linux-kernel - Re: [PATCH bpf-next v3 1/4] bpf: Show precise rejected function when attaching fexit/fmod_ret to _

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Message-ID: <CALOAHbAbZtdY8hCbFAjTBDjzCkeNFMd2qWzHBG-fAbOsFpqmpA@mail.gmail.com>
Date: Wed, 23 Jul 2025 19:37:16 +0800
From: Yafang Shao <laoar.shao@...il.com>
To: KaFai Wan <kafai.wan@...ux.dev>
Cc: ast@...nel.org, daniel@...earbox.net, john.fastabend@...il.com, 
	andrii@...nel.org, martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org, 
	yonghong.song@...ux.dev, kpsingh@...nel.org, sdf@...ichev.me, 
	haoluo@...gle.com, jolsa@...nel.org, mykolal@...com, shuah@...nel.org, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, leon.hwang@...ux.dev
Subject: Re: [PATCH bpf-next v3 1/4] bpf: Show precise rejected function when
 attaching fexit/fmod_ret to __noreturn functions

On Tue, Jul 22, 2025 at 11:35 PM KaFai Wan <kafai.wan@...ux.dev> wrote:
>
> With this change, we know the precise rejected function name when
> attaching fexit/fmod_ret to __noreturn functions from log.
>
> $ ./fexit
> libbpf: prog 'fexit': BPF program load failed: -EINVAL
> libbpf: prog 'fexit': -- BEGIN PROG LOAD LOG --
> Attaching fexit/fmod_ret to __noreturn function 'do_exit' is rejected.
>
> Suggested-by: Leon Hwang <leon.hwang@...ux.dev>
> Signed-off-by: KaFai Wan <kafai.wan@...ux.dev>

Acked-by: Yafang Shao <laoar.shao@...il.com>

> ---
>  kernel/bpf/verifier.c                               | 3 ++-
>  tools/testing/selftests/bpf/progs/fexit_noreturns.c | 2 +-
>  2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index e2fcea860755..00d287814f12 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -23946,7 +23946,8 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
>         } else if ((prog->expected_attach_type == BPF_TRACE_FEXIT ||
>                    prog->expected_attach_type == BPF_MODIFY_RETURN) &&
>                    btf_id_set_contains(&noreturn_deny, btf_id)) {
> -               verbose(env, "Attaching fexit/fmod_ret to __noreturn functions is rejected.\n");
> +               verbose(env, "Attaching fexit/fmod_ret to __noreturn function '%s' is rejected.\n",
> +                       tgt_info.tgt_name);
>                 return -EINVAL;
>         }
>
> diff --git a/tools/testing/selftests/bpf/progs/fexit_noreturns.c b/tools/testing/selftests/bpf/progs/fexit_noreturns.c
> index 54654539f550..b1c33d958ae2 100644
> --- a/tools/testing/selftests/bpf/progs/fexit_noreturns.c
> +++ b/tools/testing/selftests/bpf/progs/fexit_noreturns.c
> @@ -8,7 +8,7 @@
>  char _license[] SEC("license") = "GPL";
>
>  SEC("fexit/do_exit")
> -__failure __msg("Attaching fexit/fmod_ret to __noreturn functions is rejected.")
> +__failure __msg("Attaching fexit/fmod_ret to __noreturn function 'do_exit' is rejected.")
>  int BPF_PROG(noreturns)
>  {
>         return 0;
> --
> 2.43.0
>


-- 
Regards
Yafang