image/svg+xml XSETBV—Set Extended Control Register Instruction Operand Encoding Description Writes the contents of registers EDX:EAX into the 64-bit extended control register (XCR) specified in the ECX register. (On processors that support the Intel64 architecture, the high-order 32 bits of RCX are ignored.) The contents of the EDX register are copied to high-order 32 bits of the selected XCR and the contents of the EAX register are copied to low-order 32 bits of the XCR. (On processors that support the Intel64 architecture, the high- order 32 bits of each of RAX and RDX are ignored.) Undefined or reserved bits in an XCR should be set to values previously read. This instruction must be executed at privilege level 0 or in real-address mode; otherwise, a general protection exception #GP(0) is generated. Specifying a reserved or unimplemented XCR in ECX will also cause a general protection exception. The processor will also generate a general protection exception if software attempts to write to reserved bits in an XCR. Currently, only XCR0 is supported. Thus, all other values of ECX are reserved and will cause a #GP(0). Note that bit0 of XCR0 (corresponding to x87 state) must be set to 1; the instruction will cause a #GP(0) if an attempt is made to clear this bit. In addition, the instruction causes a #GP(0) if an attempt is made to set XCR0[2] (AVX state) while clearing XCR0[1] (SSE state); it is necessary to set both bits to use AVX instructions; Section 13.3, “Enabling the XSAVE Feature Set and XSAVE-Enabled Features,” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1 . Operation XCR[ECX] := EDX:EAX; Flags Affected None. Intel C/C++ Compiler Intrinsic Equivalent XSETBV:void _xsetbv( unsigned int, unsigned __int64); Protected Mode Exceptions #GP(0)If the current privilege level is not 0. If an invalid XCR is specified in ECX. If the value in EDX:EAX sets bits that are reserved in the XCR specified by ECX. If an attempt is made to clear bit 0 of XCR0. If an attempt is made to set XCR0[2:1] to 10b. #UD If CPUID.01H:ECX.XSAVE[bit 26] = 0. If CR4.OSXSAVE[bit 18] = 0. If the LOCK prefix is used. OpcodeInstructionOp/ En 64-Bit Mode Compat/ Leg Mode Description NP 0F 01 D1XSETBVZOValidValidWrite the value in EDX:EAX to the XCR specified by ECX. Op/EnOperand 1Operand 2Operand 3Operand 4 ZONANANANA image/svg+xml Real-Address Mode Exceptions #GPIf an invalid XCR is specified in ECX. If the value in EDX:EAX sets bits that are reserved in the XCR specified by ECX. If an attempt is made to clear bit 0 of XCR0. If an attempt is made to set XCR0[2:1] to 10b. #UD If CPUID.01H:ECX.XSAVE[bit 26] = 0. If CR4.OSXSAVE[bit 18] = 0. If the LOCK prefix is used. Virtual-8086 Mode Exceptions #GP(0)The XSETBV instruction is not recognized in virtual-8086 mode. Compatibility Mode Exceptions Same exceptions as in protected mode. 64-Bit Mode Exceptions Same exceptions as in protected mode. This UNOFFICIAL reference was generated from the official Intel® 64 and IA-32 Architectures Software Developer’s Manual by a dumb script. There is no guarantee that some parts aren't mangled or broken and is distributed WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE .