Pass Structure of Assembler - Dept. Of Information and Technology by I2ITengineeringcollege

Pass Structure of Assembler Subject : Systems Programming

Hope Foundation’s ,International Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057 Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in

Single Pass Assembler  Forward reference: reference to a label that is defined

later in the program. What is Forward reference ??Eg..

START ADD

200 AREG

A 2

END

 Table of Incomplete Instruction

Instruction Address 200 ..

Symbol A ..

Single Pass Assembler  Forward reference: reference to a label that is defined

later in the program.

Symbol A

Address

START ADD

200 AREG

A 2

END

 Table of Incomplete Instruction Instruction Address 200 ..

Symbol A ..

Single Pass Assembler  Forward reference: reference to a label that is defined later in the program.

START 200 ADD AREG ..

Target Code A 2

200

…

202

END

 Table of Incomplete Instruction Instruction Symbol Address 200 A .. ..

Symbol A ..

Address 202 ..

Target Code 200 01 01

202

Single pass Assembler Examples

SOURCE PROGRAM

AGAIN

TARGET CODE

START

101

READ

MOVER

BREG,

ONE

MOVEM

BREG,

TERM

MULT

BREG,

TERM

MOVER

CREG,

TERM

ADD

CREG,

MOVEM COMP BC MOVEM PRINT

INSTRUCTI ON Address

SYMBOL

101

102

ONE

103

TERM

104

TERM

105

TERM

ONE

106

ONE

CREG,

TERM

107

TERM

CREG,

TERM

108

104

108

TERM

AGAIN

109

110

RESULT

110 111

111

RESULT

112

LE, BREG, RESULT

STOP N

RESULT

ONE

‘1’

TERM

END

TII

113 114 115 116

Symbol Table SYMBOL

ADDRESS

113

ONE

115

TERM

116

RESULT

114

Single pass Assembler Examples SOURCE PROGRAM

AGAIN

TARGET CODE

START

101

READ

MOVER

BREG,

ONE

MOVEM

BREG,

TERM

MULT

BREG,

TERM

MOVER

CREG,

TERM

ADD

CREG,

ONE

MOVEM

CREG,

TERM

COMP

CREG,

TERM

LE,

MOVEM

BREG,

RESULT

TII

INSTRUCTI ON Address

SYMBOL

101

102

ONE

101

113

102

115

103

116

103

TERM

104

116

104

TERM

105

116

105

TERM

106

115

106

ONE

107

116

107

TERM

108

116

108

TERM

AGAIN

109

104

110

RESULT

110

114

111

RESULT

111

114

STOP

112

113

Symbol Table SYMBOL

ADDRESS

113

RESULT

114

ONE

‘1’

115

ONE

115

TERM

116

TERM

116

AGAIN

104

RESULT

114

END

Design of Two Pass Assembler  PASS I  Separate the symbol, mnemonic opcode,and operand fields.  Build the symbol table  Perform LC processing  Construct intermediate code  PASS II  Synthesize the target code

Required Data Structures for Two Pass Assembler Source Code Input PASS I

 MOT  Register Value Table  Conditional Value Table Prerequisite Output

 Intermediate Code  Symbol Table  Literal Table  Pool Table

Input

PASS II

Output Machine Code

Assembler Pass I INTERMEDIATE CODE

SOURCE PROGRAM

LOOP

(AD,01)

START

200

MOVER

AREG,

=‘5’

MOVEM

AREG,

MOVER

AREG,

MOVER

CREG,

ADD

CREG,

=‘1’

LTORG NEXT1

SUB

AREG,

ORIGIN

LOOP+1

MULT

CREG,

BACK

EQU

LOOP

END

‘=1’

(C,200)

200

(IS,04)

(L,01)

201

(IS,05)

(S,01)

202

(IS,04)

(S,01)

203

(IS,04)

(S,03)

204

(IS,01)

(L,02)

(AD,05) 205

005

206

001

207

(IS,02)

(AD,03)

(S,02)+(C,1)

203

(IS,03)

204

(DL,02)

(C,02)

(AD,04)

(S,02)

(DL,02)

(C,02)

206

(L,03) (S,03)

(AD,02) 207

001

Assembler Pass I SOURCE PROGRAM

INTERMEDIATE CODE (AD,01)

(C,200)

START

200

MOVER

AREG,

=‘5’

200

(IS,04)

(L,01)

MOVEM

ADD,

201

(IS,05)

(S,01)

MOVER

AREG,

202

(IS,04)

(S,01)

MOVER

CREG,

203

(IS,04)

(S,03)

ADD

CREG,

=‘1’

204

(IS,01)

(L,02)

SUB

AREG,

‘=1’

ORIGIN

LOOP+1

MULT

CREG,

BACK

EQU

LOOP

LTORG NEXT1

END

(AD,05) 205

005

206

001

207

(IS,02)

(AD,03)

(S,02)+(C,1)

203

(IS,03)

204

(DL,02)

(C,01)

(AD,04)

(S,02)

(DL,02)

(C,01)

205

(L,03) (S,03)

(AD,02) 206

001

Assembler Pass I SYMBOL TABLE

INTERMEDIATE CODE (AD,01)

(C,200)

INDEX

SYMBOL

ADDRESS

LENGTH

200

(IS,04)

(L,01)

204

201

(IS,05)

(S,01)

LOOP

202

(IS,04)

(S,01)

205

203

(IS,04)

(S,03)

NEXT1

207

204

(IS,01)

(L,02)

BACK

202

(AD,05) 205

005

206

001

207

(IS,02)

(AD,03)

(S,02)+(C,1)

203

(IS,03)

204

(DL,02)

(C,02)

(AD,04)

(S,02)

(DL,02)

(C,02)

206

(L,03) (S,03)

INDEX

LITERAL

ADDRESS

=‘5’

205

=‘1’

206

=‘1’

207

POOL TABLE

(AD,02) 207

LITERAL TABLE

LIT_INDEX 001

#01 #03

Assembler Examples Convert Source code into Pass I & Pass II

START

100

MOVER

AREG,

=‘5’

ADD

CREG,

=‘1’

MOVER

AREG,

ADD

AREG,

MOPVEM

AREG,

EQU

A+1

ORIGIN

A-1

SUB

AREG,

=‘1’

MULT

CREG,

‘5’

ORIGIN

L2+1

LTORG L2

EXAMPLE 2 SIMPLE

LOOP

START

100

BALR

15,

USING

R1,

TWO

R1,

FOUR

R1,

FOUR

CLI

FOUR+3,

BNE

LOOP

EQU

TWO

F’2’

FOUR

END

STOP B END

’19’

ASSUME:-BALR & BR are of two bytes…. L,A,ST,CLI,BNE are of four byte instructions…

Intermediate Code Forms  Variant I  Variant II SOURCE PROGRAM

LOOP

VARIANT –I

VARIANT -II

START

200

(AD,01)

(C,200)

(AD,01)

(C,200)

READ

(IS,09)

(S,01)

(IS,09)

MOVER

AREG,

(IS,04)

AREG,

(L,01)

(S,01)

SUB

AREG,

=‘1’

(IS,02)

(L,01)

(IS,02)

Assembler Pass II

INTERMEDIATE CODE (AD,01)

TARGET CODE

(C,200)

200

(IS,04)

(L,01)

201

(IS,05)

(S,01)

200

205

202

(IS,04)

(S,01)

201

204

203

(IS,04)

(S,03)

202

204

(IS,01)

(L,02)

203

205

204

206

(AD,05) 205

005

206

001

207

(IS,02)

(AD,03)

(S,02)+(C,1)

203

(IS,03)

204

(DL,02)

(C,02)

(AD,04)

(S,02)

(DL,02)

(C,02)

206

(L,03) (S,03)

005

206

001

207

203

205

204

(AD,02) 207

205

001 206

207

001

Assembler Examples

SOURCE PROGRAM

AGAIN

INTERMEDIATE CODE (AD,01)

(C,1000)

1000

(IS,09)

(S,01)

1001

(IS,04)

(L,01)

1002

(IS,05)

(S,02)

1003

(IS,03)

(S,02)

1004

(IS,05)

(S,02)

1005

(IS,01)

(L,01)

TERM

1006

(IS,05)

(S,02)

1007

(IS,06)

(S,01)

LE,

AGAIN

1008

(IS,07)

(S,03)

MOVEM

RESULT

1009

(IS,05)

(S,04)

START

1000

READ

MOVER

=‘1’

MOVEM

TERM

MULT

TERM

MOVER

TERM

ADD

=‘1’

MOVEM

COMP

LTORG PRINT

RESULT

STOP

()AD,05) 1010

(L,01)

1011

(IS,10)

1012

(IS,00)

(S,04)

1013

(DL,02)

(C,01)

RESULT

1014

(DL,02)

(C,20)

TERM

1034

(DL,02)

(C,01)

(AD,02)

END

THANK YOU For Details feel free to contact Prof. Sameer Mamadapure sameerm@isquareit.edu.in Department of Information Technology Hope Foundation’s International Institute of Information Technology, P-14 Rajiv Gandhi Infotech Park, MIDC Phase I Hinjawadi, Pune – 411 057 Phone - +91 20 22933441 www.isquareit.edu.in | info@isquareit.edu.in