[Bug 1843795] Re: 'mtfsf' instruction can clear FI incorrectly

[Thomas Huth]

This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'expired' now.
Please continue with the discussion here:

 https://gitlab.com/qemu-project/qemu/-/issues/266


** Changed in: qemu
       Status: New => Expired

** Bug watch added: gitlab.com/qemu-project/qemu/-/issues #266
   https://gitlab.com/qemu-project/qemu/-/issues/266

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

Title:
  'mtfsf' instruction can clear FI incorrectly

Status in QEMU:
  Expired

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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