On Tue, Mar 12, 2019 at 2:53 PM Nathan Chancellor <natechancellor@xxxxxxxxx> wrote: > > 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> Thanks for this patch. Can the maintainers please consider this an emergency patch; without it, the recent change to LLVM has caused ALL of our CI targets to go red. Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > --- > 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 > -- Thanks, ~Nick Desaulniers