linux-kernel - Re: [PATCH v2] lib/bitmap: workaround const

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Message-ID: <ZLb/bioBIHS6bjKc@yury-ThinkPad>
Date:   Tue, 18 Jul 2023 14:09:02 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Nathan Chancellor <nathan@...nel.org>,
        Tom Rix <trix@...hat.com>, oe-kbuild-all@...ts.linux.dev,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v2] lib/bitmap: workaround const_eval test build failure

On Mon, Jul 17, 2023 at 03:04:35PM -0700, Yury Norov wrote:
> When building with Clang, and when KASAN and GCOV_PROFILE_ALL are both
> enabled, the test fails to build [1]:
> 
> >> lib/test_bitmap.c:920:2: error: call to '__compiletime_assert_239' declared with 'error' attribute: BUILD_BUG_ON failed: !__builtin_constant_p(res)
>            BUILD_BUG_ON(!__builtin_constant_p(res));
>            ^
>    include/linux/build_bug.h:50:2: note: expanded from macro 'BUILD_BUG_ON'
>            BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
>            ^
>    include/linux/build_bug.h:39:37: note: expanded from macro 'BUILD_BUG_ON_MSG'
>    #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>                                        ^
>    include/linux/compiler_types.h:352:2: note: expanded from macro 'compiletime_assert'
>            _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>            ^
>    include/linux/compiler_types.h:340:2: note: expanded from macro '_compiletime_assert'
>            __compiletime_assert(condition, msg, prefix, suffix)
>            ^
>    include/linux/compiler_types.h:333:4: note: expanded from macro '__compiletime_assert'
>                            prefix ## suffix();                             \
>                            ^
>    <scratch space>:185:1: note: expanded from here
>    __compiletime_assert_239
> 
> Originally it was attributed to s390, which now looks seemingly wrong. The
> issue is not related to bitmap code itself, but it breaks build for a given
> configuration.
> 
> Disabling the const_eval test under that config may potentially hide other
> bugs. Instead, workaround it by disabling GCOV for the test_bitmap unless
> the compiler will get fixed.
> 
> [1] https://github.com/ClangBuiltLinux/linux/issues/1874
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202307171254.yFcH97ej-lkp@intel.com/
> Fixes: dc34d5036692 ("lib: test_bitmap: add compile-time optimization/evaluations assertions")
> Co-developed-by: Nathan Chancellor <nathan@...nel.org>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> Signed-off-by: Yury Norov <yury.norov@...il.com>

So, I pushed it in bitmap-for-next. If nothing wrong will appear in
~week, I'll send a pull request, so expect merging it in this cycle.

Thank you for the work!

Thanks,
Yury