[Qemu-devel] [Bug 672934] [NEW] FPU incorrect on Mac OS X

[Michael Roitzsch]

Public bug reported:

I am using the 0.13.0 release version of QEMU on Mac OS X 10.6.4. I work
for a university and the affected guest OS is our own research OS. I
believe I found a bug in QEMU's FPU emulation, which only triggers on
the Mac. You can reproduce the problem by booting the attached ISO
image.

Investigating the problem, I found that the lua interpreter in our
loader component (called "ned") internally uses doubles to represent all
lua-numbers. These doubles are showing completely wrong values on
QEMU/Mac, resulting in the lua code not processing properly.

I also attached a patch which fixes the problem for me. The attached
ZIP-file also contains "before" and "after" screenshots. Note that
booting the ISO on a real machine or on a Linux-QEMU always shows the
correct "after" behavior. Only QEMU on the Mac exhibits the wrong
"before" behavior without my patch. The patch might break other systems
setting the CONFIG_BSD flag, so maybe the preprocessor should check for
__APPLE__ instead to make the fix Mac-only.

** Affects: qemu
     Importance: Undecided
         Status: New

-- 
FPU incorrect on Mac OS X
https://bugs.launchpad.net/bugs/672934
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Status in QEMU: New

Bug description:
I am using the 0.13.0 release version of QEMU on Mac OS X 10.6.4. I work for a 
university and the affected guest OS is our own research OS. I believe I found 
a bug in QEMU's FPU emulation, which only triggers on the Mac. You can 
reproduce the problem by booting the attached ISO image.

Investigating the problem, I found that the lua interpreter in our loader 
component (called "ned") internally uses doubles to represent all lua-numbers. 
These doubles are showing completely wrong values on QEMU/Mac, resulting in the 
lua code not processing properly.

I also attached a patch which fixes the problem for me. The attached ZIP-file 
also contains "before" and "after" screenshots. Note that booting the ISO on a 
real machine or on a Linux-QEMU always shows the correct "after" behavior. Only 
QEMU on the Mac exhibits the wrong "before" behavior without my patch. The 
patch might break other systems setting the CONFIG_BSD flag, so maybe the 
preprocessor should check for __APPLE__ instead to make the fix Mac-only.