> On Feb 28, 2023, at 4:59 PM, Jakub Jelinek <ja...@redhat.com> wrote:
>
> On Tue, Feb 28, 2023 at 07:19:40PM +0000, Qing Zhao wrote:
>> Understood.
>> So, your patch fixed this bug, and then [0] arrays are instrumented by
>> default with this patch.
>>
>>> Well, it would complain about
>>> struct S { int a; int b[0]; int c; } s;
>>> ... &s.b[1] ...
>>> for C++, but not for C.
>>
>> A little confused here: [0] arrays were instrumented by default for C++ if
>> it’s not a trailing array, but not for C?
>
> Given say
> struct S { int a; int b[0]; int c; } s;
>
> int
> main ()
> {
> int *volatile p = &s.b[0];
> p = &s.b[1];
> int volatile q = s.b[0];
> }
> both -fsanitize=bounds and -fsanitize=bounds-strict behaved the same way,
> in C nothing was reported, in C++ the p = &s.b[1]; statement.
> The reasons for s.b[0] not being reported in C++ was that for
> !ignore_off_by_one, bounds was ~(size_t)0, and so index > ~(size_t)0
> is always false. While with the committed patch it is
> index >= (~(size_t)0)+1 and so always true. And in C additionally, we
> punted early because TYPE_MAX_VALUE (domain) was NULL.
Thanks for the explanation.
With your patch, both C and C++ will report for the middle [0] arrays. That’s
nice.
Qing
>
> Jakub
>
