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 18:43:35 +0000 [thread overview]
Message-ID: <20130306184335.GW17833@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <51377EFE.3070801@gmail.com>
On Wed, Mar 06, 2013 at 06:38:06PM +0100, Dirk Behme wrote:
> Am 06.03.2013 18:11, schrieb Russell King - ARM Linux:
>> 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?
>
> I'm not sure if there even is a disagreement ;)
>
> I've asked because it seems that Ivan's v2 patch [1] isn't applied
> anywhere, yet. This let me to the impression that this might not be the
> final ('agreed') fix and that something still has to be done.
Well, I don't generally pick patches off the mailing list. It's too
difficult for me to do that. Emails *very* *very* quickly get buried
and forgotten, especially as I don't look at emails each and every day
(this afternoon is the first time since Monday afternoon, and I'm not
going to look back before Monday as there's been 500 _new_ emails
which I'm still going through.)
This is exactly why I have the patch system - to help capture the
patches which need to be applied.
prev parent reply other threads:[~2013-03-06 18:43 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
2013-03-06 17:38 ` Dirk Behme
2013-03-06 18:43 ` Russell King - ARM Linux [this message]
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