Volume 3: General-Purpose and System Instructions - Stanford ...

24594 Rev. 3.10 February 2005 AMD64 TechnologyWRMSRWrite to Model-Specific RegisterWrites data to 64-bit model-specific registers (MSRs). These registers are widely usedin performance-monitoring and debugging applications, as well as testability andprogram execution tracing.This instruction writes the contents of the EDX:EAX register pair into a 64-bit modelspecificregister specified in the ECX register. The 32 bits in the EDX register aremapped into the high-order bits of the model-specific register and the 32 bits in EAXform the low-order 32 bits.This instruction must be executed at a privilege level of 0 or a general protection fault#GP(0) will be raised. This exception is also generated if an attempt is made to specifya reserved or unimplemented model-specific register in ECX.WRMSR is a serializing instruction.The CPUID instruction can provide model information useful in determining theexistence of a particular MSR.See Volume 2, System Programming, for more information about model-specificregisters, machine check architecture, performance monitoring and debug registers.Mnemonic Opcode DescriptionWRMSR 0F 30 Write EDX:EAX to the MSR specified by ECX.Related InstructionsRDMSRrFLAGS AffectedNoneWRMSR 373