Re: [Xen-devel] [PATCH for-4.6] xen/public: arm: Use __typeof__ rather than typeof

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 23/10/15 15:37, Jan Beulich wrote:
>>>> On 23.10.15 at 16:31, <ian.campbell@xxxxxxxxxx> wrote:
>> On Fri, 2015-10-23 at 08:16 -0600, Jan Beulich wrote:
>>> No, the validating script is a nice-to-have, but nothing more. What
>>> I was referring to was a patch to drop the use of this gcc extension.
>>
>> Then I'm confused. This patch turns a typeof into a __typeof__. In <
>> 56126D8702000078000A80AC@xxxxxxxxxxxxxxxxxxxxxxx> you said "typeof() is a
>> gcc extension".
>>
>> Are you now saying that __typeof__ also a gcc extension too?
>>
>> I was under the impression that __typeof__ was standard (by some cxx at
>> least) and your mail reinforced that (possibly wrong) impression.
> 
> There's no typeof or __typeof__ in C11 or any earlier standard.
> I'm sorry if earlier replies of mine gave a different impression.
> 
>> https://gcc.gnu.org/onlinedocs/gcc/Typeof.html also says that "If you are
>> writing a header file that must work when included in ISO C programs, write
>> __typeof__ instead of typeof", which also lead me to believe __typeof__ was
>> OK from this PoV.
> 
> That's solely to prevent name space issues - __typeof__ is a
> reserved name, while typeof isn't.

Thank you for the explanation. I think we can do the same as x86 does i.e:

#define set_xen_guest_handle_raw(hnd, val)                  \
    do { if ( sizeof(hnd) == 8 ) *(uint64_t *)&(hnd) = 0;   \
         (hnd).p = val;                                     \
    } while ( 0 )

I will send a new version of this patch.

Regards,


-- 
Julien Grall

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