xrstors
Restore Supervisor States
Restores supervisor state components from memory (Compact).
Pseudocode Operation
IF (CR4.OSXSAVE == 0 || CPL != 0) THEN #UD;
IF (m is not 64-byte aligned) THEN #GP(0);
state_bitmap ← EDX:EAX;
restore_xsave_state_from_memory(m, state_bitmap, supervisor=true);Example
Encoding
Operands
-
dest
Memory operand
Related
More in XSAVES
Reference
Instruction Forms
| Opcode | Instruction | Op/En | 64/32-bit Mode | CPUID | Description |
|---|---|---|---|---|---|
| NP 0F C7 /3 | XRSTORS mem | M | V/V | XSS | Restore state components specified by EDX:EAX from mem. |
| NP REX.W + 0F C7 /3 | XRSTORS64 mem | M | V/N.E. | XSS | Restore state components specified by EDX:EAX from mem. |
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 the logical-OR of XCR0 with the IA32_XSS MSR. XRSTORS 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 13.12, “Operation of XRSTORS,” 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: • Execution of XRSTORS is similar to that of the compacted form of XRSTOR; XRSTORS cannot restore from an XSAVE area in which the extended region is in the standard format (see Section 13.4.3, “Extended Region of an XSAVE Area” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1). • XRSTORS differs from XRSTOR in that it can restore state components corresponding to bits set in the IA32_XSS MSR.
• If RFBM[i] = 0, XRSTORS does not update state component i. • If RFBM[i] = 1 and bit i is clear in the XSTATE_BV field in the XSAVE header, XRSTORS initializes state component i. • If RFBM[i] = 1 and XSTATE_BV[i] = 1, XRSTORS loads state component i from the XSAVE area.
• If XRSTORS attempts to load MXCSR with an illegal value, a general-protection exception (#GP) occurs. • XRSTORS loads the internal value XRSTOR_INFO, which may be used to optimize a subsequent execution of XSAVEOPT or XSAVES. • Immediately following an execution of XRSTORS, the processor tracks as in-use (not in initial configuration) any state component i for which RFBM[i] = 1 and XSTATE_BV[i] = 1; it tracks as modified any state component i for which RFBM[i] = 0. Use of a source operand not aligned to 64-byte boundary (for 64-bit and 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 bitmaps XINUSE and XMODIFIED and of the quantity XRSTOR_INFO.
Operation
RFBM := (XCR0 OR IA32_XSS) AND EDX:EAX; /* bitwise logical OR and AND */ COMPMASK := XCOMP_BV field from XSAVE header; RSTORMASK := XSTATE_BV field from XSAVE header; FORMAT = COMPMASK AND 7FFFFFFF_FFFFFFFFH; RESTORE_FEATURES = FORMAT AND RFBM; TO_BE_RESTORED := RESTORE_FEATURES AND RSTORMASK; FORCE_INIT := RFBM AND NOT FORMAT; TO_BE_INITIALIZED = (RFBM AND NOT RSTORMASK) OR FORCE_INIT; IF TO_BE_RESTORED[0] = 1 THEN XINUSE[0] := 1; load x87 state from legacy region of XSAVE area; ELSIF TO_BE_INITIALIZED[0] = 1 THEN XINUSE[0] := 0; initialize x87 state; FI; IF TO_BE_RESTORED[1] = 1 THEN XINUSE[1] := 1; load SSE state from legacy region of XSAVE area; // this step loads the XMM registers and MXCSR ELSIF TO_BE_INITIALIZED[1] = 1 THEN set all XMM registers to 0; XINUSE[1] := 0; MXCSR := 1F80H; FI; NEXT_FEATURE_OFFSET = 576; // Legacy area and XSAVE header consume 576 bytes FOR i := 2 TO 62 IF FORMAT[i] = 1 THEN IF TO_BE_RESTORED[i] = 1 THEN XINUSE[i] := 1; load XSAVE state component i at offset NEXT_FEATURE_OFFSET from base of XSAVE area; FI; NEXT_FEATURE_OFFSET = NEXT_FEATURE_OFFSET + n (n enumerated by CPUID.0DH.i:EAX); FI; IF TO_BE_INITIALIZED[i] = 1 THEN XINUSE[i] := 0; initialize XSAVE state component i; FI; ENDFOR; XMODIFIED := NOT RFBM; IF in VMX non-root operation THEN VMXNR := 1; ELSE VMXNR := 0; FI; LAXA := linear address of XSAVE area; XRSTOR_INFO := CPL,VMXNR,LAXA,COMPMASK;
Intel C/C++ Compiler Intrinsic Equivalent
XRSTORS void _xrstors( void * , unsigned __int64); XRSTORS64 void _xrstors64( void * , unsigned __int64);