XSAVEC—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.
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