linux-kernel - Re: lib/test_bitmap.c:920:2: error: call to '__compiletime_assert_239' declared with 'error' attribute: BUILD_BUG_ON failed: !__builtin_constant

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Date:   Fri, 16 Jun 2023 16:03:21 +0200
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
CC:     kernel test robot <lkp@...el.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        <llvm@...ts.linux.dev>, <oe-kbuild-all@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>, Yury Norov <yury.norov@...il.com>
Subject: Re: lib/test_bitmap.c:920:2: error: call to
 '__compiletime_assert_239' declared with 'error' attribute: BUILD_BUG_ON
 failed: !__builtin_constant_p(res)

From: Nick Desaulniers <ndesaulniers@...gle.com>
Date: Thu, 15 Jun 2023 16:48:22 -0400

> On Thu, Jun 15, 2023 at 3:52 PM Nick Desaulniers
> <ndesaulniers@...gle.com> wrote:
>>
>> On Thu, Jun 15, 2023 at 7:22 AM Andy Shevchenko
>> <andriy.shevchenko@...ux.intel.com> wrote:

[...]

>>>>    896                bitmap_clear(bitmap, 0, BITS_PER_LONG);
>>>>    897        #if defined(__s390__) && defined(__clang__)
>>>>    898                if (!const_test_bit(7, bitmap))
>>>>    899        #else
>>>>    900                if (!test_bit(7, bitmap))
>>>>    901        #endif
>>>
>>> Hmm... Reveals the bug in clang/arm64?
>>
>> Seems related to the config.  ARCH=arm64 defconfig +
>> CONFIG_TEST_BITMAP=y doesn't trigger this for me, but the randconfig
>> does.  We'll bisect the config, and update the thread tracking this:
>> https://github.com/ClangBuiltLinux/linux/issues/1874
> 
> KASAN and GCOV together seem to be tickling this.

Thanks for root-causing this!
Should I prepare a patch which would work around KASAN + GCOV here or
you're digging the Clang sources for potential issues?

> 
>>
>>>
>>>>    919                res = !test_bit(18, &bitopvar);
>>>>  > 920                BUILD_BUG_ON(!__builtin_constant_p(res));
>>>>    921                BUILD_BUG_ON(!res);
>>>
>>>
>>> --
>>> With Best Regards,
>>> Andy Shevchenko
>>>
>>>
>>>
>>
>>
>> --
>> Thanks,
>> ~Nick Desaulniers
> 
> 
> 

Thanks,
Olek