Accessing execution parameters

You access information in the PARM field of an EXEC statement by referring to the contents of general register 1. If you do not specify the PARM field of the JCL EXEC statement, register 1 and register 15 contain the same value on initial entry.

When control is given to the program, general register 1 contains the address of a fullword which, in turn, contains the address of the data area containing the information.

The data area consists of a halfword containing the count (in binary) of the number of information characters, followed by the information field. The information field is aligned to a fullword boundary. Figure 1 shows how the PARM field information is structured.

Figure 1. Access to PARM field

                             General register 1
                        ┌──────────────────────────────────────┐
           ┌────────────┤     Address of Fullword              │
           │            └──────────────────────────────────────┘
           │ Points to
           │            ┌──────────────────────────────────────┐
           └───────────>│     Address of Data Area             ├───────────┐
                        └──────────────────────────────────────┘           │
                                                                 Points to │
           ┌───────────────────────────────────────────────────────────────┘
           │
           │            ┌─────────────────┬────────────────────┐
           └───────────>│ Count in Binary │ Information Field  │
                        └─────────────────┴────────────────────┘