XSAVEC—Save Processor Extended States with Compaction

Opcode	Instruction	Op/En	64-Bit Mode	Compat/Leg Mode	Description
0F C7 /4	XSAVEC mem	M	Valid	Valid	Save state components specified by EDX:EAX to mem with compaction.
REX.W+ 0F C7 /4	XSAVEC64 mem	M	Valid	N.E.	Save state components specified by EDX:EAX to mem with compaction.

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 13.9, “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 highlevel 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 13.5.4, “Processor Tracking of XSAVE-Managed State.”)
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”).
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.”) XSAVEC sets bit 63 of the XCOMP_BV field and sets bits 62:0 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”).

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;
COMPMASK ← RFBM OR 80000000_00000000H;
IF RFBM[0] = 1 and XINUSE[0] = 1
1.
  have its initial value of 1F80H. In this case, XSAVEC saves SSE state as long as RFBM[1] = 1.
2.
3.
  have its initial value of 1F80H. In this case, XSAVEC sets XSTATE_BV[1] to 1 as long as RFBM[1] = 1.
  THEN store x87 state into legacy region of XSAVE area;
FI;
IF RFBM[1] = 1 and (XINUSE[1] = 1 or MXCSR ≠ 1F80H)
  THEN store SSE state into legacy region of XSAVE area;
FI;
IF RFBM[2] = 1 AND XINUSE[2] = 1
  THEN store AVX state into extended region of XSAVE area;
FI;
XSTATE_BV field in XSAVE header ← XINUSE AND RFBM;
XCOMP_BV field in XSAVE header ← COMPMASK;

Flags Affected

None.

Intel C/C++ Compiler Intrinsic Equivalent

XSAVEC:	void _xsavec( void * , unsigned __int64);
XSAVEC64:	void _xsavec64( 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 or CPUID.(EAX=0DH,ECX=1):EAX.XSAVEC[bit 1] = 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 or CPUID.(EAX=0DH,ECX=1):EAX.XSAVEC[bit 1] = 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 or CPUID.(EAX=0DH,ECX=1):EAX.XSAVEC[bit 1] = 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).