Intel 253668-032US 9.11.2 Optional Extended Signature Table, 9.11.3 Processor Identification

Vol. 3 9-41
PROCESSOR MANAGEMENT AND INITIALIZATION
9.11.2 Optional Extended Signature Table
The extended signature table is a structure that may be appended to the end of the
encrypted data when the encrypted data only supports a single processor signature
(optional case). The extended signature table will always be present when the
encrypted data supports multiple processor steppings and/or models (required
case).
The extended signature table consists of a 20-byte extended signature header struc-
ture, which contains the extended signature count, the extended processor signature
table checksum, and 12 reserved bytes (Tabl e 9- 8). Following the extended signa-
ture header structure, the extended signature table contains 0-to-n extended
processor signature structures.
Each processor signature structure consist of the processor signature, processor
flags, and a checksum (Tabl e 9-9).
The extended signature count in the extended signature header structure indicates
the number of processor signature structures that exist in the extended signature
table.
The extended processor signature table checksum is a checksum of all DWORDs that
comprise the extended signature table. That includes the extended signature count,
extended processor signature table checksum, 12 reserved bytes and the n
processor signature structures. A valid extended signature table exists when the
result of a DWORD checksum is 00000000H.
9.11.3 Processor Identification
Each microcode update is designed to for a specific processor or set of processors. To
determine the correct microcode update to load, software must ensure that one of
the processor signatures embedded in the microcode update matches the 32-bit
processor signature returned by the CPUID instruction when executed by the target
processor with EAX = 1. Attempting to load a microcode update that does not match
Table 9-8. Extended Processor Signature Table Header Structure
Extended Signature Count ‘n’ Data Size + 48
Extended Processor Signature Table Checksum Data Size + 52
Reserved (12 Bytes) Data Size + 56
Table 9-9. Processor Signature Structure
Processor Signature[n] Data Size + 68 + (n * 12)
Processor Flags[n] Data Size + 72 + (n * 12)
Checksum[n] Data Size + 76 + (n * 12)