Specification Update

Errata

AT34. FXSAVE/FXRSTOR Instructions which Store to the End of the

Segment and Cause a Wrap to a Misaligned Base Address (Alignment

<= 0x10h) May Cause FPU Instruction or Operand Pointer Corruption

Problem:

If a FXSAVE/FXRSTOR instruction stores to the end of the segment causing a wrap to

a misaligned base address (alignment <= 0x10h), and one of the following conditions

is satisfied:

1. 32-bit addressing, obtained by using address-size override, when in 64-bit mode.

2. 16-bit addressing in legacy or compatibility mode.

Then, depending on the wrap-around point, one of the below saved values may be

corrupted:

• FPU Instruction Pointer Offset

• FPU Instruction Pointer Selector

• FPU Operand Pointer Selector

• FPU Operand Pointer Offset

Implication: This erratum could cause FPU Instruction or Operand pointer corruption and may lead

to unexpected operations in the floating point exception handler.

Workaround: Avoid segment base mis-alignment and address wrap-around at the segment

boundary.

Status: For the steppings affected, see the Summary Tables of Changes.

AT35. PREFETCHh Instruction Execution under Some Conditions May Lead

to Processor Livelock

Problem:

PREFETCHh instruction execution after a split load and dependent upon ongoing store

operations may lead to processor livelock.

Implication: Due to this erratum, the processor may livelock.

Workaround: It is possible for the BIOS to contain a workaround for this erratum.

Status: For the steppings affected, see the Summary Tables of Changes.

AT36. PREFETCHh Instructions May Not be Executed when Alignment Check

(AC) is Enabled

Problem:

PREFETCHT0, PREFETCHT1, PREFETCHT2 and PREFETCHNTA instructions may not be

executed when Alignment Check is enabled.

Implication: PREFETCHh instructions may not perform the data prefetch if Alignment Check is

enabled.

Workaround: Clear the AC flag (bit 18) in the EFLAGS register and/or the AM bit (bit 18) of Control

Status: For the steppings affected, see the Summary Tables of Changes.