linux-kernel - Re: [PATCH v3 2/3] linux/build

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Date:   Sun, 6 Oct 2019 11:26:23 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Rikard Falkeborn <rikard.falkeborn@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Joe Perches <joe@...ches.com>,
        Johannes Berg <johannes@...solutions.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v3 2/3] linux/build_bug.h: Change type to int

On Mon, Aug 12, 2019 at 3:50 AM Rikard Falkeborn
<rikard.falkeborn@...il.com> wrote:
>
> Having BUILD_BUG_ON_ZERO produce a value of type size_t leads to awkward
> casts in cases where the result needs to be signed, or of smaller type
> than size_t. To avoid this, cast the value to int instead and rely on
> implicit type conversions when a larger or unsigned type is needed.
>
> Suggested-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> Signed-off-by: Rikard Falkeborn <rikard.falkeborn@...il.com>

Reviewed-by: Masahiro Yamada <yamada.masahiro@...ionext.com>

> Changes in v3:
>   - This patch is new in v3
>
>  include/linux/build_bug.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h
> index 0fe5426f2bdc..e3a0be2c90ad 100644
> --- a/include/linux/build_bug.h
> +++ b/include/linux/build_bug.h
> @@ -9,11 +9,11 @@
>  #else /* __CHECKER__ */
>  /*
>   * Force a compilation error if condition is true, but also produce a
> - * result (of value 0 and type size_t), so the expression can be used
> + * result (of value 0 and type int), so the expression can be used
>   * e.g. in a structure initializer (or where-ever else comma expressions
>   * aren't permitted).
>   */
> -#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:(-!!(e)); }))
> +#define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
>  #endif /* __CHECKER__ */
>
>  /* Force a compilation error if a constant expression is not a power of 2 */
> --
> 2.22.0
>


-- 
Best Regards
Masahiro Yamada