Re: [PATCH] Drop ELF notes from non-EFI binary too

[Jan Beulich <jbeulich@suse.com>]

On 26.02.2023 00:56, Marek Marczykowski-Górecki wrote:
> The ELF is repacked from from 64bit to 32bit. With CET-related notes,
> which use 64bit fields, this results in 32bit binary with corrupted
> notes. Drop them all (except build-id and PVH note retained
> explicitly).
> 
> Suggested-by: Jan Beulich <jbeulich@suse.com>

Perhaps a misunderstanding: Yes, I did suggest this as a possibility,
but I didn't really mean we actually do so. At the very least not
without further clarifying what the cons of doing so are. The notes,
after all, are actually valid in xen-syms; they become bogus in the
course of mkelf32's processing.

> --- a/xen/arch/x86/xen.lds.S
> +++ b/xen/arch/x86/xen.lds.S
> @@ -192,13 +192,6 @@ SECTIONS
>  #endif
>  #endif
>  
> -#ifndef EFI
> -  /* Retain these just for the purpose of possible analysis tools. */
> -  DECL_SECTION(.note) {
> -       *(.note.*)
> -  } PHDR(note) PHDR(text)
> -#endif
> -
>    _erodata = .;
>  
>    . = ALIGN(SECTION_ALIGN);

Is this sufficient? .note.* isn't part of DISCARD_SECTIONS except for
xen.efi. I would expect it needs to move there from DISCARD_EFI_SECTIONS.
Otherwise, aiui, the linker's orphan section placement will kick in. Yet
at that point you'd also affect Arm and RISC-V (which, interestingly,
don't place .note.* anywhere at all right now, afaics).

Jan