Ss Final Report

8/3/2019 Ss Final Report

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Department of CSE,NMIT

NITTE MEENAKSHI INSTITUTE OF TECHNOLOGY

(An Autonomous Institution under VTU, Belgum)

Govindapura, Gollahalli, Yelahanka, Bangalore – 560064

A REPORT ON

“ASSEMBLERS”

Submitted in the partial fulfilment of the requirements for the V semester in computer science

and Engineering

SYSTEM SOFTWARE

PROJECT

BY

ASHWIN M (1NT09CS110)

DIXIT HEBBAR (1NT09CS109)




NITTE MEENAKSHI INSTITUTE OF TECHNOLOGY

(An Autonomous Institution under VTU, Belgum)

Govindapura, Gollahalli, Yelahanka, Bangalore – 560 064

Department of Computer Science & Engineering

CERTIFICATE

This is to certify that the mini- project report titled “ASSEMBLERS” is carried out by

ASHWIN.M (1NT09CS110) & DIXIT HEBBAR (1NT09CS109) , bonafide students of

Nitte Meenakshi Institute of Technology, Bangalore in partial fulfilment of SYSTEM

SOFTWARE during the academic year 2010-2011. It is certified that all

corrections/suggestions indicated for Internal Assessment have been incorporated in the

report. All the necessary requirements for the submission of the report have been satisfied.

Dr Nalini.N Mr Nagraj

HOD & Prof. of CSE Lecturer

Name of the Examiners Signature with Date

1. ________________________ ____________________

2. ________________________ ____________________




ABSTRACT

In this project we are designing and also implementing a 1-Pass assembler. They

are certain functions that any assembler has to perform such as translatingmnemonics operations codes to their machine equivalents and assigning machine

address to the various symbolic labels that are used by the programmer. The

basic importance to the given here in an assembler is that it heavily depend on

the source code it translates and machine language it produces. As we will later,

there are also many subtler ways that an assembler depends upon the machine

architecture. On the contrary, there are some features of an assembler that have

no direct relation to the architecture, in the sense, decision made by the

designers of the language.

Thus the assembler gives us a starting point from which we can understand thestudy of advanced assembler features. This frame work can also be used to

begin a design of an assembler for a completely unfamiliar machine.

This assembler also helps us generating object codes for a predefined set of

machine instructions and supports two t ypes of addressing modes.




ACKNOWLEDGEMENT

We have come to the completion of the project “ASSEMBLER”. This project

has given us enormous pleasure and satisfaction. We would be failing in our

duty if we do not acknowledge the help and support provided to us during the

course of the project. In first instance I would like to acknowledge my gratitude

to our H.O.D Dr Nalini for having provided us the invaluable suggestions for

the completion of the project. I place on record the help that rendered by

Mr.Nagraj who provided guidance at all stages. My gratitude is also due to for

this encouragement and guidance throughout the work.

ASHWIN M

DIXIT HEBBAR




SYNOPSIS

Assembler is system software which is used to convert an assembly language

program to its equivalent object code. The input to the assembler is a source

code written in assembly language (using mnemonics) and the output is the

object code. The design of an assembler depends upon the machine architecture

as the language used is mnemonic language.




One-Pass Assemblers:

• Main problem

• Forward references.

• Data items

• Labels of instructions.

• Solution

• Data items: require all such areas be defined before they arereferenced.

• Labels on instructions: no good solution.

• Main problems

• Forward references

• Data items.

• Labels on instructions.

• Two types of one-pass assembler

• Load-and-go

• Produces object code directly in memory for

immediate execution.

• The other

• Produces usual kind of object code for later execution




CONTENTS:

1. Introduction to Assembler

• Basic Assembler functions

• Process translation, loading and execution.

2. Outline of Pass1 and Pass2

3. Different types of Assemblers with their features

• Two-pass Assembler with overlay structure

• One-pass Assemblers

• Load-and-go Assemblers

4. Examples of multi pass Assemblers with features

• Microsoft MASM Assembler

• Sun Spare Assembler

• AIX Assembler for power PC:

5. Study case SIC with architecture

6. Design details

• Function prototypes

• Pass2 Assembler algorithm for Pass1, Pass2




INTRODUCTION TO ASSEMBLER

When we think of an assembler we first try to analyse what is an assembler?

How does it help for user to run the programs written high level languages?

Here is the answer that an assembler is system software that converts the

executable statements in high level languages to executable machine codes. All

assemblers may not work for all systems. The choose of assembler for a

particular system depends on the machine architecture on which the

application programs going to run .At present we have lot many assemblers.

Some of them are listed below.

1. Sparc assemblers for SunOS systems

2. Masm by Microsoft for Intel x 86 families

3. IBM AIX Assembler etc.

BASIC FUNCTION OF ASSEMBLER:

The translation of source program to object codes require us to accomplish the

following functions:

• Convert the mnemonics codes to their machine language equivalents.

• Convert the symbolic operand to their equivalent machine addresses.

• Build the machine instructions in proper format.

• Convert the data structures to internal machine representations.

• Write the object program and the assembly listing.

And also there are so many options. Some of them are listed below.

• One-pass assemblers

• Multi-pass assemblers

• Two-pass assembler with overlay structure




Communication between Modules:

The diagram below indicates the communication pathways between the modules

of an assembler. For each arrow in the diagram, the module at the tail of thearrow plays the role of a client and the module at the head of the arrow plays

the role of a server. This means that the client calls functions provided by the

server.

Two-Pass Assembler with overlay structure:

• For small memory

• Pass 1 and Pass 2 are never required at the same time.

• Three segments

• root: driver program and shared tables and subroutines.

• Pass 1.

• Pass 2.

• Tree structure.

• Overlay program.




One-Pass Assemblers:

• Main problem

• Forward references.

• Data items

• Labels of instructions.

• Solution

• Data items: require all such areas be defined before they

are referenced.

• Labels on instructions: no good solution.

• Main problems

• Forward references

• Data items.

• Labels on instructions.

• Two types of one-pass assembler

• Load-and-go

• Produces object code directly in memory

for immediate execution.

• The other

• Produces usual kind of object code for later

execution

Load –

and-go assembler:






Producing object code:

• When external working-storage devices are not available or too

slow (for the intermediate file between the two passes).

• Solution:

• When definition of symbol is encountered, the

assembler must generate another text record with the

correct operand address.

• The loader is used to complete forward references

that could not be handled by the assembler

• The object program records must be kept in theiroriginal order when they are presented to the loader.

Multi-pass assembler:

• Restriction on EQU and ORG

• No forward reference, since symbols value

can’t be defined during the first pass

• Example

• Use link list to keep track of whose value depend on

an undefined symbol

Implementation examples:

• Microsoft MASM assembler

• Sun sparc assembler

• IBM AIX assembler




Microsoft MASM assembler:

• SEGMENT

• A collection segments ,each segment is defined as

belonging to a particularclass,CODE,DATA,CONST,STACK

• Registers:CS(code),SS(stack),DS(data),ES,FS,GS

• Similar to program blocks in SIC

• ASSUME

• E.g. ASSUME ES: DATASEG2

• E.g. MOVE AX,DATASEG2

• MOVE ES, AX

• Similar to BASE in SIC

• JUMP with forward reference

• Near jump:2 or 3 bytes

• Far jump:5 bytes

• e.g. JMP TARGET

• Warning: JMP FAR PTR TARGET

• Warning: JMP SHORT TARGET

• Pass1:reserves 3bytes for jump instruction

• Phase error

• PUBLIC,EXTRN

• Similar to EXTDEF,EXTREF in SIC




SUN SPARC ASSEMBLER:

• Sections

• TEXT,.DATA,.RODATA,.BSS

• Symbols

• Global vs. weak

• Similar to the combination of EXTDEF and EXTREF

in SIC

• Delayed branches

• Delayed slots

• Annulled branch instruction

AIX assembler for PowerPC:

• Similar to system/370

• Basic relative addressing

• Save instruction space, no absolute address

• Base register table:

• General purpose registers can be used as base

register

• Easy for program relocation

• Only data whose are to be actual address needs

to be modified

• e.g. USING LENGTH, 1

USING BUFFER, 4

• Similar to BASE in SIC

• Drop




• Alignment

• Instruction (2)

• Data: halfword operand(2), fullword operand (4)

• Slack bytes

• CSECT

• Control sections: RO(read-only data), RW(read-write data),

PR(executable instructions), BS(uninitialized read/write data)

• Dummy section

The SIMPLIFIED INSTRUCTIONAL COMPUTER (SIC)

• SIC is Computer that has been carefully designed to include the hardware

features often found on real machines, while avoiding unusual or

irrelevant complexities.

• Like many other products, SIC comes in two versions: the standard model

and an XE version (XE “Extra Equipment”). The two versions have been

designed to be compatible. That is a program for standard SIC machine

will also execute properly on a SIC/XE system

SIC MACHINE ARCHITECTURE

• MEMORY: Memory consists of 8-bits byte. Any three bytes form a

word (24 bits). All addresses on SIC are bytes address. There are total of 32,768 (215) bytes in the memory.

• REGISTERS: Registers are very fast storage locations in the CPU are

temporarily used to store instructions, data or address. SIC machine has

five registers, all of which have special uses. Each register is 24 bits

length.




Mnemonic Number Special usesA 0 Accumulator; used for

arithmetic operations.

X 1 Index register; used for

addressing.

L 2 Linkage register; the jump to subroutine

(JSUB) instruction

stores the return address

in this register.

PC 8 Program counters;

contains the address of

the next instruction to

be fetched for execution.

SW 9 Status word; contains a

variety of information,including Conditional

code(CC)

• DATA FORMATS:

• Integers are stored as 24-bits binary numbers.

• 2’s compliment representation is used for negative values.

• Characters are stored using their 8-bit ASCII codes.

• There is no floating-point hardware on the standard version of SIC .

• INSTRUCTION FORMATS:

• All machine instructions on the standard versions of SIC have the

following 24-bit format:

8 1 15

Opcode X Address

• The flag bit X is used to indicate indexed-addressing mode.




ADDRESSING MODES:

• There are two addressing modes available, indicated by setting of the X

bit in the instruction. The following table describes how the target

address is calculated from the address given in the instruction.

• Parentheses are used to indicate the contents of a register or a memory

location.

• For example, (X) represents the contents of register X.

Mode

Indication Target address

calculationDirect X=0 TA=Address

Indexed X=1 TA=Address+(X)

• INSTRUCTION SET:

• SIC provides a basic set of instructions that are sufficient for most

simple tasks. These include instructions that load and store registers

(LDA, LDX, STA, STX, etc…), as well as integer arithmetic

operations (ADD, SUB, MUL, and DIV). All arithmetic operations

involve registers A and a word memory, with the result behind left in

the register.

• There is an instruction (COMP) that compares the value in register. A

with a memory; this instruction sets a condition code CC to indicate

the result (<, =, or >). Conditional jump instruction (JLT, JEQ, and

JGT) can test the setting of CC, and jump accordingly. Two

instructions are provide for subroutine linkage.

• JSUB jumps to the subroutine, placing the return in the register L; RSUB

jumps to the addr ess cont ained in reg ister L.

ONE- PASS ASSEMBLER ALOGRITHM




begin

read first input line

if OPCODE=’START’ then

begin

save #[OPERAND] as starting address

initialize LOCCTR as starting address

read next input line

end {if START}

else

initialize LOCCTR to 0

while OPCODE!=’END’ do

begin

if there is not a comment line then

begin

if there is a symbol in the LABEL field then

begin

search SYMTAB for LABEL

if found then

begin

if symbol value as null

set symbol value as LOCCTR and search

the linked list with the corresponding

operand

PTR addresses and generate operand

Addresses as corresponding symbol

Values

Set symbol value as LOCCTR in symbol




Table and delete the linked list

End

Else

Insert (LABEL, LOCCTR) into SYMTAB

End

Search OPTAB FOR OPCODE

If found then

Begin

Search SYMTAB for OPERAND address

If found then

If symbol value not equal to null then

Store symbol value as OPERAND address

Else

Insert at the end of the linked list

With a node with address as LOCCTR

Else

Insert (symbol name,null)

Add 3 to LOCCTR

End

Else if OPCODE=’WORD’ then

Add 3 to LOCCTR and convert comment to

Object code

Else if OPCODE=’RESW’ then

ADD 3 #[OPERAND] to LOCCTR

Else if OPCODE=’RESB’ then

ADD #[OPERAND] to LOCCTR




Else if OPCODE=’BYTE’ then

Begin

Find length of constant in bytes

Add length to LOCCTR

Convert constant to object code

End

If object code will not fit into current

Text record then

Begin

Write text record to object program

Initialize new text record

End

Add object code to text record

End

Write listing line

Read next input line

End

Write last text record to object program

Write end record to object program

Write last listing line

End {pass1}

PROGRAM CODE




#include<stdio.h>

#include<stdlib.h>

#include<string.h>

#include<conio.h>

int count[20];/*global declaration*/

void main()

{

FILE *f1,*f2,*f3,*f4;

int linenum,locctr,f;

char lbl[10],mne[10],opd[10],ch,menu1[10],sval[10];

char sadr[10],slbl[10],op1[10],lable[10];

void wordcount();

clrscr();

printf("Word count for input program:");

/*Count s the no of words in a gi ven line* /

wordcount();

printf("\nOutput\n");

printf("\nSourcecode \t Objectcode\n\n");

f1=fopen("INPUT.TXT","r");/*Reading the input from a file*/

f2=fopen("SYMTAB.TXT","w+");/*Creating a file called SYMTAB that

is referenced later on*/

f4=fopen("OPTAB.TXT","w");/*Creating a file called OPTAB refer enced

later*/

/*s can the first line from input file* /

fscanf(f1,"%s %s %x \n",lbl,mne,&locctr);

linenum=2;

while(!feof(f1))

{




if(count[linenum]==1)

{

fscanf(f1,"%s\n",mne);

fprintf(f4,"%x\t%s",locctr,mne);/*printing into OPTAB

file*/

}


{ fscanf(f1,"%s%s\n",mne,opd);

fprintf(f4,"%x \t %s \t %s \n",locctr,mne,opd);

/*print ing the operand value into the OPTAB */

printf("%s\t%s\t",mne,opd);

f3=fopen("OPCODE.TXT","r");

while(!feof(f3))

{ fscanf(f3,"%s %s \n",menu1,op1);

if(strcmp(mne,menu1)==0)

/*comparing mne of the INPUT fi le wi th the menu1 of the

OPTAB file*/

printf("%s\t",op1);

}

fclose(f3);

f=0;

rewind(f2);

while(!feof(f2))

{ fscanf(f2,"%s %s %s \n",sadr,slbl,sval);

if(strcmp(opd,slbl)==0)

{

printf("%s\n\n",sadr);




/*pri nt ing the SYMTAB addres s int o the out pu t window*/

f=1;

}

}

if(f==0)

printf("0000\n");

/*print ing de fault add res s int o the outpu t window*/

}


{

fscanf(f1,"%s %s %s \n",lbl ,mne,opd);

fprintf(f4,"%x\t%s\t%s\t%s\n",locctr,lbl,mne,opd);

/*upda ting OPTAB */

fprintf(f2,"%x\t%s\t%s\n",locctr,lbl,opd);

/*updat ing SYMTAB*/

if((strcmp(mne,"RESW")==0)||(strcmp(mne,"RESB")==0))

printf("%s\t%s\n\n",lbl,mne);

/*if ou tput of the strcmp is 0 then dont load the addr ess* /

else

printf("%s\t%s\t00\t000%s\n\n",lbl,mne,opd);

}

linenum+=1;

if(strcmp(mne,"WORD")==0)

locctr+=3; /*assining 3 to locctr*/

else if(strcmp(mne,"BYTE")==0)

locctr+=strlen(opd);

/*assign ing len of the op tab into thelocct r*/




else i f(strcmp(mne,"RESW")==0)

locctr+=3 * atoi(opd);

else if(strcmp(mne,"RESB")==0)

locctr+=atoi(opd);

else

locctr+=3;

}

fclose(f1);/*closing input file*/

fclose(f2);/*closing symtab file*/

fclose(f4);/*closing optab file*/

getch();

}

void wordcount()

{

FILE *f3;

int word=0,i=1;

char c;

printf("\nWordcount");

f3=fopen("INPUT.TXT","r");

/*opening a input file in read mode*/

c=fgetc(f3);

while(c!=EOF)

{

if(c==' ')

word+=1;/*increamenting word*/

if(c=='\n')

{




word+=1;

count[i]=word;/*no of words in the line no i*/

printf("\nNo of words in line no %d:%d",i,word);

i+=1;

word=0;

}

c=fgetc(f3);

}

fclose(f3);

}/*end of wordcount function*/




INPUT

WC START 1000

FIRST WORD 5

SECOND WORD 6

THIRD RESW 1

LDA FIRST

ADD SECOND

STA THIRD

END

Word count for input program:

Wordcount

No of words in line no 1:3







Output

Sourcecode Objectcode

FIRST WORD 00 0005

SECOND WORD 00 0006

THIRD RESW

LDA FIRST 00 1000

ADD SECOND 18 1003

STA THIRD 0C 1006




CONCLUSION

The design of 1-Pass assembler is successfully

completed. It has been designed keeping in mindonly the basic functions of the assembler.

Working on this project has given us

sufficient knowledge and also it has given us the

confidence in handling other such project in

future.



BIBLIOGRAPY

• System software, An introduction to the

programming,3

rdEdition-Leland L.Beck

• C Projects, -Yashvanth Kanetkar

• Let Us C, 9 th Edition – Yashvanth

Documents

Ss Final Report