Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!bbn!apple!keith
From: keith@Apple.COM (Keith Rollin)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Problems with XCMDs in MPW Object Pascal 3.0
Keywords: Object Pascal, XCMDs
Message-ID: <26942@apple.Apple.COM>
Date: 8 Mar 89 02:57:27 GMT
References: <4321@sdcc3.ucsd.EDU>
Organization: Apple Computer Inc, Cupertino, CA
Lines: 35

In article <4321@sdcc3.ucsd.EDU> am151fap@sdcc3.ucsd.EDU (Eric Krugler) writes:
>
>I'm trying to create an XCMD using MPW Pascal 3.0. The problem is that if
>I use the Object extensions provided by MPW Pascal the linker runs into
>problems. The -rt link option is used to create the XCMD resource
>and it causes A5 addressing modes to be converted to PC relative
>addressing modes, but only for JSR, JMP, LEA, or PEA instructions.
>The error that the linker produces (#41) states that a different
>instruction specifying A5 relative addressing has been found.
>
>The real question is can an XCMD, DRVR, or DA be created using the
>Object extensions of MPW Pascal and if so, how do I work around the
>problem with the linker.
>
I don't think that you will ever be able to get this to work. I've only 
looked into the inner workings of method dispatching briefly, and they seem to 
depend on several things:

1) a jump table (and No, you can't use HyperCard's).
2) selection procedures (SelProcs) in a separate segment
3) method tables (MethTables) in a separate segment.

All three of these violate the conditions for standalone code resources, which
is what an XCMD is. However, I may be wrong on some of these points. For
instance, I wasn't aware that the -rt option caused the A5 relative addressing
to become PC relative. But I still don't think that it will also change the
method dispatching architecture.


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