Thank you all for this discussion;
I have learned something new :-)
Would you kindly look at this coding and tell me, if it is correct in
your opinion,
and if it is allowed to execute this by non-privileged programs?
What macro calls do I need to get the needed definitions (CVT, ASVT, ASCB)?
Thanks in advance,
have a nice day
Bernd
*
*---------------------------------------------------------------------
* walk thru all ASCBs
*---------------------------------------------------------------------
*
L R10,16 LOAD ADDR OF CVT
USING CVT,R10 SET ADDRESSABILITY TO CVT
L R10,CVTASVT POINT TO ADDRESS SPACE VECTOR TABLE
DROP R10
USING ASVT,R10 SET ADDRESSABILITY TO ASVT
L R9,ASVTMAXU LOAD MAX. NUMBER OF ADDRESS SPACES.
LA R11,ASVTENTY LOAD ADDRESS OF FIRST ASCB POINTER
DROP R10
*
*---------------------------------------------------------------------
* R11 is moved over the table of all ASCB pointers
* R10 is no longer needed
* R9 contains the number of entries in the ASCB table
*---------------------------------------------------------------------
*
LOOPASVT DS 0H
TM 0(R11),ASVTAVAL VALID ASCB Available ?
BO NEXTASVT NO, CHECK NEXT ASVT ENTRY
*
*---------------------------------------------------------------------
* Examine ASCB
* Use R10 to address the ASCB
*---------------------------------------------------------------------
*
L R10,0(R11)
USING ASCB,R10
*
*---------------------------------------------------------------------
* access fields of current ASCB
*---------------------------------------------------------------------
*
* --- to be entered here ---
*
*---------------------------------------------------------------------
* advance R11 to next ASCB address
*---------------------------------------------------------------------
*
NEXTASVT DS 0H
LA R11,4(,R11) Advance to NEXT ASVT ENTRY
BCT R9,LOOPASVT
*
Am 05.02.2023 um 07:39 schrieb Tony Harminc:
On Sat, 4 Feb 2023 at 18:00, [email protected] <[email protected]> wrote:
I am on a z/os 2.2 system, trying to rseurrect some old code.
.
can some one confirm the instructions for Searching the
Address Space Vector Table (ASVT) on z/OS 2.2
.
This program loads R10 with CVTASVT
L R10,CVTASVT GET ASVT ADDRESS
USING ASVT,R10 ESTABLISH ADDRESSABILITY
That's fine.
It then issues a Load Address For the first entry ?
This doesn't look correct to me ?
LA R11,ASVTENTY GET # OF FIRST ENTRY
It's fine. The ASVT has a bunch of header stuff, and then an array of
fullword pointers starting at ASVTENTY. The PL/X declaration may make it a
bit clearer.
Next its test for an ASCB that is assigned.
TM 0(R11),ASVTAVAL VALID ASCB Available ?
BO RUNLOP1 NO, CHECK NEXT ASVT ENTRY
It's fine.I suppose there may be a serialization issue, e.g. an ASVT
entry's assignment status may change after you've looked. But programs that
either index the ASVT with the ASID (x 4), or those that go sequentially
through the array and do <something> with each active address space have
done it this way forever (i.e. since 1972), and I'm sure many are still out
there working fine. Like anything, it's conceivable IBM could change this
at some point, but it's such a basic interface in MVS--> z/OS that they
would surely introduce some new data structure or API to access the list of
ASCBs rather than change the ASVT and break things all over the place.
Besides the Load Address above - How should this module
advance to the Next ASVT entry ?
There's nothing wrong with the LA. The start of the array of ASCB pointers
is at whatever offset ASVTENTY is at, and that hasn't changed in 50 years.
The content of the header info has grown, but not the offset of the array
of pointers.
Shoud I issue the following to get to the next ASVT
L R10,ASVTFRST
No. I think you're thinking that the entire ASVT has multiple instances
that are chained together. There's only one, with an array of pointers on
the end. ASVTFRST points somewhere you don't want - I think the first
*available* ASCB, though IBM doesn't document the ASCB creation logic, and
I assume things have changed with reusable ASIDs. Presumably you are not
planning to modify the ASVT, so you're not looking for an available
entry... If you are, well Just Don't. But effectively ASVTFRST is element 0
of the array of ASCB pointers, and there's no ASID 0. So if you have the
address of ASVTFRST (not the address that is *in* ASVTFRST), then you can
multiply the ASID by 4 and use it as an origin-0 array index. If you start
at ASVTENTY then it's origin-1, so add 4 (or 1 before you multiply by 4).
Or if you want to look at all active ASCBs then start with the first array
element, follow the pointer *if it's active*, and do whatever it is you
want to do with each ASCB.
The current code issues the following instruction, which
looks incorrect according to IHAASVT
LA R11,4(,R11) Advance NEXT ASVT ENTRY
It's fine. I suppose if you want to be pedantic you could use L'ASVTENTY
instead of hardcoding 4, but seriously, that's not going to change, and if
it does all kinds of other things will break.
Tony H.
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