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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.10.15 at 16:31, <ian.campbell@xxxxxxxxxx> wrote:
> On Fri, 2015-10-23 at 08:16 -0600, Jan Beulich wrote:
>> > > > On 23.10.15 at 15:58, <julien.grall@xxxxxxxxxx> wrote:
>> > On 23/10/15 14:52, Jan Beulich wrote:
>> > > > > > On 23.10.15 at 15:30, <ian.campbell@xxxxxxxxxx> wrote:
>> > > > On Fri, 2015-10-23 at 14:13 +0100, Julien Grall wrote:
>> > > > > Hi,
>> > > > > 
>> > > > > On 04/10/15 20:24, Julien Grall wrote:
>> > > > > > The keyword typeof is not portable:
>> > > > > > 
>> > > > > > /usr/src/freebsd/sys/xen/hypervisor.h:93:2: error: implicit
>> > > > > > declaration
>> > > > > > of function 'typeof' is invalid in C99
>> > > > > > [-Werror,-Wimplicit-function-declaration]
>> > > > > 
>> > > > > Ping? Aside the fact that other bits of the header may not be iso
>> > > > > compliant, I still think this patch is valid.
>> > > > 
>> > > > Yes, I agree.
>> > > > Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
>> > > > 
>> > > > Jan, after your earlier comments are you happy to go ahead with
>> > > > this for
>> > > > now and sort the other possible issues separately?
>> > > 
>> > > Well - it's an improvement, sure, so I'm not intending to block it
>> > > going in if no better way can be determined in its place right away.
>> > > What makes me hesitant is that I'm not sure there indeed will be a
>> > > follow up to this any time soon.
>> > 
>> > TBH, having a script which check the validity of the headers is not in
>> > the top my todo list. Though it would be nice to have it.
>> 
>> 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.

Jan


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