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From: "Mauricio Vásquez" <mauricio@kinvolk.io>
To: netdev@vger.kernel.org, bpf@vger.kernel.org
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Quentin Monnet <quentin@isovalent.com>,
	Rafael David Tinoco <rafaeldtinoco@gmail.com>,
	Lorenzo Fontana <lorenzo.fontana@elastic.co>,
	Leonardo Di Donato <leonardo.didonato@elastic.co>
Subject: [PATCH bpf-next v7 0/7] libbpf: Implement BTFGen
Date: Tue, 15 Feb 2022 17:58:49 -0500	[thread overview]
Message-ID: <20220215225856.671072-1-mauricio@kinvolk.io> (raw)

CO-RE requires to have BTF information describing the kernel types in
order to perform the relocations. This is usually provided by the kernel
itself when it's configured with CONFIG_DEBUG_INFO_BTF. However, this
configuration is not enabled in all the distributions and it's not
available on kernels before 5.12.

It's possible to use CO-RE in kernels without CONFIG_DEBUG_INFO_BTF
support by providing the BTF information from an external source.
BTFHub[0] contains BTF files to each released kernel not supporting BTF,
for the most popular distributions.

Providing this BTF file for a given kernel has some challenges:
1. Each BTF file is a few MBs big, then it's not possible to ship the
eBPF program with all the BTF files needed to run in different kernels.
(The BTF files will be in the order of GBs if you want to support a high
number of kernels)
2. Downloading the BTF file for the current kernel at runtime delays the
start of the program and it's not always possible to reach an external
host to download such a file.

Providing the BTF file with the information about all the data types of
the kernel for running an eBPF program is an overkill in many of the
cases. Usually the eBPF programs access only some kernel fields.

This series implements BTFGen support in bpftool. This idea was
discussed during the "Towards truly portable eBPF"[1] presentation at
Linux Plumbers 2021.

There is a good example[2] on how to use BTFGen and BTFHub together
to generate multiple BTF files, to each existing/supported kernel,
tailored to one application. For example: a complex bpf object might
support nearly 400 kernels by having BTF files summing only 1.5 MB.

[0]: https://github.com/aquasecurity/btfhub/
[1]: https://www.youtube.com/watch?v=igJLKyP1lFk&t=2418s
[2]: https://github.com/aquasecurity/btfhub/tree/main/tools

v6 > v7:
- use array instead of hashmap to store ids
- use btf__add_{struct,union}() instead of memcpy()
- don't use fixed path for testing BTF file
- update example to use DECLARE_LIBBPF_OPTS()

v5 > v6:
- use BTF structure to store used member/types instead of hashmaps
- remove support for input/output folders
- remove bpf_core_{created,free}_cand_cache()
- reorganize commits to avoid having unused static functions
- remove usage of libbpf_get_error()
- fix some errno propagation issues
- do not record full types for type-based relocations
- add support for BTF_KIND_FUNC_PROTO
- implement tests based on core_reloc ones

v4 > v5:
- move some checks before invoking prog->obj->gen_loader
- use p_info() instead of printf()
- improve command output
- fix issue with record_relo_core()
- implement bash completion
- write man page
- implement some tests

v3 > v4:
- parse BTF and BTF.ext sections in bpftool and use
  bpf_core_calc_relo_insn() directly
- expose less internal details from libbpf to bpftool
- implement support for enum-based relocations
- split commits in a more granular way

v2 > v3:
- expose internal libbpf APIs to bpftool instead
- implement btfgen in bpftool
- drop btf__raw_data() from libbpf

v1 > v2:
- introduce bpf_object__prepare() and ‘record_core_relos’ to expose
  CO-RE relocations instead of bpf_object__reloc_info_gen()
- rename btf__save_to_file() to btf__raw_data()

v1: https://lore.kernel.org/bpf/20211027203727.208847-1-mauricio@kinvolk.io/
v2: https://lore.kernel.org/bpf/20211116164208.164245-1-mauricio@kinvolk.io/
v3: https://lore.kernel.org/bpf/20211217185654.311609-1-mauricio@kinvolk.io/
v4: https://lore.kernel.org/bpf/20220112142709.102423-1-mauricio@kinvolk.io/
v5: https://lore.kernel.org/bpf/20220128223312.1253169-1-mauricio@kinvolk.io/
v6: https://lore.kernel.org/bpf/20220209222646.348365-1-mauricio@kinvolk.io/

Mauricio Vásquez (6):
  libbpf: split bpf_core_apply_relo()
  libbpf: Expose bpf_core_{add,free}_cands() to bpftool
  bpftool: Add gen min_core_btf command
  bpftool: Implement "gen min_core_btf" logic
  bpftool: Implement btfgen_get_btf()
  selftests/bpf: Test "bpftool gen min_core_btf"

Rafael David Tinoco (1):
  bpftool: gen min_core_btf explanation and examples

 kernel/bpf/btf.c                              |  13 +-
 .../bpf/bpftool/Documentation/bpftool-gen.rst |  91 +++
 tools/bpf/bpftool/Makefile                    |   8 +-
 tools/bpf/bpftool/bash-completion/bpftool     |   6 +-
 tools/bpf/bpftool/gen.c                       | 591 +++++++++++++++++-
 tools/lib/bpf/libbpf.c                        |  88 +--
 tools/lib/bpf/libbpf_internal.h               |   9 +
 tools/lib/bpf/relo_core.c                     |  79 +--
 tools/lib/bpf/relo_core.h                     |  42 +-
 .../selftests/bpf/prog_tests/core_reloc.c     |  50 +-
 10 files changed, 864 insertions(+), 113 deletions(-)


             reply	other threads:[~2022-02-15 22:59 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-15 22:58 Mauricio Vásquez [this message]
2022-02-15 22:58 ` [PATCH bpf-next v7 1/7] libbpf: split bpf_core_apply_relo() Mauricio Vásquez
2022-02-16  1:52   ` Alexei Starovoitov
2022-02-15 22:58 ` [PATCH bpf-next v7 2/7] libbpf: Expose bpf_core_{add,free}_cands() to bpftool Mauricio Vásquez
2022-02-15 22:58 ` [PATCH bpf-next v7 3/7] bpftool: Add gen min_core_btf command Mauricio Vásquez
2022-02-15 22:58 ` [PATCH bpf-next v7 4/7] bpftool: Implement "gen min_core_btf" logic Mauricio Vásquez
2022-02-18 16:20   ` Quentin Monnet
2022-02-18 19:43     ` Mauricio Vásquez Bernal
2022-02-18 19:48       ` Andrii Nakryiko
2022-02-18 19:52         ` Quentin Monnet
2022-02-15 22:58 ` [PATCH bpf-next v7 5/7] bpftool: Implement btfgen_get_btf() Mauricio Vásquez
2022-02-16 18:20   ` Andrii Nakryiko
2022-02-15 22:58 ` [PATCH bpf-next v7 6/7] bpftool: gen min_core_btf explanation and examples Mauricio Vásquez
2022-02-16 18:20   ` Andrii Nakryiko
2022-02-15 22:58 ` [PATCH bpf-next v7 7/7] selftests/bpf: Test "bpftool gen min_core_btf" Mauricio Vásquez
2022-02-16 18:20   ` Andrii Nakryiko
2022-02-16 18:20 ` [PATCH bpf-next v7 0/7] libbpf: Implement BTFGen Andrii Nakryiko
2022-02-17 22:07   ` Mauricio Vásquez Bernal
2022-02-17 22:12     ` Andrii Nakryiko
2022-02-16 18:30 ` patchwork-bot+netdevbpf

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