As far as I can recall there has never been a requirement for a user SVC to change in any way whatsoever in as long as I have been in MVS, OS/390 and z/OS (hence including z/OS 1.7). User SVCs written in the 70's likely still work. There certainly might be functional reasons why one would want to change a routine (such as if you wanted to allow a larger set of callers, such as those in AMODE 64 passing data above the bar), but those reasons are no different than they would be for any other routine.
When z/Architecture was implemented, one of the reasons that AMODE 64 is indicated by the presence both of PSW bit 31 and PSW bit 32 is so that existing SVC routines that look at the PSW in the RB and treat AMODE 24 differently than AMODE 31 would, if unchanged, treat an AMODE 64 invoker the same as an AMODE 31 invoker, rather than the same as an AMODE 24 invoker. (I.e., if they tested PSW bit 32 for "1" and when "on" treated an input 32-bit GPR as a 31-bit address, as opposed to clearing the high 8 bits when PSW bit 32 was "0" for an AMODE 24 caller). Just out of curiosity, if anyone has an example of such a requirement, it might be entertaining to post... Peter Relson z/OS Core Technology Design ---------------------------------------------------------------------- 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
