FRIDAY, OCTOBER 2, 2026
s390
s390: Enforce register pair constraints for clclu instruction
Assembler now enforces register pair constraints for s390 clclu instruction.
This commit updates the s390 assembler to enforce architectural constraints on the register operands for the clclu instruction. It ensures that both R1 and R3 operands designate an even-odd pair of general registers and are even-numbered registers, preventing specification exceptions.
In Details
This patch modifies the s390 assembler to enforce the architectural requirements for the clclu instruction's R1 and R3 operands. It ensures they are even-numbered registers that form even-odd register pairs, aligning with the z/Architecture Principles of Operation and preventing specification exceptions.
For Context
- s390
- A family of mainframe computer architectures developed by IBM.
- assembler
- A program that translates assembly language into machine code.
- register pair
- On some architectures, certain instructions require two adjacent registers to function as a single, wider operand. For example, an even-numbered register and the immediately following odd-numbered register can form a pair.
- specification exception
- An error condition detected by the hardware when an instruction is executed with operands or conditions that violate the architecture's rules.
- clclu
- A s390 machine instruction for compare logical characters under mask.