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

On Tue, Feb 1, 2022 at 3:57 PM Quentin Monnet [off-list ref] wrote:

2022-01-28 17:33 UTC-0500 ~ Mauricio Vásquez [off-list ref]

quoted

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 <redacted>
Signed-off-by: Rafael David Tinoco <redacted>
Signed-off-by: Lorenzo Fontana <redacted>
Signed-off-by: Leonardo Di Donato <redacted>
---
 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.