dump/XDC: XDCMMEF - Technical and ISV overview

The Module Mapping Extraction File (XDCMMEF) program can be used to extract information that z/OS ignores when loading a program from a load library or program object library into storage.

During the loading process, z/OS uses the text records in the load module or program object and information in the relocation records to place the loaded item in storage.

In the normal z/XDC case, z/XDC can load this information from the libraries used to load the programs, because those libraries are locally available.  However, when processing a dump, the information is only available in libraries that reside on the system where the dump was created.

When XDCMMEF is run on the system where a dump was created, it creates a dataset containing the information that dump/XDC can use to determine the layout of modules loaded into storage. This information will become visible in dump/XDC.  It will include the system nucleus, and/or programs located in the (P)LPA, and/or programs located in the linklist, and/or programs loaded from user libraries.

There are several reasons why Cole Software wrote the XDCMMEF program:
  • Dumps do not contain load module (or program object) layout information.
  • This information can be very useful when examining a dump.
  • Extracting the relevant information must be done on the system that produced the dump.
  • The extracted information must be compact and easily transported.
  • The extracted information must not include information that could potentially be sensitive.

The extracted information contains a module’s ESD map (the layout of all the CSECTs within the module).

In other words, the extracted data does not contain any part of a load module that actually gets loaded into storage and executed. While the code itself is present in the dump, it is not in a form that allows it to be executed

The output dataset can be sent along with the dump, and dump/XDC can load the information from that dataset into storage, and use it instead of trying to load that information from a local dataset.

XDCMMEF’s output dataset can safely be FTP’d in binary (image) mode
The MMEF utility is distributed as a TSO XMIT package.  To extract the utility, use TSO RECEIVE.