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=-4.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 6ECA4C433E0 for ; Mon, 20 Jul 2020 15:27:05 +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 404B922482 for ; Mon, 20 Jul 2020 15:27:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 404B922482 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]:42590 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jxXh2-0000hF-GP for qemu-devel@archiver.kernel.org; Mon, 20 Jul 2020 11:27:04 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48744) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jxXfo-0008Kt-E1 for qemu-devel@nongnu.org; Mon, 20 Jul 2020 11:25:48 -0400 Received: from indium.canonical.com ([91.189.90.7]:53860) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jxXfm-0005I6-Fu for qemu-devel@nongnu.org; Mon, 20 Jul 2020 11:25:48 -0400 Received: from loganberry.canonical.com ([91.189.90.37]) by indium.canonical.com with esmtp (Exim 4.86_2 #2 (Debian)) id 1jxXfk-0000aD-8Z for ; Mon, 20 Jul 2020 15:25:44 +0000 Received: from loganberry.canonical.com (localhost [127.0.0.1]) by loganberry.canonical.com (Postfix) with ESMTP id 1C31E2E80F1 for ; Mon, 20 Jul 2020 15:25:44 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Date: Mon, 20 Jul 2020 15:17:27 -0000 From: Richard Henderson <1888165@bugs.launchpad.net> To: qemu-devel@nongnu.org X-Launchpad-Notification-Type: bug X-Launchpad-Bug: product=qemu; status=In Progress; importance=Undecided; assignee=rth@twiddle.net; X-Launchpad-Bug-Information-Type: Public X-Launchpad-Bug-Private: no X-Launchpad-Bug-Security-Vulnerability: no X-Launchpad-Bug-Commenters: jmmorlan X-Launchpad-Bug-Reporter: Jeffrey (jmmorlan) X-Launchpad-Bug-Modifier: Richard Henderson (rth) References: <159520414927.8137.962061150870003047.malonedeb@wampee.canonical.com> Message-Id: <159525824808.13304.17864642151185423756.launchpad@gac.canonical.com> Subject: [Bug 1888165] Re: loopz/loopnz clearing previous instruction's modified flags on cx -> 0 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="4809fcb62f445aaa3ae919f7f6c3cc7d156ea57a"; Instance="production-secrets-lazr.conf" X-Launchpad-Hash: cb7d58b67427f82f2d9631486c0570e87f49130a Received-SPF: none client-ip=91.189.90.7; envelope-from=bounces@canonical.com; helo=indium.canonical.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/20 11:25:44 X-ACL-Warn: Detected OS = Linux 3.11 and newer [fuzzy] X-Spam_score_int: -58 X-Spam_score: -5.9 X-Spam_bar: ----- X-Spam_report: (-5.9 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=1, RCVD_IN_DNSWL_HI=-5, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, 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 1888165 <1888165@bugs.launchpad.net> Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" ** Changed in: qemu Status: New =3D> In Progress ** Changed in: qemu Assignee: (unassigned) =3D> Richard Henderson (rth) -- = You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1888165 Title: loopz/loopnz clearing previous instruction's modified flags on cx -> 0 Status in QEMU: In Progress Bug description: If you run QBasic in qemu, printing a double-type single-digit number will print an extra decimal point (e.g. PRINT CDBL(3) prints "3.") that does not appear when running on a real CPU (or on qemu with -enable-kvm). I tracked this down to the state of the status flags after a loopnz instruction. After executing a sequence like this in qemu: mov bx,1 mov cx,1 dec bx ; sets Z bit in flags A: loopnz A ; should not modify flags Z is incorrectly clear afterwards. loopz does the same thing (but not plain loop). Interestingly, inserting pushf+popf after dec results in Z set, so loopnz/loopz does not always clear Z itself but is rather interfering with the previous instruction's flag setting. Version 5.1.0-rc0, x86-64 host. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1888165/+subscriptions