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

[Tao Chen <chen.dylane@xxxxxxxxx>]

Hi, Nakryiko, thank you for your reply. I try to familiarize with core 
in libbpf， the debug info is really helpful for me. But i use the old 
kernel btf, so origion debuginfo like:
 struct task_struct___x: found target candidate [130] struct 
task_struct in [vmlinux]
I think it may be more clear, if we print btf name when we use old 
kernel btf like:
 struct task_struct___x: found target candidate [130] struct 
task_struct in [/boot/***.btf]
The patch just solve debug info show for newbies above.

在 2024/3/22 上午2:52, Andrii Nakryiko 写道:
> On Thu, Mar 21, 2024 at 10:04 AM Tao Chen <chen.dylane@xxxxxxxxx> 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@xxxxxxxxx>
> > ---
> >   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