On August 3, 2023 10:34:24 AM PDT, Qing Zhao <qing.z...@oracle.com> wrote:
>One thing I need to point out first is, currently, even for regular fixed size
>array in the structure,
>We have this same issue, for example:
>
>#define LENGTH 10
>
>struct fix {
> size_t foo;
> int array[LENGTH];
>};
>
>…
>int main ()
>{
> struct fix *p;
> p = alloc_buf_more ();
>
> expect(__builtin_object_size(p->array, 1), LENGTH * sizeof(int));
> expect(__builtin_object_size(p->array, 0), -1);
>}
>
>Currently, for __builtin_object_size(p->array, 0), GCC return UNKNOWN for it.
>This is not a special issue for flexible array member.
Is this true with -fstrict-flex-arrays=3 ?
-Kees
>
>Qing
>
>
>On Aug 3, 2023, at 1:19 PM, Siddhesh Poyarekar <siddh...@gotplt.org> wrote:
>>
>> On 2023-08-03 12:43, Qing Zhao wrote:
>>>> Surely we could emit that for __bdos(q->array, 0) though, couldn't we?
>>> For __bdos(q->array, 0), we only have the access info for the sub-object
>>> q->array, we can surely decide the size of the sub-object q->array, but we
>>> still cannot
>>> decide the whole object that is pointed by q (the same reason as above),
>>> right?
>>
>> It's tricky, I mean we could assume p to be a valid object due to the
>> dereference and hence assume that q->foo is also valid and that there's at
>> least sizeof(*q) + q->foo * sizeof (q->array) bytes available. The question
>> then is whether q could be pointing to an element of an array of `struct
>> annotated`. Could we ever have a valid array of such structs that have a
>> flex array at the end? Wouldn't it always be a single object?
>>
>> In fact for all pointers to such structs with a flex array at the end, could
>> we always assume that it is a single object and never part of an array, and
>> hence return sizeof()?
>>
>> Thanks,
>> Sid
>
--
Kees Cook
