1 ===================== 1 =====================
2 BPF Type Format (BTF) 2 BPF Type Format (BTF)
3 ===================== 3 =====================
4 4
5 1. Introduction 5 1. Introduction
6 =============== 6 ===============
7 7
8 BTF (BPF Type Format) is the metadata format w 8 BTF (BPF Type Format) is the metadata format which encodes the debug info
9 related to BPF program/map. The name BTF was u 9 related to BPF program/map. The name BTF was used initially to describe data
10 types. The BTF was later extended to include f 10 types. The BTF was later extended to include function info for defined
11 subroutines, and line info for source/line inf 11 subroutines, and line info for source/line information.
12 12
13 The debug info is used for map pretty print, f 13 The debug info is used for map pretty print, function signature, etc. The
14 function signature enables better bpf program/ 14 function signature enables better bpf program/function kernel symbol. The line
15 info helps generate source annotated translate 15 info helps generate source annotated translated byte code, jited code and
16 verifier log. 16 verifier log.
17 17
18 The BTF specification contains two parts, 18 The BTF specification contains two parts,
19 * BTF kernel API 19 * BTF kernel API
20 * BTF ELF file format 20 * BTF ELF file format
21 21
22 The kernel API is the contract between user sp 22 The kernel API is the contract between user space and kernel. The kernel
23 verifies the BTF info before using it. The ELF 23 verifies the BTF info before using it. The ELF file format is a user space
24 contract between ELF file and libbpf loader. 24 contract between ELF file and libbpf loader.
25 25
26 The type and string sections are part of the B 26 The type and string sections are part of the BTF kernel API, describing the
27 debug info (mostly types related) referenced b 27 debug info (mostly types related) referenced by the bpf program. These two
28 sections are discussed in details in :ref:`BTF 28 sections are discussed in details in :ref:`BTF_Type_String`.
29 29
30 .. _BTF_Type_String: 30 .. _BTF_Type_String:
31 31
32 2. BTF Type and String Encoding 32 2. BTF Type and String Encoding
33 =============================== 33 ===============================
34 34
35 The file ``include/uapi/linux/btf.h`` provides 35 The file ``include/uapi/linux/btf.h`` provides high-level definition of how
36 types/strings are encoded. 36 types/strings are encoded.
37 37
38 The beginning of data blob must be:: 38 The beginning of data blob must be::
39 39
40 struct btf_header { 40 struct btf_header {
41 __u16 magic; 41 __u16 magic;
42 __u8 version; 42 __u8 version;
43 __u8 flags; 43 __u8 flags;
44 __u32 hdr_len; 44 __u32 hdr_len;
45 45
46 /* All offsets are in bytes relative t 46 /* All offsets are in bytes relative to the end of this header */
47 __u32 type_off; /* offset of t 47 __u32 type_off; /* offset of type section */
48 __u32 type_len; /* length of t 48 __u32 type_len; /* length of type section */
49 __u32 str_off; /* offset of s 49 __u32 str_off; /* offset of string section */
50 __u32 str_len; /* length of s 50 __u32 str_len; /* length of string section */
51 }; 51 };
52 52
53 The magic is ``0xeB9F``, which has different e 53 The magic is ``0xeB9F``, which has different encoding for big and little
54 endian systems, and can be used to test whethe 54 endian systems, and can be used to test whether BTF is generated for big- or
55 little-endian target. The ``btf_header`` is de 55 little-endian target. The ``btf_header`` is designed to be extensible with
56 ``hdr_len`` equal to ``sizeof(struct btf_heade 56 ``hdr_len`` equal to ``sizeof(struct btf_header)`` when a data blob is
57 generated. 57 generated.
58 58
59 2.1 String Encoding 59 2.1 String Encoding
60 ------------------- 60 -------------------
61 61
62 The first string in the string section must be 62 The first string in the string section must be a null string. The rest of
63 string table is a concatenation of other null- 63 string table is a concatenation of other null-terminated strings.
64 64
65 2.2 Type Encoding 65 2.2 Type Encoding
66 ----------------- 66 -----------------
67 67
68 The type id ``0`` is reserved for ``void`` typ 68 The type id ``0`` is reserved for ``void`` type. The type section is parsed
69 sequentially and type id is assigned to each r 69 sequentially and type id is assigned to each recognized type starting from id
70 ``1``. Currently, the following types are supp 70 ``1``. Currently, the following types are supported::
71 71
72 #define BTF_KIND_INT 1 /* 72 #define BTF_KIND_INT 1 /* Integer */
73 #define BTF_KIND_PTR 2 /* 73 #define BTF_KIND_PTR 2 /* Pointer */
74 #define BTF_KIND_ARRAY 3 /* 74 #define BTF_KIND_ARRAY 3 /* Array */
75 #define BTF_KIND_STRUCT 4 /* 75 #define BTF_KIND_STRUCT 4 /* Struct */
76 #define BTF_KIND_UNION 5 /* 76 #define BTF_KIND_UNION 5 /* Union */
77 #define BTF_KIND_ENUM 6 /* 77 #define BTF_KIND_ENUM 6 /* Enumeration up to 32-bit values */
78 #define BTF_KIND_FWD 7 /* 78 #define BTF_KIND_FWD 7 /* Forward */
79 #define BTF_KIND_TYPEDEF 8 /* 79 #define BTF_KIND_TYPEDEF 8 /* Typedef */
80 #define BTF_KIND_VOLATILE 9 /* 80 #define BTF_KIND_VOLATILE 9 /* Volatile */
81 #define BTF_KIND_CONST 10 /* 81 #define BTF_KIND_CONST 10 /* Const */
82 #define BTF_KIND_RESTRICT 11 /* 82 #define BTF_KIND_RESTRICT 11 /* Restrict */
83 #define BTF_KIND_FUNC 12 /* 83 #define BTF_KIND_FUNC 12 /* Function */
84 #define BTF_KIND_FUNC_PROTO 13 /* 84 #define BTF_KIND_FUNC_PROTO 13 /* Function Proto */
85 #define BTF_KIND_VAR 14 /* 85 #define BTF_KIND_VAR 14 /* Variable */
86 #define BTF_KIND_DATASEC 15 /* 86 #define BTF_KIND_DATASEC 15 /* Section */
87 #define BTF_KIND_FLOAT 16 /* 87 #define BTF_KIND_FLOAT 16 /* Floating point */
88 #define BTF_KIND_DECL_TAG 17 /* 88 #define BTF_KIND_DECL_TAG 17 /* Decl Tag */
89 #define BTF_KIND_TYPE_TAG 18 /* 89 #define BTF_KIND_TYPE_TAG 18 /* Type Tag */
90 #define BTF_KIND_ENUM64 19 /* 90 #define BTF_KIND_ENUM64 19 /* Enumeration up to 64-bit values */
91 91
92 Note that the type section encodes debug info, 92 Note that the type section encodes debug info, not just pure types.
93 ``BTF_KIND_FUNC`` is not a type, and it repres 93 ``BTF_KIND_FUNC`` is not a type, and it represents a defined subprogram.
94 94
95 Each type contains the following common data:: 95 Each type contains the following common data::
96 96
97 struct btf_type { 97 struct btf_type {
98 __u32 name_off; 98 __u32 name_off;
99 /* "info" bits arrangement 99 /* "info" bits arrangement
100 * bits 0-15: vlen (e.g. # of struct' 100 * bits 0-15: vlen (e.g. # of struct's members)
101 * bits 16-23: unused 101 * bits 16-23: unused
102 * bits 24-28: kind (e.g. int, ptr, ar 102 * bits 24-28: kind (e.g. int, ptr, array...etc)
103 * bits 29-30: unused 103 * bits 29-30: unused
104 * bit 31: kind_flag, currently us 104 * bit 31: kind_flag, currently used by
105 * struct, union, fwd, enu 105 * struct, union, fwd, enum and enum64.
106 */ 106 */
107 __u32 info; 107 __u32 info;
108 /* "size" is used by INT, ENUM, STRUCT 108 /* "size" is used by INT, ENUM, STRUCT, UNION and ENUM64.
109 * "size" tells the size of the type i 109 * "size" tells the size of the type it is describing.
110 * 110 *
111 * "type" is used by PTR, TYPEDEF, VOL 111 * "type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT,
112 * FUNC, FUNC_PROTO, DECL_TAG and TYPE 112 * FUNC, FUNC_PROTO, DECL_TAG and TYPE_TAG.
113 * "type" is a type_id referring to an 113 * "type" is a type_id referring to another type.
114 */ 114 */
115 union { 115 union {
116 __u32 size; 116 __u32 size;
117 __u32 type; 117 __u32 type;
118 }; 118 };
119 }; 119 };
120 120
121 For certain kinds, the common data are followe 121 For certain kinds, the common data are followed by kind-specific data. The
122 ``name_off`` in ``struct btf_type`` specifies 122 ``name_off`` in ``struct btf_type`` specifies the offset in the string table.
123 The following sections detail encoding of each 123 The following sections detail encoding of each kind.
124 124
125 2.2.1 BTF_KIND_INT 125 2.2.1 BTF_KIND_INT
126 ~~~~~~~~~~~~~~~~~~ 126 ~~~~~~~~~~~~~~~~~~
127 127
128 ``struct btf_type`` encoding requirement: 128 ``struct btf_type`` encoding requirement:
129 * ``name_off``: any valid offset 129 * ``name_off``: any valid offset
130 * ``info.kind_flag``: 0 130 * ``info.kind_flag``: 0
131 * ``info.kind``: BTF_KIND_INT 131 * ``info.kind``: BTF_KIND_INT
132 * ``info.vlen``: 0 132 * ``info.vlen``: 0
133 * ``size``: the size of the int type in bytes 133 * ``size``: the size of the int type in bytes.
134 134
135 ``btf_type`` is followed by a ``u32`` with the 135 ``btf_type`` is followed by a ``u32`` with the following bits arrangement::
136 136
137 #define BTF_INT_ENCODING(VAL) (((VAL) & 0x 137 #define BTF_INT_ENCODING(VAL) (((VAL) & 0x0f000000) >> 24)
138 #define BTF_INT_OFFSET(VAL) (((VAL) & 0x 138 #define BTF_INT_OFFSET(VAL) (((VAL) & 0x00ff0000) >> 16)
139 #define BTF_INT_BITS(VAL) ((VAL) & 0x 139 #define BTF_INT_BITS(VAL) ((VAL) & 0x000000ff)
140 140
141 The ``BTF_INT_ENCODING`` has the following att 141 The ``BTF_INT_ENCODING`` has the following attributes::
142 142
143 #define BTF_INT_SIGNED (1 << 0) 143 #define BTF_INT_SIGNED (1 << 0)
144 #define BTF_INT_CHAR (1 << 1) 144 #define BTF_INT_CHAR (1 << 1)
145 #define BTF_INT_BOOL (1 << 2) 145 #define BTF_INT_BOOL (1 << 2)
146 146
147 The ``BTF_INT_ENCODING()`` provides extra info 147 The ``BTF_INT_ENCODING()`` provides extra information: signedness, char, or
148 bool, for the int type. The char and bool enco 148 bool, for the int type. The char and bool encoding are mostly useful for
149 pretty print. At most one encoding can be spec 149 pretty print. At most one encoding can be specified for the int type.
150 150
151 The ``BTF_INT_BITS()`` specifies the number of 151 The ``BTF_INT_BITS()`` specifies the number of actual bits held by this int
152 type. For example, a 4-bit bitfield encodes `` 152 type. For example, a 4-bit bitfield encodes ``BTF_INT_BITS()`` equals to 4.
153 The ``btf_type.size * 8`` must be equal to or 153 The ``btf_type.size * 8`` must be equal to or greater than ``BTF_INT_BITS()``
154 for the type. The maximum value of ``BTF_INT_B 154 for the type. The maximum value of ``BTF_INT_BITS()`` is 128.
155 155
156 The ``BTF_INT_OFFSET()`` specifies the startin 156 The ``BTF_INT_OFFSET()`` specifies the starting bit offset to calculate values
157 for this int. For example, a bitfield struct m 157 for this int. For example, a bitfield struct member has:
158 158
159 * btf member bit offset 100 from the start of 159 * btf member bit offset 100 from the start of the structure,
160 * btf member pointing to an int type, 160 * btf member pointing to an int type,
161 * the int type has ``BTF_INT_OFFSET() = 2`` a 161 * the int type has ``BTF_INT_OFFSET() = 2`` and ``BTF_INT_BITS() = 4``
162 162
163 Then in the struct memory layout, this member 163 Then in the struct memory layout, this member will occupy ``4`` bits starting
164 from bits ``100 + 2 = 102``. 164 from bits ``100 + 2 = 102``.
165 165
166 Alternatively, the bitfield struct member can 166 Alternatively, the bitfield struct member can be the following to access the
167 same bits as the above: 167 same bits as the above:
168 168
169 * btf member bit offset 102, 169 * btf member bit offset 102,
170 * btf member pointing to an int type, 170 * btf member pointing to an int type,
171 * the int type has ``BTF_INT_OFFSET() = 0`` a 171 * the int type has ``BTF_INT_OFFSET() = 0`` and ``BTF_INT_BITS() = 4``
172 172
173 The original intention of ``BTF_INT_OFFSET()`` 173 The original intention of ``BTF_INT_OFFSET()`` is to provide flexibility of
174 bitfield encoding. Currently, both llvm and pa 174 bitfield encoding. Currently, both llvm and pahole generate
175 ``BTF_INT_OFFSET() = 0`` for all int types. 175 ``BTF_INT_OFFSET() = 0`` for all int types.
176 176
177 2.2.2 BTF_KIND_PTR 177 2.2.2 BTF_KIND_PTR
178 ~~~~~~~~~~~~~~~~~~ 178 ~~~~~~~~~~~~~~~~~~
179 179
180 ``struct btf_type`` encoding requirement: 180 ``struct btf_type`` encoding requirement:
181 * ``name_off``: 0 181 * ``name_off``: 0
182 * ``info.kind_flag``: 0 182 * ``info.kind_flag``: 0
183 * ``info.kind``: BTF_KIND_PTR 183 * ``info.kind``: BTF_KIND_PTR
184 * ``info.vlen``: 0 184 * ``info.vlen``: 0
185 * ``type``: the pointee type of the pointer 185 * ``type``: the pointee type of the pointer
186 186
187 No additional type data follow ``btf_type``. 187 No additional type data follow ``btf_type``.
188 188
189 2.2.3 BTF_KIND_ARRAY 189 2.2.3 BTF_KIND_ARRAY
190 ~~~~~~~~~~~~~~~~~~~~ 190 ~~~~~~~~~~~~~~~~~~~~
191 191
192 ``struct btf_type`` encoding requirement: 192 ``struct btf_type`` encoding requirement:
193 * ``name_off``: 0 193 * ``name_off``: 0
194 * ``info.kind_flag``: 0 194 * ``info.kind_flag``: 0
195 * ``info.kind``: BTF_KIND_ARRAY 195 * ``info.kind``: BTF_KIND_ARRAY
196 * ``info.vlen``: 0 196 * ``info.vlen``: 0
197 * ``size/type``: 0, not used 197 * ``size/type``: 0, not used
198 198
199 ``btf_type`` is followed by one ``struct btf_a 199 ``btf_type`` is followed by one ``struct btf_array``::
200 200
201 struct btf_array { 201 struct btf_array {
202 __u32 type; 202 __u32 type;
203 __u32 index_type; 203 __u32 index_type;
204 __u32 nelems; 204 __u32 nelems;
205 }; 205 };
206 206
207 The ``struct btf_array`` encoding: 207 The ``struct btf_array`` encoding:
208 * ``type``: the element type 208 * ``type``: the element type
209 * ``index_type``: the index type 209 * ``index_type``: the index type
210 * ``nelems``: the number of elements for thi 210 * ``nelems``: the number of elements for this array (``0`` is also allowed).
211 211
212 The ``index_type`` can be any regular int type 212 The ``index_type`` can be any regular int type (``u8``, ``u16``, ``u32``,
213 ``u64``, ``unsigned __int128``). The original 213 ``u64``, ``unsigned __int128``). The original design of including
214 ``index_type`` follows DWARF, which has an ``i 214 ``index_type`` follows DWARF, which has an ``index_type`` for its array type.
215 Currently in BTF, beyond type verification, th 215 Currently in BTF, beyond type verification, the ``index_type`` is not used.
216 216
217 The ``struct btf_array`` allows chaining throu 217 The ``struct btf_array`` allows chaining through element type to represent
218 multidimensional arrays. For example, for ``in 218 multidimensional arrays. For example, for ``int a[5][6]``, the following type
219 information illustrates the chaining: 219 information illustrates the chaining:
220 220
221 * [1]: int 221 * [1]: int
222 * [2]: array, ``btf_array.type = [1]``, ``bt 222 * [2]: array, ``btf_array.type = [1]``, ``btf_array.nelems = 6``
223 * [3]: array, ``btf_array.type = [2]``, ``bt 223 * [3]: array, ``btf_array.type = [2]``, ``btf_array.nelems = 5``
224 224
225 Currently, both pahole and llvm collapse multi 225 Currently, both pahole and llvm collapse multidimensional array into
226 one-dimensional array, e.g., for ``a[5][6]``, 226 one-dimensional array, e.g., for ``a[5][6]``, the ``btf_array.nelems`` is
227 equal to ``30``. This is because the original 227 equal to ``30``. This is because the original use case is map pretty print
228 where the whole array is dumped out so one-dim 228 where the whole array is dumped out so one-dimensional array is enough. As
229 more BTF usage is explored, pahole and llvm ca 229 more BTF usage is explored, pahole and llvm can be changed to generate proper
230 chained representation for multidimensional ar 230 chained representation for multidimensional arrays.
231 231
232 2.2.4 BTF_KIND_STRUCT 232 2.2.4 BTF_KIND_STRUCT
233 ~~~~~~~~~~~~~~~~~~~~~ 233 ~~~~~~~~~~~~~~~~~~~~~
234 2.2.5 BTF_KIND_UNION 234 2.2.5 BTF_KIND_UNION
235 ~~~~~~~~~~~~~~~~~~~~ 235 ~~~~~~~~~~~~~~~~~~~~
236 236
237 ``struct btf_type`` encoding requirement: 237 ``struct btf_type`` encoding requirement:
238 * ``name_off``: 0 or offset to a valid C ide 238 * ``name_off``: 0 or offset to a valid C identifier
239 * ``info.kind_flag``: 0 or 1 239 * ``info.kind_flag``: 0 or 1
240 * ``info.kind``: BTF_KIND_STRUCT or BTF_KIND 240 * ``info.kind``: BTF_KIND_STRUCT or BTF_KIND_UNION
241 * ``info.vlen``: the number of struct/union 241 * ``info.vlen``: the number of struct/union members
242 * ``info.size``: the size of the struct/unio 242 * ``info.size``: the size of the struct/union in bytes
243 243
244 ``btf_type`` is followed by ``info.vlen`` numb 244 ``btf_type`` is followed by ``info.vlen`` number of ``struct btf_member``.::
245 245
246 struct btf_member { 246 struct btf_member {
247 __u32 name_off; 247 __u32 name_off;
248 __u32 type; 248 __u32 type;
249 __u32 offset; 249 __u32 offset;
250 }; 250 };
251 251
252 ``struct btf_member`` encoding: 252 ``struct btf_member`` encoding:
253 * ``name_off``: offset to a valid C identifi 253 * ``name_off``: offset to a valid C identifier
254 * ``type``: the member type 254 * ``type``: the member type
255 * ``offset``: <see below> 255 * ``offset``: <see below>
256 256
257 If the type info ``kind_flag`` is not set, the 257 If the type info ``kind_flag`` is not set, the offset contains only bit offset
258 of the member. Note that the base type of the 258 of the member. Note that the base type of the bitfield can only be int or enum
259 type. If the bitfield size is 32, the base typ 259 type. If the bitfield size is 32, the base type can be either int or enum
260 type. If the bitfield size is not 32, the base 260 type. If the bitfield size is not 32, the base type must be int, and int type
261 ``BTF_INT_BITS()`` encodes the bitfield size. 261 ``BTF_INT_BITS()`` encodes the bitfield size.
262 262
263 If the ``kind_flag`` is set, the ``btf_member. 263 If the ``kind_flag`` is set, the ``btf_member.offset`` contains both member
264 bitfield size and bit offset. The bitfield siz 264 bitfield size and bit offset. The bitfield size and bit offset are calculated
265 as below.:: 265 as below.::
266 266
267 #define BTF_MEMBER_BITFIELD_SIZE(val) ((va 267 #define BTF_MEMBER_BITFIELD_SIZE(val) ((val) >> 24)
268 #define BTF_MEMBER_BIT_OFFSET(val) ((va 268 #define BTF_MEMBER_BIT_OFFSET(val) ((val) & 0xffffff)
269 269
270 In this case, if the base type is an int type, 270 In this case, if the base type is an int type, it must be a regular int type:
271 271
272 * ``BTF_INT_OFFSET()`` must be 0. 272 * ``BTF_INT_OFFSET()`` must be 0.
273 * ``BTF_INT_BITS()`` must be equal to ``{1,2 273 * ``BTF_INT_BITS()`` must be equal to ``{1,2,4,8,16} * 8``.
274 274
275 Commit 9d5f9f701b18 introduced ``kind_flag`` a !! 275 The following kernel patch introduced ``kind_flag`` and explained why both
276 exist. !! 276 modes exist:
>> 277
>> 278 https://github.com/torvalds/linux/commit/9d5f9f701b1891466fb3dbb1806ad97716f95cc3#diff-fa650a64fdd3968396883d2fe8215ff3
277 279
278 2.2.6 BTF_KIND_ENUM 280 2.2.6 BTF_KIND_ENUM
279 ~~~~~~~~~~~~~~~~~~~ 281 ~~~~~~~~~~~~~~~~~~~
280 282
281 ``struct btf_type`` encoding requirement: 283 ``struct btf_type`` encoding requirement:
282 * ``name_off``: 0 or offset to a valid C ide 284 * ``name_off``: 0 or offset to a valid C identifier
283 * ``info.kind_flag``: 0 for unsigned, 1 for 285 * ``info.kind_flag``: 0 for unsigned, 1 for signed
284 * ``info.kind``: BTF_KIND_ENUM 286 * ``info.kind``: BTF_KIND_ENUM
285 * ``info.vlen``: number of enum values 287 * ``info.vlen``: number of enum values
286 * ``size``: 1/2/4/8 288 * ``size``: 1/2/4/8
287 289
288 ``btf_type`` is followed by ``info.vlen`` numb 290 ``btf_type`` is followed by ``info.vlen`` number of ``struct btf_enum``.::
289 291
290 struct btf_enum { 292 struct btf_enum {
291 __u32 name_off; 293 __u32 name_off;
292 __s32 val; 294 __s32 val;
293 }; 295 };
294 296
295 The ``btf_enum`` encoding: 297 The ``btf_enum`` encoding:
296 * ``name_off``: offset to a valid C identifi 298 * ``name_off``: offset to a valid C identifier
297 * ``val``: any value 299 * ``val``: any value
298 300
299 If the original enum value is signed and the s 301 If the original enum value is signed and the size is less than 4,
300 that value will be sign extended into 4 bytes. 302 that value will be sign extended into 4 bytes. If the size is 8,
301 the value will be truncated into 4 bytes. 303 the value will be truncated into 4 bytes.
302 304
303 2.2.7 BTF_KIND_FWD 305 2.2.7 BTF_KIND_FWD
304 ~~~~~~~~~~~~~~~~~~ 306 ~~~~~~~~~~~~~~~~~~
305 307
306 ``struct btf_type`` encoding requirement: 308 ``struct btf_type`` encoding requirement:
307 * ``name_off``: offset to a valid C identifi 309 * ``name_off``: offset to a valid C identifier
308 * ``info.kind_flag``: 0 for struct, 1 for un 310 * ``info.kind_flag``: 0 for struct, 1 for union
309 * ``info.kind``: BTF_KIND_FWD 311 * ``info.kind``: BTF_KIND_FWD
310 * ``info.vlen``: 0 312 * ``info.vlen``: 0
311 * ``type``: 0 313 * ``type``: 0
312 314
313 No additional type data follow ``btf_type``. 315 No additional type data follow ``btf_type``.
314 316
315 2.2.8 BTF_KIND_TYPEDEF 317 2.2.8 BTF_KIND_TYPEDEF
316 ~~~~~~~~~~~~~~~~~~~~~~ 318 ~~~~~~~~~~~~~~~~~~~~~~
317 319
318 ``struct btf_type`` encoding requirement: 320 ``struct btf_type`` encoding requirement:
319 * ``name_off``: offset to a valid C identifi 321 * ``name_off``: offset to a valid C identifier
320 * ``info.kind_flag``: 0 322 * ``info.kind_flag``: 0
321 * ``info.kind``: BTF_KIND_TYPEDEF 323 * ``info.kind``: BTF_KIND_TYPEDEF
322 * ``info.vlen``: 0 324 * ``info.vlen``: 0
323 * ``type``: the type which can be referred b 325 * ``type``: the type which can be referred by name at ``name_off``
324 326
325 No additional type data follow ``btf_type``. 327 No additional type data follow ``btf_type``.
326 328
327 2.2.9 BTF_KIND_VOLATILE 329 2.2.9 BTF_KIND_VOLATILE
328 ~~~~~~~~~~~~~~~~~~~~~~~ 330 ~~~~~~~~~~~~~~~~~~~~~~~
329 331
330 ``struct btf_type`` encoding requirement: 332 ``struct btf_type`` encoding requirement:
331 * ``name_off``: 0 333 * ``name_off``: 0
332 * ``info.kind_flag``: 0 334 * ``info.kind_flag``: 0
333 * ``info.kind``: BTF_KIND_VOLATILE 335 * ``info.kind``: BTF_KIND_VOLATILE
334 * ``info.vlen``: 0 336 * ``info.vlen``: 0
335 * ``type``: the type with ``volatile`` quali 337 * ``type``: the type with ``volatile`` qualifier
336 338
337 No additional type data follow ``btf_type``. 339 No additional type data follow ``btf_type``.
338 340
339 2.2.10 BTF_KIND_CONST 341 2.2.10 BTF_KIND_CONST
340 ~~~~~~~~~~~~~~~~~~~~~ 342 ~~~~~~~~~~~~~~~~~~~~~
341 343
342 ``struct btf_type`` encoding requirement: 344 ``struct btf_type`` encoding requirement:
343 * ``name_off``: 0 345 * ``name_off``: 0
344 * ``info.kind_flag``: 0 346 * ``info.kind_flag``: 0
345 * ``info.kind``: BTF_KIND_CONST 347 * ``info.kind``: BTF_KIND_CONST
346 * ``info.vlen``: 0 348 * ``info.vlen``: 0
347 * ``type``: the type with ``const`` qualifie 349 * ``type``: the type with ``const`` qualifier
348 350
349 No additional type data follow ``btf_type``. 351 No additional type data follow ``btf_type``.
350 352
351 2.2.11 BTF_KIND_RESTRICT 353 2.2.11 BTF_KIND_RESTRICT
352 ~~~~~~~~~~~~~~~~~~~~~~~~ 354 ~~~~~~~~~~~~~~~~~~~~~~~~
353 355
354 ``struct btf_type`` encoding requirement: 356 ``struct btf_type`` encoding requirement:
355 * ``name_off``: 0 357 * ``name_off``: 0
356 * ``info.kind_flag``: 0 358 * ``info.kind_flag``: 0
357 * ``info.kind``: BTF_KIND_RESTRICT 359 * ``info.kind``: BTF_KIND_RESTRICT
358 * ``info.vlen``: 0 360 * ``info.vlen``: 0
359 * ``type``: the type with ``restrict`` quali 361 * ``type``: the type with ``restrict`` qualifier
360 362
361 No additional type data follow ``btf_type``. 363 No additional type data follow ``btf_type``.
362 364
363 2.2.12 BTF_KIND_FUNC 365 2.2.12 BTF_KIND_FUNC
364 ~~~~~~~~~~~~~~~~~~~~ 366 ~~~~~~~~~~~~~~~~~~~~
365 367
366 ``struct btf_type`` encoding requirement: 368 ``struct btf_type`` encoding requirement:
367 * ``name_off``: offset to a valid C identifi 369 * ``name_off``: offset to a valid C identifier
368 * ``info.kind_flag``: 0 370 * ``info.kind_flag``: 0
369 * ``info.kind``: BTF_KIND_FUNC 371 * ``info.kind``: BTF_KIND_FUNC
370 * ``info.vlen``: linkage information (BTF_FU 372 * ``info.vlen``: linkage information (BTF_FUNC_STATIC, BTF_FUNC_GLOBAL
371 or BTF_FUNC_EXTERN - see :r !! 373 or BTF_FUNC_EXTERN)
372 * ``type``: a BTF_KIND_FUNC_PROTO type 374 * ``type``: a BTF_KIND_FUNC_PROTO type
373 375
374 No additional type data follow ``btf_type``. 376 No additional type data follow ``btf_type``.
375 377
376 A BTF_KIND_FUNC defines not a type, but a subp 378 A BTF_KIND_FUNC defines not a type, but a subprogram (function) whose
377 signature is defined by ``type``. The subprogr 379 signature is defined by ``type``. The subprogram is thus an instance of that
378 type. The BTF_KIND_FUNC may in turn be referen 380 type. The BTF_KIND_FUNC may in turn be referenced by a func_info in the
379 :ref:`BTF_Ext_Section` (ELF) or in the argumen 381 :ref:`BTF_Ext_Section` (ELF) or in the arguments to :ref:`BPF_Prog_Load`
380 (ABI). 382 (ABI).
381 383
382 Currently, only linkage values of BTF_FUNC_STA 384 Currently, only linkage values of BTF_FUNC_STATIC and BTF_FUNC_GLOBAL are
383 supported in the kernel. 385 supported in the kernel.
384 386
385 2.2.13 BTF_KIND_FUNC_PROTO 387 2.2.13 BTF_KIND_FUNC_PROTO
386 ~~~~~~~~~~~~~~~~~~~~~~~~~~ 388 ~~~~~~~~~~~~~~~~~~~~~~~~~~
387 389
388 ``struct btf_type`` encoding requirement: 390 ``struct btf_type`` encoding requirement:
389 * ``name_off``: 0 391 * ``name_off``: 0
390 * ``info.kind_flag``: 0 392 * ``info.kind_flag``: 0
391 * ``info.kind``: BTF_KIND_FUNC_PROTO 393 * ``info.kind``: BTF_KIND_FUNC_PROTO
392 * ``info.vlen``: # of parameters 394 * ``info.vlen``: # of parameters
393 * ``type``: the return type 395 * ``type``: the return type
394 396
395 ``btf_type`` is followed by ``info.vlen`` numb 397 ``btf_type`` is followed by ``info.vlen`` number of ``struct btf_param``.::
396 398
397 struct btf_param { 399 struct btf_param {
398 __u32 name_off; 400 __u32 name_off;
399 __u32 type; 401 __u32 type;
400 }; 402 };
401 403
402 If a BTF_KIND_FUNC_PROTO type is referred by a 404 If a BTF_KIND_FUNC_PROTO type is referred by a BTF_KIND_FUNC type, then
403 ``btf_param.name_off`` must point to a valid C 405 ``btf_param.name_off`` must point to a valid C identifier except for the
404 possible last argument representing the variab 406 possible last argument representing the variable argument. The btf_param.type
405 refers to parameter type. 407 refers to parameter type.
406 408
407 If the function has variable arguments, the la 409 If the function has variable arguments, the last parameter is encoded with
408 ``name_off = 0`` and ``type = 0``. 410 ``name_off = 0`` and ``type = 0``.
409 411
410 2.2.14 BTF_KIND_VAR 412 2.2.14 BTF_KIND_VAR
411 ~~~~~~~~~~~~~~~~~~~ 413 ~~~~~~~~~~~~~~~~~~~
412 414
413 ``struct btf_type`` encoding requirement: 415 ``struct btf_type`` encoding requirement:
414 * ``name_off``: offset to a valid C identifi 416 * ``name_off``: offset to a valid C identifier
415 * ``info.kind_flag``: 0 417 * ``info.kind_flag``: 0
416 * ``info.kind``: BTF_KIND_VAR 418 * ``info.kind``: BTF_KIND_VAR
417 * ``info.vlen``: 0 419 * ``info.vlen``: 0
418 * ``type``: the type of the variable 420 * ``type``: the type of the variable
419 421
420 ``btf_type`` is followed by a single ``struct 422 ``btf_type`` is followed by a single ``struct btf_variable`` with the
421 following data:: 423 following data::
422 424
423 struct btf_var { 425 struct btf_var {
424 __u32 linkage; 426 __u32 linkage;
425 }; 427 };
426 428
427 ``btf_var.linkage`` may take the values: BTF_V !! 429 ``struct btf_var`` encoding:
428 see :ref:`BTF_Var_Linkage_Constants`. !! 430 * ``linkage``: currently only static variable 0, or globally allocated
>> 431 variable in ELF sections 1
429 432
430 Not all type of global variables are supported 433 Not all type of global variables are supported by LLVM at this point.
431 The following is currently available: 434 The following is currently available:
432 435
433 * static variables with or without section a 436 * static variables with or without section attributes
434 * global variables with section attributes 437 * global variables with section attributes
435 438
436 The latter is for future extraction of map key 439 The latter is for future extraction of map key/value type id's from a
437 map definition. 440 map definition.
438 441
439 2.2.15 BTF_KIND_DATASEC 442 2.2.15 BTF_KIND_DATASEC
440 ~~~~~~~~~~~~~~~~~~~~~~~ 443 ~~~~~~~~~~~~~~~~~~~~~~~
441 444
442 ``struct btf_type`` encoding requirement: 445 ``struct btf_type`` encoding requirement:
443 * ``name_off``: offset to a valid name assoc 446 * ``name_off``: offset to a valid name associated with a variable or
444 one of .data/.bss/.rodata 447 one of .data/.bss/.rodata
445 * ``info.kind_flag``: 0 448 * ``info.kind_flag``: 0
446 * ``info.kind``: BTF_KIND_DATASEC 449 * ``info.kind``: BTF_KIND_DATASEC
447 * ``info.vlen``: # of variables 450 * ``info.vlen``: # of variables
448 * ``size``: total section size in bytes (0 a 451 * ``size``: total section size in bytes (0 at compilation time, patched
449 to actual size by BPF loaders su 452 to actual size by BPF loaders such as libbpf)
450 453
451 ``btf_type`` is followed by ``info.vlen`` numb 454 ``btf_type`` is followed by ``info.vlen`` number of ``struct btf_var_secinfo``.::
452 455
453 struct btf_var_secinfo { 456 struct btf_var_secinfo {
454 __u32 type; 457 __u32 type;
455 __u32 offset; 458 __u32 offset;
456 __u32 size; 459 __u32 size;
457 }; 460 };
458 461
459 ``struct btf_var_secinfo`` encoding: 462 ``struct btf_var_secinfo`` encoding:
460 * ``type``: the type of the BTF_KIND_VAR var 463 * ``type``: the type of the BTF_KIND_VAR variable
461 * ``offset``: the in-section offset of the v 464 * ``offset``: the in-section offset of the variable
462 * ``size``: the size of the variable in byte 465 * ``size``: the size of the variable in bytes
463 466
464 2.2.16 BTF_KIND_FLOAT 467 2.2.16 BTF_KIND_FLOAT
465 ~~~~~~~~~~~~~~~~~~~~~ 468 ~~~~~~~~~~~~~~~~~~~~~
466 469
467 ``struct btf_type`` encoding requirement: 470 ``struct btf_type`` encoding requirement:
468 * ``name_off``: any valid offset 471 * ``name_off``: any valid offset
469 * ``info.kind_flag``: 0 472 * ``info.kind_flag``: 0
470 * ``info.kind``: BTF_KIND_FLOAT 473 * ``info.kind``: BTF_KIND_FLOAT
471 * ``info.vlen``: 0 474 * ``info.vlen``: 0
472 * ``size``: the size of the float type in byt 475 * ``size``: the size of the float type in bytes: 2, 4, 8, 12 or 16.
473 476
474 No additional type data follow ``btf_type``. 477 No additional type data follow ``btf_type``.
475 478
476 2.2.17 BTF_KIND_DECL_TAG 479 2.2.17 BTF_KIND_DECL_TAG
477 ~~~~~~~~~~~~~~~~~~~~~~~~ 480 ~~~~~~~~~~~~~~~~~~~~~~~~
478 481
479 ``struct btf_type`` encoding requirement: 482 ``struct btf_type`` encoding requirement:
480 * ``name_off``: offset to a non-empty string 483 * ``name_off``: offset to a non-empty string
481 * ``info.kind_flag``: 0 484 * ``info.kind_flag``: 0
482 * ``info.kind``: BTF_KIND_DECL_TAG 485 * ``info.kind``: BTF_KIND_DECL_TAG
483 * ``info.vlen``: 0 486 * ``info.vlen``: 0
484 * ``type``: ``struct``, ``union``, ``func``, 487 * ``type``: ``struct``, ``union``, ``func``, ``var`` or ``typedef``
485 488
486 ``btf_type`` is followed by ``struct btf_decl_ 489 ``btf_type`` is followed by ``struct btf_decl_tag``.::
487 490
488 struct btf_decl_tag { 491 struct btf_decl_tag {
489 __u32 component_idx; 492 __u32 component_idx;
490 }; 493 };
491 494
492 The ``name_off`` encodes btf_decl_tag attribut 495 The ``name_off`` encodes btf_decl_tag attribute string.
493 The ``type`` should be ``struct``, ``union``, 496 The ``type`` should be ``struct``, ``union``, ``func``, ``var`` or ``typedef``.
494 For ``var`` or ``typedef`` type, ``btf_decl_ta 497 For ``var`` or ``typedef`` type, ``btf_decl_tag.component_idx`` must be ``-1``.
495 For the other three types, if the btf_decl_tag 498 For the other three types, if the btf_decl_tag attribute is
496 applied to the ``struct``, ``union`` or ``func 499 applied to the ``struct``, ``union`` or ``func`` itself,
497 ``btf_decl_tag.component_idx`` must be ``-1``. 500 ``btf_decl_tag.component_idx`` must be ``-1``. Otherwise,
498 the attribute is applied to a ``struct``/``uni 501 the attribute is applied to a ``struct``/``union`` member or
499 a ``func`` argument, and ``btf_decl_tag.compon 502 a ``func`` argument, and ``btf_decl_tag.component_idx`` should be a
500 valid index (starting from 0) pointing to a me 503 valid index (starting from 0) pointing to a member or an argument.
501 504
502 2.2.18 BTF_KIND_TYPE_TAG 505 2.2.18 BTF_KIND_TYPE_TAG
503 ~~~~~~~~~~~~~~~~~~~~~~~~ 506 ~~~~~~~~~~~~~~~~~~~~~~~~
504 507
505 ``struct btf_type`` encoding requirement: 508 ``struct btf_type`` encoding requirement:
506 * ``name_off``: offset to a non-empty string 509 * ``name_off``: offset to a non-empty string
507 * ``info.kind_flag``: 0 510 * ``info.kind_flag``: 0
508 * ``info.kind``: BTF_KIND_TYPE_TAG 511 * ``info.kind``: BTF_KIND_TYPE_TAG
509 * ``info.vlen``: 0 512 * ``info.vlen``: 0
510 * ``type``: the type with ``btf_type_tag`` at 513 * ``type``: the type with ``btf_type_tag`` attribute
511 514
512 Currently, ``BTF_KIND_TYPE_TAG`` is only emitt 515 Currently, ``BTF_KIND_TYPE_TAG`` is only emitted for pointer types.
513 It has the following btf type chain: 516 It has the following btf type chain:
514 :: 517 ::
515 518
516 ptr -> [type_tag]* 519 ptr -> [type_tag]*
517 -> [const | volatile | restrict | typede 520 -> [const | volatile | restrict | typedef]*
518 -> base_type 521 -> base_type
519 522
520 Basically, a pointer type points to zero or mo 523 Basically, a pointer type points to zero or more
521 type_tag, then zero or more const/volatile/res 524 type_tag, then zero or more const/volatile/restrict/typedef
522 and finally the base type. The base type is on 525 and finally the base type. The base type is one of
523 int, ptr, array, struct, union, enum, func_pro 526 int, ptr, array, struct, union, enum, func_proto and float types.
524 527
525 2.2.19 BTF_KIND_ENUM64 528 2.2.19 BTF_KIND_ENUM64
526 ~~~~~~~~~~~~~~~~~~~~~~ 529 ~~~~~~~~~~~~~~~~~~~~~~
527 530
528 ``struct btf_type`` encoding requirement: 531 ``struct btf_type`` encoding requirement:
529 * ``name_off``: 0 or offset to a valid C ide 532 * ``name_off``: 0 or offset to a valid C identifier
530 * ``info.kind_flag``: 0 for unsigned, 1 for 533 * ``info.kind_flag``: 0 for unsigned, 1 for signed
531 * ``info.kind``: BTF_KIND_ENUM64 534 * ``info.kind``: BTF_KIND_ENUM64
532 * ``info.vlen``: number of enum values 535 * ``info.vlen``: number of enum values
533 * ``size``: 1/2/4/8 536 * ``size``: 1/2/4/8
534 537
535 ``btf_type`` is followed by ``info.vlen`` numb 538 ``btf_type`` is followed by ``info.vlen`` number of ``struct btf_enum64``.::
536 539
537 struct btf_enum64 { 540 struct btf_enum64 {
538 __u32 name_off; 541 __u32 name_off;
539 __u32 val_lo32; 542 __u32 val_lo32;
540 __u32 val_hi32; 543 __u32 val_hi32;
541 }; 544 };
542 545
543 The ``btf_enum64`` encoding: 546 The ``btf_enum64`` encoding:
544 * ``name_off``: offset to a valid C identifi 547 * ``name_off``: offset to a valid C identifier
545 * ``val_lo32``: lower 32-bit value for a 64- 548 * ``val_lo32``: lower 32-bit value for a 64-bit value
546 * ``val_hi32``: high 32-bit value for a 64-b 549 * ``val_hi32``: high 32-bit value for a 64-bit value
547 550
548 If the original enum value is signed and the s 551 If the original enum value is signed and the size is less than 8,
549 that value will be sign extended into 8 bytes. 552 that value will be sign extended into 8 bytes.
550 553
551 2.3 Constant Values <<
552 ------------------- <<
553 <<
554 .. _BTF_Function_Linkage_Constants: <<
555 <<
556 2.3.1 Function Linkage Constant Values <<
557 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ <<
558 .. table:: Function Linkage Values and Meaning <<
559 <<
560 =================== ===== =========== <<
561 kind value description <<
562 =================== ===== =========== <<
563 ``BTF_FUNC_STATIC`` 0x0 definition of su <<
564 ``BTF_FUNC_GLOBAL`` 0x1 definition of su <<
565 ``BTF_FUNC_EXTERN`` 0x2 declaration of a <<
566 =================== ===== =========== <<
567 <<
568 <<
569 .. _BTF_Var_Linkage_Constants: <<
570 <<
571 2.3.2 Variable Linkage Constant Values <<
572 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ <<
573 .. table:: Variable Linkage Values and Meaning <<
574 <<
575 ============================ ===== ======= <<
576 kind value descrip <<
577 ============================ ===== ======= <<
578 ``BTF_VAR_STATIC`` 0x0 definit <<
579 ``BTF_VAR_GLOBAL_ALLOCATED`` 0x1 definit <<
580 ``BTF_VAR_GLOBAL_EXTERN`` 0x2 declara <<
581 ============================ ===== ======= <<
582 <<
583 3. BTF Kernel API 554 3. BTF Kernel API
584 ================= 555 =================
585 556
586 The following bpf syscall command involves BTF 557 The following bpf syscall command involves BTF:
587 * BPF_BTF_LOAD: load a blob of BTF data int 558 * BPF_BTF_LOAD: load a blob of BTF data into kernel
588 * BPF_MAP_CREATE: map creation with btf key 559 * BPF_MAP_CREATE: map creation with btf key and value type info.
589 * BPF_PROG_LOAD: prog load with btf functio 560 * BPF_PROG_LOAD: prog load with btf function and line info.
590 * BPF_BTF_GET_FD_BY_ID: get a btf fd 561 * BPF_BTF_GET_FD_BY_ID: get a btf fd
591 * BPF_OBJ_GET_INFO_BY_FD: btf, func_info, l 562 * BPF_OBJ_GET_INFO_BY_FD: btf, func_info, line_info
592 and other btf related info are returned. 563 and other btf related info are returned.
593 564
594 The workflow typically looks like: 565 The workflow typically looks like:
595 :: 566 ::
596 567
597 Application: 568 Application:
598 BPF_BTF_LOAD 569 BPF_BTF_LOAD
599 | 570 |
600 v 571 v
601 BPF_MAP_CREATE and BPF_PROG_LOAD 572 BPF_MAP_CREATE and BPF_PROG_LOAD
602 | 573 |
603 V 574 V
604 ...... 575 ......
605 576
606 Introspection tool: 577 Introspection tool:
607 ...... 578 ......
608 BPF_{PROG,MAP}_GET_NEXT_ID (get prog/map 579 BPF_{PROG,MAP}_GET_NEXT_ID (get prog/map id's)
609 | 580 |
610 V 581 V
611 BPF_{PROG,MAP}_GET_FD_BY_ID (get a prog/ 582 BPF_{PROG,MAP}_GET_FD_BY_ID (get a prog/map fd)
612 | 583 |
613 V 584 V
614 BPF_OBJ_GET_INFO_BY_FD (get bpf_prog_inf 585 BPF_OBJ_GET_INFO_BY_FD (get bpf_prog_info/bpf_map_info with btf_id)
615 | 586 | |
616 V 587 V |
617 BPF_BTF_GET_FD_BY_ID (get btf_fd) 588 BPF_BTF_GET_FD_BY_ID (get btf_fd) |
618 | 589 | |
619 V 590 V |
620 BPF_OBJ_GET_INFO_BY_FD (get btf) 591 BPF_OBJ_GET_INFO_BY_FD (get btf) |
621 | 592 | |
622 V 593 V V
623 pretty print types, dump func signatures 594 pretty print types, dump func signatures and line info, etc.
624 595
625 596
626 3.1 BPF_BTF_LOAD 597 3.1 BPF_BTF_LOAD
627 ---------------- 598 ----------------
628 599
629 Load a blob of BTF data into kernel. A blob of 600 Load a blob of BTF data into kernel. A blob of data, described in
630 :ref:`BTF_Type_String`, can be directly loaded 601 :ref:`BTF_Type_String`, can be directly loaded into the kernel. A ``btf_fd``
631 is returned to a userspace. 602 is returned to a userspace.
632 603
633 3.2 BPF_MAP_CREATE 604 3.2 BPF_MAP_CREATE
634 ------------------ 605 ------------------
635 606
636 A map can be created with ``btf_fd`` and speci 607 A map can be created with ``btf_fd`` and specified key/value type id.::
637 608
638 __u32 btf_fd; /* fd pointing to 609 __u32 btf_fd; /* fd pointing to a BTF type data */
639 __u32 btf_key_type_id; /* BTF typ 610 __u32 btf_key_type_id; /* BTF type_id of the key */
640 __u32 btf_value_type_id; /* BTF typ 611 __u32 btf_value_type_id; /* BTF type_id of the value */
641 612
642 In libbpf, the map can be defined with extra a 613 In libbpf, the map can be defined with extra annotation like below:
643 :: 614 ::
644 615
645 struct { 616 struct {
646 __uint(type, BPF_MAP_TYPE_ARRAY); 617 __uint(type, BPF_MAP_TYPE_ARRAY);
647 __type(key, int); 618 __type(key, int);
648 __type(value, struct ipv_counts); 619 __type(value, struct ipv_counts);
649 __uint(max_entries, 4); 620 __uint(max_entries, 4);
650 } btf_map SEC(".maps"); 621 } btf_map SEC(".maps");
651 622
652 During ELF parsing, libbpf is able to extract 623 During ELF parsing, libbpf is able to extract key/value type_id's and assign
653 them to BPF_MAP_CREATE attributes automaticall 624 them to BPF_MAP_CREATE attributes automatically.
654 625
655 .. _BPF_Prog_Load: 626 .. _BPF_Prog_Load:
656 627
657 3.3 BPF_PROG_LOAD 628 3.3 BPF_PROG_LOAD
658 ----------------- 629 -----------------
659 630
660 During prog_load, func_info and line_info can 631 During prog_load, func_info and line_info can be passed to kernel with proper
661 values for the following attributes: 632 values for the following attributes:
662 :: 633 ::
663 634
664 __u32 insn_cnt; 635 __u32 insn_cnt;
665 __aligned_u64 insns; 636 __aligned_u64 insns;
666 ...... 637 ......
667 __u32 prog_btf_fd; /* fd poin 638 __u32 prog_btf_fd; /* fd pointing to BTF type data */
668 __u32 func_info_rec_size; /* 639 __u32 func_info_rec_size; /* userspace bpf_func_info size */
669 __aligned_u64 func_info; /* func in 640 __aligned_u64 func_info; /* func info */
670 __u32 func_info_cnt; /* number 641 __u32 func_info_cnt; /* number of bpf_func_info records */
671 __u32 line_info_rec_size; /* 642 __u32 line_info_rec_size; /* userspace bpf_line_info size */
672 __aligned_u64 line_info; /* line in 643 __aligned_u64 line_info; /* line info */
673 __u32 line_info_cnt; /* number 644 __u32 line_info_cnt; /* number of bpf_line_info records */
674 645
675 The func_info and line_info are an array of be 646 The func_info and line_info are an array of below, respectively.::
676 647
677 struct bpf_func_info { 648 struct bpf_func_info {
678 __u32 insn_off; /* [0, insn_cnt - 1] 649 __u32 insn_off; /* [0, insn_cnt - 1] */
679 __u32 type_id; /* pointing to a BTF 650 __u32 type_id; /* pointing to a BTF_KIND_FUNC type */
680 }; 651 };
681 struct bpf_line_info { 652 struct bpf_line_info {
682 __u32 insn_off; /* [0, insn_cnt - 1] 653 __u32 insn_off; /* [0, insn_cnt - 1] */
683 __u32 file_name_off; /* offset to st 654 __u32 file_name_off; /* offset to string table for the filename */
684 __u32 line_off; /* offset to string 655 __u32 line_off; /* offset to string table for the source line */
685 __u32 line_col; /* line number and c 656 __u32 line_col; /* line number and column number */
686 }; 657 };
687 658
688 func_info_rec_size is the size of each func_in 659 func_info_rec_size is the size of each func_info record, and
689 line_info_rec_size is the size of each line_in 660 line_info_rec_size is the size of each line_info record. Passing the record
690 size to kernel make it possible to extend the 661 size to kernel make it possible to extend the record itself in the future.
691 662
692 Below are requirements for func_info: 663 Below are requirements for func_info:
693 * func_info[0].insn_off must be 0. 664 * func_info[0].insn_off must be 0.
694 * the func_info insn_off is in strictly incr 665 * the func_info insn_off is in strictly increasing order and matches
695 bpf func boundaries. 666 bpf func boundaries.
696 667
697 Below are requirements for line_info: 668 Below are requirements for line_info:
698 * the first insn in each func must have a li 669 * the first insn in each func must have a line_info record pointing to it.
699 * the line_info insn_off is in strictly incr 670 * the line_info insn_off is in strictly increasing order.
700 671
701 For line_info, the line number and column numb 672 For line_info, the line number and column number are defined as below:
702 :: 673 ::
703 674
704 #define BPF_LINE_INFO_LINE_NUM(line_col) 675 #define BPF_LINE_INFO_LINE_NUM(line_col) ((line_col) >> 10)
705 #define BPF_LINE_INFO_LINE_COL(line_col) 676 #define BPF_LINE_INFO_LINE_COL(line_col) ((line_col) & 0x3ff)
706 677
707 3.4 BPF_{PROG,MAP}_GET_NEXT_ID 678 3.4 BPF_{PROG,MAP}_GET_NEXT_ID
708 ------------------------------ 679 ------------------------------
709 680
710 In kernel, every loaded program, map or btf ha 681 In kernel, every loaded program, map or btf has a unique id. The id won't
711 change during the lifetime of a program, map, 682 change during the lifetime of a program, map, or btf.
712 683
713 The bpf syscall command BPF_{PROG,MAP}_GET_NEX 684 The bpf syscall command BPF_{PROG,MAP}_GET_NEXT_ID returns all id's, one for
714 each command, to user space, for bpf program o 685 each command, to user space, for bpf program or maps, respectively, so an
715 inspection tool can inspect all programs and m 686 inspection tool can inspect all programs and maps.
716 687
717 3.5 BPF_{PROG,MAP}_GET_FD_BY_ID 688 3.5 BPF_{PROG,MAP}_GET_FD_BY_ID
718 ------------------------------- 689 -------------------------------
719 690
720 An introspection tool cannot use id to get det 691 An introspection tool cannot use id to get details about program or maps.
721 A file descriptor needs to be obtained first f 692 A file descriptor needs to be obtained first for reference-counting purpose.
722 693
723 3.6 BPF_OBJ_GET_INFO_BY_FD 694 3.6 BPF_OBJ_GET_INFO_BY_FD
724 -------------------------- 695 --------------------------
725 696
726 Once a program/map fd is acquired, an introspe 697 Once a program/map fd is acquired, an introspection tool can get the detailed
727 information from kernel about this fd, some of 698 information from kernel about this fd, some of which are BTF-related. For
728 example, ``bpf_map_info`` returns ``btf_id`` a 699 example, ``bpf_map_info`` returns ``btf_id`` and key/value type ids.
729 ``bpf_prog_info`` returns ``btf_id``, func_inf 700 ``bpf_prog_info`` returns ``btf_id``, func_info, and line info for translated
730 bpf byte codes, and jited_line_info. 701 bpf byte codes, and jited_line_info.
731 702
732 3.7 BPF_BTF_GET_FD_BY_ID 703 3.7 BPF_BTF_GET_FD_BY_ID
733 ------------------------ 704 ------------------------
734 705
735 With ``btf_id`` obtained in ``bpf_map_info`` a 706 With ``btf_id`` obtained in ``bpf_map_info`` and ``bpf_prog_info``, bpf
736 syscall command BPF_BTF_GET_FD_BY_ID can retri 707 syscall command BPF_BTF_GET_FD_BY_ID can retrieve a btf fd. Then, with
737 command BPF_OBJ_GET_INFO_BY_FD, the btf blob, 708 command BPF_OBJ_GET_INFO_BY_FD, the btf blob, originally loaded into the
738 kernel with BPF_BTF_LOAD, can be retrieved. 709 kernel with BPF_BTF_LOAD, can be retrieved.
739 710
740 With the btf blob, ``bpf_map_info``, and ``bpf 711 With the btf blob, ``bpf_map_info``, and ``bpf_prog_info``, an introspection
741 tool has full btf knowledge and is able to pre 712 tool has full btf knowledge and is able to pretty print map key/values, dump
742 func signatures and line info, along with byte 713 func signatures and line info, along with byte/jit codes.
743 714
744 4. ELF File Format Interface 715 4. ELF File Format Interface
745 ============================ 716 ============================
746 717
747 4.1 .BTF section 718 4.1 .BTF section
748 ---------------- 719 ----------------
749 720
750 The .BTF section contains type and string data 721 The .BTF section contains type and string data. The format of this section is
751 same as the one describe in :ref:`BTF_Type_Str 722 same as the one describe in :ref:`BTF_Type_String`.
752 723
753 .. _BTF_Ext_Section: 724 .. _BTF_Ext_Section:
754 725
755 4.2 .BTF.ext section 726 4.2 .BTF.ext section
756 -------------------- 727 --------------------
757 728
758 The .BTF.ext section encodes func_info, line_i !! 729 The .BTF.ext section encodes func_info and line_info which needs loader
759 which needs loader manipulation before loading !! 730 manipulation before loading into the kernel.
760 731
761 The specification for .BTF.ext section is defi 732 The specification for .BTF.ext section is defined at ``tools/lib/bpf/btf.h``
762 and ``tools/lib/bpf/btf.c``. 733 and ``tools/lib/bpf/btf.c``.
763 734
764 The current header of .BTF.ext section:: 735 The current header of .BTF.ext section::
765 736
766 struct btf_ext_header { 737 struct btf_ext_header {
767 __u16 magic; 738 __u16 magic;
768 __u8 version; 739 __u8 version;
769 __u8 flags; 740 __u8 flags;
770 __u32 hdr_len; 741 __u32 hdr_len;
771 742
772 /* All offsets are in bytes relative t 743 /* All offsets are in bytes relative to the end of this header */
773 __u32 func_info_off; 744 __u32 func_info_off;
774 __u32 func_info_len; 745 __u32 func_info_len;
775 __u32 line_info_off; 746 __u32 line_info_off;
776 __u32 line_info_len; 747 __u32 line_info_len;
777 <<
778 /* optional part of .BTF.ext header */ <<
779 __u32 core_relo_off; <<
780 __u32 core_relo_len; <<
781 }; 748 };
782 749
783 It is very similar to .BTF section. Instead of 750 It is very similar to .BTF section. Instead of type/string section, it
784 contains func_info, line_info and core_relo su !! 751 contains func_info and line_info section. See :ref:`BPF_Prog_Load` for details
785 See :ref:`BPF_Prog_Load` for details about fun !! 752 about func_info and line_info record format.
786 record format. <<
787 753
788 The func_info is organized as below.:: 754 The func_info is organized as below.::
789 755
790 func_info_rec_size /* __u32 !! 756 func_info_rec_size
791 btf_ext_info_sec for section #1 /* func_i 757 btf_ext_info_sec for section #1 /* func_info for section #1 */
792 btf_ext_info_sec for section #2 /* func_i 758 btf_ext_info_sec for section #2 /* func_info for section #2 */
793 ... 759 ...
794 760
795 ``func_info_rec_size`` specifies the size of ` 761 ``func_info_rec_size`` specifies the size of ``bpf_func_info`` structure when
796 .BTF.ext is generated. ``btf_ext_info_sec``, d 762 .BTF.ext is generated. ``btf_ext_info_sec``, defined below, is a collection of
797 func_info for each specific ELF section.:: 763 func_info for each specific ELF section.::
798 764
799 struct btf_ext_info_sec { 765 struct btf_ext_info_sec {
800 __u32 sec_name_off; /* offset to sec 766 __u32 sec_name_off; /* offset to section name */
801 __u32 num_info; 767 __u32 num_info;
802 /* Followed by num_info * record_size 768 /* Followed by num_info * record_size number of bytes */
803 __u8 data[0]; 769 __u8 data[0];
804 }; 770 };
805 771
806 Here, num_info must be greater than 0. 772 Here, num_info must be greater than 0.
807 773
808 The line_info is organized as below.:: 774 The line_info is organized as below.::
809 775
810 line_info_rec_size /* __u32 !! 776 line_info_rec_size
811 btf_ext_info_sec for section #1 /* line_i 777 btf_ext_info_sec for section #1 /* line_info for section #1 */
812 btf_ext_info_sec for section #2 /* line_i 778 btf_ext_info_sec for section #2 /* line_info for section #2 */
813 ... 779 ...
814 780
815 ``line_info_rec_size`` specifies the size of ` 781 ``line_info_rec_size`` specifies the size of ``bpf_line_info`` structure when
816 .BTF.ext is generated. 782 .BTF.ext is generated.
817 783
818 The interpretation of ``bpf_func_info->insn_of 784 The interpretation of ``bpf_func_info->insn_off`` and
819 ``bpf_line_info->insn_off`` is different betwe 785 ``bpf_line_info->insn_off`` is different between kernel API and ELF API. For
820 kernel API, the ``insn_off`` is the instructio 786 kernel API, the ``insn_off`` is the instruction offset in the unit of ``struct
821 bpf_insn``. For ELF API, the ``insn_off`` is t 787 bpf_insn``. For ELF API, the ``insn_off`` is the byte offset from the
822 beginning of section (``btf_ext_info_sec->sec_ 788 beginning of section (``btf_ext_info_sec->sec_name_off``).
823 789
824 The core_relo is organized as below.:: <<
825 <<
826 core_relo_rec_size /* __u32 <<
827 btf_ext_info_sec for section #1 /* core_r <<
828 btf_ext_info_sec for section #2 /* core_r <<
829 <<
830 ``core_relo_rec_size`` specifies the size of ` <<
831 structure when .BTF.ext is generated. All ``bp <<
832 within a single ``btf_ext_info_sec`` describe <<
833 section named by ``btf_ext_info_sec->sec_name_ <<
834 <<
835 See :ref:`Documentation/bpf/llvm_reloc.rst <bt <<
836 for more information on CO-RE relocations. <<
837 <<
838 4.2 .BTF_ids section 790 4.2 .BTF_ids section
839 -------------------- 791 --------------------
840 792
841 The .BTF_ids section encodes BTF ID values tha 793 The .BTF_ids section encodes BTF ID values that are used within the kernel.
842 794
843 This section is created during the kernel comp 795 This section is created during the kernel compilation with the help of
844 macros defined in ``include/linux/btf_ids.h`` 796 macros defined in ``include/linux/btf_ids.h`` header file. Kernel code can
845 use them to create lists and sets (sorted list 797 use them to create lists and sets (sorted lists) of BTF ID values.
846 798
847 The ``BTF_ID_LIST`` and ``BTF_ID`` macros defi 799 The ``BTF_ID_LIST`` and ``BTF_ID`` macros define unsorted list of BTF ID values,
848 with following syntax:: 800 with following syntax::
849 801
850 BTF_ID_LIST(list) 802 BTF_ID_LIST(list)
851 BTF_ID(type1, name1) 803 BTF_ID(type1, name1)
852 BTF_ID(type2, name2) 804 BTF_ID(type2, name2)
853 805
854 resulting in following layout in .BTF_ids sect 806 resulting in following layout in .BTF_ids section::
855 807
856 __BTF_ID__type1__name1__1: 808 __BTF_ID__type1__name1__1:
857 .zero 4 809 .zero 4
858 __BTF_ID__type2__name2__2: 810 __BTF_ID__type2__name2__2:
859 .zero 4 811 .zero 4
860 812
861 The ``u32 list[];`` variable is defined to acc 813 The ``u32 list[];`` variable is defined to access the list.
862 814
863 The ``BTF_ID_UNUSED`` macro defines 4 zero byt 815 The ``BTF_ID_UNUSED`` macro defines 4 zero bytes. It's used when we
864 want to define unused entry in BTF_ID_LIST, li 816 want to define unused entry in BTF_ID_LIST, like::
865 817
866 BTF_ID_LIST(bpf_skb_output_btf_ids) 818 BTF_ID_LIST(bpf_skb_output_btf_ids)
867 BTF_ID(struct, sk_buff) 819 BTF_ID(struct, sk_buff)
868 BTF_ID_UNUSED 820 BTF_ID_UNUSED
869 BTF_ID(struct, task_struct) 821 BTF_ID(struct, task_struct)
870 822
871 The ``BTF_SET_START/END`` macros pair defines 823 The ``BTF_SET_START/END`` macros pair defines sorted list of BTF ID values
872 and their count, with following syntax:: 824 and their count, with following syntax::
873 825
874 BTF_SET_START(set) 826 BTF_SET_START(set)
875 BTF_ID(type1, name1) 827 BTF_ID(type1, name1)
876 BTF_ID(type2, name2) 828 BTF_ID(type2, name2)
877 BTF_SET_END(set) 829 BTF_SET_END(set)
878 830
879 resulting in following layout in .BTF_ids sect 831 resulting in following layout in .BTF_ids section::
880 832
881 __BTF_ID__set__set: 833 __BTF_ID__set__set:
882 .zero 4 834 .zero 4
883 __BTF_ID__type1__name1__3: 835 __BTF_ID__type1__name1__3:
884 .zero 4 836 .zero 4
885 __BTF_ID__type2__name2__4: 837 __BTF_ID__type2__name2__4:
886 .zero 4 838 .zero 4
887 839
888 The ``struct btf_id_set set;`` variable is def 840 The ``struct btf_id_set set;`` variable is defined to access the list.
889 841
890 The ``typeX`` name can be one of following:: 842 The ``typeX`` name can be one of following::
891 843
892 struct, union, typedef, func 844 struct, union, typedef, func
893 845
894 and is used as a filter when resolving the BTF 846 and is used as a filter when resolving the BTF ID value.
895 847
896 All the BTF ID lists and sets are compiled in 848 All the BTF ID lists and sets are compiled in the .BTF_ids section and
897 resolved during the linking phase of kernel bu 849 resolved during the linking phase of kernel build by ``resolve_btfids`` tool.
898 850
899 5. Using BTF 851 5. Using BTF
900 ============ 852 ============
901 853
902 5.1 bpftool map pretty print 854 5.1 bpftool map pretty print
903 ---------------------------- 855 ----------------------------
904 856
905 With BTF, the map key/value can be printed bas 857 With BTF, the map key/value can be printed based on fields rather than simply
906 raw bytes. This is especially valuable for lar 858 raw bytes. This is especially valuable for large structure or if your data
907 structure has bitfields. For example, for the 859 structure has bitfields. For example, for the following map,::
908 860
909 enum A { A1, A2, A3, A4, A5 }; 861 enum A { A1, A2, A3, A4, A5 };
910 typedef enum A ___A; 862 typedef enum A ___A;
911 struct tmp_t { 863 struct tmp_t {
912 char a1:4; 864 char a1:4;
913 int a2:4; 865 int a2:4;
914 int :4; 866 int :4;
915 __u32 a3:4; 867 __u32 a3:4;
916 int b; 868 int b;
917 ___A b1:4; 869 ___A b1:4;
918 enum A b2:4; 870 enum A b2:4;
919 }; 871 };
920 struct { 872 struct {
921 __uint(type, BPF_MAP_TYPE_ARRAY); 873 __uint(type, BPF_MAP_TYPE_ARRAY);
922 __type(key, int); 874 __type(key, int);
923 __type(value, struct tmp_t); 875 __type(value, struct tmp_t);
924 __uint(max_entries, 1); 876 __uint(max_entries, 1);
925 } tmpmap SEC(".maps"); 877 } tmpmap SEC(".maps");
926 878
927 bpftool is able to pretty print like below: 879 bpftool is able to pretty print like below:
928 :: 880 ::
929 881
930 [{ 882 [{
931 "key": 0, 883 "key": 0,
932 "value": { 884 "value": {
933 "a1": 0x2, 885 "a1": 0x2,
934 "a2": 0x4, 886 "a2": 0x4,
935 "a3": 0x6, 887 "a3": 0x6,
936 "b": 7, 888 "b": 7,
937 "b1": 0x8, 889 "b1": 0x8,
938 "b2": 0xa 890 "b2": 0xa
939 } 891 }
940 } 892 }
941 ] 893 ]
942 894
943 5.2 bpftool prog dump 895 5.2 bpftool prog dump
944 --------------------- 896 ---------------------
945 897
946 The following is an example showing how func_i 898 The following is an example showing how func_info and line_info can help prog
947 dump with better kernel symbol names, function 899 dump with better kernel symbol names, function prototypes and line
948 information.:: 900 information.::
949 901
950 $ bpftool prog dump jited pinned /sys/fs/b 902 $ bpftool prog dump jited pinned /sys/fs/bpf/test_btf_haskv
951 [...] 903 [...]
952 int test_long_fname_2(struct dummy_tracepo 904 int test_long_fname_2(struct dummy_tracepoint_args * arg):
953 bpf_prog_44a040bf25481309_test_long_fname_ 905 bpf_prog_44a040bf25481309_test_long_fname_2:
954 ; static int test_long_fname_2(struct dumm 906 ; static int test_long_fname_2(struct dummy_tracepoint_args *arg)
955 0: push %rbp 907 0: push %rbp
956 1: mov %rsp,%rbp 908 1: mov %rsp,%rbp
957 4: sub $0x30,%rsp 909 4: sub $0x30,%rsp
958 b: sub $0x28,%rbp 910 b: sub $0x28,%rbp
959 f: mov %rbx,0x0(%rbp) 911 f: mov %rbx,0x0(%rbp)
960 13: mov %r13,0x8(%rbp) 912 13: mov %r13,0x8(%rbp)
961 17: mov %r14,0x10(%rbp) 913 17: mov %r14,0x10(%rbp)
962 1b: mov %r15,0x18(%rbp) 914 1b: mov %r15,0x18(%rbp)
963 1f: xor %eax,%eax 915 1f: xor %eax,%eax
964 21: mov %rax,0x20(%rbp) 916 21: mov %rax,0x20(%rbp)
965 25: xor %esi,%esi 917 25: xor %esi,%esi
966 ; int key = 0; 918 ; int key = 0;
967 27: mov %esi,-0x4(%rbp) 919 27: mov %esi,-0x4(%rbp)
968 ; if (!arg->sock) 920 ; if (!arg->sock)
969 2a: mov 0x8(%rdi),%rdi 921 2a: mov 0x8(%rdi),%rdi
970 ; if (!arg->sock) 922 ; if (!arg->sock)
971 2e: cmp $0x0,%rdi 923 2e: cmp $0x0,%rdi
972 32: je 0x0000000000000070 924 32: je 0x0000000000000070
973 34: mov %rbp,%rsi 925 34: mov %rbp,%rsi
974 ; counts = bpf_map_lookup_elem(&btf_map, & 926 ; counts = bpf_map_lookup_elem(&btf_map, &key);
975 [...] 927 [...]
976 928
977 5.3 Verifier Log 929 5.3 Verifier Log
978 ---------------- 930 ----------------
979 931
980 The following is an example of how line_info c 932 The following is an example of how line_info can help debugging verification
981 failure.:: 933 failure.::
982 934
983 /* The code at tools/testing/selftests/ 935 /* The code at tools/testing/selftests/bpf/test_xdp_noinline.c
984 * is modified as below. 936 * is modified as below.
985 */ 937 */
986 data = (void *)(long)xdp->data; 938 data = (void *)(long)xdp->data;
987 data_end = (void *)(long)xdp->data_end; 939 data_end = (void *)(long)xdp->data_end;
988 /* 940 /*
989 if (data + 4 > data_end) 941 if (data + 4 > data_end)
990 return XDP_DROP; 942 return XDP_DROP;
991 */ 943 */
992 *(u32 *)data = dst->dst; 944 *(u32 *)data = dst->dst;
993 945
994 $ bpftool prog load ./test_xdp_noinline.o 946 $ bpftool prog load ./test_xdp_noinline.o /sys/fs/bpf/test_xdp_noinline type xdp
995 ; data = (void *)(long)xdp->data; 947 ; data = (void *)(long)xdp->data;
996 224: (79) r2 = *(u64 *)(r10 -112) 948 224: (79) r2 = *(u64 *)(r10 -112)
997 225: (61) r2 = *(u32 *)(r2 +0) 949 225: (61) r2 = *(u32 *)(r2 +0)
998 ; *(u32 *)data = dst->dst; 950 ; *(u32 *)data = dst->dst;
999 226: (63) *(u32 *)(r2 +0) = r1 951 226: (63) *(u32 *)(r2 +0) = r1
1000 invalid access to packet, off=0 size= 952 invalid access to packet, off=0 size=4, R2(id=0,off=0,r=0)
1001 R2 offset is outside of the packet 953 R2 offset is outside of the packet
1002 954
1003 6. BTF Generation 955 6. BTF Generation
1004 ================= 956 =================
1005 957
1006 You need latest pahole 958 You need latest pahole
1007 959
1008 https://git.kernel.org/pub/scm/devel/pahole 960 https://git.kernel.org/pub/scm/devel/pahole/pahole.git/
1009 961
1010 or llvm (8.0 or later). The pahole acts as a 962 or llvm (8.0 or later). The pahole acts as a dwarf2btf converter. It doesn't
1011 support .BTF.ext and btf BTF_KIND_FUNC type y 963 support .BTF.ext and btf BTF_KIND_FUNC type yet. For example,::
1012 964
1013 -bash-4.4$ cat t.c 965 -bash-4.4$ cat t.c
1014 struct t { 966 struct t {
1015 int a:2; 967 int a:2;
1016 int b:3; 968 int b:3;
1017 int c:2; 969 int c:2;
1018 } g; 970 } g;
1019 -bash-4.4$ gcc -c -O2 -g t.c 971 -bash-4.4$ gcc -c -O2 -g t.c
1020 -bash-4.4$ pahole -JV t.o 972 -bash-4.4$ pahole -JV t.o
1021 File t.o: 973 File t.o:
1022 [1] STRUCT t kind_flag=1 size=4 vlen=3 974 [1] STRUCT t kind_flag=1 size=4 vlen=3
1023 a type_id=2 bitfield_size=2 bit 975 a type_id=2 bitfield_size=2 bits_offset=0
1024 b type_id=2 bitfield_size=3 bit 976 b type_id=2 bitfield_size=3 bits_offset=2
1025 c type_id=2 bitfield_size=2 bit 977 c type_id=2 bitfield_size=2 bits_offset=5
1026 [2] INT int size=4 bit_offset=0 nr_bits 978 [2] INT int size=4 bit_offset=0 nr_bits=32 encoding=SIGNED
1027 979
1028 The llvm is able to generate .BTF and .BTF.ex 980 The llvm is able to generate .BTF and .BTF.ext directly with -g for bpf target
1029 only. The assembly code (-S) is able to show 981 only. The assembly code (-S) is able to show the BTF encoding in assembly
1030 format.:: 982 format.::
1031 983
1032 -bash-4.4$ cat t2.c 984 -bash-4.4$ cat t2.c
1033 typedef int __int32; 985 typedef int __int32;
1034 struct t2 { 986 struct t2 {
1035 int a2; 987 int a2;
1036 int (*f2)(char q1, __int32 q2, ...); 988 int (*f2)(char q1, __int32 q2, ...);
1037 int (*f3)(); 989 int (*f3)();
1038 } g2; 990 } g2;
1039 int main() { return 0; } 991 int main() { return 0; }
1040 int test() { return 0; } 992 int test() { return 0; }
1041 -bash-4.4$ clang -c -g -O2 --target=bpf t !! 993 -bash-4.4$ clang -c -g -O2 -target bpf t2.c
1042 -bash-4.4$ readelf -S t2.o 994 -bash-4.4$ readelf -S t2.o
1043 ...... 995 ......
1044 [ 8] .BTF PROGBITS 996 [ 8] .BTF PROGBITS 0000000000000000 00000247
1045 000000000000016e 0000000000000000 997 000000000000016e 0000000000000000 0 0 1
1046 [ 9] .BTF.ext PROGBITS 998 [ 9] .BTF.ext PROGBITS 0000000000000000 000003b5
1047 0000000000000060 0000000000000000 999 0000000000000060 0000000000000000 0 0 1
1048 [10] .rel.BTF.ext REL 1000 [10] .rel.BTF.ext REL 0000000000000000 000007e0
1049 0000000000000040 0000000000000010 1001 0000000000000040 0000000000000010 16 9 8
1050 ...... 1002 ......
1051 -bash-4.4$ clang -S -g -O2 --target=bpf t !! 1003 -bash-4.4$ clang -S -g -O2 -target bpf t2.c
1052 -bash-4.4$ cat t2.s 1004 -bash-4.4$ cat t2.s
1053 ...... 1005 ......
1054 .section .BTF,"",@progbits 1006 .section .BTF,"",@progbits
1055 .short 60319 # 1007 .short 60319 # 0xeb9f
1056 .byte 1 1008 .byte 1
1057 .byte 0 1009 .byte 0
1058 .long 24 1010 .long 24
1059 .long 0 1011 .long 0
1060 .long 220 1012 .long 220
1061 .long 220 1013 .long 220
1062 .long 122 1014 .long 122
1063 .long 0 # 1015 .long 0 # BTF_KIND_FUNC_PROTO(id = 1)
1064 .long 218103808 # 1016 .long 218103808 # 0xd000000
1065 .long 2 1017 .long 2
1066 .long 83 # 1018 .long 83 # BTF_KIND_INT(id = 2)
1067 .long 16777216 # 1019 .long 16777216 # 0x1000000
1068 .long 4 1020 .long 4
1069 .long 16777248 # 1021 .long 16777248 # 0x1000020
1070 ...... 1022 ......
1071 .byte 0 # 1023 .byte 0 # string offset=0
1072 .ascii ".text" # 1024 .ascii ".text" # string offset=1
1073 .byte 0 1025 .byte 0
1074 .ascii "/home/yhs/tmp-pahole/t2. 1026 .ascii "/home/yhs/tmp-pahole/t2.c" # string offset=7
1075 .byte 0 1027 .byte 0
1076 .ascii "int main() { return 0; } 1028 .ascii "int main() { return 0; }" # string offset=33
1077 .byte 0 1029 .byte 0
1078 .ascii "int test() { return 0; } 1030 .ascii "int test() { return 0; }" # string offset=58
1079 .byte 0 1031 .byte 0
1080 .ascii "int" # 1032 .ascii "int" # string offset=83
1081 ...... 1033 ......
1082 .section .BTF.ext,"",@prog 1034 .section .BTF.ext,"",@progbits
1083 .short 60319 # 1035 .short 60319 # 0xeb9f
1084 .byte 1 1036 .byte 1
1085 .byte 0 1037 .byte 0
1086 .long 24 1038 .long 24
1087 .long 0 1039 .long 0
1088 .long 28 1040 .long 28
1089 .long 28 1041 .long 28
1090 .long 44 1042 .long 44
1091 .long 8 # 1043 .long 8 # FuncInfo
1092 .long 1 # 1044 .long 1 # FuncInfo section string offset=1
1093 .long 2 1045 .long 2
1094 .long .Lfunc_begin0 1046 .long .Lfunc_begin0
1095 .long 3 1047 .long 3
1096 .long .Lfunc_begin1 1048 .long .Lfunc_begin1
1097 .long 5 1049 .long 5
1098 .long 16 # 1050 .long 16 # LineInfo
1099 .long 1 # 1051 .long 1 # LineInfo section string offset=1
1100 .long 2 1052 .long 2
1101 .long .Ltmp0 1053 .long .Ltmp0
1102 .long 7 1054 .long 7
1103 .long 33 1055 .long 33
1104 .long 7182 # 1056 .long 7182 # Line 7 Col 14
1105 .long .Ltmp3 1057 .long .Ltmp3
1106 .long 7 1058 .long 7
1107 .long 58 1059 .long 58
1108 .long 8206 # 1060 .long 8206 # Line 8 Col 14
1109 1061
1110 7. Testing 1062 7. Testing
1111 ========== 1063 ==========
1112 1064
1113 The kernel BPF selftest `tools/testing/selfte 1065 The kernel BPF selftest `tools/testing/selftests/bpf/prog_tests/btf.c`_
1114 provides an extensive set of BTF-related test 1066 provides an extensive set of BTF-related tests.
1115 1067
1116 .. Links 1068 .. Links
1117 .. _tools/testing/selftests/bpf/prog_tests/bt 1069 .. _tools/testing/selftests/bpf/prog_tests/btf.c:
1118 https://git.kernel.org/pub/scm/linux/kerne 1070 https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/bpf/prog_tests/btf.c
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