linux-kernel - [PATCH] kbuild: Fix building with LLVM on NixOS

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Date: Thu,  8 Feb 2024 01:20:58 +0000
From: Yuxuan Shui <yshuiv7@...il.com>
To: llvm@...ts.linux.dev
Cc: masahiroy@...nel.org,
	nathan@...nel.org,
	nicolas@...sle.eu,
	linux-kbuild@...r.kernel.org,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	x86@...nel.org,
	hpa@...or.com,
	linux-kernel@...r.kernel.org,
	Yuxuan Shui <yshuiv7@...il.com>
Subject: [PATCH] kbuild: Fix building with LLVM on NixOS

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.

Signed-off-by: Yuxuan Shui <yshuiv7@...il.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 =
 AFLAGS_KERNEL	=
 LDFLAGS_vmlinux =
 
+LDFLAGS_MODULE += --no-dynamic-linker
+LDFLAGS_vmlinux += --no-dynamic-linker
+
 # Use USERINCLUDE when you must reference the UAPI directories only.
 USERINCLUDE    := \
 		-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: $(obj)/compressed/vmlinux FORCE
 AFLAGS_header.o += -I$(objtree)/$(obj)
 $(obj)/header.o: $(obj)/zoffset.h
 
-LDFLAGS_setup.elf	:= -m elf_i386 -z noexecstack -T
+LDFLAGS_setup.elf	:= --no-dynamic-linker -m elf_i386 -z noexecstack -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/Makefile
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 += realmode.lds
 $(obj)/realmode.lds: $(obj)/pasyms.h
 
-LDFLAGS_realmode.elf := -m elf_i386 --emit-relocs -T
+LDFLAGS_realmode.elf := --no-dynamic-linker -m elf_i386 --emit-relocs -T
 CPPFLAGS_realmode.lds += -P -C -I$(objtree)/$(obj)
 
 targets += realmode.elf
-- 
2.43.0