Jeremy Fitzhardinge wrote:
> H. Peter Anvin wrote:
>> +Field name: boot_flag
>> +Type: read
>> +Offset/size: 0x1fe/2
>> +Protocol: ALL
>> +
>> + Contains 0xAA55. This is the closest thing old Linux kernels have
>> + to a magic number.
>>
>
> Endianess? I guess a blanket statement saying that all constants are
> stored little-endian enough (which is obvious, but its always good to be
> explicit).
Next time I make a revision I'll put that in; since we're talking about
x86 here it's, as you say, obvious that it's littleendian. As such, I
think it can wait.
>> +
>> +Field name: header
>> +Type: read
>> +Offset/size: 0x202/4
>> +Protocol: 2.00+
>> +
>> + Contains the magic number "HdrS" (0x53726448).
>>
>
> This is a bit confusing from an endian perspective. Does the "HdrS"
> notation mean that it is a byte array containing 'H', 'd', 'r', 'S', as
> the string syntax suggests? Or is that the ascii interpretation of each
> byte of a 4-byte value read as a little-endian encoding from that location?
Given that we have already established littleendian byte order, it's the
same thing.
>> +
>> +Field name: version
>> +Type: read
>> +Offset/size: 0x206/2
>> +Protocol: 2.00+
>> +
>> + Contains the boot protocol version, e.g. 0x0204 for version 2.04.
>>
>
> So the version is in BCD?
Valid objection. It probably should be considered as (major, minor)
bytes, but we haven't had any releases where it hasn't also been valid
BCD. I would prefer separate bytes myself, so 2.10 = 0x20a instead of
2.10 = 0x210.
>> +Field name: readmode_swtch
>> +Type: modify (optional)
>> +Offset/size: 0x208/4
>> +Protocol: 2.00+
>> +
>> + Boot loader hook (see separate chapter.)
>>
>
> Chapter? Is there a more specific reference you could make?
Fair enough...
>> +Field name: kernel_version
>> +Type: read
>> +Offset/size: 0x20e/2
>> +Protocol: 2.00+
>> +
>> + If set to a nonzero value, contains a pointer to a null-terminated
>>
>
> "nil-terminated"? "\0-terminated"?
Uh? That seems more than a little silly. Yes, I guess formally
speaking we're talking about "NUL-terminated", but the term
"null-terminated" has over 800,000 hits on Google -- 10 times as many as
"NUL-terminated" -- and is hardly an ambiguous term ("NUL-terminated" is
ugly, and "zero-terminated" is ambiguous.)
>> + human-readable kernel version number string, less 0x200. This can
>> + be used to display the kernel version to the user. This value
>> + should be less than (0x200*setup_sects). For example, if this value
>> + is set to 0x1c00, the kernel version number string can be found at
>> + offset 0x1e00 in the kernel file. This is a valid value if and only
>> + if the "setup_sects" field contains the value 14 or higher.
>>
> How about something like:
>
> This example is only valid if "setup_sects" is greater than
>
> ((0x1e00 - 0x200) / 0x200) = 14.
Probably makes sense.
-hpa
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