XSAVE—Save Processor Extended States

Opcode	Instruction	Op/En	64-Bit Mode	Compat/Leg Mode	Description
0F AE /4	XSAVE mem	M	Valid	Valid	Save state components specified by EDX:EAX to mem.
REX.W+ 0F AE /4	XSAVE64 mem	M	Valid	N.E.	Save state components specified by EDX:EAX to mem.

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), 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 Software Developer’s Manual, Volume 1.

Section 13.6, “Operation of XSAVE,” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1 provides a detailed description of the operation of the XSAVE instruction. The following items provide a high-level outline:

XSAVE saves state component i if and only if RFBM[i] = 1.¹
XSAVE 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”).
XSAVE reads the XSTATE_BV field of the XSAVE header (see Section 13.4.2, “XSAVE Header”) and writes a modified value back to memory as follows. If RFBM[i] = 1, XSAVE writes XSTATE_BV[i] with the value of XINUSE[i]. (XINUSE is a bitmap by which the processor tracks the status of various state components. See Section 13.5.4, “Processor Tracking of XSAVE-Managed State.”) If RFBM[i] = 0, XSAVE writes XSTATE_BV[i]with the value that it read from memory (it does not modify the bit). XSAVE does not write to any part of the XSAVE header other than the XSTATE_BV field.
XSAVE always uses the standard format of the extended region of the XSAVE area (see Section 13.4.3, “Extended Region of an XSAVE Area”).

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.

Operation

RFBM ← XCR0 AND EDX:EAX;
OLD_BV ← XSTATE_BV field from XSAVE header;
IF RFBM[0] = 1
  THEN store x87 state into legacy region of XSAVE area;
FI;
IF RFBM[1] = 1
  THEN store XMM registers into legacy region of XSAVE area;
FI;
1.
  ory if either RFBM[1] or RFBM[2] is 1.
IF RFBM[2] = 1
  THEN store AVX state into extended region of XSAVE area;
FI;
IF RFBM[1] = 1 or RFBM[2] = 1
  THEN store MXCSR and MXCSR_MASK into legacy region of XSAVE area;
FI;
XSTATE_BV field in XSAVE header ← (OLD_BV AND ~RFBM) OR (XINUSE AND RFBM);

Flags Affected

None.

Intel C/C++ Compiler Intrinsic Equivalent

XSAVE:	void _xsave( void * , unsigned __int64);
XSAVE:	void _xsave64( 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[bit 26] = 0. If CR4.OSXSAVE[bit 18] = 0. If any of the LOCK, 66H, F3H or F2H prefixes is used.
#AC	If this exception is disabled a general protection exception (#GP) is signaled if the memory operand is not aligned on a 16-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 alignment check exception might be signaled for a 2-byte misalignment, whereas a general protection exception might be signaled for all other misalignments (4-, 8-, or 16-byte misalignments).

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. If CR4.OSXSAVE[bit 18] = 0. If any of the LOCK, 66H, F3H or F2H prefixes 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 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. If CR4.OSXSAVE[bit 18] = 0. If any of the LOCK, 66H, F3H or F2H prefixes is used.
#AC	If this exception is disabled a general protection exception (#GP) is signaled if the memory operand is not aligned on a 16-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 alignment check exception might be signaled for a 2-byte misalignment, whereas a general protection exception might be signaled for all other misalignments (4-, 8-, or 16-byte misalignments).