PSAAOLD is ALWAYS the home address space.
A PC-SS causes the SWITCHED TO address space to become the PRIMARY. The
secondary is set based on the PC definition, but is typically the previous
primary.
PSAAOLD is NOT changed by the hardware (other than setting it directly). The
"fixed by architecture" in this context is MVS(software) architecture. Too
many programs expect to find the ASCB pointer there.
How is the resource manager established? HOME=*MASTER* typically means an
address space resource manager, which means that there ain't no TCBs available
in the terminating memory.
Actually, TCBs are usually at the same addresses.
Finally:
EPAR Rx
L Ry,PSAAOLD-PSA
CH Rx,ASCBASID-ASCB(Ry)
On Mon, 14 Mar 2011 11:35:06 -0500 "McKown, John"
<[email protected]> wrote:
:>The documentation that I can find is not really very helpful. Or I just don't
understand it. But I'm wondering what, if any, is the relationship between
PSAAOLD and either the home address space or the primary address space. I know
that a PC can do a space switch. In that case, the primary address space
becomes the "switched to" address space. The "switched from" address space (I
think) becomes the secondary address space. And the home address space stays
the same. So, if I write some code which is invoked via a PC-ss instruction
(not likely!), is PSAAOLD updated to point to the new primary address space? Or
is it left as-is? I only ask because the address is not mentioned in the
Principles of Operation, but a comment in the DSECT says "fixed by
architecture". Which indicates to me that the hardware uses or modifies it in
some way which is not documented.
:>
:>What brought this on is a product which works on z/OS 1.10, but abends with
an S0C4-11 on z/OS 1.12. The code appears to be using a pointer to the job's
ASCB to look at some data in the job's SSIB. However, it appears that the
primary address space is not the job's, but the Master Scheduler's. This is for
an *OMVSEX substep which I __think__ is going through termination. Needless to
say that using TCB pointers from one ASCB while a different ASCB is actually
the primary is fairly well a guaranteed S0C4-11 since TCBs are not at the same
virtual address in all address spaces (in primary addressing mode as this code
is).
:>
:>Perhaps another question I should ask is: Is there a simple way to determine
if a given ASCB address is the current Primary Address Space's ASCB?
:>
:>John McKown
:>Systems Engineer IV
:>IT
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