Path: utzoo!utgpu!water!watmath!clyde!att!ucbvax!husc6!rutgers!apple!lsr
From: lsr@Apple.COM (Larry Rosenstein)
Newsgroups: comp.sys.mac.programmer
Subject: Re: 32K jump table limit
Keywords: MacApp
Message-ID: <16326@apple.Apple.COM>
Date: 30 Aug 88 06:12:42 GMT
References: <3425@Portia.Stanford.EDU>
Reply-To: lsr@apple.com.UUCP (Larry Rosenstein)
Organization: Advanced Technology Group, Apple Computer
Lines: 46

In article <3425@Portia.Stanford.EDU> rick@jessica.stanford.edu (Rick Wong) writes:
>
>Does anyone have any suggestions for dealing with this problem?
>(This looks like a job for Apple.)

This has been discussed at length on AppleLink.  Unfortunately, there is no
quick workaround.

Object Pascal uses jump table entries as method and class IDs.  Also, the
method tables themselves contain the jump table offset for the method code.
(I believe that there will be one jump table entry for each class, for each
newly-defined method, and for each implementation of a method.)  This was
done primarily as an implementation convenience.

When you optimize, the class IDs are assigned by the linker in sequence (no
jump table entry needed), and many entries in the method tables are
eliminated.  This greatly reduces the number of jump table entries required.
So one workaround is to always build an optimized version of your program.
(I believe that the MacApp team is investigating whether it is possible to
optimize an application, but still keep the MacApp debugger.  This has not
been done for the MacApp 2.0 beta release.)

The linker only creates jump table entries when it has to.  If a routine is
only referenced from within its segment, then there is no need for a jump
table entry.  Combining some of your segments may help a bit, if they
contain regular procedures and functions (not methods).  

I didn't think that MPW Pascal allocated a jump table entry for every
procedure parameter.  What you may be seeing is the fact that some MacApp
units contain a {$B-} compiler flag to force all procedure references to
have jump table entries.  I think that the MacApp team has removed these
directives from the MacApp 2.0 sources.  You can add {$B+} directives to
your units to tell the linker to use PC-relative addressing.  (We put the
$B- flag in to ensure that MacApp didn't save a PC-relative address away.
This turned out to be overkill.)

The problem is recognized by the MacApp team, and they are looking at ways
to solve the problem.  

I agree that it is unfortunate for programmers to have to worry about this.

		 Larry Rosenstein,  Object Specialist
 Apple Computer, Inc.  20525 Mariani Ave, MS 46-B  Cupertino, CA 95014
	    AppleLink:Rosenstein1    domain:lsr@Apple.COM
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