After LLVM revision r355672 [1], all known working kernel configurations
fail to link [2]:
ld: init/do_mounts.o: in function `prepare_namespace':
do_mounts.c:(.init.text+0x5ca): undefined reference to `bcmp'
ld: do_mounts.c:(.init.text+0x5e6): undefined reference to `bcmp'
ld: init/initramfs.o: in function `do_header':
initramfs.c:(.init.text+0x6e0): undefined reference to `bcmp'
ld: initramfs.c:(.init.text+0x6f8): undefined reference to `bcmp'
ld: arch/x86/kernel/setup.o: in function `setup_arch':
setup.c:(.init.text+0x21d): undefined reference to `bcmp'
Commit 6edfba1b33c7 ("[PATCH] x86_64: Don't define string functions to
builtin") removed '-ffreestanding' globally and the kernel doesn't
provide a bcmp definition so the linker cannot find a reference to it.
Fix this by explicitly telling LLVM through Clang not to emit bcmp
references. This flag does not need to be behind 'cc-option' because all
working versions of Clang support this flag.
[1]: https://github.com/llvm/llvm-project/commit/8e16d73346f8091461319a7dfc4ddd18eedcff13
[2]: https://travis-ci.com/ClangBuiltLinux/continuous-integration/builds/104027249
Link: https://github.com/ClangBuiltLinux/linux/issues/416
Link: https://bugs.llvm.org/show_bug.cgi?id=41035
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
---
Makefile | 1 +
1 file changed, 1 insertion(+)
diff --git a/Makefile b/Makefile
index 9ef547fc7ffe..6645a274b6e3 100644
--- a/Makefile
+++ b/Makefile
@@ -501,6 +501,7 @@ ifneq ($(GCC_TOOLCHAIN),)
CLANG_FLAGS += --gcc-toolchain=$(GCC_TOOLCHAIN)
endif
CLANG_FLAGS += -no-integrated-as
+CLANG_FLAGS += -fno-builtin-bcmp
KBUILD_CFLAGS += $(CLANG_FLAGS)
KBUILD_AFLAGS += $(CLANG_FLAGS)
export CLANG_FLAGS
--
2.21.0
