Registers on entry

Standard OS linkage conventions are used, and the registers on entry to the filter module are:
  • R13 contains the address of a standard 18-word save area
  • R14 contains the return address to the exit
  • R15 contains the filter's entry point address
  • R1 contains the address of a list of six fullwords that address:
    1. A fullword containing the exit_type
    2. A fullword integer containing the action code
    3. A fullword integer where the filter puts the return_code
    4. A 4-fullword handle area
    5. A fullword integer containing the ADATA record_length
    6. The ADATA record

      The high-order bit of the last fullword address is set to one.

    Figure 1 shows the six fullwords in the parameter list.

Figure 1. Filter module parameter list format