linux-kernel - [PATCH -rcu/kcsan 12/23] kcsan: Ignore GCC 11+ warnings about TSan runtime support

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Date:   Tue,  5 Oct 2021 12:58:54 +0200
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, "Paul E . McKenney" <paulmck@...nel.org>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Waiman Long <longman@...hat.com>,
        Will Deacon <will@...nel.org>, kasan-dev@...glegroups.com,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org
Subject: [PATCH -rcu/kcsan 12/23] kcsan: Ignore GCC 11+ warnings about TSan
 runtime support

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@...gle.com>
---
 scripts/Makefile.kcsan | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/scripts/Makefile.kcsan b/scripts/Makefile.kcsan
index 4c7f0d282e42..19f693b68a96 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
-- 
2.33.0.800.g4c38ced690-goog