+Field name: payload_offset
+Type: read
+Offset/size: 0x248/4
+Protocol: 2.08+
+
+ If non-zero then this field contains the offset from the end of the
+ real-mode code to the payload.
+
+ The payload may be compressed. The format of both the compressed and
+ uncompressed data should be determined using the standard magic
+ numbers. Currently only gzip compressed ELF is used.
+
+Field name: payload_length
+Type: read
+Offset/size: 0x24c/4
+Protocol: 2.08+
+
+ The length of the payload.
+
+**** THE IMAGE CHECKSUM
+
+From boot protocol version 2.08 onwards the CRC-32 is calculated over
+the entire file using the characteristic polynomial 0x04C11DB7 and an
+initial remainder of 0xffffffff. The checksum is appended to the
+file; therefore the CRC of the file up to the limit specified in the
+syssize field of the header is always 0.