Message-ID: <4DDED44E.9070402@linux.intel.com>
Date: Thu, 26 May 2011 15:29:34 -0700
From: Andi Kleen <ak@linux.intel.com>
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To: Russell King - ARM Linux <linux@arm.linux.org.uk>
CC: Nicolas Pitre <nico@fluxnic.net>, Will Deacon <will.deacon@arm.com>,
        =?ISO-8859-1?Q?M=E5ns_Rullg=E5rd?= <mans@mansr.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        lkml <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>, sam@ravnborg.org,
        linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] ARM: Do not allow unaligned accesses when	CONFIG_ALIGNMENT_TRAP
References: <1306229953.19557.14.camel@e102109-lin.cambridge.arm.com> <yw1xipt0p4i9.fsf@unicorn.mansr.com> <BANLkTi=xLE9gP5YOdr9dR0DfsY1Ymzxu+w@mail.gmail.com> <20110524171331.GA2941@arm.com> <20110525111405.GA12010@e102109-lin.cambridge.arm.com> <20110525124348.GA2340@arm.com> <yw1xaaeanbxe.fsf@unicorn.mansr.com> <BANLkTim2TOZgB-3Vkv5RcK572Qr07s3=CA@mail.gmail.com> <1306429854.26735.9.camel@e102144-lin.cambridge.arm.com> <alpine.LFD.2.00.1105261650330.3207@xanadu.home> <20110526215101.GL24876@n2100.arm.linux.org.uk>
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> Catalin said in his mail "I haven't tried with -mno-unaligned-access, I
> suspect the variables on the stack would be aligned.".  So I don't think
> we know enough to say whether -mno-unaligned-access avoids the stack
> packing.

It won't, the arm gcc code just checks flag_conserve_stack.
IMHO it's just a gcc bug. You should report it to 
http://gcc.gnu.org/bugzilla

As a temporary workaround you can disable it in the kernel too, but as soon
as the compiler it's fixed I would recommend considering to reenable it.

-Andi

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