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