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

[Russell King - ARM Linux]

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.