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.
Explicitly pass --ld-path to clang so $(LD) is respected. As clang 13.0.1 is required to build the kernel, this option is available.
Fixes: 7f3a59db274c ("kbuild: add infrastructure to build userspace programs") Cc: stable@vger.kernel.org # needs wrapping in $(cc-option) for < 6.9 Signed-off-by: Thomas Weißschuh thomas.weissschuh@linutronix.de --- Reproducer, using nolibc to avoid libc requirements for cross building:
$ tail -2 init/Makefile userprogs-always-y += test-llvm test-llvm-userccflags += -nostdlib -nolibc -static -isystem usr/ -include $(srctree)/tools/include/nolibc/nolibc.h
$ cat init/test-llvm.c int main(void) { return 0; }
$ make ARCH=arm64 LLVM=1 allnoconfig headers_install init/
Validate that init/test-llvm builds and has the correct binary format. --- Changes in v2: - Use --ld-path instead of -fuse-ld - Drop already applied patch - Link to v1: https://lore.kernel.org/r/20250213-kbuild-userprog-fixes-v1-0-f255fb477d98@l... --- Makefile | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/Makefile b/Makefile index 96407c1d6be167b04ed5883e455686918c7a75ee..b41c164533d781d010ff8b2522e523164dc375d0 100644 --- a/Makefile +++ b/Makefile @@ -1123,6 +1123,11 @@ endif KBUILD_USERCFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS)) KBUILD_USERLDFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
+# userspace programs are linked via the compiler, use the correct linker +ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_LD_IS_LLD),yy) +KBUILD_USERLDFLAGS += --ld-path=$(LD) +endif + # make the checker run with the right architecture CHECKFLAGS += --arch=$(ARCH)
--- base-commit: 0ad2507d5d93f39619fc42372c347d6006b64319 change-id: 20250213-kbuild-userprog-fixes-4f07b62ae818
Best regards,
On Mon, Feb 17, 2025 at 08:27:54AM +0100, Thomas Weißschuh wrote:
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.
Explicitly pass --ld-path to clang so $(LD) is respected. As clang 13.0.1 is required to build the kernel, this option is available.
Fixes: 7f3a59db274c ("kbuild: add infrastructure to build userspace programs") Cc: stable@vger.kernel.org # needs wrapping in $(cc-option) for < 6.9 Signed-off-by: Thomas Weißschuh thomas.weissschuh@linutronix.de
Reviewed-by: Nathan Chancellor nathan@kernel.org
Reproducer, using nolibc to avoid libc requirements for cross building:
$ tail -2 init/Makefile userprogs-always-y += test-llvm test-llvm-userccflags += -nostdlib -nolibc -static -isystem usr/ -include $(srctree)/tools/include/nolibc/nolibc.h
$ cat init/test-llvm.c int main(void) { return 0; }
$ make ARCH=arm64 LLVM=1 allnoconfig headers_install init/
Validate that init/test-llvm builds and has the correct binary format.
Changes in v2:
- Use --ld-path instead of -fuse-ld
- Drop already applied patch
- Link to v1: https://lore.kernel.org/r/20250213-kbuild-userprog-fixes-v1-0-f255fb477d98@l...
Makefile | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/Makefile b/Makefile index 96407c1d6be167b04ed5883e455686918c7a75ee..b41c164533d781d010ff8b2522e523164dc375d0 100644 --- a/Makefile +++ b/Makefile @@ -1123,6 +1123,11 @@ endif KBUILD_USERCFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS)) KBUILD_USERLDFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS)) +# userspace programs are linked via the compiler, use the correct linker +ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_LD_IS_LLD),yy) +KBUILD_USERLDFLAGS += --ld-path=$(LD) +endif
# make the checker run with the right architecture CHECKFLAGS += --arch=$(ARCH)
base-commit: 0ad2507d5d93f39619fc42372c347d6006b64319 change-id: 20250213-kbuild-userprog-fixes-4f07b62ae818
Best regards,
Thomas Weißschuh thomas.weissschuh@linutronix.de
On Mon, Feb 17, 2025 at 4:28 PM Thomas Weißschuh thomas.weissschuh@linutronix.de wrote:
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.
Explicitly pass --ld-path to clang so $(LD) is respected. As clang 13.0.1 is required to build the kernel, this option is available.
Fixes: 7f3a59db274c ("kbuild: add infrastructure to build userspace programs") Cc: stable@vger.kernel.org # needs wrapping in $(cc-option) for < 6.9 Signed-off-by: Thomas Weißschuh thomas.weissschuh@linutronix.de
Applied to linux-kbuild/fixes. Thanks.
Reproducer, using nolibc to avoid libc requirements for cross building:
$ tail -2 init/Makefile userprogs-always-y += test-llvm test-llvm-userccflags += -nostdlib -nolibc -static -isystem usr/ -include $(srctree)/tools/include/nolibc/nolibc.h
$ cat init/test-llvm.c int main(void) { return 0; }
$ make ARCH=arm64 LLVM=1 allnoconfig headers_install init/
Validate that init/test-llvm builds and has the correct binary format.
Changes in v2:
- Use --ld-path instead of -fuse-ld
- Drop already applied patch
- Link to v1: https://lore.kernel.org/r/20250213-kbuild-userprog-fixes-v1-0-f255fb477d98@l...
Makefile | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/Makefile b/Makefile index 96407c1d6be167b04ed5883e455686918c7a75ee..b41c164533d781d010ff8b2522e523164dc375d0 100644 --- a/Makefile +++ b/Makefile @@ -1123,6 +1123,11 @@ endif KBUILD_USERCFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS)) KBUILD_USERLDFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS))
+# userspace programs are linked via the compiler, use the correct linker +ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_LD_IS_LLD),yy) +KBUILD_USERLDFLAGS += --ld-path=$(LD) +endif
# make the checker run with the right architecture CHECKFLAGS += --arch=$(ARCH)
base-commit: 0ad2507d5d93f39619fc42372c347d6006b64319 change-id: 20250213-kbuild-userprog-fixes-4f07b62ae818
Best regards,
Thomas Weißschuh thomas.weissschuh@linutronix.de
linux-stable-mirror@lists.linaro.org
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Masahiro Yamada -
Nathan Chancellor -
Thomas Weißschuh