External dummy sections

An external dummy section is a reference control section that lets you describe storage areas for one or more source modules, to be used as:

Work areas for each source module
Communication areas between two or more source modules

Note: External dummy sections are also called "pseudo-registers" in other contexts.

When the assembled object modules are linked and loaded, you can dynamically allocate the storage required for all your external dummy sections at one time from one source module (for example, by using the z/OS GETMAIN macro instruction). This is not only convenient, but it saves space and reduces fragmentation of virtual storage.

Typical bind-time processing of external dummy sections involves "merging" the attributes of identically named external dummy sections, retaining the longest length and strictest alignment among all identically-named external dummy sections. In particular, the lengths of identically named external dummy sections are not additive.

To generate and use the external dummy sections, you need to specify a combination of the following:

DXD or DSECT instruction
Q-type address constant
CXD instruction

For more information about the DXD and CXD instructions, see DXD instruction and CXD instruction.

Note: The names of dummy external control sections might match the names of other external symbols that are not names of dummy control sections, without conflict.