[Qemu-devel] [Bug 1841442] Re: floating point emulation can fail to set FE_INEXACT

[Richard Henderson]

Well, maybe yes and maybe no.  What you've done is choose two targets
whose floating point emulation have not been well maintained.

If I try this same test on aarch64, it passes:

$ ~/a.out 0x0000000000000001
0x0000000000000001 0.000000
0x0

0x18
FE_INEXACT FE_UNDERFLOW 
0x0000000000000000 0.000000

$ ./aarch64-linux-user/qemu-aarch64 ~/a.out 0x0000000000000001
0x0000000000000001 0.000000
0x0

0x18
FE_INEXACT FE_UNDERFLOW 
0x0000000000000000 0.000000

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https://bugs.launchpad.net/bugs/1841442

Title:
  floating point emulation can fail to set FE_INEXACT

Status in QEMU:
  New

Bug description:
  Floating point emulation can fail to set FE_INEXACT in some
  circumstances. This shows up quite often in glibc's "math" tests.  A
  similar test is attached.

  On ppc64le native:
  --
  $ gcc nextafter.c -o nextafter -lm
  $ ./nextafter $(./nextafter)
  0x0000000000000001 0.000000
  0x0

  0xa000000
  FE_INEXACT FE_UNDERFLOW
  0x0000000000000000 0.000000
  --

  On x86_64:
  --
  $ gcc nextafter.c -o nextafter -lm
  $ ./nextafter $(./nextafter)
  0x0000000000000001 0.000000
  0x0

  0x30
  FE_INEXACT FE_UNDERFLOW 
  0x0000000000000000 0.000000
  --

  Using qemu-system-ppc64
  --
  $ ./nextafter $(./nextafter)
  0x0000000000000001 0.000000
  0x0

  0x8000000
  FE_UNDERFLOW 
  0x0000000000000000 0.000000
  --

  Using qemu-x86_64:
  --
  $ ./nextafter $(./nextafter)
  0x0000000000000001 0.000000
  0x0

  0x0

  0x0000000000000000 0.000000
  --

  QEMU versions vary, but not too much, and are pretty close to git HEAD:
  - 586f3dced9 (HEAD -> master, origin/master, origin/HEAD) Merge 
remote-tracking branch 'remotes/cohuck/tags/s390x-20190822' into staging
  - 864ab31 Update version for v4.1.0-rc4 release

  Since the issue happens nearly identically on different targets, I
  suspect the issue lies somewhere in fpu/softfloat.c.

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