kcsan: Support distinguishing volatile accesses
authorMarco Elver <elver@google.com>
Thu, 21 May 2020 14:20:39 +0000 (16:20 +0200)
committerThomas Gleixner <tglx@linutronix.de>
Thu, 11 Jun 2020 18:04:01 +0000 (20:04 +0200)
commit75d75b7a4d5489cc6a5e91ace306f6c13f376f33
tree3aa69e5ff92430125ce2678e5dd1a5d4976ca035
parent0e1aa5b62160500bb2ed3150367fba83c0a194e5
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 <elver@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200521142047.169334-4-elver@google.com
kernel/kcsan/core.c
scripts/Makefile.kcsan