<sorry, I had posted this to IBM-Main, incorrectly> >The z/OS system service GETMAIN does not preserve the high-order half of GP registers That is incorrect.
>and there are probably others in z/OS like that. If there are, please let us know. There is no documentaiton that says that this is the case. The standard linkage convention is clearly documented. All services that do not document otherwise are expected to preserve the high halves of GPRs 2-14 (although I wouldn't be shocked if "14" isn't included in some case) Back to the original question: Yes, it is the caller's responsiibility to meet the requirements of the service (which includes the size of the save area).. While it is possible to have a "tri-modal" entry point, we have typically found it not worth doing so, and have provided alternate entries for the AMODE 64 caller, as that entry requires a larger savearea and by convention has a different parameter list format (8-byte-wide entries). Peter Relson z/OS Core Technology Design
