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 v6 6/7] bpftool: gen min_core_btf explanation and examples
Date: Wed, 9 Feb 2022 17:26:45 -0500 [thread overview]
Message-ID: <20220209222646.348365-7-mauricio@kinvolk.io> (raw)
In-Reply-To: <20220209222646.348365-1-mauricio@kinvolk.io>
From: Rafael David Tinoco <rafaeldtinoco@gmail.com>
Add "min_core_btf" feature explanation and one example of how to use it
to bpftool-gen man page.
Signed-off-by: Mauricio Vásquez <mauricio@kinvolk.io>
Signed-off-by: Rafael David Tinoco <rafael.tinoco@aquasec.com>
Signed-off-by: Lorenzo Fontana <lorenzo.fontana@elastic.co>
Signed-off-by: Leonardo Di Donato <leonardo.didonato@elastic.co>
---
.../bpf/bpftool/Documentation/bpftool-gen.rst | 93 +++++++++++++++++++
1 file changed, 93 insertions(+)
diff --git a/tools/bpf/bpftool/Documentation/bpftool-gen.rst b/tools/bpf/bpftool/Documentation/bpftool-gen.rst
index bc276388f432..4e654b16dfd0 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-gen.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-gen.rst
@@ -25,6 +25,7 @@ GEN COMMANDS
| **bpftool** **gen object** *OUTPUT_FILE* *INPUT_FILE* [*INPUT_FILE*...]
| **bpftool** **gen skeleton** *FILE* [**name** *OBJECT_NAME*]
+| **bpftool** **gen min_core_btf** *INPUT* *OUTPUT* *OBJECT* [*OBJECT*...]
| **bpftool** **gen help**
DESCRIPTION
@@ -149,6 +150,26 @@ DESCRIPTION
(non-read-only) data from userspace, with same simplicity
as for BPF side.
+ **bpftool** **gen min_core_btf** *INPUT* *OUTPUT* *OBJECT* [*OBJECT*...]
+ Generate a minimum BTF file as *OUTPUT*, derived from a given
+ *INPUT* BTF file, containing all needed BTF types so one, or
+ more, given eBPF objects CO-RE relocations may be satisfied.
+
+ When kernels aren't compiled with CONFIG_DEBUG_INFO_BTF,
+ libbpf, when loading an eBPF object, has to rely in external
+ BTF files to be able to calculate CO-RE relocations.
+
+ Usually, an external BTF file is built from existing kernel
+ DWARF data using pahole. It contains all the types used by
+ its respective kernel image and, because of that, is big.
+
+ The min_core_btf feature builds smaller BTF files, customized
+ to one or multiple eBPF objects, so they can be distributed
+ together with an eBPF CO-RE based application, turning the
+ application portable to different kernel versions.
+
+ Check examples bellow for more information how to use it.
+
**bpftool gen help**
Print short help message.
@@ -215,7 +236,9 @@ This is example BPF application with two BPF programs and a mix of BPF maps
and global variables. Source code is split across two source code files.
**$ clang -target bpf -g example1.bpf.c -o example1.bpf.o**
+
**$ clang -target bpf -g example2.bpf.c -o example2.bpf.o**
+
**$ bpftool gen object example.bpf.o example1.bpf.o example2.bpf.o**
This set of commands compiles *example1.bpf.c* and *example2.bpf.c*
@@ -329,3 +352,73 @@ BPF ELF object file *example.bpf.o*.
my_static_var: 7
This is a stripped-out version of skeleton generated for above example code.
+
+min_core_btf
+------------
+
+**$ bpftool btf dump file ./5.4.0-example.btf format raw**
+
+::
+
+ [1] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
+ [2] CONST '(anon)' type_id=1
+ [3] VOLATILE '(anon)' type_id=1
+ [4] ARRAY '(anon)' type_id=1 index_type_id=21 nr_elems=2
+ [5] PTR '(anon)' type_id=8
+ [6] CONST '(anon)' type_id=5
+ [7] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=(none)
+ [8] CONST '(anon)' type_id=7
+ [9] INT 'unsigned int' size=4 bits_offset=0 nr_bits=32 encoding=(none)
+ <long output>
+
+**$ bpftool btf dump file ./one.bpf.o format raw**
+
+::
+
+ [1] PTR '(anon)' type_id=2
+ [2] STRUCT 'trace_event_raw_sys_enter' size=64 vlen=4
+ 'ent' type_id=3 bits_offset=0
+ 'id' type_id=7 bits_offset=64
+ 'args' type_id=9 bits_offset=128
+ '__data' type_id=12 bits_offset=512
+ [3] STRUCT 'trace_entry' size=8 vlen=4
+ 'type' type_id=4 bits_offset=0
+ 'flags' type_id=5 bits_offset=16
+ 'preempt_count' type_id=5 bits_offset=24
+ <long output>
+
+**$ bpftool gen min_core_btf ./5.4.0-example.btf ./5.4.0-smaller.btf ./one.bpf.o**
+
+**$ bpftool btf dump file ./5.4.0-smaller.btf format raw**
+
+::
+
+ [1] TYPEDEF 'pid_t' type_id=6
+ [2] STRUCT 'trace_event_raw_sys_enter' size=64 vlen=1
+ 'args' type_id=4 bits_offset=128
+ [3] STRUCT 'task_struct' size=9216 vlen=2
+ 'pid' type_id=1 bits_offset=17920
+ 'real_parent' type_id=7 bits_offset=18048
+ [4] ARRAY '(anon)' type_id=5 index_type_id=8 nr_elems=6
+ [5] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
+ [6] TYPEDEF '__kernel_pid_t' type_id=8
+ [7] PTR '(anon)' type_id=3
+ [8] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
+ <end>
+
+Now, the "5.4.0-smaller.btf" file may be used by libbpf as an external BTF file
+when loading the "one.bpf.o" object into the "5.4.0-example" kernel. Note that
+the generated BTF file won't allow other eBPF objects to be loaded, just the
+ones given to min_core_btf.
+
+::
+
+ struct bpf_object *obj = NULL;
+ struct bpf_object_open_opts openopts = {};
+
+ openopts.sz = sizeof(struct bpf_object_open_opts);
+ openopts.btf_custom_path = "./5.4.0-smaller.btf";
+
+ obj = bpf_object__open_file("./one.bpf.o", &openopts);
+
+ ...
--
2.25.1
next prev parent reply other threads:[~2022-02-09 22:28 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-09 22:26 [PATCH bpf-next v6 0/7] libbpf: Implement BTFGen Mauricio Vásquez
2022-02-09 22:26 ` [PATCH bpf-next v6 1/7] libbpf: split bpf_core_apply_relo() Mauricio Vásquez
2022-02-12 0:42 ` Andrii Nakryiko
2022-02-09 22:26 ` [PATCH bpf-next v6 2/7] libbpf: Expose bpf_core_{add,free}_cands() to bpftool Mauricio Vásquez
2022-02-12 0:42 ` Andrii Nakryiko
2022-02-09 22:26 ` [PATCH bpf-next v6 3/7] bpftool: Add gen min_core_btf command Mauricio Vásquez
2022-02-12 0:42 ` Andrii Nakryiko
2022-02-09 22:26 ` [PATCH bpf-next v6 4/7] bpftool: Implement minimize_btf() and relocations recording for BTFGen Mauricio Vásquez
2022-02-12 0:42 ` Andrii Nakryiko
2022-02-15 22:56 ` Mauricio Vásquez Bernal
2022-02-16 1:23 ` Andrii Nakryiko
2022-02-09 22:26 ` [PATCH bpf-next v6 5/7] bpftool: Implement btfgen_get_btf() Mauricio Vásquez
2022-02-12 0:42 ` Andrii Nakryiko
2022-02-15 22:56 ` Mauricio Vásquez Bernal
2022-02-09 22:26 ` Mauricio Vásquez [this message]
2022-02-12 0:42 ` [PATCH bpf-next v6 6/7] bpftool: gen min_core_btf explanation and examples Andrii Nakryiko
2022-02-15 22:56 ` Mauricio Vásquez Bernal
2022-02-16 1:26 ` Andrii Nakryiko
2022-02-09 22:26 ` [PATCH bpf-next v6 7/7] selftests/bpf: Test "bpftool gen min_core_btf" Mauricio Vásquez
2022-02-12 0:42 ` Andrii Nakryiko
2022-02-15 22:56 ` Mauricio Vásquez Bernal
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20220209222646.348365-7-mauricio@kinvolk.io \
--to=mauricio@kinvolk.io \
--cc=andrii@kernel.org \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=leonardo.didonato@elastic.co \
--cc=lorenzo.fontana@elastic.co \
--cc=netdev@vger.kernel.org \
--cc=quentin@isovalent.com \
--cc=rafaeldtinoco@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).