Re: [RFC 20/22] x86/relocs: Add option to generate 64-bit relocations

[H. Peter Anvin]

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From: hpa@xxxxxxxxx
Message-ID: <0EF6FAAA-A99C-4F0D-9E4A-AD25E93957FB@xxxxxxxxx>

On July 19, 2017 4:25:56 PM PDT, Thomas Garnier <thgarnie@xxxxxxxxxx> wrote:
>On Wed, Jul 19, 2017 at 4:08 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
>> On 07/19/17 15:47, Thomas Garnier wrote:
>>> On Wed, Jul 19, 2017 at 3:33 PM, H. Peter Anvin <hpa@xxxxxxxxx>
>wrote:
>>>> On 07/18/17 15:33, Thomas Garnier wrote:
>>>>> The x86 relocation tool generates a list of 32-bit signed
>integers. There
>>>>> was no need to use 64-bit integers because all addresses where
>above the 2G
>>>>> top of the memory.
>>>>>
>>>>> This change add a large-reloc option to generate 64-bit unsigned
>integers.
>>>>> It can be used when the kernel plan to go below the top 2G and
>32-bit
>>>>> integers are not enough.
>>>>
>>>> Why on Earth?  This would only be necessary if the *kernel itself*
>was
>>>> more than 2G, which isn't going to happen for the forseeable
>future.
>>>
>>> Because the relocation integer is an absolute address, not an offset
>>> in the binary. Next iteration, I can try using a 32-bit offset for
>>> everyone.
>>
>> It is an absolute address *as the kernel was originally linked*, for
>> obvious reasons.
>
>Sure when the kernel was just above 0xffffffff80000000, it doesn't
>work when it goes down to 0xffffffff00000000. That's why using an
>offset might make more sense in general.
>
>>
>>         -hpa
>>

What is the motivation for changing the pre linked address at all?
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