XSAVES—Save Processor Extended States Supervisor

Opcode /Instruction Op/En 64/32 bit Mode Support CPUID Feature Flag Description

NP 0F C7 /5

XSAVES mem

 M V/V XSS Save state components specified by EDX:EAX to mem with compaction, optimizing if possible.

NP REX.W + 0F C7 /5

XSAVES64 mem

 M V/N.E. XSS Save state components specified by EDX:EAX to mem with compaction, optimizing if possible.

Instruction Operand Encoding

Op/En Operand 1 Operand 2 Operand 3 Operand 4
M ModRM:r/m (w) N/A N/A N/A

Description

Performs 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), the logical-AND of EDX:EAX and the logical-OR of XCR0 with the IA32_XSS MSR. XSAVES may be executed only if CPL = 0.

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 13.11, “Operation of XSAVES,” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1 provides a detailed description of the operation of the XSAVES instruction. The following items provide a high-level outline:

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.

1.

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, the init optimization does not apply and XSAVEC will save SSE state as long as RFBM[1] = 1 and the modified optimization is not being applied.

2.

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, XSAVES sets XSTATE_BV[1] to 1 as long as RFBM[1] = 1.

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 bitmap XMODIFIED and of the quantity XRSTOR_INFO.

Operation

RFBM := (XCR0 OR IA32_XSS) AND EDX:EAX;
                                                              /* bitwise logical OR and AND */
IF in VMX non-root operation
    THEN VMXNR := 1;
    ELSE VMXNR := 0;
FI;
LAXA := linear address of XSAVE area;
COMPMASK := RFBM OR 80000000_00000000H;
TO_BE_SAVED := RFBM AND XINUSE;
IF XRSTOR_INFO = CPL,VMXNR,LAXA,COMPMASK
    THEN TO_BE_SAVED := TO_BE_SAVED AND XMODIFIED;
FI;
IF MXCSR ≠ 1F80H AND RFBM[1]
    THEN TO_BE_SAVED[1] = 1;
FI;
IF TO_BE_SAVED[0] = 1
    THEN store x87 state into legacy region of XSAVE area;
FI;
IF TO_BE_SAVED[1] = 1
    THEN store SSE state into legacy region of XSAVE area; // this step saves the XMM registers, MXCSR, and MXCSR_MASK
FI;
NEXT_FEATURE_OFFSET = 576;
                                              // Legacy area and XSAVE header consume 576 bytes
FOR i := 2 TO 62
    IF RFBM[i] = 1
         THEN
              IF TO_BE_SAVED[i]
                    THEN
                         save XSAVE state component i at offset NEXT_FEATURE_OFFSET from base of XSAVE area;
                         IF i = 8
                                         // state component 8 is for PT state
                              THEN IA32_RTIT_CTL.TraceEn[bit 0] := 0;
                         FI;
              FI;
              NEXT_FEATURE_OFFSET = NEXT_FEATURE_OFFSET + n (n enumerated by CPUID(EAX=0DH,ECX=i):EAX);
    FI;
ENDFOR;
NEW_HEADER := RFBM AND XINUSE;
IF MXCSR ≠ 1F80H AND RFBM[1]
    THEN NEW_HEADER[1] = 1;
FI;
XSTATE_BV field in XSAVE header := NEW_HEADER;
XCOMP_BV field in XSAVE header := COMPMASK;

Flags Affected

None.

Intel C/C++ Compiler Intrinsic Equivalent

XSAVES void _xsaves( void * , unsigned __int64);

XSAVES64 void _xsaves64( void * , unsigned __int64);

Protected Mode Exceptions

#GP(0)

If CPL > 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[bit 26] = 0 or CPUID.(EAX=0DH,ECX=1):EAX.XSS[bit 3] = 0.

If CR4.OSXSAVE[bit 18] = 0.

If the LOCK prefix is used.

Real-Address Mode Exceptions

#GP

If 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[bit 26] = 0 or CPUID.(EAX=0DH,ECX=1):EAX.XSS[bit 3] = 0.

If CR4.OSXSAVE[bit 18] = 0.

If the LOCK prefix is used.

Virtual-8086 Mode Exceptions

Same exceptions as in protected mode.

Compatibility Mode Exceptions

Same exceptions as in protected mode.

64-Bit Mode Exceptions

#GP(0)

If CPL > 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[bit 26] = 0 or CPUID.(EAX=0DH,ECX=1):EAX.XSS[bit 3] = 0.

If CR4.OSXSAVE[bit 18] = 0.

If the LOCK prefix is used.