netdev - Re: [PATCHv3 bpf-next 3/7] bpf: Add bpf_get_func

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Date:   Wed, 7 Jul 2021 17:06:17 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>,
        kernel test robot <lkp@...el.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alan Maguire <alan.maguire@...cle.com>
Subject: Re: [PATCHv3 bpf-next 3/7] bpf: Add bpf_get_func_ip helper for
 tracing programs

On Wed, Jul 7, 2021 at 2:53 PM Jiri Olsa <jolsa@...hat.com> wrote:
>
> Adding bpf_get_func_ip helper for BPF_PROG_TYPE_TRACING programs,
> specifically for all trampoline attach types.
>
> The trampoline's caller IP address is stored in (ctx - 8) address.
> so there's no reason to actually call the helper, but rather fixup
> the call instruction and return [ctx - 8] value directly (suggested
> by Alexei).
>
> [fixed has_get_func_ip wrong return type]
> Reported-by: kernel test robot <lkp@...el.com>
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  include/uapi/linux/bpf.h       |  7 +++++
>  kernel/bpf/verifier.c          | 53 ++++++++++++++++++++++++++++++++++
>  kernel/trace/bpf_trace.c       | 15 ++++++++++
>  tools/include/uapi/linux/bpf.h |  7 +++++
>  4 files changed, 82 insertions(+)
>

[...]

>  static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
>                              int *insn_idx_p)
>  {
> @@ -6225,6 +6256,12 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
>         if (func_id == BPF_FUNC_get_stackid || func_id == BPF_FUNC_get_stack)
>                 env->prog->call_get_stack = true;
>
> +       if (func_id == BPF_FUNC_get_func_ip) {
> +               if (has_get_func_ip(env))

from has_xxx name I'd expect it returns true/false, so this reads
super confusing. check_get_func_ip would be a bit more consistent with
other cases like this (still reads confusing to me, but that's ok)

> +                       return -ENOTSUPP;
> +               env->prog->call_get_func_ip = true;
> +       }
> +
>         if (changes_data)
>                 clear_all_pkt_pointers(env);
>         return 0;

[...]