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How Systems Programmers Make Changes to LPA Modules

One final point concerns how systems programmers make changes to LPA modules. Because LPA is read‑only and is frozen between IPLs, systems programmers need a way of making changes to LPA modules. They usually use one of the following methods to do this; they:

• Use the IBM‑provided modified link pack area (MLPA).
• Use the real storage fixed link pack area (FLPA).
• MODREP LPA modules.

MODREP is a technique that loads a module into some accessible area of storage (usually CSA). Then the LPA directory is updated to point to the new module instead of the old one in LPA. MODREPs can be detected from the LPA Display (3.4) by looking for module addresses that fall above or below the bounds of the virtual storage LPA. There are numerous products and system programming tools that perform this type of processing. One such example is CA SYSVIEW.

Before you begin your review of the link pack area, read the following section on fixed and modified LPA. They should always be considered as part of an LPA review.