From 75d75b7a4d5489cc6a5e91ace306f6c13f376f33 Mon Sep 17 00:00:00 2001 From: Marco Elver Date: Thu, 21 May 2020 16:20:39 +0200 Subject: kcsan: Support distinguishing volatile accesses In the kernel, the "volatile" keyword is used in various concurrent contexts, whether in low-level synchronization primitives or for legacy reasons. If supported by the compiler, it will be assumed that aligned volatile accesses up to sizeof(long long) (matching compiletime_assert_rwonce_type()) are atomic. Recent versions of Clang [1] (GCC tentative [2]) can instrument volatile accesses differently. Add the option (required) to enable the instrumentation, and provide the necessary runtime functions. None of the updated compilers are widely available yet (Clang 11 will be the first release to support the feature). [1] https://github.com/llvm/llvm-project/commit/5a2c31116f412c3b6888be361137efd705e05814 [2] https://gcc.gnu.org/pipermail/gcc-patches/2020-April/544452.html This change allows removing of any explicit checks in primitives such as READ_ONCE() and WRITE_ONCE(). [ bp: Massage commit message a bit. ] Signed-off-by: Marco Elver Signed-off-by: Borislav Petkov Signed-off-by: Thomas Gleixner Acked-by: Will Deacon Acked-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20200521142047.169334-4-elver@google.com --- scripts/Makefile.kcsan | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'scripts') diff --git a/scripts/Makefile.kcsan b/scripts/Makefile.kcsan index 20337a7ecf54..75d2942b9437 100644 --- a/scripts/Makefile.kcsan +++ b/scripts/Makefile.kcsan @@ -9,7 +9,10 @@ else cc-param = --param -$(1) endif +# Keep most options here optional, to allow enabling more compilers if absence +# of some options does not break KCSAN nor causes false positive reports. CFLAGS_KCSAN := -fsanitize=thread \ - $(call cc-option,$(call cc-param,tsan-instrument-func-entry-exit=0) -fno-optimize-sibling-calls) + $(call cc-option,$(call cc-param,tsan-instrument-func-entry-exit=0) -fno-optimize-sibling-calls) \ + $(call cc-param,tsan-distinguish-volatile=1) endif # CONFIG_KCSAN -- cgit v1.2.3