Datasheet

Errata
64 Specification Update
AH58. MOV To/From Debug Registers Causes Debug Exception
Problem: When in V86 mode, if a MOV instruction is executed to/from a debug register, a
general-protection exception (#GP) should be generated. However, in the case when
the general detect enable flag (GD) bit is set, the observed behavior is that a debug
exception (#DB) is generated instead.
Implication: With debug-register protection enabled (that is, the GD bit set), when attempting to
execute a MOV on debug registers in V86 mode, a debug exception will be generated
instead of the expected general-protection fault.
Workaround: In general, operating systems do not set the GD bit when they are in V86 mode. The
GD bit is generally set and used by debuggers. The debug exception handler should
check that the exception did not occur in V86 mode before continuing. If the exception
did occur in V86 mode, the exception may be directed to the general-protection
exception handler.
Status: For the steppings affected, see the Summary Tables of Changes.