netdev - Re: [PATCH bpf-next v4 6/8] bpftool: Implement btfgen()

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Date:   Fri, 14 Jan 2022 18:15:15 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Mauricio Vásquez <mauricio@...volk.io>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Quentin Monnet <quentin@...valent.com>,
        Rafael David Tinoco <rafaeldtinoco@...il.com>,
        Lorenzo Fontana <lorenzo.fontana@...stic.co>,
        Leonardo Di Donato <leonardo.didonato@...stic.co>
Subject: Re: [PATCH bpf-next v4 6/8] bpftool: Implement btfgen()

On Wed, Jan 12, 2022 at 6:27 AM Mauricio Vásquez <mauricio@...volk.io> wrote:
>
> btfgen() receives the path of a source and destination BTF files and a
> list of BPF objects. This function records the relocations for all
> objects and then generates the BTF file by calling btfgen_get_btf()
> (implemented in the following commits).
>
> btfgen_record_obj() loads the BTF and BTF.ext sections of the BPF
> objects and loops through all CO-RE relocations. It uses
> bpf_core_calc_relo_insn() from libbpf and passes the target spec to
> btfgen_record_reloc() that saves the types involved in such relocation.
>
> Signed-off-by: Mauricio Vásquez <mauricio@...volk.io>
> Signed-off-by: Rafael David Tinoco <rafael.tinoco@...asec.com>
> Signed-off-by: Lorenzo Fontana <lorenzo.fontana@...stic.co>
> Signed-off-by: Leonardo Di Donato <leonardo.didonato@...stic.co>
> ---
>  tools/bpf/bpftool/gen.c | 221 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 219 insertions(+), 2 deletions(-)
>

[...]

> +       info = btfgen_new_info(src_btf);
> +       if (!info) {
> +               p_err("failed to allocate info structure: %s", strerror(errno));
> +               err = -errno;
> +               goto out;
> +       }
> +
> +       for (int i = 0; objspaths[i] != NULL; i++) {
> +               printf("OBJ : %s\n", objspaths[i]);

same as in previous patches, OBJ, DBTF, that's quite cryptic. Is this
used for some parsing of the output or it's just debugging leftovers?

> +
> +               err = btfgen_record_obj(info, objspaths[i]);
> +               if (err)
> +                       goto out;
> +       }
> +
> +       btf_new = btfgen_get_btf(info);
> +       if (!btf_new) {
> +               err = -errno;
> +               p_err("error generating btf: %s", strerror(errno));
> +               goto out;
> +       }
> +
> +       printf("DBTF: %s\n", dst_btf);
> +       err = btf_save_raw(btf_new, dst_btf);
> +       if (err) {
> +               p_err("error saving btf file: %s", strerror(errno));
> +               goto out;
> +       }
> +
> +out:
> +       btf__free(btf_new);
> +       btfgen_free_info(info);
> +
> +       return err;
> +}
> +
>  static int is_file(const char *path)
>  {
>         struct stat st;
> --
> 2.25.1
>