Ping: [PATCH] x86/EFI: sanitize DLL characteristics in binary

[Jan Beulich <jbeulich@xxxxxxxx>]

On 02.04.2025 10:51, Jan Beulich wrote:
> In GNU ld --disable-reloc-section implies --disable-dynamicbase (and
> also --disable-high-entropy-va, just fyi). Therefore to yield
> functionally identical binaries independent of whether mkreloc needs to
> come into play, add --dynamicbase as well.
> 
> GNU ld further defaults to --high-entropy-va (along with --dynamicbase
> and --nxcompat) unless "Cygwin-like". This seems wrong to me; that
> default should be dependent upon "MinGW-like" instead; for the purpose
> of building EFI binaries with a PE32+-capable ELF linker neither
> "Cygwin-like" nor "MinGW-like" ought to be true. We certainly don't mean
> to have this bit set in the DLL characteristics, so suppress its
> setting.
> 
> Sadly while --high-entropy-va is supported by GNU ld 2.25,
> --disable-high-entropy-va was introduced only in 2.36. Luckily the
> defaulting to --high-entropy-va was also only introduced in 2.36. Plus
> --disable-reloc-section was introduced precisely there, too. Hence
> leverage the probing we do as to base relocation generation, to also
> determine whether to pass --disable-high-entropy-va.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Despite the file being modified suggesting this needs an x86 maintainer
ack, I think it's rather one of the two of you who should ack (or
otherwise comment on) this.

Jan

> ---
> I remain uncertain about the applicability of DLL characteristics to
> non-DLLs, i.e. images without IMAGE_FILE_DLL set; current MS doc says
> nothing either way. Yet producing consistent binaries still seems
> desirable, even if the field wasn't to be used by loaders.
> 
> --- a/xen/arch/x86/arch.mk
> +++ b/xen/arch/x86/arch.mk
> @@ -113,6 +113,7 @@ efi-nr-fixups := $(shell LC_ALL=C $(OBJD
>  
>  ifeq ($(efi-nr-fixups),2)
>  MKRELOC := :
> +EFI_LDFLAGS += --disable-high-entropy-va
>  else
>  MKRELOC := arch/x86/efi/mkreloc
>  # If the linker produced fixups but not precisely two of them, we need to
> @@ -123,6 +124,8 @@ EFI_LDFLAGS += --disable-reloc-section
>  endif
>  endif
>  
> +EFI_LDFLAGS += --dynamicbase
> +
>  endif # $(XEN_BUILD_PE)
>  
>  export XEN_BUILD_EFI XEN_BUILD_PE