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Re: [PATCH for-4.22?] x86/EFI: arrange for non-discardable .reloc in xen.efi
- To: Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 17 Jun 2026 12:20:56 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Marek Marczykowski <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, Daniel Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- Delivery-date: Wed, 17 Jun 2026 11:21:07 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 17/06/2026 11:37 am, Jan Beulich wrote:
> On 17.06.2026 12:29, Roger Pau Monné wrote:
>> On Tue, Jun 16, 2026 at 06:17:54PM +0200, Jan Beulich wrote:
>>> Loaders respecting IMAGE_SCN_MEM_DISCARDABLE would not load such sections,
>>> yet we need to access it ourselves when switching out of "physical mode".
>>> Leverage behavior new to GNU ld 2.46: Any contribution to .reloc which
>>> doesn't have the discardable flag set (which cannot even be expressed in
>>> ELF) will yield the output section also non-discardable.
>>>
>>> Since for intermediate binaries we don't care about section attributes,
>>> link in the new object only on the final linking pass.
>> I'm not sure I follow. Xen already does generate a custom .reloc
>> section without the IMAGE_SCN_MEM_DISCARDABLE attribute when using
>> the mkreloc utility, and hence the .reloc section should never be
>> marked as discardable?
> mkreloc is used only when we recognize the linker to be incapable of
> producing (correct) base relocations.
I wasn't even aware of that behaviour.
So we've got even more completely undocumented and obscure toolchain
restrictions and behaviours.
What else? It needs at least enumerating somewhere so people stand a
chance of being able figure out which toolstack they need in order to
get a functioning xen.efi.
I'm going to insist that a doc happens, and that this patch patches it
adding in the Binutils 2.46 requirement.
But I'll write the doc if you can summarise the other checks I'm not
aware of.
~Andrew
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