On Wed, 18 Jun 2025 at 12:31, Schmitt, Michael <[email protected]> wrote:
> I don't just mean undocumented op codes, I'm also including documented > opcodes but undocumented operand values. > There are long-standing rumours that MVCOS (MVC On Steroids...) has more options than are documented. There have been un- or little-documented instructions for which some operands were later documented in the PofO. I'm thinking of Move Page (MVPG), which supported expanded storage in iirc ESA/390, then had the expanded storage operands dropped, and lately has had storage key related options added. What remains true in all this is that in problem state there should be no instructions - documented or not - that can cause an integrity exposure. (Of course an OS can have integrity exposures that allow unprivileged programs to do Bad Stuff, but at the architectural level no amount of issuing instructions is allowed to break the rules.) The same is certainly not true of running in supervisor state. Tony H. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
