netdev - Re: [PATCH v2 bpf-next 1/9] libbpf: generalize libbpf externs support

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Date:   Fri, 19 Jun 2020 14:57:09 -0700
From:   Hao Luo <haoluo@...gle.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Kernel Team <kernel-team@...com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Song Liu <songliubraving@...com>,
        Quentin Monnet <quentin@...valent.com>
Subject: Re: [PATCH v2 bpf-next 1/9] libbpf: generalize libbpf externs support

Only two small places on this version, otherwise it looks good to me.
I can offer my reviewed-by, if need. :)

Thanks for the patch!

Reviewed-by: Hao Luo <haoluo@...gle.com>

On Fri, Jun 19, 2020 at 1:34 PM Andrii Nakryiko <andriin@...com> wrote:
>
> Switch existing Kconfig externs to be just one of few possible kinds of more
> generic externs. This refactoring is in preparation for ksymbol extern
> support, added in the follow up patch. There are no functional changes
> intended.
>
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---

[...]

> @@ -2756,23 +2796,29 @@ static int cmp_externs(const void *_a, const void *_b)

[...]

> +
> +       if (a->type == EXT_KCFG) {
> +               /* descending order by alignment requirements */
> +               if (a->kcfg.align != b->kcfg.align)
> +                       return a->kcfg.align > b->kcfg.align ? -1 : 1;
> +               /* ascending order by size, within same alignment class */
> +               if (a->kcfg.sz != b->kcfg.sz)
> +                       return a->kcfg.sz < b->kcfg.sz ? -1 : 1;
> +               /* resolve ties by name */
> +       }
> +
>         return strcmp(a->name, b->name);
>  }

I assume the comment /* resolve ties by name */ is intended to be
close to strcmp?

> @@ -2818,22 +2864,39 @@ static int bpf_object__collect_externs(struct bpf_object *obj)
>                 ext->name = btf__name_by_offset(obj->btf, t->name_off);
>                 ext->sym_idx = i;
>                 ext->is_weak = GELF_ST_BIND(sym.st_info) == STB_WEAK;
> -               ext->sz = btf__resolve_size(obj->btf, t->type);
> -               if (ext->sz <= 0) {
> -                       pr_warn("failed to resolve size of extern '%s': %d\n",
> -                               ext_name, ext->sz);
> -                       return ext->sz;
> -               }
> -               ext->align = btf__align_of(obj->btf, t->type);
> -               if (ext->align <= 0) {
> -                       pr_warn("failed to determine alignment of extern '%s': %d\n",
> -                               ext_name, ext->align);
> -                       return -EINVAL;
> -               }
> -               ext->type = find_extern_type(obj->btf, t->type,
> -                                            &ext->is_signed);
> -               if (ext->type == EXT_UNKNOWN) {
> -                       pr_warn("extern '%s' type is unsupported\n", ext_name);
> +
> +               ext->sec_btf_id = find_extern_sec_btf_id(obj->btf, ext->btf_id);
> +               if (ext->btf_id <= 0) {
> +                       pr_warn("failed to find BTF for extern '%s' [%d] section: %d\n",
> +                               ext_name, ext->btf_id, ext->sec_btf_id);
> +                       return ext->sec_btf_id;
> +               }

Did you mean "ext->sec_btf_id <= 0" rather than "ext->btf_id <= 0"?