image/svg+xmlXRSTOR—Restore Processor Extended StatesInstruction Operand EncodingDescriptionPerforms a full or partial restore of processor state components from the XSAVE area located at the memory address specified by the source operand. The implicit EDX:EAX register pair specifies a 64-bit instruction mask. The specific state components restored correspond to the bits set in the requested-feature bitmap (RFBM), which is the logical-AND of EDX:EAX and XCR0.The format of the XSAVE area is detailed in Section 13.4, “XSAVE Area,” of Intel® 64 and IA-32 Architectures Soft-ware Developer’s Manual, Volume 1. Like FXRSTOR and FXSAVE, the memory format used for x87 state depends on a REX.W prefix; see Section 13.5.1, “x87 State” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1.Section 13.8, “Operation of XRSTOR,” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1 provides a detailed description of the operation of the XRSTOR instruction. The following items provide a high-level outline:•Execution of XRSTOR may take one of two forms: standard and compacted. Bit63 of the XCOMP_BV field in the XSAVE header determines which form is used: value 0 specifies the standard form, while value 1 specifies the compacted form.•If RFBM[i]= 0, XRSTOR does not update state component i.1•If RFBM[i]= 1 and biti is clear in the XSTATE_BV field in the XSAVE header, XRSTOR initializes state component i.•If RFBM[i]= 1 and XSTATE_BV[i]= 1, XRSTOR loads state componenti from the XSAVE area.•The standard form of XRSTOR treats MXCSR (which is part of state component 1 — SSE) differently from the XMM registers. If either form attempts to load MXCSR with an illegal value, a general-protection exception (#GP) occurs.•XRSTOR loads the internal value XRSTOR_INFO, which may be used to optimize a subsequent execution of XSAVEOPT or XSAVES.•Immediately following an execution of XRSTOR, the processor tracks as in-use (not in initial configuration) any state componenti for which RFBM[i]= 1 and XSTATE_BV[i]= 1; it tracks as modified any state component ifor which RFBM[i]= 0.Use of a source operand not aligned to 64-byte boundary (for 64-bit and 32-bit modes) results in a general-protec-tion (#GP) exception. In 64-bit mode, the upper 32 bits of RDX and RAX are ignored.See Section 13.6, “Processor Tracking of XSAVE-Managed State,” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1 for discussion of the bitmaps XINUSE and XMODIFIED and of the quantity XRSTOR_INFO.Opcode /InstructionOp/ En64/32 bit Mode SupportCPUID Feature FlagDescriptionNP 0F AE /5XRSTOR memMV/VXSAVERestore state components specified by EDX:EAX from mem.NP REX.W + 0F AE /5XRSTOR64 memMV/N.E.XSAVERestore state components specified by EDX:EAX from mem.Op/EnOperand 1Operand 2Operand 3Operand 4MModRM:r/m (r)NANANA1.There is an exception if RFBM[1]= 0 and RFBM[2]= 1. In this case, the standard form of XRSTOR will load MXCSR from memory, even though MXCSR is part of state component 1 — SSE. The compacted form of XRSTOR does not make this exception.

image/svg+xmlOperationRFBM := XCR0 AND EDX:EAX;/* bitwise logical AND */COMPMASK := XCOMP_BV field from XSAVE header;RSTORMASK := XSTATE_BV field from XSAVE header;IF COMPMASK[63] = 0THEN/* Standard form of XRSTOR */TO_BE_RESTORED := RFBM AND RSTORMASK;TO_BE_INITIALIZED := RFBM AND NOT RSTORMASK;IF TO_BE_RESTORED[0] = 1THENXINUSE[0] := 1;load x87 state from legacy region of XSAVE area;ELSIF TO_BE_INITIALIZED[0] = 1THENXINUSE[0] := 0;initialize x87 state;FI;IF RFBM[1] = 1 OR RFBM[2]= 1THEN load MXCSR from legacy region of XSAVE area;FI;IF TO_BE_RESTORED[1] = 1THENXINUSE[1] := 1;load XMM registers from legacy region of XSAVE area; // this step does not load MXCSRELSIF TO_BE_INITIALIZED[1] = 1THENXINUSE[1] := 0;set all XMM registers to 0; // this step does not initialize MXCSRFI;FOR i := 2 TO 62 IF TO_BE_RESTORED[i] = 1THENXINUSE[i] := 1;load XSAVE state component i at offset n from base of XSAVE area;// n enumerated by CPUID(EAX=0DH,ECX=i):EBX)ELSIF TO_BE_INITIALIZED[i] = 1THENXINUSE[i] := 0;initialize XSAVE state component i;FI;ENDFOR;ELSE/* Compacted form of XRSTOR */IF CPUID.(EAX=0DH,ECX=1):EAX.XSAVEC[bit1]= 0THEN/* compacted form not supported */#GP(0);

image/svg+xmlFI;FORMAT = COMPMASK AND 7FFFFFFF_FFFFFFFFH;RESTORE_FEATURES = FORMAT AND RFBM;TO_BE_RESTORED := RESTORE_FEATURES AND RSTORMASK;FORCE_INIT := RFBM AND NOT FORMAT;TO_BE_INITIALIZED = (RFBM AND NOT RSTORMASK) OR FORCE_INIT;IF TO_BE_RESTORED[0] = 1THENXINUSE[0] := 1;load x87 state from legacy region of XSAVE area;ELSIF TO_BE_INITIALIZED[0] = 1THENXINUSE[0] := 0;initialize x87 state;FI;IF TO_BE_RESTORED[1] = 1THENXINUSE[1] := 1;load SSE state from legacy region of XSAVE area; // this step loads the XMM registers and MXCSRELSIF TO_BE_INITIALIZED[1] = 1THENset all XMM registers to 0;XINUSE[1] := 0;MXCSR := 1F80H;FI;NEXT_FEATURE_OFFSET = 576;// Legacy area and XSAVE header consume 576 bytesFOR i := 2 TO 62 IF FORMAT[i] = 1THENIF TO_BE_RESTORED[i] = 1THENXINUSE[i] := 1;load XSAVE state component i at offset NEXT_FEATURE_OFFSET from base of XSAVE area;FI;NEXT_FEATURE_OFFSET = NEXT_FEATURE_OFFSET + n (n enumerated by CPUID(EAX=0DH,ECX=i):EAX);FI;IF TO_BE_INITIALIZED[i] = 1THENXINUSE[i] := 0;initialize XSAVE state component i;FI;ENDFOR;FI;XMODIFIED := NOT RFBM;IF in VMX non-root operationTHEN VMXNR := 1;ELSE VMXNR := 0;FI;

image/svg+xmlLAXA := linear address of XSAVE area;XRSTOR_INFO := CPL,VMXNR,LAXA,COMPMASK;Flags AffectedNone.Intel C/C++ Compiler Intrinsic EquivalentXRSTOR:void _xrstor( void * , unsigned __int64);XRSTOR:void _xrstor64( void * , unsigned __int64);Protected Mode Exceptions#GP(0)If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.If a memory operand is not aligned on a 64-byte boundary, regardless of segment.If bit63 of the XCOMP_BV field of the XSAVE header is 1 and CPUID.(EAX=0DH,ECX=1):EAX.XSAVEC[bit 1]= 0.If the standard form is executed and a bit in XCR0 is 0 and the corresponding bit in the XSTATE_BV field of the XSAVE header is 1.If the standard form is executed and bytes 23:8 of the XSAVE header are not all zero.If the compacted form is executed and a bit in XCR0 is 0 and the corresponding bit in the XCOMP_BV field of the XSAVE header is 1.If the compacted form is executed and a bit in the XCOMP_BV field in the XSAVE header is 0 and the corresponding bit in the XSTATE_BV field is 1.If the compacted form is executed and bytes 63:16 of the XSAVE header are not all zero.If attempting to write any reserved bits of the MXCSR register with 1.#SS(0)If a memory operand effective address is outside the SS segment limit.#PF(fault-code)If a page fault occurs.#NM If CR0.TS[bit 3] = 1.#UD If CPUID.01H:ECX.XSAVE[bit 26] = 0.If CR4.OSXSAVE[bit 18] = 0.If the LOCK prefix is used.#AC If this exception is disabled a general protection exception (#GP) is signaled if the memory operand is not aligned on a 64-byte boundary, as described above. If the alignment check exception (#AC) is enabled (and the CPL is 3), signaling of #AC is not guaranteed and may vary with implementation, as follows. In all implementations where #AC is not signaled, a general protection exception is signaled in its place. In addition, the width of the alignment check may also vary with implementation. For instance, for a given implementation, an align-ment check exception might be signaled for a 2-byte misalignment, whereas a general protec-tion exception might be signaled for all other misalignments (4-, 8-, or 16-byte misalignments).Real-Address Mode Exceptions#GPIf a memory operand is not aligned on a 64-byte boundary, regardless of segment.If any part of the operand lies outside the effective address space from 0 to FFFFH.If bit63 of the XCOMP_BV field of the XSAVE header is 1 and CPUID.(EAX=0DH,ECX=1):EAX.XSAVEC[bit 1]= 0.If the standard form is executed and a bit in XCR0 is 0 and the corresponding bit in the XSTATE_BV field of the XSAVE header is 1.If the standard form is executed and bytes 23:8 of the XSAVE header are not all zero.If the compacted form is executed and a bit in XCR0 is 0 and the corresponding bit in the XCOMP_BV field of the XSAVE header is 1.

image/svg+xmlIf the compacted form is executed and a bit in the XCOMP_BV field in the XSAVE header is 0 and the corresponding bit in the XSTATE_BV field is 1.If the compacted form is executed and bytes 63:16 of the XSAVE header are not all zero.If attempting to write any reserved bits of the MXCSR register with 1.#NM If CR0.TS[bit 3] = 1.#UD If CPUID.01H:ECX.XSAVE[bit 26] = 0.If CR4.OSXSAVE[bit 18] = 0.If the LOCK prefix is used.Virtual-8086 Mode ExceptionsSame exceptions as in protected modeCompatibility Mode ExceptionsSame exceptions as in protected mode.64-Bit Mode Exceptions#GP(0)If a memory address is in a non-canonical form.If a memory operand is not aligned on a 64-byte boundary, regardless of segment.If bit63 of the XCOMP_BV field of the XSAVE header is 1 and CPUID.(EAX=0DH,ECX=1):EAX.XSAVEC[bit 1]= 0.If the standard form is executed and a bit in XCR0 is 0 and the corresponding bit in the XSTATE_BV field of the XSAVE header is 1.If the standard form is executed and bytes 23:8 of the XSAVE header are not all zero.If the compacted form is executed and a bit in XCR0 is 0 and the corresponding bit in the XCOMP_BV field of the XSAVE header is 1.If the compacted form is executed and a bit in the XCOMP_BV field in the XSAVE header is 0 and the corresponding bit in the XSTATE_BV field is 1.If the compacted form is executed and bytes 63:16 of the XSAVE header are not all zero.If attempting to write any reserved bits of the MXCSR register with 1.#SS(0)If a memory address referencing the SS segment is in a non-canonical form.#PF(fault-code)If a page fault occurs.#NM If CR0.TS[bit 3] = 1.#UD If CPUID.01H:ECX.XSAVE[bit 26] = 0.If CR4.OSXSAVE[bit 18] = 0.If the LOCK prefix is used.#AC If this exception is disabled a general protection exception (#GP) is signaled if the memory operand is not aligned on a 64-byte boundary, as described above. If the alignment check exception (#AC) is enabled (and the CPL is 3), signaling of #AC is not guaranteed and may vary with implementation, as follows. In all implementations where #AC is not signaled, a general protection exception is signaled in its place. In addition, the width of the alignment check may also vary with implementation. For instance, for a given implementation, an align-ment check exception might be signaled for a 2-byte misalignment, whereas a general protec-tion exception might be signaled for all other misalignments (4-, 8-, or 16-byte misalignments).

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