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[109.43.177.15]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3718985ae26sm2849734f8f.55.2024.08.15.22.44.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 15 Aug 2024 22:44:30 -0700 (PDT) Message-ID: <66f144dd-f098-443b-8a34-d68bbdecc48f@redhat.com> Date: Fri, 16 Aug 2024 07:44:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/4] meson: hide tsan related warnings To: Peter Maydell , =?UTF-8?Q?Daniel_P=2E_Berrang=C3=A9?= Cc: Pierrick Bouvier , qemu-devel@nongnu.org, Beraldo Leal , David Hildenbrand , Marcelo Tosatti , =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= , Paolo Bonzini , kvm@vger.kernel.org, Wainer dos Santos Moschetta , qemu-s390x@nongnu.org, =?UTF-8?Q?Marc-Andr=C3=A9_Lureau?= , Richard Henderson , =?UTF-8?Q?Alex_Benn=C3=A9e?= , Ilya Leoshkevich References: <20240814224132.897098-1-pierrick.bouvier@linaro.org> <20240814224132.897098-2-pierrick.bouvier@linaro.org> From: Thomas Huth Content-Language: en-US Autocrypt: addr=thuth@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.131, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 15/08/2024 19.54, Peter Maydell wrote: > On Thu, 15 Aug 2024 at 12:05, Daniel P. Berrangé wrote: >> >> On Thu, Aug 15, 2024 at 11:12:39AM +0100, Peter Maydell wrote: >>> On Wed, 14 Aug 2024 at 23:42, Pierrick Bouvier >>> wrote: >>>> >>>> When building with gcc-12 -fsanitize=thread, gcc reports some >>>> constructions not supported with tsan. >>>> Found on debian stable. >>>> >>>> qemu/include/qemu/atomic.h:36:52: error: ‘atomic_thread_fence’ is not supported with ‘-fsanitize=thread’ [-Werror=tsan] >>>> 36 | #define smp_mb() ({ barrier(); __atomic_thread_fence(__ATOMIC_SEQ_CST); }) >>>> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >>>> >>>> Signed-off-by: Pierrick Bouvier >>>> --- >>>> meson.build | 10 +++++++++- >>>> 1 file changed, 9 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/meson.build b/meson.build >>>> index 81ecd4bae7c..52e5aa95cc0 100644 >>>> --- a/meson.build >>>> +++ b/meson.build >>>> @@ -499,7 +499,15 @@ if get_option('tsan') >>>> prefix: '#include ') >>>> error('Cannot enable TSAN due to missing fiber annotation interface') >>>> endif >>>> - qemu_cflags = ['-fsanitize=thread'] + qemu_cflags >>>> + tsan_warn_suppress = [] >>>> + # gcc (>=11) will report constructions not supported by tsan: >>>> + # "error: ‘atomic_thread_fence’ is not supported with ‘-fsanitize=thread’" >>>> + # https://gcc.gnu.org/gcc-11/changes.html >>>> + # However, clang does not support this warning and this triggers an error. >>>> + if cc.has_argument('-Wno-tsan') >>>> + tsan_warn_suppress = ['-Wno-tsan'] >>>> + endif >>> >>> That last part sounds like a clang bug -- -Wno-foo is supposed >>> to not be an error on compilers that don't implement -Wfoo for >>> any value of foo (unless some other warning/error would also >>> be emitted). >> >> -Wno-foo isn't an error, but it is a warning... which we then >> turn into an error due to -Werror, unless we pass -Wno-unknown-warning-option >> to clang. > > Which is irritating if you want to be able to blanket say > '-Wno-silly-compiler-warning' and not see any of that > warning regardless of compiler version. That's why the > gcc behaviour is the way it is (i.e. -Wno-such-thingy > is neither a warning nor an error if it would be the only > warning/error), and if clang doesn't match it that's a shame. I thought that Clang would behave the same way as GCC, but apparently it does not (anymore?): $ gcc -Wno-flux-capacitors testprg.c -o testprg $ clang -Wno-flux-capacitors testprg.c -o testprg warning: unknown warning option '-Wno-flux-capacitors' [-Wunknown-warning-option] 1 warning generated. Thomas