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To: Horst von Brand <vonbrand@inf.utfsm.cl>
Cc: jt@hpl.hp.com, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Invalid compilation without -fno-strict-aliasing
References: <200302261538.h1QFcAiF004085@eeyore.valparaiso.cl>
From: Falk Hueffner <falk.hueffner@student.uni-tuebingen.de>
Date: 26 Feb 2003 17:04:05 +0100
In-Reply-To: <200302261538.h1QFcAiF004085@eeyore.valparaiso.cl>
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Horst von Brand <vonbrand@inf.utfsm.cl> writes:

> Jean Tourrilhes <jt@bougret.hpl.hp.com> said:
> > 	if((stream + event_len) < ends) {
> > 		iwe->len = event_len;
> > 		memcpy(stream, (char *) iwe, event_len);
> > 		stream += event_len;
> > 	}
> > 	return stream;
> > }
> 
> The compiler is free to assume char *stream and struct iw_event *iwe
> point to separate areas of memory, due to strict aliasing.

The relevant paragraph of the C99 standard is:

An object shall have its stored value accessed only by an lvalue
expression that has one of the following types:

-- a type compatible with the effective type of the object,
-- a qualified version of a type compatible with the effective type of
   the object,
-- a type that is the signed or unsigned type corresponding to the
   effective type of the object,
-- a type that is the signed or unsigned type corresponding to a
   qualified version of the effective type of the object,
-- an aggregate or union type that includes one of the aforementioned
   types among its members (including, recursively, a member of a
   subaggregate or contained union), or
-- a character type.

I can't really spot any lvalue here that might violate this rule.  It
would be nice if somebody could report a bug with a testcase.

-- 
	Falk
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