[Qemu-devel] [Bug 1603734] Re: Hang in fsqrt

[Peter Maydell]

Thanks for this bug report. The problem here is that QEMU is not
correctly handling the obsolete "unnormal" 80-bit floating point format.
The Intel architecture reference says that this should be handled by
raising the invalid-input exception and returning the default NaN.

See also the discussion in the mailing list thread "Hang bug in 80-bit
float square root implementation", though the patch there is not the
correct fix for the bug.

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https://bugs.launchpad.net/bugs/1603734

Title:
  Hang in fsqrt

Status in QEMU:
  New

Bug description:
  At least qemu-i368 and qemu-x86_64 hang in floatx80_sqrt in versions
  2.6.0 and git (2.6.50) for some input values, likely due to an
  infinite loop at fpu/softfloat.c:6569.

  Steps to reproduce:
  1) Compile attached code: gcc -o test test.c -lm
  2) `qemu-i368 test` and `qemu-x86_64 test` will hang at 100% cpu

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