Specification Update

Errata
Specification Update 33
AM43 IA32_FMASK is Reset during an INIT
Problem: IA32_FMASK MSR (0xC0000084) is reset during INIT.
Implication: If an INIT takes place after IA32_FMASK is programmed, the processor will overwrite
the value back to the default value.
Workaround: Operating system software should initialize IA32_FMASK after INIT.
Status: For the steppings affected, see the Summary Tables of Changes.
AM44 An Enabled Debug Breakpoint or Single Step Trap May Be Taken after MOV
SS/POP SS Instruction if it is Followed by an Instruction That Signals a
Floating Point Exception
Problem: A MOV SS/POP SS instruction should inhibit all interrupts including debug breakpoints
until after execution of the following instruction. This is intended to allow the
sequential execution of MOV SS/POP SS and MOV [r/e]SP, [r/e]BP instructions without
having an invalid stack during interrupt handling. However, an enabled debug
breakpoint or single step trap may be taken after MOV SS/POP SS if this instruction is
followed by an instruction that signals a floating point exception rather than a MOV
[r/e]SP, [r/e]BP instruction. This results in a debug exception being signaled on an
unexpected instruction boundary since the MOV SS/POP SS and the following
instruction should be executed atomically.
Implication: This can result in incorrect signaling of a debug exception and possibly a mismatched
Stack Segment and Stack Pointer. If MOV SS/POP SS is not followed by a MOV
[r/e]SP, [r/e]BP, there may be a mismatched Stack Segment and Stack Pointer on
any exception. Intel has not observed this erratum with any commercially available
software, or system.
Workaround: As recommended in the IA32 Intel® Architecture Software Developer’s Manual, the
use of MOV SS/POP SS in conjunction with MOV [r/e]SP, [r/e]BP will avoid the failure
since the MOV [r/e]SP, [r/e]BP will not generate a floating point exception. Developers
of debug tools should be aware of the potential incorrect debug event signaling
created by this erratum.
Status: For the steppings affected, see the Summary Tables of Changes.
AM45 Last Branch Records (LBR) Updates May be Incorrect after a Task Switch
Problem: A Task-State Segment (TSS) task switch may incorrectly set the LBR_FROM value to
the LBR_TO value.
Implication: The LBR_FROM will have the incorrect address of the Branch Instruction.
Workaround: None Identified.
Status: For the steppings affected, see the Summary Tables of Changes.