 0, XSAVEOPT writes XSTATE_BV[<em>i</em>] with the value that it read from memory (it does not modify the bit). XSAVEOPT does not write to any part of the XSAVE header other than the XSTATE_BV field.</li>
<li>XSAVEOPT always uses the standard format of the extended region of the XSAVE area (see Section 13.4.3, “Extended Region of an XSAVE Area”).</li></ul>
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<p>1. There is an exception made for MXCSR and MXCSR_MASK, which belong to state component 1 — SSE. XSAVEOPT always saves these to mem