netdev - Re: [PATCH bpf-next v5 5/9] bpftool: Implement btfgen()

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Message-ID: <CAHap4zvBfyFYB8rQo_s3aXGAyG3hEwJ4Xsn4pdrPr5k=GhwQZA@mail.gmail.com>
Date:   Thu, 3 Feb 2022 14:10:05 -0500
From:   Mauricio Vásquez Bernal <mauricio@...volk.io>
To:     Quentin Monnet <quentin@...valent.com>
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>,
        Rafael David Tinoco <rafaeldtinoco@...il.com>,
        Lorenzo Fontana <lorenzo.fontana@...stic.co>,
        Leonardo Di Donato <leonardo.didonato@...stic.co>
Subject: Re: [PATCH bpf-next v5 5/9] bpftool: Implement btfgen()

On Tue, Feb 1, 2022 at 3:57 PM Quentin Monnet <quentin@...valent.com> wrote:
>
> 2022-01-28 17:33 UTC-0500 ~ Mauricio Vásquez <mauricio@...volk.io>
> > 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/Makefile |   8 +-
> >  tools/bpf/bpftool/gen.c    | 221 ++++++++++++++++++++++++++++++++++++-
> >  2 files changed, 223 insertions(+), 6 deletions(-)
> >
> > diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
> > index 83369f55df61..97d447135536 100644
> > --- a/tools/bpf/bpftool/Makefile
> > +++ b/tools/bpf/bpftool/Makefile
> > @@ -34,10 +34,10 @@ LIBBPF_BOOTSTRAP_INCLUDE := $(LIBBPF_BOOTSTRAP_DESTDIR)/include
> >  LIBBPF_BOOTSTRAP_HDRS_DIR := $(LIBBPF_BOOTSTRAP_INCLUDE)/bpf
> >  LIBBPF_BOOTSTRAP := $(LIBBPF_BOOTSTRAP_OUTPUT)libbpf.a
> >
> > -# We need to copy hashmap.h and nlattr.h which is not otherwise exported by
> > -# libbpf, but still required by bpftool.
> > -LIBBPF_INTERNAL_HDRS := $(addprefix $(LIBBPF_HDRS_DIR)/,hashmap.h nlattr.h)
> > -LIBBPF_BOOTSTRAP_INTERNAL_HDRS := $(addprefix $(LIBBPF_BOOTSTRAP_HDRS_DIR)/,hashmap.h)
> > +# We need to copy hashmap.h, nlattr.h, relo_core.h and libbpf_internal.h
> > +# which are not otherwise exported by libbpf, but still required by bpftool.
> > +LIBBPF_INTERNAL_HDRS := $(addprefix $(LIBBPF_HDRS_DIR)/,hashmap.h nlattr.h relo_core.h libbpf_internal.h)
> > +LIBBPF_BOOTSTRAP_INTERNAL_HDRS := $(addprefix $(LIBBPF_BOOTSTRAP_HDRS_DIR)/,hashmap.h relo_core.h libbpf_internal.h)
>
> Do you directly call functions from relo_core.h, or is it only required
> to compile libbpf_internal.h? (Asking because I'm wondering if there
> would be a way to have one fewer header copied).

bpf_core_calc_relo_insn() and bpf_core_calc_relo_insn() are used.