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

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Date:   Tue, 31 Aug 2021 19:59:31 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        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 Tue, Aug 31, 2021 at 7:27 PM Kumar Kartikeya Dwivedi
<memxor@...il.com> wrote:
> > > @@ -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?
> >
>
> That makes sense. This is all new to me, so I went with what was described in
> e6ac2450d6de (bpf: Support bpf program calling kernel function), but I'll rework
> it to encode the btf fd like that in the next spin. It also makes the everything
> far simpler.

Hmm. kfunc call is a call insn. There is no imm[1].