Yes, the high bit convention has to change for interfaces that accept 64 bit addresses. The issue is that in order to change the convention for 32 bit programs, either 1 - an additional AMODE would need to be supported by the hardware, or 2 - EVERY existing program would have to be redesigned and retested in order to follow a new convention. The limited benefit of allowing for an extra 2GiB of virtual storage to an address space that can, using 64 bit addressing, already support 16 exabytes - 2GiB seems like a massive waste of resources.
Wayne Driscoll Rocket Software Note - All opinions are strictly my own. -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Paul Edwards Sent: Monday, May 7, 2018 8:51 AM To: [email protected] Subject: Re: GETMAIN LOC=32 On Mon, 7 May 2018 08:42:00 -0500, Joel C. Ewing <[email protected]> wrote: >From the early days of S/360 the high-order bit of a full-word address >pointer has a documented function in standard subroutine linkage of >indicating the last parameter address for subroutines that accept a >variable number of parameters, so even if the architecture might not >restrict using that bit for memory addressing, long-standing software >standards for AMODE24 and AMODE31 do. > >Changing the documented conventions for using the high-order bit of a >32-bit address word This convention *already* has to change for anyone considering moving to AM64 and using 64-bit pointers. There's no reason why it should be mandatory for a full 64-bit application, but disallowed for a 32-bit program. Updating 32-bit programs to conform to AM64 requirements is far less onerous than the massive changes required to create a 64-bit application. > to create a new "AMODE32" would potentially adversely effect too many >things for minimal benefit. Nobody is affected, and the benefit of going from a 2 GiB address space to a 4 GiB address space is a great improvement. BFN. Paul. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ================================ Rocket Software, Inc. and subsidiaries ■ 77 Fourth Avenue, Waltham MA 02451 ■ Main Office Toll Free Number: +1 855.577.4323 Contact Customer Support: https://my.rocketsoftware.com/RocketCommunity/RCEmailSupport Unsubscribe from Marketing Messages/Manage Your Subscription Preferences - http://www.rocketsoftware.com/manage-your-email-preferences Privacy Policy - http://www.rocketsoftware.com/company/legal/privacy-policy ================================ This communication and any attachments may contain confidential information of Rocket Software, Inc. All unauthorized use, disclosure or distribution is prohibited. If you are not the intended recipient, please notify Rocket Software immediately and destroy all copies of this communication. Thank you. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
