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    Subject[PATCH AUTOSEL 4.14 18/30] compiler.h: fix error in BUILD_BUG_ON() reporting
    Date
    From: Vegard Nossum <vegard.nossum@oracle.com>

    [ Upstream commit af9c5d2e3b355854ff0e4acfbfbfadcd5198a349 ]

    compiletime_assert() uses __LINE__ to create a unique function name. This
    means that if you have more than one BUILD_BUG_ON() in the same source
    line (which can happen if they appear e.g. in a macro), then the error
    message from the compiler might output the wrong condition.

    For this source file:

    #include <linux/build_bug.h>

    #define macro() \
    BUILD_BUG_ON(1); \
    BUILD_BUG_ON(0);

    void foo()
    {
    macro();
    }

    gcc would output:

    ./include/linux/compiler.h:350:38: error: call to `__compiletime_assert_9' declared with attribute error: BUILD_BUG_ON failed: 0
    _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)

    However, it was not the BUILD_BUG_ON(0) that failed, so it should say 1
    instead of 0. With this patch, we use __COUNTER__ instead of __LINE__, so
    each BUILD_BUG_ON() gets a different function name and the correct
    condition is printed:

    ./include/linux/compiler.h:350:38: error: call to `__compiletime_assert_0' declared with attribute error: BUILD_BUG_ON failed: 1
    _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)

    Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>
    Reviewed-by: Daniel Santos <daniel.santos@pobox.com>
    Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
    Cc: Ian Abbott <abbotti@mev.co.uk>
    Cc: Joe Perches <joe@perches.com>
    Link: http://lkml.kernel.org/r/20200331112637.25047-1-vegard.nossum@oracle.com
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    include/linux/compiler.h | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/include/linux/compiler.h b/include/linux/compiler.h
    index f84d332085c31..3ffe3f3f79035 100644
    --- a/include/linux/compiler.h
    +++ b/include/linux/compiler.h
    @@ -331,7 +331,7 @@ unsigned long read_word_at_a_time(const void *addr)
    * compiler has support to do so.
    */
    #define compiletime_assert(condition, msg) \
    - _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
    + _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)

    #define compiletime_assert_atomic_type(t) \
    compiletime_assert(__native_word(t), \
    --
    2.20.1
    \
     
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