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[188.79.232.91]) by smtp.gmail.com with ESMTPSA id n5-20020a05600c294500b003fbc0a49b57sm1001932wmd.6.2023.07.04.22.14.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 04 Jul 2023 22:14:12 -0700 (PDT) Message-ID: Date: Wed, 5 Jul 2023 07:14:10 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: intermittent clang sanitizer failure during 'make check-tcg': null pointer deref in IntervalTreeNode Content-Language: en-US To: Peter Maydell , QEMU Developers References: From: Richard Henderson In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2a00:1450:4864:20::330; envelope-from=richard.henderson@linaro.org; helo=mail-wm1-x330.google.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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.09, RCVD_IN_DNSWL_NONE=-0.0001, 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 7/4/23 18:20, Peter Maydell wrote: > If you build QEMU with the clang UB sanitizer and do a > 'make check-tcg' run, it can fail like this: > > TEST vma-pthread-with-libinsn.so on aarch64 > ../../util/interval-tree.c:751:32: runtime error: member access within > null pointer of type 'IntervalTreeNode' (aka 'struct > IntervalTreeNode') > SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior > ../../util/interval-tree.c:751:32 in > > SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior > ../../util/interval-tree.c:751:32 in > make[1]: *** [Makefile:181: run-plugin-vma-pthread-with-libinsn.so] Error 124 > make: *** [/mnt/nvmedisk/linaro/qemu-from-laptop/qemu/tests/Makefile.include:56: > run-tcg-tests-aarch64-linux-user] Error 2 > > I only saw this once; when I re-ran the test passed... Hmm. The 751:32 reference is "left->subtree_last". Three lines above we checked if (node->rb.rb_left) { but then read it again within the IF IntervalTreeNode *left = rb_to_itree(node->rb.rb_left); I suspect a normal optimizing compiler combines these two reads, but UBSAN does not and thus the check and the use race. On the to-do list... r~