Am 23.11.2010 15:01, schrieb AmÃrico Wang:
> On Mon, Nov 15, 2010 at 08:12:21PM +0100, 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.
>>
>
> Yeah, this is not clearly defined by C99 I think, but we can still
> find some clues in 6.2.6.1, Paragraph 6,
>
> "
> When a value is stored in an object of structure or union type,
> including in a member object, the bytes of the object representation
> that correspond to any padding bytes take unspecified values.
> "
>
> So we can't rely on the compiler to initialize the padding bytes
> too.
>
hi all,
as we see this is not a question of c99.
Maybe we can convince the gcc people to make 0 padding default. That will not solve the
problems for other compilers but when they claim "works like gcc" we can press then to
support this also. I can imagine that this will close some other subtle leaks also.
People that still want a "undefined" (for what ever reason) can use an option to enable it
again (e.g. --no-zero-padding).
do anyone have a contact so we can forward that request ?
re,
wh
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