linux-kernel - Re: [PATCH bpf-next 2/3] bpf: Show precise rejected function when attaching to __btf

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Message-ID: <CALOAHbCMCnYe=d04Ong5GzdMjK553CooF5XrBi0kQUwoh0oDrA@mail.gmail.com>
Date: Fri, 11 Jul 2025 17:57:14 +0800
From: Yafang Shao <laoar.shao@...il.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: KaFai Wan <mannkafai@...il.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Eduard <eddyz87@...il.com>, 
	Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, LKML <linux-kernel@...r.kernel.org>, 
	bpf <bpf@...r.kernel.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next 2/3] bpf: Show precise rejected function when
 attaching to __btf_id functions

On Fri, Jul 11, 2025 at 1:19 AM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Thu, Jul 10, 2025 at 9:27 AM KaFai Wan <mannkafai@...il.com> wrote:
> >
> > Show the precise rejected function name when attaching tracing to
> > __btf_id functions.
> >
> > $ ./fentry
> > libbpf: prog 'migrate_disable': BPF program load failed: -EINVAL
> > libbpf: prog 'migrate_disable': -- BEGIN PROG LOAD LOG --
> > Attaching tracing to __btf_id function 'migrate_disable' is rejected.
> >
> > Signed-off-by: KaFai Wan <mannkafai@...il.com>
> > ---
> >  kernel/bpf/verifier.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 275d82fb1a1a..2779d63e1f8b 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -23938,6 +23938,8 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
> >                         return ret;
> >         } else if (prog->type == BPF_PROG_TYPE_TRACING &&
> >                    btf_id_set_contains(&btf_id_deny, btf_id)) {
> > +               verbose(env, "Attaching tracing to __btf_id function '%s' is rejected.\n",
> > +                       tgt_info.tgt_name);
>
> "Attaching tracing to __btf_id" ?! What does it mean?

The term "tracing" refers to BPF_PROG_TYPE_TRACING. I believe it is
useful because it helps identify which functions cannot be attached by
a given BPF program type.
Perhaps we should replace "tracing" with "a tracing prog" for clarity?

> Drop "__btf_id" and "tracing" bits.

-- 
Regards
Yafang