S0C5 addressing exception

S0C5 is an addressing exception: the program used an address that is not valid — for example, dereferencing a null or garbage pointer.

What it means

• The CPU could not translate the address the program asked for.
• In COBOL this points at pointer handling: SET ADDRESS, or a linkage-section item used without a proper CALL.

Common causes

• Uninitialized pointer (never SET) used to address data.
• Pointer explicitly set to NULL and then dereferenced.
• LINKAGE SECTION item referenced in a program that was not CALLed with that parameter.
• Overlay corrupted a pointer value.

How to diagnose

• Check register contents in the dump for zero or garbage pointer values.
• Trace where the pointer was last set.
• Confirm the program is CALLed with the expected parameters if LINKAGE is involved.

How to fix it

• Initialize pointers (SET ptr TO NULL) and test before use.
• Guard linkage items: only reference them when the program is properly CALLed.

Example: Null-check pointers before use

A one-line NULL test prevents the abend.

Interview tip

• Q: How would you troubleshoot a S0C5 addressing exception in production?
• A: I would inspect the pointer value in the dump, trace its last SET, and confirm whether the program was invoked with the right parameters.

Prevention checklist

• Initialize all pointers.
• Validate CALL interfaces between programs.