On Wed, Apr 24, 2024 at 06:02:30PM +0000, Jim Mulder wrote: > From software point of view, the only difference between an operation > exception for a 00xx or 00xxxxx or 00xxxxxx.... in the instruction > stream vs an invalid opcode B2xx.... in the instruction stream > would be the Instruction Length Code, and I don't think that would > be an important distinction to software.
> The invalid 00 opcode provides sufficient capability to cause an > operation exception, with diagnostic information of an arbitrary length > following the 00 opcode. What's important is that the 00xx invalid opcode is only 2 bytes so it only requires overlaying 1 instruction. A 4 byte (or longer) invalid opcode wouldn't fit if the original instruction was 2 bytes and there were branches to the instruction after it -- they would wind up branching into the middile of the 4 byte invalid opcode. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
