Tutorial 3: Code Generation

Transcription

1 S C I E N C E P A S S I O N T E C H N O L O G Y Tutorial 3: Code Generation Univ.-Prof. Dr. Franz Wotawa, DI Roxane Koitz, Stephan Frühwirt, Christopher Liebmann, Martin Zimmermann Institute for Software Technology 1 u

2 Compiler Phases Jova Input Program Java Byte Code 2

3 Compiler Phases Jova Input Program Java Byte Code 3

4 Grammar (Jova.g4) Workflow (1/2) ANTLR Lexer and Parser ANTLR visitor / listener Source Code (*.jova file) Syntax tree Symbol table Lexical and syntactical errors Debugging output Type checking errors Debugging output 4

5 Workflow (2/2) Syntax tree Jasmin code (.j file) Byte code (.class file) Symbol table Jasmin 5

6 What is Jasmin? Assembler for Java bytecode Input: <filename>.j file contains assembly of the original code written in Jasmin assembler language Output: executable Java.class file 6

7 Pipeline Create Assembly Produce jasmin assembly Result: <filename>.j Convert Invoke java jar jasmin.jar <filename>.j Result: <filename>.class Execute Invoke java <filename> Result: executes main method of class 7

8 Jasmin syntax One class per.j file One statement per line Assembly setup: Required options Methods Statements (JVM instructions) 8

9 File structure: Class options.source: e.g.:.class: e.g.:.super: always:.field: e.g.: Source of assembly.source MyClass.jova Resulting java class description.class public MyClass Superclass of resulting java class.super java/lang/object Specify fields of class.field public my_field I 9

10 File structure: Methods.method <method signature> e.g..method public mymethod(i)v.limit stack n n: choose realistic number.limit locals n n = #parameters + #local_vars + #temp_var <instructions> return requires matching type on top-of-stack for non-void returns (e.g. ireturn).end method 10

11 Default Constructor needs to be defined for every class since Jova does not have Constructors you can use the same definition for every class:.method public <init>()v.limit stack 1.limit locals 1 aload_0 invokespecial java/lang/object/<init>()v return.end method 11

12 Example: DoNix File: DoNix.j.source nosource.class public DoNix.super java/lang/object.method public static main([ljava/lang/string;)v.limit stack 0.limit locals 1 ;nothing to do here return.end method 12

13 Data Management Two data structures per method (invocation/frame) Stack Local array Operations to manipulate both Build-in datatypes Primitive Types (int, float, byte, char, ) Reference Types (class types, array types, interface types) Very limited support for boolean 13

14 Data Management: Stack Each method has its own operand stack Size is definable per method (just assume a realistic number) LIFO Stack operations Push values onto stack Pop/Fetch values from stack Instructions which require one or multiple values on stack (order does matter!) 14

15 Data Management: Local Variable Array Each method has its own local variable array Definable size for each method (0-based indices) Typing Can store arbitrary types Items need to be initialized before read access Contains Method parameters (stored in lowest indices) At index 0 the this reference 15

16 Data Managment: Types a few primitives Integer Void Boolean indicated by letter I indicated by letter V indicated by letter Z Objects following the format Lpackage/Classname; e.g. Ljava/lang/String; String object Array indicated by a leading [ e.g. [Ljava/lang/String; array of Strings 16

17 Instructions Can involve stack and local array Most instructions operate on expected types Instruction template: <T><instr> where <T> = type letter <instr> = operation E.g.: iadd, fadd Instructions which do not operate on specific type E.g.: swap, dup 17

18 Instructions: Stack - Locals interaction iload n istore n aload n astore n pushes integer, stored in index n of local array, onto stack pops integer from stack and stores it into index n of local array pushes object, stored in index n of local array, onto stack pops object from stack and stores it into index n of local array 18

19 Instructions: Constants sipush n / bipush n Pushes integer constant onto stack E.g. sipush 10 For m1-5 you can also use iconst_<n> ldc <string> Pushes string constant <string> onto stack E.g. ldc Hello World Note: Strings are Objects (variable access with astore/aload) 19

20 Instructions: Arithmetic Operators iadd isub imul idiv irem ineg add two integers subtract two integers multiply two integers divide two integers modulo division of two integers toggles sign of int on top of stack 20

21 Example: BasicInstructions File: BasicInstructions.j.source nosource.class public BasicInstructions.super java/lang/object.method public static main([ljava/lang/string;)v.limit stack 3.limit locals 2 sipush 5 ;push integer 5 onto stack istore 0 ;pop integer 5 and store in index 0 ldc "Hello i11" ;push string i11 onto stack astore 1 ;store string in index 1 iload 0 ;load 5 dup ;duplicate stack entry 5 sipush 2 ;push integer 2 onto stack isub ;pop 5 and 2 and store result 3 onto stack iadd ;pop 5 and 3 and store result 8 onto stack istore 0 ;store result 8 in index 0 return.end method 21

22 Example: BasicInstructions File: BasicInstructions.j sipush 5 local array args stack 22

23 Example: BasicInstructions File: BasicInstructions.j istore 0 local array args stack 5 23

24 Example: BasicInstructions File: BasicInstructions.j ldc "Hello i11" 5 local array stack 24

25 Example: BasicInstructions File: BasicInstructions.j astore 1 5 local array stack Hello i11 25

26 Example: BasicInstructions File: BasicInstructions.j local array 5 Hello i11 iload 0 stack 26

27 Example: BasicInstructions File: BasicInstructions.j dup local array 5 Hello i11 stack 5 27

28 Example: BasicInstructions File: BasicInstructions.j local array 5 Hello i11 stack sipush

29 Example: BasicInstructions File: BasicInstructions.j local array 5 Hello i11 isub stack

30 Example: BasicInstructions File: BasicInstructions.j local array 5 Hello i11 stack iadd

31 Example: BasicInstructions File: BasicInstructions.j local array 5 Hello i11 stack istore

32 Example: BasicInstructions File: BasicInstructions.j local array 8 Hello i11 stack return 32

33 Instructions: Logical Operators iand ior inot bitwise and of two integers bitwise or of two integers does not exist! Note: Needs to be assembled using custom labels and conditional jump operations 33

34 Instructions: Relational Operators Do not exist! Need to be assembled using custom labels and conditional jump operations 34

35 Instructions: Labels and Jumps <labelname>: sets a label in the assembly goto <labelname> continues execution of current method at position of the label <labelname> if_icmpxx <labelname> pops two elements of the stack, relates them and jumps to <labelname> if comparison computes to true 35

36 Instructions: if_icmp variations if_icmplt relation using < if_icmple relation using <= if_icmpge relation using >= if_icmpgt relation using > if_icmpeq relation using == if_icmpne relation using!= 36

37 Example: LabelsAndJumps File: LabelsAndJumps.j.source nosource.class public LabelsAndJumps.super java/lang/object 37.method public static main([ljava/lang/string;)v.limit stack 2.limit locals 2 sipush 10 istore 0 ;store 10 in index 0 goto L_skip_redef sipush 20 istore 0 ;store 20 to index 0 - skipped L_skip_redef: iload 0 ;push value of index 0: 10 sipush 15 ;push 15 if_icmplt L_is_lesser ldc "greater" ;push string to stack - skipped goto L_end L_is_lesser: ldc "lesser" ;push string to stack L_end: return.end method ; result: string "lesser" on top of stack

38 Example: LabelsAndJumps File: LabelsAndJumps.j sipush 10 local array args stack 38

39 Example: LabelsAndJumps File: LabelsAndJumps.j istore 0 local array args stack 10 39

40 Example: LabelsAndJumps File: LabelsAndJumps.j goto L_skip_redef sipush 20 istore 0 L_skip_redef: local array 10 stack 40

41 Example: LabelsAndJumps File: LabelsAndJumps.j sipush 20 istore 0 L_skip_redef: local array 10 stack 41

42 Example: LabelsAndJumps File: LabelsAndJumps.j local array 10 iload 0 stack 42

43 Example: LabelsAndJumps File: LabelsAndJumps.j local array 10 sipush 15 stack 10 43

44 Example: LabelsAndJumps File: LabelsAndJumps.j local array 10 if_icmplt L_is_lesser ldc "greater" goto L_end L_is_lesser: ldc "lesser" L_end: stack

45 Example: LabelsAndJumps File: LabelsAndJumps.j local array 10 stack ldc "greater" goto L_end L_is_lesser: 45

46 Example: LabelsAndJumps File: LabelsAndJumps.j local array 10 stack ldc "lesser" 46

47 Example: LabelsAndJumps File: LabelsAndJumps.j local array 10 stack lesser L_end: 47

48 Example: LabelsAndJumps File: LabelsAndJumps.j local array 10 stack lesser return 48

49 Instructions: field access Call put-/getfield of object on stack Call using putfield <class ID>/<field ID> <type> getfield <class ID>/<field ID> <type> Requires value and object on stack Example Jova-field: Jasmin-signature: assembly: public int my_field MyClass/my_field I putfield MyClass/my_field I 49

50 Instructions: non-static method calls Call method of object on stack Call using invokevirtual <class ID>/<method signature> Requires parameters and object on stack (in correct order!) Example method: public int mymethod(int a) Jasmin- sig.: MyClass/myMethod(I)I invokevirtual MyClass/myMethod(I)I invokation: 50

51 Instructions: print Based on virtual invokation How to: 1. Push PrintStream object onto stack getstatic java/lang/system/out Ljava/io/PrintStream; 2. Push value onto stack (iload, aload, etc.) 3. Invoke matching PrintStream method invokevirtual java/io/printstream/print(i)v invokevirtual java/io/printstream/print(ljava/lang/string;)v invokevirtual java/io/printstream/print(z)v 51

52 Hints Try and write some simple Jasmin code yourselves Use aload_0 to get this reference Number your labels Map Jova/internal variables to locals array indices Instruction swap/dup may be useful in some cases Use the online documentation to find additional instructions/explanations When in doubt: model a problem in Java - compile it - and use javap -c <Class> to decompile the.class files 52

53 References: Jasmin User Guide: The Structure of the Java Virtual Machine: /html/jvms-2.html 53

54 Questions? 54