Re: latest pahole breaks libbpf CI and let's talk about staging

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Thu, Jun 17, 2021 at 7:48 AM Arnaldo Carvalho de Melo
<arnaldo.melo@gmail.com> 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 <arnaldo.melo@gmail.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' [27] 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' [27] 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 :)

>
> - Arnaldo