netdev - Re: [PATCH bpf-next RFC v1 3/8] libbpf: Support kernel module function calls

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Message-ID: <CAEf4Bza11W+NPt1guXj87fy_xcsWLHeFLNK0OkzL9A+TfcYhog@mail.gmail.com>
Date:   Tue, 31 Aug 2021 17:55:14 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next RFC v1 3/8] libbpf: Support kernel module
 function calls

On Mon, Aug 30, 2021 at 10:34 AM Kumar Kartikeya Dwivedi
<memxor@...il.com> wrote:
>

-ENOCOMMITMESSAGE?

> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
> ---
>  tools/lib/bpf/bpf.c             |  3 ++
>  tools/lib/bpf/libbpf.c          | 71 +++++++++++++++++++++++++++++++--
>  tools/lib/bpf/libbpf_internal.h |  2 +
>  3 files changed, 73 insertions(+), 3 deletions(-)
>

[...]

> @@ -515,6 +521,13 @@ struct bpf_object {
>         void *priv;
>         bpf_object_clear_priv_t clear_priv;
>
> +       struct {
> +               struct hashmap *map;
> +               int *fds;
> +               size_t cap_cnt;
> +               __u32 n_fds;
> +       } kfunc_btf_fds;
> +
>         char path[];
>  };
>  #define obj_elf_valid(o)       ((o)->efile.elf)
> @@ -5327,6 +5340,7 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog)
>                         ext = &obj->externs[relo->sym_off];
>                         insn[0].src_reg = BPF_PSEUDO_KFUNC_CALL;
>                         insn[0].imm = ext->ksym.kernel_btf_id;
> +                       insn[0].off = ext->ksym.offset;

Just a few lines above we use insn[1].imm =
ext->ksym.kernel_btf_obj_fd; for EXT_KSYM (for variables). Why are you
inventing a new form if we already have a pretty consistent pattern?

>                         break;
>                 case RELO_SUBPROG_ADDR:
>                         if (insn[0].src_reg != BPF_PSEUDO_FUNC) {

[...]