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1================
2bpftool-gen
3================
4-------------------------------------------------------------------------------
5tool for BPF code-generation
6-------------------------------------------------------------------------------
7
8:Manual section: 8
9
10SYNOPSIS
11========
12
13 **bpftool** [*OPTIONS*] **gen** *COMMAND*
14
15 *OPTIONS* := { { **-j** | **--json** } [{ **-p** | **--pretty** }] }
16
17 *COMMAND* := { **object** | **skeleton** | **help** }
18
19GEN COMMANDS
20=============
21
22| **bpftool** **gen object** *OUTPUT_FILE* *INPUT_FILE* [*INPUT_FILE*...]
23| **bpftool** **gen skeleton** *FILE* [**name** *OBJECT_NAME*]
24| **bpftool** **gen help**
25
26DESCRIPTION
27===========
28 **bpftool gen object** *OUTPUT_FILE* *INPUT_FILE* [*INPUT_FILE*...]
29 Statically link (combine) together one or more *INPUT_FILE*'s
30 into a single resulting *OUTPUT_FILE*. All the files involved
31 are BPF ELF object files.
32
33 The rules of BPF static linking are mostly the same as for
34 user-space object files, but in addition to combining data
35 and instruction sections, .BTF and .BTF.ext (if present in
36 any of the input files) data are combined together. .BTF
37 data is deduplicated, so all the common types across
38 *INPUT_FILE*'s will only be represented once in the resulting
39 BTF information.
40
41 BPF static linking allows to partition BPF source code into
42 individually compiled files that are then linked into
43 a single resulting BPF object file, which can be used to
44 generated BPF skeleton (with **gen skeleton** command) or
45 passed directly into **libbpf** (using **bpf_object__open()**
46 family of APIs).
47
48 **bpftool gen skeleton** *FILE*
49 Generate BPF skeleton C header file for a given *FILE*.
50
51 BPF skeleton is an alternative interface to existing libbpf
52 APIs for working with BPF objects. Skeleton code is intended
53 to significantly shorten and simplify code to load and work
54 with BPF programs from userspace side. Generated code is
55 tailored to specific input BPF object *FILE*, reflecting its
56 structure by listing out available maps, program, variables,
57 etc. Skeleton eliminates the need to lookup mentioned
58 components by name. Instead, if skeleton instantiation
59 succeeds, they are populated in skeleton structure as valid
60 libbpf types (e.g., **struct bpf_map** pointer) and can be
61 passed to existing generic libbpf APIs.
62
63 In addition to simple and reliable access to maps and
64 programs, skeleton provides a storage for BPF links (**struct
65 bpf_link**) for each BPF program within BPF object. When
66 requested, supported BPF programs will be automatically
67 attached and resulting BPF links stored for further use by
68 user in pre-allocated fields in skeleton struct. For BPF
69 programs that can't be automatically attached by libbpf,
70 user can attach them manually, but store resulting BPF link
71 in per-program link field. All such set up links will be
72 automatically destroyed on BPF skeleton destruction. This
73 eliminates the need for users to manage links manually and
74 rely on libbpf support to detach programs and free up
75 resources.
76
77 Another facility provided by BPF skeleton is an interface to
78 global variables of all supported kinds: mutable, read-only,
79 as well as extern ones. This interface allows to pre-setup
80 initial values of variables before BPF object is loaded and
81 verified by kernel. For non-read-only variables, the same
82 interface can be used to fetch values of global variables on
83 userspace side, even if they are modified by BPF code.
84
85 During skeleton generation, contents of source BPF object
86 *FILE* is embedded within generated code and is thus not
87 necessary to keep around. This ensures skeleton and BPF
88 object file are matching 1-to-1 and always stay in sync.
89 Generated code is dual-licensed under LGPL-2.1 and
90 BSD-2-Clause licenses.
91
92 It is a design goal and guarantee that skeleton interfaces
93 are interoperable with generic libbpf APIs. User should
94 always be able to use skeleton API to create and load BPF
95 object, and later use libbpf APIs to keep working with
96 specific maps, programs, etc.
97
98 As part of skeleton, few custom functions are generated.
99 Each of them is prefixed with object name. Object name can
100 either be derived from object file name, i.e., if BPF object
101 file name is **example.o**, BPF object name will be
102 **example**. Object name can be also specified explicitly
103 through **name** *OBJECT_NAME* parameter. The following
104 custom functions are provided (assuming **example** as
105 the object name):
106
107 - **example__open** and **example__open_opts**.
108 These functions are used to instantiate skeleton. It
109 corresponds to libbpf's **bpf_object__open**\ () API.
110 **_opts** variants accepts extra **bpf_object_open_opts**
111 options.
112
113 - **example__load**.
114 This function creates maps, loads and verifies BPF
115 programs, initializes global data maps. It corresponds to
116 libppf's **bpf_object__load**\ () API.
117
118 - **example__open_and_load** combines **example__open** and
119 **example__load** invocations in one commonly used
120 operation.
121
122 - **example__attach** and **example__detach**
123 This pair of functions allow to attach and detach,
124 correspondingly, already loaded BPF object. Only BPF
125 programs of types supported by libbpf for auto-attachment
126 will be auto-attached and their corresponding BPF links
127 instantiated. For other BPF programs, user can manually
128 create a BPF link and assign it to corresponding fields in
129 skeleton struct. **example__detach** will detach both
130 links created automatically, as well as those populated by
131 user manually.
132
133 - **example__destroy**
134 Detach and unload BPF programs, free up all the resources
135 used by skeleton and BPF object.
136
137 If BPF object has global variables, corresponding structs
138 with memory layout corresponding to global data data section
139 layout will be created. Currently supported ones are: *.data*,
140 *.bss*, *.rodata*, and *.kconfig* structs/data sections.
141 These data sections/structs can be used to set up initial
142 values of variables, if set before **example__load**.
143 Afterwards, if target kernel supports memory-mapped BPF
144 arrays, same structs can be used to fetch and update
145 (non-read-only) data from userspace, with same simplicity
146 as for BPF side.
147
148 **bpftool gen help**
149 Print short help message.
150
151OPTIONS
152=======
153 .. include:: common_options.rst
154
155EXAMPLES
156========
157**$ cat example1.bpf.c**
158
159::
160
161 #include <stdbool.h>
162 #include <linux/ptrace.h>
163 #include <linux/bpf.h>
164 #include <bpf/bpf_helpers.h>
165
166 const volatile int param1 = 42;
167 bool global_flag = true;
168 struct { int x; } data = {};
169
170 SEC("raw_tp/sys_enter")
171 int handle_sys_enter(struct pt_regs *ctx)
172 {
173 static long my_static_var;
174 if (global_flag)
175 my_static_var++;
176 else
177 data.x += param1;
178 return 0;
179 }
180
181**$ cat example2.bpf.c**
182
183::
184
185 #include <linux/ptrace.h>
186 #include <linux/bpf.h>
187 #include <bpf/bpf_helpers.h>
188
189 struct {
190 __uint(type, BPF_MAP_TYPE_HASH);
191 __uint(max_entries, 128);
192 __type(key, int);
193 __type(value, long);
194 } my_map SEC(".maps");
195
196 SEC("raw_tp/sys_exit")
197 int handle_sys_exit(struct pt_regs *ctx)
198 {
199 int zero = 0;
200 bpf_map_lookup_elem(&my_map, &zero);
201 return 0;
202 }
203
204This is example BPF application with two BPF programs and a mix of BPF maps
205and global variables. Source code is split across two source code files.
206
207**$ clang -target bpf -g example1.bpf.c -o example1.bpf.o**
208**$ clang -target bpf -g example2.bpf.c -o example2.bpf.o**
209**$ bpftool gen object example.bpf.o example1.bpf.o example2.bpf.o**
210
211This set of commands compiles *example1.bpf.c* and *example2.bpf.c*
212individually and then statically links respective object files into the final
213BPF ELF object file *example.bpf.o*.
214
215**$ bpftool gen skeleton example.bpf.o name example | tee example.skel.h**
216
217::
218
219 /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
220
221 /* THIS FILE IS AUTOGENERATED! */
222 #ifndef __EXAMPLE_SKEL_H__
223 #define __EXAMPLE_SKEL_H__
224
225 #include <stdlib.h>
226 #include <bpf/libbpf.h>
227
228 struct example {
229 struct bpf_object_skeleton *skeleton;
230 struct bpf_object *obj;
231 struct {
232 struct bpf_map *rodata;
233 struct bpf_map *data;
234 struct bpf_map *bss;
235 struct bpf_map *my_map;
236 } maps;
237 struct {
238 struct bpf_program *handle_sys_enter;
239 struct bpf_program *handle_sys_exit;
240 } progs;
241 struct {
242 struct bpf_link *handle_sys_enter;
243 struct bpf_link *handle_sys_exit;
244 } links;
245 struct example__bss {
246 struct {
247 int x;
248 } data;
249 } *bss;
250 struct example__data {
251 _Bool global_flag;
252 long int handle_sys_enter_my_static_var;
253 } *data;
254 struct example__rodata {
255 int param1;
256 } *rodata;
257 };
258
259 static void example__destroy(struct example *obj);
260 static inline struct example *example__open_opts(
261 const struct bpf_object_open_opts *opts);
262 static inline struct example *example__open();
263 static inline int example__load(struct example *obj);
264 static inline struct example *example__open_and_load();
265 static inline int example__attach(struct example *obj);
266 static inline void example__detach(struct example *obj);
267
268 #endif /* __EXAMPLE_SKEL_H__ */
269
270**$ cat example.c**
271
272::
273
274 #include "example.skel.h"
275
276 int main()
277 {
278 struct example *skel;
279 int err = 0;
280
281 skel = example__open();
282 if (!skel)
283 goto cleanup;
284
285 skel->rodata->param1 = 128;
286
287 err = example__load(skel);
288 if (err)
289 goto cleanup;
290
291 err = example__attach(skel);
292 if (err)
293 goto cleanup;
294
295 /* all libbpf APIs are usable */
296 printf("my_map name: %s\n", bpf_map__name(skel->maps.my_map));
297 printf("sys_enter prog FD: %d\n",
298 bpf_program__fd(skel->progs.handle_sys_enter));
299
300 /* detach and re-attach sys_exit program */
301 bpf_link__destroy(skel->links.handle_sys_exit);
302 skel->links.handle_sys_exit =
303 bpf_program__attach(skel->progs.handle_sys_exit);
304
305 printf("my_static_var: %ld\n",
306 skel->bss->handle_sys_enter_my_static_var);
307
308 cleanup:
309 example__destroy(skel);
310 return err;
311 }
312
313**# ./example**
314
315::
316
317 my_map name: my_map
318 sys_enter prog FD: 8
319 my_static_var: 7
320
321This is a stripped-out version of skeleton generated for above example code.
1.. SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
2
3================
4bpftool-gen
5================
6-------------------------------------------------------------------------------
7tool for BPF code-generation
8-------------------------------------------------------------------------------
9
10:Manual section: 8
11
12.. include:: substitutions.rst
13
14SYNOPSIS
15========
16
17**bpftool** [*OPTIONS*] **gen** *COMMAND*
18
19*OPTIONS* := { |COMMON_OPTIONS| | { **-L** | **--use-loader** } }
20
21*COMMAND* := { **object** | **skeleton** | **help** }
22
23GEN COMMANDS
24=============
25
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**
31
32DESCRIPTION
33===========
34bpftool gen object *OUTPUT_FILE* *INPUT_FILE* [*INPUT_FILE*...]
35 Statically link (combine) together one or more *INPUT_FILE*'s into a single
36 resulting *OUTPUT_FILE*. All the files involved are BPF ELF object files.
37
38 The rules of BPF static linking are mostly the same as for user-space
39 object files, but in addition to combining data and instruction sections,
40 .BTF and .BTF.ext (if present in any of the input files) data are combined
41 together. .BTF data is deduplicated, so all the common types across
42 *INPUT_FILE*'s will only be represented once in the resulting BTF
43 information.
44
45 BPF static linking allows to partition BPF source code into individually
46 compiled files that are then linked into a single resulting BPF object
47 file, which can be used to generated BPF skeleton (with **gen skeleton**
48 command) or passed directly into **libbpf** (using **bpf_object__open()**
49 family of APIs).
50
51bpftool gen skeleton *FILE*
52 Generate BPF skeleton C header file for a given *FILE*.
53
54 BPF skeleton is an alternative interface to existing libbpf APIs for
55 working with BPF objects. Skeleton code is intended to significantly
56 shorten and simplify code to load and work with BPF programs from userspace
57 side. Generated code is tailored to specific input BPF object *FILE*,
58 reflecting its structure by listing out available maps, program, variables,
59 etc. Skeleton eliminates the need to lookup mentioned components by name.
60 Instead, if skeleton instantiation succeeds, they are populated in skeleton
61 structure as valid libbpf types (e.g., **struct bpf_map** pointer) and can
62 be passed to existing generic libbpf APIs.
63
64 In addition to simple and reliable access to maps and programs, skeleton
65 provides a storage for BPF links (**struct bpf_link**) for each BPF program
66 within BPF object. When requested, supported BPF programs will be
67 automatically attached and resulting BPF links stored for further use by
68 user in pre-allocated fields in skeleton struct. For BPF programs that
69 can't be automatically attached by libbpf, user can attach them manually,
70 but store resulting BPF link in per-program link field. All such set up
71 links will be automatically destroyed on BPF skeleton destruction. This
72 eliminates the need for users to manage links manually and rely on libbpf
73 support to detach programs and free up resources.
74
75 Another facility provided by BPF skeleton is an interface to global
76 variables of all supported kinds: mutable, read-only, as well as extern
77 ones. This interface allows to pre-setup initial values of variables before
78 BPF object is loaded and verified by kernel. For non-read-only variables,
79 the same interface can be used to fetch values of global variables on
80 userspace side, even if they are modified by BPF code.
81
82 During skeleton generation, contents of source BPF object *FILE* is
83 embedded within generated code and is thus not necessary to keep around.
84 This ensures skeleton and BPF object file are matching 1-to-1 and always
85 stay in sync. Generated code is dual-licensed under LGPL-2.1 and
86 BSD-2-Clause licenses.
87
88 It is a design goal and guarantee that skeleton interfaces are
89 interoperable with generic libbpf APIs. User should always be able to use
90 skeleton API to create and load BPF object, and later use libbpf APIs to
91 keep working with specific maps, programs, etc.
92
93 As part of skeleton, few custom functions are generated. Each of them is
94 prefixed with object name. Object name can either be derived from object
95 file name, i.e., if BPF object file name is **example.o**, BPF object name
96 will be **example**. Object name can be also specified explicitly through
97 **name** *OBJECT_NAME* parameter. The following custom functions are
98 provided (assuming **example** as the object name):
99
100 - **example__open** and **example__open_opts**.
101 These functions are used to instantiate skeleton. It corresponds to
102 libbpf's **bpf_object__open**\ () API. **_opts** variants accepts extra
103 **bpf_object_open_opts** options.
104
105 - **example__load**.
106 This function creates maps, loads and verifies BPF programs, initializes
107 global data maps. It corresponds to libbpf's **bpf_object__load**\ ()
108 API.
109
110 - **example__open_and_load** combines **example__open** and
111 **example__load** invocations in one commonly used operation.
112
113 - **example__attach** and **example__detach**.
114 This pair of functions allow to attach and detach, correspondingly,
115 already loaded BPF object. Only BPF programs of types supported by libbpf
116 for auto-attachment will be auto-attached and their corresponding BPF
117 links instantiated. For other BPF programs, user can manually create a
118 BPF link and assign it to corresponding fields in skeleton struct.
119 **example__detach** will detach both links created automatically, as well
120 as those populated by user manually.
121
122 - **example__destroy**.
123 Detach and unload BPF programs, free up all the resources used by
124 skeleton and BPF object.
125
126 If BPF object has global variables, corresponding structs with memory
127 layout corresponding to global data data section layout will be created.
128 Currently supported ones are: *.data*, *.bss*, *.rodata*, and *.kconfig*
129 structs/data sections. These data sections/structs can be used to set up
130 initial values of variables, if set before **example__load**. Afterwards,
131 if target kernel supports memory-mapped BPF arrays, same structs can be
132 used to fetch and update (non-read-only) data from userspace, with same
133 simplicity as for BPF side.
134
135bpftool gen subskeleton *FILE*
136 Generate BPF subskeleton C header file for a given *FILE*.
137
138 Subskeletons are similar to skeletons, except they do not own the
139 corresponding maps, programs, or global variables. They require that the
140 object file used to generate them is already loaded into a *bpf_object* by
141 some other means.
142
143 This functionality is useful when a library is included into a larger BPF
144 program. A subskeleton for the library would have access to all objects and
145 globals defined in it, without having to know about the larger program.
146
147 Consequently, there are only two functions defined for subskeletons:
148
149 - **example__open(bpf_object\*)**.
150 Instantiates a subskeleton from an already opened (but not necessarily
151 loaded) **bpf_object**.
152
153 - **example__destroy()**.
154 Frees the storage for the subskeleton but *does not* unload any BPF
155 programs or maps.
156
157bpftool gen min_core_btf *INPUT* *OUTPUT* *OBJECT* [*OBJECT*...]
158 Generate a minimum BTF file as *OUTPUT*, derived from a given *INPUT* BTF
159 file, containing all needed BTF types so one, or more, given eBPF objects
160 CO-RE relocations may be satisfied.
161
162 When kernels aren't compiled with CONFIG_DEBUG_INFO_BTF, libbpf, when
163 loading an eBPF object, has to rely on external BTF files to be able to
164 calculate CO-RE relocations.
165
166 Usually, an external BTF file is built from existing kernel DWARF data
167 using pahole. It contains all the types used by its respective kernel image
168 and, because of that, is big.
169
170 The min_core_btf feature builds smaller BTF files, customized to one or
171 multiple eBPF objects, so they can be distributed together with an eBPF
172 CO-RE based application, turning the application portable to different
173 kernel versions.
174
175 Check examples below for more information on how to use it.
176
177bpftool gen help
178 Print short help message.
179
180OPTIONS
181=======
182.. include:: common_options.rst
183
184-L, --use-loader
185 For skeletons, generate a "light" skeleton (also known as "loader"
186 skeleton). A light skeleton contains a loader eBPF program. It does not use
187 the majority of the libbpf infrastructure, and does not need libelf.
188
189EXAMPLES
190========
191**$ cat example1.bpf.c**
192
193::
194
195 #include <stdbool.h>
196 #include <linux/ptrace.h>
197 #include <linux/bpf.h>
198 #include <bpf/bpf_helpers.h>
199
200 const volatile int param1 = 42;
201 bool global_flag = true;
202 struct { int x; } data = {};
203
204 SEC("raw_tp/sys_enter")
205 int handle_sys_enter(struct pt_regs *ctx)
206 {
207 static long my_static_var;
208 if (global_flag)
209 my_static_var++;
210 else
211 data.x += param1;
212 return 0;
213 }
214
215**$ cat example2.bpf.c**
216
217::
218
219 #include <linux/ptrace.h>
220 #include <linux/bpf.h>
221 #include <bpf/bpf_helpers.h>
222
223 struct {
224 __uint(type, BPF_MAP_TYPE_HASH);
225 __uint(max_entries, 128);
226 __type(key, int);
227 __type(value, long);
228 } my_map SEC(".maps");
229
230 SEC("raw_tp/sys_exit")
231 int handle_sys_exit(struct pt_regs *ctx)
232 {
233 int zero = 0;
234 bpf_map_lookup_elem(&my_map, &zero);
235 return 0;
236 }
237
238**$ cat example3.bpf.c**
239
240::
241
242 #include <linux/ptrace.h>
243 #include <linux/bpf.h>
244 #include <bpf/bpf_helpers.h>
245 /* This header file is provided by the bpf_testmod module. */
246 #include "bpf_testmod.h"
247
248 int test_2_result = 0;
249
250 /* bpf_Testmod.ko calls this function, passing a "4"
251 * and testmod_map->data.
252 */
253 SEC("struct_ops/test_2")
254 void BPF_PROG(test_2, int a, int b)
255 {
256 test_2_result = a + b;
257 }
258
259 SEC(".struct_ops")
260 struct bpf_testmod_ops testmod_map = {
261 .test_2 = (void *)test_2,
262 .data = 0x1,
263 };
264
265This is example BPF application with three BPF programs and a mix of BPF
266maps and global variables. Source code is split across three source code
267files.
268
269**$ clang --target=bpf -g example1.bpf.c -o example1.bpf.o**
270
271**$ clang --target=bpf -g example2.bpf.c -o example2.bpf.o**
272
273**$ clang --target=bpf -g example3.bpf.c -o example3.bpf.o**
274
275**$ bpftool gen object example.bpf.o example1.bpf.o example2.bpf.o example3.bpf.o**
276
277This set of commands compiles *example1.bpf.c*, *example2.bpf.c* and
278*example3.bpf.c* individually and then statically links respective object
279files into the final BPF ELF object file *example.bpf.o*.
280
281**$ bpftool gen skeleton example.bpf.o name example | tee example.skel.h**
282
283::
284
285 /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
286
287 /* THIS FILE IS AUTOGENERATED! */
288 #ifndef __EXAMPLE_SKEL_H__
289 #define __EXAMPLE_SKEL_H__
290
291 #include <stdlib.h>
292 #include <bpf/libbpf.h>
293
294 struct example {
295 struct bpf_object_skeleton *skeleton;
296 struct bpf_object *obj;
297 struct {
298 struct bpf_map *rodata;
299 struct bpf_map *data;
300 struct bpf_map *bss;
301 struct bpf_map *my_map;
302 struct bpf_map *testmod_map;
303 } maps;
304 struct {
305 struct example__testmod_map__bpf_testmod_ops {
306 const struct bpf_program *test_1;
307 const struct bpf_program *test_2;
308 int data;
309 } *testmod_map;
310 } struct_ops;
311 struct {
312 struct bpf_program *handle_sys_enter;
313 struct bpf_program *handle_sys_exit;
314 } progs;
315 struct {
316 struct bpf_link *handle_sys_enter;
317 struct bpf_link *handle_sys_exit;
318 } links;
319 struct example__bss {
320 struct {
321 int x;
322 } data;
323 int test_2_result;
324 } *bss;
325 struct example__data {
326 _Bool global_flag;
327 long int handle_sys_enter_my_static_var;
328 } *data;
329 struct example__rodata {
330 int param1;
331 } *rodata;
332 };
333
334 static void example__destroy(struct example *obj);
335 static inline struct example *example__open_opts(
336 const struct bpf_object_open_opts *opts);
337 static inline struct example *example__open();
338 static inline int example__load(struct example *obj);
339 static inline struct example *example__open_and_load();
340 static inline int example__attach(struct example *obj);
341 static inline void example__detach(struct example *obj);
342
343 #endif /* __EXAMPLE_SKEL_H__ */
344
345**$ cat example.c**
346
347::
348
349 #include "example.skel.h"
350
351 int main()
352 {
353 struct example *skel;
354 int err = 0;
355
356 skel = example__open();
357 if (!skel)
358 goto cleanup;
359
360 skel->rodata->param1 = 128;
361
362 /* Change the value through the pointer of shadow type */
363 skel->struct_ops.testmod_map->data = 13;
364
365 err = example__load(skel);
366 if (err)
367 goto cleanup;
368
369 /* The result of the function test_2() */
370 printf("test_2_result: %d\n", skel->bss->test_2_result);
371
372 err = example__attach(skel);
373 if (err)
374 goto cleanup;
375
376 /* all libbpf APIs are usable */
377 printf("my_map name: %s\n", bpf_map__name(skel->maps.my_map));
378 printf("sys_enter prog FD: %d\n",
379 bpf_program__fd(skel->progs.handle_sys_enter));
380
381 /* detach and re-attach sys_exit program */
382 bpf_link__destroy(skel->links.handle_sys_exit);
383 skel->links.handle_sys_exit =
384 bpf_program__attach(skel->progs.handle_sys_exit);
385
386 printf("my_static_var: %ld\n",
387 skel->bss->handle_sys_enter_my_static_var);
388
389 cleanup:
390 example__destroy(skel);
391 return err;
392 }
393
394**# ./example**
395
396::
397
398 test_2_result: 17
399 my_map name: my_map
400 sys_enter prog FD: 8
401 my_static_var: 7
402
403This is a stripped-out version of skeleton generated for above example code.
404
405min_core_btf
406------------
407
408**$ bpftool btf dump file 5.4.0-example.btf format raw**
409
410::
411
412 [1] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
413 [2] CONST '(anon)' type_id=1
414 [3] VOLATILE '(anon)' type_id=1
415 [4] ARRAY '(anon)' type_id=1 index_type_id=21 nr_elems=2
416 [5] PTR '(anon)' type_id=8
417 [6] CONST '(anon)' type_id=5
418 [7] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=(none)
419 [8] CONST '(anon)' type_id=7
420 [9] INT 'unsigned int' size=4 bits_offset=0 nr_bits=32 encoding=(none)
421 <long output>
422
423**$ bpftool btf dump file one.bpf.o format raw**
424
425::
426
427 [1] PTR '(anon)' type_id=2
428 [2] STRUCT 'trace_event_raw_sys_enter' size=64 vlen=4
429 'ent' type_id=3 bits_offset=0
430 'id' type_id=7 bits_offset=64
431 'args' type_id=9 bits_offset=128
432 '__data' type_id=12 bits_offset=512
433 [3] STRUCT 'trace_entry' size=8 vlen=4
434 'type' type_id=4 bits_offset=0
435 'flags' type_id=5 bits_offset=16
436 'preempt_count' type_id=5 bits_offset=24
437 <long output>
438
439**$ bpftool gen min_core_btf 5.4.0-example.btf 5.4.0-smaller.btf one.bpf.o**
440
441**$ bpftool btf dump file 5.4.0-smaller.btf format raw**
442
443::
444
445 [1] TYPEDEF 'pid_t' type_id=6
446 [2] STRUCT 'trace_event_raw_sys_enter' size=64 vlen=1
447 'args' type_id=4 bits_offset=128
448 [3] STRUCT 'task_struct' size=9216 vlen=2
449 'pid' type_id=1 bits_offset=17920
450 'real_parent' type_id=7 bits_offset=18048
451 [4] ARRAY '(anon)' type_id=5 index_type_id=8 nr_elems=6
452 [5] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
453 [6] TYPEDEF '__kernel_pid_t' type_id=8
454 [7] PTR '(anon)' type_id=3
455 [8] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
456 <end>
457
458Now, the "5.4.0-smaller.btf" file may be used by libbpf as an external BTF file
459when loading the "one.bpf.o" object into the "5.4.0-example" kernel. Note that
460the generated BTF file won't allow other eBPF objects to be loaded, just the
461ones given to min_core_btf.
462
463::
464
465 LIBBPF_OPTS(bpf_object_open_opts, opts, .btf_custom_path = "5.4.0-smaller.btf");
466 struct bpf_object *obj;
467
468 obj = bpf_object__open_file("one.bpf.o", &opts);
469
470 ...