On Wed, Dec 9, 2020 at 5:56 AM 'Fangrui Song' via Clang Built Linux <clang-built-linux@xxxxxxxxxxxxxxxx> wrote: > On 2020-12-08, 'Sami Tolvanen' via Clang Built Linux wrote: > >On Tue, Dec 8, 2020 at 4:15 AM Arnd Bergmann <arnd@xxxxxxxxxx> wrote: > >> So far I have > >> not managed to get a working build out of it, the main problem so far being > >> that it is really slow to build because the link stage only uses one CPU. > >> These are the other issues I've seen so far: > > ld.lld ThinLTO uses the number of (physical cores enabled by affinity) by default. Ah, I see. Do you know if it's also possible to do something like -flto=jobserver to integrate better with the kernel build system? I tend to run multiple builds under a top-level makefile with 'make -j30' in order to use 30 of the 32 threads and leave the scheduling to jobserver instead of the kernel. If the linker itself is multithreaded but the jobserver thinks it is a single thread, could end up with 30 concurrent linkers each trying to use 16 cores. > >> - CONFIG_CPU_BIG_ENDIAN doesn't seem to work with lld, and LTO > >> doesn't work with ld.bfd. > >> I've added a CPU_LITTLE_ENDIAN dependency to > >> ARCH_SUPPORTS_LTO_CLANG{,THIN} > > > >Ah, good point. I'll fix this in v9. > > Full/Thin LTO should work with GNU ld and gold with LLVMgold.so built from > llvm-project (https://llvm.org/docs/GoldPlugin.html ). You'll need to make sure > that LLVMgold.so is newer than clang. (Newer clang may introduce bitcode > attributes which are unrecognizable by older LLVMgold.so/ld.lld) The current patch series requires LLD: config HAS_LTO_CLANG def_bool y depends on CC_IS_CLANG && CLANG_VERSION >= 110000 && LD_IS_LLD Is this something we should change then, or try to keep it simple with the current approach, leaving LTO disabled for big-endian builds and hosts without a working lld? Arnd