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.
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
