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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Song Liu <songliubraving@fb.com>
Cc: Song Liu <liu.song.a23@gmail.com>,
	Andrii Nakryiko <andriin@fb.com>, bpf <bpf@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>,
	Alexei Starovoitov <ast@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Kernel Team <Kernel-team@fb.com>
Subject: Re: [PATCH bpf-next 2/8] libbpf: extract BTF loading and simplify ELF parsing logic
Date: Mon, 17 Jun 2019 11:35:29 -0700
Message-ID: <CAEf4BzbP4Urmg3m-ynSv8XAVhhm-4Rk3+F7zguZ7E7-oGBuWOQ@mail.gmail.com> (raw)
In-Reply-To: <8F07D61C-2751-44A6-9E89-9BE6781FEF81@fb.com>

On Mon, Jun 17, 2019 at 11:07 AM Song Liu <songliubraving@fb.com> wrote:
>
>
>
> > On Jun 17, 2019, at 10:24 AM, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
> >
> > On Sat, Jun 15, 2019 at 1:26 PM Song Liu <liu.song.a23@gmail.com> wrote:
> >>
> >> On Mon, Jun 10, 2019 at 9:49 PM Andrii Nakryiko <andriin@fb.com> wrote:
> >>>
> >>> As a preparation for adding BTF-based BPF map loading, extract .BTF and
> >>> .BTF.ext loading logic. Also simplify error handling in
> >>> bpf_object__elf_collect() by returning early, as there is no common
> >>> clean up to be done.
> >>>
> >>> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
> >>> ---
> >>> tools/lib/bpf/libbpf.c | 137 ++++++++++++++++++++++-------------------
> >>> 1 file changed, 75 insertions(+), 62 deletions(-)
> >>>
> >>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> >>> index ba89d9727137..9e39a0a33aeb 100644
> >>> --- a/tools/lib/bpf/libbpf.c
> >>> +++ b/tools/lib/bpf/libbpf.c
> >>> @@ -1078,6 +1078,58 @@ static void bpf_object__sanitize_btf_ext(struct bpf_object *obj)
> >>>        }
> >>> }
> >>>
> >>> +static int bpf_object__load_btf(struct bpf_object *obj,
> >>> +                               Elf_Data *btf_data,
> >>> +                               Elf_Data *btf_ext_data)
> >>> +{
> >>> +       int err = 0;
> >>> +
> >>> +       if (btf_data) {
> >>> +               obj->btf = btf__new(btf_data->d_buf, btf_data->d_size);
> >>> +               if (IS_ERR(obj->btf)) {
> >>> +                       pr_warning("Error loading ELF section %s: %d.\n",
> >>> +                                  BTF_ELF_SEC, err);
> >>> +                       goto out;
> >>
> >> If we goto out here, we will return 0.
> >
> >
> > Yes, it's intentional. BTF is treated as optional, so if we fail to
> > load it, libbpf will emit warning, but will proceed as nothing
> > happened and no BTF was supposed to be loaded.
> >
> >>
> >>> +               }
> >>> +               err = btf__finalize_data(obj, obj->btf);
> >>> +               if (err) {
> >>> +                       pr_warning("Error finalizing %s: %d.\n",
> >>> +                                  BTF_ELF_SEC, err);
> >>> +                       goto out;
> >>> +               }
> >>> +               bpf_object__sanitize_btf(obj);
> >>> +               err = btf__load(obj->btf);
> >>> +               if (err) {
> >>> +                       pr_warning("Error loading %s into kernel: %d.\n",
> >>> +                                  BTF_ELF_SEC, err);
> >>> +                       goto out;
> >>> +               }
> >>> +       }
> >>> +       if (btf_ext_data) {
> >>> +               if (!obj->btf) {
> >>> +                       pr_debug("Ignore ELF section %s because its depending ELF section %s is not found.\n",
> >>> +                                BTF_EXT_ELF_SEC, BTF_ELF_SEC);
> >>> +                       goto out;
> >>
> >> We will also return 0 when goto out here.
> >
> >
> > See above, it's original behavior of libbpf.
> >
> >>
> >>> +               }
> >>> +               obj->btf_ext = btf_ext__new(btf_ext_data->d_buf,
> >>> +                                           btf_ext_data->d_size);
> >>> +               if (IS_ERR(obj->btf_ext)) {
> >>> +                       pr_warning("Error loading ELF section %s: %ld. Ignored and continue.\n",
> >>> +                                  BTF_EXT_ELF_SEC, PTR_ERR(obj->btf_ext));
> >>> +                       obj->btf_ext = NULL;
> >>> +                       goto out;
> >> And, here. And we will not free obj->btf.
> >
> > This is situation in which we successfully loaded .BTF, but failed to
> > load .BTF.ext. In that case we'll warn about .BTF.ext, but will drop
> > it and continue with .BTF only.
> >
>
> Yeah, that makes sense.
>
> Shall we let bpf_object__load_btf() return void? Since it always
> returns 0?

This is split into bpf_object__init_btf and
bpf_object__sanitize_and_load_btf in patch #6, both of which can
return errors. So probably not worth changing just for one patch.

>
> Thanks,
> Song
>
> <snip>
>

  reply index

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-11  4:47 [PATCH bpf-next 0/8] BTF-defined BPF map definitions Andrii Nakryiko
2019-06-11  4:47 ` [PATCH bpf-next 1/8] libbpf: add common min/max macro to libbpf_internal.h Andrii Nakryiko
2019-06-15 20:26   ` Song Liu
2019-06-11  4:47 ` [PATCH bpf-next 2/8] libbpf: extract BTF loading and simplify ELF parsing logic Andrii Nakryiko
2019-06-15 20:25   ` Song Liu
2019-06-15 20:28     ` Song Liu
2019-06-17 17:46       ` Andrii Nakryiko
2019-06-17 17:24     ` Andrii Nakryiko
2019-06-17 18:07       ` Song Liu
2019-06-17 18:35         ` Andrii Nakryiko [this message]
2019-06-11  4:47 ` [PATCH bpf-next 3/8] libbpf: refactor map initialization Andrii Nakryiko
2019-06-11  4:47 ` [PATCH bpf-next 4/8] libbpf: identify maps by section index in addition to offset Andrii Nakryiko
2019-06-11  4:47 ` [PATCH bpf-next 5/8] libbpf: split initialization and loading of BTF Andrii Nakryiko
2019-06-15 21:21   ` Song Liu
2019-06-11  4:47 ` [PATCH bpf-next 6/8] libbpf: allow specifying map definitions using BTF Andrii Nakryiko
2019-06-15 22:00   ` Song Liu
2019-06-17 18:33     ` Andrii Nakryiko
2019-06-11  4:47 ` [PATCH bpf-next 7/8] selftests/bpf: add test for BTF-defined maps Andrii Nakryiko
2019-06-15 22:05   ` Song Liu
2019-06-11  4:47 ` [PATCH bpf-next 8/8] selftests/bpf: switch tests to BTF-defined map definitions Andrii Nakryiko
2019-06-14 23:23   ` Stanislav Fomichev
2019-06-14 23:43     ` Andrii Nakryiko
2019-06-15  0:01       ` Stanislav Fomichev
2019-06-17 19:30         ` Andrii Nakryiko
2019-06-17 21:07           ` Stanislav Fomichev
2019-06-11  5:21 ` [PATCH bpf-next 0/8] BTF-defined BPF " Andrii Nakryiko

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