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Re: [PATCH v2 4/5] x86: Compensate relocation in case of EFI


  • To: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Tue, 20 Aug 2024 15:04:15 +0200
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  • Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Tue, 20 Aug 2024 13:04:24 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 14.08.2024 10:34, Frediano Ziglio wrote:
> If code is loaded by EFI the loader will relocate the image
> under 4GB. This causes offsets in x86 code generated by
> sym_offs(SYMBOL) to be relocated too (basically they won't be
> offsets from image base).

In turn meaning that ...

> --- a/xen/arch/x86/boot/head.S
> +++ b/xen/arch/x86/boot/head.S
> @@ -380,7 +380,8 @@ x86_32_switch:
>          lgdt    gdt_boot_descr(%rip)
>  
>          /* Store Xen image load base address in place accessible for 32-bit 
> code. */
> -        lea     __image_base__(%rip),%esi
> +        lea     __image_base__(%rip), %esi
> +        sub     $sym_offs(__image_base__), %esi

... the comment needs updating too then, as %esi won't necessarily hold
the load base address any longer (if I understand correctly what's going
on here).

Jan



 


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