Re: [PATCH v2 2/4] x86/efi: discard multiboot support for PE binary

[Teddy Astie <teddy.astie@xxxxxxxxxx>]

Le 11/06/2026 à 17:33, Frediano Ziglio a écrit :
> From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>
> The multiboot headers (.text.header section) are not consumed in the PE
> binary, hence discard them in the linker script when doing a PE build.
>
> The multiboot and PVH entry points are not used in the PE binary, hence
> discard them in the linker script when doing a PE build.
nit: it looks like both paragraph state the same thing

> That removes some relocations that otherwise appear due to the usage of the
> start and __efi64_mb2_start symbols in the multiboot2 header.
>
> Section discarding is not done updating DISCARD_SECTIONS definition as the
> change is specific for x86.
>
> No functional change intended.
Given that this now prevents booting using multiboot2 when using the PE 
build, this is a functional change, even though it's strongly 
discouraged (not officially supported).
I would add a changelog entry to actually state this change (eventually 
reminding that this was not actually supported anyway).
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>
> --
> Changes since v1:
> - improve commit message;
> - change section orders to avoid changing code order in final executable;
> - merge 2 commits;
> - removed deprecated documentation section.
> ---
>   docs/hypervisor-guide/x86/how-xen-boots.rst | 6 ------
>   xen/arch/x86/boot/head.S                    | 3 ++-
>   xen/arch/x86/xen.lds.S                      | 5 +++++
>   3 files changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/docs/hypervisor-guide/x86/how-xen-boots.rst 
> b/docs/hypervisor-guide/x86/how-xen-boots.rst
> index 8b3229005c..b6d852050a 100644
> --- a/docs/hypervisor-guide/x86/how-xen-boots.rst
> +++ b/docs/hypervisor-guide/x86/how-xen-boots.rst
> @@ -82,12 +82,6 @@ When a PEI-capable toolchain is found, the objects are 
> linked together and a
>   PE32+ binary is created.  It can be run directly from the EFI shell, and has
>   ``efi_start`` as its entry symbol.
>   
> -.. note::
> -
> -   xen.efi does contain all MB1/MB2/PVH tags included in the rest of the
> -   build.  However, entry via anything other than the EFI64 protocol is
> -   unsupported, and won't work.
> -
>   
>   Boot
>   ----
> diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
> index 77bb7a9e21..90faf411b9 100644
> --- a/xen/arch/x86/boot/head.S
> +++ b/xen/arch/x86/boot/head.S
> @@ -152,7 +152,7 @@ vga_text_buffer:
>   efi_platform:
>           .byte   0
>   
> -        .section .init.text, "ax", @progbits
> +        .section .init.multiboot, "ax", @progbits
>   
>   early_error: /* Here to improve the disassembly. */
>   
> @@ -710,6 +710,7 @@ trampoline_setup:
>           /* Jump into the relocated trampoline. */
>           lret
>   
> +        .section .init.text, "ax", @progbits
>   ENTRY(trampoline_start)
>   #include "trampoline.S"
>   ENTRY(trampoline_end)
> diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
> index f758940674..749d9719cc 100644
> --- a/xen/arch/x86/xen.lds.S
> +++ b/xen/arch/x86/xen.lds.S
> @@ -57,6 +57,10 @@ SECTIONS
>     __image_base__ = .;
>   #else
>     . = __image_base__;
> +  /DISCARD/ : {
> +    *(.text.header)
> +    *(.init.multiboot)
> +  }
>   #endif
>   
>   #if 0
> @@ -195,6 +199,7 @@ SECTIONS
>     DECL_SECTION(.init.text) {
>   #endif
>          _sinittext = .;
> +       *(.init.multiboot)
>          *(.init.text)
>          *(.text.startup)
>          _einittext = .;
Teddy

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