Re: [PATCH v3 3/4] x86/efi: avoid a relocation in efi_arch_post_exit_boot()

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Tue, Jun 16, 2026 at 11:13:35AM +0100, Frediano Ziglio wrote:
> From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> 
> Instead of using the absolute __start_xen address, calculate it as an
> offset from the current instruction pointer.  The relocation would be
> problematic if the generated PE binary had .init.text as a standalone
> section with just read and execute permissions."
> 
> Removing this relocation is necessary to make it safe to split .init.
> 
> No functional change intended.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>

Acked-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> --
> Changes since v1:
> - Improve commit message.
> ---
>  xen/arch/x86/efi/efi-boot.h | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/x86/efi/efi-boot.h b/xen/arch/x86/efi/efi-boot.h
> index d738b839ee..b983f054b5 100644
> --- a/xen/arch/x86/efi/efi-boot.h
> +++ b/xen/arch/x86/efi/efi-boot.h
> @@ -270,7 +270,9 @@ static void __init noreturn efi_arch_post_exit_boot(void)
>  
>                     /* Jump to higher mappings. */
>                     "mov    stack_start(%%rip), %%rsp\n\t"
> -                   "movabs $__start_xen, %[rip]\n\t"
> +                   "lea    __start_xen(%%rip), %[rip]\n\t"
> +                   "add    %[offset], %[rip]\n\t"
> +
>                     "push   %[cs]\n\t"
>                     "push   %[rip]\n\t"
>                     "lretq"
> @@ -278,7 +280,8 @@ static void __init noreturn efi_arch_post_exit_boot(void)
>                       [cr4] "+&r" (cr4)
>                     : [cr3] "r" (idle_pg_table),
>                       [cs] "i" (__HYPERVISOR_CS),
> -                     [ds] "r" (__HYPERVISOR_DS)
> +                     [ds] "r" (__HYPERVISOR_DS),
> +                     [offset] "r" (__XEN_VIRT_START - xen_phys_start)
>                     : "memory" );
>      unreachable();
>  }
> -- 
> 2.43.0
> 

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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