I have now proved the concept sufficiently.

If you write your programs a certain way, you can
stand up a clone anywhere (e.g. you can run VSE
programs on z/OS). But I have my own environment -
z/PDOS-generic, so that's what I am using.

Here is what a VSE program looks like when running:

(I renamed the executable from pdptest.exe to vsetest.exe)

18:48:59 /(0009) vsetest.exe
18:48:59 got request to open vsetest.exe
18:48:59 in LoadVSE
18:48:59 about to call app at address 04ECE818
18:48:59 got service call 0
18:48:59 len is 8
18:48:59 msg is MADE IT!
18:48:59 got service call 7
18:48:59 return from app is hex 3
18:48:59
18:48:59 enter a command

That same program running under DOS/VS:

19:00:12 BG
19:00:12 *
19:00:12 BG
19:00:12 *
19:00:12 BG
19:00:12 * Now run the app
19:00:12 BG
19:00:12 *
19:00:12 BG
19:00:12 MADE IT!
19:00:12 BG
19:00:12 *
19:00:12 BG


Using this JCL:

* First we get the main phase off tape, and into 80-byte blocks
* using objmaint
*
// UPSI 1
// ASSGN SYS004,TAPE
// DLBL UOUT,'PDPPUNCH.DAT',0,SD
// EXTENT SYS005,,,,10000,2000 SPACE-PHASE
// ASSGN SYS005,SYS000
// EXEC OBJMAINT,SIZE=AUTO
./COPY
/*
// UPSI 0
// ASSGN SYS005,SYSLST
// ASSGN SYS004,UA
*
*
*
*
*
*
*
* Then we put the phase into the CIL, using LNKEDT
*
// DLBL IJSYSLN,,0,SD
// EXTENT SYSLNK,,,,12000,2000 SPACE-LINK
ASSGN SYSLNK,SYS000
// OPTION CATAL
// DLBL IJSYSIN,'PDPPUNCH.DAT'
ASSGN SYSIPT,SYS000
?INCLUDE
CLOSE SYSIPT,READER
// EXEC LNKEDT
ASSGN SYSLNK,UA
*
*
*
*
*
*
* Now run the app
*
// EXEC PDPTEST,SIZE=AUTO,PARM='PaulEdwards two Three'



And here is the program itself:

000000? 40D7C8C1 E2C540D7 C4D7E3C5 E2E36BE2? ?PHASE PDPTEST,S
000010? 4EE77DF0 F0F0F0F5 F07D4040 40404040? +X'000050'
000020? 40404040 40404040 40404040 40404040
000030? 40404040 40404040 40404040 40404040
000040? 40404040 40404040 40404040 40404040
000050? 02C5E2C4 40404040 40400010 40400001? .ESD? ? ? ..? ..
000060? D7C4D7E3 C5E2E340 007000C8 40001330? PDPTEST ...H ...
000070? 40404040 40404040 40404040 40404040
000080? 40404040 40404040 40404040 40404040
000090? 40404040 40404040 40404040 F0F0F0F1? ? ? ? ? ? ? 0001
0000A0? 02E3E7E3 407000C8 40400038 40400001? .TXT ..H? ..? ..
0000B0? 47F0F010 D7C7C3E7 00000004 00000000? .00.PGCX........
0000C0? 5810F070 58101000 12114780 F02C90EC? ..0.........0...
0000D0? D00C41D0 D05018CF 47F0C040 18CF187E? }..}}&...0{ ...=
0000E0? 5830C074 5840C078 40404040 F0F0F0F2? ..{.. {.? ? 0002
0000F0? 02E3E7E3 40700100 40400038 40400001? .TXT ...? ..? ..
000100? 5850C07C 41D0C088 4190D050 5090D04C? .&{@.}{h..}&&.}<
000110? 58F0C080 05EF58F0 C07418E7 5810C070? .0{....0{..X..{.
000120? 58101000 12114780 C06E5BD0 C08458E0? ........{>$}{d.\
000130? D00C980C D01407FE 40404040 F0F0F0F3? }.q.}...? ? 0003
000140? 02E3E7E3 40700138 40400038 40400001? .TXT ...? ..? ..
000150? 007000D4 00000003 00000004 00000005? ...M............
000160? 0070122C 00000050 00000000 00000000? .......&........
...
001AB0? 05EF1F22 18F258D0 D00458ED 000C980C? .....2.}}.....q.
001AC0? D01407FE 00000000 D4C1C4C5 40C9E35A? }.......MADE IT!
001AD0? 00000150 00701340 40404040 F0F0F8F5? ...&...? ? ?0085
001AE0? 02E3E7E3 40701328 40400038 40400001? .TXT ...? ..? ..
001AF0? 09000000 00000000 00701344 FFFF8000? ................
001B00? 00000007 00000008 00701250 47F0F00A? ...........&.00.
001B10? 055F5F73 766390EC D00C58F0 D04C50D0? .^^.....}..0}<&}
001B20? F00450F0 D00818DF 40404040 F0F0F8F6? 0.&0}...? ? 0086
001B30? 02E3E7E3 40701360 40400038 40400001? .TXT ..-? ..? ..
001B40? 18B105C0 5AF0C080 50F0D04C 58A0C084? ...{!0{.&0}<..{d
001B50? 5820C088 58202000 12224770 C040D203? ..{h........{ K.
001B60? D058B000 D203D05C B004D203 D060B008? }...K.}*..K.}-..
001B70? 4110D058 58F0C08C 40404040 F0F0F8F7? ..}..0{.? ? 0087
001B80? 02E3E7E3 40701398 40400038 40400001? .TXT ..q? ..? ..
001B90? 05EF182F 5020D068 47F0C06E 5820C088? ....&.}..0{>..{h
001BA0? 58202000 D203D058 B000D203 D05CB004? ....K.}...K.}*..
001BB0? D203D060 B0085820 220C4110 D05841F0? K.}-........}..0
001BC0? 200005EF 182F5020 40404040 F0F0F8F8? ......&.? ? 0088
001BD0? 02E3E7E3 407013D0 40400028 40400001? .TXT ..}? ..? ..
001BE0? D06858F0 D06858D0 D00458ED 000C980C? }..0}..}}.....q.
001BF0? D01407FE 00000070 007013F4 007000D4? }..........4...M
001C00? 007010F0 00701364 40404040 40404040? ...0....
001C10? 40404040 40404040 40404040 F0F0F8F9? ? ? ? ? ? ? 0089
001C20? 02D9D3C4 40404040 40400038 40404040? .RLD? ? ? ..
001C30? 00010001 0D700138 0D700148 0D7011C8? ...............H
001C40? 0D7011D4 0D7011D8 0D701224 0D701228? ...M...Q........
001C50? 0D701324 0D701330 0D701340 0D7013E8? ........... ...Y
001C60? 0D7013EC 0C7013F0 40404040 F0F0F9F0? .......0? ? 0090
001C70? 02D9D3C4 40404040 40400004 40404040? .RLD? ? ? ..
001C80? 00010001 0D7013F4 40404040 40404040? .......4
001C90? 40404040 40404040 40404040 40404040
001CA0? 40404040 40404040 40404040 40404040
001CB0? 40404040 40404040 40404040 F0F0F9F1? ? ? ? ? ? ? 0091
001CC0? 02C5D5C4 407000C8 40404040 40400001? .END ..H? ? ? ..
001CD0? 40404040 40404040 40404040 40404040
001CE0? 40404040 40404040 40404040 40404040
001CF0? 40404040 40404040 40404040 40404040
001D00? 40404040 40404040 40404040 F0F0F9F2? ? ? ? ? ? ? 0092
001D10? 615C4040 40404040 40404040 40404040? /*
001D20? 40404040 40404040 40404040 40404040
001D30? 40404040 40404040 40404040 40404040
001D40? 40404040 40404040 40404040 40404040
001D50? 40404040 40404040 40404040 40404040

(and attached in full)

There is still one technical problem I'm waiting on
(malformed RLD), but it doesn't stop it from running.


The technique I am using involves getting z/PDOS-generic
to zap the executable on loading. The start assembler needs
to look like this:

__crt0:
? ? ? ? ?B? ? ?skiphdr
#? ? ? ? ?.byte "PGCX"? # PDOS-generic (or compatible) extension
# Needs to be in EBCDIC
? ? ? ? ?.byte 0xd7, 0xc7, 0xc3, 0xe7
#? ? ? ? ?.long 4? ?# length of header data
? ? ? ? ?.DC? ?F'4'
? ? ? ? ?.globl __pgparm
__pgparm: .long 0? ?# This will be zapped by z/PDOS-generic if running under it
skiphdr:
? ? ? ? ?L? ? ?R1,=V(__pgparm)
? ? ? ? ?L? ? ?R1,0(,R1)
? ? ? ? ?LTR? ?R1,R1
? ? ? ? ?BZ? ? notpdos
? ? ? ? ?STM? ?r14,r12,12(r13)
? ? ? ? ?LA? ? r13,80(,r13)
? ? ? ? ?LR? ? r12,r15
? ? ? ? ?.drop r15
? ? ? ? ?.using __crt0, r12
? ? ? ? ?B? ? ?BYPASS1
notpdos:
? ? ? ? ?LR? ? r12,r15


pgparm gets zapped by z/pdos-generic like this:

#ifdef NEED_VSE
? ? os.Xservice = service_call;
? ? if (memcmp(entry_point + 4, "PGCX", 4) == 0)
? ? {
? ? ? ? *(void **)(entry_point + 12) = &os;
? ? }
#endif


Service calls are handled like this:

#ifdef NEED_VSE

#include <mfsup.h>

static int service_call(int svcnum, void *a, void *b)
{
? ? printf("got service call %d\n", svcnum);
? ? if (svcnum == 0)
? ? {
? ? ? ? REGS *regs;
? ? ? ? CCB *ccb;
? ? ? ? CCW *ccw;
? ? ? ? char *msg;

? ? ? ? regs = a;
? ? ? ? ccb = (CCB *)regs->r[1];
? ? ? ? ccw = ccb->actual.ccw_address;
? ? ? ? msg = (char *)(ccw->actual.addr & 0xffffff);
? ? ? ? printf("len is %d\n", ccw->actual.len);
? ? ? ? printf("msg is %.*s\n", ccw->actual.len, msg);
? ? }
? ? return (0);
}
#endif


This C code in the application avoids doing a real SVC:

int __svc(int svcnum, void *regsin, void *regsout)
{
? ? if (__pgparm == 0)
? ? {
? ? ? ? return (__svcreal(svcnum, regsin, regsout));
? ? }
? ? else
? ? {
? ? ? ? return (__pgparm->Xservice(svcnum, regsin, regsout));
? ? }
}

On real DOS/VSE (or z/VSE) it will do a real SVC.


It is my intention to stand up CMS and MVS mini-clones
the same way.

To the point where they can at least run arbitrary C programs.

I'm not sure what to do then though. I'm not sure if there
is a market for a mini clone of a mainframe OS. I'm not
necessarily trying to be in a market though. But maybe it
would be good if someone else was so that IBM had some
competition. I was thinking of maybe setting up a rival to
India in Vietnam.

BFN. Paul.

Yes, you can just inspect low memory to locate the COMRG.

In the early days of COBOL programming in CICS/VS 1.1 on DOS/VS, there
was a mechanism that allowed me to define a COBOL area that had a
pointer set to 20, and lo and behold you could access the date from the
COMRG without issuing an SVC which was not a good idea in a CICS
application.? The date was what I needed.? But anything was there for
the reading.

By avoiding SVC 33, CICS, the partition, did not lose control.

How COBOL implemented CICS table accesses via a COBOL defined
base-address register field was the basis for the pointer.

Just FYI from the early days.? CICS/VS with COBOL applications provided
no mechanism for accessing the date (that I recall).? IBM support found
my solution "interesting".

Harold Grovesteen

On 9/11/24 16:36, Paul Edwards wrote:
> On Wed, Sep 11, 2024 at 11:34 PM, Fish Fish wrote:
>
>> Each partition has its own Communications Region. Address 20 is always set to
>> the address of the given partition's Communications Region control block by
>> the dispatcher. It is a part of task dispatching. So while that particular
>> partition is running, address 20 always points to its COMRG.
> Thanks for that explanation.
>
>>> Or alternatively - use the abstraction - SVC 33 can go and
>>> inspect low memory itself?
>> That is not the purpose of SVC 33.
> Ok - I had the wrong concept there - thanks.
>
> BFN. Paul.
>
>
>
>
>