ras%hep.nrc.CDN@ean.ubc.ca (Rudolph Shally) (05/07/88)
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?
Please reply to:
ras@hep.nrc.cdn (Rudolph Shally)
LEICHTER@Venus.YCC.Yale.EDU ("Jerry Leichter ", LEICHTER-JERRY@CS.YALE.EDU) (05/15/88)
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? There is no automatic way to do this. What you are asking for is essentially the converse of the usual shareable image mechanism: A shareable image provides a table of entry points, and when an image starts up, its indirect pointers to entry points within the shareable image are resolved into actual addresses, based on where the shareable image was loaded. What you want is for indirect pointers within the shareable image to be fixed up. This would require an entirely different mechanism; for one thing, the pointers TO the shareable image can be, and are, fixed up in place - but the shareable image itself can't be changed - other processes may be using it. You'll have to do this yourself: Within your main code, provide a "transfer vector table", just like the transfer vector table used in the shareable image, and handled automatically. During initialization, provide the address of the table to the shareable image and have it store it. Then have the shareable image, when it wants to call something like QNEXT, actually use an indirect reference into the "transfer vector table". The cleanest way to do this may be make the dummy QNEXT contain the code that finds the appropriate "transfer vector table" entry and calls it. (Of course, what it probably does is load the index into R0 and transfer to some common access code.) Then as far as the rest of the shareable image is concerned, QNEXT is just a normal function. If you do this, QNEXT should NOT be a universal symbol (to avoid complaints from the Linker when the "real" QNEXT gets defined). -- Jerry
ZWARTS@HGRRUG51.BITNET (05/19/88)
>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 easiest way to do this is by passing the routine QNEXT as a argument, instead of using it as a global defined routine. However, this solution is not always possible. What I once did was the following: 1) I created a shareable image with only the dummy routine QNEXT (using transfer vectors etc.). 2) I rebuilt the original shareable image by linking it against the dummy QNEXT in the shareable image from step 1). 3) The user links his program, except his QNEXT against both shareable images. 4) I wrote a procedure for the user to create a shareable image with his QNEXT, using exactly the same transfer vectors as in case 1) of the dummy QNEXT. 5) The user defines a logical name so that the image-activator uses the user's QNEXT, not the dummy one. F. Zwarts Phone: (+31)50-633619 Kernfysisch Versneller Instituut Bitnet/Earn: ZWARTS@HGRRUG51 Zernikelaan 25 Surfnet: KVIANA::ZWARTS 9747 AA Groningen Telefax: (+31)50-634003 The Netherlands Telex: 53410 rugro nl