Page 130 - DCAP507_SYSTEM_SOFTWARE

System Software Nisha Sethi, Lovely Professional University

Notes Unit 9: Design of an Absolute Loader

CONTENTS

Objectives
Introduction
9.1 Design of an Absolute Loader
9.2 Design of a Direct Linking Loader
9.2.1 Specification of Problem

9.2.2 Specification of Data Structures
9.2.3 Algorithm
9.3 Summary

9.4 Keywords
9.5 Review Questions
9.6 Further Readings

Objectives

After studying this unit, you will be able to:

 Understand the design of Absolute Loader
 Discuss the design of direct linking loader

Introduction

By means of an absolute loading scheme the programmer and the assembler execute the tasks of
location, relocation, and linking. Thus, it is only essential for the loader to read records of the
object file and shift the text on the records into the absolute locations declared by the assembler.
In this unit, you will understand the design of Absolute Loader and design of direct linking
loader.

9.1 Design of an Absolute Loader

There are two kinds of information that the object file must contain from the assembler to the
loader. Primarily, it must transmit the machine instructions that the assembler has formed
along with the allocated core locations. Next, it must transmit the entry point of the program,
which is where the loader is to transport control when all instructions are loaded. The algorithm
for an absolute loader is pretty simple. The object file for this loader comprises of a series of text
records completed by a transfer record. So, the loader should read one record at a time, moving
the text to the location stated on the record, until the transfer record is accomplished. Here the
assembled instructions are in core, and it is only essential to transmit to the entry point stated on
the transfer record. A flowchart for this process is depicted in figure 9.1.

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