From: Nathan Chancellor natechancellor@gmail.com
[ Upstream commit 2b2a25845d534ac6d55086e35c033961fdd83a26 ]
Currently, the VDSO is being linked through $(CC). This does not match how the rest of the kernel links objects, which is through the $(LD) variable.
When clang is built in a default configuration, it first attempts to use the target triple's default linker, which is just ld. However, the user can override this through the CLANG_DEFAULT_LINKER cmake define so that clang uses another linker by default, such as LLVM's own linker, ld.lld. This can be useful to get more optimized links across various different projects.
However, this is problematic for the s390 vDSO because ld.lld does not have any s390 emulatiom support:
https://github.com/llvm/llvm-project/blob/llvmorg-10.0.1-rc1/lld/ELF/Driver....
Thus, if a user is using a toolchain with ld.lld as the default, they will see an error, even if they have specified ld.bfd through the LD make variable:
$ make -j"$(nproc)" -s ARCH=s390 CROSS_COMPILE=s390x-linux-gnu- LLVM=1 \ LD=s390x-linux-gnu-ld \ defconfig arch/s390/kernel/vdso64/ ld.lld: error: unknown emulation: elf64_s390 clang-11: error: linker command failed with exit code 1 (use -v to see invocation)
Normally, '-fuse-ld=bfd' could be used to get around this; however, this can be fragile, depending on paths and variable naming. The cleaner solution for the kernel is to take advantage of the fact that $(LD) can be invoked directly, which bypasses the heuristics of $(CC) and respects the user's choice. Similar changes have been done for ARM, ARM64, and MIPS.
Link: https://lkml.kernel.org/r/20200602192523.32758-1-natechancellor@gmail.com Link: https://github.com/ClangBuiltLinux/linux/issues/1041 Signed-off-by: Nathan Chancellor natechancellor@gmail.com Reviewed-by: Nick Desaulniers ndesaulniers@google.com [heiko.carstens@de.ibm.com: add --build-id flag] Signed-off-by: Heiko Carstens heiko.carstens@de.ibm.com Signed-off-by: Vasily Gorbik gor@linux.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/s390/kernel/vdso64/Makefile | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/arch/s390/kernel/vdso64/Makefile b/arch/s390/kernel/vdso64/Makefile index bec19e7e6e1cf..4a66a1cb919b1 100644 --- a/arch/s390/kernel/vdso64/Makefile +++ b/arch/s390/kernel/vdso64/Makefile @@ -18,8 +18,8 @@ KBUILD_AFLAGS_64 += -m64 -s
KBUILD_CFLAGS_64 := $(filter-out -m64,$(KBUILD_CFLAGS)) KBUILD_CFLAGS_64 += -m64 -fPIC -shared -fno-common -fno-builtin -KBUILD_CFLAGS_64 += -nostdlib -Wl,-soname=linux-vdso64.so.1 \ - -Wl,--hash-style=both +ldflags-y := -fPIC -shared -nostdlib -soname=linux-vdso64.so.1 \ + --hash-style=both --build-id -T
$(targets:%=$(obj)/%.dbg): KBUILD_CFLAGS = $(KBUILD_CFLAGS_64) $(targets:%=$(obj)/%.dbg): KBUILD_AFLAGS = $(KBUILD_AFLAGS_64) @@ -37,8 +37,8 @@ KASAN_SANITIZE := n $(obj)/vdso64_wrapper.o : $(obj)/vdso64.so
# link rule for the .so file, .lds has to be first -$(obj)/vdso64.so.dbg: $(src)/vdso64.lds $(obj-vdso64) FORCE - $(call if_changed,vdso64ld) +$(obj)/vdso64.so.dbg: $(obj)/vdso64.lds $(obj-vdso64) FORCE + $(call if_changed,ld)
# strip rule for the .so file $(obj)/%.so: OBJCOPYFLAGS := -S @@ -50,8 +50,6 @@ $(obj-vdso64): %.o: %.S FORCE $(call if_changed_dep,vdso64as)
# actual build commands -quiet_cmd_vdso64ld = VDSO64L $@ - cmd_vdso64ld = $(CC) $(c_flags) -Wl,-T $(filter %.lds %.o,$^) -o $@ quiet_cmd_vdso64as = VDSO64A $@ cmd_vdso64as = $(CC) $(a_flags) -c -o $@ $<