bpftool/Documentation/bpftool-gen.rst

1 .. SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
4 bpftool-gen
6 -------------------------------------------------------------------------------
7 tool for BPF code-generation
8 -------------------------------------------------------------------------------
17 	**bpftool** [*OPTIONS*] **gen** *COMMAND*
19 	*OPTIONS* := { |COMMON_OPTIONS| | { **-L** | **--use-loader** } }
23 GEN COMMANDS
26 |	**bpftool** **gen object** *OUTPUT_FILE* *INPUT_FILE* [*INPUT_FILE*...]
27 |	**bpftool** **gen skeleton** *FILE* [**name** *OBJECT_NAME*]
28 |	**bpftool** **gen subskeleton** *FILE* [**name** *OBJECT_NAME*]
29 |	**bpftool** **gen min_core_btf** *INPUT* *OUTPUT* *OBJECT* [*OBJECT*...]
30 |	**bpftool** **gen help**
34 	**bpftool gen object** *OUTPUT_FILE* *INPUT_FILE* [*INPUT_FILE*...]
40 		  user-space object files, but in addition to combining data
50 		  generated BPF skeleton (with **gen skeleton** command) or
54 	**bpftool gen skeleton** *FILE*
74 		  user in pre-allocated fields in skeleton struct. For BPF
77 		  in per-program link field. All such set up links will be
84 		  global variables of all supported kinds: mutable, read-only,
85 		  as well as extern ones. This interface allows to pre-setup
87 		  verified by kernel. For non-read-only variables, the same
94 		  object file are matching 1-to-1 and always stay in sync.
95 		  Generated code is dual-licensed under LGPL-2.1 and
96 		  BSD-2-Clause licenses.
113 		  - **example__open** and **example__open_opts**.
119 		  - **example__load**.
124 		  - **example__open_and_load** combines **example__open** and
128 		  - **example__attach** and **example__detach**
131 		    programs of types supported by libbpf for auto-attachment
132 		    will be auto-attached and their corresponding BPF links
139 		  - **example__destroy**
149 		  Afterwards, if target kernel supports memory-mapped BPF
151 		  (non-read-only) data from userspace, with same simplicity
154 	**bpftool gen subskeleton** *FILE*
170 		  - **example__open(bpf_object\*)**
174 		  - **example__destroy()**
178 	**bpftool** **gen min_core_btf** *INPUT* *OUTPUT* *OBJECT* [*OBJECT*...]
181 		  more, given eBPF objects CO-RE relocations may be satisfied.
185 		  BTF files to be able to calculate CO-RE relocations.
193 		  together with an eBPF CO-RE based application, turning the
198 	**bpftool gen help**
205 	-L, --use-loader
263 **$ clang --target=bpf -g example1.bpf.c -o example1.bpf.o**
265 **$ clang --target=bpf -g example2.bpf.c -o example2.bpf.o**
267 **$ bpftool gen object example.bpf.o example1.bpf.o example2.bpf.o**
273 **$ bpftool gen skeleton example.bpf.o name example | tee example.skel.h**
277   /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
343   	skel->rodata->param1 = 128;
354   	printf("my_map name: %s\n", bpf_map__name(skel->maps.my_map));
356   	       bpf_program__fd(skel->progs.handle_sys_enter));
358   	/* detach and re-attach sys_exit program */
359   	bpf_link__destroy(skel->links.handle_sys_exit);
360   	skel->links.handle_sys_exit =
361   		bpf_program__attach(skel->progs.handle_sys_exit);
364   	       skel->bss->handle_sys_enter_my_static_var);
379 This is a stripped-out version of skeleton generated for above example code.
382 ------------
384 **$ bpftool btf dump file 5.4.0-example.btf format raw**
389   [2] CONST '(anon)' type_id=1
391   [4] ARRAY '(anon)' type_id=1 index_type_id=21 nr_elems=2
403   [1] PTR '(anon)' type_id=2
404   [2] STRUCT 'trace_event_raw_sys_enter' size=64 vlen=4
415 **$ bpftool gen min_core_btf 5.4.0-example.btf 5.4.0-smaller.btf one.bpf.o**
417 **$ bpftool btf dump file 5.4.0-smaller.btf format raw**
422   [2] STRUCT 'trace_event_raw_sys_enter' size=64 vlen=1
424   [3] STRUCT 'task_struct' size=9216 vlen=2
434 Now, the "5.4.0-smaller.btf" file may be used by libbpf as an external BTF file
435 when loading the "one.bpf.o" object into the "5.4.0-example" kernel. Note that
441   LIBBPF_OPTS(bpf_object_open_opts, opts, .btf_custom_path = "5.4.0-smaller.btf");