netdev - Re: [PATCH v2 bpf-next 00/14] bpf: Support calling kernel function

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Date:   Sat, 27 Mar 2021 15:07:59 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Martin KaFai Lau <kafai@...com>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        kernel-team <kernel-team@...com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 bpf-next 00/14] bpf: Support calling kernel function

On Sat, Mar 27, 2021 at 2:28 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Sat, Mar 27, 2021 at 2:25 PM Cong Wang <xiyou.wangcong@...il.com> wrote:
> >
> > Hi,
> >
> > On Wed, Mar 24, 2021 at 8:40 PM Martin KaFai Lau <kafai@...com> wrote:
> > > Martin KaFai Lau (14):
> > >   bpf: Simplify freeing logic in linfo and jited_linfo
> > >   bpf: Refactor btf_check_func_arg_match
> > >   bpf: Support bpf program calling kernel function
> > >   bpf: Support kernel function call in x86-32
> > >   tcp: Rename bictcp function prefix to cubictcp
> > >   bpf: tcp: Put some tcp cong functions in allowlist for bpf-tcp-cc
> >
> > I got the following link error which is likely caused by one of your
> > patches in this series.
> >
> > FAILED unresolved symbol cubictcp_state
> > make: *** [Makefile:1199: vmlinux] Error 255
>
> I don't see it and bpf CI doesn't see it either.
> Without steps to reproduce your observation isn't helpful.

Just `make` is sufficient to reproduce it here:

# make
  CALL    scripts/checksyscalls.sh
  CALL    scripts/atomic/check-atomics.sh
  DESCEND  objtool
  DESCEND  bpf/resolve_btfids
  CHK     include/generated/compile.h
  GEN     .version
  CHK     include/generated/compile.h
  UPD     include/generated/compile.h
  CC      init/version.o
  AR      init/built-in.a
  LD      vmlinux.o
  MODPOST vmlinux.symvers
  MODINFO modules.builtin.modinfo
  GEN     modules.builtin
  LD      .tmp_vmlinux.btf
  BTF     .btf.vmlinux.bin.o
  LD      .tmp_vmlinux.kallsyms1
  KSYMS   .tmp_vmlinux.kallsyms1.S
  AS      .tmp_vmlinux.kallsyms1.S
  LD      .tmp_vmlinux.kallsyms2
  KSYMS   .tmp_vmlinux.kallsyms2.S
  AS      .tmp_vmlinux.kallsyms2.S
  LD      vmlinux
  BTFIDS  vmlinux
FAILED unresolved symbol cubictcp_state
make: *** [Makefile:1199: vmlinux] Error 255

I suspect it is related to the kernel config or linker version.

# grep TCP_CONG .config
CONFIG_TCP_CONG_ADVANCED=y
CONFIG_TCP_CONG_BIC=m
CONFIG_TCP_CONG_CUBIC=y
CONFIG_TCP_CONG_WESTWOOD=m
CONFIG_TCP_CONG_HTCP=m
CONFIG_TCP_CONG_HSTCP=m
CONFIG_TCP_CONG_HYBLA=m
CONFIG_TCP_CONG_VEGAS=m
CONFIG_TCP_CONG_NV=m
CONFIG_TCP_CONG_SCALABLE=m
CONFIG_TCP_CONG_LP=m
CONFIG_TCP_CONG_VENO=m
CONFIG_TCP_CONG_YEAH=m
CONFIG_TCP_CONG_ILLINOIS=m
CONFIG_TCP_CONG_DCTCP=m
CONFIG_TCP_CONG_CDG=m
CONFIG_TCP_CONG_BBR=m
CONFIG_DEFAULT_TCP_CONG="cubic"

# gcc --version
gcc (Debian 8.3.0-6) 8.3.0
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

# pahole --version
v1.17

Also, reverting this whole patchset also makes it go away.

Thanks.