Processing Nonstandard Labels

Generally, the nonstandard label processing routines:

Must be read-only. You cannot store into the routine, nor can you use macro instructions that store into the routine.
Are entered in the addressing mode that is determined by the AMODE option when they are link-edited.
Must save the contents of registers 2 through 14 (in your own work area). Before returning control, your routine must restore the contents of these registers.
Use the XCTL macro instruction (E-form) to exit from your routine and return control to a specific control program module. These modules differ depending on the control program routine from which control was received and the type of label processing being performed. Module names are shown in Table 1 for each SKC SKC control program routine and for each type of label processing routine.

Table 1. Control Program and Label Processing Routine Modules
Label Processing Routine	Control Program Routine	Control Program Module Name
Input Header	Open	IGG0190B
	EOV	IGG0550D
Input Trailer	EOV	IGG0550B
Output Header	Open	IGG0190R
	EOV	IGG0550H
Output Trailer	EOV	IGG0550F
	Close	IGG0200B
Restart Header	Restart	IGC0K05B

Use the GETMAIN or STORAGE macro instruction to obtain virtual storage for all your work areas, including areas used to read in or create a label. Use the FREEMAIN or STORAGE macro instruction to release this virtual storage.

Support for RACF protection of tape volumes might be a part of nonstandard label processing routines.