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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id s1sm40072wmj.8.2021.07.05.09.43.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 05 Jul 2021 09:43:57 -0700 (PDT) Subject: Re: [PULL 0/2] Libslirp patches To: Peter Maydell , Stefan Hajnoczi References: <20210529185522.78816-1-marcandre.lureau@redhat.com> <4b3021c2-ac50-d763-4113-10a200bdc9ac@redhat.com> From: Paolo Bonzini Message-ID: <3b61a958-021d-bf2d-9fbb-09451f5fe22c@redhat.com> Date: Mon, 5 Jul 2021 18:43:56 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=pbonzini@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.442, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no 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: =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , Richard Henderson , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , QEMU Developers , Samuel Thibault Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 05/07/21 18:31, Peter Maydell wrote: > 8 here means "8 bytes", not "8 bits". And indeed on i386 you can't > do 8-byte atomics with simple insns. You can, there's a cmpxchg8b instruction. The problem is that somehow configure's view of this disagrees with what happens during compilation. If anybody can send a config.log and make V=1 log, I can look at it. Paolo > The compiler's answer to this > is "emit a call to a helper in libatomic, which will emulate an > atomic access by taking some kind of lock". We don't ever want to > fall back to "take a lock" because sometimes our accesses to the > atomic variables are from TCG generated code -- this is why we > don't link against libatomic. The problem is that we have not > correctly detected that this compiler can't do inline atomics > for 64-bit values and avoided using them. But at least we have > made this a compile failure rather than a silently-wrong-code bug:-)