linux-kernel - [PATCH 2/2] kbuild: userprogs: use lld to link through clang

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Message-Id: <20250213-kbuild-userprog-fixes-v1-2-f255fb477d98@linutronix.de>
Date: Thu, 13 Feb 2025 15:55:18 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Masahiro Yamada <masahiroy@...nel.org>, 
 Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>, 
 Nick Desaulniers <ndesaulniers@...gle.com>, 
 Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
 Sam Ravnborg <sam@...nborg.org>
Cc: linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
 llvm@...ts.linux.dev, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>, 
 stable@...r.kernel.org
Subject: [PATCH 2/2] kbuild: userprogs: use lld to link through clang

The userprog infrastructure links objects files through $(CC).
Either explicitly by manually calling $(CC) on multiple object files or
implicitly by directly compiling a source file to an executable.
The documentation at Documentation/kbuild/llvm.rst indicates that ld.lld would
be used for linking if LLVM=1 is specified.
However clang instead will use either a globally installed cross linker from
$PATH called ${target}-ld or fall back to the system linker, which probably
does not support crosslinking.
For the normal kernel build this is not an issue because the linker is always
executed directly, without the compiler being involved.

Fix this by passing -fuse-lld and let clang find its matching lld.

Fixes: 7f3a59db274c ("kbuild: add infrastructure to build userspace programs")
Cc: stable@...r.kernel.org
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
---
 Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Makefile b/Makefile
index bb5737ce7f9e79f4023c9c1f578a49a951d1e239..b4c208ae4041c1f4e32c2a158322422ce7353d06 100644
--- a/Makefile
+++ b/Makefile
@@ -510,6 +510,7 @@ OBJCOPY		= $(LLVM_PREFIX)llvm-objcopy$(LLVM_SUFFIX)
 OBJDUMP		= $(LLVM_PREFIX)llvm-objdump$(LLVM_SUFFIX)
 READELF		= $(LLVM_PREFIX)llvm-readelf$(LLVM_SUFFIX)
 STRIP		= $(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX)
+KBUILD_USERLDFLAGS += -fuse-ld=lld
 else
 CC		= $(CROSS_COMPILE)gcc
 LD		= $(CROSS_COMPILE)ld

-- 
2.48.1