linux-kernel - Re: [PATCH] libbpf: add specific btf name info when do core

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Message-ID: <CAEf4BzYJeEViQaRJb6u06GJSLa6uBmykRZa4JnWJ9VXw+WoX2g@mail.gmail.com>
Date: Thu, 21 Mar 2024 11:52:34 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Tao Chen <chen.dylane@...il.com>
Cc: Andrii Nakryiko <andrii@...nel.org>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] libbpf: add specific btf name info when do core

On Thu, Mar 21, 2024 at 10:04 AM Tao Chen <chen.dylane@...il.com> wrote:
>
> No logic changed, just add specific btf name when core info
> print, maybe it seems more understandable.
>
> Signed-off-by: Tao Chen <chen.dylane@...il.com>
> ---
>  tools/lib/bpf/libbpf.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
>

Can you elaborate on what problem you are trying to solve?
Conceptually libbpf does look for types in vmlinux (meaning main
kernel BTF), even if user overrides BTF location (presumably because
of old kernel). So even when we emit "vmlinux" in logs, it seems
correct.

pw-bot: cr


> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index afd09571c482..b32154288b4a 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -5653,7 +5653,8 @@ static int load_module_btfs(struct bpf_object *obj)
>  }
>
>  static struct bpf_core_cand_list *
> -bpf_core_find_cands(struct bpf_object *obj, const struct btf *local_btf, __u32 local_type_id)
> +bpf_core_find_cands(struct bpf_object *obj, const struct btf *local_btf, __u32 local_type_id,
> +                   const char *targ_btf_path)
>  {
>         struct bpf_core_cand local_cand = {};
>         struct bpf_core_cand_list *cands;
> @@ -5680,7 +5681,8 @@ bpf_core_find_cands(struct bpf_object *obj, const struct btf *local_btf, __u32 l
>
>         /* Attempt to find target candidates in vmlinux BTF first */
>         main_btf = obj->btf_vmlinux_override ?: obj->btf_vmlinux;
> -       err = bpf_core_add_cands(&local_cand, local_essent_len, main_btf, "vmlinux", 1, cands);
> +       err = bpf_core_add_cands(&local_cand, local_essent_len, main_btf,
> +                                targ_btf_path ?: "vmlinux", 1, cands);
>         if (err)
>                 goto err_out;
>
> @@ -5793,7 +5795,8 @@ static int bpf_core_resolve_relo(struct bpf_program *prog,
>                                  int relo_idx,
>                                  const struct btf *local_btf,
>                                  struct hashmap *cand_cache,
> -                                struct bpf_core_relo_res *targ_res)
> +                                struct bpf_core_relo_res *targ_res,
> +                                const char *targ_btf_path)
>  {
>         struct bpf_core_spec specs_scratch[3] = {};
>         struct bpf_core_cand_list *cands = NULL;
> @@ -5813,7 +5816,7 @@ static int bpf_core_resolve_relo(struct bpf_program *prog,
>
>         if (relo->kind != BPF_CORE_TYPE_ID_LOCAL &&
>             !hashmap__find(cand_cache, local_id, &cands)) {
> -               cands = bpf_core_find_cands(prog->obj, local_btf, local_id);
> +               cands = bpf_core_find_cands(prog->obj, local_btf, local_id, targ_btf_path);
>                 if (IS_ERR(cands)) {
>                         pr_warn("prog '%s': relo #%d: target candidate search failed for [%d] %s %s: %ld\n",
>                                 prog_name, relo_idx, local_id, btf_kind_str(local_type),
> @@ -5920,7 +5923,8 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
>                         if (prog->obj->gen_loader)
>                                 continue;
>
> -                       err = bpf_core_resolve_relo(prog, rec, i, obj->btf, cand_cache, &targ_res);
> +                       err = bpf_core_resolve_relo(prog, rec, i, obj->btf, cand_cache, &targ_res,
> +                                                   targ_btf_path);
>                         if (err) {
>                                 pr_warn("prog '%s': relo #%d: failed to relocate: %d\n",
>                                         prog->name, i, err);
> --
> 2.34.1
>