Function:

FRSTOR loads the FPU internal registers (including ST-registers) and the
environment from the memory operand. See <FPU State image layout>.

If either of the two last bytes of the image being read by FRSTOR cannot
be read for whatever reason, the instruction cannot be restarted on
some 387s.

A workaround is to attempt to read those bytes before the FRSTOR is
executed or to align the image on a 128 byte boundary so it is
unlikely to fall outside a segment or page boundary.
Should that be the case, the integer unit can cause an exception or
make sure the page (in case of a swapped page) is read into memory
before FRSTOR starts.




FSAVE  Save FPU state to memory
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