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From: Paul Mackerras <paulus@samba.org>
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Date: Fri, 4 Jan 2002 20:29:19 +1100 (EST)
To: Pavel Machek <pavel@suse.cz>
Cc: Tom Rini <trini@kernel.crashing.org>,
        David Woodhouse <dwmw2@infradead.org>,
        Alan Cox <alan@lxorguk.ukuu.org.uk>, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.linuxppc.org
Subject: Re: [PATCH] C undefined behavior fix
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Pavel Machek writes:

> gcc is allowed not to pass it anywhere. You may not second guess
> optimizer. If it is not defined, it is not defined.
> 
> Imagine
> 
> strcpy(a, "xyzzy"+b);
> if (b>16)
> 	printf("foo");
> 
> . gcc is permitted to kill printf(), because if b<0 or b>16 behaviour is
> undefined. So gcc may assume b<=16.

So... I'm curious.  How is the result of virt_to_phys ever anything
other than undefined?

Paul.
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