Messages in this thread | | | From | (Linus Torvalds) | Subject | Re: Ingo's PIII FXSTOR patch [2 Mar] causes problems | Date | 16 Apr 1999 04:24:52 GMT |
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In article <371693F9.EE78C6FE@redhat.com>, Doug Ledford <dledford@redhat.com> wrote: > >I'm currently furthering Ingo's original work on this (it was the basis >for some code that was used in the March 17th PIII Xeon launch event by >Intel). As it turns out, if you really pay attention to detail, it is >*impossible* to reconstruct the complete FPU state that you would >normally get from fsave using only fxsave. The changes to the Tag Word >make it impossible (the fxsave uses a lossy form of saving the tag word >and we can't get that lost information back).
I haven't looked into the exact details, but I guess you're referring to the fact that fxsave only saves the "empty" bit.
That's not lossy: the rest of the tag information is implicit in the actual value of the stack entry.
It shoul dbe really easy to convert between the new and the old format: let the hardware do it for you:
fxrestore new-format fnsave old-format
I don't see any loss of information anywhere.. Am I overlooking something?
Linus
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