Sections, elements, and parts
In the load module model, a
control section is the smallest subdivision of a program
that can be relocated as a unit.
The assembled control sections contain the object code for machine
instructions, data constants, and areas.
In the program object model, elements and parts are the smallest subdivisions
of a program that can be relocated as a unit.
Sections allow grouping all element and part contributions
under a single name.
The assembled sections, elements, and parts contain the object code
for the machine instructions, data, and areas.
Consider the concept of a control section at different processing
times:
- At coding time
- You create a control section
or an element or part
when you write the instructions it contains.
In addition, you establish the addressability of each
component within the source module, and provide any symbolic linkages between
components that lie in different source modules. You also
write the linker control statements to combine sections
into a load module or program object, and to provide an entry point address for the
beginning of program execution.
- At assembly time
- High Level Assembler translates the source statements
into object code. Each source module is assembled into one object
module. The contents of the object module are relocatable.
- At linking time
- As specified by linker or binder control statements,
the linker or binder
combines the object code of one or more sections into one
load module or program object. It also calculates the addresses
needed to accommodate common sections and external dummy
sections from different object
modules. In addition, it calculates the space needed to accommodate
external dummy sections.
You can specify the relocatable address of the starting point for
program execution in a linker control statement or
request a starting address
in the operand field of an assembler END instruction.
- At program fetch time
- The control program loads the load module or program object
into virtual storage. All
the relocatable addresses are converted to fixed locations in storage.
- At execution time
- The control program passes control to the
loaded program now in virtual storage, and your program is run.
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