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XGETBV

Retrieves the contents of the extended control register specified by the immediate value (ECX) and stores the result in the destination register pair (EDX:EAX).

The table after the description covers what the source and destinations can be.

DO NOT support LOCK

The instruction is only available in 64-bit mode and compatibility mode. It is NOT supported in 32-bit mode. If executed in 32-bit mode, it will trigger an invalid opcode exception.

The immediate value provided in ECX MUST be a valid index for an extended control register (e.g., XCR0). If the requested register is not supported by the processor or is disabled in the BIOS/firmware, the instruction SHALL trigger a general-protection exception (#GP(0)). Use the CPUID instruction to verify support for the specific extended state before execution to avoid #GP.