.. SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)

================
bpftool-btf
================
-------------------------------------------------------------------------------
tool for inspection of BTF data
-------------------------------------------------------------------------------

:Manual section: 8

.. include:: substitutions.rst

SYNOPSIS
========

**bpftool** [*OPTIONS*] **btf** *COMMAND*

*OPTIONS* := { |COMMON_OPTIONS| | { **-B** | **--base-btf** } }

*COMMANDS* := { **dump** | **help** }

BTF COMMANDS
=============

| **bpftool** **btf** { **show** | **list** } [**id** *BTF_ID*]
| **bpftool** **btf dump** *BTF_SRC* [**format** *FORMAT*] [**root_id** *ROOT_ID*]
| **bpftool** **btf help**
|
| *BTF_SRC* := { **id** *BTF_ID* | **prog** *PROG* | **map** *MAP* [{**key** | **value** | **kv** | **all**}] | **file** *FILE* }
| *FORMAT* := { **raw** | **c** [**unsorted**] }
| *MAP* := { **id** *MAP_ID* | **pinned** *FILE* }
| *PROG* := { **id** *PROG_ID* | **pinned** *FILE* | **tag** *PROG_TAG* | **name** *PROG_NAME* }

DESCRIPTION
===========
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* [format *FORMAT*] [root_id *ROOT_ID*]
    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. With C-style
    formatting, the output is sorted by default. Use the **unsorted** option
    to avoid sorting the output.

    **root_id** option can be used to filter a dump to a single type and all
    its dependent types. It cannot be used with any other types of filtering
    (such as the "key", "value", or "kv" arguments when dumping BTF for a map).
    It can be passed multiple times to dump multiple types.

bpftool btf help
    Print short help message.

OPTIONS
=======
.. 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.

EXAMPLES
========
**# 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
