FRIDAY, OCTOBER 2, 2026
s390
s390: Enforce register pair constraints for kxbr instruction
Assembler now enforces FP register pair constraints for s390 kxbr instruction.
This commit updates the s390 assembler to enforce architectural constraints on the floating-point register operands for the kxbr instruction. It ensures that both R1 and R2 operands designate valid floating-point-register pairs, preventing specification exceptions.
In Details
This change updates the s390 assembler to enforce the architectural requirement that the kxbr instruction's R1 and R2 operands must be valid floating-point-register pairs. This ensures correct instruction encoding and adherence to the z/Architecture Principles of Operation, 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.
- floating-point register
- Specialized registers used to store and manipulate floating-point numbers.
- 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.
- kxbr
- A s390 machine instruction that operates on floating-point registers.