Re: [PATCH v2 09/10] bug.h: Add BUILD_BUG_ON_MSG & BUILD_BUG_INTERNAL{,2}

Borislav Petkov
2012-10-05T20:59:07Z

On Fri, Oct 05, 2012 at 02:42:48PM -0500, danielfsantos@att.net wrote:
> Add BUILD_BUG_ON_MSG which behaves like BUILD_BUG_ON (with optimizations
> turned enabled), except that it allows you to specify the error message
> you want emitted as the third parameter. Under the hood, this relies on
> BUILD_BUG_INTERNAL{,2}, which does the actual work and is pretty-much
> identical to BUILD_BUG_ON.
>
> Signed-off-by: Daniel Santos <daniel.santos@pobox.com>
> ---
> include/linux/bug.h | 26 ++++++++++++++++++++++++++
> 1 files changed, 26 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/bug.h b/include/linux/bug.h
> index 1b43ea2..91bd9d5 100644
> --- a/include/linux/bug.h
> +++ b/include/linux/bug.h
> @@ -16,6 +16,7 @@ struct pt_regs;
> #define BUILD_BUG_ON_NOT_POWER_OF_2(n)
> #define BUILD_BUG_ON_ZERO(e) (0)
> #define BUILD_BUG_ON_NULL(e) ((void*)0)
> +#define BUILD_BUG_ON_MSG(cond, msg) (0)
> #define BUILD_BUG_ON(condition) (0)
> #define BUILD_BUG() (0)
> #else /* __CHECKER__ */
> @@ -38,6 +39,31 @@ struct pt_regs;
> */
> #define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))
>
> +#define _CONCAT1(a, b) a##b
> +#define CONCAT(a, b) _CONCAT1(a, b)

Let's call the indirection _CONCAT without the "1".

> +#define UNIQUIFY(prefix) CONCAT(prefix, __LINE__)
> +
> +#define BUILD_BUG_INTERNAL2(condition, msg, fn) \
> + do { \
> + extern void fn (void) __compiletime_error(msg); \
> + __compiletime_error_fallback(condition); \
> + if (condition) \
> + fn(); \
> + } while (0)
> +
> +#define BUILD_BUG_INTERNAL(condition, msg, fn) \
> + BUILD_BUG_INTERNAL2(condition, msg, fn)

Ditto. BUILD_BUG_INTERNAL2 should be __BUILD_BUG_INTERNAL and the one
calling it _BUILD_BUG_INTERNAL (with one underscore).

> +
> +/**
> + * BUILD_BUG_ON_MSG - break compile if a condition is true & emit supplied
> + * error message.
> + * @condition: the condition which the compiler should know is false.
> + *
> + * See BUILD_BUG_ON for description.
> + */
> +#define BUILD_BUG_ON_MSG(cond, msg) \
> + BUILD_BUG_INTERNAL(cond, msg, UNIQUIFY(__build_bug_on_failed_))

Btw, why are we adding the line at all? It is issued by gcc anyway:

cc -Wall macros.c -o macros
macros.c: In function ‘main’:
macros.c:22:1: error: ‘__build_bug_on_failed_22’ undeclared (first use in this function)
^^^^

It is in front of the filename here.

macros.c:22:1: note: each undeclared identifier is reported only once for each function it appears in
make: *** [macros] Error 1

Thanks.

--
Regards/Gruss,
Boris.