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[73.47.162.176]) by smtp.gmail.com with ESMTPSA id a19sm188307pfd.165.2020.06.05.10.37.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Jun 2020 10:37:57 -0700 (PDT) From: Robert Foley To: qemu-devel@nongnu.org Subject: [PATCH v2 12/13] docs: Added details on TSan to testing.rst Date: Fri, 5 Jun 2020 13:34:21 -0400 Message-Id: <20200605173422.1490-13-robert.foley@linaro.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200605173422.1490-1-robert.foley@linaro.org> References: <20200605173422.1490-1-robert.foley@linaro.org> Received-SPF: pass client-ip=2607:f8b0:4864:20::442; envelope-from=robert.foley@linaro.org; helo=mail-pf1-x442.google.com X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: peter.puhov@linaro.org, cota@braap.org, alex.bennee@linaro.org, robert.foley@linaro.org Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" Adds TSan details to testing.rst. This includes background and reference details on TSan, and details on how to build and test with TSan both with and without docker. Signed-off-by: Robert Foley Reviewed-by: Emilio G. Cota Reviewed-by: Alex Bennée --- docs/devel/testing.rst | 107 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 107 insertions(+) diff --git a/docs/devel/testing.rst b/docs/devel/testing.rst index 770a987ea4..c1ff24370b 100644 --- a/docs/devel/testing.rst +++ b/docs/devel/testing.rst @@ -397,6 +397,113 @@ list is in the ``make docker`` help text. The frequently used ones are: * ``DEBUG=1``: enables debug. See the previous "Debugging a Docker test failure" section. +Thread Sanitizer +================ + +Thread Sanitizer (TSan) is a tool which can detect data races. QEMU supports +building and testing with this tool. + +For more information on TSan: + +https://github.com/google/sanitizers/wiki/ThreadSanitizerCppManual + +Thread Sanitizer in Docker +--------------------------- +TSan is currently supported in the ubuntu2004 docker. + +The test-tsan test will build using TSan and then run make check. + +.. code:: + + make docker-test-tsan@ubuntu2004 + +TSan warnings under docker are placed in files located at build/tsan/. + +We recommend using DEBUG=1 to allow launching the test from inside the docker, +and to allow review of the warnings generated by TSan. + +Building and Testing with TSan +------------------------------ + +It is possible to build and test with TSan, with a few additional steps. +These steps are normally done automatically in the docker. + +There is a one time patch needed in clang-9 or clang-10 at this time: + +.. code:: + + sed -i 's/^const/static const/g' \ + /usr/lib/llvm-10/lib/clang/10.0.0/include/sanitizer/tsan_interface.h + +To configure the build for TSan: + +.. code:: + + ../configure --enable-tsan --cc=clang-10 --cxx=clang++-10 \ + --disable-werror --extra-cflags="-O0" + +The runtime behavior of TSAN is controlled by the TSAN_OPTIONS environment +variable. + +More information on the TSAN_OPTIONS can be found here: + +https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags + +For example: + +.. code:: + + export TSAN_OPTIONS=suppressions=/tests/tsan/suppressions.tsan \ + detect_deadlocks=false history_size=7 exitcode=0 \ + log_path=/tsan/tsan_warning + +The above exitcode=0 has TSan continue without error if any warnings are found. +This allows for running the test and then checking the warnings afterwards. +If you want TSan to stop and exit with error on warnings, use exitcode=66. + +TSan Suppressions +----------------- +Keep in mind that for any data race warning, although there might be a data race +detected by TSan, there might be no actual bug here. TSan provides several +different mechanisms for suppressing warnings. In general it is recommended +to fix the code if possible to eliminate the data race rather than suppress +the warning. + +A few important files for suppressing warnings are: + +tests/tsan/suppressions.tsan - Has TSan warnings we wish to suppress at runtime. +The comment on each supression will typically indicate why we are +suppressing it. More information on the file format can be found here: + +https://github.com/google/sanitizers/wiki/ThreadSanitizerSuppressions + +tests/tsan/blacklist.tsan - Has TSan warnings we wish to disable +at compile time for test or debug. +Add flags to configure to enable: + +"--extra-cflags=-fsanitize-blacklist=/tests/tsan/blacklist.tsan" + +More information on the file format can be found here under "Blacklist Format": + +https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags + +TSan Annotations +---------------- +include/qemu/tsan.h defines annotations. See this file for more descriptions +of the annotations themselves. Annotations can be used to suppress +TSan warnings or give TSan more information so that it can detect proper +relationships between accesses of data. + +Annotation examples can be found here: + +https://github.com/llvm/llvm-project/tree/master/compiler-rt/test/tsan/ + +Good files to start with are: annotate_happens_before.cpp and ignore_race.cpp + +The full set of annotations can be found here: + +https://github.com/llvm/llvm-project/blob/master/compiler-rt/lib/tsan/rtl/tsan_interface_ann.cpp + VM testing ==========