lib/bitmap: workaround const_eval test build failure

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] ClangBuiltLinux#1874

Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Fixes: dc34d50 ("lib: test_bitmap: add compile-time optimization/evaluations assertions")
Co-developed-by: Nathan Chancellor <[email protected]>
Signed-off-by: Nathan Chancellor <[email protected]>
Signed-off-by: Yury Norov <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>
Reviewed-by: Alexander Lobakin <[email protected]>

lib/Makefile

@@ -82,7 +82,13 @@ obj-$(CONFIG_TEST_STATIC_KEYS) += test_static_key_base.o
 obj-$(CONFIG_TEST_DYNAMIC_DEBUG) += test_dynamic_debug.o
 obj-$(CONFIG_TEST_PRINTF) += test_printf.o
 obj-$(CONFIG_TEST_SCANF) += test_scanf.o
+
 obj-$(CONFIG_TEST_BITMAP) += test_bitmap.o
+ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_KASAN),yy)
+# FIXME: Clang breaks test_bitmap_const_eval when KASAN and GCOV are enabled
+GCOV_PROFILE_test_bitmap.o := n
+endif
+
 obj-$(CONFIG_TEST_UUID) += test_uuid.o
 obj-$(CONFIG_TEST_XARRAY) += test_xarray.o
 obj-$(CONFIG_TEST_MAPLE_TREE) += test_maple_tree.o

lib/test_bitmap.c

@@ -1161,6 +1161,10 @@ static void __init test_bitmap_print_buf(void)
 	}
 }
 
+/*
+ * FIXME: Clang breaks compile-time evaluations when KASAN and GCOV are enabled.
+ * To workaround it, GCOV is force-disabled in Makefile for this configuration.
+ */
 static void __init test_bitmap_const_eval(void)
 {
 	DECLARE_BITMAP(bitmap, BITS_PER_LONG);
@@ -1186,11 +1190,7 @@ static void __init test_bitmap_const_eval(void)
 	 * the compiler is fixed.
 	 */
 	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)` */