Re: [PATCH 1/2] build_bug.h: remove negative-array fallback for BUILD_BUG_ON()
On Fri, Nov 16, 2018 at 8:01 PM Kees Cook wrote:
>
> On Fri, Nov 16, 2018 at 12:19 AM, Masahiro Yamada
> 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.
> >
> > A fallback for -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
>
> Acked-by: Kees Cook
Acked-by: Miguel Ojeda
Cheers,
Miguel
Re: [PATCH 1/2] build_bug.h: remove negative-array fallback for BUILD_BUG_ON()
On Fri, Nov 16, 2018 at 12:19 AM, Masahiro Yamada
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.
>
> A fallback for -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
Acked-by: Kees Cook
-Kees
> ---
>
> 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
>
--
Kees Cook
[PATCH 1/2] build_bug.h: remove negative-array fallback for BUILD_BUG_ON()
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.
A fallback for -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
---
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
