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diff --git a/Documentation/bpf/drgn.rst b/Documentation/bpf/drgn.rst new file mode 100644 index 000000000..41f223c31 --- /dev/null +++ b/Documentation/bpf/drgn.rst @@ -0,0 +1,213 @@ +.. SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) + +============== +BPF drgn tools +============== + +drgn scripts is a convenient and easy to use mechanism to retrieve arbitrary +kernel data structures. drgn is not relying on kernel UAPI to read the data. +Instead it's reading directly from ``/proc/kcore`` or vmcore and pretty prints +the data based on DWARF debug information from vmlinux. + +This document describes BPF related drgn tools. + +See `drgn/tools`_ for all tools available at the moment and `drgn/doc`_ for +more details on drgn itself. + +bpf_inspect.py +-------------- + +Description +=========== + +`bpf_inspect.py`_ is a tool intended to inspect BPF programs and maps. It can +iterate over all programs and maps in the system and print basic information +about these objects, including id, type and name. + +The main use-case `bpf_inspect.py`_ covers is to show BPF programs of types +``BPF_PROG_TYPE_EXT`` and ``BPF_PROG_TYPE_TRACING`` attached to other BPF +programs via ``freplace``/``fentry``/``fexit`` mechanisms, since there is no +user-space API to get this information. + +Getting started +=============== + +List BPF programs (full names are obtained from BTF):: + + % sudo bpf_inspect.py prog + 27: BPF_PROG_TYPE_TRACEPOINT tracepoint__tcp__tcp_send_reset + 4632: BPF_PROG_TYPE_CGROUP_SOCK_ADDR tw_ipt_bind + 49464: BPF_PROG_TYPE_RAW_TRACEPOINT raw_tracepoint__sched_process_exit + +List BPF maps:: + + % sudo bpf_inspect.py map + 2577: BPF_MAP_TYPE_HASH tw_ipt_vips + 4050: BPF_MAP_TYPE_STACK_TRACE stack_traces + 4069: BPF_MAP_TYPE_PERCPU_ARRAY ned_dctcp_cntr + +Find BPF programs attached to BPF program ``test_pkt_access``:: + + % sudo bpf_inspect.py p | grep test_pkt_access + 650: BPF_PROG_TYPE_SCHED_CLS test_pkt_access + 654: BPF_PROG_TYPE_TRACING test_main linked:[650->25: BPF_TRAMP_FEXIT test_pkt_access->test_pkt_access()] + 655: BPF_PROG_TYPE_TRACING test_subprog1 linked:[650->29: BPF_TRAMP_FEXIT test_pkt_access->test_pkt_access_subprog1()] + 656: BPF_PROG_TYPE_TRACING test_subprog2 linked:[650->31: BPF_TRAMP_FEXIT test_pkt_access->test_pkt_access_subprog2()] + 657: BPF_PROG_TYPE_TRACING test_subprog3 linked:[650->21: BPF_TRAMP_FEXIT test_pkt_access->test_pkt_access_subprog3()] + 658: BPF_PROG_TYPE_EXT new_get_skb_len linked:[650->16: BPF_TRAMP_REPLACE test_pkt_access->get_skb_len()] + 659: BPF_PROG_TYPE_EXT new_get_skb_ifindex linked:[650->23: BPF_TRAMP_REPLACE test_pkt_access->get_skb_ifindex()] + 660: BPF_PROG_TYPE_EXT new_get_constant linked:[650->19: BPF_TRAMP_REPLACE test_pkt_access->get_constant()] + +It can be seen that there is a program ``test_pkt_access``, id 650 and there +are multiple other tracing and ext programs attached to functions in +``test_pkt_access``. + +For example the line:: + + 658: BPF_PROG_TYPE_EXT new_get_skb_len linked:[650->16: BPF_TRAMP_REPLACE test_pkt_access->get_skb_len()] + +, means that BPF program id 658, type ``BPF_PROG_TYPE_EXT``, name +``new_get_skb_len`` replaces (``BPF_TRAMP_REPLACE``) function ``get_skb_len()`` +that has BTF id 16 in BPF program id 650, name ``test_pkt_access``. + +Getting help: + +.. code-block:: none + + % sudo bpf_inspect.py + usage: bpf_inspect.py [-h] {prog,p,map,m} ... + + drgn script to list BPF programs or maps and their properties + unavailable via kernel API. + + See https://github.com/osandov/drgn/ for more details on drgn. + + optional arguments: + -h, --help show this help message and exit + + subcommands: + {prog,p,map,m} + prog (p) list BPF programs + map (m) list BPF maps + +Customization +============= + +The script is intended to be customized by developers to print relevant +information about BPF programs, maps and other objects. + +For example, to print ``struct bpf_prog_aux`` for BPF program id 53077: + +.. code-block:: none + + % git diff + diff --git a/tools/bpf_inspect.py b/tools/bpf_inspect.py + index 650e228..aea2357 100755 + --- a/tools/bpf_inspect.py + +++ b/tools/bpf_inspect.py + @@ -112,7 +112,9 @@ def list_bpf_progs(args): + if linked: + linked = f" linked:[{linked}]" + + - print(f"{id_:>6}: {type_:32} {name:32} {linked}") + + if id_ == 53077: + + print(f"{id_:>6}: {type_:32} {name:32}") + + print(f"{bpf_prog.aux}") + + + def list_bpf_maps(args): + +It produces the output:: + + % sudo bpf_inspect.py p + 53077: BPF_PROG_TYPE_XDP tw_xdp_policer + *(struct bpf_prog_aux *)0xffff8893fad4b400 = { + .refcnt = (atomic64_t){ + .counter = (long)58, + }, + .used_map_cnt = (u32)1, + .max_ctx_offset = (u32)8, + .max_pkt_offset = (u32)15, + .max_tp_access = (u32)0, + .stack_depth = (u32)8, + .id = (u32)53077, + .func_cnt = (u32)0, + .func_idx = (u32)0, + .attach_btf_id = (u32)0, + .linked_prog = (struct bpf_prog *)0x0, + .verifier_zext = (bool)0, + .offload_requested = (bool)0, + .attach_btf_trace = (bool)0, + .func_proto_unreliable = (bool)0, + .trampoline_prog_type = (enum bpf_tramp_prog_type)BPF_TRAMP_FENTRY, + .trampoline = (struct bpf_trampoline *)0x0, + .tramp_hlist = (struct hlist_node){ + .next = (struct hlist_node *)0x0, + .pprev = (struct hlist_node **)0x0, + }, + .attach_func_proto = (const struct btf_type *)0x0, + .attach_func_name = (const char *)0x0, + .func = (struct bpf_prog **)0x0, + .jit_data = (void *)0x0, + .poke_tab = (struct bpf_jit_poke_descriptor *)0x0, + .size_poke_tab = (u32)0, + .ksym_tnode = (struct latch_tree_node){ + .node = (struct rb_node [2]){ + { + .__rb_parent_color = (unsigned long)18446612956263126665, + .rb_right = (struct rb_node *)0x0, + .rb_left = (struct rb_node *)0xffff88a0be3d0088, + }, + { + .__rb_parent_color = (unsigned long)18446612956263126689, + .rb_right = (struct rb_node *)0x0, + .rb_left = (struct rb_node *)0xffff88a0be3d00a0, + }, + }, + }, + .ksym_lnode = (struct list_head){ + .next = (struct list_head *)0xffff88bf481830b8, + .prev = (struct list_head *)0xffff888309f536b8, + }, + .ops = (const struct bpf_prog_ops *)xdp_prog_ops+0x0 = 0xffffffff820fa350, + .used_maps = (struct bpf_map **)0xffff889ff795de98, + .prog = (struct bpf_prog *)0xffffc9000cf2d000, + .user = (struct user_struct *)root_user+0x0 = 0xffffffff82444820, + .load_time = (u64)2408348759285319, + .cgroup_storage = (struct bpf_map *[2]){}, + .name = (char [16])"tw_xdp_policer", + .security = (void *)0xffff889ff795d548, + .offload = (struct bpf_prog_offload *)0x0, + .btf = (struct btf *)0xffff8890ce6d0580, + .func_info = (struct bpf_func_info *)0xffff889ff795d240, + .func_info_aux = (struct bpf_func_info_aux *)0xffff889ff795de20, + .linfo = (struct bpf_line_info *)0xffff888a707afc00, + .jited_linfo = (void **)0xffff8893fad48600, + .func_info_cnt = (u32)1, + .nr_linfo = (u32)37, + .linfo_idx = (u32)0, + .num_exentries = (u32)0, + .extable = (struct exception_table_entry *)0xffffffffa032d950, + .stats = (struct bpf_prog_stats *)0x603fe3a1f6d0, + .work = (struct work_struct){ + .data = (atomic_long_t){ + .counter = (long)0, + }, + .entry = (struct list_head){ + .next = (struct list_head *)0x0, + .prev = (struct list_head *)0x0, + }, + .func = (work_func_t)0x0, + }, + .rcu = (struct callback_head){ + .next = (struct callback_head *)0x0, + .func = (void (*)(struct callback_head *))0x0, + }, + } + + +.. Links +.. _drgn/doc: https://drgn.readthedocs.io/en/latest/ +.. _drgn/tools: https://github.com/osandov/drgn/tree/master/tools +.. _bpf_inspect.py: + https://github.com/osandov/drgn/blob/master/tools/bpf_inspect.py |