From:	MERC::"uunet!WKUVX1.BITNET!MacroMan" 21-MAR-1993 15:38:09.29
To:	MACRO32 <MACRO32@WKUVX1.BITNET>
CC:	
Subj:	Re: Sys. Serv. Hook (Was RE: Imp terminates Qio !)

>synchronisation (ie SETIPL).  I'm not letting you off for the superfluous
>$DELTVA thoug.  8-)

OK! Fair enuf!

The 'superfluous' $DELTVA _was_ to focus the attention on the referenced
chapters in the "Book of Ruth".  _I_ know the $CRETVA will delete the
range! (pg. 409 sect: 15.3 'Demand Zero VA Sace Creation', steps 3 & 4)

>> The real challenge of that ditty was to devise a mechanism to execute the
>> "set prompt" code in exec mode and keep the functions of the hook routine
>> process specific.  The WRTATTN AST on the mailbox worked out real nice.
>
>I was going to do that myself -- I'd pulled the revectoring trick to do
>the same thing, but was just working in the access mode of the caller.
>That meant abandoning ship id the access mode was user, but that was
>mostly OK since most $SETDDIRs happen at supervisor mode (ie from DCL).
>This worked fine at V5.3, but broke in 5.4 (which I only just found the
>disk space for this week) as the default directory string (or something)
>appears to be unreachable in supervisor mode.

YES! The access mode of that page was changed.  I had some code myself
which broke. (I think it was 5.4) I thought about (for the setddir hook)
changing the page protection but decided against it when I thought up
the mbx mechanism.

>> Got any other ideas on how to do it?  It may prove to be a bit more
>> interesting than the discussion ensuing about RMSing with the UAF!
>
>Someone suggested user system services.

The "Book of Ruth" was queried.  The answer is on the board.

Survey says... XXX Bzzzt!

A per-process sys. serv. dispatcher loaded for a user system service from
the protected image is _removed_ at image rundown.  The user service will
be available when the hook loading routine runs but will disappear when
the images runs down, replacing the JSB <user disp.> at @CTL$GL_USERCHME
with a RSB.   No more user mode CHME or CHMK system service dispatching.
(as the term states, it's a _USER_MODE_ system service dispatcher)

Ref: VMS IDSM V5.2 Sect 6.4 and Sect 26.3 step 22.

BJS- /Brian Schenkenberger/Schenkenberg@Eisner.DECUS.Org/Space for Rent/
    /VMS Software Support/Vitronics, Inc./Eatontown, NJ/(908) 542-0600/
   /Independent Consult./Tmesis Consulting/Jackson, NJ/(908) 363-7551/
  /<VAXman or Schenkenberger>@Monmouth-ETDL1.Army.Mil/CIS: 70253,114/