Re: [Xen-devel] [PATCH v2 01/16] xen/mm: Don't use _{g, m}fn for defining INVALID_{G, M}FN

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.06.17 at 11:14, <tim@xxxxxxx> wrote:
> At 01:32 -0600 on 20 Jun (1497922345), Jan Beulich wrote:
>> >>> On 19.06.17 at 18:57, <julien.grall@xxxxxxx> wrote:
>> > --- a/xen/include/xen/mm.h
>> > +++ b/xen/include/xen/mm.h
>> > @@ -56,7 +56,7 @@
>> >  
>> >  TYPE_SAFE(unsigned long, mfn);
>> >  #define PRI_mfn          "05lx"
>> > -#define INVALID_MFN      _mfn(~0UL)
>> > +#define INVALID_MFN      (mfn_t){ ~0UL }
>> 
>> While I don't expect anyone to wish to use a suffix expression on
>> this constant, for maximum compatibility this should still be fully
>> parenthesized, I think. Of course this should be easy enough to
>> do while committing.
>> 
>> Are you able to assure us that clang supports this gcc extension
>> (compound literal for non-compound types)
> 
> AIUI this is a C99 feature, not a GCCism.

Most parts of it yes (it is a gcc extension in C89 mode only), but the
specific use here isn't afaict: Compound literals outside of functions
are static objects, and hence couldn't be used as initializers of other
objects.

>  Clang supports it as far back as 3.0: https://godbolt.org/g/YY97uj 

Good.

Jan


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