Path: utzoo!attcan!uunet!husc6!mailrus!ames!ll-xn!mit-eddie!bu-cs!purdue!decwrl!labrea!agate!ucbvax!uwastm.phys.washington.EDU!WHIT
From: WHIT@uwastm.phys.washington.EDU ("John Whitmore, III ")
Newsgroups: comp.os.vms
Subject: Shareable images ...
Message-ID: <8805230938.AA14597@ucbvax.Berkeley.EDU>
Date: 18 May 88 01:32:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 40

>From: Rudolph Shally <ras%hep.nrc.cdn%ean.ubc.ca@RELAY.CS.NET>
>To: Richard Seymour <SEYMOUR@phast>
>Reply-to: INFO-VAX@KL.SRI.COM
>Comments: To: info-vax@KL.SRI.COM
>
>The problem is how to override a routine in a shareable image.
>The image contains several routines, say 1000 and many of those
>call another routine (say QNEXTE) in the same image. QNEXTE
>in turn, calls another routine, say, QNEXT. In VAX macro the call is
>(in QNEXTE):
>
>       CALLS   #0,QNEXT
>
>The trouble is that QNEXT is supposed to be a user supplied routine
>while I had to include a dummy routine QNEXT in the shareable image
>since everything must be linked. When the user links his main program
>and his own QNEXT with the shareable image the linker won't accept
>the user supplied routine QNEXT since a dummy version is already
>in the shareable image. How can one owerride the dummy routine?

      The creating LINK for the shared executable had to include
a reference for the QNEXT routine, or fail to LINK successfully.
The reference can be any of a number of things: a *.OBJ object module
file, a shareable image, or an object or shareable image library
      Unfortunately, the shared executable will incorporate
an object module if it is given one, and this cannot be later
"un-LINKed" to allow the user his desired QNEXT routine.
Shared executables to the rescue!  One must create a shared
executable (if necessary, tutoring the users so they can do it
for themselves) containing a dummy QNEXT routine, and allow the
user the option of
      $LINK/EXE=user_qnext.exe user_qnext/SHAREABLE
      $DEFINE QNEXT_IMAGE disk:[userdir]user_qnext.exe
      $LINK program,QNEXTE_IMAGE_OPTION/OPTION
where the QNEXTE_IMAGE_OPTION file contains
      QNEXTE_IMAGE/SHARE,-
      QNEXT_IMAGE/SHARE
      .
      .
      .