Specifications

Product Errata 69
Revision Guide for AMD Athlon™ 64 and AMD Opteron™ Processors
25759 Rev. 3.79 July 2009
109 Certain Reverse REP MOVS May Produce Unpredictable
Behavior
Description
In certain situations a REP MOVS instruction may lead to incorrect results. An incorrect address size,
data size or source operand segment may be used or a succeeding instruction may be skipped. This
may occur under the following conditions:
• EFLAGS.DF=1 (the string is being moved in the reverse direction).
• The number of items being moved (RCX) is between 1 and 20.
• The REP MOVS instruction is preceded by some microcoded instruction that has not completely
retired by the time the REP MOVS begins execution. The set of such instructions includes
BOUND, CLI, LDS, LES, LFS, LGS, LSS, IDIV, and most microcoded x87 instructions.
Potential Effect on System
Incorrect results may be produced or the system may hang.
Suggested Workaround
Contact your AMD representative for information on a BIOS update.
Fix Planned
Yes