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Embedded Systems

The Pentium F00F Bug

By Robert R. Collins, May 01, 1998

When x86 processors encounter an invalid instruction, the processor is supposed to generate an invalid opcode exception. If this mechanism fails, however, the program can bring the system down -- and that's what happens with the F00F bug.


The Pentium F00F Bug

The Pentium F00F Bug

By Robert R. Collins

Dr. Dobb's Journal May 1998 

Sequence  Address   Data      Mnemonic                        Timestamp
-------------------------------------------------------------------------
  426333  00060FF8  00080496    ( LOCKED MEM READ )               60 ns
          00060FFC  00008E00    ( LOCKED MEM READ )
  426334  0001E8B8  BFF0FFFF    ( LOCKED MEM READ )              170 ns
          0001E8BC  00009B01    ( LOCKED MEM READ )
  426335  0001EEA0  00010002    ( LOCKED MEM WRITE               120 ns
  426336  0001EE9C  00000008    ( MEM WRITE )                     60 ns
  426337  0001EE98  000003EE    ( MEM WRITE )                     50 ns

Example 4: F00F bug with cache disabled.

Copyright © 1998, Dr. Dobb's Journal



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