lkml.org 
[lkml]   [2018]   [Nov]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v3 2/3] build_bug.h: remove negative-array fallback for BUILD_BUG_ON()
On Mon, Nov 19, 2018 at 2:32 AM Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
>
> The kernel can only be compiled with an optimization option (-O2, -Os,
> or the currently proposed -Og). Hence, __OPTIMIZE__ is always defined
> in the kernel source.
>
> The fallback for the -O0 case is just hypothetical and pointless.
> Moreover, commit 0bb95f80a38f ("Makefile: Globally enable VLA warning")
> enabled -Wvla warning. The use of variable length arrays is banned.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> Acked-by: Kees Cook <keescook@chromium.org>
> ---
>
> Changes in v3: None
> Changes in v2: None
>
> include/linux/build_bug.h | 14 --------------
> 1 file changed, 14 deletions(-)
>
> diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h
> index 43d1fd5..d415c64 100644
> --- a/include/linux/build_bug.h
> +++ b/include/linux/build_bug.h
> @@ -51,23 +51,9 @@
> * If you have some code which relies on certain constants being equal, or
> * some other compile-time-evaluated condition, you should use BUILD_BUG_ON to
> * detect if someone changes it.
> - *
> - * The implementation uses gcc's reluctance to create a negative array, but gcc
> - * (as of 4.4) only emits that error for obvious cases (e.g. not arguments to
> - * inline functions). Luckily, in 4.3 they added the "error" function
> - * attribute just for this type of case. Thus, we use a negative sized array
> - * (should always create an error on gcc versions older than 4.4) and then call
> - * an undefined function with the error attribute (should always create an
> - * error on gcc 4.3 and later). If for some reason, neither creates a
> - * compile-time error, we'll still have a link-time error, which is harder to
> - * track down.
> */
> -#ifndef __OPTIMIZE__
> -#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
> -#else
> #define BUILD_BUG_ON(condition) \
> BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
> -#endif
>
> /**
> * BUILD_BUG - break compile if used.
> --
> 2.7.4
>

Yep seems fine.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested an arm64 defconfig with Clang + this patch. Then tested again
with a `BUILD_BUG_ON(4 != 5)` to verify this still breaks the build.
Tested-by: Nick Desaulniers <ndesaulniers@google.com>

--
Thanks,
~Nick Desaulniers

\
 
 \ /
  Last update: 2018-11-19 19:11    [W:0.064 / U:0.288 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site