linux-kernel - Re: [RFC PATCH] x86/doc/boot_protocol: Correct the description of "reloc"

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Message-ID: <3073CD01-65C5-4BEC-B2FC-F76DD0E70D73@zytor.com>
Date:   Thu, 26 Sep 2019 00:58:19 -0700
From:   hpa@...or.com
To:     Cao jin <caoj.fnst@...fujitsu.com>, Ingo Molnar <mingo@...nel.org>
CC:     x86@...nel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, corbet@....net
Subject: Re: [RFC PATCH] x86/doc/boot_protocol: Correct the description of "reloc"

On September 26, 2019 12:55:51 AM PDT, Cao jin <caoj.fnst@...fujitsu.com> wrote:
>On 9/26/19 2:01 PM, Ingo Molnar wrote:
>> * Cao jin <caoj.fnst@...fujitsu.com> 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@...fujitsu.com>
>>> ---
>>> 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.
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.