Subject: [PATCH] [RFC] arm: fix memset-related crashes caused by recent GCC (4.7.2) optimizations

From: [email-masked] (Dirk Behme)
Date: Wed, 6 Mar 2013 08:05:49 +0100

On 06.03.2013 02:42, Will Deacon wrote:
> Hi Dirk,
> 
> On Tue, Mar 05, 2013 at 01:50:06PM +0000, 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?
> 
> I thought that the conclusion was to go with Ivan's suggestion since memset
> is the only function which doesn't follow what the compiler expects.

Ok, thanks! :)

Could we get Ivan's v2 patch integrated or at least sent to the patch 
system, then, please?

Many thanks,

Dirk