Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 (Tek) 9/28/84 based on 9/17/84; site tekigm.UUCP
Path: utzoo!watmath!clyde!cbosgd!ihnp4!houxm!vax135!cornell!uw-beaver!tektronix!tekigm!jonk
From: jonk@tekigm.UUCP (Jonathan W. Krueger)
Newsgroups: net.unix-wizards
Subject: Re: Xenix286 Wonders, Bugs, and Patches...
Message-ID: <334@tekigm.UUCP>
Date: Tue, 14-May-85 15:52:09 EDT
Article-I.D.: tekigm.334
Posted: Tue May 14 15:52:09 1985
Date-Received: Fri, 17-May-85 00:03:54 EDT
References: <10550@brl-tgr.ARPA>
Reply-To: jonk@tekigm.UUCP (Jonathan W. Krueger)
Organization: Tektronix, Beaverton OR
Lines: 32

'#define'ing NULL to be simply 0 (zero) can and will screw up C programs
on the '286 (or '86) which make the assumption that
sizeof(int) == sizeof(int *).  The following exemplefies this:
        baz()
	{
	  ...
	  foo( NULL, more_args_of_various_sizes, ... );
	  ...
	}

	foo( p, more_params_of_various_sizes, ... );
	    struct whatever *p;
	    typeof more_para....;
	{ if ( p == NULL ) /* then */ { ... }
	  ...
	}

The Xenix '286 C compiler generates the call to foo with an "int" 0 (2 bytes),
not a "long" 0 (4 bytes).  foo expects 4 bytes in that position.  This is
partly why on Xenix-286 you find three (or more) packagings of the standard C
library: one for each compiler memory model, small, medium and large.  Another
reason is that larger programs need to use "far jumps" rather than "near
jumps."

Of course, I trust you to tell me if I'm wrong.

			-- Humbly,
			   Jonathan W. Krueger
			...ihnp4!tektronix!tekigm!jonk

			"To change my opinion,
			 you must first change my reality."