RE: [PATCH for-4.14] compilers/clang: always use _Static_assert with clang

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Wei Liu <wl@xxxxxxx>
> Sent: 02 June 2020 10:23
> To: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; paul@xxxxxxx; Andrew Cooper 
> <andrew.cooper3@xxxxxxxxxx>; George
> Dunlap <george.dunlap@xxxxxxxxxx>; Ian Jackson <ian.jackson@xxxxxxxxxxxxx>; 
> Jan Beulich
> <jbeulich@xxxxxxxx>; Julien Grall <julien@xxxxxxx>; Stefano Stabellini 
> <sstabellini@xxxxxxxxxx>; Wei
> Liu <wl@xxxxxxx>
> Subject: Re: [PATCH for-4.14] compilers/clang: always use _Static_assert with 
> clang
> 
> On Tue, Jun 02, 2020 at 11:16:02AM +0200, Roger Pau Monne wrote:
> > All versions of clang used by Xen support _Static_assert, so use it
> > unconditionally when building Xen with clang.
> >
> > No functional change expected.
> >
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> 
> Reviewed-by: Wei Liu <wl@xxxxxxx>
> 
> > ---
> > Not sure whether this fully qualifies as a bugfix, as the current
> > behavior should also work fine under clang. Note that all versions of
> > clang from 3.5 to trunk (11) seem to return __GNUC__ == 4 and
> > __GNUC_MINOR__ == 2.
> 
> IMHO it wouldn't hurt to apply this patch since any breakage is easy to
> catch.

Yes, seems reasonable.

Release-acked-by: Paul Durrant <paul@xxxxxxx>

> 
> > ---
> >  xen/include/xen/lib.h | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/xen/include/xen/lib.h b/xen/include/xen/lib.h
> > index e5b0a007b8..076bcfb67d 100644
> > --- a/xen/include/xen/lib.h
> > +++ b/xen/include/xen/lib.h
> > @@ -25,7 +25,9 @@
> >  #define BUG_ON(p)  do { if (unlikely(p)) BUG();  } while (0)
> >  #define WARN_ON(p) do { if (unlikely(p)) WARN(); } while (0)
> >
> > -#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
> > +/* All clang versions supported by Xen have _Static_assert. */
> > +#if defined(__clang__) || \
> > +    (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6))
> >  /* Force a compilation error if condition is true */
> >  #define BUILD_BUG_ON(cond) ({ _Static_assert(!(cond), "!(" #cond ")"); })
> >
> > --
> > 2.26.2
> >