Jingling Xue - Computer Science and Engineeringcs3131/Lectures/lec9.pdf6e 01 00 16 28 5b 4c 6a 61 76...

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COMP3131/9102: Programming Languages and Compilers

Jingling Xue

School of Computer Science and Engineering

The University of New South Wales

Sydney, NSW 2052, Australia

http://www.cse.unsw.edu.au/~cs3131

http://www.cse.unsw.edu.au/~cs9102

Copyright @2018, Jingling Xue

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Lecture 9: JVM

1. Our code generation

2. JVM:

• Data types

• Operand stack

• Local variable array (indices)

• Instructions ( ⇐⇒ Jasmin instructions)

• Parameter-passing ( ⇐⇒ Jasmin method invocations)

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An Example

void whileInt() {int i = 0;while (i < 100) {

i++;}

}

is compiled to

Method void whileInt()0 iconst_01 istore_1 // i’s index is 12 goto 85 iinc 1 1 // i++8 iload_19 bipush 100

11 if_icmplt 514 return

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The VC Compiler

Source Code (gcd.vc)

Assignment 1: Scanner

Assignment 2 & 3: Parser

Assignment 4: Semantic Analyser

Assignment 5: Code Generator

Jasmin Assembly Code (gcd.j)

Jasmin Assembler

Java Virtual Machine

Results

VC

.lan

g.S

yst

em.c

lass

Tokens

AST

Decorated AST

Java Byte Code (gcd.class)

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Standard Environment: Built-in Functions/** System.java*/

package VC.lang;

import java.io.*;import java.util.StringTokenizer;

public class System {

private static BufferedReader reader =new BufferedReader(new InputStreamReader(java.lang.System.in));

public final static int getInt() {try {

java.lang.System.out.print("Enter an integer: ");String s = reader.readLine();StringTokenizer st = new StringTokenizer(s);int i = Integer.parseInt(st.nextToken());java.lang.System.out.println("You have entered " + i + ".");return i;

} catch (java.io.IOException e) {java.lang.System.out.println("Caught IOException: " + e.getMessage());java.lang.System.exit(1);return -1;

}}

public final static void putBool(boolean b) {java.lang.System.out.print(b);

}

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public final static void putBoolLn(boolean b) {java.lang.System.out.println(b);

}

public final static void putInt(int i) {java.lang.System.out.print(i);

}

public final static void putIntLn(int i) {java.lang.System.out.println(i);

}

public final static float getFloat() {try {

java.lang.System.out.print("Enter a float: ");String s = reader.readLine();StringTokenizer st = new StringTokenizer(s);float f = Float.parseFloat(st.nextToken());java.lang.System.out.println("You have entered " + f + ".");return f;

} catch (java.io.IOException e) {java.lang.System.out.println("Caught IOException: " + e.getMessage());java.lang.System.exit(1);return -1.0F;

}}

public final static void putFloat(float f) {java.lang.System.out.print(f);

}

public final static void putFloatLn(float f) {java.lang.System.out.println(f);

}

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public final static void putString(String s) {java.lang.System.out.print(s);

}

public final static void putStringLn(String s) {java.lang.System.out.println(s);

}

public final static void putLn() {java.lang.System.out.println();

}

}

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References

• Jasmin home page: http://jasmin.sourceforge.net/

• Tim Lindholm and Frank Yellin, The Java Virtual

Machine Specification, 2nd Edition, Addison-Wesley,

1999. (The entire book is available on-line; see the subject Resource Page.)

• Vill Venners, Inside the Java 2 Virtual Machine, 2nd

Edition, McGraw-Hill, 1999.

(Some chapters available on-line; see the subject Resource Page.)

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Jasmin Assembly Language

• Sun has not defined an assembler format

• Jasmin is a Java assembler, which has been installed in the

class account and can be invoked as follows:

% 3131

% jasmin gcd.j --> the output is gcd.class

% java gcd

• Install from http://jasmin.sourceforge.net/ on

your own computer

• Read also the Jasmin User Guide there:

http://jasmin.sourceforge.net/guide.html

• Jasmin page contains pointers to other assembly languages

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Jasmin Assembly Language v.s Java Byte Code

• 1-to-1 correspondence

– Operation codes (opcodes) represented by mnemonics

– Name indices written in symbolic form

– Local variables are encoded by indices (integers)

• Examples:

Jasmin Instructions Java Byte Code---------------------------------------------iload 0x60bipush 20 0x1614getstatic Test.i 0xb2????--------------------------------------------- where ????is an index into the constant pool entry for Test.i

• Constant pool will be discussed in Lecture 11 but its

understanding unnecessary for Assignment 5

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gcd.java

// find the greatest common divisor of two integers

public class gcd {

static int gcd(int a, int b) {

if (b == 0)

return a;

else

return gcd(b, a - (a/b) *b);

}

public static void main(String argv[]) {

int i = 2;

int j = 4;

System.out.println(gcd(i, j));

}

}

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gcd.j;; Produced by JasminVisitor (BCEL);; http://www.inf.fu-berlin.de/~dahm/BCEL/

.source gcd.java

.class public gcd

.super java/lang/Object

.method public <init>()V

.limit stack 1

.limit locals 1

.var 0 is this Lgcd; from Label0 to Label1

Label0:.line 3

aload_0invokespecial java/lang/Object/<init>()V

Label1:return

.end method

.method static gcd(II)I

.limit stack 4

.limit locals 2

.var 0 is a I from Label1 to Label2

.var 1 is b I from Label1 to Label2

Label1:.line 5

iload_1ifne Label0

.line 6iload_0

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ireturnLabel0:.line 8

iload_1iload_0iload_0iload_1idiviload_1imulisubinvokestatic gcd/gcd(II)I

Label2:ireturn

.end method

.method public static main([Ljava/lang/String;)V

.limit stack 3

.limit locals 3

.var 0 is argv [Ljava/lang/String; from Label0 to Label1

.var 1 is i I from Label2 to Label1

.var 2 is j I from Label4 to Label1

Label0:.line 12

iconst_2istore_1

Label2:.line 13

iconst_4istore_2

Label4:.line 14

getstatic java.lang.System.out Ljava/io/PrintStream;

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iload_1iload_2invokestatic gcd/gcd(II)Iinvokevirtual java/io/PrintStream/println(I)V

Label1:.line 15

return

.end method

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Java Class File: gcd.class (Output of od -An -tx1 gcd.class)ca fe ba be 00 03 00 2d 00 1e 0a 00 06 00 11 0a

00 05 00 12 09 00 13 00 14 0a 00 15 00 16 07 00

0b 07 00 17 01 00 06 3c 69 6e 69 74 3e 01 00 03

28 29 56 01 00 04 43 6f 64 65 01 00 0f 4c 69 6e

65 4e 75 6d 62 65 72 54 61 62 6c 65 01 00 03 67

63 64 01 00 05 28 49 49 29 49 01 00 04 6d 61 69

6e 01 00 16 28 5b 4c 6a 61 76 61 2f 6c 61 6e 67

2f 53 74 72 69 6e 67 3b 29 56 01 00 0a 53 6f 75

72 63 65 46 69 6c 65 01 00 08 67 63 64 2e 6a 61

76 61 0c 00 07 00 08 0c 00 0b 00 0c 07 00 18 0c

00 19 00 1a 07 00 1b 0c 00 1c 00 1d 01 00 10 6a

61 76 61 2f 6c 61 6e 67 2f 4f 62 6a 65 63 74 01

00 10 6a 61 76 61 2f 6c 61 6e 67 2f 53 79 73 74

65 6d 01 00 03 6f 75 74 01 00 15 4c 6a 61 76 61

2f 69 6f 2f 50 72 69 6e 74 53 74 72 65 61 6d 3b

01 00 13 6a 61 76 61 2f 69 6f 2f 50 72 69 6e 74

53 74 72 65 61 6d 01 00 07 70 72 69 6e 74 6c 6e

01 00 04 28 49 29 56 00 21 00 05 00 06 00 00 00

00 00 03 00 01 00 07 00 08 00 01 00 09 00 00 00

1d 00 01 00 01 00 00 00 05 2a b7 00 01 b1 00 00

00 01 00 0a 00 00 00 06 00 01 00 00 00 03 00 08

00 0b 00 0c 00 01 00 09 00 00 00 32 00 04 00 02

00 00 00 12 1b 9a 00 05 1a ac 1b 1a 1a 1b 6c 1b

68 64 b8 00 02 ac 00 00 00 01 00 0a 00 00 00 0e

00 03 00 00 00 05 00 04 00 06 00 06 00 08 00 09

00 0d 00 0e 00 01 00 09 00 00 00 34 00 03 00 03

00 00 00 10 05 3c 07 3d b2 00 03 1b 1c b8 00 02

b6 00 04 b1 00 00 00 01 00 0a 00 00 00 12 00 04

00 00 00 0c 00 02 00 0d 00 04 00 0e 00 0f 00 0f

00 01 00 0f 00 00 00 02 00 10

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BCEL (Byte Code Engineering Library)

• Home page: http://jakarta.apache.org/bcel/

• Formerly known as JavaClass

• BCEL comes with a Jasmin disassembler, which has been installed inthe class account and can be invoked as follows:

% 3131

% jasmind gcd.class --> this produces gcd.j

• jasmind is a shell command:#!/bin/csh

#

# jasmind - runs the Jasmin disassembler

#

# Usage:

# jasmind classname.class

#

setenv CLASSPATH ~cs3131/JavaTools/JavaClass

exec java JasminVisitor $*

• Install from the BCEL home page on your own computer.

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Multi-Level Machine Model

JVM

Jasmin

VC

Java C

• There is a virtual machine and a language at each level

• Each level builds on the functionality of the level below

and provides the functionality to the level above

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Lecture 9: JVM

1. Our code generation√

2. JVM:

• Data types

• Operand stack

• Local variable array (indices)



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JVM Data Types

TYPE RANGE FIELD DESC

boolean {0, 1} Z

byte 8 bit signed 2’s complement (−27 to 27 − 1) B

short 16 bit signed 2’s complement (−215 to 215−1) S

int 32 bit signed 2’s complement (−231 to 231−1) I

long 64 bit signed 2’s complement (−263 to 263−1) L

char 16 bit unsigned Unicode (0 to 216 − 1) C

float 32-bit IEEE 754 single-precision F

double 64-bit IEEE 754 double-precision D

reference 32 bit unsigned reference (0 to 232 − 1) Slide 483

returnAddress 32 bit unsigned reference (0 to 232 − 1) N/A

• All (except returnAddress) mapped 1-to-1 to Java’s primitive types

• returnAddress used with jsr/jsr w/ret for handling exceptions

• boolean, byte, char and short are all implemented as int, but arrays ofthese types may be stored in arrays of less than 32 bits

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JVM Data Types (Cont’d)

TYPE FIELD DESCRIPTOR

class reference Lclass-name;

interface reference Linterface-name;

array reference [[· · · [ component-type

void V

• class and interface names are qualified names with ”.” replaced by ”/”

• The no. of [ is equal to the no. of dimensions of the array

Type Field Descriptor-------------------------------------

Object Ljava/lang/Object;String Ljava/lang/String;String[] [Ljava/lang/String;int [] [Ifloat [][] [[F

-------------------------------------

• See $4.3.2, The JVM Spec for a formal definition

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Boolean, Byte, Short and Char Represented as Intpublic class IntTypes {

public static void main(String argv[]) {boolean z = true;byte b = 1;short s = 2;char c = ’a’;

}}.method public static main([Ljava/lang/String;)V...

.line 3iconst_1istore_1



.line 6bipush 97istore 4

Label0:.line 8

return.end method

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An Example for Printing Data Type Descriptorspublic class Desc {


Object o = new Object();

int [] i = new int[10];

float [][] f = new float[10][10];

String s1 = "Hello World!";

String [] s2 = { "Hello", "World!"};

System.out.println("Th class name of Object is: " + o.getClass());

System.out.println("Th class name of int[] is: " + i.getClass());

System.out.println("Th class name of float[][] is: " + f.getClass());

System.out.println("Th class name of String: " + s1.getClass());

System.out.println("Th class name of String[]: " + s2.getClass());

}

}

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Method Descriptors

• (ParameterType∗) ReturnType

• Examples:

Method Declaration Method Descriptor

------------ -------------------------------------

int gcd(int i, int j) (II)I

void main(String argv[]) ([Ljava/lang/String;)V

char foo(float f, String) (FLjava/lang/String;)C

------------ -------------------------------------

• See $4.3.3, The JVM Spec for a formal definition

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Operand Stack

• Accessed by pushing and popping values

– storing operands and receiving the operations’ results

– passing arguments and receiving method results

– This unified view is one of the main reasons why code generationfor stack-based machines is easier than registers-based machines

• A new op stack is created every time a method is called

• Integral expression:

1 + 2 * 3 + 4

• Jasmin code (without being optimised):

iconst_1iconst_2iconst_3imuliaddiconst_4iadd

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Local Variable Array

1. A new local variable array is created each time a method is called

2. Local variables addressed by indexing, starting from 0

3. Instance methods:

• slot 0 given to this

• Parameters (if any) given consecutive indices, starting from 1

• The indices allocated to the other variables in any order

4. Class methods:

• Parameters (if any) given consecutive indices, starting from 0

• The indices allocated to the other variables in any order

5. One slot can hold a value of boolean, byte, char, short, int, float,reference and returnAdrress

6. One pair of slots can hold a value of long and double

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Local Variable Indices: Class Methods

1. Class method:public static void foo() {

int i1 = 1; // index 0



int i = i1 + i2 * i3; // index 3

}

2. Jasmin code:iconst_1

istore_0

iconst_2

istore_1

iconst_3

istore_2

iload_0

iload_1

iload_2

imul

iadd

istore_3

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Local Variable Indices: Instance Methods

1. Instance method:public void foo() { // "this" given index 0




int i = i1 + i2 * i3; // index 4

}

2. Jasmin code:iconst_1

istore_1

iconst_2

istore_2

iconst_3

istore_3

iload_1

iload_2

iload_3

imul

iadd

istore_4

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Local Variable Indices: Double Word variables1. The Long type:

public static void foo() {int i1 = 1; // index 0long i2 = 2; // indices 1 and 2int i3 = 3; // index 3long i = i1 + i2 * i3; // indices 4 and 5

}

2. Jasmin code:iconst_1istore_0ldc2_w 2lstore_1iconst_3istore_3iload_0i2llload_1iload_3i2llmulladdlstore 4

3. Accessing index 2 or 5 is disallowed

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Lecture 9: JVM

1. Our code generation√

2. JVM:

• Data types√

• Operand stack√

• Local variable array (indices)√



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Jasmin (or JVM) Instructions

1. Arithmetic Instructions

2. Load and store instructions

3. Control transfer instructions

4. Type conversion instructions

5. Operand stack management instructions

6. Object creation and manipulation

7. Method invocation instructions

8. Throwing instructions (not used)

9. Implementing finally (not used)

10. Synchronisation (not used)

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Arithmetic Instructions ($3.11.3, JVM Spec)

• add: iadd, fadd,

• subtract: isub, fsub

• multiply: imul, fmul

• divide: idiv, fdiv

• negative: ineg, fneg

• comparison: fcmpg, fcmpl

• ...

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Load and Store Instructions

• Loading a local variable into the operand stack:

iload iload_0, ..., iload_3

fload fload_0, ..., fload_3

aload aload_0, ..., aload_3 // for array and object refs

iaload // load from an int array

faload // load from a float array

• Storing a value from the operand stack into a local variable:

istore istore_0, ..., istore_3

fstore fstore_0, ..., fstore_3

astore astore_0, ..., astore_3 // for array and object refs

iastore // store into an int array

fastore // store into a float array

• Load a constant into the operand stack:

bipush, sipush, ldc, iconst_m1, iconst_0, ..., iconst_5,

fconst_0, ..., fconst_2

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Example: Load and Stored (Slide 487 Repeated)

1. Integral expression:

1 + 2 * 3 + 4

2. Jasmin code:

iconst_1

iconst_2

iconst_3

imul

iadd

iconst_4

iadd

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Example: Load and Store (Cont’d)

1. Integral expression:

1 + 100 * 200 + 40000

2. Jasmin code:

iconst_1

bipush 100

sipush 200

imul

iadd

ldc 40000

iadd

3. bipush: −27 – 27 − 1

4. sipush: −215 – 215 − 1

5. ldc val, where val is an int, float or string

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Example: Load and Store (Cont’d)

1. Floating-point expression:

1.0F + 2.0F * 3.0F + 4.0F

2. Jasmin code:

fconst_1

fconst_2

ldc 3.0

fmul

fadd

ldc 4.0

fadd

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Example: Load and Store for Arrays

1. Array operations:

a[0] = 100;

i = a[0]

2. Jasmin code – (assuming a and i have the indices 1 and 2, resp.)

// a[0] = 100;

aload_1

iconst_0

bipush 100

iastore

// i = a[0];

aload_1

iconst_0

iaload

istore_2

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Control Transfer Instructions

1. Unconditional: goto

2. Instructions on int:

ifeq ifne ifle iflt ifne ifge

if_icmpeq if_icmpne if_icmple

if_icmplt if_icmpge if_icmpgt

3. For floating-point operands, use first

fcmpg or fcmpl

and then

ifeq ifne ifle iflt ifne ifge

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if icmge label

op stack (before)

+--------------------

| ... value1 value2

+--------------------

op stack (after)

+-----

| ...

+-----

1. Pop off the two ints off and compare them

2. If value1 >= value2, jump to label. Otherwise, execution

continues at the next instruction

Other if icmpxx instructions are similar.

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Example 1: Control Transfer Instructions

1. Ctrl1.javapublic class Ctrl1 {


int i = 1, int j = 2, int k;

if (i < j)

k = 0;

else

k = 1;

}

}

2. Ctrl1.j (irrelevant lines removed).method public static main([Ljava/lang/String;)V

iconst_1

istore_1

iconst_2

istore_2

iload_1

iload_2

if_icmpge Label0

iconst_0

istore_3

goto Label1

Label0:

iconst_1

istore_3

Label1:

return

.end method

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Example 2: Control Transfer Instructions

1. Ctrl2.javapublic class Ctrl1 {


float i = 1, float j = 2, float k;

if (i < j)

k = 0.0F;

else

k = 1.0F;

}

}

2. Ctrl2.j (irrelevant lines removed).method public static main([Ljava/lang/String;)V

fconst_1

fstore_1

fconst_2

fstore_2

fload_1

fload_2

fcmpg

ifge Label0

fconst_0

fstore_3

goto Label1

Label0:

fconst_1

fstore_3

Label1:

return

.end method

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fcmpg and fcmpl

op stack (before):

+--------------------

| ... value1 value2

+--------------------

op stack (after):

+-------- +--------- +----------

| ... 0 | ... -1 | ... 1

+-------- +--------- +---------

value1 = value2 value1 < value2 value1 > value2

• If either is NaN, fcmpg pushes 1 and fcmpl pushes -1.

• See JVM SPEC $7.5 for an explanation why the two

instructions are provided (https://docs.oracle.com/

javase/specs/jvms/se7/html/jvms-3.html#

jvms-3.5)

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https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-3.html#jvms-3.5



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Type Conversion Instructions

1. Source:

int i = 1; // index 1

float f = i; // index 2

2. Jasmin code:

iconst_1

istore_1

iload_1

i2f

fstore 2

3. Only i2f is used in the VC compiler

4. i2c, i2b, f2i, etc. not used

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Operand Stack Management Instructions

• Instructions:

– dup: duplicate the stack top operand

– pop: remove the stack top operand

– swap: swap the top two operands

– others: pop2, dup2, etc.

• Only the first two will be used in the VC compiler:

– dup: for translating a = b = ...

– pop: for translating expression statements such as 1;

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Example: dup in Translating Compound Assignments

1. Assignment expressions:

int i; \\ index 1

int j; \\ index 2

int k; \\ index 3

i = j = k = 1;

2. Jasmin code:

iconst_1

dup

istore_3

dup

istore_2

istore_1

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Example: pop in Translating VC Expression Statements

1. Assignment expressions:

int i; // index 1

1 + (i = 2);

2. Jasmin code:

iconst_1

iconst_2

dup

istore_1

iadd

pop

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Object Creation and Manipulation

• Create a new class instance: new

• Access fields of classes: getstatic, putstatic, getfield, putfield

• Create a new array: newarray, anewarray, multianewarray(only the first is used)

• Load an array component onto the operand stack: iaload, faload,baload, caload, ...

• Store a value from the operand stack as an array component: iastore,fastore, bastore, castore, ...

• ...

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Example: Object Creation and Manipulation• Static and field variables:

public class StaticField {

static int i = 1;

int j = 1;


StaticField o = new StaticField();

System.out.println(i);

System.out.println(o.j);

}

}

• Jasmin code (irrelevant lines removed)

.field static i I

.field j I


.line 5

new StaticField

dup

invokespecial StaticField/<init>()V

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astore_1

.line 6


getstatic StaticField.i I

invokevirtual java/io/PrintStream/println(I)V

.line 7


aload_1

getfield StaticField.j I

invokevirtual java/io/PrintStream/println(I)V

Label0:

.line 8

return

.end method

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The Syntax for Field Instructions

• Syntax:

getstatic field-spec type-descriptor

where field-spec consists of a classname followed by a

field name.

• Examples:

getstatic java/lang/System/out Ljava/io/PrintStream;

getstatic StaticField/i I

getfield and putfield not used in the VC compiler

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Arrays

• Java Statements // assuming a is at slot 1 (by compiler)

int a[] = new int[10];

a[1] = a[2] + 1;

• Bytecode:

bipush 10

newarray int

astore_1

aload_1

iconst_1

aload_1

iconst_2

iaload

iconst_1

iadd

iastore

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Method Invocation Instructions

• Method calls:

invokestatic

invokevirtual

invokespecial // also known as invokenonvirtual

-- the instance initialisation method <init>

-- a private method of "this"

-- a method in a super class of "this"

invokeinterface

(why invokeinterface?

stackoverflow.com/questions/1504633/what-is-the-point-of-invokeinterface)

• Method returns:

return

ireturn

freturn

...

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The Syntax for Method Invocation Instructions

• The syntax for invokestatic/virtual/special

invokexx method-spec

where method-spec consists of a classname, a method

name and a descriptor.

• invokeinterface not used in the VC compiler

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Method Invocation Instructions (Cont’d)

• invokestatic

op stack after

+----------------------- +--------------------

| ... arg1 arg2 ... argn | ... result (if any)

+----------------------- +-------------------

before

• invokevirtual and invokespecial

op stack after

+-------------------------- +--------------------

| ... objref arg1 ... argn | ... result (if any)

+-------------------------- +-------------------

before

• invokevirtual: on the dynamic type of objref• invokespecial: based on the static class of objref

• Note that programmer-defined operators (methods) are treatedexactly the same as the built-in operators (e.g., + and −)

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Example: Static Method Invocation

1. Met1.java:public class Met1 {

static int add(int i1, int i2) {return i1 + i2;

}public static void main(String argv[]) {

add(1, 2);}

}

2. Met1.j (irrelevant lines removed):.method static add(II)I .limit stack 2 .limit locals 2

iload_0iload_1iaddireturn

.end method

.method public static main([Ljava/lang/String;)V .limit stack 2 .limit locals 1iconst_1iconst_2invokestatic Met1/add(II)Ipopreturn

.end method

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Example 9: Instance Method Invocation

1. Met2.java:public class Met2 {

int add(int i1, int i2) {

return i1 + i2;

}


Met2 m = new Met2();

m.add(1, 2);

}

}

2. Met2.j (irrelevant lines removed):.method add(II)I .limit stack 2 .limit locals 3

iload_1

iload_2

iadd

ireturn

.end method

.method public static main([Ljava/lang/String;)V .limit stack 3 .limit locals 2

new Met2

dup

invokespecial Met2/<init>()V

astore_1

aload_1

iconst_1

iconst_2

invokevirtual Met2/add(II)I

return

.end method

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Polymorphism: invokevirtual and invokespecial

public class Fruit {


Apple apple = new Apple();

Fruit fruit = apple;

fruit.whoAmI();

}

void whoAmI() {

System.out.println("This is a fruit.");

}

}

class Apple extends Fruit {

void whoAmI() {

System.out.println("This is an apple.");

super.whoAmI();

}

}

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Fruit.j;; Produced by JasminVisitor (BCEL package)

;; http://www.inf.fu-berlin.de/~dahm/JavaClass/

;; Mon Oct 09 16:09:47 GMT+10:00 2000

.source Fruit.java

.class public Fruit

.super java/lang/Object

.method public <init>()V

.limit stack 1

.limit locals 1

.var 0 is this LFruit; from Label0 to Label1

Label0:

.line 1

aload_0

invokespecial java/lang/Object/<init>()V

Label1:

return

.end method


.limit stack 2

.limit locals 3

.var 0 is arg0 [Ljava/lang/String; from Label0 to Label1

Label0:

.line 4

new Apple

dup

invokespecial Apple/<init>()V

astore_1

.line 6

aload_1

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astore_2

.line 7

aload_2

invokevirtual Fruit/whoAmI()V <=== a virtual call

Label1:

.line 3

return

.end method

.method whoAmI()V

.limit stack 2

.limit locals 1

.var 0 is this LFruit; from Label0 to Label1

Label0:

.line 11


ldc "This is a fruit."

invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V

Label1:

.line 10

return

.end method

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Apple.j.source Fruit.java

.class Apple

.super Fruit

.method <init>()V

.limit stack 1

.limit locals 1

.var 0 is this LApple; from Label0 to Label1

Label0:

.line 16

aload_0

invokespecial Fruit/<init>()V

Label1:

return

.end method

.method whoAmI()V

.limit stack 2

.limit locals 1

.var 0 is this LApple; from Label0 to Label1

Label0:

.line 18


ldc "This is an apple."

invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V

.line 19

aload_0

invokespecial Fruit/whoAmI()V <=== a static call

Label1:

.line 17

return

.end method

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Jasmin Directives

• Jasmin home page

.source .class .super .limit .method

.field static .end .var .line

• Example: gcd.j (Slide 475)

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Jasmin File Structure (syntax.bnf)Jasmin Syntax Jonathan Meyer, April 1996

This file contains a simplified BNF version of the Jasmin syntax.

jasmin_file ::=

’.class’ [ <access> ] <name> <break>

’.super’ <name> <break>

[ <fields> ]

[ <methods> ]

<fields> ::= <field> [ <field> ... ]

<field> ::=

’.field’ <access> <name> <signature> [ = <default> ] <break>

<default> ::= <int> | <quoted_string> | <float>

<methods> ::= <method> [ <method> ... ]

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<method> ::=

’.method’ <access> <name> <break>

[ <statements> ]

’.end’ ’method’ <break>

<statements> ::= <statement> [ <statement> ... ]

<statement> ::=

<directive> <break>

|

<instruction> <break>

|

<label> ’:’ <break>

<directive> ::=

’.limit’ ’stack’ <val>

|

’.limit’ ’locals’ <val>

|

’.throws’ <classname>

|

’.catch’ <classname> ’from’ <label1> ’to’ <label2> ’using’ <label3>

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Understanding Jasmin Assembly Language

1. Read syntax.bnf to understand Jasmin’s syntax

2. Read Jasmin User Guide to Jasmin’s syntax

3. Read Jasmin instruction reference manual to understand itsinstructions (1-to-1 mapped to JVM instructions)

4. To under a particular feature, do the following:

(a) Design a Java program Test.java

(b) Run javac -g Test.java (-g turns on all debugging info)

(c) Run jasmind Test.class (jasmind runs java JasminVisitor Test.class)or javap -c Test

(d) Read Jasmin code in Test.j

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Reading (in Order of Increasing Importance)

• on-line JVM instructions

http://cs.au.dk/~mis/dOvs/jvmspec/ref-Java.html

• Play around the tools mentioned in this lecture:

– All available in the class account

– Install them on your PC if you have one

• The JVM Spec Book

– Chapter 3 (instructions)

– Chapter 7 (more examples on compiling Java)

• “Inside the JVM” book (Chapter 5)

Next Class: Java Bytecode Generation (Assignment 5)

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http://cs.au.dk/~mis/dOvs/jvmspec/ref-Java.html

Jingling Xue - Computer Science and Engineeringcs3131/Lectures/lec9.pdf6e 01 00 16 28 5b 4c 6a 61 76...

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