XFEATURE_ENABLED_MASK
set_xcr(XFEATURE_ENABLED_MASK, flags);
(get_xcr(XFEATURE_ENABLED_MASK) & XFEATURE_FP_INITIAL);
features = get_xcr(XFEATURE_ENABLED_MASK);
allowed_bits = get_xcr(XFEATURE_ENABLED_MASK);