From: linux@arm.linux.org.uk (Russell King - ARM Linux)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] [RFC] arm: fix memset-related crashes caused by recent GCC (4.7.2) optimizations
Date: Wed, 6 Mar 2013 17:11:10 +0000 [thread overview]
Message-ID: <20130306171110.GQ17833@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <5135F80E.3070307@gmail.com>
On Tue, Mar 05, 2013 at 02:50:06PM +0100, Dirk Behme wrote:
> On 12.02.2013 17:36, Will Deacon wrote:
>> On Tue, Feb 12, 2013 at 03:58:01PM +0000, Russell King - ARM Linux wrote:
>>> On Tue, Feb 12, 2013 at 02:00:08PM +0000, Will Deacon wrote:
>>>> Interesting... the GCC documentation also states that ffreestanding implies
>>>> fno-builtin, so memset and co shouldn't be targetted for this sort of
>>>> optimisation by GCC. Have you observed this problem even when passing this
>>>> option?
>>>
>>> Rather than wondering whether we should be using -ffreestanding or not
>>> (which, x86 people have strongly resisted) I suggest that we just fix
>>> our memset() implementation to be compliant.
>>>
>>> The reason it's not compliant is that I saw no reason for it to be
>>> compliant back in the gcc 2.7.x days, and it's persisted like that for
>>> the last 19-ish years. If GCC is now making use of the return value,
>>> then we need to fix that and undo the "optimization" in our string.h.
>>>
>>> So let's just bite the bullet, make the asm memset() compliant, and
>>> clean up string.h.
>>
>> That would be the ideal thing to do, because it allows the compiler to
>> optimise around these functions, however it does mean we need to check/fix
>> *all* of the string functions at least (if we don't pass -fno-builtin then
>> any builtin function is up for optimisation, including strcpy etc).
>
> Do we already have an agreed solution for this issue anywhere, now?
No idea. I've stated above what I think should happen. Where's the
disagreement?
next prev parent reply other threads:[~2013-03-06 17:11 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-02 8:33 [PATCH] [RFC] arm: fix memset-related crashes caused by recent GCC (4.7.2) optimizations Ivan Djelic
2013-02-09 11:05 ` Ivan Djelic
2013-02-09 14:48 ` Nicolas Pitre
2013-02-11 12:35 ` Ivan Djelic
2013-02-11 18:17 ` Ben Dooks
2013-02-11 21:39 ` Ivan Djelic
2013-02-11 18:41 ` Will Deacon
2013-02-11 19:42 ` Ivan Djelic
2013-02-12 14:00 ` Will Deacon
2013-02-12 15:58 ` Russell King - ARM Linux
2013-02-12 16:36 ` Will Deacon
2013-02-12 16:37 ` Russell King - ARM Linux
2013-02-12 16:38 ` Will Deacon
2013-03-05 13:50 ` Dirk Behme
2013-03-06 1:42 ` Will Deacon
2013-03-06 7:05 ` Dirk Behme
2013-03-06 17:11 ` Russell King - ARM Linux [this message]
2013-03-06 17:38 ` Dirk Behme
2013-03-06 18:43 ` Russell King - ARM Linux
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