linux-kernel - [PATCH] lib/bitmap: waive const_eval test as it breaks the build

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Date:   Mon, 17 Jul 2023 12:58:13 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Yury Norov <yury.norov@...il.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>,
        Nathan Chancellor <nathan@...nel.org>,
        Tom Rix <trix@...hat.com>, oe-kbuild-all@...ts.linux.dev
Subject: [PATCH] lib/bitmap: waive const_eval test as it breaks the build

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"
+#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