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

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Message-ID: <d1b23ebb-21ac-558b-36a8-918b0c6cf909@isovalent.com>
Date:   Tue, 1 Feb 2022 20:57:43 +0000
From:   Quentin Monnet <quentin@...valent.com>
To:     Mauricio Vásquez <mauricio@...volk.io>,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Cc:     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()

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).