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From: dg@wrs.UUCP (David Goodenough)
Newsgroups: comp.lang.c
Subject: Near / Far Calls (was Re: Types)
Message-ID: <342@wrs.UUCP>
Date: Tue, 8-Sep-87 19:36:04 EDT
Article-I.D.: wrs.342
Posted: Tue Sep  8 19:36:04 1987
Date-Received: Fri, 11-Sep-87 01:59:18 EDT
References: <7264@brl-adm.ARPA> <734@sdchema.sdchem.UUCP> <293@osupyr.UUCP> <296@swlabs.UUCP> <613@sugar.UUCP> <4779@sdcrdcf.UUCP>
Reply-To: dg@wrs.UUCP (David Goodenough)
Organization: Wind River Systems, Emeryville, CA
Lines: 36

In article <613@sugar.UUCP> peter@sugar.UUCP (Peter da Silva) writes:
>> [ description of how to make an assembler that handles long/short branches ]
>But that doesn't resolve the problem of how to deal with near and far
>cals to seperately compiled code. If the calling sequence of the 8086
>was a little more logical, you could have 2 entry points for the routine:
>near and far. The near would just push the segment and fall through to
>the far. Unfortunately, segment is not the top of the stack in a far
>call. See Kernighan's April column in Computer Language.

I may be missing the point here, but as I remember, the objection was that
the offending push can't be done without destroying a register. However since
*ALL* C's I've seen are able to return a value, you just use that register
i.e. AX on the 8086, and since AX is probably going to get munged in the
procedure you are safe:

nearentry:
	pop	ax	; save pc in ax
	push	cs	; do the push everyones bitching about
	push	ax	; restore pc

farentry:
	code ......


	retfar		; or however you do a far return

Caveat:
	I do agree with his point that if you need to preserve all regs thru
a procedure then this is a problem, but in C this is not usually the case.
--
		dg@wrs.UUCP - David Goodenough

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