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=-0.8 required=3.0 tests=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 AE145C3A5A3 for ; Tue, 27 Aug 2019 04:39:50 +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 807E720828 for ; Tue, 27 Aug 2019 04:39:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 807E720828 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=twiddle.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:46526 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i2TGn-0004hf-Nb for qemu-devel@archiver.kernel.org; Tue, 27 Aug 2019 00:39:49 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:34388) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i2TCv-0001SP-K6 for qemu-devel@nongnu.org; Tue, 27 Aug 2019 00:35:50 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i2TCt-000241-8F for qemu-devel@nongnu.org; Tue, 27 Aug 2019 00:35:48 -0400 Received: from indium.canonical.com ([91.189.90.7]:46252) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1i2TCs-00022K-Cp for qemu-devel@nongnu.org; Tue, 27 Aug 2019 00:35:46 -0400 Received: from loganberry.canonical.com ([91.189.90.37]) by indium.canonical.com with esmtp (Exim 4.86_2 #2 (Debian)) id 1i2TCp-0005Vj-1q for ; Tue, 27 Aug 2019 04:35:43 +0000 Received: from loganberry.canonical.com (localhost [127.0.0.1]) by loganberry.canonical.com (Postfix) with ESMTP id ECBB82E80D8 for ; Tue, 27 Aug 2019 04:35:40 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Date: Tue, 27 Aug 2019 04:29:44 -0000 From: Richard Henderson To: qemu-devel@nongnu.org X-Launchpad-Notification-Type: bug X-Launchpad-Bug: product=qemu; status=Confirmed; importance=Undecided; assignee=None; X-Launchpad-Bug-Information-Type: Public X-Launchpad-Bug-Private: no X-Launchpad-Bug-Security-Vulnerability: no X-Launchpad-Bug-Commenters: 7-pc rth X-Launchpad-Bug-Reporter: Paul Clarke (7-pc) X-Launchpad-Bug-Modifier: Richard Henderson (rth) References: <156686849716.6431.16425651381928336460.malonedeb@gac.canonical.com> Message-Id: <156688018436.7204.445680632475167875.malone@gac.canonical.com> 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="19031"; Instance="launchpad-lazr.conf" X-Launchpad-Hash: 076326b736c1bec9e998fa34b6964b95b6417c46 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 91.189.90.7 Subject: [Qemu-devel] [Bug 1841491] Re: floating point emulation can fail to set FE_UNDERFLOW 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 1841491 <1841491@bugs.launchpad.net> Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" The float test failure is part of a larger problem for target/powerpc in which all float routines are implemented incorrectly. They are all implemented as double operations with rounding to float as a second step. Which not only produces incorrect exceptions, as in this case, but incorrect numerical results from the double rounding. This should probably be split to a separate bug... ** Changed in: qemu Status: New =3D> Confirmed -- = You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1841491 Title: floating point emulation can fail to set FE_UNDERFLOW Status in QEMU: Confirmed Bug description: Floating point emulation can fail to set FE_UNDERFLOW in some circumstances. This shows up often in glibc's "math" tests. A similar test is attached. This is similar to bug #1841442, but not the same problem, and I don't think the fix will be in the same code. On ppc64le native: -- $ gcc -c -O2 fma.c $ gcc -O2 test-fma.c fma.o -lm -o test-fma $ ./test-fma $(./test-fma) fma(0x1.ffffffffffffcp-1022, 0x1.0000000000001p-1, 0x0.0000000000001p-102= 2) 0x0 0xa000000 FE_INEXACT FE_UNDERFLOW = 0x1p-1022 -- On qemu-system-ppc64: -- $ ./test-fma $(./test-fma) fma(0x1.ffffffffffffcp-1022, 0x1.0000000000001p-1, 0x0.0000000000001p-102= 2) 0x0 0x2000000 FE_INEXACT = 0x1p-1022 -- QEMU versions vary, but not too much, and are pretty close to git HEAD: - 586f3dced9 (HEAD -> master, origin/master, origin/HEAD) Merge remote-tr= acking branch 'remotes/cohuck/tags/s390x-20190822' into staging - 864ab31 Update version for v4.1.0-rc4 release There are worse symptoms on qemu-x86_64, but this is apparently not surprising per https://bugs.launchpad.net/qemu/+bug/1841442/comments/6. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1841491/+subscriptions