linux-kernel - Re: [PATCH bpf-next v8 4/5] libbpf: Init kprobe prog expected_attach

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Message-ID: <CAEf4BzYz9_0Po-JLU+Z4kB7L5snuh2KFSTO0X9KK00GKSq91Sw@mail.gmail.com>
Date: Mon, 24 Feb 2025 17:15:25 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Tao Chen <chen.dylane@...ux.dev>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, eddyz87@...il.com, 
	haoluo@...gle.com, jolsa@...nel.org, qmo@...nel.org, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org, chen.dylane@...il.com
Subject: Re: [PATCH bpf-next v8 4/5] libbpf: Init kprobe prog
 expected_attach_type for kfunc probe

On Mon, Feb 24, 2025 at 9:03 AM Tao Chen <chen.dylane@...ux.dev> wrote:
>
> Kprobe prog type kfuncs like bpf_session_is_return and
> bpf_session_cookie will check the expected_attach_type,
> so init the expected_attach_type here.
>
> Signed-off-by: Tao Chen <chen.dylane@...ux.dev>
> ---
>  tools/lib/bpf/libbpf_probes.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
> index 8efebc18a215..bb5b457ddc80 100644
> --- a/tools/lib/bpf/libbpf_probes.c
> +++ b/tools/lib/bpf/libbpf_probes.c
> @@ -126,6 +126,7 @@ static int probe_prog_load(enum bpf_prog_type prog_type,
>                 break;
>         case BPF_PROG_TYPE_KPROBE:
>                 opts.kern_version = get_kernel_version();
> +               opts.expected_attach_type = BPF_TRACE_KPROBE_SESSION;

so KPROBE_SESSION is relative recent feature, if we unconditionally
specify this, we'll regress some feature probes for old kernels where
KPROBE_SESSION isn't supported, no?

pw-bot: cr

>                 break;
>         case BPF_PROG_TYPE_LIRC_MODE2:
>                 opts.expected_attach_type = BPF_LIRC_MODE2;
> --
> 2.43.0
>