linux/Documentation/bpf/drgn.rst
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   1.. SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
   2
   3==============
   4BPF drgn tools
   5==============
   6
   7drgn scripts is a convenient and easy to use mechanism to retrieve arbitrary
   8kernel data structures. drgn is not relying on kernel UAPI to read the data.
   9Instead it's reading directly from ``/proc/kcore`` or vmcore and pretty prints
  10the data based on DWARF debug information from vmlinux.
  11
  12This document describes BPF related drgn tools.
  13
  14See `drgn/tools`_ for all tools available at the moment and `drgn/doc`_ for
  15more details on drgn itself.
  16
  17bpf_inspect.py
  18--------------
  19
  20Description
  21===========
  22
  23`bpf_inspect.py`_ is a tool intended to inspect BPF programs and maps. It can
  24iterate over all programs and maps in the system and print basic information
  25about these objects, including id, type and name.
  26
  27The main use-case `bpf_inspect.py`_ covers is to show BPF programs of types
  28``BPF_PROG_TYPE_EXT`` and ``BPF_PROG_TYPE_TRACING`` attached to other BPF
  29programs via ``freplace``/``fentry``/``fexit`` mechanisms, since there is no
  30user-space API to get this information.
  31
  32Getting started
  33===============
  34
  35List BPF programs (full names are obtained from BTF)::
  36
  37    % sudo bpf_inspect.py prog
  38        27: BPF_PROG_TYPE_TRACEPOINT         tracepoint__tcp__tcp_send_reset
  39      4632: BPF_PROG_TYPE_CGROUP_SOCK_ADDR   tw_ipt_bind
  40     49464: BPF_PROG_TYPE_RAW_TRACEPOINT     raw_tracepoint__sched_process_exit
  41
  42List BPF maps::
  43
  44      % sudo bpf_inspect.py map
  45        2577: BPF_MAP_TYPE_HASH                tw_ipt_vips
  46        4050: BPF_MAP_TYPE_STACK_TRACE         stack_traces
  47        4069: BPF_MAP_TYPE_PERCPU_ARRAY        ned_dctcp_cntr
  48
  49Find BPF programs attached to BPF program ``test_pkt_access``::
  50
  51      % sudo bpf_inspect.py p | grep test_pkt_access
  52         650: BPF_PROG_TYPE_SCHED_CLS          test_pkt_access
  53         654: BPF_PROG_TYPE_TRACING            test_main                        linked:[650->25: BPF_TRAMP_FEXIT test_pkt_access->test_pkt_access()]
  54         655: BPF_PROG_TYPE_TRACING            test_subprog1                    linked:[650->29: BPF_TRAMP_FEXIT test_pkt_access->test_pkt_access_subprog1()]
  55         656: BPF_PROG_TYPE_TRACING            test_subprog2                    linked:[650->31: BPF_TRAMP_FEXIT test_pkt_access->test_pkt_access_subprog2()]
  56         657: BPF_PROG_TYPE_TRACING            test_subprog3                    linked:[650->21: BPF_TRAMP_FEXIT test_pkt_access->test_pkt_access_subprog3()]
  57         658: BPF_PROG_TYPE_EXT                new_get_skb_len                  linked:[650->16: BPF_TRAMP_REPLACE test_pkt_access->get_skb_len()]
  58         659: BPF_PROG_TYPE_EXT                new_get_skb_ifindex              linked:[650->23: BPF_TRAMP_REPLACE test_pkt_access->get_skb_ifindex()]
  59         660: BPF_PROG_TYPE_EXT                new_get_constant                 linked:[650->19: BPF_TRAMP_REPLACE test_pkt_access->get_constant()]
  60
  61It can be seen that there is a program ``test_pkt_access``, id 650 and there
  62are multiple other tracing and ext programs attached to functions in
  63``test_pkt_access``.
  64
  65For example the line::
  66
  67         658: BPF_PROG_TYPE_EXT                new_get_skb_len                  linked:[650->16: BPF_TRAMP_REPLACE test_pkt_access->get_skb_len()]
  68
  69, means that BPF program id 658, type ``BPF_PROG_TYPE_EXT``, name
  70``new_get_skb_len`` replaces (``BPF_TRAMP_REPLACE``) function ``get_skb_len()``
  71that has BTF id 16 in BPF program id 650, name ``test_pkt_access``.
  72
  73Getting help:
  74
  75.. code-block:: none
  76
  77    % sudo bpf_inspect.py
  78    usage: bpf_inspect.py [-h] {prog,p,map,m} ...
  79
  80    drgn script to list BPF programs or maps and their properties
  81    unavailable via kernel API.
  82
  83    See https://github.com/osandov/drgn/ for more details on drgn.
  84
  85    optional arguments:
  86      -h, --help      show this help message and exit
  87
  88    subcommands:
  89      {prog,p,map,m}
  90        prog (p)      list BPF programs
  91        map (m)       list BPF maps
  92
  93Customization
  94=============
  95
  96The script is intended to be customized by developers to print relevant
  97information about BPF programs, maps and other objects.
  98
  99For example, to print ``struct bpf_prog_aux`` for BPF program id 53077:
 100
 101.. code-block:: none
 102
 103    % git diff
 104    diff --git a/tools/bpf_inspect.py b/tools/bpf_inspect.py
 105    index 650e228..aea2357 100755
 106    --- a/tools/bpf_inspect.py
 107    +++ b/tools/bpf_inspect.py
 108    @@ -112,7 +112,9 @@ def list_bpf_progs(args):
 109             if linked:
 110                 linked = f" linked:[{linked}]"
 111
 112    -        print(f"{id_:>6}: {type_:32} {name:32} {linked}")
 113    +        if id_ == 53077:
 114    +            print(f"{id_:>6}: {type_:32} {name:32}")
 115    +            print(f"{bpf_prog.aux}")
 116
 117
 118     def list_bpf_maps(args):
 119
 120It produces the output::
 121
 122    % sudo bpf_inspect.py p
 123     53077: BPF_PROG_TYPE_XDP                tw_xdp_policer
 124    *(struct bpf_prog_aux *)0xffff8893fad4b400 = {
 125            .refcnt = (atomic64_t){
 126                    .counter = (long)58,
 127            },
 128            .used_map_cnt = (u32)1,
 129            .max_ctx_offset = (u32)8,
 130            .max_pkt_offset = (u32)15,
 131            .max_tp_access = (u32)0,
 132            .stack_depth = (u32)8,
 133            .id = (u32)53077,
 134            .func_cnt = (u32)0,
 135            .func_idx = (u32)0,
 136            .attach_btf_id = (u32)0,
 137            .linked_prog = (struct bpf_prog *)0x0,
 138            .verifier_zext = (bool)0,
 139            .offload_requested = (bool)0,
 140            .attach_btf_trace = (bool)0,
 141            .func_proto_unreliable = (bool)0,
 142            .trampoline_prog_type = (enum bpf_tramp_prog_type)BPF_TRAMP_FENTRY,
 143            .trampoline = (struct bpf_trampoline *)0x0,
 144            .tramp_hlist = (struct hlist_node){
 145                    .next = (struct hlist_node *)0x0,
 146                    .pprev = (struct hlist_node **)0x0,
 147            },
 148            .attach_func_proto = (const struct btf_type *)0x0,
 149            .attach_func_name = (const char *)0x0,
 150            .func = (struct bpf_prog **)0x0,
 151            .jit_data = (void *)0x0,
 152            .poke_tab = (struct bpf_jit_poke_descriptor *)0x0,
 153            .size_poke_tab = (u32)0,
 154            .ksym_tnode = (struct latch_tree_node){
 155                    .node = (struct rb_node [2]){
 156                            {
 157                                    .__rb_parent_color = (unsigned long)18446612956263126665,
 158                                    .rb_right = (struct rb_node *)0x0,
 159                                    .rb_left = (struct rb_node *)0xffff88a0be3d0088,
 160                            },
 161                            {
 162                                    .__rb_parent_color = (unsigned long)18446612956263126689,
 163                                    .rb_right = (struct rb_node *)0x0,
 164                                    .rb_left = (struct rb_node *)0xffff88a0be3d00a0,
 165                            },
 166                    },
 167            },
 168            .ksym_lnode = (struct list_head){
 169                    .next = (struct list_head *)0xffff88bf481830b8,
 170                    .prev = (struct list_head *)0xffff888309f536b8,
 171            },
 172            .ops = (const struct bpf_prog_ops *)xdp_prog_ops+0x0 = 0xffffffff820fa350,
 173            .used_maps = (struct bpf_map **)0xffff889ff795de98,
 174            .prog = (struct bpf_prog *)0xffffc9000cf2d000,
 175            .user = (struct user_struct *)root_user+0x0 = 0xffffffff82444820,
 176            .load_time = (u64)2408348759285319,
 177            .cgroup_storage = (struct bpf_map *[2]){},
 178            .name = (char [16])"tw_xdp_policer",
 179            .security = (void *)0xffff889ff795d548,
 180            .offload = (struct bpf_prog_offload *)0x0,
 181            .btf = (struct btf *)0xffff8890ce6d0580,
 182            .func_info = (struct bpf_func_info *)0xffff889ff795d240,
 183            .func_info_aux = (struct bpf_func_info_aux *)0xffff889ff795de20,
 184            .linfo = (struct bpf_line_info *)0xffff888a707afc00,
 185            .jited_linfo = (void **)0xffff8893fad48600,
 186            .func_info_cnt = (u32)1,
 187            .nr_linfo = (u32)37,
 188            .linfo_idx = (u32)0,
 189            .num_exentries = (u32)0,
 190            .extable = (struct exception_table_entry *)0xffffffffa032d950,
 191            .stats = (struct bpf_prog_stats *)0x603fe3a1f6d0,
 192            .work = (struct work_struct){
 193                    .data = (atomic_long_t){
 194                            .counter = (long)0,
 195                    },
 196                    .entry = (struct list_head){
 197                            .next = (struct list_head *)0x0,
 198                            .prev = (struct list_head *)0x0,
 199                    },
 200                    .func = (work_func_t)0x0,
 201            },
 202            .rcu = (struct callback_head){
 203                    .next = (struct callback_head *)0x0,
 204                    .func = (void (*)(struct callback_head *))0x0,
 205            },
 206    }
 207
 208
 209.. Links
 210.. _drgn/doc: https://drgn.readthedocs.io/en/latest/
 211.. _drgn/tools: https://github.com/osandov/drgn/tree/master/tools
 212.. _bpf_inspect.py:
 213   https://github.com/osandov/drgn/blob/master/tools/bpf_inspect.py
 214