Checking the contents of the parameter area

Generally the mainline routine sets up a parameter area containing information for use by the recovery routine. Key information that a recovery routine might determine from the parameter area includes:

When and where the error occurred
Whether this is a repeated error.

The recovery routine can tell when and where the error occurred through “footprints,” a technique explained under Deciding what to include in the parameter area. Footprints can help the recovery routine to avoid getting into a loop in which the routine requests a retry, and the same error occurs again (recursion). For example, if the recovery routine supplies a bad retry address to the system, and the processing of the first instruction at the given address causes a program check, the first recovery routine to get control is the one that just requested the retry. If the recovery routine requests another retry at the same address, the loop is created.

Note: For an FRR, the system initializes the parameter area to zeros. If an FRR receives control when the parameter area still contains zeros, the error probably occurred before the mainline code initialized the parameter area.

See Setting up, passing, and accessing the parameter area for more information about what the parameter area can contain, and the techniques you can use to provide the most useful information to the recovery routine.