# git rev-parse -q --verify e893cdee5343060f224768d7657829c2da2e2848^{commit} e893cdee5343060f224768d7657829c2da2e2848 already have revision, skipping fetch # git checkout -q -f -B kisskb e893cdee5343060f224768d7657829c2da2e2848 # git clean -qxdf # < git log -1 # commit e893cdee5343060f224768d7657829c2da2e2848 # Author: Nathan Chancellor # Date: Wed May 11 11:50:01 2022 -0700 # # powerpc/vdso: Link with ld.lld when requested # # The PowerPC vDSO uses $(CC) to link, which differs from the rest of the # kernel, which uses $(LD) directly. As a result, the default linker of # the compiler is used, which may differ from the linker requested by the # builder. For example: # # $ 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) # # LLVM=1 sets LD=ld.lld but ld.lld is not used to link the vDSO; GNU ld is # because "ld" is the default linker for clang on most Linux platforms. # # This is a problem for Clang's Link Time Optimization as implemented in # the kernel because use of GNU ld with LTO requires the LLVMgold plugin, # which is not technically supported for ld.bfd per # https://llvm.org/docs/GoldPlugin.html. Furthermore, if LLVMgold.so is # missing from a user's system, the build will fail, even though LTO as it # is implemented in the kernel requires ld.lld to avoid this dependency in # the first place. # # Ultimately, the PowerPC vDSO should be converted to compiling and # linking with $(CC) and $(LD) respectively but there were issues last # time this was tried, potentially due to older but supported tool # versions. To avoid regressing GCC + binutils, use the compiler option # '-fuse-ld', which 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'. # # Signed-off-by: Nathan Chancellor # Tested-by: Alexey Kardashevskiy # Reviewed-by: Nick Desaulniers # Reviewed-by: Alexey Kardashevskiy # Signed-off-by: Michael Ellerman # Link: https://github.com/ClangBuiltLinux/linux/issues/774 # Link: https://github.com/llvm/llvm-project/commit/1bc5c84710a8c73ef21295e63c19d10a8c71f2f5 # Link: https://lore.kernel.org/r/20220511185001.3269404-3-nathan@kernel.org # < /opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux-ld --version # < git log --format=%s --max-count=1 e893cdee5343060f224768d7657829c2da2e2848 # < make -s -j 32 ARCH=x86 O=/kisskb/build/powerpc-next_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux- x86_64_defconfig # < make -s -j 32 ARCH=x86 O=/kisskb/build/powerpc-next_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux- help # make -s -j 32 ARCH=x86 O=/kisskb/build/powerpc-next_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux- olddefconfig # make -s -j 32 ARCH=x86 O=/kisskb/build/powerpc-next_x86_64_defconfig_x86_64-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.5.0-nolibc/x86_64-linux/bin/x86_64-linux- Completed OK # rm -rf /kisskb/build/powerpc-next_x86_64_defconfig_x86_64-gcc8 # Build took: 0:01:41.738361