Loader and Link-editor: Once the
assembler procedures an object program, that program must be placed into memory
and executed. The assembler could place the object program directly in memory
and transfer control to it, thereby causing the machine language program to be
execute. This would waste core by
leaving the assembler in memory while the user’s program was being executed.
Also the programmer would have to retranslate his program with each execution,
thus wasting translation time. To over come this problems of wasted translation
time and memory. System programmers developed another component called loader
“A loader is a program that places
programs into memory and prepares them for execution.”
It would be more efficient if
subroutines could be translated into object form the loader could”relocate”
directly behind the user’s program. The task of adjusting programs o they may
be placed in arbitrary core locations is called relocation. Relocation loaders
perform four functions.
1.
Allocate
space in memory for the programs.
2.
Resolve
symbolic references between object decks (linking).
3.
Adjust
all address-dependent locations, such as address constants, to correspond to
the allocation space (relocation).
4.
Physically
place the machine instructions and data into memory (loading).
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