COMP3131/9102: Programming Languages and Compilers

Transcription

1 COMP3131/9102: Programming Languages and Compilers Jingling Xue School of Computer Science and Engineering The University of New South Wales Sydney, NSW 2052, Australia Jingling Xue COMP3131/9102 Page 464 May 6, 2018

2 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) COMP3131/9102 Page 465 May 6, 2018

3 void whileint() { int i = 0; while (i < 100) { i++; An Example is compiled to Method void whileint() 0 iconst_0 1 istore_1 // i s index is 1 2 goto 8 5 iinc 1 1 // i++ 8 iload_1 9 bipush if_icmplt 5 14 return COMP3131/9102 Page 466 May 6, 2018

4 VC.lang.System.class The VC Compiler Source Code (gcd.vc) Assignment 1: Scanner Tokens Assignment 2 & 3: Parser AST Assignment 4: Semantic Analyser Decorated AST Assignment 5: Code Generator Jasmin Assembly Code (gcd.j) Jasmin Assembler Java Byte Code (gcd.class) Java Virtual Machine Results COMP3131/9102 Page 467 May 6, 2018

5 /* * System.java */ Standard Environment: Built-in Functions 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); COMP3131/9102 Page 468 May 6, 2018

6 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); COMP3131/9102 Page 469 May 6, 2018

7 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(); COMP3131/9102 Page 470 May 6, 2018

8 References Jasmin home page: Tim Lindholm and Frank Yellin, The Java Virtual Machine Specification, 2nd Edition, Addison-Wesley, (The entire book is available on-line; see the subject Resource Page.) Vill Venners, Inside the Java 2 Virtual Machine, 2nd Edition, McGraw-Hill, (Some chapters available on-line; see the subject Resource Page.) COMP3131/9102 Page 471 May 6, 2018

9 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 fromhttp://jasmin.sourceforge.net/ on your own computer Read also the Jasmin User Guide there: Jasmin page contains pointers to other assembly languages COMP3131/9102 Page 472 May 6, 2018

10 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 0x60 bipush 20 0x1614 getstatic 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 COMP3131/9102 Page 473 May 6, 2018

11 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)); COMP3131/9102 Page 474 May 6, 2018

12 ;; Produced by JasminVisitor (BCEL) ;; gcd.java.class public gcd.super java/lang/object gcd.j.method public <init>()v.limit stack 1.limit locals 1.var 0 is this Lgcd; from Label0 to Label1 Label0:.line 3 Label1:.end method aload_0 invokespecial java/lang/object/<init>()v return.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.line 6 iload_1 ifne Label0 iload_0 COMP3131/9102 Page 475 May 6, 2018

13 Label0:.line 8 Label2:.end method ireturn iload_1 iload_0 iload_0 iload_1 idiv iload_1 imul isub invokestatic gcd/gcd(ii)i ireturn.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_2 istore_1 Label2:.line 13 iconst_4 istore_2 Label4:.line 14 getstatic java.lang.system.out Ljava/io/PrintStream; COMP3131/9102 Page 476 May 6, 2018

14 iload_1 iload_2 invokestatic gcd/gcd(ii)i invokevirtual java/io/printstream/println(i)v Label1:.line 15 return.end method COMP3131/9102 Page 477 May 6, 2018

15 Java Class File: gcd.class (Output of od -An -tx1 gcd.class) ca fe ba be d 00 1e 0a a a b c 69 6e e f f 4c 69 6e 65 4e 75 6d c d e b 4c 6a f 6c 61 6e 67 2f e 67 3b a 53 6f c e 6a c c 00 0b 00 0c c a b 0c 00 1c 00 1d a f 6c 61 6e 67 2f 4f 62 6a a f 6c 61 6e 67 2f d f c 6a f 69 6f 2f e d 3b a f 69 6f 2f e d e 74 6c 6e d a b b a b 00 0c b 9a a ac 1b 1a 1a 1b 6c 1b b ac a e d 00 0e c 07 3d b b 1c b b b a c d e 00 0f 00 0f f COMP3131/9102 Page 478 May 6, 2018

16 BCEL (Byte Code Engineering Library) Home page: Formerly known as JavaClass BCEL comes with a Jasmin disassembler, which has been installed in the 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. COMP3131/9102 Page 479 May 6, 2018

17 Multi-Level Machine Model VC Jasmin JVM 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 COMP3131/9102 Page 480 May 6, 2018

18 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) COMP3131/9102 Page 481 May 6, 2018

19 JVM Data Types TYPE RANGE FIELD DESC boolean {0, 1 Z byte 8 bit signed 2 s complement ( 2 7 to 2 7 1) B short 16 bit signed 2 s complement ( 2 15 to2 15 1) S int 32 bit signed 2 s complement ( 2 31 to2 31 1) I long 64 bit signed 2 s complement ( 2 63 to2 63 1) L char 16 bit unsigned Unicode (0 to ) C float 32-bit IEEE 754 single-precision F double 64-bit IEEE 754 double-precision D reference 32 bit unsigned reference (0 to2 32 1) Slide 483 returnaddress 32 bit unsigned reference (0 to2 32 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 of these types may be stored in arrays of less than 32 bits COMP3131/9102 Page 482 May 6, 2018

20 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 [] [I float [][] [[F See $4.3.2, The JVM Spec for a formal definition COMP3131/9102 Page 483 May 6, 2018

21 Boolean, Byte, Short and Char Represented as Int public 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 3.line 4.line 5.line 6 Label0:.line 8 iconst_1 istore_1 iconst_1 istore_2 iconst_2 istore_3 bipush 97 istore 4 return.end method COMP3131/9102 Page 484 May 6, 2018

22 An Example for Printing Data Type Descriptors public class Desc { public static void main(string argv[]) { 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()); COMP3131/9102 Page 485 May 6, 2018

23 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 COMP3131/9102 Page 486 May 6, 2018

24 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 generation for stack-based machines is easier than registers-based machines A new op stack is created every time a method is called Integral expression: * Jasmin code (without being optimised): iconst_1 iconst_2 iconst_3 imul iadd iconst_4 iadd COMP3131/9102 Page 487 May 6, 2018

25 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 COMP3131/9102 Page 488 May 6, 2018

26 Local Variable Indices: Class Methods 1. Class method: public static void foo() { int i1 = 1; // index 0 int i2 = 2; // index 1 int i3 = 3; // index 2 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 COMP3131/9102 Page 489 May 6, 2018

27 Local Variable Indices: Instance Methods 1. Instance method: public void foo() { // "this" given index 0 int i1 = 1; // index 1 int i2 = 2; // index 2 int i3 = 3; // index 3 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 COMP3131/9102 Page 490 May 6, 2018

28 Local Variable Indices: Double Word variables 1. The Long type: public static void foo() { int i1 = 1; // index 0 long i2 = 2; // indices 1 and 2 int i3 = 3; // index 3 long i = i1 + i2 * i3; // indices 4 and 5 2. Jasmin code: iconst_1 istore_0 ldc2_w 2 lstore_1 iconst_3 istore_3 iload_0 i2l lload_1 iload_3 i2l lmul ladd lstore 4 3. Accessing index 2 or 5 is disallowed COMP3131/9102 Page 491 May 6, 2018

29 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) COMP3131/9102 Page 492 May 6, 2018

30 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) COMP3131/9102 Page 493 May 6, 2018

31 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... COMP3131/9102 Page 494 May 6, 2018

32 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 COMP3131/9102 Page 495 May 6, 2018

33 Example: Load and Stored (Slide 487 Repeated) 1. Integral expression: * Jasmin code: iconst_1 iconst_2 iconst_3 imul iadd iconst_4 iadd COMP3131/9102 Page 496 May 6, 2018

34 Example: Load and Store (Cont d) 1. Integral expression: * Jasmin code: iconst_1 bipush 100 sipush 200 imul iadd ldc iadd 3. bipush: sipush: ldc val, where val is an int, float or string COMP3131/9102 Page 497 May 6, 2018

35 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 COMP3131/9102 Page 498 May 6, 2018

36 1. Array operations: Example: Load and Store for Arrays 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 COMP3131/9102 Page 499 May 6, 2018

37 1. Unconditional: goto 2. Instructions on int: Control Transfer Instructions 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 COMP3131/9102 Page 500 May 6, 2018

38 op stack (before) value1 value op stack (after) if icmge label 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. COMP3131/9102 Page 501 May 6, 2018

39 1. Ctrl1.java Example 1: Control Transfer Instructions public class Ctrl1 { public static void main(string argv[]) { 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 COMP3131/9102 Page 502 May 6, 2018

40 1. Ctrl2.java Example 2: Control Transfer Instructions public class Ctrl1 { public static void main(string argv[]) { 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 COMP3131/9102 Page 503 May 6, 2018

41 fcmpg and fcmpl op stack (before): value1 value op stack (after): 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 ( javase/specs/jvms/se7/html/jvms-3.html# jvms-3.5) COMP3131/9102 Page 504 May 6, 2018

42 1. Source: 2. Jasmin code: Type Conversion Instructions int i = 1; // index 1 float f = i; // index 2 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 COMP3131/9102 Page 505 May 6, 2018

43 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; COMP3131/9102 Page 506 May 6, 2018

44 Example: dup in Translating Compound Assignments 1. Assignment expressions: 2. Jasmin code: int i; \\ index 1 int j; \\ index 2 int k; \\ index 3 i = j = k = 1; iconst_1 dup istore_3 dup istore_2 istore_1 COMP3131/9102 Page 507 May 6, 2018

45 Example: pop in Translating VC Expression Statements 1. Assignment expressions: 2. Jasmin code: int i; // index (i = 2); iconst_1 iconst_2 dup istore_1 iadd pop COMP3131/9102 Page 508 May 6, 2018

46 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, COMP3131/9102 Page 509 May 6, 2018

47 Example: Object Creation and Manipulation Static and field variables: public class StaticField { static int i = 1; int j = 1; public static void main(string argv[]) { 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.method public static main([ljava/lang/string;)v.line 5 new StaticField dup invokespecial StaticField/<init>()V COMP3131/9102 Page 510 May 6, 2018

48 .line 6.line 7 Label0:.line 8 astore_1 return.end method getstatic java.lang.system.out Ljava/io/PrintStream; getstatic StaticField.i I invokevirtual java/io/printstream/println(i)v getstatic java.lang.system.out Ljava/io/PrintStream; aload_1 getfield StaticField.j I invokevirtual java/io/printstream/println(i)v COMP3131/9102 Page 511 May 6, 2018

49 Syntax: The Syntax for Field Instructions 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 COMP3131/9102 Page 512 May 6, 2018

50 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 COMP3131/9102 Page 513 May 6, 2018

51 Method calls: Method Invocation Instructions 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/ /what-is-the-point-of-invokeinterface) Method returns: return ireturn freturn... COMP3131/9102 Page 514 May 6, 2018

52 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 COMP3131/9102 Page 515 May 6, 2018

53 invokestatic Method Invocation Instructions (Cont d) 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 treated exactly the same as the built-in operators (e.g., + and ) COMP3131/9102 Page 516 May 6, 2018

54 1. Met1.java: Example: Static Method Invocation 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_0 iload_1 iadd ireturn.end method.method public static main([ljava/lang/string;)v.limit stack 2.limit locals 1 iconst_1 iconst_2 invokestatic Met1/add(II)I pop return.end method COMP3131/9102 Page 517 May 6, 2018

55 1. Met2.java: Example 9: Instance Method Invocation public class Met2 { int add(int i1, int i2) { return i1 + i2; public static void main(string argv[]) { 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 COMP3131/9102 Page 518 May 6, 2018

56 Polymorphism: invokevirtual and invokespecial public class Fruit { public static void main(string argv[]) { 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(); COMP3131/9102 Page 519 May 6, 2018

57 ;; Produced by JasminVisitor (BCEL package) ;; ;; Mon Oct 09 16:09:47 GMT+10: source Fruit.java.class public Fruit.super java/lang/object Fruit.j.method public <init>()v.limit stack 1.limit locals 1.var 0 is this LFruit; from Label0 to Label1 Label0:.line 1 Label1: aload_0 invokespecial java/lang/object/<init>()v return.end method.method public static main([ljava/lang/string;)v.limit stack 2.limit locals 3.var 0 is arg0 [Ljava/lang/String; from Label0 to Label1 Label0:.line 4.line 6 new Apple dup invokespecial Apple/<init>()V astore_1 aload_1 COMP3131/9102 Page 520 May 6, 2018

58 .line 7 Label1:.line 3 astore_2 aload_2 invokevirtual Fruit/whoAmI()V <=== a virtual call return.end method.method whoami()v.limit stack 2.limit locals 1.var 0 is this LFruit; from Label0 to Label1 Label0:.line 11 getstatic java.lang.system.out Ljava/io/PrintStream; ldc "This is a fruit." invokevirtual java/io/printstream/println(ljava/lang/string;)v Label1:.line 10 return.end method COMP3131/9102 Page 521 May 6, 2018

59 .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 Apple.j.method whoami()v.limit stack 2.limit locals 1.var 0 is this LApple; from Label0 to Label1 Label0:.line 18 getstatic java.lang.system.out Ljava/io/PrintStream; ldc "This is an apple." invokevirtual java/io/printstream/println(ljava/lang/string;)v.line 19 Label1:.line 17 return.end method aload_0 invokespecial Fruit/whoAmI()V <=== a static call COMP3131/9102 Page 522 May 6, 2018

60 Jasmin Directives Jasmin home page.source.class.super.limit.method.field static.end.var.line Example: gcd.j (Slide 475) COMP3131/9102 Page 523 May 6, 2018

61 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>... ] COMP3131/9102 Page 524 May 6, 2018

62 <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> COMP3131/9102 Page 525 May 6, 2018

63 <instruction> ::= <simple_instruction> <complex_instruction> <simple_instruction> ::= <insn> <insn> <int> <int> <insn> <int> <insn> <num> <insn> <word> <insn> <word> <int> <insn> <word> <word> <insn> <quoted_string> <complex_instruction> ::= <lookupswitch> <tableswitch> COMP3131/9102 Page 526 May 6, 2018

64 <lookupswitch> ::= lookupswitch <nl> <int> : <label> <nl> <int> : <label> <nl>... default : <label> <tableswitch> ::= tableswitch <low> <nl> <label> <nl> <label> <nl>... default : <label> <access> ::= <access_item> [ <access_item>... ] <access_item> ::= public private protected static final synchronized volatile transient native interface abstract COMP3131/9102 Page 527 May 6, 2018

65 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 its instructions (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 COMP3131/9102 Page 528 May 6, 2018

66 Reading (in Order of Increasing Importance) on-line JVM instructions 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) COMP3131/9102 Page 529 May 6, 2018