From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ruediger Helsch <rh@unifix.de>
To: Jim Wilson <wilson@cygnus.com>
Cc: Ian Lance Taylor <ian@cygnus.com>, rms@gnu.ai.mit.edu, drepper@cygnus.com, dm@sgi.com, gcc2@cygnus.com, gas2@cygnus.com
Subject: Re: global vars and symbol visibility for mips32/elf 
Date: Tue, 13 Aug 1996 16:06:00 -0000
Message-id: <Pine.LNX.3.91.960813235516.19616B-100000@anna.unifix.de>
References: <199608131920.MAA26625@cygnus.com>
X-SW-Source: 1996/msg00092.html

On Tue, 13 Aug 1996, Jim Wilson wrote:

> 	Wrong.  A standard conforming compiler will conclaim about a multiply
> 	defined symbol.
> 
> This is not correct.  You have missed a subtle point here.
> 
> A program that has multiple external definitions is not a strictly conforming
> program.  If you want your programs to be strictly conforming, then you can not
> rely on common.
> 
> A conforming compiler must accept any strictly conforming program.  However, a
> conforming compiler can have extensions that allow it to accept non-strictly
> conforming programs providing that such extensions do not change the behaviour
> of any strictly conforming program.
> 
> The standard says that a program with multiple external definitions results
> in undefined behaviour.  A standard conforming compiler can do anything when
> an input program triggers undefined behaviour.  Normally, we give a warning
> to encourage portable programming.  In this particular case, gcc chooses to
> have an extensions that allows such programs to work.
> 
> This extension is even sanctioned by the standard (in a sense), as it is
> documented in the section on common extensions.

But the standard allows such behaviour only if no strictly 
standard-conforming program is broken by the extension.  The following
program is strictly conforming and should continue to run:

	#include <assert.h>
	int optind[30000], optarg[30000];

	main()
	{
		int i;
		for (i = 0; i < 30000; i++) {
			optind[i] = 1;
			optarg[i] = 2;
		}

		for (i = 0; i < 30000; i++) {
			assert(optind[i] == 1);
			assert(optarg[i] == 2);
		}
		return 0;
	}

Try this to see whether your compiler conforms to the C standard!

Ruediger Helsch <rh@unifix.de>