CS 614: Theory and Construction of Compilers

Lecture 7

Fall 2003

Department of Computer Science

University of Alabama

Joel Jones

Lecture 7 ©2003 Joel Jones 2

Outline

(f)lex Diversion Introduction to Java Cup Reading & Questions for Next Class

Lecture 7 ©2003 Joel Jones 3

A Design Problem

You have a binary file that somehow has been corrupted

You need to recover as much as possible from the file

• Pair Up: (Let’s make this interactive—ask me questions)

• • How do you approach this problem?

• • What information do you gather?

• • How do you use this knowledge to build a tool?

Lecture 7 ©2003 Joel Jones 4

A Brief (f)lex Diversion

Despite their name, lexical analyzers can be used on binary files

This is somewhat difficult with JLex, due to conversions of byte input to character input

Lecture 7 ©2003 Joel Jones 5

Reading Binary Files With Flex%{static void printAddress(char* text);…%}ADDRESS \xFF\xFF\x00\x00\xFFNOTE \xFF\xFF\xFF\xFF\x00TODO \xFF\xFF\xFF\xFF\x00\x01EVENT \x55\x54\x55\x54\x55\x54\x00\x00%%[ \t\n]+ /* eat whitespace */{ADDRESS}[^\0]+ { printAddress(yytext + 8); }{NOTE}[\0\x3c\x22][^\0]+ { printNote(yytext + 6); }{TODO}........[^\0]+ { printToDo(yytext + 14); }{EVENT}[^\0]+ { printEvent(yytext + 8); }. /* eat everything else */

Lecture 7 ©2003 Joel Jones 6

Reading Binary Files With Flex

%%

main(int argc, char** argv){ argv++; argc++; /* skip over program name */ if (argc > 0) yyin = fopen(argv[0], "r"); else yyin = stdin; yylex();}

Lecture 7 ©2003 Joel Jones 7

Fundamental of LALR Parsing Bottom-up

Unlike recursive-descent which is top-down Model is finite-automata with a stack

The parsers state represents what is expected next in the input Transition to next state based upon the top of the stack, next

(1) input symbol, and current state Stack contains symbols, both terminals and nonterminals On transition, stack may pushed (shift), popped (reduce), or

unchanged (epsilon)

Lecture 7 ©2003 Joel Jones 8

Purpose of Parser Generator

Translate a specification of a grammar into a parser

Most parser generators are for Context-free Grammars (CFG) and produce LALR(1) or LL(1) parsers

Grammar specification is annotated with action routines that are executed when a reduction is made

Lecture 7 ©2003 Joel Jones 9

Java Cup

Accepts specification of a CFG and produces an LALR(1) parser (expressed in Java) with action routines expressed in Java

Similar to yacc in its specification language, but with a few improvements (better name management)

Lecture 7 ©2003 Joel Jones 10

java_cup_spec ::= package_spec import_list code_part init_code scan_code symbol_list precedence_list start_spec

production_list

Java Cup Specification Structure

Great, but what does it mean? Package and import controls Java naming Code and init_code allows insertion of code in generated output Scan code specifies how scanner (lexer) is invoked Symbol list and precedence list specify terminal and non-

terminal names and their precedence Start and production specify grammar and its start point

Lecture 7 ©2003 Joel Jones 11

Example Java Cup Specification (partial)

import java_cup.runtime.*;

/* Terminals (tokens returned by the scanner). */terminal SEMI, PLUS, MINUS, TIMES, DIVIDE, MOD;terminal Integer NUMBER;

/* Non terminals */non terminal expr_list, expr_part;

/* Precedences */precedence left PLUS, MINUS;

/* The grammar */expr_list ::= expr_list expr_part | expr_part;

Lecture 7 ©2003 Joel Jones 12

Running Java Cup Manually Download and build Java Cup

export CLASSPATH=~/src/java_cup_v10k ./INSTALL

Run Java Cup on the specification java Java_cup Main Arith.y -or- java_cup Arith.y

Run Jlex on scanner specification jlex Number.l

Build parser and scanner javac parser.java javac Number.l.java

(cont.)

Lecture 7 ©2003 Joel Jones 13

Running Java Cup Manually (cont.) Build driver program

java ParseDemo.java

Run driver program java ParseDemo << EOF

Lecture 7 ©2003 Joel Jones 14

Reading & Questions for Next Class Java Cup Web page

http://www.cs.princeton.edu/~appel/modern/java/CUP/