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

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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@xxxxxxxxx> 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.

?

:-)

- Arnaldo



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