qemu-devel
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Qemu-devel] [Bug 1793119] Re: Wrong floating-point emulation on AArch64


From: Koutheir Attouchi
Subject: [Qemu-devel] [Bug 1793119] Re: Wrong floating-point emulation on AArch64 with FPCR set to zero
Date: Tue, 18 Sep 2018 16:56:38 -0000

Thanks for the update. Is there a fix/patch for the issue?

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1793119

Title:
  Wrong floating-point emulation on AArch64 with FPCR set to zero

Status in QEMU:
  Confirmed

Bug description:
  On AArch64, with FPCR set to Zero (i.e., FPU set to IEEE-754 compliant
  mode), floating-point emulation does not produce the same results as
  real hardware (e.g., Raspberry Pi 3 with AArch64 Linux).

  I attached a sample that reproduces the issue. It divides `x` by `y`
  and puts the result in `r`. The expected result of the operation is
  `q`.

  Output on real hardware:
  =========================================================
  fpcr = 0x07000000.
  x = 0x03250f416dcdc6d0. y = 0x00029f4e5837c977. r = 0x7ff0000000000000. q = 
0x43300fde9cbcf023.
  fpcr = 0x00000000.
  x = 0x03250f416dcdc6d0. y = 0x00029f4e5837c977. r = 0x43300fde9cbcf023. q = 
0x43300fde9cbcf023.
  =========================================================

  Notice that after setting FPCR to zero, `r` equals `q`.

  Output on qemu 3.0.0 (Linux user-mode emulation):
  =========================================================
  fpcr = 0x07000000.
  x = 0x03250f416dcdc6d0. y = 0x00029f4e5837c977. r = 0x7ff0000000000000. q = 
0x43300fde9cbcf023.
  fpcr = 0x00000000.
  x = 0x03250f416dcdc6d0. y = 0x00029f4e5837c977. r = 0x43300fde9cbcf024. q = 
0x43300fde9cbcf023.
  =========================================================

  Notice that after setting FPCR to zero, `r` is not equal to `q`.

  Also notice that, using another proprietary operating system, the same
  issue arises between a real board and QEMU. This might be an issue in
  emulation of the AArch64 instruction "fdiv".

  Build command line: aarch64-linux-gnu-gcc -static -O0 -o sample1
  sample1.c

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1793119/+subscriptions



reply via email to

[Prev in Thread] Current Thread [Next in Thread]