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From: "Alex Bennée" <alex.bennee@linaro.org>
To: qemu-devel@nongnu.org
Subject: [Qemu-devel] [Bug 1843795] Re: 'mtfsf' instruction can clear FI incorrectly
Date: Thu, 12 Sep 2019 18:32:22 -0000	[thread overview]
Message-ID: <156831314322.17231.11777012720914361981.launchpad@gac.canonical.com> (raw)
In-Reply-To: 156830716414.515.16944012251535902875.malonedeb@wampee.canonical.com

** Tags added: fpu ppc testcase

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https://bugs.launchpad.net/bugs/1843795

Title:
  'mtfsf' instruction can clear FI incorrectly

Status in QEMU:
  New

Bug description:
  Using mtfsf instruction can clear the FPSCR FI bit incorrectly.  This code snippet exhibits the issue:
  --
    fpscr.ll = 0x1fffffff;
    __builtin_mtfsf (0b11111111, fpscr.d);
    fpscr.d = __builtin_mffs ();
  --

  On POWER9 hardware:
  mffs    : FPSCR = 0x000000007ffff7ff

  On qemu (git master; "-cpu POWER9"):
  --
  $ ./mtfsf
  mffs    : FPSCR = 0x000000007ffdffff
  --

  Two differences:
  bit 52: "reserved", so maybe a "don't care" case
  bit 46: "FI"

  $ git log -1 master
  commit 89ea03a7dc83ca36b670ba7f787802791fcb04b1
  Merge: 019217c 2531164
  Author: Peter Maydell <peter.maydell@linaro.org>
  Date:   Mon Sep 9 09:48:34 2019 +0100

  I tracked the clear is coming from do_float_check_status, likely the
  one in gen_mtfsf, but then I get lost figuring out what _should_ be
  happening. :-/

  Test attached.

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  reply	other threads:[~2019-09-12 18:43 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-12 16:52 [Qemu-devel] [Bug 1843795] [NEW] 'mtfsf' instruction can clear FI incorrectly Paul Clarke
2019-09-12 18:32 ` Alex Bennée [this message]
2021-04-22  7:32 ` [Bug 1843795] " Thomas Huth
2021-04-22 15:27 ` Paul Clarke
2021-05-11  5:37 ` Thomas Huth

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