Awesome
libbpf-bootstrap: demo BPF applications
minimal
minimal is just that – a minimal practical BPF application example. It
doesn't use or require BPF CO-RE, so should run on quite old kernels. It
installs a tracepoint handler which is triggered once every second. It uses
bpf_printk() BPF helper to communicate with the world. To see it's output,
read /sys/kernel/debug/tracing/trace_pipe file as a root:
$ cd examples/c
$ make minimal
$ sudo ./minimal
$ sudo cat /sys/kernel/debug/tracing/trace_pipe
<...>-3840345 [010] d... 3220701.101143: bpf_trace_printk: BPF triggered from PID 3840345.
<...>-3840345 [010] d... 3220702.101265: bpf_trace_printk: BPF triggered from PID 3840345.
minimal is great as a bare-bones experimental playground to quickly try out
new ideas or BPF features.
minimal_ns
minimal_ns is as same as minimal but for namespaced environments.
minimal would not work in environments that have namespace, like containers,
or WSL2, because the perceived pid of the process in the namespace is not the
actual pid of the process. For executing minimal in namespaced environments
you need to use minimal_ns instead.
$ cd examples/c
$ make minimal_ns
$ sudo ./minimal_ns
$ sudo cat /sys/kernel/debug/tracing/trace_pipe
<...>-3840345 [022] d...1 8804.331204: bpf_trace_printk: BPF triggered from PID 9087.
<...>-3840345 [022] d...1 8804.331215: bpf_trace_printk: BPF triggered from PID 9087.
minimal_Legacy
This version of minimal is modified to allow running on even older kernels
that do not allow global variables. bpf_printk uses global variables unless
BPF_NO_GLOBAL_DATA is defined before including bpf_helpers.h. Additionally,
the global variable my_pid has been replaced with an array of one element to
hold the process pid.
$ cd examples/c
$ make minimal_legacy
$ sudo ./minimal_legacy
$ sudo cat /sys/kernel/debug/tracing/trace_pipe
minimal_legacy-52030 [001] .... 491227.784078: 0x00000001: BPF triggered from PID 52030.
minimal_legacy-52030 [001] .... 491228.840571: 0x00000001: BPF triggered from PID 52030.
minimal_legacy-52030 [001] .... 491229.841643: 0x00000001: BPF triggered from PID 52030.
minimal_legacy-52030 [001] .... 491230.842432: 0x00000001: BPF triggered from PID 52030.
bootstrap
bootstrap is an example of a simple (but realistic) BPF application. It
tracks process starts (exec() family of syscalls, to be precise) and exits
and emits data about filename, PID and parent PID, as well as exit status and
duration of the process life. With -d <min-duration-ms> you can specify
minimum duration of the process to log. In such mode process start
(technically, exec()) events are not output (see example output below).
bootstrap was created in the similar spirit as
libbpf-tools from
BCC package, but is designed to be more stand-alone and with simpler Makefile
to simplify adoption to user's particular needs. It demonstrates the use of
typical BPF features:
- cooperating BPF programs (tracepoint handlers for process
execandexitevents, in this particular case); - BPF map for maintaining the state;
- BPF ring buffer for sending data to user-space;
- global variables for application behavior parameterization.
- it utilizes BPF CO-RE and vmlinux.h to read extra process information from
kernel's
struct task_struct.
bootstrap is intended to be the starting point for your own BPF application,
with things like BPF CO-RE and vmlinux.h, consuming BPF ring buffer data,
command line arguments parsing, graceful Ctrl-C handling, etc. all taken care
of for you, which are crucial but mundane tasks that are no fun, but necessary
to be able to do anything useful. Just copy/paste and do simple renaming to get
yourself started.
Here's an example output in minimum process duration mode:
$ sudo ./bootstrap -d 50
TIME EVENT COMM PID PPID FILENAME/EXIT CODE
19:18:32 EXIT timeout 3817109 402466 [0] (126ms)
19:18:32 EXIT sudo 3817117 3817111 [0] (259ms)
19:18:32 EXIT timeout 3817110 402466 [0] (264ms)
19:18:33 EXIT python3.7 3817083 1 [0] (1026ms)
19:18:38 EXIT python3 3817429 3817424 [1] (60ms)
19:18:38 EXIT sh 3817424 3817420 [0] (79ms)
19:18:38 EXIT timeout 3817420 402466 [0] (80ms)
19:18:43 EXIT timeout 3817610 402466 [0] (70ms)
19:18:43 EXIT grep 3817619 3817617 [1] (271ms)
19:18:43 EXIT timeout 3817609 402466 [0] (321ms)
19:18:44 EXIT iostat 3817585 3817531 [0] (3006ms)
19:18:44 EXIT tee 3817587 3817531 [0] (3005ms)
...
uprobe
uprobe is an example of dealing with user-space entry and exit (return) probes,
uprobe and uretprobe, in libbpf lingo. It attaches uprobe and uretprobe
BPF programs to its own functions (uprobed_add() and uprobed_sub()) and logs input arguments
and return result, respectively, using bpf_printk() macro. The user-space
function is triggered once every second:
$ sudo ./uprobe
libbpf: loading object 'uprobe_bpf' from buffer
...
Successfully started!
...........
You can see uprobe demo output in /sys/kernel/debug/tracing/trace_pipe:
$ sudo cat /sys/kernel/debug/tracing/trace_pipe
uprobe-1809291 [007] .... 4017233.106596: 0: uprobed_add ENTRY: a = 0, b = 1
uprobe-1809291 [007] .... 4017233.106605: 0: uprobed_add EXIT: return = 1
uprobe-1809291 [007] .... 4017233.106606: 0: uprobed_sub ENTRY: a = 0, b = 0
uprobe-1809291 [007] .... 4017233.106607: 0: uprobed_sub EXIT: return = 0
uprobe-1809291 [007] .... 4017234.106694: 0: uprobed_add ENTRY: a = 1, b = 2
uprobe-1809291 [007] .... 4017234.106697: 0: uprobed_add EXIT: return = 3
uprobe-1809291 [007] .... 4017234.106700: 0: uprobed_sub ENTRY: a = 1, b = 1
uprobe-1809291 [007] .... 4017234.106701: 0: uprobed_sub EXIT: return = 0
usdt
usdt is an example of dealing with USDT probe. It attaches USDT BPF programs to
the libc:setjmp probe, which is triggered by calling setjmp in user-space program once per second and logs USDT arguments using bpf_printk() macro:
$ sudo ./usdt
libbpf: loading object 'usdt_bpf' from buffer
...
Successfully started!
...........
You can see usdt demo output in /sys/kernel/debug/tracing/trace_pipe:
$ sudo cat /sys/kernel/debug/tracing/trace_pipe
usdt-1919077 [005] d..21 537310.886092: bpf_trace_printk: USDT auto attach to libc:setjmp: arg1 = 55d03d6a42a0, arg2 = 0, arg3 = 55d03d65e54e
usdt-1919077 [005] d..21 537310.886105: bpf_trace_printk: USDT manual attach to libc:setjmp: arg1 = 55d03d6a42a0, arg2 = 0, arg3 = 55d03d65e54e
usdt-1919077 [005] d..21 537311.886214: bpf_trace_printk: USDT auto attach to libc:setjmp: arg1 = 55d03d6a42a0, arg2 = 0, arg3 = 55d03d65e54e
usdt-1919077 [005] d..21 537311.886227: bpf_trace_printk: USDT manual attach to libc:setjmp: arg1 = 55d03d6a42a0, arg2 = 0, arg3 = 55d03d65e54e
fentry
fentry is an example that uses fentry and fexit BPF programs for tracing. It
attaches fentry and fexit traces to do_unlinkat() which is called when a
file is deleted and logs the return value, PID, and filename to the
trace pipe.
Important differences, compared to kprobes, are improved performance and usability. In this example, better usability is shown with the ability to directly dereference pointer arguments, like in normal C, instead of using various read helpers. The big distinction between fexit and kretprobe programs is that fexit one has access to both input arguments and returned result, while kretprobe can only access the result.
fentry and fexit programs are available starting from 5.5 kernels.
$ sudo ./fentry
libbpf: loading object 'fentry_bpf' from buffer
...
Successfully started!
..........
The fentry output in /sys/kernel/debug/tracing/trace_pipe should look
something like this:
$ sudo cat /sys/kernel/debug/tracing/trace_pipe
rm-9290 [004] d..2 4637.798698: bpf_trace_printk: fentry: pid = 9290, filename = test_file
rm-9290 [004] d..2 4637.798843: bpf_trace_printk: fexit: pid = 9290, filename = test_file, ret = 0
rm-9290 [004] d..2 4637.798698: bpf_trace_printk: fentry: pid = 9290, filename = test_file2
rm-9290 [004] d..2 4637.798843: bpf_trace_printk: fexit: pid = 9290, filename = test_file2, ret = 0
kprobe
kprobe is an example of dealing with kernel-space entry and exit (return)
probes, kprobe and kretprobe, in libbpf lingo. It attaches kprobe and
kretprobe BPF programs to the do_unlinkat() function and logs the PID,
filename, and return result, respectively, using bpf_printk() macro.
$ sudo ./kprobe
libbpf: loading object 'kprobe_bpf' from buffer
...
Successfully started!
...........
The kprobe demo output in /sys/kernel/debug/tracing/trace_pipe should look
something like this:
$ sudo cat /sys/kernel/debug/tracing/trace_pipe
rm-9346 [005] d..3 4710.951696: bpf_trace_printk: KPROBE ENTRY pid = 9346, filename = test1
rm-9346 [005] d..4 4710.951819: bpf_trace_printk: KPROBE EXIT: ret = 0
rm-9346 [005] d..3 4710.951852: bpf_trace_printk: KPROBE ENTRY pid = 9346, filename = test2
rm-9346 [005] d..4 4710.951895: bpf_trace_printk: KPROBE EXIT: ret = 0
xdp
xdp is an example written in Rust (using libbpf-rs). It attaches to
the ingress path of networking device and logs the size of each packet,
returning XDP_PASS to allow the packet to be passed up to the kernel’s
networking stack.
$ sudo ./target/release/xdp 1
..........
The xdp output in /sys/kernel/debug/tracing/trace_pipe should look
something like this:
$ sudo cat /sys/kernel/debug/tracing/trace_pipe
<...>-823887 [000] d.s1 602386.079100: bpf_trace_printk: packet size: 75
<...>-823887 [000] d.s1 602386.079141: bpf_trace_printk: packet size: 66
<...>-2813507 [000] d.s1 602386.696702: bpf_trace_printk: packet size: 77
<...>-2813507 [000] d.s1 602386.696735: bpf_trace_printk: packet size: 66
tc
tc (short for Traffic Control) is an example of handling ingress network traffics.
It creates a qdisc on the lo interface and attaches the tc_ingress BPF program to it.
It reports the metadata of the IP packets that coming into the lo interface.
$ sudo ./tc
...
Successfully started! Please run `sudo cat /sys/kernel/debug/tracing/trace_pipe` to see output of the BPF program.
......
The tc output in /sys/kernel/debug/tracing/trace_pipe should look
something like this:
$ sudo cat /sys/kernel/debug/tracing/trace_pipe
node-1254811 [007] ..s1 8737831.671074: 0: Got IP packet: tot_len: 79, ttl: 64
sshd-1254728 [006] ..s1 8737831.674334: 0: Got IP packet: tot_len: 79, ttl: 64
sshd-1254728 [006] ..s1 8737831.674349: 0: Got IP packet: tot_len: 72, ttl: 64
node-1254811 [007] ..s1 8737831.674550: 0: Got IP packet: tot_len: 71, ttl: 64
profile
profile is an example written in Rust and C using the
blazesym symbolization library. It
attaches to perf events, sampling on every processor periodically. It
shows addresses, symbols, file names, and line numbers of stacktraces (if
available).
$ sudo ./target/release/profile
COMM: swapper/2 (pid=0) @ CPU 2
Kernel:
0xffffffffb59141f8: mwait_idle_with_hints.constprop.0 @ 0xffffffffb59141b0+0x48
0xffffffffb5f731ce: intel_idle @ 0xffffffffb5f731b0+0x1e
0xffffffffb5c7bf09: cpuidle_enter_state @ 0xffffffffb5c7be80+0x89
0xffffffffb5c7c309: cpuidle_enter @ 0xffffffffb5c7c2e0+0x29
0xffffffffb516f57c: do_idle @ 0xffffffffb516f370+0x20c
0xffffffffb516f829: cpu_startup_entry @ 0xffffffffb516f810+0x19
0xffffffffb5075bfa: start_secondary @ 0xffffffffb5075ae0+0x11a
0xffffffffb500015a: secondary_startup_64_no_verify @ 0xffffffffb5000075+0xe5
No Userspace Stack
C version and Rust version show the same content. Both of them use blazesym
to symbolize stacktraces.
sockfilter
sockfilter is an example of monitoring packet and dealing with __sk_buff
structure. It attaches socket BPF program to sock_queue_rcv_skb() function
and retrieve information from BPF_MAP_TYPE_RINGBUF, then print
protocol, src IP, src port, dst IP, dst port in standard output.
Currently, most of the IPv4 protocols defined in uapi/linux/in.h are included,
please check ipproto_mapping of examples/c/sockfilter.c for the supported protocols.
$ sudo ./sockfilter -i <interface>
interface:lo protocol: UDP 127.0.0.1:51845(src) -> 127.0.0.1:53(dst)
interface:lo protocol: UDP 127.0.0.1:41552(src) -> 127.0.0.1:53(dst)
task_iter
task_iter is an example of using BPF Iterators.
This example iterates over all tasks on the host and gets their pid, process name,
kernel stack, and their state. Note: you can use BlazeSym to symbolize the kernel stacktraces
(like in profile) but that code is omitted for simplicity.
$ sudo ./task_iter
Task Info. Pid: 3647645. Process Name: TTLSFWorker59. Kernel Stack Len: 3. State: INTERRUPTIBLE
Task Info. Pid: 1600495. Process Name: tmux: client. Kernel Stack Len: 6. State: INTERRUPTIBLE
Task Info. Pid: 1600497. Process Name: tmux: server. Kernel Stack Len: 0. State: RUNNING
Task Info. Pid: 1600498. Process Name: bash. Kernel Stack Len: 5. State: INTERRUPTIBLE
lsm
lsm serves as an illustrative example of utilizing LSM BPF. In this example, the bpf() system call is effectively blocked. Once the lsm program is operational, its successful execution can be confirmed by using the bpftool prog list command.
$ sudo ./lsm
libbpf: loading object 'lsm_bpf' from buffer
...
Successfully started! Please run `sudo cat /sys/kernel/debug/tracing/trace_pipe` to see output of the BPF programs.
..........
The output from lsm in /sys/kernel/debug/tracing/trace_pipe is expected to resemble the following:
$ sudo cat /sys/kernel/debug/tracing/trace_pipe
bpftool-70646 [002] ...11 279318.416393: bpf_trace_printk: LSM: block bpf() worked
bpftool-70646 [002] ...11 279318.416532: bpf_trace_printk: LSM: block bpf() worked
bpftool-70646 [002] ...11 279318.416533: bpf_trace_printk: LSM: block bpf() worked
When the bpf() system call gets blocked, the bpftool prog list command yields the following output:
$ sudo bpftool prog list
Error: can't get next program: Operation not permitted
Building
libbpf-bootstrap supports multiple build systems that do the same thing. This serves as a cross reference for folks coming from different backgrounds.
Install Dependencies
You will need clang (at least v11 or later), libelf and zlib to build
the examples, package names may vary across distros.
On Ubuntu/Debian, you need:
$ apt install clang libelf1 libelf-dev zlib1g-dev
On CentOS/Fedora, you need:
$ dnf install clang elfutils-libelf elfutils-libelf-devel zlib-devel
Getting the source code
Download the git repository and check out submodules:
$ git clone --recurse-submodules https://github.com/libbpf/libbpf-bootstrap
C Examples
Makefile build:
$ git submodule update --init --recursive # check out libbpf
$ cd examples/c
$ make
$ sudo ./bootstrap
TIME EVENT COMM PID PPID FILENAME/EXIT CODE
00:21:22 EXIT python3.8 4032353 4032352 [0] (123ms)
00:21:22 EXEC mkdir 4032379 4032337 /usr/bin/mkdir
00:21:22 EXIT mkdir 4032379 4032337 [0] (1ms)
00:21:22 EXEC basename 4032382 4032381 /usr/bin/basename
00:21:22 EXIT basename 4032382 4032381 [0] (0ms)
00:21:22 EXEC sh 4032381 4032380 /bin/sh
00:21:22 EXEC dirname 4032384 4032381 /usr/bin/dirname
00:21:22 EXIT dirname 4032384 4032381 [0] (1ms)
00:21:22 EXEC readlink 4032387 4032386 /usr/bin/readlink
^C
CMake build:
$ git submodule update --init --recursive # check out libbpf
$ mkdir build && cd build
$ cmake ../examples/c
$ make
$ sudo ./bootstrap
<...>
XMake build (Linux):
$ git submodule update --init --recursive # check out libbpf
$ cd examples/c
$ xmake
$ xmake run bootstrap
XMake build (Android):
$ git submodule update --init --recursive # check out libbpf
$ cd examples/c
$ xmake f -p android
$ xmake
Install Xmake
$ bash <(wget https://xmake.io/shget.text -O -)
$ source ~/.xmake/profile
Rust Examples
Install libbpf-cargo:
$ cargo install libbpf-cargo
Build using cargo:
$ cd examples/rust
$ cargo build --release
$ sudo ./target/release/xdp 1
<...>
Troubleshooting
Libbpf debug logs are quire helpful to pinpoint the exact source of problems, so it's usually a good idea to look at them before starting to debug or posting question online.
./minimal is always running with libbpf debug logs turned on.
For ./bootstrap, run it in verbose mode (-v) to see libbpf debug logs:
$ sudo ./bootstrap -v
libbpf: loading object 'bootstrap_bpf' from buffer
libbpf: elf: section(2) tp/sched/sched_process_exec, size 384, link 0, flags 6, type=1
libbpf: sec 'tp/sched/sched_process_exec': found program 'handle_exec' at insn offset 0 (0 bytes), code size 48 insns (384 bytes)
libbpf: elf: section(3) tp/sched/sched_process_exit, size 432, link 0, flags 6, type=1
libbpf: sec 'tp/sched/sched_process_exit': found program 'handle_exit' at insn offset 0 (0 bytes), code size 54 insns (432 bytes)
libbpf: elf: section(4) license, size 13, link 0, flags 3, type=1
libbpf: license of bootstrap_bpf is Dual BSD/GPL
...