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)	NA	NA	NA

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 logicalAND 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 Software 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 highlevel outline:

Execution of XSAVES is similar to that of XSAVEC. XSAVES differs from XSAVEC in that it can save state components corresponding to bits set in the IA32_XSS MSR and that it may use the modified optimization.
XSAVES saves state component i 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 XSAVEManaged State” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1.) Even if both bits are 1, XSAVES may optimize and not save state component i if (1) state component i has not been modified since the last execution of XRSTOR or XRSTORS; and (2) this execution of XSAVES correspond to that last execution of XRSTOR or XRSTORS as determined by XRSTOR_INFO (see the Operation section below).
XSAVES 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).
XSAVES writes the logical AND of RFBM and XINUSE to the XSTATE_BV field of the XSAVE header.²(See Section 13.4.2, “XSAVE Header” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1.) XSAVES sets bit 63 of the XCOMP_BV field and sets bits 62:0 of that field to RFBM[62:0]. XSAVES does not write to any parts of the XSAVE header other than the XSTATE_BV and XCOMP_BV fields.
XSAVES 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).

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.

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.

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]
    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;
XSTATE_BV field in XSAVE header ← TO_BE_SAVED;
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.
#GP	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.