cvttsd2si xmm9, xmm15 should be... cvttsd2si ecx, xmm15 vcvttsd2si, vcvtsd2si, sd2si is decoded as if some loads could be only 4 bytes, all are 8... ss2si is decdoed as if some loads could be 8 bytes, all are 4... movdir64b is decodable in protected mode, real mode pconfig is decodable in protected mode, real mode lsl seems just... wrong. check alternate prefixes in 32-/61-bit