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From: Masahiro Yamada <masahiroy@kernel.org>
Date: Tue, 13 Feb 2024 06:29:55 +0900
Message-ID: <CAK7LNAT0KT7sbZJZNXtq5waM-UjUm4zHyf9xHZc3uHLvZ_eAfA@mail.gmail.com>
Subject: Re: [PATCH] kbuild: Fix building with LLVM on NixOS
To: Yuxuan Shui <yshuiv7@gmail.com>
Cc: llvm@lists.linux.dev, nathan@kernel.org, nicolas@fjasle.eu, 
	linux-kbuild@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, 
	bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, 
	linux-kernel@vger.kernel.org, Fangrui Song <maskray@google.com>
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+Cc: Fangrui Song <maskray@google.com>


On Thu, Feb 8, 2024 at 10:22=E2=80=AFAM Yuxuan Shui <yshuiv7@gmail.com> wro=
te:
>
> NixOS is designed to have immutable packages, and explicit dependencies.
> It allows multiple different versions of the same shared library to
> co-exist in its file system.
>
> Each application built with Nix, the NixOS package manager, will have
> paths to its dependency shared libraries hardcoded into its executable,
> this includes the dynamic linker. To achieve this, Nix adds a
> --dynamic-linker linker flag when building any application.
>
> This isn't a problem if the kernel is built with ld.bfd, because ld.bfd
> ignores the --dynamic-linker flag when the resulting binary doesn't have
> a DT_NEEDED entry. However, ld.lld respects --dynamic-linker
> unconditionally, which breaks linking in several cases.
>
> This commit adds an explicit --no-dynamic-linker flag which overrides
> the flag added by Nix.


I expect some Acks from LLVM folks (especially, from Frangrui)
if this is the right thing to do.


> Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
> ---
>  Makefile                      | 3 +++
>  arch/x86/boot/Makefile        | 2 +-
>  arch/x86/realmode/rm/Makefile | 2 +-
>  3 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index a171eafce2a3b..10ed19caecb1b 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -531,6 +531,9 @@ RUSTFLAGS_KERNEL =3D
>  AFLAGS_KERNEL  =3D
>  LDFLAGS_vmlinux =3D
>
> +LDFLAGS_MODULE +=3D --no-dynamic-linker
> +LDFLAGS_vmlinux +=3D --no-dynamic-linker
> +
>  # Use USERINCLUDE when you must reference the UAPI directories only.
>  USERINCLUDE    :=3D \
>                 -I$(srctree)/arch/$(SRCARCH)/include/uapi \
> diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
> index 3cece19b74732..390a4604166eb 100644
> --- a/arch/x86/boot/Makefile
> +++ b/arch/x86/boot/Makefile
> @@ -102,7 +102,7 @@ $(obj)/zoffset.h: $(obj)/compressed/vmlinux FORCE
>  AFLAGS_header.o +=3D -I$(objtree)/$(obj)
>  $(obj)/header.o: $(obj)/zoffset.h
>
> -LDFLAGS_setup.elf      :=3D -m elf_i386 -z noexecstack -T
> +LDFLAGS_setup.elf      :=3D --no-dynamic-linker -m elf_i386 -z noexecsta=
ck -T
>  $(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) FORCE
>         $(call if_changed,ld)
>
> diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefil=
e
> index f614009d3e4e2..4b42006d9ce02 100644
> --- a/arch/x86/realmode/rm/Makefile
> +++ b/arch/x86/realmode/rm/Makefile
> @@ -50,7 +50,7 @@ $(obj)/pasyms.h: $(REALMODE_OBJS) FORCE
>  targets +=3D realmode.lds
>  $(obj)/realmode.lds: $(obj)/pasyms.h
>
> -LDFLAGS_realmode.elf :=3D -m elf_i386 --emit-relocs -T
> +LDFLAGS_realmode.elf :=3D --no-dynamic-linker -m elf_i386 --emit-relocs =
-T
>  CPPFLAGS_realmode.lds +=3D -P -C -I$(objtree)/$(obj)
>
>  targets +=3D realmode.elf
> --
> 2.43.0
>


--=20
Best Regards
Masahiro Yamada