AI and mainframe assembler

ChatGPT returned this analysis:

MYPGM    CSECT , 
         BAKR  R14,0 
         LR    R12,R15
         USING MYPGM,R12
*
         MVI   FIELD1,C'A'     <-- OK
         MVI   FIELD2,C'B'     <-- POTENTIAL PROBLEM
         MVI   FIELD3,C'C'     <-- OK
*
         PR    , 
FIELD1   DS    C' '
FIELD2   EQU   0               <-- DEFINITE PROBLEM
FIELD3   DS    C' '
         DROP  R12 
         END  

Issue:

• FIELD2 EQU 0 defines FIELD2 as an absolute address 0.
• MVI FIELD2,C'B' attempts to store the value 'B' at memory location 0, which is almost always not owned or not accessible by user programs.

Result: That instruction attempts to modify address zero, triggering a S0C4 ABEND (protection exception).

Grok returned this analysis:

The instruction that would cause an S0C4 ABEND (protection exception) in the provided HLASM program is:

MVI   FIELD2,C'B'

• In the program, FIELD2 is defined using EQU 0, which means FIELD2 is a symbolic constant with the value 0, not a storage location. It does not allocate any actual memory that can be modified.
• The instruction MVI FIELD2,C'B' attempts to move the character 'B' into the address represented by FIELD2, which is 0. Address 0 is typically in a protected area of storage (low core) on a z/OS system, and attempting to write to it will cause a protection exception, resulting in an S0C4 ABEND.

Thus, the MVI FIELD2,C'B' instruction is the culprit, as it attempts to write to an invalid address (0).

Gemini returned this analysis:

The instruction that would cause an S0C4 ABEND is:

MVI   FIELD2,C'B'

The root cause of the abend lies in how FIELD2 is defined in the program's data section:

FIELD2   EQU   0

When the processor attempts to execute this MVI instruction, the system's memory protection hardware will detect the unauthorized attempt to write to a protected location, triggering a protection exception, which results in the S0C4 abend.

Copilot returned this analysis:

The instruction that would likely cause a S0C4 ABEND (protection exception or invalid address reference) is:

MVI   FIELD2,C'B'

Here's why:

• FIELD2 is defined as EQU 0, which means it's equated to absolute address 0.
• The MVI instruction tries to move an immediate byte ('B') to the storage location specified by the operand—in this case, address 0.
• Writing to address 0 is not permitted in z/OS user programs, and attempting to do so triggers a S0C4 ABEND due to an invalid storage reference.

The assembler allows this because EQU just assigns a value—it doesn't reserve storage. But when executed, that MVI is essentially trying to write to the zero location in memory, which is a big no-no in virtual storage environments. Sneaky little time bomb, isn’t it?

Claude generated a lot of analysis and this the synopsis:

Problem Instruction

The instruction that would cause a S0C4 ABEND on a z/OS system is:

            MVI   FIELD2,C'B'
        

Root Cause Analysis

The problem lies in how FIELD2 is defined in the program:

FIELD2   EQU   0

This EQU 0 directive assigns FIELD2 the absolute address 0 (null pointer). When the MVI FIELD2,C'B' instruction executes, it attempts to store the character 'B' at memory address 0, which is protected memory on z/OS systems.