[PATCH 2/7] efi: Allow runtime relocate to be disabled

[Jiaxun Yang]

在2024年5月21日五月 下午2:58，Ilias Apalodimas写道：
> Hi Jiaxun,
>
> On Fri, 17 May 2024 at 19:33, Jiaxun Yang <jiaxun.yang at flygoat.com> wrote:
>>
>> Allow runtime relocate to be disabled because on MIPS we
>> never do that. It's guaranteed that OS won't call
>> set_virtual_address_map and convert_pointer as well.
>
> Who guarantees that? Is it only for Linux?
Hi Ilias,

It's guarantee by all the existing implementations, ventoy,
linux etc.

It's nearly impossible to run MIPS OS in virtual (or paged)
segment. All MIPS OS and bootloaders are running in KSEG/XKPHYS
segment, which directly mapping lower bits of virtual address
into physical address. So I suppose set_virtual_address_map
is unnecessary on MIPS because the mapping for U-Boot is
always here and can't be disabled in hardware.

>
>>
>> On MIPS KSEG0 is always mapped to memory and there is no
>> way to disable it for kernel mode. Both EFI runtime and
>> kernel lays in this segment, so relocation is totally
>> unnecessary.
>>
>> Also U-Boot does not use traditional .dyn.rel to perform
>> relocation on MIPS, that makes implementation of runtime
>> relocation pretty hard.
>
> It already works on other architectures so I suppose it's only a
> matter of adding it?

MIPS is odd here, we are not compiling U-Boot with -fPIC, instead
we use our own tools to generate relocation records and embedded
them into U-Boot.

Adding relocation support requires modifications to that tool
"tools/mips-relocs.c" and also processing our own record format
here.

Given that set_virtual_address_map have no practice use on MIPS,
I think the best way to handle it is to leave set_virtual_address_map
alone.

Thanks
>
> Thanks
> /Ilias
>>
[...]
-- 
- Jiaxun