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

[Yafang Shao <laoar.shao@gmail.com>]

On Tue, Jul 22, 2025 at 11:35 PM KaFai Wan <kafai.wan@linux.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@linux.dev>
> Signed-off-by: KaFai Wan <kafai.wan@linux.dev>

Acked-by: Yafang Shao <laoar.shao@gmail.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