Specifications

26 Product Errata
25759 Rev. 3.79 July 2009
Revision Guide for AMD Athlon™ 64 and AMD Opteron™ Processors
61 Real Mode RDPMC with Illegal ECX May Cause Unpredictable
Operation
Description
Illegal values of ECX (that is, ECX > 3) for the RDPMC (Read Performance Monitor Counter)
instruction correctly cause the processor to take a general protection exception.
However, if the RDPMC instruction is executed in real mode with a specific illegal value of ECX = 9,
then the processor may incorrectly enter the GP fault handler as if it were in 32-bit mode.
Potential Effect on System
Incorrect instruction decode leading to unpredictable system failure.
Suggested Workaround
When in real mode, restrict use of the RDPMC instruction to the legal counter values (0–3). This
circumstance is not expected to occur in normal operation and has only been detected in a simulation
environment.
Fix Planned
Yes