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

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On Thu, Jun 17, 2021 at 12:53 PM Arnaldo Carvalho de Melo
<arnaldo.melo@xxxxxxxxx> wrote:
>
> Em Thu, Jun 17, 2021 at 11:48:47AM -0300, Arnaldo Carvalho de Melo escreveu:
> > 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...
>
> So I updated clang and now I'm stumbling on another one, again using
> pahole 1.21 + fixes, without any of my changes, is this a known issue?
>
> [root@seventh bpf]# pwd
> /mnt/linux/tools/testing/selftests/bpf
> [root@seventh bpf]# git log --oneline -5
> 94f0b2d4a1d0 (HEAD -> master, torvalds/master) proc: only require mm_struct for writing

Please use bpf-next tree. Bleeding edge clang started generating new
ELF relocation types, so you need bleeding edge libbpfs in selftests
to handle that during static linking.

> a33d62662d27 afs: Fix an IS_ERR() vs NULL check
> 009c9aa5be65 (tag: v5.13-rc6) Linux 5.13-rc6
> e4e453434a19 Merge tag 'perf-tools-fixes-for-v5.13-2021-06-13' of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux
> 960f0716d80f Merge tag 'nfs-for-5.13-3' of git://git.linux-nfs.org/projects/trondmy/linux-nfs
> [root@seventh bpf]#
> [root@seventh bpf]# make run_tests

I never use make run_tests.

Try `make clean && make -j60 && sudo ./test_progs`.

> <SNIP>
>   GEN-SKEL [test_progs] atomic_bounds.skel.h
>   GEN-SKEL [test_progs] atomics.skel.h
>   GEN-SKEL [test_progs] bind4_prog.skel.h
> libbpf: elf: skipping unrecognized data section(6) .rodata.str1.1
>   GEN-SKEL [test_progs] bind6_prog.skel.h
> libbpf: elf: skipping unrecognized data section(6) .rodata.str1.1
>   GEN-SKEL [test_progs] bind_perm.skel.h
>   GEN-SKEL [test_progs] bpf_cubic.skel.h
> libbpf: ELF relo #0 in section #15 has unexpected type 2 in /mnt/linux/tools/testing/selftests/bpf/bpf_cubic.o
> Error: failed to link '/mnt/linux/tools/testing/selftests/bpf/bpf_cubic.o': Unknown error -22 (-22)
> make: *** [Makefile:456: /mnt/linux/tools/testing/selftests/bpf/bpf_cubic.skel.h] Error 234
> [root@seventh bpf]# clang -v |& head -2
> clang version 13.0.0 (https://github.com/llvm/llvm-project dee2c76b4c46e71903e3d86ab7555a80d51d1288)
> Target: x86_64-unknown-linux-gnu
> [root@seventh bpf]#
>
> - Arnaldo
>
> > 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.
> >
> > ?
> >
> > :-)



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