Implementing the NEWS User Exit › NEWS Exit Coding Requirements

NEWS Exit Coding Requirements

This section describes the coding requirements for NEWS exits.

Maintain Registers on Entry to an Exit

You must observe standard linkage conventions when coding an exit.

On entry, the registers must be saved in the caller’s save area, and on exit, restored (except R15, which must contain a return code).

On entry, register contents are as follows:

On exit, the same registers should be restored except for R15, the exit return code.

Parameter List Format

The parameter list addressed by Register 1 on entry consists of one or two contiguous fullwords. If there are two fullwords, the first contains the address of another fullword that holds a function code indicating the reason that the exit is being called.

The second fullword of the parameter list is present for function codes 0 and 4 only. The high-order bit of this last (or solitary) fullword is not set; therefore, the length of the parameter list must be determined by examination of the function code as follows:

• For function code 0, the second word of the parameter list contains the address of an area that contains system data that may be of value to the exit in determining its processing options.
• For function code 4, the second word of the parameter list contains the address of the CNM record being passed to the exit for examination.
• For function code 8, the parameter list contains one word.

The following illustration shows the structure of the NEWS user exit parameter list pointers.