RFC: Fix powerpc64 build with GCC 5.0

[Adhemerval Zanella]

On 30-12-2014 18:46, Joseph Myers wrote:
> On Tue, 30 Dec 2014, Adhemerval Zanella wrote:
>
>> And this comes from sysdep.h:
>>
>>         if (__builtin_classify_type (__arg3) != 5 && sizeof (__arg3) > 8) \
>>           __illegally_sized_syscall_arg3 (); \
>>
>> My understanding is since we already testing if argument is a 'pointer_type_class'
>> (__builtin_classify_type equal to 5), thus the sizeof test is superfluous.  Would be
>> a correct fix to just remove these tests? Thoughts?
> I don't think either test is superfluous.
>
> The point of checking __builtin_classify_type is to avoid errors on string 
> literal arguments, where sizeof inhibits array-to-pointer conversion (but 
> __builtin_classify_type doesn't, so string literals count as pointers for 
> __builtin_classify_type).
>
> If __builtin_classify_type (__arg3) != 5, that means the argument - after 
> array-to-pointer conversion - is *not* a pointer.  Pointers would never 
> satisfy sizeof (__arg3) > 8, but non-pointers might (e.g. structures) and 
> in that case would be invalid syscall arguments.
>
> Assuming we want this checking at all (and if anything, my inclination 
> would be that it should go in some sort of generic __check_syscall_arg 
> macros in generic sysdeps/unix files, not be architecture-specific), my 
> inclination would be to insert an explicit cast to (const struct timespec 
> *) in utimensat.c, with a comment to explain why it's there.
>
I see what I overlook then and I will prepare a patch using casts to cleanup
powerpc build.  Thanks!