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

[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?