C Compiler

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In this project, a C programming language compiler was made which can produce “Assembly Code” & “Optimized Assembly Code” for 8066 micro-processor.

Description

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This compiler can only handle a subset of C language as structure, unions, pointers, recursive function as function parameter haven’t been handled.

Bison and Flex was used to parse and tokenize the input file and to detect any error.

For simplicity, for printing purpose printf(arg) or println(arg) was implemented.

[Note]: As, recursion was not handled so recursive function won’t work properly and parser is smart enough to catch any semantic and lexical error present in provided C code.

A sample C code:

int main(){
    int a, b;
    a = 5;
    b = a + 10;
    
    /* ****************************************************** */
    /*    Both println() and printf() is for showing output   */
    /* ****************************************************** */
    printf(a);
    println(b);
}

From this input an unoptimized assembly code was generated which was optimized later

• Unoptimized Assembly Code:

.MODEL SMALL			

.STACK 100H			

.DATA
	main_return_val DW ?
	a2 DW ?
	b2 DW ?
	t1 DW ?

.CODE
PRINT_INT PROC						
	PUSH AX						
	PUSH BX						
	PUSH CX						
	PUSH DX						

	OR AX, AX						
	JGE END_IF1						
	PUSH AX						
	MOV DL,'-'						
	MOV AH, 2						
	INT 21H						
	POP AX						
	NEG AX						

END_IF1:						
	XOR CX, CX						
	MOV BX, 10D						

REPEAT1:						
	XOR DX, DX						
	DIV BX						
	PUSH DX						
	INC CX						

	OR AX, AX						
	JNE REPEAT1						

	MOV AH, 2						

PRINT_LOOP:						
	POP DX						
	OR DL, 30H						
	INT 21H						
	LOOP PRINT_LOOP						
	MOV AH, 2						
	MOV DL, 10						
	INT 21H						

	MOV DL, 13						
	INT 21H						

	POP DX						
	POP CX						
	POP BX						
	POP AX						
	RET						
PRINT_INT ENDP

MAIN PROC									
	MOV AX,  @DATA									
	MOV DS ,AX
	MOV AX, 5
	MOV a2, AX

	MOV AX, a2
	ADD AX, 10
	MOV t1, AX

	MOV AX, t1
	MOV b2, AX
	
	MOV AX, a2
	CALL PRINT_INT

	MOV AX, b2
	CALL PRINT_INT

LABEL_RETURN_main:
	MOV AH, 4CH									
	INT 21H									
END MAIN

From this unoptimized code segment an optimized code segment was generated

• Optimized Assembly Code:

.MODEL SMALL

.STACK 100H	

.DATA
	main_return_val DW ?
	a2 DW ?
	b2 DW ?
	t1 DW ?
	
.CODE
PRINT_INT PROC						
	PUSH AX						
	PUSH BX						
	PUSH CX						
	PUSH DX	
    
	OR AX, AX						
	JGE END_IF1						
	PUSH AX						
	MOV DL,'-'						
	MOV AH, 2						
	INT 21H						
	POP AX						
	NEG AX
    
END_IF1:						
	XOR CX, CX						
	MOV BX, 10D	
    
REPEAT1:						
	XOR DX, DX						
	DIV BX						
	PUSH DX						
	INC CX						
	OR AX, AX						
	JNE REPEAT1						
	MOV AH, 2
    
PRINT_LOOP:						
	POP DX						
	OR DL, 30H						
	INT 21H						
	LOOP PRINT_LOOP						
	MOV AH, 2						
	MOV DL, 10						
	INT 21H						
	MOV DL, 13						
	INT 21H
    
	POP DX						
	POP CX						
	POP BX						
	POP AX						
	RET						
PRINT_INT ENDP

MAIN PROC									
	MOV AX, @DATA									
	MOV DS ,AX
	
	MOV AX, 5
	MOV a2, AX
	ADD AX, 10
	MOV t1, AX
	MOV b2, AX
	MOV AX, a2
	CALL PRINT_INT
	MOV AX, b2
	CALL PRINT_INT
	
LABEL_RETURN_main:
	MOV AH, 4CH									
	INT 21H									
END MAIN

Environment

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• This project was done in Linux operating system but it can be done in any operating system

Tools

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Tools used for the project,

• FLEX
  • Flex is a free and open-source software alternative to lex. It is a computer program that generates lexical analyzers.
• BISON:
  • Bison, is a parser generator that is part of the GNU Project. Bison reads a specification of a context-free language, warns about any parsing ambiguities, and generates a parser that reads sequences of tokens and decides whether the sequence conforms to the syntax specified by the grammar.
  • The grammar that was implemented can be found here

Languages

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• C++
• Assembly [x86 8066]

Files

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Here is a small details of the file-system:

• SymbolInfo.h: This file contains information of any valid token. For an example,

int a;

will be stored as <ID, a> or <ID, location of a in Symbol Table> in symbol table. The information name and type was stored. This file provide a Class named SymbolInfo to store informations.

• ExtraSymbolInfo.h: This file contains additional information of the tokens and most importantly, for Intermediate Code Generation this file was used to store assembly code
• ScopeTable.h: Provide an interface to store each symbol’s scope like global or local.
• SymbolTable.h: Actual file that handles and stores all information and processing related to any valid token.
• StringHandler.h: A simple file used for generating label and variable and also for optimization purpose.
• SymbolTable.cpp: Simply combines SymbolInfo.h, ExtraSymbolInfo.h ScopeTable.h SymbolTable.h.
• Lexer.l: The lexed file that has rule to tokenize a valid C code and handle any lexical errors.
• Parser.y: The parser file that has the parsing rule with specific grammar that can be found here
• Script.sh: The shell-script with all necessary command to parse and execute the code.
• Input.c: Input file to test validity of the program.
• log.txt: File to show outputs.
• error.txt: File to show errors(if any).
• code.asm: File with unoptimized assembly code.
• optimized_code.asm: File with optimized assembly code.

[Note]: code.asm and optimized_code.asm will only generate when there is no error in the provided input file.

How to Run

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• Clone the repository into your local machine

  git clone https://github.com/rng70/C-Compiler

• Give proper permission to Script.sh file

  chmod +x Script.sh

• Run the Script file

  ./Script.sh

• Then run code.asm in emu8066 simulator.

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