tools/bpf/bpftool/Documentation/bpftool-btf.rst
.. SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
:Manual section: 8
.. include:: substitutions.rst
**bpftool** [*OPTIONS*] **btf** *COMMAND*
*OPTIONS* := { |COMMON_OPTIONS| | { **-B** | **--base-btf** } }
*COMMANDS* := { **dump** | **help** }
| bpftool btf { show | list } [id BTF_ID] | bpftool btf dump BTF_SRC [format FORMAT] | bpftool btf help | | BTF_SRC := { id BTF_ID | prog PROG | map MAP [{key | value | kv | all}] | file FILE } | FORMAT := { raw | c } | MAP := { id MAP_ID | pinned FILE } | PROG := { id PROG_ID | pinned FILE | tag PROG_TAG }
**bpftool btf { show | list }** [**id** *BTF_ID*]
Show information about loaded BTF objects. If a BTF ID is
specified, show information only about given BTF object,
otherwise list all BTF objects currently loaded on the
system.
Since Linux 5.8 bpftool is able to discover information about
processes that hold open file descriptors (FDs) against BTF
objects. On such kernels bpftool will automatically emit this
information as well.
**bpftool btf dump** *BTF_SRC*
Dump BTF entries from a given *BTF_SRC*.
When **id** is specified, BTF object with that ID will be
loaded and all its BTF types emitted.
When **map** is provided, it's expected that map has
associated BTF object with BTF types describing key and
value. It's possible to select whether to dump only BTF
type(s) associated with key (**key**), value (**value**),
both key and value (**kv**), or all BTF types present in
associated BTF object (**all**). If not specified, **kv**
is assumed.
When **prog** is provided, it's expected that program has
associated BTF object with BTF types.
When specifying *FILE*, an ELF file is expected, containing
.BTF section with well-defined BTF binary format data,
typically produced by clang or pahole.
**format** option can be used to override default (raw)
output format. Raw (**raw**) or C-syntax (**c**) output
formats are supported.
**bpftool btf help**
Print short help message.
.. include:: common_options.rst
-B, --base-btf *FILE*
Pass a base BTF object. Base BTF objects are typically used
with BTF objects for kernel modules. To avoid duplicating
all kernel symbols required by modules, BTF objects for
modules are "split", they are built incrementally on top of
the kernel (vmlinux) BTF object. So the base BTF reference
should usually point to the kernel BTF.
When the main BTF object to process (for example, the
module BTF to dump) is passed as a *FILE*, bpftool attempts
to autodetect the path for the base object, and passing
this option is optional. When the main BTF object is passed
through other handles, this option becomes necessary.
# bpftool btf dump id 1226
::
[1] PTR '(anon)' type_id=2 [2] STRUCT 'dummy_tracepoint_args' size=16 vlen=2 'pad' type_id=3 bits_offset=0 'sock' type_id=4 bits_offset=64 [3] INT 'long long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none) [4] PTR '(anon)' type_id=5 [5] FWD 'sock' fwd_kind=union
This gives an example of default output for all supported BTF kinds.
$ cat prog.c
::
struct fwd_struct;
enum my_enum { VAL1 = 3, VAL2 = 7, };
typedef struct my_struct my_struct_t;
struct my_struct { const unsigned int const_int_field; int bitfield_field: 4; char arr_field[16]; const struct fwd_struct *restrict fwd_field; enum my_enum enum_field; volatile my_struct_t *typedef_ptr_field; };
union my_union { int a; struct my_struct b; };
struct my_struct struct_global_var attribute((section("data_sec"))) = { .bitfield_field = 3, .enum_field = VAL1, }; int global_var attribute((section("data_sec"))) = 7;
attribute((noinline)) int my_func(union my_union *arg1, int arg2) { static int static_var attribute((section("data_sec"))) = 123; static_var++; return static_var; }
$ bpftool btf dump file prog.o
::
[1] PTR '(anon)' type_id=2 [2] UNION 'my_union' size=48 vlen=2 'a' type_id=3 bits_offset=0 'b' type_id=4 bits_offset=0 [3] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED [4] STRUCT 'my_struct' size=48 vlen=6 'const_int_field' type_id=5 bits_offset=0 'bitfield_field' type_id=3 bits_offset=32 bitfield_size=4 'arr_field' type_id=8 bits_offset=40 'fwd_field' type_id=10 bits_offset=192 'enum_field' type_id=14 bits_offset=256 'typedef_ptr_field' type_id=15 bits_offset=320 [5] CONST '(anon)' type_id=6 [6] INT 'unsigned int' size=4 bits_offset=0 nr_bits=32 encoding=(none) [7] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED [8] ARRAY '(anon)' type_id=7 index_type_id=9 nr_elems=16 [9] INT 'ARRAY_SIZE_TYPE' size=4 bits_offset=0 nr_bits=32 encoding=(none) [10] RESTRICT '(anon)' type_id=11 [11] PTR '(anon)' type_id=12 [12] CONST '(anon)' type_id=13 [13] FWD 'fwd_struct' fwd_kind=union [14] ENUM 'my_enum' size=4 vlen=2 'VAL1' val=3 'VAL2' val=7 [15] PTR '(anon)' type_id=16 [16] VOLATILE '(anon)' type_id=17 [17] TYPEDEF 'my_struct_t' type_id=4 [18] FUNC_PROTO '(anon)' ret_type_id=3 vlen=2 'arg1' type_id=1 'arg2' type_id=3 [19] FUNC 'my_func' type_id=18 [20] VAR 'struct_global_var' type_id=4, linkage=global-alloc [21] VAR 'global_var' type_id=3, linkage=global-alloc [22] VAR 'my_func.static_var' type_id=3, linkage=static [23] DATASEC 'data_sec' size=0 vlen=3 type_id=20 offset=0 size=48 type_id=21 offset=0 size=4 type_id=22 offset=52 size=4
The following commands print BTF types associated with specified map's key, value, both key and value, and all BTF types, respectively. By default, both key and value types will be printed.
# bpftool btf dump map id 123 key
::
[39] TYPEDEF 'u32' type_id=37
# bpftool btf dump map id 123 value
::
[86] PTR '(anon)' type_id=87
# bpftool btf dump map id 123 kv
::
[39] TYPEDEF 'u32' type_id=37 [86] PTR '(anon)' type_id=87
# bpftool btf dump map id 123 all
::
[1] PTR '(anon)' type_id=0 . . . [2866] ARRAY '(anon)' type_id=52 index_type_id=51 nr_elems=4
All the standard ways to specify map or program are supported:
# bpftool btf dump map id 123
# bpftool btf dump map pinned /sys/fs/bpf/map_name
# bpftool btf dump prog id 456
# bpftool btf dump prog tag b88e0a09b1d9759d
# bpftool btf dump prog pinned /sys/fs/bpf/prog_name
| | # bpftool btf dump file /sys/kernel/btf/i2c_smbus | (or) | # I2C_SMBUS_ID=$(bpftool btf show -p | jq '.[] | select(.name=="i2c_smbus").id') | # bpftool btf dump id ${I2C_SMBUS_ID} -B /sys/kernel/btf/vmlinux
::
[104848] STRUCT 'i2c_smbus_alert' size=40 vlen=2 'alert' type_id=393 bits_offset=0 'ara' type_id=56050 bits_offset=256 [104849] STRUCT 'alert_data' size=12 vlen=3 'addr' type_id=16 bits_offset=0 'type' type_id=56053 bits_offset=32 'data' type_id=7 bits_offset=64 [104850] PTR '(anon)' type_id=104848 [104851] PTR '(anon)' type_id=104849 [104852] FUNC 'i2c_register_spd' type_id=84745 linkage=static [104853] FUNC 'smbalert_driver_init' type_id=1213 linkage=static [104854] FUNC_PROTO '(anon)' ret_type_id=18 vlen=1 'ara' type_id=56050 [104855] FUNC 'i2c_handle_smbus_alert' type_id=104854 linkage=static [104856] FUNC 'smbalert_remove' type_id=104854 linkage=static [104857] FUNC_PROTO '(anon)' ret_type_id=18 vlen=2 'ara' type_id=56050 'id' type_id=56056 [104858] FUNC 'smbalert_probe' type_id=104857 linkage=static [104859] FUNC 'smbalert_work' type_id=9695 linkage=static [104860] FUNC 'smbus_alert' type_id=71367 linkage=static [104861] FUNC 'smbus_do_alert' type_id=84827 linkage=static