On 7/27/19 12:36 AM, Sedat Dilek wrote: > On Sat, Jul 27, 2019 at 4:24 AM Alexei Starovoitov > <alexei.starovoitov@xxxxxxxxx> wrote: >> >> On Fri, Jul 26, 2019 at 2:19 PM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote: >>> >>> On Fri, Jul 26, 2019 at 11:10 PM Yonghong Song <yhs@xxxxxx> wrote: >>>> >>>> >>>> >>>> On 7/26/19 2:02 PM, Sedat Dilek wrote: >>>>> On Fri, Jul 26, 2019 at 10:38 PM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote: >>>>>> >>>>>> Hi Yonghong Song, >>>>>> >>>>>> On Fri, Jul 26, 2019 at 5:45 PM Yonghong Song <yhs@xxxxxx> wrote: >>>>>>> >>>>>>> >>>>>>> >>>>>>> On 7/26/19 1:26 AM, Sedat Dilek wrote: >>>>>>>> Hi, >>>>>>>> >>>>>>>> I have opened a new issue in the ClangBuiltLinux issue tracker. >>>>>>> >>>>>>> Glad to know clang 9 has asm goto support and now It can compile >>>>>>> kernel again. >>>>>>> >>>>>> >>>>>> Yupp. >>>>>> >>>>>>>> >>>>>>>> I am seeing a problem in the area bpf/seccomp causing >>>>>>>> systemd/journald/udevd services to fail. >>>>>>>> >>>>>>>> [Fri Jul 26 08:08:43 2019] systemd[453]: systemd-udevd.service: Failed >>>>>>>> to connect stdout to the journal socket, ignoring: Connection refused >>>>>>>> >>>>>>>> This happens when I use the (LLVM) LLD ld.lld-9 linker but not with >>>>>>>> BFD linker ld.bfd on Debian/buster AMD64. >>>>>>>> In both cases I use clang-9 (prerelease). >>>>>>> >>>>>>> Looks like it is a lld bug. >>>>>>> >>>>>>> I see the stack trace has __bpf_prog_run32() which is used by >>>>>>> kernel bpf interpreter. Could you try to enable bpf jit >>>>>>> sysctl net.core.bpf_jit_enable = 1 >>>>>>> If this passed, it will prove it is interpreter related. >>>>>>> >>>>>> >>>>>> After... >>>>>> >>>>>> sysctl -w net.core.bpf_jit_enable=1 >>>>>> >>>>>> I can start all failed systemd services. >>>>>> >>>>>> systemd-journald.service >>>>>> systemd-udevd.service >>>>>> haveged.service >>>>>> >>>>>> This is in maintenance mode. >>>>>> >>>>>> What is next: Do set a permanent sysctl setting for net.core.bpf_jit_enable? >>>>>> >>>>> >>>>> This is what I did: >>>> >>>> I probably won't have cycles to debug this potential lld issue. >>>> Maybe you already did, I suggest you put enough reproducible >>>> details in the bug you filed against lld so they can take a look. >>>> >>> >>> I understand and will put the journalctl-log into the CBL issue >>> tracker and update informations. >>> >>> Thanks for your help understanding the BPF correlations. >>> >>> Is setting 'net.core.bpf_jit_enable = 2' helpful here? >> >> jit_enable=1 is enough. >> Or use CONFIG_BPF_JIT_ALWAYS_ON to workaround. >> >> It sounds like clang miscompiles interpreter. >> modprobe test_bpf >> should be able to point out which part of interpreter is broken. > > Maybe we need something like... > > "bpf: Disable GCC -fgcse optimization for ___bpf_prog_run()" > > ...for clang? Not sure how do you get conclusion it is gcse causing the problem. But anyway, adding such flag in the kernel is not a good idea. clang/llvm should be fixed instead. Esp. there is still time for 9.0.0 release to fix bugs. > > - Sedat - > > [1] https://git.kernel.org/linus/3193c0836f203a91bef96d88c64cccf0be090d9c >
