回答我的最后一个问题。我发现,如果 proto_tree_add_item 的最后一个参数非零,则它将将该字段解释为 little-endian。
见 proto.h
/*
* We might also, in the future, want to allow a field specifier to
* indicate the encoding of the field, or at least its default
* encoding, as most fields in most protocols always use the
* same encoding (although that's not true of all fields, so we
* still need to be able to specify that at run time).
*
* So, for now, we define ENC_BIG_ENDIAN and ENC_LITTLE_ENDIAN as
* bit flags, to be combined, in the future, with other information
* to specify the encoding in the last argument to
* proto_tree_add_item(), and possibly to specify in a field
* definition (e.g., ORed in with the type value).
*
* Currently, proto_tree_add_item() treats its last argument as a
* Boolean - if it's zero, the field is big-endian, and if it's non-zero,
* the field is little-endian - and other code in epan/proto.c does
* the same. We therefore define ENC_BIG_ENDIAN as 0x00000000 and
* ENC_LITTLE_ENDIAN as 0x80000000 - we're using the high-order bit
* so that we could put a field type and/or a value such as a character
* encoding in the lower bits.
*/