Page 134 - DCAP507_SYSTEM_SOFTWARE

System Software

Notes i=0;
}
count=0;
}
}
Self Assessment

Fill in the blanks:
1. By means of an ............................. loading scheme the programmer and the assembler execute
the tasks of location, relocation, and linking.

2. There are two kinds of information that the object file must contain from the assembler to
the .............................
3. The ............................. for absolute loader comprises of a series of text records completed by
a transfer record.

9.2 Design of a Direct Linking Loader

The obscure traits have been omitted, and where substitute formats are probable, only the
simplest is provided. The design steps followed will parallel those taken in the plan of an
assembler.

Notes Since the direct-linking loader requires to know the absolute (load time) values of
some external symbols before it can carry out the alterations on address constants, it needs
two passes.

9.2.1 Specification of Problem

The organization helps the tasks to be done by its relocating loader. A direct access machine was
essential to relocate the address part on almost all instructions. In the mainframe system,
instruction relocation is finished by the utilization of the base register, which is set by neither
the assembler nor the loader. Thus, the mainframe relocating loader can treat instructions
precisely like non relocatable data (full word constants, characters, etc.). Nevertheless, address
constants must still be relocated.

Example: The following instructions:

Irrespective of where the program is loaded, the LOAD instruction will be unaffected as long as
DATA remains 96 bytes from the starting of the program. The real load address may effect in a
different address for the S-field, based upon the program's load location.

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