Re: [PATCH v7 2/4] x86/efi: discard multiboot and PVH support for PE binary

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Mon, Jul 06, 2026 at 11:45:55AM +0100, Frediano Ziglio wrote:
> From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> 
> Multiboot and PVH booting are not supported for PE, hence discards them
> in the linker script when doing a PE build.
> 
> 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.
> 
> 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;
> - change section orders to avoid changing code order in final executable;
> - merge 2 commits;
> - removed deprecated documentation section.
> 
> Changes since v2:
> - Update commit message, join 2 sentences together.
> 
> Changes since v3:
> - Added Acked-by.
> 
> Changes since v4:
> - more clear subject;
> - removed more code/data from EFI output;
> - removed Acked-by.
> 
> Changes since v5:
> - simplify section exclusion using more wildcard;
> - exclude more multiboot functions.
> ---
>  docs/hypervisor-guide/x86/how-xen-boots.rst | 6 ------
>  xen/arch/x86/boot/head.S                    | 8 ++++----
>  xen/arch/x86/xen.lds.S                      | 7 +++++++
>  xen/tools/combine_two_binaries.py           | 2 +-
>  4 files changed, 12 insertions(+), 11 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 68b963ce6f..981f262b5e 100644
> --- a/xen/arch/x86/boot/head.S
> +++ b/xen/arch/x86/boot/head.S
> @@ -126,7 +126,7 @@ multiboot2_header:
>          .size multiboot2_header, . - multiboot2_header
>          .type multiboot2_header, @object
>  
> -        .section .init.rodata, "a", @progbits
> +        .section .init.rodata.multiboot, "a", @progbits
>  
>  .Lbad_cpu_msg: .asciz "ERR: Not a 64-bit CPU!"
>  .Lbad_ldr_msg: .asciz "ERR: Not a Multiboot bootloader!"
> @@ -137,8 +137,7 @@ multiboot2_header:
>  .Lno_nx_msg:   .asciz "ERR: Not an NX-capable CPU!"
>  #endif
>  
> -        .section .init.data, "aw", @progbits
> -        .subsection 1 /* Put data here after the page tables (in x86_64.S). 
> */
> +        .section .init.data.multiboot, "aw", @progbits
>          .align 4
>  
>          .word   0
> @@ -154,7 +153,7 @@ vga_text_buffer:
>  efi_platform:
>          .byte   0
>  
> -        .section .init.text, "ax", @progbits
> +        .section .init.multiboot, "ax", @progbits
>  
>  early_error: /* Here to improve the disassembly. */
>  
> @@ -712,6 +711,7 @@ 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 8e63cf5bc2..4ed1d2bec1 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 = .;
> @@ -220,6 +225,7 @@ SECTIONS
>         *(.init.rodata.cf_clobber)
>         __initdata_cf_clobber_end = .;
>  
> +       *(.init.rodata.multiboot)
>         *(.init.rodata)
>         *(.init.rodata.*)
>  
> @@ -234,6 +240,7 @@ SECTIONS
>         *(.initcall1.init)
>         __initcall_end = .;
>  
> +       *(.init.data.multiboot)
>         *(.init.data)
>         *(.init.data.rel)
>         *(.init.data.rel.*)
> diff --git a/xen/tools/combine_two_binaries.py 
> b/xen/tools/combine_two_binaries.py
> index 581e57cbc0..5f0433dcad 100755
> --- a/xen/tools/combine_two_binaries.py
> +++ b/xen/tools/combine_two_binaries.py
> @@ -33,7 +33,7 @@ parser.add_argument('--map', dest='mapfile',
>  parser.add_argument('--exports', dest='exports',
>                      help='Symbols to export')
>  parser.add_argument('--section-header', dest='section_header',
> -                    default='.section .init.text, "ax", @progbits',
> +                    default='.section .init.multiboot, "ax", @progbits',
>                      help='Section header declaration')
>  parser.add_argument('-v', '--verbose',
>                      action='store_true')
> -- 
> 2.43.0
> 

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

Attachment: signature.asc
Description: PGP signature