To avoid confusion in interpreting frames, the communication buffer should always begin with EFI_SMM_COMMUNICATE_HEADER
Designates an array of bytes that is MessageLength in size.
Allows for disambiguation of the message format.
Describes the size of Data (in bytes) and does not include the size of the header.
See Implementation
To avoid confusion in interpreting frames, the communication buffer should always begin with EFI_SMM_COMMUNICATE_HEADER