XRSTOR (Restore Processor Extended States)

Opcodes

Opcode Instruction Op/En 64-Bit Mode Compat/Leg Mode Description
0F AE /5 XRSTOR mem M Valid Valid Restore state components specified by EDX:EAX from mem.
REX.W+ 0F AE /5 XRSTOR64 mem M Valid N.E. Restore state components specified by EDX:EAX from mem.

Instruction Operand Encoding

Op/En Operand 1 Operand 2 Operand 3 Operand 4
M ModRM:r/m (r) NA NA NA

Description

Performs a full or partial restore of processor state components from the XSAVE area located at the memory address specified by the source operand. The implicit EDX:EAX register pair specifies a 64-bit instruction mask. The specific state components restored 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 Soft-ware Developer’s Manual, Volume 1.

Section 13.7, “Operation of XRSTOR,” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1 provides a detailed description of the operation of the XRSTOR instruction. The following items provide a high-level outline:

for which RFBM[i] = 0.

i

Use of a source operand not aligned to 64-byte boundary (for 64-bit and 32-bit modes) results in a general-protec-tion (#GP) exception. In 64-bit mode, the upper 32 bits of RDX and RAX are ignored.

Operation

RFBM ← XCR0 AND EDX:EAX;
                                    /* bitwise logical AND */
COMPMASK ← XCOMP_BV field from XSAVE header;
RSTORMASK ← XSTATE_BV field from XSAVE header;
IF in VMX non-root operation
    THEN VMXNR ← 1;
1.
    There is an exception if RFBM[1] = 0 and RFBM[2] = 1. In this case, the standard form of XRSTOR will load MXCSR from memory, even though MXCSR is part of state component 1 — SSE. The compacted form of XRSTOR does not make this exception.
    ELSE VMXNR ← 0;
FI;
LAXA ← linear address of XSAVE area;
IF COMPMASK[63] = 0
    THEN
         /* Standard form of XRSTOR */
         If RFBM[0] = 1
              THEN
                    IF RSTORMASK[0] = 1
                         THEN load x87 state from legacy region of XSAVE area;
                         ELSE initialize x87 state;
                    FI;
         FI;
         If RFBM[1] = 1
              THEN
                    IF RSTORMASK[1] = 1
                         THEN load XMM registers from legacy region of XSAVE area;
                         ELSE set all XMM registers to 0;
                    FI;
         FI;
         If RFBM[2] = 1
              THEN
                    IF RSTORMASK[2] = 1
                         THEN load AVX state from extended region (standard format) of XSAVE area;
                         ELSE initialize AVX state;
                    FI;
         FI;
         If RFBM[1] = 1 or RFBM[2] = 1
              THEN load MXCSR from legacy region of XSAVE area;
         FI;
FI;
    ELSE
         /* Compacted form of XRSTOR */
         IF CPUID.(EAX=0DH,ECX=1):EAX.XSAVEC[bit 1] = 0
              THEN
                         /* compacted form not supported */
                    #GP(0);
         FI;
         If RFBM[0] = 1
              THEN
                    IF RSTORMASK[0] = 1
                         THEN load x87 state from legacy region of XSAVE area;
                         ELSE initialize x87 state;
                    FI;
         FI;
         If RFBM[1] = 1
              THEN
                    IF RSTORMASK[1] = 1
                         THEN load SSE state from legacy region of XSAVE area;
                         ELSE initialize SSE state;
                    FI;
         FI;
         If RFBM[2] = 1
              THEN
                    IF RSTORMASK[2] = 1
                         THEN load AVX state from extended region (compacted format) of XSAVE area;
                         ELSE initialize AVX state;
                    FI;
         FI;
FI;
XRSTOR_INFO ← (cid:162)CPL,VMXNR,LAXA,COMPMASK(cid:178);

Flags Affected

None.

Intel C/C++ Compiler Intrinsic Equivalent

XRSTOR:

void _xrstor( void * , unsigned __int64);

XRSTOR:

void _xrstor64( 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. If bit 63 of the XCOMP_BV field of the XSAVE header is 1 and CPUID.(EAX=0DH,ECX=1):EAX.XSAVEC[bit 1] = 0. If the standard form is executed and a bit in XCR0 is 0 and the corresponding bit in the XSTATE_BV field of the XSAVE header is 1. If the standard form is executed and bytes 23:8 of the XSAVE header are not all zero. If the compacted form is executed and a bit in XCR0 is 0 and the corresponding bit in the XCOMP_BV field of the XSAVE header is 1. If the compacted form is executed and a bit in the XCOMP_BV field in the XSAVE header is 0 and the corresponding bit in the XSTATE_BV field is 1. If the compacted form is executed and bytes 63:16 of the XSAVE header are not all zero. If attempting to write any reserved bits of the MXCSR register with 1.
#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 align-ment check exception might be signaled for a 2-byte misalignment, whereas a general protec-tion 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. If bit 63 of the XCOMP_BV field of the XSAVE header is 1 and CPUID.(EAX=0DH,ECX=1):EAX.XSAVEC[bit 1] = 0. If the standard form is executed and a bit in XCR0 is 0 and the corresponding bit in the XSTATE_BV field of the XSAVE header is 1. If the standard form is executed and bytes 23:8 of the XSAVE header are not all zero. If the compacted form is executed and a bit in XCR0 is 0 and the corresponding bit in the XCOMP_BV field of the XSAVE header is 1. If the compacted form is executed and a bit in the XCOMP_BV field in the XSAVE header is 0 and the corresponding bit in the XSTATE_BV field is 1. If the compacted form is executed and bytes 63:16 of the XSAVE header are not all zero. If attempting to write any reserved bits of the MXCSR register with 1.
#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 a memory address is in a non-canonical form. If a memory operand is not aligned on a 64-byte boundary, regardless of segment. If bit 63 of the XCOMP_BV field of the XSAVE header is 1 and CPUID.(EAX=0DH,ECX=1):EAX.XSAVEC[bit 1] = 0. If the standard form is executed and a bit in XCR0 is 0 and the corresponding bit in the XSTATE_BV field of the XSAVE header is 1. If the standard form is executed and bytes 23:8 of the XSAVE header are not all zero. If the compacted form is executed and a bit in XCR0 is 0 and the corresponding bit in the XCOMP_BV field of the XSAVE header is 1. If the compacted form is executed and a bit in the XCOMP_BV field in the XSAVE header is 0 and the corresponding bit in the XSTATE_BV field is 1. If the compacted form is executed and bytes 63:16 of the XSAVE header are not all zero. If attempting to write any reserved bits of the MXCSR register with 1.
#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 align-ment check exception might be signaled for a 2-byte misalignment, whereas a general protec-tion exception might be signaled for all other misalignments (4-, 8-, or 16-byte misalignments).