On 7/27/19 1:16 AM, Sedat Dilek wrote: > On Sat, Jul 27, 2019 at 9:36 AM Sedat Dilek <sedat.dilek@xxxxxxxxx> 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. > > Just to clarify: > This does not happen with clang-9 + ld.bfd (GNU/ld linker). > >>> 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 if something like GCC's... > > -fgcse > > Perform a global common subexpression elimination pass. This pass also > performs global constant and copy propagation. > > Note: When compiling a program using computed gotos, a GCC extension, > you may get better run-time performance if you disable the global > common subexpression elimination pass by adding -fno-gcse to the > command line. > > Enabled at levels -O2, -O3, -Os. > > ...is available for clang. > > I tried with hopping to turn off "global common subexpression elimination": > > diff --git a/arch/x86/net/Makefile b/arch/x86/net/Makefile > index 383c87300b0d..92f934a1e9ff 100644 > --- a/arch/x86/net/Makefile > +++ b/arch/x86/net/Makefile > @@ -3,6 +3,8 @@ > # Arch-specific network modules > # > > +KBUILD_CFLAGS += -O0 This won't work. First, you added to the wrong file. The interpreter is at kernel/bpf/core.c. Second, kernel may have compilation issues with -O0. > + > ifeq ($(CONFIG_X86_32),y) > obj-$(CONFIG_BPF_JIT) += bpf_jit_comp32.o > else > > Still see... > BROKEN: test_bpf: #294 BPF_MAXINSNS: Jump, gap, jump, ... jited:0 > > - Sedat - >
