1================
2bpftool-btf
3================
4-------------------------------------------------------------------------------
5tool for inspection of BTF data
6-------------------------------------------------------------------------------
7
8:Manual section: 8
9
10SYNOPSIS
11========
12
13	**bpftool** [*OPTIONS*] **btf** *COMMAND*
14
15	*OPTIONS* := { { **-j** | **--json** } [{ **-p** | **--pretty** }] | {**-d** | **--debug** } |
16		{ **-B** | **--base-btf** } }
17
18	*COMMANDS* := { **dump** | **help** }
19
20BTF COMMANDS
21=============
22
23|	**bpftool** **btf** { **show** | **list** } [**id** *BTF_ID*]
24|	**bpftool** **btf dump** *BTF_SRC* [**format** *FORMAT*]
25|	**bpftool** **btf help**
26|
27|	*BTF_SRC* := { **id** *BTF_ID* | **prog** *PROG* | **map** *MAP* [{**key** | **value** | **kv** | **all**}] | **file** *FILE* }
28|	*FORMAT* := { **raw** | **c** }
29|	*MAP* := { **id** *MAP_ID* | **pinned** *FILE* }
30|	*PROG* := { **id** *PROG_ID* | **pinned** *FILE* | **tag** *PROG_TAG* }
31
32DESCRIPTION
33===========
34	**bpftool btf { show | list }** [**id** *BTF_ID*]
35		  Show information about loaded BTF objects. If a BTF ID is
36		  specified, show information only about given BTF object,
37		  otherwise list all BTF objects currently loaded on the
38		  system.
39
40		  Since Linux 5.8 bpftool is able to discover information about
41		  processes that hold open file descriptors (FDs) against BTF
42		  objects. On such kernels bpftool will automatically emit this
43		  information as well.
44
45	**bpftool btf dump** *BTF_SRC*
46		  Dump BTF entries from a given *BTF_SRC*.
47
48		  When **id** is specified, BTF object with that ID will be
49		  loaded and all its BTF types emitted.
50
51		  When **map** is provided, it's expected that map has
52		  associated BTF object with BTF types describing key and
53		  value. It's possible to select whether to dump only BTF
54		  type(s) associated with key (**key**), value (**value**),
55		  both key and value (**kv**), or all BTF types present in
56		  associated BTF object (**all**). If not specified, **kv**
57		  is assumed.
58
59		  When **prog** is provided, it's expected that program has
60		  associated BTF object with BTF types.
61
62		  When specifying *FILE*, an ELF file is expected, containing
63		  .BTF section with well-defined BTF binary format data,
64		  typically produced by clang or pahole.
65
66		  **format** option can be used to override default (raw)
67		  output format. Raw (**raw**) or C-syntax (**c**) output
68		  formats are supported.
69
70	**bpftool btf help**
71		  Print short help message.
72
73OPTIONS
74=======
75	.. include:: common_options.rst
76
77	-B, --base-btf *FILE*
78		  Pass a base BTF object. Base BTF objects are typically used
79		  with BTF objects for kernel modules. To avoid duplicating
80		  all kernel symbols required by modules, BTF objects for
81		  modules are "split", they are built incrementally on top of
82		  the kernel (vmlinux) BTF object. So the base BTF reference
83		  should usually point to the kernel BTF.
84
85		  When the main BTF object to process (for example, the
86		  module BTF to dump) is passed as a *FILE*, bpftool attempts
87		  to autodetect the path for the base object, and passing
88		  this option is optional. When the main BTF object is passed
89		  through other handles, this option becomes necessary.
90
91EXAMPLES
92========
93**# bpftool btf dump id 1226**
94
95::
96
97  [1] PTR '(anon)' type_id=2
98  [2] STRUCT 'dummy_tracepoint_args' size=16 vlen=2
99          'pad' type_id=3 bits_offset=0
100          'sock' type_id=4 bits_offset=64
101  [3] INT 'long long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
102  [4] PTR '(anon)' type_id=5
103  [5] FWD 'sock' fwd_kind=union
104
105This gives an example of default output for all supported BTF kinds.
106
107**$ cat prog.c**
108
109::
110
111  struct fwd_struct;
112
113  enum my_enum {
114          VAL1 = 3,
115          VAL2 = 7,
116  };
117
118  typedef struct my_struct my_struct_t;
119
120  struct my_struct {
121          const unsigned int const_int_field;
122          int bitfield_field: 4;
123          char arr_field[16];
124          const struct fwd_struct *restrict fwd_field;
125          enum my_enum enum_field;
126          volatile my_struct_t *typedef_ptr_field;
127  };
128
129  union my_union {
130          int a;
131          struct my_struct b;
132  };
133
134  struct my_struct struct_global_var __attribute__((section("data_sec"))) = {
135          .bitfield_field = 3,
136          .enum_field = VAL1,
137  };
138  int global_var __attribute__((section("data_sec"))) = 7;
139
140  __attribute__((noinline))
141  int my_func(union my_union *arg1, int arg2)
142  {
143          static int static_var __attribute__((section("data_sec"))) = 123;
144          static_var++;
145          return static_var;
146  }
147
148**$ bpftool btf dump file prog.o**
149
150::
151
152  [1] PTR '(anon)' type_id=2
153  [2] UNION 'my_union' size=48 vlen=2
154          'a' type_id=3 bits_offset=0
155          'b' type_id=4 bits_offset=0
156  [3] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
157  [4] STRUCT 'my_struct' size=48 vlen=6
158          'const_int_field' type_id=5 bits_offset=0
159          'bitfield_field' type_id=3 bits_offset=32 bitfield_size=4
160          'arr_field' type_id=8 bits_offset=40
161          'fwd_field' type_id=10 bits_offset=192
162          'enum_field' type_id=14 bits_offset=256
163          'typedef_ptr_field' type_id=15 bits_offset=320
164  [5] CONST '(anon)' type_id=6
165  [6] INT 'unsigned int' size=4 bits_offset=0 nr_bits=32 encoding=(none)
166  [7] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED
167  [8] ARRAY '(anon)' type_id=7 index_type_id=9 nr_elems=16
168  [9] INT '__ARRAY_SIZE_TYPE__' size=4 bits_offset=0 nr_bits=32 encoding=(none)
169  [10] RESTRICT '(anon)' type_id=11
170  [11] PTR '(anon)' type_id=12
171  [12] CONST '(anon)' type_id=13
172  [13] FWD 'fwd_struct' fwd_kind=union
173  [14] ENUM 'my_enum' size=4 vlen=2
174          'VAL1' val=3
175          'VAL2' val=7
176  [15] PTR '(anon)' type_id=16
177  [16] VOLATILE '(anon)' type_id=17
178  [17] TYPEDEF 'my_struct_t' type_id=4
179  [18] FUNC_PROTO '(anon)' ret_type_id=3 vlen=2
180          'arg1' type_id=1
181          'arg2' type_id=3
182  [19] FUNC 'my_func' type_id=18
183  [20] VAR 'struct_global_var' type_id=4, linkage=global-alloc
184  [21] VAR 'global_var' type_id=3, linkage=global-alloc
185  [22] VAR 'my_func.static_var' type_id=3, linkage=static
186  [23] DATASEC 'data_sec' size=0 vlen=3
187          type_id=20 offset=0 size=48
188          type_id=21 offset=0 size=4
189          type_id=22 offset=52 size=4
190
191The following commands print BTF types associated with specified map's key,
192value, both key and value, and all BTF types, respectively. By default, both
193key and value types will be printed.
194
195**# bpftool btf dump map id 123 key**
196
197::
198
199  [39] TYPEDEF 'u32' type_id=37
200
201**# bpftool btf dump map id 123 value**
202
203::
204
205  [86] PTR '(anon)' type_id=87
206
207**# bpftool btf dump map id 123 kv**
208
209::
210
211  [39] TYPEDEF 'u32' type_id=37
212  [86] PTR '(anon)' type_id=87
213
214**# bpftool btf dump map id 123 all**
215
216::
217
218  [1] PTR '(anon)' type_id=0
219  .
220  .
221  .
222  [2866] ARRAY '(anon)' type_id=52 index_type_id=51 nr_elems=4
223
224All the standard ways to specify map or program are supported:
225
226**# bpftool btf dump map id 123**
227
228**# bpftool btf dump map pinned /sys/fs/bpf/map_name**
229
230**# bpftool btf dump prog id 456**
231
232**# bpftool btf dump prog tag b88e0a09b1d9759d**
233
234**# bpftool btf dump prog pinned /sys/fs/bpf/prog_name**
235
236|
237| **# bpftool btf dump file /sys/kernel/btf/i2c_smbus**
238| (or)
239| **# I2C_SMBUS_ID=$(bpftool btf show -p | jq '.[] | select(.name=="i2c_smbus").id')**
240| **# bpftool btf dump id ${I2C_SMBUS_ID} -B /sys/kernel/btf/vmlinux**
241
242::
243
244  [104848] STRUCT 'i2c_smbus_alert' size=40 vlen=2
245          'alert' type_id=393 bits_offset=0
246          'ara' type_id=56050 bits_offset=256
247  [104849] STRUCT 'alert_data' size=12 vlen=3
248          'addr' type_id=16 bits_offset=0
249          'type' type_id=56053 bits_offset=32
250          'data' type_id=7 bits_offset=64
251  [104850] PTR '(anon)' type_id=104848
252  [104851] PTR '(anon)' type_id=104849
253  [104852] FUNC 'i2c_register_spd' type_id=84745 linkage=static
254  [104853] FUNC 'smbalert_driver_init' type_id=1213 linkage=static
255  [104854] FUNC_PROTO '(anon)' ret_type_id=18 vlen=1
256          'ara' type_id=56050
257  [104855] FUNC 'i2c_handle_smbus_alert' type_id=104854 linkage=static
258  [104856] FUNC 'smbalert_remove' type_id=104854 linkage=static
259  [104857] FUNC_PROTO '(anon)' ret_type_id=18 vlen=2
260          'ara' type_id=56050
261          'id' type_id=56056
262  [104858] FUNC 'smbalert_probe' type_id=104857 linkage=static
263  [104859] FUNC 'smbalert_work' type_id=9695 linkage=static
264  [104860] FUNC 'smbus_alert' type_id=71367 linkage=static
265  [104861] FUNC 'smbus_do_alert' type_id=84827 linkage=static
266