xsaves

Save Supervisor States

XSAVES m

Saves supervisor state components to memory (Compact).

Details

Saves processor extended state components (both user and supervisor states) to memory in compact form, controlled by the XCR0 and IA32_XSS MSRs and a mask in EDX:EAX. This instruction is a supervisor-mode only operation requiring CPL=0 and XSAVES feature support. No EFLAGS are modified; memory layout is compact and may trigger #GP if state is invalid.

Pseudocode Operation

IF CPL != 0 THEN #GP(0) FI;
IF CPUID.XSAVES = 0 THEN #UD FI;
mask ← (EDX << 32) | EAX;
save_regions ← GET_SAVE_REGIONS_MASKED(XCR0, IA32_XSS, mask);
COMPACT_SAVE_STATE(dest, save_regions);

Example

XSAVES [rbp-8]

Encoding

Binary Layout

ModRM

Format Legacy

Opcode NP 0F C7 /5

Extension XSAVES

Operands

dest
Memory operand

Reference (Intel® SDM)

Instruction Forms

Opcode	Instruction	Op/En	64/32-bit Mode	CPUID	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.

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 the 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 the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1. Section 13.11, “Operation of XSAVES,” of the 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: • 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 the 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 the 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 the 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 the 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. 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. XSAVES—Save Processor Extended States Supervisor Vol. 2D 6-66 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.0DH.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;

Intel C/C++ Compiler Intrinsic Equivalent

XSAVES void _xsaves( void * , unsigned __int64);
XSAVES64 void _xsaves64( void * , unsigned __int64);

Flags Affected

None. XSAVES—Save Processor Extended States Supervisor Vol. 2D 6-67

Exceptions

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[26] = 0 or CPUID.0DH.01H:EAX.XSAVES[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[26] = 0 or CPUID.0DH.01H:EAX.XSAVES[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[26] = 0 or CPUID.0DH.01H:EAX.XSAVES[3] = 0. If CR4.OSXSAVE[bit 18] = 0. If the LOCK prefix is used. XSAVES—Save Processor Extended States Supervisor Vol. 2D 6-68