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From: gwyn@brl-smoke.ARPA (Doug Gwyn )
Newsgroups: net.unix-wizards
Subject: Re: Microport Unix -- Large Model Problems
Message-ID: <5299@brl-smoke.ARPA>
Date: Sat, 8-Nov-86 03:16:50 EST
Article-I.D.: brl-smok.5299
Posted: Sat Nov  8 03:16:50 1986
Date-Received: Sun, 9-Nov-86 03:38:23 EST
References: <1376@batcomputer.TN.CORNELL.EDU> <840@ur-valhalla.UUCP> <5068@ukme.ukma.uky.csnet>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 24

In article <5068@ukme.ukma.uky.csnet> david@ukme.UUCP (David Herron, NPR Lover) writes:
-In article <840@ur-valhalla.UUCP> dave@valhalla.UUCP (Dave Carlson) writes:
->A potential problem I smacked into yesterday when porting BSD to SV/AT
->is ioctl(2) expects as the third argument:
->union   { int iarg;
->        char *cparg;}
->Problem is that the union will pull 4 bytes off the stack (in large model)
->but the program calling with an integer will only push 2 bytes.  Oh S*$&!
->I cast my integer args long and everything seems ok but what a pain...
-
-Argh!  And you're doing a port of an operating system???
-
-UNIONS are the SAME size regardless of WHICH part of them you use!
-
-A user which passes an int to a routine expecting a union is ASKING
-for trouble!

Oh, good grief!  Mr. Carlson is talking about ioctl(), which is a
well-known function whose third argument has a type that depends on
its second argument's value; usually it's an (int) or a (struct termio *).
The problem is not his; rather it is due to the SV/AT implementor
changing ioctl()'s third argument to be a union.  This is in violation
of the SVID and of common sense, since (as Mr. Carlson reports) this
breaks correctly-written code.