On Tue, May 10, 2022 at 04:22:12PM +1000, Alexey Kardashevskiy wrote: > > > On 5/10/22 06:46, Nathan Chancellor wrote: > > The PowerPC vDSO is linked with $(CC) instead of $(LD), which means the > > default linker of the compiler is used instead of the linker requested > > by the builder. > > > > $ make ARCH=powerpc LLVM=1 mrproper defconfig arch/powerpc/kernel/vdso/ > > ... > > > > $ llvm-readelf -p .comment arch/powerpc/kernel/vdso/vdso{32,64}.so.dbg > > > > File: arch/powerpc/kernel/vdso/vdso32.so.dbg > > String dump of section '.comment': > > [ 0] clang version 14.0.0 (Fedora 14.0.0-1.fc37) > > > > File: arch/powerpc/kernel/vdso/vdso64.so.dbg > > String dump of section '.comment': > > [ 0] clang version 14.0.0 (Fedora 14.0.0-1.fc37) > > > > The compiler option '-fuse-ld' tells the compiler which linker to use > > when it is invoked as both the compiler and linker. Use '-fuse-ld=lld' > > when LD=ld.lld has been specified (CONFIG_LD_IS_LLD) so that the vDSO is > > linked with the same linker as the rest of the kernel. > > > > $ llvm-readelf -p .comment arch/powerpc/kernel/vdso/vdso{32,64}.so.dbg > > > > File: arch/powerpc/kernel/vdso/vdso32.so.dbg > > String dump of section '.comment': > > [ 0] Linker: LLD 14.0.0 > > [ 14] clang version 14.0.0 (Fedora 14.0.0-1.fc37) > > > > File: arch/powerpc/kernel/vdso/vdso64.so.dbg > > String dump of section '.comment': > > [ 0] Linker: LLD 14.0.0 > > [ 14] clang version 14.0.0 (Fedora 14.0.0-1.fc37) > > > > LD can be a full path to ld.lld, which will not be handled properly by > > '-fuse-ld=lld' if the full path to ld.lld is outside of the compiler's > > search path. '-fuse-ld' can take a path to the linker but it is > > deprecated in clang 12.0.0; '--ld-path' is preferred for this scenario. > > > > Use '--ld-path' if it is supported, as it will handle a full path or > > just 'ld.lld' properly. See the LLVM commit below for the full details > > of '--ld-path'. > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/774 > > Link: > > https://github.com/llvm/llvm-project/commit/1bc5c84710a8c73ef21295e63c19d10a8c71f2f5 > > Signed-off-by: Nathan Chancellor <nat...@kernel.org> > > --- > > arch/powerpc/kernel/vdso/Makefile | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/arch/powerpc/kernel/vdso/Makefile > > b/arch/powerpc/kernel/vdso/Makefile > > index 954974287ee7..096b0bf1335f 100644 > > --- a/arch/powerpc/kernel/vdso/Makefile > > +++ b/arch/powerpc/kernel/vdso/Makefile > > @@ -48,6 +48,7 @@ UBSAN_SANITIZE := n > > KASAN_SANITIZE := n > > ccflags-y := -shared -fno-common -fno-builtin -nostdlib > > -Wl,--hash-style=both > > +ccflags-$(CONFIG_LD_IS_LLD) += $(call > > cc-option,--ld-path=$(LD),-fuse-ld=lld) > > > Out of curiosity - how does this work exactly? I can see --ld-path= in the > output so it works but there is no -fuse-ld=lld, is the second argument of > cc-option only picked when the first one is not supported?
Correct. See Documentation/kbuild/makefiles.rst for more information about those macros if you are curious. > Anyway, > > Tested-by: Alexey Kardashevskiy <a...@ozlabs.ru> > Reviewed-by: Alexey Kardashevskiy <a...@ozlabs.ru> Thanks a lot! Cheers, Nathan