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

[Tim Deegan <tim@xxxxxxx>]

At 03:36 -0600 on 20 Jun (1497929778), Jan Beulich wrote:
> >>> 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.

Ah, I see.  So would it be better to use

  #define INVALID_MFN ((const mfn_t) { ~0UL })

?

Tim.

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