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review.shift-gmbh.com / SHIFTPHONES / mainline / linux / a5a6c66df6bf951007f434fad04d777289f00aa6 / . / Documentation / bpf / drgn.rst
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Andrey Ignatov8c061862020-03-24 11:51:35 -0700[diff] [blame]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