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Date: Sun, 30 Dec 2012 15:03:14 -0500
From: Diane Bruce <db@db.net>
To: Christoph Mallon <christoph.mallon@gmx.de>
Subject: Re: Fwd: Re: Bug in r244780
Message-ID: <20121230200314.GA35356@night.db.net>
References: <20121229150648.GB66011@ithaqua.etoilebsd.net>
 <20121229160219.GA14487@night.db.net> <50DF41BE.9020206@gmx.de>
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Cc: toolchain@FreeBSD.org, Baptiste Daroussin <bapt@FreeBSD.org>
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On Sat, Dec 29, 2012 at 08:17:18PM +0100, Christoph Mallon wrote:
> On 29.12.2012 17:02, Diane Bruce wrote:
> >>  	/* Create new group and copy old group into it. */
> >> -	if ((newgr = malloc(len)) == NULL)
> >> +	if ((dst = malloc(len)) == NULL)
> >>  		return (NULL);
> >> +	newgr = (struct group*)dst;
> > 
> > Unfortunately the new compiler (clang) will error out on this. It's
> > really anal. The error will be that it cannot convert char * alignment
> > to struct group * alignment. 1 vs. 4 (or 8). BTDT
> 
> This sounds like a bug.
> First, it should not be an error, but at most a warning.

Please take this up with toolchain@FreeBSD.org

> Second, the cast is fine, as the pointer itself is a result of malloc().
> Obviously clang only checks the type of the variable.
> Probably, the diagnostic can be suppressed with an intermediate cast to void*.
> Third, the other casts (newgr + 1 casted to a char** and so on) are borderline invalid due to strict aliasing rules.
> Therefore I prefer my method of chopping off bytes of a char buffer instead of munging differently typed pointers.
> 
> 	Christoph

- Diane
-- 
- db@FreeBSD.org db@db.net http://www.db.net/~db