Re: xen.efi has MEM_DISCARDABLE flag in Characteristics field of .reloc section

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.07.2025 10:28, Yann Sionneau wrote:
> On 7/17/25 10:22, Jan Beulich wrote:
>> On 17.07.2025 09:32, Yann Sionneau wrote:
>>> Hello Demi Marie, Jan, Nick, all,
>>>
>>> Thank you Demi Marie for bringing this topic on the mailing list.
>>>
>>> I discussed it a bit with Jan on Matrix but the situation is not pretty,
>>> there is no clean solution that stands out easily.
>>>
>>> As Jan said, it seems .reloc is meant to be discardable, so we can't
>>> blame binutils LD for putting it:
>>>
>>> https://github.com/bminor/binutils-gdb/commit/25c80428af3311e761c87d8f706596b9701602ec#diff-078cf751467928c038996b40073a682425712b9b01182424e68cf18fb08a75b5R953-R977
>>>
>>> And we can't obviously blame the loaders for honoring this flag.
>>>
>>> Most reasonable solution indeed would be to ask binutils to add a link
>>> flag to say "please do not put the DISCARDABLE flag on the .reloc section"
>>>
>>> I'm adding Nick Clifton from binutils in CC so that he can comment on
>>> this possible outcome or any other possible solution.
>>>
>>> In the mean time, while waiting for a solution to emerge (and be merged,
>>> and released) what do we do?
>>>
>>> Do we put some hack in Xen build Makefiles so that xen.efi is
>>> post-processed to strip this bit?
>>>
>>> This could be the temporary solution.
>>
>> As indicated - I don't think this is just a temporary solution. Beyond Xen,
>> I simply don't see value in adding a linker flag (which then, sooner or
>> later, llvm would also need to support just for Xen). The question rather
>> is how to make the Xen side hack as little hacky as possible, without
>> relying on the fragile behavior of objcopy.
> 
> Ok I didn't understand your previous answer, it's more clear now, thank you.
> Would you consider using a tool like this less fragile than objcopy: 
> https://github.com/fallen/keeprelocs ?

Well, something like that. Generalized enough to at least be halfway easy to
later also use for further purposes, and if at all possible using the header
we already have for PE (efi/pe.h).

Jan