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

[Wei Liu <wl@xxxxxxx>]

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.

> ---
>  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
>