Never use an undefined value ECx before usng the RDMsR or wRMsR instrucion If ECX fore the read or write machine-specific register instruction. the value returned. EDx EAX. is the machine check exception address. EDX:EAX is where all data reside when the value is the machine check written or read from the model-specific registers.) ECX exception type, if ECXE0EH. the test register 12(TR12) is accessed. Note that these are inter- nal registers designed for in-house testing. The contents of these registers are proprietary to Intel and should not be used during normal programming