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Message-ID: <20230717203105.GA2212488@dev-arch.thelio-3990X>
Date: Mon, 17 Jul 2023 13:31:05 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Yury Norov <yury.norov@...il.com>
Cc: linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
Nick Desaulniers <ndesaulniers@...gle.com>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Alexander Lobakin <alexandr.lobakin@...el.com>,
Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
Tom Rix <trix@...hat.com>, oe-kbuild-all@...ts.linux.dev
Subject: Re: [PATCH] lib/bitmap: waive const_eval test as it breaks the build
Hi Yury,
On Mon, Jul 17, 2023 at 12:58:13PM -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 also not related to bitmap code itself, but it breaks build for
> a given configuration. So, disabling the test unless the compiler will
> get fixed.
>
> [1] https://github.com/ClangBuiltLinux/linux/issues/1874
>
> Fixes: dc34d5036692 ("lib: test_bitmap: add compile-time optimization/evaluations assertions")
> Signed-off-by: Yury Norov <yury.norov@...il.com>
> ---
> lib/test_bitmap.c | 17 +++++------------
> 1 file changed, 5 insertions(+), 12 deletions(-)
>
> diff --git a/lib/test_bitmap.c b/lib/test_bitmap.c
> index 187f5b2db4cf..a791fdb7a8c9 100644
> --- a/lib/test_bitmap.c
> +++ b/lib/test_bitmap.c
> @@ -1163,6 +1163,9 @@ static void __init test_bitmap_print_buf(void)
>
> static void __init test_bitmap_const_eval(void)
> {
> +#if defined(CONFIG_CC_IS_CLANG) && defined(CONFIG_KASAN) && defined(CONFIG_GCOV_PROFILE_ALL)
> +#warning "FIXME: Clang breaks compile time evaluations when KASAN and GCOV are enabled"
Making this a '#warning' will basically just replace the current error
with a different one in the face of CONFIG_WERROR, which seems pointless
to me:
lib/test_bitmap.c:1167:2: error: "FIXME: Clang breaks compile time evaluations when KASAN and GCOV are enabled" [-Werror,-W#warnings]
1167 | #warning "FIXME: Clang breaks compile time evaluations when KASAN and GCOV are enabled"
| ^
1 error generated.
Could we just opt out of GCOV for test_bitmap.c if KASAN is enabled with
clang? That does not seem too bad of a workaround. I highly doubt there
are many people who are interested in debugging test_bitmap.c with KASAN
while profiling it with GCOV when building with clang, since they would
have hit this already and reported it already; as far as I can tell,
only the Intel robot has reported this with a randconfig.
diff --git a/lib/Makefile b/lib/Makefile
index 42d307ade225..c6f60ae42769 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -83,6 +83,10 @@ obj-$(CONFIG_TEST_DYNAMIC_DEBUG) += test_dynamic_debug.o
obj-$(CONFIG_TEST_PRINTF) += test_printf.o
obj-$(CONFIG_TEST_SCANF) += test_scanf.o
obj-$(CONFIG_TEST_BITMAP) += test_bitmap.o
+# https://github.com/ClangBuiltLinux/linux/issues/1874
+ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_KASAN),yy)
+GCOV_PROFILE_test_bitmap.o := n
+endif
obj-$(CONFIG_TEST_UUID) += test_uuid.o
obj-$(CONFIG_TEST_XARRAY) += test_xarray.o
obj-$(CONFIG_TEST_MAPLE_TREE) += test_maple_tree.o
Cheers,
Nathan
> +#else
> DECLARE_BITMAP(bitmap, BITS_PER_LONG);
> unsigned long initvar = BIT(2);
> unsigned long bitopvar = 0;
> @@ -1177,20 +1180,9 @@ static void __init test_bitmap_const_eval(void)
> * in runtime.
> */
>
> - /*
> - * Equals to `unsigned long bitmap[1] = { GENMASK(6, 5), }`.
> - * Clang on s390 optimizes bitops at compile-time as intended, but at
> - * the same time stops treating @bitmap and @bitopvar as compile-time
> - * constants after regular test_bit() is executed, thus triggering the
> - * build bugs below. So, call const_test_bit() there directly until
> - * the compiler is fixed.
> - */
> + /* Equals to `unsigned long bitmap[1] = { GENMASK(6, 5), }` */
> bitmap_clear(bitmap, 0, BITS_PER_LONG);
> -#if defined(__s390__) && defined(__clang__)
> - if (!const_test_bit(7, bitmap))
> -#else
> if (!test_bit(7, bitmap))
> -#endif
> bitmap_set(bitmap, 5, 2);
>
> /* Equals to `unsigned long bitopvar = BIT(20)` */
> @@ -1220,6 +1212,7 @@ static void __init test_bitmap_const_eval(void)
> /* ~BIT(25) */
> BUILD_BUG_ON(!__builtin_constant_p(~var));
> BUILD_BUG_ON(~var != ~BIT(25));
> +#endif
> }
>
> static void __init selftest(void)
> --
> 2.39.2
>
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