Word-1 of the Conventional Save Area

[Adam Johanson]

Could someone please enlighten me as to what the purpose is/was of the 
first word of a save area?

   Usually when I'm going through a dump it's not important, but I have seen 
LE put some control information in there. I've also heard of programmers 
putting program-specific stuff in there, but I'm curious as to what the 
original 
purpose was of it.

   Thanks.

Adam Johanson
IMS Systems Programming
USAA

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Word-1 of the Conventional Save Area

[Kenneth J. Kripke]

I think Word-1 of the save area...bytes 0-3 were used by PL/1 for the Pseudo 
Register.  
kkri...@mindspring.com

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Word-1 of the Conventional Save Area

[Peter Relson]

>What if R13 has been destroyed somehow? You can do forward chaining by
>starting at TCBFSA to the first save area, then using the pointer in
>word 3 of the save areas to >chain forward until it is zero. That is
>what the SYSUDUMP formatter does. But I do agree that the forward chain
>is not always reliable. It is for every compiled language that I'm
>aware of. But it depends on the HLASM programmer following the
>convention if there is any assembler along the line.

The only thing thiat is predictable these days is chaining backwards from
the current save area.
You cannot predictably chain forward unless you happen to know that all
uses of your savearea were for 31-bit 72-byte cases (and not for 64-bit
144-byte cases, for example) and, of couse, that they follow the savearea
chaining protocol..

>Back in the old days ISTR it set x'FF' to indicate the end of the savearea
chain.

Good memory, When the "T" parameter of RETURN was specified, prior to
MVS/XA X'FF' was placed in the high byte of the reg 14 slot. As of MVS/XA
(actually the point-release just after MVS/XA, perhaps no one had noticed
for the original release of MVS/XA), that was changed to instead place
x'01' in the low byte of the reg 14 slot. (for relatively obvious AMODE 31
reasons).
Does anyone actually use this? (Just curious, not thinking of removing it)


Someone mentioned clearing the chain when returning.  Some of our best
debuggers do some of their best work taking advantage of residual
information, as that can give a hint of what had happened "just before".
The data might not be predictable but sometimes is useful.

Peter Relson
z/OS Core Technology Design
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Re: Word-1 of the Conventional Save Area

[zMan]

On Thu, Feb 4, 2010 at 12:30 PM, Adam Johanson wrote:

> Could someone please enlighten me as to what the purpose is/was of the
> first word of a save area?
>
>   Usually when I'm going through a dump it's not important, but I have seen
> LE put some control information in there. I've also heard of programmers
> putting program-specific stuff in there, but I'm curious as to what the
> original
> purpose was of it.
>

ISTR it was used by PL/I. Which, if you recall, was going to be The
Language, used by everyone for everything, so wasting a fullword (worth
something, back then!) was deemed reasonable.

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Re: Word-1 of the Conventional Save Area

[Rick Fochtman]

---
Could someone please enlighten me as to what the purpose is/was of the 
first word of a save area?


Usually when I'm going through a dump it's not important, but I have 
seen LE put some control information in there. I've also heard of 
programmers putting program-specific stuff in there, but I'm curious as 
to what the original purpose was of it.

-
That first word has been used at various times for control and/or flag 
information by various processors, most notably PL/1 and ALGOL in S/360 
days. While some consider it a artifact now, of no useful value, others 
may still use it for flag bits, etc.


Rick

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Re: Word-1 of the Conventional Save Area

[zMan]

On Thu, Feb 4, 2010 at 3:53 PM, Rick Fochtman  wrote:

> That first word has been used at various times for control and/or flag
> information by various processors, most notably PL/1 and ALGOL in S/360
> days.
>

PL/I. Not PL/1.

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Re: Word-1 of the Conventional Save Area

[Greg Price]

zMan wrote:
> ISTR it was used by PL/I.

That's what IHASAVER would seem to indicate.

Cheers,
Greg

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Re: Word-1 of the Conventional Save Area

[Paul Gilmartin]

On Fri, 5 Feb 2010 07:44:14 -0500, Peter Relson wrote:
>
>(actually the point-release just after MVS/XA, perhaps no one had noticed
>for the original release of MVS/XA), that was changed to instead place
>x'01' in the low byte of the reg 14 slot. (for relatively obvious AMODE 31
>
In the RETURN macro, I see OI, not MVI (but I didn't search for the MVI).

-- gil

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Re: Word-1 of the Conventional Save Area

[Robert A. Rosenberg]

At 14:53 -0600 on 02/04/2010, Rick Fochtman wrote about Re: Word-1 of 
the Conventional Save Area:


That first word has been used at various times for control and/or 
flag information by various processors, most notably PL/1 and ALGOL 
in S/360 days. While some consider it a artifact now, of no useful 
value, others may still use it for flag bits, etc.


It is currently used to indicate (via a FMTx value) when the format 
of the save area is something other than the standard 18F format 
(word1,backlink,forwardlink,R14,R15,R0-12).


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Re: Word-1 of the Conventional Save Area

[Tom Marchant]

On Fri, 5 Feb 2010 15:20:25 -0500, Robert A. Rosenberg wrote:

>It is currently used to indicate (via a FMTx value) when the format
>of the save area is something other than the standard 18F format
>(word1,backlink,forwardlink,R14,R15,R0-12).

The OP's question was about the first word in the save area (word 0),
despite "Word-1" in the subject line.

The values F4SA, etc. (not FMTx) go in the second word of the save area
(word 1).  That's the same word that contains the address of the previous
save area in the "standard" 72-byte save area.  They do not describe the
format of the save area in which it is contained.  They describe the way
that the program that allocated the save area saved the registers in the
caller's save area upon entry.

-- 
Tom Marchant

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Re: Word-1 of the Conventional Save Area

[Adam Johanson]

Peter Relson wrote:
>Good memory, When the "T" parameter of RETURN was specified, prior to
>MVS/XA X'FF' was placed in the high byte of the reg 14 slot. As of MVS/XA
>(actually the point-release just after MVS/XA, perhaps no one had noticed
f>or the original release of MVS/XA), that was changed to instead place
>'01' in the low byte of the reg 14 slot. (for relatively obvious AMODE 31
>reasons).
>Does anyone actually use this? (Just curious, not thinking of removing it)

   Yeah, I recognize this from going through IMS dumps that IMS will set this 
bit on to indicate that the program returned. I also recall seeing it 
documented in the IMS Diagnosis G&R that they do this.

Adam Johanson
IMS Systems Programming
USAA

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Re: Word-1 of the Conventional Save Area

[Bernd Oppolzer]

We did this, too, in our site-specific standard start-and-end-macro.
So odd addresses in the RET field in the save areas show that the active
save area is above this position (in forward direction). But this is 
kind of

redundant, if you have reg 13. But sometimes, when debugging, you are
happy if there is a little bit of redundance :-)

Kind regards

Bernd


Adam Johanson schrieb:
Yeah, I recognize this from going through IMS dumps that IMS will set this 
bit on to indicate that the program returned. I also recall seeing it 
documented in the IMS Diagnosis G&R that they do this.


Adam Johanson
IMS Systems Programming
USAA

  


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Re: Word-1 of the Conventional Save Area

[Peter Relson]

>>was changed to instead place x'01' in the low byte 

>In the RETURN macro, I see OI, not MVI (but I didn't search for the MVI).

I mis-wrote; you're right. It should have been 
"place x'01' in the low bit"

Peter Relson
z/OS Core Technology Design

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Re: Word-1 of the Conventional Save Area

[Shmuel Metz (Seymour J.)]

In , on 02/04/2010
   at 11:30 AM, Adam Johanson  said:

>Could someone please enlighten me as to what the purpose is/was of the 
>first word of a save area?

PL/I used it; the exact usage depended on which PL/I compiler you're
talking about. I don't know whether it is still used.
 
-- 
 Shmuel (Seymour J.) Metz, SysProg and JOAT
 ISO position; see  
We don't care. We don't have to care, we're Congress.
(S877: The Shut up and Eat Your spam act of 2003)

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