linux-kernel - [PATCH v3 06/25] kcsan, kbuild: Add option for barrier instrumentation only

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Date:   Tue, 30 Nov 2021 12:44:14 +0100
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>,
        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, llvm@...ts.linux.dev, x86@...nel.org
Subject: [PATCH v3 06/25] kcsan, kbuild: Add option for barrier
 instrumentation only

Source files that disable KCSAN via KCSAN_SANITIZE := n, remove all
instrumentation, including explicit barrier instrumentation. With
instrumentation for memory barriers, in few places it is required to
enable just the explicit instrumentation for memory barriers to avoid
false positives.

Providing the Makefile variable KCSAN_INSTRUMENT_BARRIERS_obj.o or
KCSAN_INSTRUMENT_BARRIERS (for all files) set to 'y' only enables the
explicit barrier instrumentation.

Signed-off-by: Marco Elver <elver@...gle.com>
---
 scripts/Makefile.lib | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index d1f865b8c0cb..ab17f7b2e33c 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -182,6 +182,11 @@ ifeq ($(CONFIG_KCSAN),y)
 _c_flags += $(if $(patsubst n%,, \
 	$(KCSAN_SANITIZE_$(basetarget).o)$(KCSAN_SANITIZE)y), \
 	$(CFLAGS_KCSAN))
+# Some uninstrumented files provide implied barriers required to avoid false
+# positives: set KCSAN_INSTRUMENT_BARRIERS for barrier instrumentation only.
+_c_flags += $(if $(patsubst n%,, \
+	$(KCSAN_INSTRUMENT_BARRIERS_$(basetarget).o)$(KCSAN_INSTRUMENT_BARRIERS)n), \
+	-D__KCSAN_INSTRUMENT_BARRIERS__)
 endif
 
 # $(srctree)/$(src) for including checkin headers from generated source files
-- 
2.34.0.rc2.393.gf8c9666880-goog