object", null); ...
... ASMifierClassVisitor { mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null); mv.visitCode(); mv.visitVarInsn(ALOAD, 0); mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V"); mv.visitInsn(RETURN); mv.visitMaxs(1, 1); mv.visitEnd(); } { mv = cw.visitMethod(ACC_PUBLIC + ACC_STATIC, "main", "([Ljava/lang/String;)V", null, null); mv.visitCode(); mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;"); mv.visitLdcInsn("Hello, world"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/ String;)V"); mv.visitInsn(RETURN); mv.visitMaxs(2, 1); mv.visitEnd(); } cw.visitEnd(); return cw.toByteArray(); } }
Thank you!
Thank you! (Just Kidding)
Let’s try something a little easier...
BiteScript • (J)Ruby DSL for emitting JVM bytecode • Internal DSL • Primitive “macro” support • Reads like javap -c (but nicer) • http://github.com/headius/bitescript
Installation • Download JRuby from http://jruby.org • Unpack, optionally add bin/ to PATH • Ahead of PATH if you have Ruby already • [bin/]jruby -S gem install bitescript • `bite myfile.bs` to run myfile.bs file • `bitec myfile.bs` to compile myfile.bs file
BiteScript Users • Mirah • Ruby-like language for writing Java code • BiteScript for JVM bytecode backend • BrainF*ck implementation • Other miscellaneous bytecode experiments
JiteScript • Java API that mimics BiteScript • Using a few cute tricks ;-) • Pretty close to javap output • Typical Java library installation • http://github.com/qmx/jitescript
JiteScript Users • dyn.js • invokedynamic-based JavaScript impl • ???
javap -c ~/projects/bytecode_for_dummies ➔ javap -c HelloWorld Compiled from "HelloWorld.java" public class HelloWorld extends java.lang.Object{ public HelloWorld(); 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 8:! return }
BiteScript main do getstatic java.lang.System, "out", java.io.PrintStream ldc "Hello, world!" invokevirtual java.io.PrintStream, "println", [java.lang.Void::TYPE, java.lang.Object] returnvoid end
BiteScript import java.lang.System JRuby’s “import” import java.io.PrintStream for Java classes main do getstatic System, "out", PrintStream ldc "Hello, world!" invokevirtual PrintStream, "println", [void, object] returnvoid end Shortcuts for void, int, string, object, etc
BiteScript main do ldc "Hello, world!" aprintln returnvoid A BiteScript “macro” end
BiteScript macro :aprintln do getstatic System, "out", PrintStream swap invokevirtual PrintStream, "println", [void, object] end
The Basics • Stack machine • Basic operations • Flow control • Class structures • Exception handling
Stack Machine • The “operand stack” holds operands • Operations push and/or pop stack values • Exceptions: nop, wide, goto, jsr/ret • Stack must be consistent • Largest part of bytecode verifier • Stack is explicitly sized per method
The JVM Stack Depth Value import java.lang.System import java.io.PrintStream 0 main do 1 getstatic System, "out", PrintStream ldc "Hello, world!" invokevirtual PrintStream, "println", 2 [void, object] returnvoid 3 end 4
The JVM Stack Depth Value import java.lang.System import java.io.PrintStream 0 out (a PS) main do 1 getstatic System, "out", PrintStream ldc "Hello, world!" invokevirtual PrintStream, "println", 2 [void, object] returnvoid 3 end 4
The JVM Stack Depth Value import java.lang.System import java.io.PrintStream 0 “Hello, world!” main do 1 out (a PS) getstatic System, "out", PrintStream ldc "Hello, world!" invokevirtual PrintStream, "println", 2 [void, object] returnvoid 3 end 4
The JVM Stack Depth Value import java.lang.System import java.io.PrintStream 0 main do 1 getstatic System, "out", PrintStream ldc "Hello, world!" invokevirtual PrintStream, "println", 2 [void, object] returnvoid 3 end 4
The JVM Stack Depth Value import java.lang.System import java.io.PrintStream 0 main do 1 getstatic System, "out", PrintStream ldc "Hello, world!" invokevirtual PrintStream, "println", 2 [void, object] returnvoid 3 end 4
Basic Operations • Stack manipulation • Local variables • Math • Boolean
Stack Operations 0x00 nop Do nothing. 0x57 pop Discard top value from stack 0x58 pop2 Discard top two values 0x59 dup Duplicate and push top value again 0x5A dup_x1 Dup and push top value below second value 0x5B dup_x2 Dup and push top value below third value 0x5C dup2 Dup top two values and push 0x5D dup2_x1 ...below second value 0x5E dup2_x2 ...below third value 0x5F swap Swap top two values
Stack Juggling Depth Value dup 0 value_0 pop swap 1 value_1 dup_x1 2 dup2_x2 3 4
Stack Juggling Depth Value dup 0 value_0 pop swap 1 value_0 dup_x1 2 value_1 dup2_x2 3 4
Stack Juggling Depth Value dup 0 value_0 pop swap 1 value_1 dup_x1 2 dup2_x2 3 4
Stack Juggling Depth Value dup 0 value_1 pop swap 1 value_0 dup_x1 2 dup2_x2 3 4
Stack Juggling Depth Value dup 0 value_1 pop swap 1 value_0 dup_x1 2 value_1 dup2_x2 3 4
Stack Juggling Depth Value dup 0 value_1 pop swap 1 value_0 dup_x1 2 value_1 dup2_x2 3 value_1 4 value_0
Typed Opcodes <type><operation> b byte Constant values s short Local vars (load, store) c char Array operations (aload, astore) i int Math ops (add, sub, mul, div) l long Boolean and bitwise f float d double Comparisons a reference Conversions
Where’s boolean? • Boolean is generally int 0 or 1 • Boolean operations push int 0 or 1 • Boolean branches expect 0 or nonzero • To set a boolean...use int 0 or 1
Constant Values 0x01 aconst_null Push null on stack 0x02-0x08 iload_[m1-5] Push integer [-1 to 5] on stack 0x09-0x0A lconst_[0,1] Push long [0 or 1] on stack 0x0B-0x0D fconst_[0,1,2] Push float [0.0, 1.0, 2.0] on stack 0x0E-0x0F dconst_[0,1] Push double [0.0, 1.0] on stack 0x10 bipush Push byte value to stack as integer 0x11 sipush Push short value to stack as integer 0x12 ldc Push 32-bit constant to stack (int, float, string) 0x14 ldc2_w Push 64-bit constant to stack (long, double)
Why So Many? • Reducing bytecode size • Special iconst_0 and friends take no args • bipush, sipush: only 8, 16 bits arguments • Pre-optimizing JVM • Specialized instructions can be optimized • Doesn’t matter at all now
Constant Values Depth Value ldc "hello" 0 dconst_1 1 aconst_null bipush 4 2 ldc_float 2.0 3 4 5
Constant Values Depth Value ldc "hello" 0 “hello” dconst_1 1 aconst_null bipush 4 2 ldc_float 2.0 3 4 5
Constant Values Depth Value ldc "hello" 0 dconst_1 1.0d 1 aconst_null bipush 4 2 “hello” ldc_float 2.0 3 4 5
Woah, Two Slots? • JVM stack slots (and local vars) are 32-bit • 64-bit values take up two slots • “wide” before or “w” suffix • 64-bit field updates not atomic! • Mind those concurrent longs/doubles!
Constant Values Depth Value ldc "hello" 0 null dconst_1 1 aconst_null 1.0d bipush 4 2 ldc_float 2.0 3 “hello” 4 5
Constant Values Depth Value ldc "hello" 0 4 dconst_1 1 null aconst_null bipush 4 2 ldc_float 2.0 1.0d 3 4 “hello” 5
Constant Values Depth Value ldc "hello" 0 2.0f dconst_1 1 4 aconst_null bipush 4 2 null ldc_float 2.0 3 1.0 4 5 “hello”
Local Variable Table • Local variables numbered from 0 • Instance methods have “this” at 0 • Separate table maps numbers to names • Explicitly sized in method definition
Local Variables 0x15 iload Load integer from local variable onto stack 0x16 lload ...long... 0x17 fload ...float... 0x18 dload ...double... 0x19 aload ...reference... 0x1A-0x2D Packed loads iload_0, aload_3, etc 0x36 istore Store integer from stack into local variable 0x37 lstore ...long... 0x38 fstore ...float... 0x39 dstore ...double... 0x3A astore ...reference... 0x3B-0x4E Packed stores fstore_2, dstore_0, etc 0x84 iinc Add given amount to int local variable
Local Variables Var Value Depth Value ldc "hello" 0 bipush 4 0 istore 3 1 dconst_0 1 dstore 1 2 astore 0 2 aload 0 3 iinc 3, 5 3 4 4
Local Variables Var Value Depth Value ldc "hello" 0 bipush 4 0 “hello” istore 3 1 dconst_0 1 dstore 1 2 astore 0 2 aload 0 3 iinc 3, 5 3 4 4
Local Variables Var Value Depth Value ldc "hello" 0 bipush 4 0 4 istore 3 1 dconst_0 1 “hello” dstore 1 2 astore 0 2 aload 0 3 iinc 3, 5 3 4 4
Local Variables Var Value Depth Value ldc "hello" 0 bipush 4 0 “hello” istore 3 1 dconst_0 1 dstore 1 2 astore 0 2 aload 0 3 4 iinc 3, 5 3 4 4
Local Variables Var Value Depth Value ldc "hello" 0 bipush 4 0 istore 3 0.0 1 dconst_0 1 dstore 1 2 astore 0 2 “hello” aload 0 3 4 iinc 3, 5 3 4 4
Local Variables Var Value Depth Value ldc "hello" 0 bipush 4 0 “hello” istore 3 1 dconst_0 1 0.0 dstore 1 2 astore 0 2 aload 0 3 4 iinc 3, 5 3 4 4
Local Variables Var Value Depth Value ldc "hello" 0 “hello” bipush 4 0 istore 3 1 dconst_0 1 0.0 dstore 1 2 astore 0 2 aload 0 3 4 iinc 3, 5 3 4 4
Local Variables Var Value Depth Value ldc "hello" 0 “hello” bipush 4 0 “hello” istore 3 1 dconst_0 1 0.0 dstore 1 2 astore 0 2 aload 0 3 4 iinc 3, 5 3 4 4
Local Variables Var Value Depth Value ldc "hello" 0 “hello” bipush 4 0 “hello” istore 3 1 dconst_0 1 0.0 dstore 1 2 astore 0 2 aload 0 3 9 iinc 3, 5 3 4 4
Arrays 0x2E-0x35 [i,l,f,d,a,b,c,d]aload Load [int, long, ...] from array (on stack) to stack 0x4F-0x56 [i,l,f,d,a,b,c,d]astore Store [int, long, ...] from stack to array (on stack) 0xBC newarray Construct new primitive array 0xBD anewarray Construct new reference array 0xBE arraylength Get array length 0xC5 multianewarray Create multi-dimensional array
Arrays Depth Value iconst_2 newarray int 0 dup iconst_0 1 iconst_m1 2 iastore iconst_0 3 iaload 4 5
Arrays Depth Value iconst_2 newarray int 0 2 dup iconst_0 1 iconst_m1 2 iastore iconst_0 3 iaload 4 5
Arrays Depth Value iconst_2 newarray int 0 int[2] {0,0} dup iconst_0 1 iconst_m1 2 iastore iconst_0 3 iaload 4 5
Arrays Depth Value iconst_2 newarray int 0 int[2] {0,0} dup iconst_0 1 int[2] {0,0} iconst_m1 2 iastore iconst_0 3 iaload 4 5
Arrays Depth Value iconst_2 newarray int 0 0 dup iconst_0 1 int[2] {0,0} iconst_m1 2 int[2] {0,0} iastore iconst_0 3 iaload 4 5
Arrays Depth Value iconst_2 newarray int 0 -1 dup iconst_0 1 0 iconst_m1 2 int[2] {0,0} iastore iconst_0 3 int[2] {0,0} iaload 4 5
Arrays Depth Value iconst_2 newarray int 0 int[2] {-1, 0} dup iconst_0 1 iconst_m1 2 iastore iconst_0 3 iaload 4 5
Arrays Depth Value iconst_2 newarray int 0 0 dup iconst_0 1 int[2] {-1, 0} iconst_m1 2 iastore iconst_0 3 iaload 4 5
Arrays Depth Value iconst_2 newarray int 0 -1 dup iconst_0 1 iconst_m1 2 iastore iconst_0 3 iaload 4 5
Math Operations add subtract multiply divide remainder negate + - * / % -() int iadd isub imul idiv irem ineg long ladd lsub lmul ldiv lrem lneg float fadd fsub fmul fdiv frem fneg double dadd dsub dmul ddiv drem dneg
Boolean and Bitwise unsigned shift left shift right and or xor shift right int ishl ishr iushr iand ior ixor
Conversions To: int long float double byte char short int - i2l i2f i2d i2b i2c i2s From: long l2i - l2f l2d - - - float f2i f2l - f2d - - - double d2i d2l d2f - - - -
Comparisons 0x94 lcmp Compare two longs, push int -1, 0, 1 0x95 fcmpl Compare two floats, push in -1, 0, 1 (-1 for NaN) 0x96 fcmpg Compare two floats, push in -1, 0, 1 (1 for NaN) 0x97 dcmpl Compare two doubles, push in -1, 0, 1 (-1 for NaN) 0x98 dcmpg Compare two doubles, push in -1, 0, 1 (1 for NaN)
Flow Control • Inspect stack and branch • Or just branch, via goto • Labels mark branch targets • Wide variety of tests
Flow Control 0x99 ifeq If zero on stack, branch 0x9A ifne If nonzero on stack, branch 0x9B iflt If stack value is less than zero, branch 0x9C ifge If stack value is greater than or equal to zero, branch 0x9D ifgt If stack value is greater than zero, branch 0x9E ifle If stack value is less than or equal to zero, branch 0x9F if_icmpeq If two integers on stack are eq, branch 0xA0 if_icmpne If two integers on stack are ne, branch 0xA1 if_icmplt If two integers on stack are lt, branch 0xA2 if_icmpge If two integers on stack are ge, branch 0xA3 if_icmpgt If tw If two integers on stack are gt, branch 0xA4 if_icmple If two integers on stack are le, branch 0xA5 if_acmpeq If two references on stack are the same, branch 0xA6 if_acmpne If two references on stack are different, branch 0xA7 goto GOTO!
Other Flow Control 0xA8 jsr Jump to subroutine (deprecated) 0xA9 ret Return from subroutine (deprecated) 0xAA tableswitch Branch using an indexed table of jump offsets 0xAB lookupswitch Branch using a lookup-based table of jump offsets 0xAC-0xB0 [i,l,f,d,a]return Return (int, long, float, double, reference) value 0xB1 return Void return (exit method, return nothing) 0xC6 ifnull If reference on stack is null 0xC7 ifnonnull If reference on stack is not null
Flow Control aload 0 ldc 0 aaload Depth Value ldc "branch" String[] invokevirtual string, "equals", 0 {“branch”} [boolean, object] ifne :branch 1 ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
Flow Control aload 0 ldc 0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 0 [boolean, object] ifne :branch 1 String[]{“branch”} ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
Flow Control aload 0 ldc 0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 “branch” [boolean, object] ifne :branch 1 ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
Flow Control aload 0 ldc 0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 “branch” [boolean, object] ifne :branch 1 “branch” ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
Flow Control aload 0 ldc 0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 1 [boolean, object] ifne :branch 1 ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
Flow Control aload 0 ldc 0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 [boolean, object] ifne :branch 1 ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
Flow Control aload 0 ldc 0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 [boolean, object] ifne :branch 1 ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
Flow Control aload 0 ldc 0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 “Equal!” [boolean, object] ifne :branch 1 ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
Flow Control aload 0 ldc 0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 [boolean, object] ifne :branch 1 ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
Classes and Types • Signatures!!! • Probably the most painful part • ...but not a big deal if you understand
Using Classes 0xB2 getstatic Fetch static field from class 0xB3 putstatic Set static field in class 0xB4 getfield Get instance field from object 0xB5 setfield Set instance field in object 0xB6 invokevirtual Invoke instance method on object 0xB7 invokespecial Invoke constructor or “super” on object 0xB8 invokestatic Invoke static method on class 0xB9 invokeinterface Invoke interface method on object 0xBA invokedynamic Invoke method dynamically on object (Java 7) 0xBB new Construct new instance of object 0xC0 checkcast Attempt to cast object to type 0xC1 instanceof Push nonzero if object is instanceof specified type
Using Classes new ArrayList dup invokespecial ArrayList, '<init>', Depth Value [void] an ArrayList checkcast Collection 0 (uninitialized) dup ldc "first element" 1 invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
Using Classes new ArrayList dup invokespecial ArrayList, '<init>', Depth Value [void] an ArrayList checkcast Collection 0 (uninitialized) dup an ArrayList ldc "first element" 1 (uninitialized) invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
Using Classes new ArrayList dup invokespecial ArrayList, '<init>', Depth Value [void] checkcast Collection 0 an ArrayList dup ldc "first element" 1 invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
Using Classes new ArrayList dup invokespecial ArrayList, '<init>', Depth Value [void] checkcast Collection 0 a Collection dup ldc "first element" 1 invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
Using Classes new ArrayList dup invokespecial ArrayList, '<init>', Depth Value [void] checkcast Collection 0 a Collection dup ldc "first element" 1 a Collection invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
Using Classes new ArrayList dup invokespecial ArrayList, '<init>', Depth Value [void] “first checkcast Collection 0 element” dup ldc "first element" 1 a Collection invokeinterface Collection, 'add', [boolean, object] 2 a Collection pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
Using Classes new ArrayList dup invokespecial ArrayList, '<init>', Depth Value [void] checkcast Collection 0 1 (true) dup ldc "first element" 1 a Collection invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
Using Classes new ArrayList dup invokespecial ArrayList, '<init>', Depth Value [void] checkcast Collection 0 a Collection dup ldc "first element" 1 invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
Using Classes new ArrayList dup invokespecial ArrayList, '<init>', Depth Value [void] checkcast Collection 0 an ArrayList dup ldc "first element" 1 invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
Using Classes new ArrayList dup invokespecial ArrayList, '<init>', Depth Value [void] checkcast Collection 0 0 dup ldc "first element" 1 an ArrayList invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
Using Classes new ArrayList dup invokespecial ArrayList, '<init>', Depth Value [void] “first checkcast Collection 0 element” dup ldc "first element" 1 invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
Using Classes new ArrayList dup invokespecial ArrayList, '<init>', Depth Value [void] checkcast Collection 0 dup ldc "first element" 1 invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
Invokedynamic • New bytecode in Java 7 • Target method is wired up by user code • Method handles are the wiring
Emitting Invokedynamic • Signature is still required • But can be almost anything • Method name is still required • But can be almost anything • MethodHandle for bootstrapping • Bytecode-level function pointer, basically
java.lang.invoke • MethodHandles • Function points • Adapters (arg juggling, catch, conditionals) • CallSites • Place to bind your MH chain • SwitchPoint • Zero-cost volatile boolean branch
import java.lang.invoke.MethodHandle import java.lang.invoke.MethodType import java.lang.invoke.CallSite import java.lang.invoke.ConstantCallSite import java.lang.invoke.MethodHandles::Lookup JClass = java.lang.Class
Target Method # The method we want to invoke, prints given string public_static_method :print, [], void, string do aload 0 aprintln returnvoid end
Invokedynamic # Our main method, which does one invokedynamic main do # handle for our bootstrap, which binds invokedynamic to a CallSite bootstrap = mh_invokestatic this, 'bootstrap', CallSite, Lookup, string, MethodType ldc 'Hello, invokedynamic!' invokedynamic 'print', [void, string], bootstrap returnvoid end
Invokedynamic # Our main method, which does one invokedynamic main do # handle for our bootstrap, which binds invokedynamic to a CallSite bootstrap = mh_invokestatic this, 'bootstrap', CallSite, Lookup, string, MethodType ldc 'Hello, invokedynamic!' invokedynamic 'print', [void, string], bootstrap returnvoid end
Invokedynamic # Our main method, which does one invokedynamic main do # handle for our bootstrap, which binds invokedynamic to a CallSite bootstrap = mh_invokestatic this, 'bootstrap', CallSite, Lookup, string, MethodType ldc 'Hello, invokedynamic!' invokedynamic 'print', [void, string], bootstrap returnvoid end
Invokedynamic # Our main method, which does one invokedynamic main do # handle for our bootstrap, which binds invokedynamic to a CallSite bootstrap = mh_invokestatic this, 'bootstrap', CallSite, Lookup, string, MethodType ldc 'Hello, invokedynamic!' invokedynamic 'print', [void, string], bootstrap returnvoid end
Bootstrap # The bootstrap method, which binds our dynamic call public_static_method :bootstrap, [], CallSite, Lookup, string, MethodType do # Constant since we bind just once directly new ConstantCallSite dup # Locate the method indicated by name + type on current class aload 0 # Lookup ldc this # this class aload 1 # String aload 2 # MethodType invokevirtual Lookup, 'findStatic', [MethodHandle, JClass, string, MethodType] # finish constructing call site and return invokespecial ConstantCallSite, '<init>', [void, MethodHandle] areturn end
Bootstrap # The bootstrap method, which binds our dynamic call public_static_method :bootstrap, [], CallSite, Lookup, string, MethodType do # Constant since we bind just once directly new ConstantCallSite dup # Locate the method indicated by name + type on current class aload 0 # Lookup ldc this # this class aload 1 # String aload 2 # MethodType invokevirtual Lookup, 'findStatic', [MethodHandle, JClass, string, MethodType] # finish constructing call site and return invokespecial ConstantCallSite, '<init>', [void, MethodHandle] areturn end
Bootstrap # The bootstrap method, which binds our dynamic call public_static_method :bootstrap, [], CallSite, Lookup, string, MethodType do # Constant since we bind just once directly new ConstantCallSite dup # Locate the method indicated by name + type on current class aload 0 # Lookup ldc this # this class aload 1 # String aload 2 # MethodType invokevirtual Lookup, 'findStatic', [MethodHandle, JClass, string, MethodType] # finish constructing call site and return invokespecial ConstantCallSite, '<init>', [void, MethodHandle] areturn end
Bootstrap # The bootstrap method, which binds our dynamic call public_static_method :bootstrap, [], CallSite, Lookup, string, MethodType do # Constant since we bind just once directly new ConstantCallSite dup # Locate the method indicated by name + type on current class aload 0 # Lookup ldc this # this class aload 1 # String aload 2 # MethodType invokevirtual Lookup, 'findStatic', [MethodHandle, JClass, string, MethodType] # finish constructing call site and return invokespecial ConstantCallSite, '<init>', [void, MethodHandle] areturn end
Bootstrap # The bootstrap method, which binds our dynamic call public_static_method :bootstrap, [], CallSite, Lookup, string, MethodType do # Constant since we bind just once directly new ConstantCallSite dup # Locate the method indicated by name + type on current class aload 0 # Lookup ldc this # this class aload 1 # String aload 2 # MethodType invokevirtual Lookup, 'findStatic', [MethodHandle, JClass, string, MethodType] # finish constructing call site and return invokespecial ConstantCallSite, '<init>', [void, MethodHandle] areturn end
Exceptions and Synchronization Table structure for a method indicating start/end of - trycatch try/catch and logic to run on exception 0xC2 monitorenter Enter synchronized block against object on stack 0xC3 monitorexit Exit synchronized block (against same object)
More Examples • A simple loop • Fibonacci
A Simple Loop main do aload 0 push_int 0 aaload label :top dup aprintln goto :top returnvoid end
Fibonacci public_static_method "fib", [], int, int do iload 0 ldc 2 if_icmpge :recurse iload 0 ireturn label :recurse iload 0 ldc 1 isub invokestatic this, "fib", [int, int] iload 0 ldc 2 isub invokestatic this, "fib", [int, int] iadd ireturn end
main do load_times istore 1 Fibonacci ldc "Raw bytecode fib(45) performance:" aprintln label :top iload 1 ifeq :done iinc 1, -1 start_timing 2 ldc 45 invokestatic this, "fib", [int, int] pop end_timing 2 ldc "Time: " aprintln lprintln 2 goto :top label :done returnvoid end
main do load_times istore 1 Fibonacci ldc "Raw bytecode fib(45) performance:" aprintln label :top iload 1 ifeq :done iinc 1, -1 start_timing 2 Macros ldc 45 invokestatic this, "fib", [int, int] pop end_timing 2 ldc "Time: " aprintln lprintln 2 goto :top label :done returnvoid end
Fibonacci macro :load_times do aload 0 ldc 0 aaload # number of times invokestatic JInteger, 'parseInt', [int, string] end
Fibonacci macro :start_timing do |i| load_time lstore i end
Fibonacci macro :load_time do invokestatic System, "currentTimeMillis", long end
Fibonacci macro :end_timing do |i| load_time lload i lsub lstore i end
Fibonacci macro :lprintln do |i| getstatic System, "out", PrintStream lload i invokevirtual PrintStream, "println", [void, long] end
Real-world Cases • Reflection-free invocation • JRuby, Groovy, other languages • Bytecoded data objects • Hibernate, other data layers • java.lang.reflect.Proxy and others • Language compilers
Tools • BiteScript • So much fun • Ruby, so that’s even better • JiteScript • ASM - defacto standard library
Part 2 Topics • Tracking your bytecode • Dumping JVM JIT through the JVM assembly output • How the JVM optimizes • x86 assembler language running code for dummies! • Monitoring JVM JIT compilation • Inspecting JVM inlining
Pluggity • Many thanks to Engine Yard • JRuby and Java PaaS • JRuby support and services • sales@engineyard.com
Pluggity
Pluggity • Migrating to JRuby on Rails 5:30 Mon, Parc 55 Market Street • JVM JIT for Dummies Part 2 10:00 Wed, Parc 55 Market street • JRuby + Java + Cloud 3:00 Wed, Parc 55 Embarcadero • Real World JRuby 4:30 Wed, Parc 55 Market Street
Pluggity • JRuby meetup/party Engine Yard HQ 500 Third Street, Suite 510 Tuesday, 6:30PM • Try JRuby on EY Cloud http://engineyard.com/tryjruby
Thank you! • headius@headius.com, @headius • http://blog.headius.com • http://github.com/headius/bitescript • “java virtual machine specification” • “jvm opcodes”

More Related Content

KEY
Øredev 2011 - JVM JIT for Dummies (What the JVM Does With Your Bytecode When ...
byCharles Nutter
 
PPT
Java Basics
bySunil OS
 
PDF
Bytecode manipulation with Javassist and ASM
byashleypuls
 
PPTX
Lecture - 2 Environment setup & JDK, JRE, JVM
bymanish kumar
 
PDF
Low Level View of Android System Architecture
byNational Cheng Kung University
 
PDF
Introduction to Kotlin coroutines
byRoman Elizarov
 
ODP
Contenedores de java swing
byJessicavergara273
 
KEY
JavaOne 2012 - JVM JIT for Dummies
byCharles Nutter
 
Øredev 2011 - JVM JIT for Dummies (What the JVM Does With Your Bytecode When ...
byCharles Nutter
 
Java Basics
bySunil OS
 
Bytecode manipulation with Javassist and ASM
byashleypuls
 
Lecture - 2 Environment setup & JDK, JRE, JVM
bymanish kumar
 
Low Level View of Android System Architecture
byNational Cheng Kung University
 
Introduction to Kotlin coroutines
byRoman Elizarov
 
Contenedores de java swing
byJessicavergara273
 
JavaOne 2012 - JVM JIT for Dummies
byCharles Nutter
 

Viewers also liked

PDF
Fast as C: How to Write Really Terrible Java
byCharles Nutter
 
PPTX
JVM: A Platform for Multiple Languages
byKris Mok
 
PDF
Down the Rabbit Hole
byCharles Nutter
 
PDF
STOP! VIEW THIS! 10-Step Checklist When Uploading to Slideshare
byEmpowered Presentations
 
PDF
Win32/Flamer: Reverse Engineering and Framework Reconstruction
byAlex Matrosov
 
PDF
How To Get More From SlideShare - Super-Simple Tips For Content Marketing
byContent Marketing Institute
 
PPT
Akaun Chapter 5
byWanBK Leo
 
PDF
A Guide to SlideShare Analytics - Excerpts from Hubspot's Step by Step Guide ...
bySlideshare
 
PDF
How to Make Awesome SlideShares: Tips & Tricks
bySlideshare
 
PDF
Getting Started With SlideShare
bySlideshare
 
PDF
Masters of SlideShare
byKapost
 
PPTX
What to Upload to SlideShare
bySlideshare
 
PDF
What Makes Great Infographics
bySlideshare
 
PDF
10 Ways to Win at SlideShare SEO & Presentation Optimization
byOneupweb
 
PDF
Down the Rabbit Hole: An Adventure in JVM Wonderland
byCharles Nutter
 
PPTX
Nashorn on JDK 8 (ADC2013)
byKris Mok
 
Fast as C: How to Write Really Terrible Java
byCharles Nutter
 
JVM: A Platform for Multiple Languages
byKris Mok
 
Down the Rabbit Hole
byCharles Nutter
 
STOP! VIEW THIS! 10-Step Checklist When Uploading to Slideshare
byEmpowered Presentations
 
Win32/Flamer: Reverse Engineering and Framework Reconstruction
byAlex Matrosov
 
How To Get More From SlideShare - Super-Simple Tips For Content Marketing
byContent Marketing Institute
 
Akaun Chapter 5
byWanBK Leo
 
A Guide to SlideShare Analytics - Excerpts from Hubspot's Step by Step Guide ...
bySlideshare
 
How to Make Awesome SlideShares: Tips & Tricks
bySlideshare
 
Getting Started With SlideShare
bySlideshare
 
Masters of SlideShare
byKapost
 
What to Upload to SlideShare
bySlideshare
 
What Makes Great Infographics
bySlideshare
 
10 Ways to Win at SlideShare SEO & Presentation Optimization
byOneupweb
 
Down the Rabbit Hole: An Adventure in JVM Wonderland
byCharles Nutter
 
Nashorn on JDK 8 (ADC2013)
byKris Mok
 

Similar to JavaOne 2011 - JVM Bytecode for Dummies

PDF
Understanding the Dalvik Virtual Machine
byNational Cheng Kung University
 
PDF
JVM for Dummies - OSCON 2011
byCharles Nutter
 
PDF
No dark magic - Byte code engineering in the real world
bytcurdt
 
PDF
Understanding the Dalvik bytecode with the Dedexer tool
byGabor Paller
 
PPTX
Java byte code & virtual machine
byLaxman Puri
 
PPTX
Java introduction
byThe icfai university jaipur
 
PDF
Jvm internals
byLuiz Fernando Teston
 
PDF
An Introduction to Java Compiler and Runtime
byOmar Bashir
 
PPTX
JAVA BYTE CODE
byJaved Ahmed Samo
 
PPT
Oop lecture2
byShahriar Robbani
 
PDF
Advanced Debugging Using Java Bytecodes
byGanesh Samarthyam
 
PDF
Introduction to the Java bytecode - So@t - 20130924
byyohanbeschi
 
PPTX
Mastering Java Bytecode - JAX.de 2012
byAnton Arhipov
 
PPT
Mastering Java ByteCode
byEcommerce Solution Provider SysIQ
 
PPTX
GOTO Night with Charles Nutter Slides
byAlexandra Masterson
 
PDF
Java Bytecode for Discriminating Developers - JavaZone 2011
byAnton Arhipov
 
PDF
College Project - Java Disassembler - Description
byGanesh Samarthyam
 
PDF
Ola Bini Evolving The Java Platform
bydeimos
 
PPTX
Java Starting
byRaja Sekhar
 
ODP
I Know Kung Fu - Juggling Java Bytecode
byAlexander Shopov
 
Understanding the Dalvik Virtual Machine
byNational Cheng Kung University
 
JVM for Dummies - OSCON 2011
byCharles Nutter
 
No dark magic - Byte code engineering in the real world
bytcurdt
 
Understanding the Dalvik bytecode with the Dedexer tool
byGabor Paller
 
Java byte code & virtual machine
byLaxman Puri
 
Java introduction
byThe icfai university jaipur
 
Jvm internals
byLuiz Fernando Teston
 
An Introduction to Java Compiler and Runtime
byOmar Bashir
 
JAVA BYTE CODE
byJaved Ahmed Samo
 
Oop lecture2
byShahriar Robbani
 
Advanced Debugging Using Java Bytecodes
byGanesh Samarthyam
 
Introduction to the Java bytecode - So@t - 20130924
byyohanbeschi
 
Mastering Java Bytecode - JAX.de 2012
byAnton Arhipov
 
Mastering Java ByteCode
byEcommerce Solution Provider SysIQ
 
GOTO Night with Charles Nutter Slides
byAlexandra Masterson
 
Java Bytecode for Discriminating Developers - JavaZone 2011
byAnton Arhipov
 
College Project - Java Disassembler - Description
byGanesh Samarthyam
 
Ola Bini Evolving The Java Platform
bydeimos
 
Java Starting
byRaja Sekhar
 
I Know Kung Fu - Juggling Java Bytecode
byAlexander Shopov
 

More from Charles Nutter

PDF
Invokedynamic in 45 Minutes
byCharles Nutter
 
PDF
Beyond JVM - YOW! Brisbane 2013
byCharles Nutter
 
PDF
JRuby and Invokedynamic - Japan JUG 2015
byCharles Nutter
 
PDF
Beyond JVM - YOW Melbourne 2013
byCharles Nutter
 
PDF
JRuby 9000 - Taipei Ruby User's Group 2015
byCharles Nutter
 
PDF
Beyond JVM - YOW! Sydney 2013
byCharles Nutter
 
PDF
JRuby: The Hard Parts
byCharles Nutter
 
KEY
Why JRuby? - RubyConf 2012
byCharles Nutter
 
PDF
Ruby Performance - The Last Mile - RubyConf India 2016
byCharles Nutter
 
PDF
Bringing Concurrency to Ruby - RubyConf India 2014
byCharles Nutter
 
PDF
JRuby 9000 - Optimizing Above the JVM
byCharles Nutter
 
PDF
The Year of JRuby - RubyC 2018
byCharles Nutter
 
KEY
Aloha RubyConf 2012 - JRuby
byCharles Nutter
 
PDF
The Future of JRuby - Baruco 2013
byCharles Nutter
 
PDF
Doing Open Source the Right Way
byCharles Nutter
 
PDF
Invokedynamic: Tales from the Trenches
byCharles Nutter
 
PDF
Over 9000: JRuby in 2015
byCharles Nutter
 
PDF
InvokeBinder: Fluent Programming for Method Handles
byCharles Nutter
 
PDF
High Performance Ruby - E4E Conference 2013
byCharles Nutter
 
PDF
Open Source Software Needs You!
byCharles Nutter
 
Invokedynamic in 45 Minutes
byCharles Nutter
 
Beyond JVM - YOW! Brisbane 2013
byCharles Nutter
 
JRuby and Invokedynamic - Japan JUG 2015
byCharles Nutter
 
Beyond JVM - YOW Melbourne 2013
byCharles Nutter
 
JRuby 9000 - Taipei Ruby User's Group 2015
byCharles Nutter
 
Beyond JVM - YOW! Sydney 2013
byCharles Nutter
 
JRuby: The Hard Parts
byCharles Nutter
 
Why JRuby? - RubyConf 2012
byCharles Nutter
 
Ruby Performance - The Last Mile - RubyConf India 2016
byCharles Nutter
 
Bringing Concurrency to Ruby - RubyConf India 2014
byCharles Nutter
 
JRuby 9000 - Optimizing Above the JVM
byCharles Nutter
 
The Year of JRuby - RubyC 2018
byCharles Nutter
 
Aloha RubyConf 2012 - JRuby
byCharles Nutter
 
The Future of JRuby - Baruco 2013
byCharles Nutter
 
Doing Open Source the Right Way
byCharles Nutter
 
Invokedynamic: Tales from the Trenches
byCharles Nutter
 
Over 9000: JRuby in 2015
byCharles Nutter
 
InvokeBinder: Fluent Programming for Method Handles
byCharles Nutter
 
High Performance Ruby - E4E Conference 2013
byCharles Nutter
 
Open Source Software Needs You!
byCharles Nutter
 

Recently uploaded

PPTX
Coded Agents – with UiPath SDK + LangGraph [Virtual Hands-on Workshop]
byUiPathCommunity
 
PPTX
Conversational Agents – Building Intelligent Assistants [Virtual Hands-on Wor...
byUiPathCommunity
 
PDF
DevFest El Jadida 2025 - Product Thinking
byElmehdi AMLOU
 
PDF
Real-Time Data Insight Using Microsoft Forms for Business
byElevate
 
PDF
Cross-Cultural Agile Development -Challenges and Strategies for Overcoming Them-
byTakashi Makino
 
PDF
Access Control 2025: From Security Silo to Software-Defined Ecosystem
byMemoori
 
PDF
Eredità digitale sugli smartphone: cosa resta di noi nei dispositivi mobili
bySpeck&Tech
 
PDF
AI Meets Integration: Delivering AI-Ready Data in Real Time.pdf
byPrecisely
 
PDF
Cybersecurity: Safeguarding Digital Assets
byYasir Naveed Riaz
 
PPTX
Data Privacy and Protection: Safeguarding Information in a Connected World
byYasir Naveed Riaz
 
PPTX
From Backup to Resilience: How MSPs Are Preparing for 2026
byMSP360
 
PPTX
Cybercrime in the Digital Age: Risks, Impact & Protection
byYasir Naveed Riaz
 
PPTX
Building Cyber Resilience for 2026: Best Practices for a Secure, AI-Driven Bu...
byYasir Naveed Riaz
 
PDF
Internet_of_Things_IoT_for_Next_Generation_Smart_Systems_Utilizing.pdf
byRoshanSyed12
 
PPTX
AI's Impact on Cybersecurity - Challenges and Opportunities
byYasir Naveed Riaz
 
PDF
TrustArc Webinar - Looking Ahead: The 2026 Privacy Landscape
byTrustArc
 
PDF
Is It Possible to Have Wi-Fi Without an Internet Provider
bySidra Jefferi
 
PDF
The major tech developments for 2026 by Pluralsight, a research and training ...
byChris Skinner
 
PDF
Energy Storage Landscape Clean Energy Ministerial
bySurajitBanerjee38
 
PDF
Decoding the DNA: The Digital Networks Act, the Open Internet, and IP interco...
byCSUC - Consorci de Serveis Universitaris de Catalunya
 
Coded Agents – with UiPath SDK + LangGraph [Virtual Hands-on Workshop]
byUiPathCommunity
 
Conversational Agents – Building Intelligent Assistants [Virtual Hands-on Wor...
byUiPathCommunity
 
DevFest El Jadida 2025 - Product Thinking
byElmehdi AMLOU
 
Real-Time Data Insight Using Microsoft Forms for Business
byElevate
 
Cross-Cultural Agile Development -Challenges and Strategies for Overcoming Them-
byTakashi Makino
 
Access Control 2025: From Security Silo to Software-Defined Ecosystem
byMemoori
 
Eredità digitale sugli smartphone: cosa resta di noi nei dispositivi mobili
bySpeck&Tech
 
AI Meets Integration: Delivering AI-Ready Data in Real Time.pdf
byPrecisely
 
Cybersecurity: Safeguarding Digital Assets
byYasir Naveed Riaz
 
Data Privacy and Protection: Safeguarding Information in a Connected World
byYasir Naveed Riaz
 
From Backup to Resilience: How MSPs Are Preparing for 2026
byMSP360
 
Cybercrime in the Digital Age: Risks, Impact & Protection
byYasir Naveed Riaz
 
Building Cyber Resilience for 2026: Best Practices for a Secure, AI-Driven Bu...
byYasir Naveed Riaz
 
Internet_of_Things_IoT_for_Next_Generation_Smart_Systems_Utilizing.pdf
byRoshanSyed12
 
AI's Impact on Cybersecurity - Challenges and Opportunities
byYasir Naveed Riaz
 
TrustArc Webinar - Looking Ahead: The 2026 Privacy Landscape
byTrustArc
 
Is It Possible to Have Wi-Fi Without an Internet Provider
bySidra Jefferi
 
The major tech developments for 2026 by Pluralsight, a research and training ...
byChris Skinner
 
Energy Storage Landscape Clean Energy Ministerial
bySurajitBanerjee38
 
Decoding the DNA: The Digital Networks Act, the Open Internet, and IP interco...
byCSUC - Consorci de Serveis Universitaris de Catalunya
 

JavaOne 2011 - JVM Bytecode for Dummies

  • 1.
    JVM Bytecode for Dummies (and for the rest of you, as well)
  • 2.
    Intro • Charles OliverNutter • “JRuby Guy” • Sun Microsystems 2006-2009 • Engine Yard 2009- • Primarily responsible for compiler, perf • Lots of bytecode generation
  • 3.
    Two Parts • JVM Bytecode • Inspection • Generation • How it works • JVM JIT • How it works • Monitoring • Assembly (don’t be scared!)
  • 4.
    Two Parts } • JVM Bytecode • Inspection Today • Generation • How it works } • JVM JIT • How it works Session 25141 Hilton Yosemite ABC • Monitoring Wednesday 10AM • Assembly (don’t be scared!)
  • 5.
    Bytecode Definition • “...instruction sets designed for efficient execution by a software interpreter ...” • “... suitable for further compilation into machine code.
  • 6.
    Byte Code • One-byteinstructions • 256 possible “opcodes” • 200 in use on current JVMs • Room for more :-) • Little variation since Java 1.0
  • 7.
    Microsoft’s CLR • Stack-based,but not interpreted • Two-byte “Wordcodes” • Similar operations to JVM
  • 8.
    Why Learn It •Know your platform • Full understanding from top to bottom • Bytecode generation is fun and easy • Build your own language? • May need to read bytecode someday • Many libraries generate bytecode
  • 9.
    Hello World public classHelloWorld { public static void main(String[] args) { System.out.println("Hello, world"); } }
  • 10.
    javap • Java classfile disassembler • Basic operation shows class structure • Methods, superclasses, interface, etc • -c flag includes bytecode • -public, -private, -protected • -verbose for stack size, locals, args
  • 11.
    javap ~/projects/bytecode_for_dummies ➔ javapHelloWorld Compiled from "HelloWorld.java" public class HelloWorld extends java.lang.Object{ public HelloWorld(); public static void main(java.lang.String[]); }
  • 12.
    javap -c ~/projects/bytecode_for_dummies ➔javap -c HelloWorld Compiled from "HelloWorld.java" public class HelloWorld extends java.lang.Object{ public HelloWorld(); 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 8:! return }
  • 13.
    javap -verbose ~/projects/bytecode_for_dummies ➔javap -c -verbose HelloWorld Compiled from "HelloWorld.java" public class HelloWorld extends java.lang.Object SourceFile: "HelloWorld.java" minor version: 0 major version: 50 Constant pool: const #1 = Method! #6.#15;!// java/lang/Object."<init>":()V const #2 = Field!#16.#17;! / java/lang/System.out:Ljava/io/PrintStream; / const #3 = String! #18;! / Hello, world / const #4 = Method! #19.#20;! / java/io/PrintStream.println:(Ljava/lang/String;)V / const #5 = class!#21;! / HelloWorld / ... {
  • 14.
    javap -verbose ... public HelloWorld(); Code: Stack=1, Locals=1, Args_size=1 0:!aload_0 1:!invokespecial! #1; //Method java/lang/Object."<init>":()V 4:!return LineNumberTable: line 1: 0
  • 15.
    javap -verbose public staticvoid main(java.lang.String[]); Code: Stack=2, Locals=1, Args_size=1 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 8:! return LineNumberTable: line 3: 0 line 4: 8 }
  • 16.
    TraceClassVisitor $ java -cp<ASM stuff> org.objectweb.asm.util.TraceClassVisitor HelloWorld.class // class version 50.0 (50) // access flags 33 public class HelloWorld { // access flags 1 public <init>()V ALOAD 0 INVOKESPECIAL java/lang/Object.<init> ()V RETURN MAXSTACK = 1 MAXLOCALS = 1 // access flags 9 public static main([Ljava/lang/String;)V GETSTATIC java/lang/System.out : Ljava/io/PrintStream; LDC "Hello, world" INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V RETURN MAXSTACK = 2 MAXLOCALS = 1 }
  • 17.
    ASMifierClassVisitor $ java -cp <ASM stuff> org.objectweb.asm.util.ASMifierClassVisitor HelloWorld.class import java.util.*; import org.objectweb.asm.*; import org.objectweb.asm.attrs.*; public class HelloWorldDump implements Opcodes { public static byte[] dump () throws Exception { ClassWriter cw = new ClassWriter(0); FieldVisitor fv; MethodVisitor mv; AnnotationVisitor av0; cw.visit(V1_6, ACC_PUBLIC + ACC_SUPER, "HelloWorld", null, "java/lang/Object", null); ...
  • 18.
    ... ASMifierClassVisitor { mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null); mv.visitCode(); mv.visitVarInsn(ALOAD, 0); mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V"); mv.visitInsn(RETURN); mv.visitMaxs(1, 1); mv.visitEnd(); } { mv = cw.visitMethod(ACC_PUBLIC + ACC_STATIC, "main", "([Ljava/lang/String;)V", null, null); mv.visitCode(); mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;"); mv.visitLdcInsn("Hello, world"); mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/ String;)V"); mv.visitInsn(RETURN); mv.visitMaxs(2, 1); mv.visitEnd(); } cw.visitEnd(); return cw.toByteArray(); } }
  • 19.
  • 20.
    Thank you! (Just Kidding)
  • 21.
    Let’s try somethinga little easier...
  • 22.
    BiteScript • (J)Ruby DSLfor emitting JVM bytecode • Internal DSL • Primitive “macro” support • Reads like javap -c (but nicer) • http://github.com/headius/bitescript
  • 23.
    Installation • Download JRubyfrom http://jruby.org • Unpack, optionally add bin/ to PATH • Ahead of PATH if you have Ruby already • [bin/]jruby -S gem install bitescript • `bite myfile.bs` to run myfile.bs file • `bitec myfile.bs` to compile myfile.bs file
  • 24.
    BiteScript Users • Mirah • Ruby-like language for writing Java code • BiteScript for JVM bytecode backend • BrainF*ck implementation • Other miscellaneous bytecode experiments
  • 25.
    JiteScript • Java APIthat mimics BiteScript • Using a few cute tricks ;-) • Pretty close to javap output • Typical Java library installation • http://github.com/qmx/jitescript
  • 26.
    JiteScript Users • dyn.js • invokedynamic-based JavaScript impl • ???
  • 27.
    javap -c ~/projects/bytecode_for_dummies ➔javap -c HelloWorld Compiled from "HelloWorld.java" public class HelloWorld extends java.lang.Object{ public HelloWorld(); 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 8:! return }
  • 28.
    BiteScript main do getstatic java.lang.System, "out", java.io.PrintStream ldc "Hello, world!" invokevirtual java.io.PrintStream, "println", [java.lang.Void::TYPE, java.lang.Object] returnvoid end
  • 29.
    BiteScript import java.lang.System JRuby’s “import” import java.io.PrintStream for Java classes main do getstatic System, "out", PrintStream ldc "Hello, world!" invokevirtual PrintStream, "println", [void, object] returnvoid end Shortcuts for void, int, string, object, etc
  • 30.
    BiteScript main do ldc "Hello, world!" aprintln returnvoid A BiteScript “macro” end
  • 31.
    BiteScript macro :aprintln do getstatic System, "out", PrintStream swap invokevirtual PrintStream, "println", [void, object] end
  • 32.
    The Basics • Stackmachine • Basic operations • Flow control • Class structures • Exception handling
  • 33.
    Stack Machine • The“operand stack” holds operands • Operations push and/or pop stack values • Exceptions: nop, wide, goto, jsr/ret • Stack must be consistent • Largest part of bytecode verifier • Stack is explicitly sized per method
  • 34.
    The JVM Stack Depth Value import java.lang.System import java.io.PrintStream 0 main do 1 getstatic System, "out", PrintStream ldc "Hello, world!" invokevirtual PrintStream, "println", 2 [void, object] returnvoid 3 end 4
  • 35.
    The JVM Stack Depth Value import java.lang.System import java.io.PrintStream 0 out (a PS) main do 1 getstatic System, "out", PrintStream ldc "Hello, world!" invokevirtual PrintStream, "println", 2 [void, object] returnvoid 3 end 4
  • 36.
    The JVM Stack Depth Value import java.lang.System import java.io.PrintStream 0 “Hello, world!” main do 1 out (a PS) getstatic System, "out", PrintStream ldc "Hello, world!" invokevirtual PrintStream, "println", 2 [void, object] returnvoid 3 end 4
  • 37.
    The JVM Stack Depth Value import java.lang.System import java.io.PrintStream 0 main do 1 getstatic System, "out", PrintStream ldc "Hello, world!" invokevirtual PrintStream, "println", 2 [void, object] returnvoid 3 end 4
  • 38.
    The JVM Stack Depth Value import java.lang.System import java.io.PrintStream 0 main do 1 getstatic System, "out", PrintStream ldc "Hello, world!" invokevirtual PrintStream, "println", 2 [void, object] returnvoid 3 end 4
  • 39.
    Basic Operations • Stackmanipulation • Local variables • Math • Boolean
  • 40.
    Stack Operations 0x00 nop Do nothing. 0x57 pop Discard top value from stack 0x58 pop2 Discard top two values 0x59 dup Duplicate and push top value again 0x5A dup_x1 Dup and push top value below second value 0x5B dup_x2 Dup and push top value below third value 0x5C dup2 Dup top two values and push 0x5D dup2_x1 ...below second value 0x5E dup2_x2 ...below third value 0x5F swap Swap top two values
  • 41.
    Stack Juggling Depth Value dup 0 value_0 pop swap 1 value_1 dup_x1 2 dup2_x2 3 4
  • 42.
    Stack Juggling Depth Value dup 0 value_0 pop swap 1 value_0 dup_x1 2 value_1 dup2_x2 3 4
  • 43.
    Stack Juggling Depth Value dup 0 value_0 pop swap 1 value_1 dup_x1 2 dup2_x2 3 4
  • 44.
    Stack Juggling Depth Value dup 0 value_1 pop swap 1 value_0 dup_x1 2 dup2_x2 3 4
  • 45.
    Stack Juggling Depth Value dup 0 value_1 pop swap 1 value_0 dup_x1 2 value_1 dup2_x2 3 4
  • 46.
    Stack Juggling Depth Value dup 0 value_1 pop swap 1 value_0 dup_x1 2 value_1 dup2_x2 3 value_1 4 value_0
  • 47.
    Typed Opcodes <type><operation> b byte Constant values s short Local vars (load, store) c char Array operations (aload, astore) i int Math ops (add, sub, mul, div) l long Boolean and bitwise f float d double Comparisons a reference Conversions
  • 48.
    Where’s boolean? • Booleanis generally int 0 or 1 • Boolean operations push int 0 or 1 • Boolean branches expect 0 or nonzero • To set a boolean...use int 0 or 1
  • 49.
    Constant Values 0x01 aconst_null Push null on stack 0x02-0x08 iload_[m1-5] Push integer [-1 to 5] on stack 0x09-0x0A lconst_[0,1] Push long [0 or 1] on stack 0x0B-0x0D fconst_[0,1,2] Push float [0.0, 1.0, 2.0] on stack 0x0E-0x0F dconst_[0,1] Push double [0.0, 1.0] on stack 0x10 bipush Push byte value to stack as integer 0x11 sipush Push short value to stack as integer 0x12 ldc Push 32-bit constant to stack (int, float, string) 0x14 ldc2_w Push 64-bit constant to stack (long, double)
  • 50.
    Why So Many? •Reducing bytecode size • Special iconst_0 and friends take no args • bipush, sipush: only 8, 16 bits arguments • Pre-optimizing JVM • Specialized instructions can be optimized • Doesn’t matter at all now
  • 51.
    Constant Values Depth Value ldc "hello" 0 dconst_1 1 aconst_null bipush 4 2 ldc_float 2.0 3 4 5
  • 52.
    Constant Values Depth Value ldc "hello" 0 “hello” dconst_1 1 aconst_null bipush 4 2 ldc_float 2.0 3 4 5
  • 53.
    Constant Values Depth Value ldc "hello" 0 dconst_1 1.0d 1 aconst_null bipush 4 2 “hello” ldc_float 2.0 3 4 5
  • 54.
    Woah, Two Slots? •JVM stack slots (and local vars) are 32-bit • 64-bit values take up two slots • “wide” before or “w” suffix • 64-bit field updates not atomic! • Mind those concurrent longs/doubles!
  • 55.
    Constant Values Depth Value ldc "hello" 0 null dconst_1 1 aconst_null 1.0d bipush 4 2 ldc_float 2.0 3 “hello” 4 5
  • 56.
    Constant Values Depth Value ldc "hello" 0 4 dconst_1 1 null aconst_null bipush 4 2 ldc_float 2.0 1.0d 3 4 “hello” 5
  • 57.
    Constant Values Depth Value ldc "hello" 0 2.0f dconst_1 1 4 aconst_null bipush 4 2 null ldc_float 2.0 3 1.0 4 5 “hello”
  • 58.
    Local Variable Table •Local variables numbered from 0 • Instance methods have “this” at 0 • Separate table maps numbers to names • Explicitly sized in method definition
  • 59.
    Local Variables 0x15 iload Load integer from local variable onto stack 0x16 lload ...long... 0x17 fload ...float... 0x18 dload ...double... 0x19 aload ...reference... 0x1A-0x2D Packed loads iload_0, aload_3, etc 0x36 istore Store integer from stack into local variable 0x37 lstore ...long... 0x38 fstore ...float... 0x39 dstore ...double... 0x3A astore ...reference... 0x3B-0x4E Packed stores fstore_2, dstore_0, etc 0x84 iinc Add given amount to int local variable
  • 60.
    Local Variables Var Value Depth Value ldc "hello" 0 bipush 4 0 istore 3 1 dconst_0 1 dstore 1 2 astore 0 2 aload 0 3 iinc 3, 5 3 4 4
  • 61.
    Local Variables Var Value Depth Value ldc "hello" 0 bipush 4 0 “hello” istore 3 1 dconst_0 1 dstore 1 2 astore 0 2 aload 0 3 iinc 3, 5 3 4 4
  • 62.
    Local Variables Var Value Depth Value ldc "hello" 0 bipush 4 0 4 istore 3 1 dconst_0 1 “hello” dstore 1 2 astore 0 2 aload 0 3 iinc 3, 5 3 4 4
  • 63.
    Local Variables Var Value Depth Value ldc "hello" 0 bipush 4 0 “hello” istore 3 1 dconst_0 1 dstore 1 2 astore 0 2 aload 0 3 4 iinc 3, 5 3 4 4
  • 64.
    Local Variables Var Value Depth Value ldc "hello" 0 bipush 4 0 istore 3 0.0 1 dconst_0 1 dstore 1 2 astore 0 2 “hello” aload 0 3 4 iinc 3, 5 3 4 4
  • 65.
    Local Variables Var Value Depth Value ldc "hello" 0 bipush 4 0 “hello” istore 3 1 dconst_0 1 0.0 dstore 1 2 astore 0 2 aload 0 3 4 iinc 3, 5 3 4 4
  • 66.
    Local Variables Var Value Depth Value ldc "hello" 0 “hello” bipush 4 0 istore 3 1 dconst_0 1 0.0 dstore 1 2 astore 0 2 aload 0 3 4 iinc 3, 5 3 4 4
  • 67.
    Local Variables Var Value Depth Value ldc "hello" 0 “hello” bipush 4 0 “hello” istore 3 1 dconst_0 1 0.0 dstore 1 2 astore 0 2 aload 0 3 4 iinc 3, 5 3 4 4
  • 68.
    Local Variables Var Value Depth Value ldc "hello" 0 “hello” bipush 4 0 “hello” istore 3 1 dconst_0 1 0.0 dstore 1 2 astore 0 2 aload 0 3 9 iinc 3, 5 3 4 4
  • 69.
    Arrays 0x2E-0x35 [i,l,f,d,a,b,c,d]aload Load [int, long, ...] from array (on stack) to stack 0x4F-0x56 [i,l,f,d,a,b,c,d]astore Store [int, long, ...] from stack to array (on stack) 0xBC newarray Construct new primitive array 0xBD anewarray Construct new reference array 0xBE arraylength Get array length 0xC5 multianewarray Create multi-dimensional array
  • 70.
    Arrays Depth Value iconst_2 newarray int 0 dup iconst_0 1 iconst_m1 2 iastore iconst_0 3 iaload 4 5
  • 71.
    Arrays Depth Value iconst_2 newarray int 0 2 dup iconst_0 1 iconst_m1 2 iastore iconst_0 3 iaload 4 5
  • 72.
    Arrays Depth Value iconst_2 newarray int 0 int[2] {0,0} dup iconst_0 1 iconst_m1 2 iastore iconst_0 3 iaload 4 5
  • 73.
    Arrays Depth Value iconst_2 newarray int 0 int[2] {0,0} dup iconst_0 1 int[2] {0,0} iconst_m1 2 iastore iconst_0 3 iaload 4 5
  • 74.
    Arrays Depth Value iconst_2 newarray int 0 0 dup iconst_0 1 int[2] {0,0} iconst_m1 2 int[2] {0,0} iastore iconst_0 3 iaload 4 5
  • 75.
    Arrays Depth Value iconst_2 newarray int 0 -1 dup iconst_0 1 0 iconst_m1 2 int[2] {0,0} iastore iconst_0 3 int[2] {0,0} iaload 4 5
  • 76.
    Arrays Depth Value iconst_2 newarray int 0 int[2] {-1, 0} dup iconst_0 1 iconst_m1 2 iastore iconst_0 3 iaload 4 5
  • 77.
    Arrays Depth Value iconst_2 newarray int 0 0 dup iconst_0 1 int[2] {-1, 0} iconst_m1 2 iastore iconst_0 3 iaload 4 5
  • 78.
    Arrays Depth Value iconst_2 newarray int 0 -1 dup iconst_0 1 iconst_m1 2 iastore iconst_0 3 iaload 4 5
  • 79.
    Math Operations add subtract multiply divide remainder negate + - * / % -() int iadd isub imul idiv irem ineg long ladd lsub lmul ldiv lrem lneg float fadd fsub fmul fdiv frem fneg double dadd dsub dmul ddiv drem dneg
  • 80.
    Boolean and Bitwise unsigned shift left shift right and or xor shift right int ishl ishr iushr iand ior ixor
  • 81.
    Conversions To: int long float double byte char short int - i2l i2f i2d i2b i2c i2s From: long l2i - l2f l2d - - - float f2i f2l - f2d - - - double d2i d2l d2f - - - -
  • 82.
    Comparisons 0x94 lcmp Compare two longs, push int -1, 0, 1 0x95 fcmpl Compare two floats, push in -1, 0, 1 (-1 for NaN) 0x96 fcmpg Compare two floats, push in -1, 0, 1 (1 for NaN) 0x97 dcmpl Compare two doubles, push in -1, 0, 1 (-1 for NaN) 0x98 dcmpg Compare two doubles, push in -1, 0, 1 (1 for NaN)
  • 83.
    Flow Control • Inspectstack and branch • Or just branch, via goto • Labels mark branch targets • Wide variety of tests
  • 84.
    Flow Control 0x99 ifeq If zero on stack, branch 0x9A ifne If nonzero on stack, branch 0x9B iflt If stack value is less than zero, branch 0x9C ifge If stack value is greater than or equal to zero, branch 0x9D ifgt If stack value is greater than zero, branch 0x9E ifle If stack value is less than or equal to zero, branch 0x9F if_icmpeq If two integers on stack are eq, branch 0xA0 if_icmpne If two integers on stack are ne, branch 0xA1 if_icmplt If two integers on stack are lt, branch 0xA2 if_icmpge If two integers on stack are ge, branch 0xA3 if_icmpgt If tw If two integers on stack are gt, branch 0xA4 if_icmple If two integers on stack are le, branch 0xA5 if_acmpeq If two references on stack are the same, branch 0xA6 if_acmpne If two references on stack are different, branch 0xA7 goto GOTO!
  • 85.
    Other Flow Control 0xA8 jsr Jump to subroutine (deprecated) 0xA9 ret Return from subroutine (deprecated) 0xAA tableswitch Branch using an indexed table of jump offsets 0xAB lookupswitch Branch using a lookup-based table of jump offsets 0xAC-0xB0 [i,l,f,d,a]return Return (int, long, float, double, reference) value 0xB1 return Void return (exit method, return nothing) 0xC6 ifnull If reference on stack is null 0xC7 ifnonnull If reference on stack is not null
  • 86.
    Flow Control aload 0 ldc0 aaload Depth Value ldc "branch" String[] invokevirtual string, "equals", 0 {“branch”} [boolean, object] ifne :branch 1 ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
  • 87.
    Flow Control aload 0 ldc0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 0 [boolean, object] ifne :branch 1 String[]{“branch”} ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
  • 88.
    Flow Control aload 0 ldc0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 “branch” [boolean, object] ifne :branch 1 ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
  • 89.
    Flow Control aload 0 ldc0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 “branch” [boolean, object] ifne :branch 1 “branch” ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
  • 90.
    Flow Control aload 0 ldc0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 1 [boolean, object] ifne :branch 1 ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
  • 91.
    Flow Control aload 0 ldc0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 [boolean, object] ifne :branch 1 ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
  • 92.
    Flow Control aload 0 ldc0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 [boolean, object] ifne :branch 1 ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
  • 93.
    Flow Control aload 0 ldc0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 “Equal!” [boolean, object] ifne :branch 1 ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
  • 94.
    Flow Control aload 0 ldc0 aaload Depth Value ldc "branch" invokevirtual string, "equals", 0 [boolean, object] ifne :branch 1 ldc "Not equal!" 2 aprintln goto :end 3 label :branch ldc "Equal!" 4 aprintln label :end 5 returnvoid
  • 95.
    Classes and Types •Signatures!!! • Probably the most painful part • ...but not a big deal if you understand
  • 96.
    Using Classes 0xB2 getstatic Fetch static field from class 0xB3 putstatic Set static field in class 0xB4 getfield Get instance field from object 0xB5 setfield Set instance field in object 0xB6 invokevirtual Invoke instance method on object 0xB7 invokespecial Invoke constructor or “super” on object 0xB8 invokestatic Invoke static method on class 0xB9 invokeinterface Invoke interface method on object 0xBA invokedynamic Invoke method dynamically on object (Java 7) 0xBB new Construct new instance of object 0xC0 checkcast Attempt to cast object to type 0xC1 instanceof Push nonzero if object is instanceof specified type
  • 97.
    Using Classes new ArrayList dup invokespecialArrayList, '<init>', Depth Value [void] an ArrayList checkcast Collection 0 (uninitialized) dup ldc "first element" 1 invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
  • 98.
    Using Classes new ArrayList dup invokespecialArrayList, '<init>', Depth Value [void] an ArrayList checkcast Collection 0 (uninitialized) dup an ArrayList ldc "first element" 1 (uninitialized) invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
  • 99.
    Using Classes new ArrayList dup invokespecialArrayList, '<init>', Depth Value [void] checkcast Collection 0 an ArrayList dup ldc "first element" 1 invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
  • 100.
    Using Classes new ArrayList dup invokespecialArrayList, '<init>', Depth Value [void] checkcast Collection 0 a Collection dup ldc "first element" 1 invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
  • 101.
    Using Classes new ArrayList dup invokespecialArrayList, '<init>', Depth Value [void] checkcast Collection 0 a Collection dup ldc "first element" 1 a Collection invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
  • 102.
    Using Classes new ArrayList dup invokespecialArrayList, '<init>', Depth Value [void] “first checkcast Collection 0 element” dup ldc "first element" 1 a Collection invokeinterface Collection, 'add', [boolean, object] 2 a Collection pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
  • 103.
    Using Classes new ArrayList dup invokespecialArrayList, '<init>', Depth Value [void] checkcast Collection 0 1 (true) dup ldc "first element" 1 a Collection invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
  • 104.
    Using Classes new ArrayList dup invokespecialArrayList, '<init>', Depth Value [void] checkcast Collection 0 a Collection dup ldc "first element" 1 invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
  • 105.
    Using Classes new ArrayList dup invokespecialArrayList, '<init>', Depth Value [void] checkcast Collection 0 an ArrayList dup ldc "first element" 1 invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
  • 106.
    Using Classes new ArrayList dup invokespecialArrayList, '<init>', Depth Value [void] checkcast Collection 0 0 dup ldc "first element" 1 an ArrayList invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
  • 107.
    Using Classes new ArrayList dup invokespecialArrayList, '<init>', Depth Value [void] “first checkcast Collection 0 element” dup ldc "first element" 1 invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
  • 108.
    Using Classes new ArrayList dup invokespecialArrayList, '<init>', Depth Value [void] checkcast Collection 0 dup ldc "first element" 1 invokeinterface Collection, 'add', [boolean, object] 2 pop checkcast ArrayList 3 ldc 0 invokevirtual ArrayList, 'get', 4 [object, int] aprintln 5 returnvoid
  • 109.
    Invokedynamic • New bytecodein Java 7 • Target method is wired up by user code • Method handles are the wiring
  • 110.
    Emitting Invokedynamic • Signatureis still required • But can be almost anything • Method name is still required • But can be almost anything • MethodHandle for bootstrapping • Bytecode-level function pointer, basically
  • 111.
    java.lang.invoke • MethodHandles • Function points • Adapters (arg juggling, catch, conditionals) • CallSites • Place to bind your MH chain • SwitchPoint • Zero-cost volatile boolean branch
  • 112.
    import java.lang.invoke.MethodHandle import java.lang.invoke.MethodType import java.lang.invoke.CallSite import java.lang.invoke.ConstantCallSite import java.lang.invoke.MethodHandles::Lookup JClass = java.lang.Class
  • 113.
    Target Method # Themethod we want to invoke, prints given string public_static_method :print, [], void, string do aload 0 aprintln returnvoid end
  • 114.
    Invokedynamic # Our mainmethod, which does one invokedynamic main do # handle for our bootstrap, which binds invokedynamic to a CallSite bootstrap = mh_invokestatic this, 'bootstrap', CallSite, Lookup, string, MethodType ldc 'Hello, invokedynamic!' invokedynamic 'print', [void, string], bootstrap returnvoid end
  • 115.
    Invokedynamic # Our mainmethod, which does one invokedynamic main do # handle for our bootstrap, which binds invokedynamic to a CallSite bootstrap = mh_invokestatic this, 'bootstrap', CallSite, Lookup, string, MethodType ldc 'Hello, invokedynamic!' invokedynamic 'print', [void, string], bootstrap returnvoid end
  • 116.
    Invokedynamic # Our mainmethod, which does one invokedynamic main do # handle for our bootstrap, which binds invokedynamic to a CallSite bootstrap = mh_invokestatic this, 'bootstrap', CallSite, Lookup, string, MethodType ldc 'Hello, invokedynamic!' invokedynamic 'print', [void, string], bootstrap returnvoid end
  • 117.
    Invokedynamic # Our mainmethod, which does one invokedynamic main do # handle for our bootstrap, which binds invokedynamic to a CallSite bootstrap = mh_invokestatic this, 'bootstrap', CallSite, Lookup, string, MethodType ldc 'Hello, invokedynamic!' invokedynamic 'print', [void, string], bootstrap returnvoid end
  • 118.
    Bootstrap # The bootstrapmethod, which binds our dynamic call public_static_method :bootstrap, [], CallSite, Lookup, string, MethodType do # Constant since we bind just once directly new ConstantCallSite dup # Locate the method indicated by name + type on current class aload 0 # Lookup ldc this # this class aload 1 # String aload 2 # MethodType invokevirtual Lookup, 'findStatic', [MethodHandle, JClass, string, MethodType] # finish constructing call site and return invokespecial ConstantCallSite, '<init>', [void, MethodHandle] areturn end
  • 119.
    Bootstrap # The bootstrapmethod, which binds our dynamic call public_static_method :bootstrap, [], CallSite, Lookup, string, MethodType do # Constant since we bind just once directly new ConstantCallSite dup # Locate the method indicated by name + type on current class aload 0 # Lookup ldc this # this class aload 1 # String aload 2 # MethodType invokevirtual Lookup, 'findStatic', [MethodHandle, JClass, string, MethodType] # finish constructing call site and return invokespecial ConstantCallSite, '<init>', [void, MethodHandle] areturn end
  • 120.
    Bootstrap # The bootstrapmethod, which binds our dynamic call public_static_method :bootstrap, [], CallSite, Lookup, string, MethodType do # Constant since we bind just once directly new ConstantCallSite dup # Locate the method indicated by name + type on current class aload 0 # Lookup ldc this # this class aload 1 # String aload 2 # MethodType invokevirtual Lookup, 'findStatic', [MethodHandle, JClass, string, MethodType] # finish constructing call site and return invokespecial ConstantCallSite, '<init>', [void, MethodHandle] areturn end
  • 121.
    Bootstrap # The bootstrapmethod, which binds our dynamic call public_static_method :bootstrap, [], CallSite, Lookup, string, MethodType do # Constant since we bind just once directly new ConstantCallSite dup # Locate the method indicated by name + type on current class aload 0 # Lookup ldc this # this class aload 1 # String aload 2 # MethodType invokevirtual Lookup, 'findStatic', [MethodHandle, JClass, string, MethodType] # finish constructing call site and return invokespecial ConstantCallSite, '<init>', [void, MethodHandle] areturn end
  • 122.
    Bootstrap # The bootstrapmethod, which binds our dynamic call public_static_method :bootstrap, [], CallSite, Lookup, string, MethodType do # Constant since we bind just once directly new ConstantCallSite dup # Locate the method indicated by name + type on current class aload 0 # Lookup ldc this # this class aload 1 # String aload 2 # MethodType invokevirtual Lookup, 'findStatic', [MethodHandle, JClass, string, MethodType] # finish constructing call site and return invokespecial ConstantCallSite, '<init>', [void, MethodHandle] areturn end
  • 123.
    Exceptions and Synchronization Table structure for a method indicating start/end of - trycatch try/catch and logic to run on exception 0xC2 monitorenter Enter synchronized block against object on stack 0xC3 monitorexit Exit synchronized block (against same object)
  • 124.
    More Examples • Asimple loop • Fibonacci
  • 125.
    A Simple Loop main do aload 0 push_int 0 aaload label :top dup aprintln goto :top returnvoid end
  • 126.
    Fibonacci public_static_method "fib", [],int, int do iload 0 ldc 2 if_icmpge :recurse iload 0 ireturn label :recurse iload 0 ldc 1 isub invokestatic this, "fib", [int, int] iload 0 ldc 2 isub invokestatic this, "fib", [int, int] iadd ireturn end
  • 127.
    main do load_times istore 1 Fibonacci ldc "Raw bytecode fib(45) performance:" aprintln label :top iload 1 ifeq :done iinc 1, -1 start_timing 2 ldc 45 invokestatic this, "fib", [int, int] pop end_timing 2 ldc "Time: " aprintln lprintln 2 goto :top label :done returnvoid end
  • 128.
    main do load_times istore 1 Fibonacci ldc "Raw bytecode fib(45) performance:" aprintln label :top iload 1 ifeq :done iinc 1, -1 start_timing 2 Macros ldc 45 invokestatic this, "fib", [int, int] pop end_timing 2 ldc "Time: " aprintln lprintln 2 goto :top label :done returnvoid end
  • 129.
    Fibonacci macro :load_times do aload 0 ldc 0 aaload # number of times invokestatic JInteger, 'parseInt', [int, string] end
  • 130.
    Fibonacci macro :start_timing do|i| load_time lstore i end
  • 131.
    Fibonacci macro :load_time do invokestatic System, "currentTimeMillis", long end
  • 132.
    Fibonacci macro :end_timing do|i| load_time lload i lsub lstore i end
  • 133.
    Fibonacci macro :lprintln do|i| getstatic System, "out", PrintStream lload i invokevirtual PrintStream, "println", [void, long] end
  • 134.
    Real-world Cases • Reflection-freeinvocation • JRuby, Groovy, other languages • Bytecoded data objects • Hibernate, other data layers • java.lang.reflect.Proxy and others • Language compilers
  • 135.
    Tools • BiteScript •So much fun • Ruby, so that’s even better • JiteScript • ASM - defacto standard library
  • 136.
    Part 2 Topics • Tracking your bytecode • Dumping JVM JIT through the JVM assembly output • How the JVM optimizes • x86 assembler language running code for dummies! • Monitoring JVM JIT compilation • Inspecting JVM inlining
  • 137.
    Pluggity • Many thanksto Engine Yard • JRuby and Java PaaS • JRuby support and services • sales@engineyard.com
  • 138.
  • 139.
    Pluggity • Migrating toJRuby on Rails 5:30 Mon, Parc 55 Market Street • JVM JIT for Dummies Part 2 10:00 Wed, Parc 55 Market street • JRuby + Java + Cloud 3:00 Wed, Parc 55 Embarcadero • Real World JRuby 4:30 Wed, Parc 55 Market Street
  • 140.
    Pluggity • JRuby meetup/party Engine Yard HQ 500 Third Street, Suite 510 Tuesday, 6:30PM • Try JRuby on EY Cloud http://engineyard.com/tryjruby
  • 141.
    Thank you! • headius@headius.com,@headius • http://blog.headius.com • http://github.com/headius/bitescript • “java virtual machine specification” • “jvm opcodes”

Editor's Notes