================
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bpftool-btf
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================
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-------------------------------------------------------------------------------
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tool for inspection of BTF data
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-------------------------------------------------------------------------------
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:Manual section: 8
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SYNOPSIS
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========
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**bpftool** [*OPTIONS*] **btf** *COMMAND*
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*OPTIONS* := { { **-j** | **--json** } [{ **-p** | **--pretty** }] }
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*COMMANDS* := { **dump** | **help** }
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BTF COMMANDS
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=============
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| **bpftool** **btf** { **show** | **list** } [**id** *BTF_ID*]
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| **bpftool** **btf dump** *BTF_SRC* [**format** *FORMAT*]
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| **bpftool** **btf help**
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| *BTF_SRC* := { **id** *BTF_ID* | **prog** *PROG* | **map** *MAP* [{**key** | **value** | **kv** | **all**}] | **file** *FILE* }
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| *FORMAT* := { **raw** | **c** }
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| *MAP* := { **id** *MAP_ID* | **pinned** *FILE* }
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| *PROG* := { **id** *PROG_ID* | **pinned** *FILE* | **tag** *PROG_TAG* }
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DESCRIPTION
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===========
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**bpftool btf { show | list }** [**id** *BTF_ID*]
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Show information about loaded BTF objects. If a BTF ID is
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specified, show information only about given BTF object,
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otherwise list all BTF objects currently loaded on the
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system.
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Since Linux 5.8 bpftool is able to discover information about
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processes that hold open file descriptors (FDs) against BTF
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objects. On such kernels bpftool will automatically emit this
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information as well.
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**bpftool btf dump** *BTF_SRC*
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Dump BTF entries from a given *BTF_SRC*.
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When **id** is specified, BTF object with that ID will be
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loaded and all its BTF types emitted.
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When **map** is provided, it's expected that map has
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associated BTF object with BTF types describing key and
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value. It's possible to select whether to dump only BTF
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type(s) associated with key (**key**), value (**value**),
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both key and value (**kv**), or all BTF types present in
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associated BTF object (**all**). If not specified, **kv**
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is assumed.
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When **prog** is provided, it's expected that program has
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associated BTF object with BTF types.
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When specifying *FILE*, an ELF file is expected, containing
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.BTF section with well-defined BTF binary format data,
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typically produced by clang or pahole.
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**format** option can be used to override default (raw)
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output format. Raw (**raw**) or C-syntax (**c**) output
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formats are supported.
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**bpftool btf help**
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Print short help message.
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OPTIONS
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=======
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.. include:: common_options.rst
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EXAMPLES
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========
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**# bpftool btf dump id 1226**
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::
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[1] PTR '(anon)' type_id=2
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[2] STRUCT 'dummy_tracepoint_args' size=16 vlen=2
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'pad' type_id=3 bits_offset=0
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'sock' type_id=4 bits_offset=64
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[3] INT 'long long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
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[4] PTR '(anon)' type_id=5
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[5] FWD 'sock' fwd_kind=union
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This gives an example of default output for all supported BTF kinds.
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**$ cat prog.c**
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::
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struct fwd_struct;
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enum my_enum {
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VAL1 = 3,
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VAL2 = 7,
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};
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typedef struct my_struct my_struct_t;
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struct my_struct {
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const unsigned int const_int_field;
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int bitfield_field: 4;
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char arr_field[16];
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const struct fwd_struct *restrict fwd_field;
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enum my_enum enum_field;
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volatile my_struct_t *typedef_ptr_field;
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};
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union my_union {
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int a;
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struct my_struct b;
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};
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struct my_struct struct_global_var __attribute__((section("data_sec"))) = {
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.bitfield_field = 3,
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.enum_field = VAL1,
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};
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int global_var __attribute__((section("data_sec"))) = 7;
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__attribute__((noinline))
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int my_func(union my_union *arg1, int arg2)
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{
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static int static_var __attribute__((section("data_sec"))) = 123;
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static_var++;
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return static_var;
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}
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**$ bpftool btf dump file prog.o**
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::
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[1] PTR '(anon)' type_id=2
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[2] UNION 'my_union' size=48 vlen=2
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'a' type_id=3 bits_offset=0
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'b' type_id=4 bits_offset=0
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[3] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
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[4] STRUCT 'my_struct' size=48 vlen=6
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'const_int_field' type_id=5 bits_offset=0
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'bitfield_field' type_id=3 bits_offset=32 bitfield_size=4
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'arr_field' type_id=8 bits_offset=40
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'fwd_field' type_id=10 bits_offset=192
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'enum_field' type_id=14 bits_offset=256
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'typedef_ptr_field' type_id=15 bits_offset=320
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[5] CONST '(anon)' type_id=6
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[6] INT 'unsigned int' size=4 bits_offset=0 nr_bits=32 encoding=(none)
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[7] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED
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[8] ARRAY '(anon)' type_id=7 index_type_id=9 nr_elems=16
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[9] INT '__ARRAY_SIZE_TYPE__' size=4 bits_offset=0 nr_bits=32 encoding=(none)
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[10] RESTRICT '(anon)' type_id=11
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[11] PTR '(anon)' type_id=12
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[12] CONST '(anon)' type_id=13
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[13] FWD 'fwd_struct' fwd_kind=union
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[14] ENUM 'my_enum' size=4 vlen=2
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'VAL1' val=3
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'VAL2' val=7
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[15] PTR '(anon)' type_id=16
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[16] VOLATILE '(anon)' type_id=17
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[17] TYPEDEF 'my_struct_t' type_id=4
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[18] FUNC_PROTO '(anon)' ret_type_id=3 vlen=2
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'arg1' type_id=1
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'arg2' type_id=3
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[19] FUNC 'my_func' type_id=18
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[20] VAR 'struct_global_var' type_id=4, linkage=global-alloc
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[21] VAR 'global_var' type_id=3, linkage=global-alloc
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[22] VAR 'my_func.static_var' type_id=3, linkage=static
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[23] DATASEC 'data_sec' size=0 vlen=3
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type_id=20 offset=0 size=48
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type_id=21 offset=0 size=4
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type_id=22 offset=52 size=4
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The following commands print BTF types associated with specified map's key,
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value, both key and value, and all BTF types, respectively. By default, both
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key and value types will be printed.
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**# bpftool btf dump map id 123 key**
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::
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[39] TYPEDEF 'u32' type_id=37
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**# bpftool btf dump map id 123 value**
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::
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[86] PTR '(anon)' type_id=87
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**# bpftool btf dump map id 123 kv**
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::
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[39] TYPEDEF 'u32' type_id=37
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[86] PTR '(anon)' type_id=87
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**# bpftool btf dump map id 123 all**
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::
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[1] PTR '(anon)' type_id=0
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.
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.
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.
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[2866] ARRAY '(anon)' type_id=52 index_type_id=51 nr_elems=4
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All the standard ways to specify map or program are supported:
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**# bpftool btf dump map id 123**
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**# bpftool btf dump map pinned /sys/fs/bpf/map_name**
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**# bpftool btf dump prog id 456**
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**# bpftool btf dump prog tag b88e0a09b1d9759d**
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**# bpftool btf dump prog pinned /sys/fs/bpf/prog_name**
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