linux-kernel - Re: [PATCH v2 2/2] build_bug.h: remove all dummy BUILD_BUG

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Date:   Fri, 16 Nov 2018 13:01:29 -0600
From:   Kees Cook <keescook@...omium.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] build_bug.h: remove all dummy BUILD_BUG_ON stubs
 for sparse

On Fri, Nov 16, 2018 at 12:27 AM, Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
> The introduction of these dummy BUILD_BUG_ON stubs dates back to
> commit 903c0c7cdc21 ("sparse: define dummy BUILD_BUG_ON definition
> for sparse"). At that time, BUILD_BUG_ON() was implemented with the
> negative array trick, which Sparse complains about even if the
> condition can be optimized and evaluated to 0 at compile-time.
>
> With the previous commit, the leftover negative array trick is gone.
> Sparse is happy with the current BUILD_BUG_ON(), which is implemented
> by using the 'error' attribute.
>
> There might be a little room for argument about BUILD_BUG_ON_ZERO().
> Sparse reports 'invalid bitfield width, -1' for non-zero value,
> and 'bad integer constant expression' for non-constant value.
> This is the same criteria as GCC uses. So, if those Sparse errors
> occurred, they would cause errors for GCC as well. (Hence, such
> errors would have been detected by the normal compile test process.)
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>
> Changes in v2:
>  - Fix a coding style error (two consecutive blank lines)
>
>  include/linux/build_bug.h | 12 ------------
>  1 file changed, 12 deletions(-)
>
> diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h
> index d415c64..6625c88 100644
> --- a/include/linux/build_bug.h
> +++ b/include/linux/build_bug.h
> @@ -4,16 +4,6 @@
>
>  #include <linux/compiler.h>
>
> -#ifdef __CHECKER__
> -#define __BUILD_BUG_ON_NOT_POWER_OF_2(n) (0)
> -#define BUILD_BUG_ON_NOT_POWER_OF_2(n) (0)
> -#define BUILD_BUG_ON_ZERO(e) (0)
> -#define BUILD_BUG_ON_INVALID(e) (0)
> -#define BUILD_BUG_ON_MSG(cond, msg) (0)
> -#define BUILD_BUG_ON(condition) (0)
> -#define BUILD_BUG() (0)
> -#else /* __CHECKER__ */
> -
>  /* Force a compilation error if a constant expression is not a power of 2 */
>  #define __BUILD_BUG_ON_NOT_POWER_OF_2(n)       \
>         BUILD_BUG_ON(((n) & ((n) - 1)) != 0)
> @@ -64,6 +54,4 @@
>   */
>  #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
>
> -#endif /* __CHECKER__ */
> -
>  #endif /* _LINUX_BUILD_BUG_H */
> --
> 2.7.4
>



-- 
Kees Cook