Null pointer and null address detection

Null pointer and null address detection provides you with the capability to detect the occurrences in your application where an instruction references a null address or reads from a null pointer.

This support uses the program event recording (PER) zero-address-detection facility. A PER zero address detection event occurs when an instruction accesses storage by using an operand address formed from a general register that contains zero. For more information about the detection event, see z/Architecture® Principles of Operation.

Use this support with caution. Many detection events might occur during system processing, which do not represent any problems or defects.

This support provides a breakpoint type called Stop at null pointers and addresses to stop at detection events and an option to log detection events to a file on the z/TPF file system.

The logging capability is independent of the breakpoint. If you do not set this breakpoint but turn on the logging option, the z/TPF debugger does not stop the application when a detection event occurs, but the event is written to the log file.