System Programming :: Assembler

Dr. Mahesh R. Sanghavi
Unit- I
Introduction
SPOS
By

Unit- I
Course Outcome
SPOS
To analyze & synthesize various
system software & understand the
design of two pass assemblers.

Unit- I
Outline
SPOS
Introduction
Software
Assemblers

Unit- I
SPOS
instruct
Component
System
is
Collection
of
eg.
College
Programming
is
Way to
compute
the
Various Task
To perform
system programming is an art of designing and implementing system Programs.
System introduction

Unit- I
System introduction
SPOS
Software
Collection
is
of
Many
Programs
Software
System
Software
Application
Software
assist general
user application
Operating System
Assembler
software developed
for the specific goal
Media player
Adobe Reader

Unit- I
SPOS
System Program
Required
Effective Execution
General user Programs
Computer System
are
for
of
on
System Programming
designing and implementing
system programs
Is an art of
System introduction

Unit- I
System Software
SPOS
Text Editor
Editor
Computer
Program
A user
create and revise a
document
Text Editor
Program
Primary
Elements
Edited
Character
String
is
In which
being are
is
That allows
to
Notepad
Example

Unit- I
SPOS
Text Editor
program
Used for
is
Editing plain
text files
With the help
Text Editor
of
Write Your Program
You can
C | Java
Prog.
Example
System Software

Unit- I
SPOS
System Software
Loders
Program
Object Code
As input
is
That takes
Prepares
and
Execution
Them for
Initiates
it
Execution

Unit- I
SPOS
Loders
System Software
Relocation
Linking
Allocation
Loading
Functions

Unit- I
SPOS
Loders
System Software
Allocation
Functions
Loader allocates space for programs in main
memory.

Unit- I
SPOS
Loders
System Software
Relocation
Functions
● Adjusting all address dependent location.
● E.g. If we have two Programs Program A and Program B.
● Program A is saved at location 100.
● And user wants to save Program B on same location.
That is physically not possible.
● So loader relocates program B to some another free
location

Unit- I
SPOS
Loders
System Software
Linking
Functions
● If we have different modules of our
program.
● Loader links object modules with each
other.

Unit- I
SPOS
Loders
System Software
Loading
Functions
Physically loading the machine instructions and
data into main memory.

Unit- I
SPOS
Outline
❏ Review of previous session
❏ Assembler
❏ Macro Processor
❏ Compiler
❏ Debugger
❏ Assembly Language

Unit- I
SPOS
Assembler
Machine Lang.
Assembly Lang.
Program Assembler
Translate

Unit- I
SPOS
Macro Processor
Macro
Sequence
Source Lang. Code
Referred many times
Allows
of
Defined @ once
To be

Unit- I
SPOS
Macro
Macro Processor
Syntax
Macro name [ set of parameters ]
// macro body
Mend
★ A macro processor takes a source with
macro definition and macro calls and
replaces each macro call with its body

Unit- I
SPOS
Compiler
Low Level Lang.
High Level Lang.
Compiler
Converts

Unit- I
SPOS
Compiler
Benefits of writing a program in a high level language
Increases productivity Machine Independence
It is very easy to write a program in a
high level language
A program written in a high level language is
machine independent.

Unit- I
SPOS
Debugger
Debugging tool helps programmer for testing and debugging
programs
It provides some facilities:
•Setting breakpoints.
•Displaying values of variables.

Unit- I
SPOS
Assembly Language
● Assembly language is middle level language.
● An assembly language is machine dependent.
● It differs from computer to computer.
● Writing programs in assembly language is very easy as compared to
machine(binary) language

Unit- I
SPOS
Assembly Language
Assembly language programming Terms
Location Counter points to the next instruction
(LC)
Literals Constant Values

Unit- I
SPOS
Assembly Language
Assembly language programming Terms
Symbols Name of variables and labels
Procedures Methods | Function

Unit- I
SPOS
Assembly Language
Assembly language Statements:
Imperative
Statements
Declarative/Declaration
Statements
Assembler Directive

Unit- I
SPOS
Assembly Language
Imperative
Statements
❏ Imperative means mnemonics
❏ These are executable statements.
❏ Each imperative statement indicates an
action to be taken during execution of the
program

Unit- I
SPOS
Assembly Language
Declarative/Declaration
Statements
❏ Declaration statements are for
reserving memory for variables.
❏ We can specify the initial value of
a variable.
Types
DS DC
Declare Storage Declare Constant

Unit- I
SPOS
Assembly Language
Declare Storage
Syntax
[ Label ] DS < Constraint Specifying size >
X DS 1
Example

Unit- I
SPOS
Assembly Language
Declare Constant
Syntax
[ Label ] DC < Constraint Specifying values >
X DC ‘ 5 ’
Example

Unit- I
SPOS
Assembly Language
Assembler Directive
❏ Assembler directive instruct the
assembler to perform certain actions
during assembly of a program
Some assembler directive are:
START < Address Constant >
END

Unit- I
SPOS
Assembly Language
Advance Assembler Directive
Origin
EQU
USING
DROP
LTORG

Unit- I
SPOS
Outline
❏ Review of previous session ❏ Identify Statement
❏ Pass 1 Assembler
❏ Machine Structure

Unit- I
SPOS
Assembly Language
Sample Assembly language Code
1. START 100
2. MOVER A REG, X
3. MOVER B REG, Y
4. ADD A REG, Y
5. MOVEM A REG, X
6. X DC ‘10’
7. Y DS 1
8. END

Unit- I
SPOS
Assembly Language
Identify types of statement 1. START 100
IS DS AD
Sr. No
1.
2.
3.
4.
2. MOVER B REG, Y
3. MOVER B REG, Y
4. ADD A REG, Y
Code

Unit- I
SPOS
Assembly Language
Identify types of statement 5. MOVEM A REG, X
IS DS AD
Sr. No
5.
6.
7.
8.
6. X DC ‘10’
7. Y DS 1
8. End
Code

Unit- I
SPOS
Assembly Language
Some Definitions
LC
Symbol Literals
Procedures

Unit- I
SPOS
Machine Structure

Unit- I
SPOS
Machine Structure
Machine Instruction Format

Unit- I
SPOS
Assembler
Assembler
Pass 1
Assembler Pass 2
Assembler
Separate Generate the
machine code
Determine Storage
Requirement
Build the Symbol
Table
Labels
Operand Fields
Mnemonic Opcode

Unit- I
SPOS
Pass 1 Assembler
Uses
How pass 1 assembler works?
Machine opcode Table
Symbol Table Pool Table
Literal Table
Data Structure
Pass 1
Assembler
❏ Contents of MOT are fixed for an assembler.

Unit- I
SPOS
Apply LC
Observe code
Pass 1 Assembler

Unit- I
SPOS
Symbol Table
Construct
Pass 1 Assembler

Unit- I
SPOS
Construct
Literal Table
Pass 1 Assembler

Unit- I
SPOS
Pool table contains starting
literal(index ) of each pool.
Pool Table
Pass 1 Assembler

Unit- I
SPOS
|
Construct
Machine Code Intermediate Code
Machine opcode Table
needs
Pass 1 Assembler

Unit- I
SPOS
Enhanced Machine Opcode Table
Pass 1 Assembler

Unit- I
SPOS
Intermediate code
❏ For every line of assembly statement, one
line of intermediate code is generated
❏ Each mnemonic field is represented as
(Statement Class , Machine code)
Pass 1 Assembler

Unit- I
SPOS
Intermediate code
Statement Class
Can be
IS DS | DC AD
MOVER AREG, X
Mnemonic Field Operand Field
IC for mnemonic field of above line is ,
(Statement Class , Machine code)
( IS,04 )
From MOT
Pass 1 Assembler

Unit- I
SPOS
Intermediate code
Operand Field
S
Symbol
L
Literal
RG
Register
CC
Condition Codes
C
Constant
Operand Field
( operand Class , reference )
represented
For a symbol or literal the reference field
contains the index of the operands entry in
symbol table or literal table.
START 200 (AD, 01) (C, 200)
E.g.
MOVER AREG, X
(IS, 04) (RG, 01) (S, 0)
Mnemonic
code
Pass 1 Assembler

Unit- I
SPOS
Intermediate code

Unit- I
SPOS
Example 2
Assignment

Unit- I
SPOS
Outline
❏ Review of previous session
❏ Pass 2 Assembler

Unit- I
SPOS
Pass 2 Assembler
Pass 2 Assembler
Intermediate code Machine Code
Pass 2 Assembler
❏ Processes the intermediate representation (IR) to
synthesize the target program.

Unit- I
SPOS
Pass 2 Assembler
Pass 2 Assembler
Data Structure
Pass I Pass II
Intermediate code
Source
Program
Target
Program
Data Access
Control transfer

Unit- I
SPOS
Pass 2 Assembler
Analysis Phase Synthesis Phase
Vs

Unit- I
SPOS
Assembler

Unit- I
SPOS
Assembler
Pass 1 Pass 2
Intermediate Code Machine Code
Output of Pass 1 | Pass 2 Assembler
Generates Generates

Unit- I
SPOS
Assembler
Variants
Variants I Variants II
Variants of Intermediate Code

Unit- I
SPOS
Assembler
Variants I
In Variant I, each operand is represented by a pair of the form
(operand class, code).
The operand class is one of:
1. S for symbol
2. L for literal
3. C for constant
4. RG for register.

Unit- I
SPOS
Assembler
Variants I

Unit- I
SPOS
Assembler
Variants II
In variant II, operands are processed selectively.
Constants and literals are processed. Symbols, condition
codes and CPU registers are not processed.

Unit- I
SPOS
Assembler
Variants II

System Programming :: Assembler

System Programming :: Assembler

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