1===================== 2BPF Type Format (BTF) 3===================== 4 51. Introduction 6*************** 7 8BTF (BPF Type Format) is the metadata format which encodes the debug info 9related to BPF program/map. The name BTF was used initially to describe data 10types. The BTF was later extended to include function info for defined 11subroutines, and line info for source/line information. 12 13The debug info is used for map pretty print, function signature, etc. The 14function signature enables better bpf program/function kernel symbol. The line 15info helps generate source annotated translated byte code, jited code and 16verifier log. 17 18The BTF specification contains two parts, 19 * BTF kernel API 20 * BTF ELF file format 21 22The kernel API is the contract between user space and kernel. The kernel 23verifies the BTF info before using it. The ELF file format is a user space 24contract between ELF file and libbpf loader. 25 26The type and string sections are part of the BTF kernel API, describing the 27debug info (mostly types related) referenced by the bpf program. These two 28sections are discussed in details in :ref:`BTF_Type_String`. 29 30.. _BTF_Type_String: 31 322. BTF Type and String Encoding 33******************************* 34 35The file ``include/uapi/linux/btf.h`` provides high-level definition of how 36types/strings are encoded. 37 38The beginning of data blob must be:: 39 40 struct btf_header { 41 __u16 magic; 42 __u8 version; 43 __u8 flags; 44 __u32 hdr_len; 45 46 /* All offsets are in bytes relative to the end of this header */ 47 __u32 type_off; /* offset of type section */ 48 __u32 type_len; /* length of type section */ 49 __u32 str_off; /* offset of string section */ 50 __u32 str_len; /* length of string section */ 51 }; 52 53The magic is ``0xeB9F``, which has different encoding for big and little 54endian systems, and can be used to test whether BTF is generated for big- or 55little-endian target. The ``btf_header`` is designed to be extensible with 56``hdr_len`` equal to ``sizeof(struct btf_header)`` when a data blob is 57generated. 58 592.1 String Encoding 60=================== 61 62The first string in the string section must be a null string. The rest of 63string table is a concatenation of other null-terminated strings. 64 652.2 Type Encoding 66================= 67 68The type id ``0`` is reserved for ``void`` type. The type section is parsed 69sequentially and type id is assigned to each recognized type starting from id 70``1``. Currently, the following types are supported:: 71 72 #define BTF_KIND_INT 1 /* Integer */ 73 #define BTF_KIND_PTR 2 /* Pointer */ 74 #define BTF_KIND_ARRAY 3 /* Array */ 75 #define BTF_KIND_STRUCT 4 /* Struct */ 76 #define BTF_KIND_UNION 5 /* Union */ 77 #define BTF_KIND_ENUM 6 /* Enumeration */ 78 #define BTF_KIND_FWD 7 /* Forward */ 79 #define BTF_KIND_TYPEDEF 8 /* Typedef */ 80 #define BTF_KIND_VOLATILE 9 /* Volatile */ 81 #define BTF_KIND_CONST 10 /* Const */ 82 #define BTF_KIND_RESTRICT 11 /* Restrict */ 83 #define BTF_KIND_FUNC 12 /* Function */ 84 #define BTF_KIND_FUNC_PROTO 13 /* Function Proto */ 85 86Note that the type section encodes debug info, not just pure types. 87``BTF_KIND_FUNC`` is not a type, and it represents a defined subprogram. 88 89Each type contains the following common data:: 90 91 struct btf_type { 92 __u32 name_off; 93 /* "info" bits arrangement 94 * bits 0-15: vlen (e.g. # of struct's members) 95 * bits 16-23: unused 96 * bits 24-27: kind (e.g. int, ptr, array...etc) 97 * bits 28-30: unused 98 * bit 31: kind_flag, currently used by 99 * struct, union and fwd 100 */ 101 __u32 info; 102 /* "size" is used by INT, ENUM, STRUCT and UNION. 103 * "size" tells the size of the type it is describing. 104 * 105 * "type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT, 106 * FUNC and FUNC_PROTO. 107 * "type" is a type_id referring to another type. 108 */ 109 union { 110 __u32 size; 111 __u32 type; 112 }; 113 }; 114 115For certain kinds, the common data are followed by kind-specific data. The 116``name_off`` in ``struct btf_type`` specifies the offset in the string table. 117The following sections detail encoding of each kind. 118 1192.2.1 BTF_KIND_INT 120~~~~~~~~~~~~~~~~~~ 121 122``struct btf_type`` encoding requirement: 123 * ``name_off``: any valid offset 124 * ``info.kind_flag``: 0 125 * ``info.kind``: BTF_KIND_INT 126 * ``info.vlen``: 0 127 * ``size``: the size of the int type in bytes. 128 129``btf_type`` is followed by a ``u32`` with the following bits arrangement:: 130 131 #define BTF_INT_ENCODING(VAL) (((VAL) & 0x0f000000) >> 24) 132 #define BTF_INT_OFFSET(VAL) (((VAL & 0x00ff0000)) >> 16) 133 #define BTF_INT_BITS(VAL) ((VAL) & 0x000000ff) 134 135The ``BTF_INT_ENCODING`` has the following attributes:: 136 137 #define BTF_INT_SIGNED (1 << 0) 138 #define BTF_INT_CHAR (1 << 1) 139 #define BTF_INT_BOOL (1 << 2) 140 141The ``BTF_INT_ENCODING()`` provides extra information: signedness, char, or 142bool, for the int type. The char and bool encoding are mostly useful for 143pretty print. At most one encoding can be specified for the int type. 144 145The ``BTF_INT_BITS()`` specifies the number of actual bits held by this int 146type. For example, a 4-bit bitfield encodes ``BTF_INT_BITS()`` equals to 4. 147The ``btf_type.size * 8`` must be equal to or greater than ``BTF_INT_BITS()`` 148for the type. The maximum value of ``BTF_INT_BITS()`` is 128. 149 150The ``BTF_INT_OFFSET()`` specifies the starting bit offset to calculate values 151for this int. For example, a bitfield struct member has: 152 * btf member bit offset 100 from the start of the structure, 153 * btf member pointing to an int type, 154 * the int type has ``BTF_INT_OFFSET() = 2`` and ``BTF_INT_BITS() = 4`` 155 156Then in the struct memory layout, this member will occupy ``4`` bits starting 157from bits ``100 + 2 = 102``. 158 159Alternatively, the bitfield struct member can be the following to access the 160same bits as the above: 161 * btf member bit offset 102, 162 * btf member pointing to an int type, 163 * the int type has ``BTF_INT_OFFSET() = 0`` and ``BTF_INT_BITS() = 4`` 164 165The original intention of ``BTF_INT_OFFSET()`` is to provide flexibility of 166bitfield encoding. Currently, both llvm and pahole generate 167``BTF_INT_OFFSET() = 0`` for all int types. 168 1692.2.2 BTF_KIND_PTR 170~~~~~~~~~~~~~~~~~~ 171 172``struct btf_type`` encoding requirement: 173 * ``name_off``: 0 174 * ``info.kind_flag``: 0 175 * ``info.kind``: BTF_KIND_PTR 176 * ``info.vlen``: 0 177 * ``type``: the pointee type of the pointer 178 179No additional type data follow ``btf_type``. 180 1812.2.3 BTF_KIND_ARRAY 182~~~~~~~~~~~~~~~~~~~~ 183 184``struct btf_type`` encoding requirement: 185 * ``name_off``: 0 186 * ``info.kind_flag``: 0 187 * ``info.kind``: BTF_KIND_ARRAY 188 * ``info.vlen``: 0 189 * ``size/type``: 0, not used 190 191``btf_type`` is followed by one ``struct btf_array``:: 192 193 struct btf_array { 194 __u32 type; 195 __u32 index_type; 196 __u32 nelems; 197 }; 198 199The ``struct btf_array`` encoding: 200 * ``type``: the element type 201 * ``index_type``: the index type 202 * ``nelems``: the number of elements for this array (``0`` is also allowed). 203 204The ``index_type`` can be any regular int type (``u8``, ``u16``, ``u32``, 205``u64``, ``unsigned __int128``). The original design of including 206``index_type`` follows DWARF, which has an ``index_type`` for its array type. 207Currently in BTF, beyond type verification, the ``index_type`` is not used. 208 209The ``struct btf_array`` allows chaining through element type to represent 210multidimensional arrays. For example, for ``int a[5][6]``, the following type 211information illustrates the chaining: 212 213 * [1]: int 214 * [2]: array, ``btf_array.type = [1]``, ``btf_array.nelems = 6`` 215 * [3]: array, ``btf_array.type = [2]``, ``btf_array.nelems = 5`` 216 217Currently, both pahole and llvm collapse multidimensional array into 218one-dimensional array, e.g., for ``a[5][6]``, the ``btf_array.nelems`` is 219equal to ``30``. This is because the original use case is map pretty print 220where the whole array is dumped out so one-dimensional array is enough. As 221more BTF usage is explored, pahole and llvm can be changed to generate proper 222chained representation for multidimensional arrays. 223 2242.2.4 BTF_KIND_STRUCT 225~~~~~~~~~~~~~~~~~~~~~ 2262.2.5 BTF_KIND_UNION 227~~~~~~~~~~~~~~~~~~~~ 228 229``struct btf_type`` encoding requirement: 230 * ``name_off``: 0 or offset to a valid C identifier 231 * ``info.kind_flag``: 0 or 1 232 * ``info.kind``: BTF_KIND_STRUCT or BTF_KIND_UNION 233 * ``info.vlen``: the number of struct/union members 234 * ``info.size``: the size of the struct/union in bytes 235 236``btf_type`` is followed by ``info.vlen`` number of ``struct btf_member``.:: 237 238 struct btf_member { 239 __u32 name_off; 240 __u32 type; 241 __u32 offset; 242 }; 243 244``struct btf_member`` encoding: 245 * ``name_off``: offset to a valid C identifier 246 * ``type``: the member type 247 * ``offset``: <see below> 248 249If the type info ``kind_flag`` is not set, the offset contains only bit offset 250of the member. Note that the base type of the bitfield can only be int or enum 251type. If the bitfield size is 32, the base type can be either int or enum 252type. If the bitfield size is not 32, the base type must be int, and int type 253``BTF_INT_BITS()`` encodes the bitfield size. 254 255If the ``kind_flag`` is set, the ``btf_member.offset`` contains both member 256bitfield size and bit offset. The bitfield size and bit offset are calculated 257as below.:: 258 259 #define BTF_MEMBER_BITFIELD_SIZE(val) ((val) >> 24) 260 #define BTF_MEMBER_BIT_OFFSET(val) ((val) & 0xffffff) 261 262In this case, if the base type is an int type, it must be a regular int type: 263 264 * ``BTF_INT_OFFSET()`` must be 0. 265 * ``BTF_INT_BITS()`` must be equal to ``{1,2,4,8,16} * 8``. 266 267The following kernel patch introduced ``kind_flag`` and explained why both 268modes exist: 269 270 https://github.com/torvalds/linux/commit/9d5f9f701b1891466fb3dbb1806ad97716f95cc3#diff-fa650a64fdd3968396883d2fe8215ff3 271 2722.2.6 BTF_KIND_ENUM 273~~~~~~~~~~~~~~~~~~~ 274 275``struct btf_type`` encoding requirement: 276 * ``name_off``: 0 or offset to a valid C identifier 277 * ``info.kind_flag``: 0 278 * ``info.kind``: BTF_KIND_ENUM 279 * ``info.vlen``: number of enum values 280 * ``size``: 4 281 282``btf_type`` is followed by ``info.vlen`` number of ``struct btf_enum``.:: 283 284 struct btf_enum { 285 __u32 name_off; 286 __s32 val; 287 }; 288 289The ``btf_enum`` encoding: 290 * ``name_off``: offset to a valid C identifier 291 * ``val``: any value 292 2932.2.7 BTF_KIND_FWD 294~~~~~~~~~~~~~~~~~~ 295 296``struct btf_type`` encoding requirement: 297 * ``name_off``: offset to a valid C identifier 298 * ``info.kind_flag``: 0 for struct, 1 for union 299 * ``info.kind``: BTF_KIND_FWD 300 * ``info.vlen``: 0 301 * ``type``: 0 302 303No additional type data follow ``btf_type``. 304 3052.2.8 BTF_KIND_TYPEDEF 306~~~~~~~~~~~~~~~~~~~~~~ 307 308``struct btf_type`` encoding requirement: 309 * ``name_off``: offset to a valid C identifier 310 * ``info.kind_flag``: 0 311 * ``info.kind``: BTF_KIND_TYPEDEF 312 * ``info.vlen``: 0 313 * ``type``: the type which can be referred by name at ``name_off`` 314 315No additional type data follow ``btf_type``. 316 3172.2.9 BTF_KIND_VOLATILE 318~~~~~~~~~~~~~~~~~~~~~~~ 319 320``struct btf_type`` encoding requirement: 321 * ``name_off``: 0 322 * ``info.kind_flag``: 0 323 * ``info.kind``: BTF_KIND_VOLATILE 324 * ``info.vlen``: 0 325 * ``type``: the type with ``volatile`` qualifier 326 327No additional type data follow ``btf_type``. 328 3292.2.10 BTF_KIND_CONST 330~~~~~~~~~~~~~~~~~~~~~ 331 332``struct btf_type`` encoding requirement: 333 * ``name_off``: 0 334 * ``info.kind_flag``: 0 335 * ``info.kind``: BTF_KIND_CONST 336 * ``info.vlen``: 0 337 * ``type``: the type with ``const`` qualifier 338 339No additional type data follow ``btf_type``. 340 3412.2.11 BTF_KIND_RESTRICT 342~~~~~~~~~~~~~~~~~~~~~~~~ 343 344``struct btf_type`` encoding requirement: 345 * ``name_off``: 0 346 * ``info.kind_flag``: 0 347 * ``info.kind``: BTF_KIND_RESTRICT 348 * ``info.vlen``: 0 349 * ``type``: the type with ``restrict`` qualifier 350 351No additional type data follow ``btf_type``. 352 3532.2.12 BTF_KIND_FUNC 354~~~~~~~~~~~~~~~~~~~~ 355 356``struct btf_type`` encoding requirement: 357 * ``name_off``: offset to a valid C identifier 358 * ``info.kind_flag``: 0 359 * ``info.kind``: BTF_KIND_FUNC 360 * ``info.vlen``: 0 361 * ``type``: a BTF_KIND_FUNC_PROTO type 362 363No additional type data follow ``btf_type``. 364 365A BTF_KIND_FUNC defines not a type, but a subprogram (function) whose 366signature is defined by ``type``. The subprogram is thus an instance of that 367type. The BTF_KIND_FUNC may in turn be referenced by a func_info in the 368:ref:`BTF_Ext_Section` (ELF) or in the arguments to :ref:`BPF_Prog_Load` 369(ABI). 370 3712.2.13 BTF_KIND_FUNC_PROTO 372~~~~~~~~~~~~~~~~~~~~~~~~~~ 373 374``struct btf_type`` encoding requirement: 375 * ``name_off``: 0 376 * ``info.kind_flag``: 0 377 * ``info.kind``: BTF_KIND_FUNC_PROTO 378 * ``info.vlen``: # of parameters 379 * ``type``: the return type 380 381``btf_type`` is followed by ``info.vlen`` number of ``struct btf_param``.:: 382 383 struct btf_param { 384 __u32 name_off; 385 __u32 type; 386 }; 387 388If a BTF_KIND_FUNC_PROTO type is referred by a BTF_KIND_FUNC type, then 389``btf_param.name_off`` must point to a valid C identifier except for the 390possible last argument representing the variable argument. The btf_param.type 391refers to parameter type. 392 393If the function has variable arguments, the last parameter is encoded with 394``name_off = 0`` and ``type = 0``. 395 3963. BTF Kernel API 397***************** 398 399The following bpf syscall command involves BTF: 400 * BPF_BTF_LOAD: load a blob of BTF data into kernel 401 * BPF_MAP_CREATE: map creation with btf key and value type info. 402 * BPF_PROG_LOAD: prog load with btf function and line info. 403 * BPF_BTF_GET_FD_BY_ID: get a btf fd 404 * BPF_OBJ_GET_INFO_BY_FD: btf, func_info, line_info 405 and other btf related info are returned. 406 407The workflow typically looks like: 408:: 409 410 Application: 411 BPF_BTF_LOAD 412 | 413 v 414 BPF_MAP_CREATE and BPF_PROG_LOAD 415 | 416 V 417 ...... 418 419 Introspection tool: 420 ...... 421 BPF_{PROG,MAP}_GET_NEXT_ID (get prog/map id's) 422 | 423 V 424 BPF_{PROG,MAP}_GET_FD_BY_ID (get a prog/map fd) 425 | 426 V 427 BPF_OBJ_GET_INFO_BY_FD (get bpf_prog_info/bpf_map_info with btf_id) 428 | | 429 V | 430 BPF_BTF_GET_FD_BY_ID (get btf_fd) | 431 | | 432 V | 433 BPF_OBJ_GET_INFO_BY_FD (get btf) | 434 | | 435 V V 436 pretty print types, dump func signatures and line info, etc. 437 438 4393.1 BPF_BTF_LOAD 440================ 441 442Load a blob of BTF data into kernel. A blob of data, described in 443:ref:`BTF_Type_String`, can be directly loaded into the kernel. A ``btf_fd`` 444is returned to a userspace. 445 4463.2 BPF_MAP_CREATE 447================== 448 449A map can be created with ``btf_fd`` and specified key/value type id.:: 450 451 __u32 btf_fd; /* fd pointing to a BTF type data */ 452 __u32 btf_key_type_id; /* BTF type_id of the key */ 453 __u32 btf_value_type_id; /* BTF type_id of the value */ 454 455In libbpf, the map can be defined with extra annotation like below: 456:: 457 458 struct bpf_map_def SEC("maps") btf_map = { 459 .type = BPF_MAP_TYPE_ARRAY, 460 .key_size = sizeof(int), 461 .value_size = sizeof(struct ipv_counts), 462 .max_entries = 4, 463 }; 464 BPF_ANNOTATE_KV_PAIR(btf_map, int, struct ipv_counts); 465 466Here, the parameters for macro BPF_ANNOTATE_KV_PAIR are map name, key and 467value types for the map. During ELF parsing, libbpf is able to extract 468key/value type_id's and assign them to BPF_MAP_CREATE attributes 469automatically. 470 471.. _BPF_Prog_Load: 472 4733.3 BPF_PROG_LOAD 474================= 475 476During prog_load, func_info and line_info can be passed to kernel with proper 477values for the following attributes: 478:: 479 480 __u32 insn_cnt; 481 __aligned_u64 insns; 482 ...... 483 __u32 prog_btf_fd; /* fd pointing to BTF type data */ 484 __u32 func_info_rec_size; /* userspace bpf_func_info size */ 485 __aligned_u64 func_info; /* func info */ 486 __u32 func_info_cnt; /* number of bpf_func_info records */ 487 __u32 line_info_rec_size; /* userspace bpf_line_info size */ 488 __aligned_u64 line_info; /* line info */ 489 __u32 line_info_cnt; /* number of bpf_line_info records */ 490 491The func_info and line_info are an array of below, respectively.:: 492 493 struct bpf_func_info { 494 __u32 insn_off; /* [0, insn_cnt - 1] */ 495 __u32 type_id; /* pointing to a BTF_KIND_FUNC type */ 496 }; 497 struct bpf_line_info { 498 __u32 insn_off; /* [0, insn_cnt - 1] */ 499 __u32 file_name_off; /* offset to string table for the filename */ 500 __u32 line_off; /* offset to string table for the source line */ 501 __u32 line_col; /* line number and column number */ 502 }; 503 504func_info_rec_size is the size of each func_info record, and 505line_info_rec_size is the size of each line_info record. Passing the record 506size to kernel make it possible to extend the record itself in the future. 507 508Below are requirements for func_info: 509 * func_info[0].insn_off must be 0. 510 * the func_info insn_off is in strictly increasing order and matches 511 bpf func boundaries. 512 513Below are requirements for line_info: 514 * the first insn in each func must have a line_info record pointing to it. 515 * the line_info insn_off is in strictly increasing order. 516 517For line_info, the line number and column number are defined as below: 518:: 519 520 #define BPF_LINE_INFO_LINE_NUM(line_col) ((line_col) >> 10) 521 #define BPF_LINE_INFO_LINE_COL(line_col) ((line_col) & 0x3ff) 522 5233.4 BPF_{PROG,MAP}_GET_NEXT_ID 524 525In kernel, every loaded program, map or btf has a unique id. The id won't 526change during the lifetime of a program, map, or btf. 527 528The bpf syscall command BPF_{PROG,MAP}_GET_NEXT_ID returns all id's, one for 529each command, to user space, for bpf program or maps, respectively, so an 530inspection tool can inspect all programs and maps. 531 5323.5 BPF_{PROG,MAP}_GET_FD_BY_ID 533 534An introspection tool cannot use id to get details about program or maps. 535A file descriptor needs to be obtained first for reference-counting purpose. 536 5373.6 BPF_OBJ_GET_INFO_BY_FD 538========================== 539 540Once a program/map fd is acquired, an introspection tool can get the detailed 541information from kernel about this fd, some of which are BTF-related. For 542example, ``bpf_map_info`` returns ``btf_id`` and key/value type ids. 543``bpf_prog_info`` returns ``btf_id``, func_info, and line info for translated 544bpf byte codes, and jited_line_info. 545 5463.7 BPF_BTF_GET_FD_BY_ID 547======================== 548 549With ``btf_id`` obtained in ``bpf_map_info`` and ``bpf_prog_info``, bpf 550syscall command BPF_BTF_GET_FD_BY_ID can retrieve a btf fd. Then, with 551command BPF_OBJ_GET_INFO_BY_FD, the btf blob, originally loaded into the 552kernel with BPF_BTF_LOAD, can be retrieved. 553 554With the btf blob, ``bpf_map_info``, and ``bpf_prog_info``, an introspection 555tool has full btf knowledge and is able to pretty print map key/values, dump 556func signatures and line info, along with byte/jit codes. 557 5584. ELF File Format Interface 559**************************** 560 5614.1 .BTF section 562================ 563 564The .BTF section contains type and string data. The format of this section is 565same as the one describe in :ref:`BTF_Type_String`. 566 567.. _BTF_Ext_Section: 568 5694.2 .BTF.ext section 570==================== 571 572The .BTF.ext section encodes func_info and line_info which needs loader 573manipulation before loading into the kernel. 574 575The specification for .BTF.ext section is defined at ``tools/lib/bpf/btf.h`` 576and ``tools/lib/bpf/btf.c``. 577 578The current header of .BTF.ext section:: 579 580 struct btf_ext_header { 581 __u16 magic; 582 __u8 version; 583 __u8 flags; 584 __u32 hdr_len; 585 586 /* All offsets are in bytes relative to the end of this header */ 587 __u32 func_info_off; 588 __u32 func_info_len; 589 __u32 line_info_off; 590 __u32 line_info_len; 591 }; 592 593It is very similar to .BTF section. Instead of type/string section, it 594contains func_info and line_info section. See :ref:`BPF_Prog_Load` for details 595about func_info and line_info record format. 596 597The func_info is organized as below.:: 598 599 func_info_rec_size 600 btf_ext_info_sec for section #1 /* func_info for section #1 */ 601 btf_ext_info_sec for section #2 /* func_info for section #2 */ 602 ... 603 604``func_info_rec_size`` specifies the size of ``bpf_func_info`` structure when 605.BTF.ext is generated. ``btf_ext_info_sec``, defined below, is a collection of 606func_info for each specific ELF section.:: 607 608 struct btf_ext_info_sec { 609 __u32 sec_name_off; /* offset to section name */ 610 __u32 num_info; 611 /* Followed by num_info * record_size number of bytes */ 612 __u8 data[0]; 613 }; 614 615Here, num_info must be greater than 0. 616 617The line_info is organized as below.:: 618 619 line_info_rec_size 620 btf_ext_info_sec for section #1 /* line_info for section #1 */ 621 btf_ext_info_sec for section #2 /* line_info for section #2 */ 622 ... 623 624``line_info_rec_size`` specifies the size of ``bpf_line_info`` structure when 625.BTF.ext is generated. 626 627The interpretation of ``bpf_func_info->insn_off`` and 628``bpf_line_info->insn_off`` is different between kernel API and ELF API. For 629kernel API, the ``insn_off`` is the instruction offset in the unit of ``struct 630bpf_insn``. For ELF API, the ``insn_off`` is the byte offset from the 631beginning of section (``btf_ext_info_sec->sec_name_off``). 632 6335. Using BTF 634************ 635 6365.1 bpftool map pretty print 637============================ 638 639With BTF, the map key/value can be printed based on fields rather than simply 640raw bytes. This is especially valuable for large structure or if your data 641structure has bitfields. For example, for the following map,:: 642 643 enum A { A1, A2, A3, A4, A5 }; 644 typedef enum A ___A; 645 struct tmp_t { 646 char a1:4; 647 int a2:4; 648 int :4; 649 __u32 a3:4; 650 int b; 651 ___A b1:4; 652 enum A b2:4; 653 }; 654 struct bpf_map_def SEC("maps") tmpmap = { 655 .type = BPF_MAP_TYPE_ARRAY, 656 .key_size = sizeof(__u32), 657 .value_size = sizeof(struct tmp_t), 658 .max_entries = 1, 659 }; 660 BPF_ANNOTATE_KV_PAIR(tmpmap, int, struct tmp_t); 661 662bpftool is able to pretty print like below: 663:: 664 665 [{ 666 "key": 0, 667 "value": { 668 "a1": 0x2, 669 "a2": 0x4, 670 "a3": 0x6, 671 "b": 7, 672 "b1": 0x8, 673 "b2": 0xa 674 } 675 } 676 ] 677 6785.2 bpftool prog dump 679===================== 680 681The following is an example showing how func_info and line_info can help prog 682dump with better kernel symbol names, function prototypes and line 683information.:: 684 685 $ bpftool prog dump jited pinned /sys/fs/bpf/test_btf_haskv 686 [...] 687 int test_long_fname_2(struct dummy_tracepoint_args * arg): 688 bpf_prog_44a040bf25481309_test_long_fname_2: 689 ; static int test_long_fname_2(struct dummy_tracepoint_args *arg) 690 0: push %rbp 691 1: mov %rsp,%rbp 692 4: sub $0x30,%rsp 693 b: sub $0x28,%rbp 694 f: mov %rbx,0x0(%rbp) 695 13: mov %r13,0x8(%rbp) 696 17: mov %r14,0x10(%rbp) 697 1b: mov %r15,0x18(%rbp) 698 1f: xor %eax,%eax 699 21: mov %rax,0x20(%rbp) 700 25: xor %esi,%esi 701 ; int key = 0; 702 27: mov %esi,-0x4(%rbp) 703 ; if (!arg->sock) 704 2a: mov 0x8(%rdi),%rdi 705 ; if (!arg->sock) 706 2e: cmp $0x0,%rdi 707 32: je 0x0000000000000070 708 34: mov %rbp,%rsi 709 ; counts = bpf_map_lookup_elem(&btf_map, &key); 710 [...] 711 7125.3 Verifier Log 713================ 714 715The following is an example of how line_info can help debugging verification 716failure.:: 717 718 /* The code at tools/testing/selftests/bpf/test_xdp_noinline.c 719 * is modified as below. 720 */ 721 data = (void *)(long)xdp->data; 722 data_end = (void *)(long)xdp->data_end; 723 /* 724 if (data + 4 > data_end) 725 return XDP_DROP; 726 */ 727 *(u32 *)data = dst->dst; 728 729 $ bpftool prog load ./test_xdp_noinline.o /sys/fs/bpf/test_xdp_noinline type xdp 730 ; data = (void *)(long)xdp->data; 731 224: (79) r2 = *(u64 *)(r10 -112) 732 225: (61) r2 = *(u32 *)(r2 +0) 733 ; *(u32 *)data = dst->dst; 734 226: (63) *(u32 *)(r2 +0) = r1 735 invalid access to packet, off=0 size=4, R2(id=0,off=0,r=0) 736 R2 offset is outside of the packet 737 7386. BTF Generation 739***************** 740 741You need latest pahole 742 743 https://git.kernel.org/pub/scm/devel/pahole/pahole.git/ 744 745or llvm (8.0 or later). The pahole acts as a dwarf2btf converter. It doesn't 746support .BTF.ext and btf BTF_KIND_FUNC type yet. For example,:: 747 748 -bash-4.4$ cat t.c 749 struct t { 750 int a:2; 751 int b:3; 752 int c:2; 753 } g; 754 -bash-4.4$ gcc -c -O2 -g t.c 755 -bash-4.4$ pahole -JV t.o 756 File t.o: 757 [1] STRUCT t kind_flag=1 size=4 vlen=3 758 a type_id=2 bitfield_size=2 bits_offset=0 759 b type_id=2 bitfield_size=3 bits_offset=2 760 c type_id=2 bitfield_size=2 bits_offset=5 761 [2] INT int size=4 bit_offset=0 nr_bits=32 encoding=SIGNED 762 763The llvm is able to generate .BTF and .BTF.ext directly with -g for bpf target 764only. The assembly code (-S) is able to show the BTF encoding in assembly 765format.:: 766 767 -bash-4.4$ cat t2.c 768 typedef int __int32; 769 struct t2 { 770 int a2; 771 int (*f2)(char q1, __int32 q2, ...); 772 int (*f3)(); 773 } g2; 774 int main() { return 0; } 775 int test() { return 0; } 776 -bash-4.4$ clang -c -g -O2 -target bpf t2.c 777 -bash-4.4$ readelf -S t2.o 778 ...... 779 [ 8] .BTF PROGBITS 0000000000000000 00000247 780 000000000000016e 0000000000000000 0 0 1 781 [ 9] .BTF.ext PROGBITS 0000000000000000 000003b5 782 0000000000000060 0000000000000000 0 0 1 783 [10] .rel.BTF.ext REL 0000000000000000 000007e0 784 0000000000000040 0000000000000010 16 9 8 785 ...... 786 -bash-4.4$ clang -S -g -O2 -target bpf t2.c 787 -bash-4.4$ cat t2.s 788 ...... 789 .section .BTF,"",@progbits 790 .short 60319 # 0xeb9f 791 .byte 1 792 .byte 0 793 .long 24 794 .long 0 795 .long 220 796 .long 220 797 .long 122 798 .long 0 # BTF_KIND_FUNC_PROTO(id = 1) 799 .long 218103808 # 0xd000000 800 .long 2 801 .long 83 # BTF_KIND_INT(id = 2) 802 .long 16777216 # 0x1000000 803 .long 4 804 .long 16777248 # 0x1000020 805 ...... 806 .byte 0 # string offset=0 807 .ascii ".text" # string offset=1 808 .byte 0 809 .ascii "/home/yhs/tmp-pahole/t2.c" # string offset=7 810 .byte 0 811 .ascii "int main() { return 0; }" # string offset=33 812 .byte 0 813 .ascii "int test() { return 0; }" # string offset=58 814 .byte 0 815 .ascii "int" # string offset=83 816 ...... 817 .section .BTF.ext,"",@progbits 818 .short 60319 # 0xeb9f 819 .byte 1 820 .byte 0 821 .long 24 822 .long 0 823 .long 28 824 .long 28 825 .long 44 826 .long 8 # FuncInfo 827 .long 1 # FuncInfo section string offset=1 828 .long 2 829 .long .Lfunc_begin0 830 .long 3 831 .long .Lfunc_begin1 832 .long 5 833 .long 16 # LineInfo 834 .long 1 # LineInfo section string offset=1 835 .long 2 836 .long .Ltmp0 837 .long 7 838 .long 33 839 .long 7182 # Line 7 Col 14 840 .long .Ltmp3 841 .long 7 842 .long 58 843 .long 8206 # Line 8 Col 14 844 8457. Testing 846********** 847 848Kernel bpf selftest `test_btf.c` provides extensive set of BTF-related tests. 849