Page 148 - DCAP507_SYSTEM_SOFTWARE

System Software

Notes 14. The definite relocated address of the address constant is computed as the sum of the PLA
and the ADDR field stated on the ................................... record.
15. The Program Load Address is augmented by the length of the segment and saved in
..................................., turning out to be the PLA for the next segment.

9.3 Summary

 By means of an absolute loading scheme the programmer and the assembler execute the
tasks of location, relocation, and linking.
 The object file for absolute loader comprises of a series of text records completed by a
transfer record.

 The direct linking loader processes programs produced by the assembler, FORTRAN
compiler, or some other compiler.

 The ESD records enclose the information essential to build the external symbol dictionary
or symbol table.
 External symbols are symbols that can be referred away from the subroutine level.

 The TXT records enclose blocks of data and the relative address at which the data is to be
positioned.
 The END record states the end of the object file. If the assembler END record has a symbol
in the operand field, it states a start of execution point for the whole program (all
subroutines).

 The Global External Symbol Table (GEST) is used to amass the external symbols defined
by means of a Segment Definition (SD) or Local Definition (LD) entry on an External
Symbol Dictionary (ESD) record.

9.4 Keywords

Absolute Loading: By means of an absolute loading scheme the programmer and the assembler
execute the tasks of location, relocation, and linking.
External Symbols: External symbols are symbols that can be referred away from the subroutine
level.
Global External Symbol Table: The Global External Symbol Table (GEST) is used to amass the
external symbols defined by means of a Segment Definition (SD) or Local Definition (LD) entry
on an External Symbol Dictionary (ESD) record.

Object File: The object file for absolute loader comprises of a series of text records completed by
a transfer record.

9.5 Review Questions

1. Describe functions of absolute loader.

2. Illustrate the concept of Design of an Absolute Loader.
3. Describe databases required by each pass of loader.
4. Explain the design of direct linking loader.
5. What are the various segments to the object file? Illustrate.

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