image/svg+xmlXSAVEC—Save Processor Extended States with CompactionInstruction Operand EncodingDescriptionPerforms a full or partial save of processor state components to the XSAVE area located at the memory address specified by the destination operand. The implicit EDX:EAX register pair specifies a 64-bit instruction mask. The specific state components saved 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 13.10, “Operation of XSAVEC,” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1 provides a detailed description of the operation of the XSAVEC instruction. The following items provide a high-level outline:Execution of XSAVEC is similar to that of XSAVE. XSAVEC differs from XSAVE in that it uses compaction and that it may use the init optimization.XSAVEC saves state component i if and only if RFBM[i]= 1 and XINUSE[i]= 1.1 (XINUSE is a bitmap by which the processor tracks the status of various state components. See Section 13.6, “Processor Tracking of XSAVE-Managed State” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1.)XSAVEC does not modify bytes 511:464 of the legacy region of the XSAVE area (see Section 13.4.1, “Legacy Region of an XSAVE Area” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1).XSAVEC writes the logical AND of RFBM and XINUSE to the XSTATE_BV field of the XSAVE header.2,3 (See Section 13.4.2, “XSAVE Header” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1.) XSAVEC sets bit63 of the XCOMP_BV field and sets bits62:0 of that field to RFBM[62:0]. XSAVEC does not write to any parts of the XSAVE header other than the XSTATE_BV and XCOMP_BV fields.XSAVEC always uses the compacted format of the extended region of the XSAVE area (see Section 13.4.3, “Extended Region of an XSAVE Area” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1).Use of a destination operand not aligned to 64-byte boundary (in either 64-bit or 32-bit modes) results in a general-protection (#GP) exception. In 64-bit mode, the upper 32 bits of RDX and RAX are ignored.Opcode /InstructionOp/ En64/32 bit Mode SupportCPUID Feature FlagDescriptionNP 0F C7 /4XSAVEC memMV/VXSAVECSave state components specified by EDX:EAX to mem with compaction.NP REX.W + 0F C7 /4XSAVEC64 memMV/N.E.XSAVECSave state components specified by EDX:EAX to mem with compaction.Op/EnOperand 1Operand 2Operand 3Operand 4MModRM:r/m (w)NANANA1.There is an exception for state component 1 (SSE). MXCSR is part of SSE state, but XINUSE[1] may be 0 even if MXCSR does not have its initial value of 1F80H. In this case, XSAVEC saves SSE state as long as RFBM[1]= 1.2.Unlike XSAVE and XSAVEOPT, XSAVEC clears bits in the XSTATE_BV field that correspond to bits that are clear in RFBM.3.There is an exception for state component 1 (SSE). MXCSR is part of SSE state, but XINUSE[1] may be 0 even if MXCSR does not have its initial value of 1F80H. In this case, XSAVEC sets XSTATE_BV[1] to 1 as long as RFBM[1]= 1.

image/svg+xmlOperationRFBM := XCR0 AND EDX:EAX;/* bitwise logical AND */TO_BE_SAVED := RFBM AND XINUSE;/* bitwise logical AND */If MXCSR 1F80H AND RFBM[1]TO_BE_SAVED[1] = 1;FI;IF TO_BE_SAVED[0]= 1THEN store x87 state into legacy region of XSAVE area;FI;IF TO_BE_SAVED[1]= 1THEN store SSE state into legacy region of XSAVE area; // this step saves the XMM registers, MXCSR, and MXCSR_MASKFI;NEXT_FEATURE_OFFSET = 576;// Legacy area and XSAVE header consume 576 bytesFOR i := 2 TO 62IF RFBM[i] = 1THENIF TO_BE_SAVED[i]THEN save 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;ENDFOR;XSTATE_BV field in XSAVE header := TO_BE_SAVED;XCOMP_BV field in XSAVE header := RFBM OR 80000000_00000000H;Flags AffectedNone.Intel C/C++ Compiler Intrinsic EquivalentXSAVEC:void _xsavec( void * , unsigned __int64);XSAVEC64:void _xsavec64( 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.#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[bit26] = 0 or CPUID.(EAX=0DH,ECX=1):EAX.XSAVEC[bit1]= 0.If CR4.OSXSAVE[bit 18] = 0.If the LOCK prefix is used.

image/svg+xml#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.#NM If CR0.TS[bit 3] = 1.#UD If CPUID.01H:ECX.XSAVE[bit26] = 0 or CPUID.(EAX=0DH,ECX=1):EAX.XSAVEC[bit1]= 0.If CR4.OSXSAVE[bit 18] = 0.If the LOCK prefix is used.Virtual-8086 Mode ExceptionsSame exceptions as in protected mode.Compatibility Mode ExceptionsSame exceptions as in protected mode.64-Bit Mode Exceptions#GP(0)If the memory address is in a non-canonical form.If a memory operand is not aligned on a 64-byte boundary, regardless of segment.#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[bit26] = 0 or CPUID.(EAX=0DH,ECX=1):EAX.XSAVEC[bit1]= 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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