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