We have already discovered this the hard way! We have a C-callable assembler
routine to load modules
using SVC 8. Its parameter is a C string which is copied into an 8 byte,
space-filled area.
The loop was terminated by a fragment:
CLI 0(R5),0 correct
BE ENDLOOP
CLC 0(R5),C' ' wrong!!
BE ENDLOOP
We had been getting away with the typo in the second compare instruction for
about the last 25 years;
it is actually comparing 5 bytes at address 0 with those at +X'40' and the
compare had been failing
because the area at +X'40' is all zeros. Come z/OS 2.5 address 0 - 4 is now all
zeros, the compare
succeeds, the loop terminates immediately and SVC 8 fails with abend S806!
I have spent quite a bit of time preparing zaps for product versions going back
some years. ☹
Robin
-----Original Message-----
From: IBM Mainframe Discussion List <[email protected]> On Behalf Of Jim
Mulder
Sent: 25 November 2021 08:15
To: [email protected]
Subject: Re: PSA 0
0 was the address of the restart new PSW in ESA/390. When we implemented
zArchitecture 20 years ago, we set the obsolete ESA/390 interrupt new PSWs
such that if someone tried to simulate an interrupt by doing a LPSW for one of
them, the result would be a 0E1 wait state with a unique reason code. We
figured that after 20 years of that, we had already gotten whatever value that
there might have been from that, and it might now be better not to have things
like 000A0000 and
000130E1
hanging around down there where some program that has a null pointer bug might
pick them up and end up trying to use them as addresses and get into even more
weird results or storage overlays (since those are often valid GETMAINed
addresses).
So in z/OS 2.5, we changed those back to being reserved fields that are
initialized to zeroes.
Jim Mulder z/OS Diagnosis, Design, Development, Test IBM Corp.
Poughkeepsie NY
"IBM Mainframe Discussion List" <[email protected]> wrote on
11/24/2021 05:58:15 PM:
> From: "Hank Oerlemans"
> <[email protected]>
> To: [email protected]
> Date: 11/24/2021 07:57 PM
> Subject: PSA 0
> Sent by: "IBM Mainframe Discussion List" <[email protected]>
>
> A random neuron thinks there was an announcement but if anyone can
> shed some light I'm curious about Address 0.
>
> I am used to seeing X'000A0000' then X'000130E1' in the first 8-bytes.
> This is no longer so. All zeros. A good thing !
>
> SA22-7832-12 of Pops doesn't mention anything in CH. 3.
>
> So was there any kind of announcement for z/OS 2.5 ?
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