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<section id="bpf-drgn-tools">
<h1>BPF drgn tools<a class="headerlink" href="#bpf-drgn-tools" title="Link to this heading">¶</a></h1>
<p>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 <code class="docutils literal notranslate"><span class="pre">/proc/kcore</span></code> or vmcore and pretty prints
the data based on DWARF debug information from vmlinux.</p>
<p>This document describes BPF related drgn tools.</p>
<p>See <a class="reference external" href="https://github.com/osandov/drgn/tree/master/tools">drgn/tools</a> for all tools available at the moment and <a class="reference external" href="https://drgn.readthedocs.io/en/latest/">drgn/doc</a> for
more details on drgn itself.</p>
<section id="bpf-inspect-py">
<h2>bpf_inspect.py<a class="headerlink" href="#bpf-inspect-py" title="Link to this heading">¶</a></h2>
<section id="description">
<h3>Description<a class="headerlink" href="#description" title="Link to this heading">¶</a></h3>
<p><a class="reference external" href="https://github.com/osandov/drgn/blob/master/tools/bpf_inspect.py">bpf_inspect.py</a> 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.</p>
<p>The main use-case <a class="reference external" href="https://github.com/osandov/drgn/blob/master/tools/bpf_inspect.py">bpf_inspect.py</a> covers is to show BPF programs of types
<code class="docutils literal notranslate"><span class="pre">BPF_PROG_TYPE_EXT</span></code> and <code class="docutils literal notranslate"><span class="pre">BPF_PROG_TYPE_TRACING</span></code> attached to other BPF
programs via <code class="docutils literal notranslate"><span class="pre">freplace</span></code>/<code class="docutils literal notranslate"><span class="pre">fentry</span></code>/<code class="docutils literal notranslate"><span class="pre">fexit</span></code> mechanisms, since there is no
user-space API to get this information.</p>
</section>
<section id="getting-started">
<h3>Getting started<a class="headerlink" href="#getting-started" title="Link to this heading">¶</a></h3>
<p>List BPF programs (full names are obtained from BTF):</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>% 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
</pre></div>
</div>
<p>List BPF maps:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>% 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
</pre></div>
</div>
<p>Find BPF programs attached to BPF program <code class="docutils literal notranslate"><span class="pre">test_pkt_access</span></code>:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>% 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()]
</pre></div>
</div>
<p>It can be seen that there is a program <code class="docutils literal notranslate"><span class="pre">test_pkt_access</span></code>, id 650 and there
are multiple other tracing and ext programs attached to functions in
<code class="docutils literal notranslate"><span class="pre">test_pkt_access</span></code>.</p>
<p>For example the line:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>658: BPF_PROG_TYPE_EXT new_get_skb_len linked:[650->16: BPF_TRAMP_REPLACE test_pkt_access->get_skb_len()]
</pre></div>
</div>
<p>, means that BPF program id 658, type <code class="docutils literal notranslate"><span class="pre">BPF_PROG_TYPE_EXT</span></code>, name
<code class="docutils literal notranslate"><span class="pre">new_get_skb_len</span></code> replaces (<code class="docutils literal notranslate"><span class="pre">BPF_TRAMP_REPLACE</span></code>) function <code class="docutils literal notranslate"><span class="pre">get_skb_len()</span></code>
that has BTF id 16 in BPF program id 650, name <code class="docutils literal notranslate"><span class="pre">test_pkt_access</span></code>.</p>
<p>Getting help:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>% 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
</pre></div>
</div>
</section>
<section id="customization">
<h3>Customization<a class="headerlink" href="#customization" title="Link to this heading">¶</a></h3>
<p>The script is intended to be customized by developers to print relevant
information about BPF programs, maps and other objects.</p>
<p>For example, to print <code class="docutils literal notranslate"><span class="pre">struct</span> <span class="pre">bpf_prog_aux</span></code> for BPF program id 53077:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>% 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):
</pre></div>
</div>
<p>It produces the output:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>% 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,
},
}
</pre></div>
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