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SubjectRe: [PATCH 0/6] i386 virtualization patches, Set 3 wrote:
> This round attempts to conclude all of the LDT related cleanup with some
> finally nice looking LDT code, fixes for the UML build, a bugfix for
> really rather nasty kprobes problems, and the basic framework for an LDT
> test suite. It is really rather unfortunate that this code is so
> difficult to test, even with DOSemu and Wine, there are still very nasty
> corner cases here - anyone want an iret to 16-bit stack test?.
> I was going to attempt to clean up the math-emu code to make it use the
> nice new segment and descriptor table accessors, but it quickly became
> apparent that this would be a long, tedious, error prone process that
> would eventually result in the death of a large section of my brain.
> In addition, it is not very fun to test this on the actual hardware it
> is designed to run on (although I did manage to track down a 386 with
> detachable i387 coprocessor, the owner is not sure it still boots).
> Someday it would be nice to have an audit of this code; it appears to
> be riddled with bugs relating to segmentation, for example it assumes
> LDT segments on overrides, does not use the mm->context semaphore to
> protect LDT access, and generally looks scarily out of date in both
> function and appearance.

If you really want to test the math emu code, you can hack check_x87 in
head.S to always leave the fpu disabled. Then you can test it on any
cpu, not just a 386.

Brian Gerst
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