[PATCH] check_native: Get rid of alloca

[Florian Weimer]

* Andreas Schwab:

> On Jun 01 2023, Florian Weimer wrote:
>
>> * Andreas Schwab:
>>
>>> On Jun 01 2023, Florian Weimer via Libc-alpha wrote:
>>>
>>>> * Adhemerval Zanella Netto via Libc-alpha:
>>>>
>>>>> +static void
>>>>> +iclose (int *fd)
>>>>> +{
>>>>> +  if (*fd >= 0)
>>>>> +    __close_nocancel_nostatus (*fd);
>>>>> +}
>>>>> +
>>>>>  void
>>>>>  __check_native (uint32_t a1_index, int *a1_native,
>>>>>  		uint32_t a2_index, int *a2_native)
>>>>>  {
>>>>> -  int fd = __socket (PF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE);
>>>>> +  int __attribute__ ((__cleanup__ (iclose))) fd
>>>>> +    = __socket (PF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_ROUTE);
>>>>> +  if (fd < 0)
>>>>> +    return;
>>>>
>>>> I think introducing attribute cleanup where equivalent functionality can
>>>> be implemented otherwise requires a discussion first.
>>>
>>> The cleanup attribute requires compiling the function and all callees
>>> with -fasynchronous-unwind-tables.
>>
>> I think GCC will still call the destructor on normal scope exit (if no
>> exception is thrown), even with -fno-exceptions.  That should be
>> sufficient here?
>
> The cancellation could be asynchronous.

The current code does handle cancellation.  Isn't sendto a cancellation
point?

In any case, we'd have to build with -fexceptions to turn the destructor
into a cancellation handler, not -fasynchronous-unwind-tables.

Thanks,
Florian