Re: Hooking display file I/O

From: Steve Richter <srichter@AutoCoder.com>
> >The way to do this is to monkey with a local copy of SEPT, instead of with
> >the global system-wide SEPT. The PCO (Process communication obj)
> >contains a pointer to the SEPT to be used by this process. Changing
> >that pointer to point to your own copy (which you make with a single
> >CPYBWP-instruction) requires you to set the tag bit for the pointer.
>
> Why do you have to set the tag bit?
>

here is how I would install my own SEPT (which initially is just a copy
of IBM's):

DCL SYSPTR .SEPT(6440) BAS(@SEPT);
DCL DD PCO CHAR(256) BASPCO;
   DCL SPCPTR @SEPT  DEF(PCO) POS( 1);

DCL DD IBM-SEPT CHAR(103040) BAS(@SEPT);
DCL DD MY-SEPT  CHAR(103040) BDRY(16);

DCL DD MY-PTR CHAR(16) BDRY(16);
    DCL SPCPTR .MY-SEPT DEF(MY-PTR) POS(1) INIT(MY-SEPT);

ENTRY * EXT;
    CPYBWP       MY-SEPT, IBM-SEPT;
    CPYBWP       PCO, MY-PTR;
    RTX          *;

Having my own SEPT, I can now change entries. These changes
will only impact my own process (which is good during testing).



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