Re: [Xen-devel] [PATCH 2/2] xen/mm: Introduce {G, M}FN_INVALID_INITIALIZER

[Julien Grall <julien.grall@xxxxxxx>]

On 27/06/2017 10:46, Tim Deegan wrote:
> At 10:33 +0100 on 27 Jun (1498559600), Julien Grall wrote:
> > The current implementation of {G,M}FN_INVALID cannot be used to
> > initialize global variable because the initializer element is not a
> > constant.
> >
> > Due to a bug in GCC 4.9 and older ([1]), it is not easy to find a common
> > value to initialize a variable and directly passed as an argument.
> >
> > Introduce 2 news define {G,M}FN_INVALID_INITIALIZER to be used for
> > initializing a variable.
> >
> > [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64856
> >
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> Acked-by: Tim Deegan <tim@xxxxxxx> (and Ack for the revert too)
> but please choose either { ~0UL } or {~0UL} and use it for both.
Whoops. Sorry for that. I will stick to {~0UL} unless someone prefer the 
{ ~0UL }.
Cheers,

> > ---
> >     Build tested it with:
> >         * ARM: GCC 4.9.4, 5.1, 4.3, 6.1.1, 7.1.0
> >         * x86: Clang 3.5.0, 3.6.0, 3.6.2, 3.8.0, 3.9.0, 4.0.0
> >
> >     With introducing a dummy global variable common/mm.c:
> >
> >     mfn_t foo = INVALID_MFN_INITIALIZER
> > ---
> >  xen/include/xen/mm.h | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
> > index 0050fba498..251db4ffa1 100644
> > --- a/xen/include/xen/mm.h
> > +++ b/xen/include/xen/mm.h
> > @@ -57,6 +57,11 @@
> >  TYPE_SAFE(unsigned long, mfn);
> >  #define PRI_mfn          "05lx"
> >  #define INVALID_MFN      _mfn(~0UL)
> > +/*
> > + * To be used for global variable initialization. This workaround a bug
> > + * in GCC < 5.0.
> > + */
> > +#define INVALID_MFN_INITIALIZER {~0UL}
> >
> >  #ifndef mfn_t
> >  #define mfn_t /* Grep fodder: mfn_t, _mfn() and mfn_x() are defined above */
> > @@ -90,6 +95,11 @@ static inline bool_t mfn_eq(mfn_t x, mfn_t y)
> >  TYPE_SAFE(unsigned long, gfn);
> >  #define PRI_gfn          "05lx"
> >  #define INVALID_GFN      _gfn(~0UL)
> > +/*
> > + * To be used for global variable initialization. This workaround a bug
> > + * in GCC < 5.0 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64856
> > + */
> > +#define INVALID_GFN_INITIALIZER { ~0UL }
> >
> >  #ifndef gfn_t
> >  #define gfn_t /* Grep fodder: gfn_t, _gfn() and gfn_x() are defined above */
> > --
> > 2.11.0
--
Julien Grall

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