From: =?iso-8859-1?Q?M=E5ns_Rullg=E5rd?= <mans@mansr.com>
To: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
        =?iso-8859-1?Q?M=E5ns_Rull?= =?iso-8859-1?Q?g=E5rd?= 
	<mans@mansr.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        akpm@linux-foundation.org, sam@ravnborg.org, ak@linux.intel.com
Subject: Re: [PATCH] ARM: Do not allow unaligned accesses when CONFIG_ALIGNMENT_TRAP
References: <20110523111648.10474.78396.stgit@e102109-lin.cambridge.arm.com>
	<20110523132124.GI17672@n2100.arm.linux.org.uk>
	<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>
Date: Thu, 26 May 2011 19:14:47 +0100
In-Reply-To: <1306429854.26735.9.camel@e102144-lin.cambridge.arm.com> (Will
	Deacon's message of "Thu, 26 May 2011 18:10:54 +0100")
Message-ID: <yw1xvcwxfhwo.fsf@unicorn.mansr.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.2 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1369
Lines: 35

Will Deacon <will.deacon@arm.com> writes:

> This issue seems to be caused by passing -fconserve-stack to GCC. This
> was added in 8f7f5c9f ("kbuild: set -fconserve-stack option for gcc
> 4.5") and as you can see from the archive:
>
> http://lkml.org/lkml/2009/9/20/39
>
> it was thought to only have an impact on inlining decisions. Looking at
> the documentation for GCC 4.6:
>
> -fconserve-stack
>           Attempt to minimize stack usage. The compiler will attempt to
> use less stack space, even if that makes the program slower. This option
> implies setting the ‘large-stack-frame’ parameter to 100 and the
> ‘large-stack-frame-growth’ parameter to 400.
>
> So it sounds like we might not want to enable this blindly across all
> architectures. Indeed, on ARM, it encourages the compiler to pack
> variables on the stack which leads to the weird and wonderful alignment
> situation that has been encountered in this thread.
>
> Can we remove -fconserve-stack from the top-level Makefile (or at least
> make it conditional by architecture)?

Sounds like a good idea to me.

-- 
Måns Rullgård
mans@mansr.com
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/