On Tue, Jun 02, 2020 at 12:52:26PM -0700, Nick Desaulniers wrote: > On Tue, Jun 2, 2020 at 12:25 PM Nathan Chancellor > <natechancellor@xxxxxxxxx> wrote: > > > > 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.cpp#L132-L150 > > > > 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://github.com/ClangBuiltLinux/linux/issues/1041 > > Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx> > > Thanks, with this, I'm more confident that the linker flags don't change. > Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> ... > > -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 -T I added the --build-id flag according to commit 7a0a93c51799 ("arm64: vdso: Explicitly add build-id option") and applied the patch. Thanks!
