BPF drgn tools

drgn scripts is a convenient and easy to use mechanism to retrieve arbitrarykernel 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 printsthe data based on DWARF debug information from vmlinux.

This document describes BPF related drgn tools.

Seedrgn/tools for all tools available at the moment anddrgn/doc formore details on drgn itself.

bpf_inspect.py

Description

bpf_inspect.py is a tool intended to inspect BPF programs and maps. It caniterate over all programs and maps in the system and print basic informationabout these objects, including id, type and name.

The main use-casebpf_inspect.py covers is to show BPF programs of typesBPF_PROG_TYPE_EXT andBPF_PROG_TYPE_TRACING attached to other BPFprograms viafreplace/fentry/fexit mechanisms, since there is nouser-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 programtest_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 programtest_pkt_access, id 650 and thereare multiple other tracing and ext programs attached to functions intest_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, typeBPF_PROG_TYPE_EXT, namenew_get_skb_len replaces (BPF_TRAMP_REPLACE) functionget_skb_len()that has BTF id 16 in BPF program id 650, nametest_pkt_access.

Getting help:

% sudo bpf_inspect.pyusage: bpf_inspect.py [-h] {prog,p,map,m} ...drgn script to list BPF programs or maps and their propertiesunavailable via kernel API.See https://github.com/osandov/drgn/ for more details on drgn.optional arguments:  -h, --help      show this help message and exitsubcommands:  {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 relevantinformation about BPF programs, maps and other objects.

For example, to printstructbpf_prog_aux for BPF program id 53077:

% git diffdiff --git a/tools/bpf_inspect.py b/tools/bpf_inspect.pyindex 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,        },}