1 .. SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
2
3 ================
4 bpftool-btf
5 ================
6 -------------------------------------------------------------------------------
7 tool for inspection of BTF data
8 -------------------------------------------------------------------------------
9
10 :Manual section: 8
11
12 .. include:: substitutions.rst
13
14 SYNOPSIS
15 ========
16
17 **bpftool** [*OPTIONS*] **btf** *COMMAND*
18
19 *OPTIONS* := { |COMMON_OPTIONS| | { **-B** | **--base-btf** } }
20
21 *COMMANDS* := { **dump** | **help** }
22
23 BTF COMMANDS
24 =============
25
26 | **bpftool** **btf** { **show** | **list** } [**id** *BTF_ID*]
27 | **bpftool** **btf dump** *BTF_SRC* [**format** *FORMAT*]
28 | **bpftool** **btf help**
29 |
30 | *BTF_SRC* := { **id** *BTF_ID* | **prog** *PROG* | **map** *MAP* [{**key** | **value** | **kv** | **all**}] | **file** *FILE* }
31 | *FORMAT* := { **raw** | **c** [**unsorted**] }
32 | *MAP* := { **id** *MAP_ID* | **pinned** *FILE* }
33 | *PROG* := { **id** *PROG_ID* | **pinned** *FILE* | **tag** *PROG_TAG* | **name** *PROG_NAME* }
34
35 DESCRIPTION
36 ===========
37 bpftool btf { show | list } [id *BTF_ID*]
38 Show information about loaded BTF objects. If a BTF ID is specified, show
39 information only about given BTF object, otherwise list all BTF objects
40 currently loaded on the system.
41
42 Since Linux 5.8 bpftool is able to discover information about processes
43 that hold open file descriptors (FDs) against BTF objects. On such kernels
44 bpftool will automatically emit this information as well.
45
46 bpftool btf dump *BTF_SRC*
47 Dump BTF entries from a given *BTF_SRC*.
48
49 When **id** is specified, BTF object with that ID will be loaded and all
50 its BTF types emitted.
51
52 When **map** is provided, it's expected that map has associated BTF object
53 with BTF types describing key and value. It's possible to select whether to
54 dump only BTF type(s) associated with key (**key**), value (**value**),
55 both key and value (**kv**), or all BTF types present in associated BTF
56 object (**all**). If not specified, **kv** is assumed.
57
58 When **prog** is provided, it's expected that program has associated BTF
59 object with BTF types.
60
61 When specifying *FILE*, an ELF file is expected, containing .BTF section
62 with well-defined BTF binary format data, typically produced by clang or
63 pahole.
64
65 **format** option can be used to override default (raw) output format. Raw
66 (**raw**) or C-syntax (**c**) output formats are supported. With C-style
67 formatting, the output is sorted by default. Use the **unsorted** option
68 to avoid sorting the output.
69
70 bpftool btf help
71 Print short help message.
72
73 OPTIONS
74 =======
75 .. include:: common_options.rst
76
77 -B, --base-btf *FILE*
78 Pass a base BTF object. Base BTF objects are typically used with BTF
79 objects for kernel modules. To avoid duplicating all kernel symbols
80 required by modules, BTF objects for modules are "split", they are
81 built incrementally on top of the kernel (vmlinux) BTF object. So the
82 base BTF reference should usually point to the kernel BTF.
83
84 When the main BTF object to process (for example, the module BTF to
85 dump) is passed as a *FILE*, bpftool attempts to autodetect the path
86 for the base object, and passing this option is optional. When the main
87 BTF object is passed through other handles, this option becomes
88 necessary.
89
90 EXAMPLES
91 ========
92 **# bpftool btf dump id 1226**
93
94 ::
95
96 [1] PTR '(anon)' type_id=2
97 [2] STRUCT 'dummy_tracepoint_args' size=16 vlen=2
98 'pad' type_id=3 bits_offset=0
99 'sock' type_id=4 bits_offset=64
100 [3] INT 'long long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
101 [4] PTR '(anon)' type_id=5
102 [5] FWD 'sock' fwd_kind=union
103
104 This gives an example of default output for all supported BTF kinds.
105
106 **$ cat prog.c**
107
108 ::
109
110 struct fwd_struct;
111
112 enum my_enum {
113 VAL1 = 3,
114 VAL2 = 7,
115 };
116
117 typedef struct my_struct my_struct_t;
118
119 struct my_struct {
120 const unsigned int const_int_field;
121 int bitfield_field: 4;
122 char arr_field[16];
123 const struct fwd_struct *restrict fwd_field;
124 enum my_enum enum_field;
125 volatile my_struct_t *typedef_ptr_field;
126 };
127
128 union my_union {
129 int a;
130 struct my_struct b;
131 };
132
133 struct my_struct struct_global_var __attribute__((section("data_sec"))) = {
134 .bitfield_field = 3,
135 .enum_field = VAL1,
136 };
137 int global_var __attribute__((section("data_sec"))) = 7;
138
139 __attribute__((noinline))
140 int my_func(union my_union *arg1, int arg2)
141 {
142 static int static_var __attribute__((section("data_sec"))) = 123;
143 static_var++;
144 return static_var;
145 }
146
147 **$ bpftool btf dump file prog.o**
148
149 ::
150
151 [1] PTR '(anon)' type_id=2
152 [2] UNION 'my_union' size=48 vlen=2
153 'a' type_id=3 bits_offset=0
154 'b' type_id=4 bits_offset=0
155 [3] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
156 [4] STRUCT 'my_struct' size=48 vlen=6
157 'const_int_field' type_id=5 bits_offset=0
158 'bitfield_field' type_id=3 bits_offset=32 bitfield_size=4
159 'arr_field' type_id=8 bits_offset=40
160 'fwd_field' type_id=10 bits_offset=192
161 'enum_field' type_id=14 bits_offset=256
162 'typedef_ptr_field' type_id=15 bits_offset=320
163 [5] CONST '(anon)' type_id=6
164 [6] INT 'unsigned int' size=4 bits_offset=0 nr_bits=32 encoding=(none)
165 [7] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED
166 [8] ARRAY '(anon)' type_id=7 index_type_id=9 nr_elems=16
167 [9] INT '__ARRAY_SIZE_TYPE__' size=4 bits_offset=0 nr_bits=32 encoding=(none)
168 [10] RESTRICT '(anon)' type_id=11
169 [11] PTR '(anon)' type_id=12
170 [12] CONST '(anon)' type_id=13
171 [13] FWD 'fwd_struct' fwd_kind=union
172 [14] ENUM 'my_enum' size=4 vlen=2
173 'VAL1' val=3
174 'VAL2' val=7
175 [15] PTR '(anon)' type_id=16
176 [16] VOLATILE '(anon)' type_id=17
177 [17] TYPEDEF 'my_struct_t' type_id=4
178 [18] FUNC_PROTO '(anon)' ret_type_id=3 vlen=2
179 'arg1' type_id=1
180 'arg2' type_id=3
181 [19] FUNC 'my_func' type_id=18
182 [20] VAR 'struct_global_var' type_id=4, linkage=global-alloc
183 [21] VAR 'global_var' type_id=3, linkage=global-alloc
184 [22] VAR 'my_func.static_var' type_id=3, linkage=static
185 [23] DATASEC 'data_sec' size=0 vlen=3
186 type_id=20 offset=0 size=48
187 type_id=21 offset=0 size=4
188 type_id=22 offset=52 size=4
189
190 The following commands print BTF types associated with specified map's key,
191 value, both key and value, and all BTF types, respectively. By default, both
192 key and value types will be printed.
193
194 **# bpftool btf dump map id 123 key**
195
196 ::
197
198 [39] TYPEDEF 'u32' type_id=37
199
200 **# bpftool btf dump map id 123 value**
201
202 ::
203
204 [86] PTR '(anon)' type_id=87
205
206 **# bpftool btf dump map id 123 kv**
207
208 ::
209
210 [39] TYPEDEF 'u32' type_id=37
211 [86] PTR '(anon)' type_id=87
212
213 **# bpftool btf dump map id 123 all**
214
215 ::
216
217 [1] PTR '(anon)' type_id=0
218 .
219 .
220 .
221 [2866] ARRAY '(anon)' type_id=52 index_type_id=51 nr_elems=4
222
223 All the standard ways to specify map or program are supported:
224
225 **# bpftool btf dump map id 123**
226
227 **# bpftool btf dump map pinned /sys/fs/bpf/map_name**
228
229 **# bpftool btf dump prog id 456**
230
231 **# bpftool btf dump prog tag b88e0a09b1d9759d**
232
233 **# bpftool btf dump prog pinned /sys/fs/bpf/prog_name**
234
235 |
236 | **# bpftool btf dump file /sys/kernel/btf/i2c_smbus**
237 | (or)
238 | **# I2C_SMBUS_ID=$(bpftool btf show -p | jq '.[] | select(.name=="i2c_smbus").id')**
239 | **# bpftool btf dump id ${I2C_SMBUS_ID} -B /sys/kernel/btf/vmlinux**
240
241 ::
242
243 [104848] STRUCT 'i2c_smbus_alert' size=40 vlen=2
244 'alert' type_id=393 bits_offset=0
245 'ara' type_id=56050 bits_offset=256
246 [104849] STRUCT 'alert_data' size=12 vlen=3
247 'addr' type_id=16 bits_offset=0
248 'type' type_id=56053 bits_offset=32
249 'data' type_id=7 bits_offset=64
250 [104850] PTR '(anon)' type_id=104848
251 [104851] PTR '(anon)' type_id=104849
252 [104852] FUNC 'i2c_register_spd' type_id=84745 linkage=static
253 [104853] FUNC 'smbalert_driver_init' type_id=1213 linkage=static
254 [104854] FUNC_PROTO '(anon)' ret_type_id=18 vlen=1
255 'ara' type_id=56050
256 [104855] FUNC 'i2c_handle_smbus_alert' type_id=104854 linkage=static
257 [104856] FUNC 'smbalert_remove' type_id=104854 linkage=static
258 [104857] FUNC_PROTO '(anon)' ret_type_id=18 vlen=2
259 'ara' type_id=56050
260 'id' type_id=56056
261 [104858] FUNC 'smbalert_probe' type_id=104857 linkage=static
262 [104859] FUNC 'smbalert_work' type_id=9695 linkage=static
263 [104860] FUNC 'smbus_alert' type_id=71367 linkage=static
264 [104861] FUNC 'smbus_do_alert' type_id=84827 linkage=static
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