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