On September 26, 2019 1:20:02 AM PDT, Cao jin <caoj.fnst@xxxxxxxxxxxxxx> wrote:
>On 9/26/19 3:58 PM, hpa@xxxxxxxxx wrote:
>> On September 26, 2019 12:55:51 AM PDT, Cao jin
><caoj.fnst@xxxxxxxxxxxxxx> wrote:
>>> On 9/26/19 2:01 PM, Ingo Molnar wrote:
>>>> * Cao jin <caoj.fnst@xxxxxxxxxxxxxx> wrote:
>>>>
>>>>> The fields marked with (reloc) actually are not dedicated for
>>> writing,
>>>>> but communicating info for relocatable kernel with boot loaders.
>For
>>>>> example:
>>>>>
>>>>> ============ ============
>>>>> Field name: pref_address
>>>>> Type: read (reloc)
>>>>> Offset/size: 0x258/8
>>>>> Protocol: 2.10+
>>>>> ============ ============
>>>>>
>>>>> ============ ========================
>>>>> Field name: code32_start
>>>>> Type: modify (optional, reloc)
>>>>> Offset/size: 0x214/4
>>>>> Protocol: 2.00+
>>>>> ============ ========================
>>>>>
>>>>> Signed-off-by: Cao jin <caoj.fnst@xxxxxxxxxxxxxx>
>>>>> ---
>>>>> Unless I have incorrect non-native understanding for "fill in", I
>>> think
>>>>> this is inaccurate.
>>>>>
>>>>> Documentation/x86/boot.rst | 2 +-
>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/Documentation/x86/boot.rst
>b/Documentation/x86/boot.rst
>>>>> index 08a2f100c0e6..a611bf04492d 100644
>>>>> --- a/Documentation/x86/boot.rst
>>>>> +++ b/Documentation/x86/boot.rst
>>>>> @@ -243,7 +243,7 @@ bootloader ("modify").
>>>>>
>>>>> All general purpose boot loaders should write the fields marked
>>>>> (obligatory). Boot loaders who want to load the kernel at a
>>>>> -nonstandard address should fill in the fields marked (reloc);
>other
>>>>> +nonstandard address should consult with the fields marked
>(reloc);
>>> other
>>>>> boot loaders can ignore those fields.
>>>>>
>>>>> The byte order of all fields is littleendian (this is x86, after
>>> all.)
>>>>
>>>> Well, this documentation is written from the point of view of a
>>>> *bootloader*, not the kernel. So the 'fill in' says that the
>>> bootloader
>>>> should write those fields - which is correct, right?
>>>>
>>>
>>> Take pref_address or relocatable_kernel for example, they have type:
>>> read (reloc), does boot loader need to write them? I don't see grub
>>> does
>>> this at least.
>>
>> Read means the boot later reads them.
>>
>
>Sorry I don't know what is going wrong in my mind. For me, if
>pref_address has "read (reloc)", base on the current document, it means
>boot loader will read it and also write it, which is conflicting. And
>the purpose of pref_address should just inform boot loader that kernel
>whats itself to be loaded at certain address, it don't want to be
>written.
read (reloc) means it is information for the boot loader to read, but that it can ignore it completely if it does not want to relocate the kernel.
--
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