14-06-2012, 05:12 PM
Direct linking loader
DIRECT LINKING LOADER.pptx (Size: 82.88 KB / Downloads: 89)
A Direct linking loader is a general relocatable loader.
Allowing the programmer the multiple procedure segment and multiple data segment.
It gives complete freedom in referring data and instructions contained in other segments.
The assembler must give the loader the following information with each procedure or data segment.
the length of segment
A list of all the symbols in the segment that may be referred by other segment and their relative location within the segment.
Information as to where address constants are located in the segment and adscription of how to revise their values.
The machine code translation of the source program and the relative address assigned.
Card number 14 contains define constant(DC) pseudo-op .
It instruct the assembler to create a constant with the value of address of the TABLE , and causes this constant to be placed in the location labeled POINTER
Assembler does not know the final absolute address of TABLE
It knows the address is the 28th byte from the beginning of this program
Design of an absolute Loader
In absolute loading scheme the programmer and assembler perform the task of allocation ,relocation and linking
It is only necessary for the loader to read cards of the object deck and move the text on the cards into the absolute location specified by the assembler.
There are two types of information that the object deck must communicate from assembler to the loader.
First, it must convey the machine instructions that the assembler has created along the assigned core locations.
Second ,it must convey the machine instructions that the assembler has created along with the assigned core locations.