Specification Update

Errata
40 Specification Update
AT66. Debug Register May Contain Incorrect Information on a MOVSS or
POPSS Instruction Followed by SYSRET
Problem: In IA-32e mode, if a MOVSS or POPSS instruction with a debug breakpoint is
followed by the SYSRET instruction, incorrect information may exist in the
Debug Status Register (DR6).
Implication: When debugging or when developing debuggers, this behavior should be
noted. This erratum will not occur under normal usage of the MOVSS or
POPSS instructions (i.e., following them with a MOV ESP instruction).
Workaround: Do not attempt to put a breakpoint on MOVSS and POPSS instructions that
are followed by a SYSRET.
Status: For the steppings affected, see the Summary Tables of Changes.
AT67. VM Bit is Cleared on Second Fault Handled by Task Switch from
Virtual-8086 (VM86)
Problem: Following a task switch to any fault handler that was initiated while the
processor was in VM86 mode, if there is an additional fault while servicing the
original task switch then the VM bit will be incorrectly cleared in EFLAGS, data
segments will not be pushed and the processor will not return to the correct
mode upon completion of the second fault handler via IRET.
Implication: When the OS recovers from the second fault handler, the processor will no
longer be in VM86 mode. Normally, operating systems should prevent
interrupt task switches from faulting, thus the scenario should not occur
under normal circumstances.
Workaround: None identified.
Status: For the steppings affected, see the Summary Tables of Changes.
AT68. The BS Flag in DR6 May be Set for Non-Single-Step #DB Exception
Problem: DR6 BS (Single Step, bit 14) flag may be incorrectly set when the TF (Trap
Flag, bit 8) of the EFLAGS Register is set, and a #DB (Debug Exception)
occurs due to one of the following:
•DR7 GD (General Detect, bit 13) being bit set;
•INT1 instruction;
•Code breakpoint
Implication: The BS flag may be incorrectly set for non-single-step #DB exception.
Workaround: None identified.
Status: For the steppings affected, see the Summary Tables of Changes.