Re: Curosity Question About ESTA and MSTA
The short answer to your question is No. I think you have a fundamental misunderstanding of the operation of the Linkage Stack mechanism. You should carefully read "Chapter 2. Linkage stack" within IBM publication SA23-1394-00 "z/OS MVS Programming: Extended Addressability Guide" (this is the z/OS 2.1 version, but nothing of great significance has changed in this area for quite some time). The Modifiable Area of a Linkage Stack frame is typically intended to be used in association with ARR's. For some relevant discussion, look at "Chapter 18. Providing recovery" within IBM publication SA23-1371-02 "z/OS MVS Programming: Authorized Assembler Services Guide Version 2 Release 1" With respect to the z/Architecture perspective on the Modifiable Area of a Linkage Stack frame, read subtopic "Adding and Retrieving Information" within major topic "Linkage-Stack Introduction" within IBM publication SA22-7832-11 "z/Architecture Principles of Operation". Here is the text extracted from that subtopic: + Adding and Retrieving Information + + The instruction MODIFY STACKED STATE can be used by a program to + place two words of information, contained in a designated + general-register pair, in an area, called the modifiable area, of + the current linkage-stack state entry (a branch state entry or a + program-call state entry). This is intended to allow a called + program to establish a recovery routine that will be given control + by the control program, if necessary. Bob
Re: Curosity Question About ESTA and MSTA
No, MSTA will not change these fields. But I am curious as to what you are trying to build and why you want to change the AX while in stacked state/PC routine. On Sun, 10 Jun 2018 18:58:16 GMT "esst...@juno.com" wrote: :>Is this possible ? :> :>A hypothetical scenario - :> :>A Long Running Started Task issues an Extract Stacked State Instruction (ESTA) using code zero. :>LA R2,00 :>ESTA R0,R2 :>. :>Code zero returns the PKM, SASN, EAX, and PASN of the Started Task. :>The Started Task provides the EAX to other jobs. :>. :>A Problem Program (Non Supervisor state) retrieves the Started task EAX. :>. :>The Problem Program issues an Extract Stacked State Instruction to obtain an save its PKM, SASN, EAX, and PASN. :>. :>Can the Problem Program Issue a Modify Stack State Instruction (MSTA) :>replacing its own EAX with that EAX of the Started Task ? :>. :>For some reason I expected this to be an Exception of some sort. :>ESTA and MSTA are not privileged instructions. :>. :>Would this sequence of Instructions actually change the problem programs EAX in other words giving it the EAX of the Started Task ? :>. :>. :>Paul :>. -- Binyamin Dissen http://www.dissensoftware.com Director, Dissen Software, Bar & Grill - Israel Should you use the mailblocks package and expect a response from me, you should preauthorize the dissensoftware.com domain. I very rarely bother responding to challenge/response systems, especially those from irresponsible companies.
