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Date:      Fri, 25 Jan 2008 13:43:08 +0000
From:      Nicholas Clark <nick@ccl4.org>
To:        Dag-Erling =?iso-8859-1?Q?Sm=F8rgrav?= <des@des.no>
Cc:        freebsd-arm@freebsd.org
Subject:   Re: sshd broken on arm?
Message-ID:  <20080125134308.GR81396@plum.flirble.org>
In-Reply-To: <86hch25als.fsf@ds4.des.no>
References:  <479880A7.1030107@digiware.nl> <20080124.084828.1608359032.imp@bsdimp.com> <864pd386mj.fsf@ds4.des.no> <20080124.110954.179240992.imp@bsdimp.com> <47991E08.6070609@digiware.nl> <20080125041540.GA30262@zibbi.meraka.csir.co.za> <4799A2B3.4060003@digiware.nl> <86prvq5eua.fsf@ds4.des.no> <20080125113916.GP81396@plum.flirble.org> <86hch25als.fsf@ds4.des.no>

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On Fri, Jan 25, 2008 at 01:54:39PM +0100, Dag-Erling Smrgrav wrote:
> Nicholas Clark <nick@ccl4.org> writes:
> > On Fri, Jan 25, 2008 at 12:23:09PM +0100, Dag-Erling Smrgrav wrote:
> > > None of this matters.  What John pointed out means that the code is
> > > wrong and the compiler is right.  The code is not allowed to assume
> > > that an object is correctly aligned unless it is of a type that
> > > requires the correct alignment.  The easiest way to do this is with
> > > a union, e.g.
> > Whilst that is correct, why is the compiler changing the alignment of the
> > struct for different optimiser settings but all other flags identical?
> 
> Because *it is not a struct*.

Aha. That was what I missed.

> It is an array of char, and char has no special alignment requirement.
> 
> The bug is in the code, which uses pointer aliasing in a way that is
> strictly speaking legal but which places responsibility for alignment
> issues squarely in the code and not the compiler.

Yes, I agree. In which case I agree with whoever said previously that the
fix needs to be taken upstream, but in turn that they may have already fixed
it as (IIRC) FreeBSD is using a non-current version of openssh.

Nicholas Clark



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