Re: gcc-14 Wflex-array-member-not-at-end may-be-ub in struct pthread

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 19/07/23 11:17, Adhemerval Zanella Netto wrote:
> 
> 
> On 08/07/23 16:21, Cristian Rodríguez via Libc-alpha wrote:
>> On Wed, Jul 5, 2023 at 2:13 PM Cristian Rodríguez <cristian@rodriguez.im>
>> wrote:
>>
>>>
>>>
>>> On Wed, Jul 5, 2023 at 11:53 AM Paul Eggert <eggert@cs.ucla.edu> wrote:
>>>
>>>> On 2023-07-05 06:46, Cristian Rodríguez via Libc-alpha wrote:
>>>>>    char end_padding[]; --> This is incorrect, since struct rseq
>>>> contains a
>>>>> flexible array it must be the last member..
>>>>
>>>> ? struct rseq doesn't contain a flexible array on the master branch, so
>>>> there's no error here.
>>>>
>>>
>>> I may be missing something but I have struct rseq containing a final
>>> flexible array..
>>>
>>> /*
>>>          * Flexible array member at end of structure, after last feature
>>> field.
>>>          */
>>>         char end[];
>>> }
>>>
>>> this happens because:
>>>
>>> #ifdef __has_include
>>> # if __has_include ("linux/rseq.h")
>>> #  define __GLIBC_HAVE_KERNEL_RSEQ --> that is defined
>>> # endif
>>>
>>>
>>>> Perhaps you tried to nest 'struct pthread' inside another struct? If so,
>>>> the C standard doesn't allow that but the attached untested patch should
>>>> be a trivial fix.
>>>>
>>>
>>> Your patch does indeed silence this particular warning, thanks.
>>>
>>
>> I suggest you add this patch to the release queue. because as far as I can
>> tell, It is UB when the kernel headers are present on the system.
> 
> The flexible array on rseq was added on linux 6.3, should we treat this as
> release blocker?

Also, glibc currently does not handle AT_RSEQ_FEATURE_SIZE/AT_RSEQ_ALIGN. Is
this a potential issue for newer kernels?