[PATCH kcsan 12/29] kcsan: Ignore GCC 11+ warnings about TSan runtime support

["Paul E. McKenney" <paulmck@kernel.org>]

From: Marco Elver <elver@google.com>

GCC 11 has introduced a new warning option, -Wtsan [1], to warn about
unsupported operations in the TSan runtime. But KCSAN != TSan runtime,
so none of the warnings apply.

[1] https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Warning-Options.html

Ignore the warnings.

Currently the warning only fires in the test for __atomic_thread_fence():

kernel/kcsan/kcsan_test.c: In function ‘test_atomic_builtins’:
kernel/kcsan/kcsan_test.c:1234:17: warning: ‘atomic_thread_fence’ is not supported with ‘-fsanitize=thread’ [-Wtsan]
 1234 |                 __atomic_thread_fence(__ATOMIC_SEQ_CST);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

which exists to ensure the KCSAN runtime keeps supporting the builtin
instrumentation.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 scripts/Makefile.kcsan | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/scripts/Makefile.kcsan b/scripts/Makefile.kcsan
index 4c7f0d282e42f..19f693b68a968 100644
--- a/scripts/Makefile.kcsan
+++ b/scripts/Makefile.kcsan
@@ -13,6 +13,12 @@ kcsan-cflags := -fsanitize=thread -fno-optimize-sibling-calls \
 	$(call cc-option,$(call cc-param,tsan-compound-read-before-write=1),$(call cc-option,$(call cc-param,tsan-instrument-read-before-write=1))) \
 	$(call cc-param,tsan-distinguish-volatile=1)
 
+ifdef CONFIG_CC_IS_GCC
+# GCC started warning about operations unsupported by the TSan runtime. But
+# KCSAN != TSan, so just ignore these warnings.
+kcsan-cflags += -Wno-tsan
+endif
+
 ifndef CONFIG_KCSAN_WEAK_MEMORY
 kcsan-cflags += $(call cc-option,$(call cc-param,tsan-instrument-func-entry-exit=0))
 endif
-- 
2.31.1.189.g2e36527f23