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



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
>



-- 
Thomas.

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