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Multiboot2 Header Tags: Unclear definition of type
From: |
Hans Ulrich Niedermann |
Subject: |
Multiboot2 Header Tags: Unclear definition of type |
Date: |
Sat, 23 May 2020 12:17:24 +0200 |
Quoting the Multiboot2 specification:
> 3.1.3 General tag structure
> ---------------------------
>
> Tags constitutes a buffer of structures following each other padded
> when necessary in order for each tag to start at 8-bytes aligned
> address. Tags are terminated by a tag of type '0' and size '8'.
> Every structure has following format:
>
> +-------------------+
> u16 | type |
> u16 | flags |
> u32 | size |
> +-------------------+
>
> 'type' is divided into 2 parts. Lower contains an identifier of
> contents of the rest of the tag. 'size' contains the size of tag
> including header fields. If bit '0' of 'flags' (also known as
> 'optional') is set, the bootloader may ignore this tag if it lacks
> relevant support. Tags are terminated by a tag of type '0' and size
> '8'.
How is 'type' divided into two parts? The rest of the MB2 specification
only defines some constants in the range of 0 to about 0x10 as values
for 'type', but there is no mention of upper or lower parts at all.
(And if there were, I would expect u8 fields for type and whatever the
upper is supposed to be.)
I suspect the phrasing with parts and lower is a remnant of a previous
iteration, and 'type' is just meant to be a 16 bit integer constant.
Does anyone have any insights into this?
Uli
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