From: Andrii Nakryiko <email@example.com> To: Arnaldo Carvalho de Melo <firstname.lastname@example.org> Cc: Yonghong Song <email@example.com>, bpf <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org Subject: Re: latest pahole breaks libbpf CI and let's talk about staging Date: Thu, 17 Jun 2021 14:52:57 -0700 [thread overview] Message-ID: <CAEf4BzZWq21zP+1C4=qqWGQ3WUXK-pvt+rWpcsh_971qAw4Wzw@mail.gmail.com> (raw) In-Reply-To: <YMuzAfK6vwbeN3XX@kernel.org> On Thu, Jun 17, 2021 at 1:39 PM Arnaldo Carvalho de Melo <email@example.com> wrote: > > Em Thu, Jun 17, 2021 at 01:00:11PM -0700, Andrii Nakryiko escreveu: > > On Thu, Jun 17, 2021 at 7:48 AM Arnaldo Carvalho de Melo > > <firstname.lastname@example.org> wrote: > > > > > > Em Wed, Jun 16, 2021 at 03:36:54PM -0700, Andrii Nakryiko escreveu: > > > > On Wed, Jun 16, 2021 at 1:41 PM Arnaldo Carvalho de Melo <email@example.com> wrote: > > > > > And if I use pahole's BTF loader I find the info about that function: > > > > > > > > > > [acme@seventh linux]$ strace -e openat -o /tmp/bla pfunct -F btf tcp_cong_avoid_ai ; grep vmlinux /tmp/bla > > > > > void tcp_cong_avoid_ai(struct tcp_sock * tp, u32 w, u32 acked); > > > > > openat(AT_FDCWD, "/sys/kernel/btf/vmlinux", O_RDONLY) = 3 > > > > > > > > > > So this should be unrelated to the breakage you noticed in the CI. > > > > > > > > > > I'm trying to to reproduce the CI breakage by building the kernel and > > > > > running selftests after a reboot. > > > > > > > > > > I suspect I'm missing something, can you see what it is? > > > > > > > > Oh, I didn't realize initially what it is. This is not kernel-related, > > > > you are right. You just need newer Clang. Can you please use nightly > > > > version or build from sources? Basically, your Clang is too old and it > > > > doesn't generate BTF information for extern functions in BPF code. > > > > > > Oh well, I thought that that clang was new enough, the system being > > > Fedora rawhide: > > > > > > [acme@seventh ~]$ clang -v |& head -1 > > > clang version 12.0.0 (https://github.com/llvm/llvm-project 87369c626114ae17f4c637635c119e6de0856a9a) > > > > > > I'm now building the single-repo main... > > > > > > Would you consider a patch for libbpf that would turn this: > > > > > > > > > libbpf: failed to find BTF for extern 'tcp_cong_avoid_ai'  section: -2 > > > > > > Error: failed to open BPF object file: No such file or directory > > > > > > make: *** [Makefile:460: /mnt/linux/tools/testing/selftests/bpf/bpf_cubic.skel.h] Error 255 > > > > > > make: *** Deleting file '/mnt/linux/tools/testing/selftests/bpf/bpf_cubic.skel.h' > > > > > > make: Leaving directory '/mnt/linux/tools/testing/selftests/bpf' > > > > > > Into: > > > > > > libbpf: failed to find BTF for extern 'tcp_cong_avoid_ai'  section: -2 > > > HINT: Please update your clang/llvm toolchain to at least cset abcdef123456 > > > HINT: That is where clang started generating BTF information for extern functions in BPF code. > > > > > > ? > > > > > > :-) > > > > I'd rather not :) > > Not even a "please update clang?" > It could be old clang, it could also be because BPF program wasn't built with BTF (i.e., you didn't specify -g during clang invocation), it could probably be due to some other problems as well. I don't want libbpf to turn into a library that's constantly trying to guess possible problems. It will become a complete mess to maintain. And when it will still be wrong sometimes, causing more harm than being helpful. Especially for relatively uncommon problems like this. Those people who are trying to use features like BPF unstable helpers (calling whitelisted kernel functions), should know that they need Clang of some version and build with BTF. We have that also mentioned in selftest/bpf/README.rst. I'd rather not duplicate all that in libbpf code as well. > "-2" and "Error 255" doesn't seem that helpful :-\ But "failed to find BTF for extern 'tcp_cong_avoid_ai'" is pretty helpful. -2 is for more involved debugging, if necessary. > > - Arnaldo
next prev parent reply other threads:[~2021-06-17 21:53 UTC|newest] Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-06-15 23:30 Andrii Nakryiko 2021-06-16 14:56 ` Arnaldo Carvalho de Melo 2021-06-16 16:40 ` Arnaldo Carvalho de Melo 2021-06-16 20:41 ` Arnaldo Carvalho de Melo 2021-06-16 22:36 ` Andrii Nakryiko 2021-06-17 14:48 ` Arnaldo Carvalho de Melo 2021-06-17 19:53 ` Arnaldo Carvalho de Melo 2021-06-17 20:03 ` Andrii Nakryiko 2021-06-17 20:41 ` Arnaldo Carvalho de Melo 2021-06-17 21:56 ` Andrii Nakryiko 2021-06-17 20:00 ` Andrii Nakryiko 2021-06-17 20:39 ` Arnaldo Carvalho de Melo 2021-06-17 21:52 ` Andrii Nakryiko [this message] 2021-06-18 17:21 ` Arnaldo Carvalho de Melo 2021-06-16 17:40 ` Andrii Nakryiko 2021-06-16 18:25 ` Arnaldo Carvalho de Melo 2021-06-16 22:38 ` Andrii Nakryiko 2021-06-17 0:16 ` Arnaldo Carvalho de Melo 2021-06-17 4:26 ` Andrii Nakryiko
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