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

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Message-ID: <20210329190851.2vy4yfrbfgiypxuz@kafai-mbp.dhcp.thefacebook.com>
Date:   Mon, 29 Mar 2021 12:08:51 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Lorenz Bauer <lmb@...udflare.com>
CC:     Cong Wang <xiyou.wangcong@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.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 Mon, Mar 29, 2021 at 05:06:26PM +0100, Lorenz Bauer wrote:
> On Mon, 29 Mar 2021 at 02:25, Martin KaFai Lau <kafai@...com> wrote:
> >
> > > > >
> > > > > # pahole --version
> > > > > v1.17
> > > >
> > > > That is the most likely reason.
> > > > In lib/Kconfig.debug
> > > > we have pahole >= 1.19 requirement for BTF in modules.
> > > > Though your config has CUBIC=y I suspect something odd goes on.
> > > > Could you please try the latest pahole 1.20 ?
> > >
> > > Sure, I will give it a try tomorrow, I am not in control of the CI I ran.
> > Could you also check the CONFIG_DYNAMIC_FTRACE and also try 'y' if it
> > is not set?
> 
> I hit the same problem on newer pahole:
> 
> $ pahole --version
> v1.20
> 
> CONFIG_DYNAMIC_FTRACE=y resolves the issue.
Thanks for checking.

pahole only generates the btf_id for external function
and ftrace-able function.  Some functions in the bpf_tcp_ca_kfunc_ids list
are static (e.g. cubictcp_init), so it fails during resolve_btfids.

I will post a patch to limit the bpf_tcp_ca_kfunc_ids list
to CONFIG_DYNAMIC_FTRACE.  I will address the pahole
generation in a followup and then remove this
CONFIG_DYNAMIC_FTRACE limitation.