On 11/15/2010 09:12 PM, Eric Dumazet wrote:
> Le dimanche 14 novembre 2010 Ã 18:06 -0800, Andrew Morton a Ãcrit :
>> On Sun, 14 Nov 2010 12:25:33 +0300 Vasiliy Kulikov <segoon@xxxxxxxxxxxx> wrote:
>>>
>>> if (timeval) {
>>> - rtv.tv_sec = rts.tv_sec;
>>> - rtv.tv_usec = rts.tv_nsec / NSEC_PER_USEC;
>>> + struct timeval rtv = {
>>> + .tv_sec = rts.tv_sec,
>>> + .tv_usec = rts.tv_nsec / NSEC_PER_USEC
>>> + };
>>>
>>> if (!copy_to_user(p, &rtv, sizeof(rtv)))
>>> return ret;
>>
>> Please check the assembly code - this will still leave four bytes of
>> uninitalised stack data in 'rtv', surely.
>
> Thats a good question.
>
> In my understanding, gcc should initialize all holes (and other not
> mentioned fields) with 0, even for automatic storage [C99 only mandates
> this on static storage]
>
> I tested on x86_64 and this is the case, but could not find a definitive
> answer in gcc documentation.
>
> This kind of construct is widely used in networking tree.
>
> Maybe we should ask to gcc experts if this behavior is guaranteed by
> gcc, or if we must review our code ;(
>
> CC Jakub
>
> Thanks !
>
This is what I thought too. If it is not there are tones of bugs I wrote
of code that relays on this behaviour.
It would be interesting to know for sure
Thanks
Boaz
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