> :>> :>Which control registers did you have in mind? > > :>> How about CR4? > > :>Stupendously bad idea. Don't even hallucinate about it. > > Why?
Aside from the severe integrity risks... CR3 and CR4 are not supposed to be loaded individually. CR4 has the EAX and PASN and now the PASN sequence no. too. The only legal ways it can be set are via the LASP, PC and PR/PT/PTI instructions. LASP is not a recognized interface for use outside of the control program. The operating system has an internal service that uses LASP, which (implicitly) loads CR3 and CR4 and does all of the related ASN translation in a single operation. The PC instruction requires overt setup via OS services, so it is ok and when the PT/PTI instructions are used in the normal fashion to return from a basic PC-SS they are ok too. However, just like LCTL, there is nothing to stop you from using them directly to alter the PASN - even though it's a really bad idea. As of z/OS 1.6 and on hardware with the ASN reuse facility (z990 and z9) the high order halves of the control registers that have ASNs will contain a sequence number. The OS knows the right number and you may or may not. Having access to the wrong address space can have some seriously unintended consequences. There are also space switch events that will be recognized if/when the new PASN/SASN differs from the current. They will mostly "just work" unless the target address space is not designated (via a bit in the ASTE/ASCE) as valid for cross memory access. If you successfully alter the PASN (or SASN) and an interrupt occurs (e.g. page fault) the bind-break routine is going to catch you at it and issue a S058 abend. There are a whole bunch of integrity issues. When you use the official interfaces, the OS keeps you out of the weeds. When you DIY you're on your own. In this particular area, I wouldn't even consider coloring outside the lines. The results can be really ugly and there just isn't any need for it. CC ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
