From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5C659C11F66 for ; Tue, 13 Jul 2021 04:33:23 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id DD0A061004 for ; Tue, 13 Jul 2021 04:33:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DD0A061004 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=bugs.launchpad.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:60436 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1m3A6k-0006gn-3Q for qemu-devel@archiver.kernel.org; Tue, 13 Jul 2021 00:33:22 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:33408) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m39zl-0006o4-Jm for qemu-devel@nongnu.org; Tue, 13 Jul 2021 00:26:09 -0400 Received: from indium.canonical.com ([91.189.90.7]:40808) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1m39zj-0008U6-V8 for qemu-devel@nongnu.org; Tue, 13 Jul 2021 00:26:09 -0400 Received: from loganberry.canonical.com ([91.189.90.37]) by indium.canonical.com with esmtp (Exim 4.93 #5 (Debian)) id 1m39zW-0003ex-77 for ; Tue, 13 Jul 2021 04:25:54 +0000 Received: from loganberry.canonical.com (localhost [127.0.0.1]) by loganberry.canonical.com (Postfix) with ESMTP id BFC922E81AC for ; Tue, 13 Jul 2021 04:25:51 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Date: Tue, 13 Jul 2021 04:17:23 -0000 From: Launchpad Bug Tracker <1915327@bugs.launchpad.net> To: qemu-devel@nongnu.org X-Launchpad-Notification-Type: bug X-Launchpad-Bug: product=qemu; status=Expired; importance=Undecided; assignee=None; X-Launchpad-Bug-Tags: i386 tcg X-Launchpad-Bug-Information-Type: Public X-Launchpad-Bug-Private: no X-Launchpad-Bug-Security-Vulnerability: no X-Launchpad-Bug-Commenters: iii-i janitor th-huth X-Launchpad-Bug-Reporter: Ilya Leoshkevich (iii-i) X-Launchpad-Bug-Modifier: Launchpad Janitor (janitor) References: <161298968608.29108.9925609875505640314.malonedeb@soybean.canonical.com> Message-Id: <162614984350.15811.8705644630794054093.malone@loganberry.canonical.com> Subject: [Bug 1915327] Re: x86_64 cmpxchg behavior in qemu tcg does not match the real CPU X-Launchpad-Message-Rationale: Subscriber (QEMU) @qemu-devel-ml X-Launchpad-Message-For: qemu-devel-ml Precedence: bulk X-Generated-By: Launchpad (canonical.com); Revision="1b66c075b8638845e61f40eb9036fabeaa01f591"; Instance="production" X-Launchpad-Hash: 992a6aeb3e7face4548938a2682ede626a13e081 Received-SPF: none client-ip=91.189.90.7; envelope-from=bounces@canonical.com; helo=indium.canonical.com X-Spam_score_int: -65 X-Spam_score: -6.6 X-Spam_bar: ------ X-Spam_report: (-6.6 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.248, RCVD_IN_DNSWL_HI=-5, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Bug 1915327 <1915327@bugs.launchpad.net> Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" [Expired for QEMU because there has been no activity for 60 days.] ** Changed in: qemu Status: Incomplete =3D> Expired -- = You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1915327 Title: x86_64 cmpxchg behavior in qemu tcg does not match the real CPU Status in QEMU: Expired Bug description: QEMU version: 1214d55d1c (HEAD, origin/master, origin/HEAD) Merge remote-tracking branc= h 'remotes/nvme/tags/nvme-next-pull-request' into staging Consider the following little program: $ cat 1.c #include int main() { int mem =3D 0x12345678; register long rax asm("rax") =3D 0x1234567812345678; register int edi asm("edi") =3D 0x77777777; asm("cmpxchg %[edi],%[mem]" : [ mem ] "+m"(mem), [ rax ] "+r"(rax) : [ edi ] "r"(edi)); long rax2 =3D rax; printf("rax2 =3D %lx\n", rax2); } According to the Intel Manual, cmpxchg should not touch the accumulator in case the values are equal, which is indeed the case on the real CPU: $ gcc 1.c $ ./a.out = rax2 =3D 1234567812345678 However, QEMU appears to zero extend EAX to RAX: $ qemu-x86_64 ./a.out = rax2 =3D 12345678 This is also the case for lock cmpxchg. Found in BPF development context: https://lore.kernel.org/bpf/b1792bb3c51eb3e94b9d27e67665d3f2209bba7e.came= l@linux.ibm.com To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1915327/+subscriptions