netdev - Re: [PATCH bpf-next v4 2/3] libbpf: support detecting and attaching of writable tracepoint program

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Message-ID: <CAEf4Bzaf5qQOV7jA_U0+E3LhB0X57yJVL0ATqdr-Hui3Rz--=g@mail.gmail.com>
Date:   Fri, 1 Oct 2021 15:21:04 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Hou Tao <houtao1@...wei.com>
Cc:     Alexei Starovoitov <ast@...nel.org>, Yonghong Song <yhs@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next v4 2/3] libbpf: support detecting and attaching
 of writable tracepoint program

On Thu, Sep 30, 2021 at 2:00 AM Hou Tao <houtao1@...wei.com> wrote:
>
> Program on writable tracepoint is BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE,
> but its attachment is the same as BPF_PROG_TYPE_RAW_TRACEPOINT.
>
> Signed-off-by: Hou Tao <houtao1@...wei.com>
> ---
>  tools/lib/bpf/libbpf.c | 21 ++++++++++++++++-----
>  1 file changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 7544d7d09160..80faa53dff35 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -8005,6 +8005,8 @@ static const struct bpf_sec_def section_defs[] = {
>         SEC_DEF("tp/",                  TRACEPOINT, 0, SEC_NONE, attach_tp),
>         SEC_DEF("raw_tracepoint/",      RAW_TRACEPOINT, 0, SEC_NONE, attach_raw_tp),
>         SEC_DEF("raw_tp/",              RAW_TRACEPOINT, 0, SEC_NONE, attach_raw_tp),
> +       SEC_DEF("raw_tracepoint.w/",    RAW_TRACEPOINT_WRITABLE, 0, SEC_NONE, attach_raw_tp),
> +       SEC_DEF("raw_tp.w/",            RAW_TRACEPOINT_WRITABLE, 0, SEC_NONE, attach_raw_tp),
>         SEC_DEF("tp_btf/",              TRACING, BPF_TRACE_RAW_TP, SEC_ATTACH_BTF, attach_trace),
>         SEC_DEF("fentry/",              TRACING, BPF_TRACE_FENTRY, SEC_ATTACH_BTF, attach_trace),
>         SEC_DEF("fmod_ret/",            TRACING, BPF_MODIFY_RETURN, SEC_ATTACH_BTF, attach_trace),
> @@ -9762,12 +9764,21 @@ struct bpf_link *bpf_program__attach_raw_tracepoint(const struct bpf_program *pr
>
>  static struct bpf_link *attach_raw_tp(const struct bpf_program *prog, long cookie)
>  {
> -       const char *tp_name;
> +       static const char *prefixes[] = {
> +               "raw_tp/",
> +               "raw_tracepoint/",
> +               "raw_tp.w/",
> +               "raw_tracepoint.w/",
> +       };
> +       size_t i;
> +       const char *tp_name = NULL;
>
> -       if (str_has_pfx(prog->sec_name, "raw_tp/"))
> -               tp_name = prog->sec_name + sizeof("raw_tp/") - 1;
> -       else
> -               tp_name = prog->sec_name + sizeof("raw_tracepoint/") - 1;
> +       for (i = 0; i < ARRAY_SIZE(prefixes); i++) {
> +               if (str_has_pfx(prog->sec_name, prefixes[i])) {
> +                       tp_name = prog->sec_name + strlen(prefixes[i]);
> +                       break;
> +               }
> +       }

Let's add if (!tp_name) check here for the future if we forget to
update this prefixes list. It's going to be a really unpleasant
SIGSEGV otherwise.

>
>         return bpf_program__attach_raw_tracepoint(prog, tp_name);
>  }
> --
> 2.29.2
>