Unlocking eBPF: How Kernel‑Level Observability Powers Modern Cloud‑Native Apps

eBPF (extended Berkeley Packet Filter) is a sandboxed virtual machine inside the Linux kernel that allows safe, just‑in‑time compiled programs to be attached to kernel or user‑space events. It enables non‑kernel developers to extend kernel functionality for networking, security, tracing, and performance monitoring.

Key Characteristics

Safety : The BPF verifier builds a directed‑acyclic graph of the program, rejects unreachable code and illegal instructions.

Efficiency : JIT compilation turns bytecode into native instructions, avoiding user‑space data copies.

Standard API : Helper functions, BTF type information, and perf maps provide a uniform interface.

Power : Supports many program types (socket_filter, kprobe, tracepoint, XDP, cgroup_skb, etc.) and a variety of map storage back‑ends.

Typical Use Cases

Network optimization : XDP and socket filters run at near‑native speed, enabling fast packet parsing and custom routing policies.

Fault diagnosis : kprobes and tracepoints expose kernel and user‑space events without the overhead of traditional sampling tools.

Security enforcement : Observe system calls, network packets, and socket operations to apply fine‑grained filtering.

Performance monitoring : Dynamically collect custom metrics and perform edge‑side aggregation, surpassing static counters such as sar.

How to Build an eBPF Program

Write the eBPF logic in C (or use higher‑level languages that generate C).

Compile the source to BPF bytecode with clang -target bpf -O2 -c prog.c -o prog.o.

Load the bytecode into the kernel via the bpf() system call (e.g., using libbpf, libbpfgo, or bcc).

The kernel verifier checks safety, then the JIT compiles the program for execution.

Program state is stored in BPF maps; user‑space reads or updates maps with bpf() commands ( BPF_MAP_*_ELEM).

Program Types

List supported types on a host: bpftool feature probe | grep program_type Typical output includes:

socket_filter
kprobe
tracepoint
xdp
cgroup_skb
cgroup_sock
perf_event
...

Finding Probe Points

Kernel events :

List available tracepoints: ls /sys/kernel/debug/tracing/events Query with bpftrace: bpftrace -l 'tracepoint:syscalls:*' List perf events: sudo perf list tracepoint User‑space events :

Static binaries: readelf -Ws /path/to/binary or readelf -n /path/to/binary to discover symbols and USDT info.

bpftrace queries:

bpftrace -l 'uprobe:/usr/lib/x86_64-linux-gnu/libc.so.6:*'
 bpftrace -l 'usdt:/usr/lib/x86_64-linux-gnu/libc.so.6:*'

Mapping Problems to Probes

Apply the 80/20 rule: first identify the core part of the software stack that most failures surface from, then attach kprobes, tracepoints, or uprobes to those locations. Example for packet loss:

sudo bpftrace -e 'kprobe:kfree_skb /comm=="myprocess"/ { printf("kstack: %s
", kstack); }'

The command prints the kernel stack trace for each kfree_skb invocation, helping locate the root cause.

Core eBPF Implementation Details

Verifier : Constructs a DAG of instructions and simulates execution to guarantee safety.

JIT Compiler : Translates verified bytecode to native CPU instructions.

Execution Context : Five 64‑bit registers, a program counter, and a 512‑byte stack.

Helpers : A limited set of kernel‑provided functions, varying by program type.

Maps & Context : Persistent key/value stores accessible from both kernel and user space.

The primary system call is:

int bpf(int cmd, union bpf_attr *attr, unsigned int size);

Key cmd values include BPF_PROG_LOAD, BPF_MAP_CREATE, BPF_OBJ_PIN, BPF_PROG_ATTACH, and map‑related commands for lookup, update, and deletion.

Loading, Attaching, and Using Maps

Load a program with BPF_PROG_LOAD (returns a file descriptor).

Attach the program to an event, e.g.,

b.attach_kprobe(event="tcp_v4_connect", fn_name="handle_connect")

(internally creates a perf event and links the BPF program via PERF_EVENT_IOC_SET_BPF).

Interact with maps using BPF_MAP_*_ELEM commands to store or retrieve state.

eBPF Tooling Ecosystem

Infrastructure : Linux kernel (>= 4.14) and LLVM.

Libraries :

Go: https://github.com/cilium/ebpf , https://github.com/aquasecurity/libbpfgo

C/C++: https://github.com/libbpf/libbpf

Applications :

BCC – https://github.com/iovisor/bcc

bpftrace – https://github.com/iovisor/bpftrace

Cilium – https://github.com/cilium/cilium

Falco – https://github.com/falcosecurity/falco

Katran – https://github.com/facebookincubator/katran

Hubble – https://github.com/cilium/hubble

Kindling – https://github.com/CloudDectective-Harmonycloud/kindling

Pixie – https://github.com/pixie-io/pixie

kubectl‑trace – https://github.com/iovisor/kubectl-trace

L3AF – https://github.com/l3af-project/l3afd

ply – https://github.com/iovisor/ply

Tracee – https://github.com/aquasecurity/tracee

Resources :

eBPF project list – https://ebpf.io/projects

Awesome eBPF – https://github.com/zoidbergwill/awesome-ebpf

Best Practices

Start with the most impactful 80 % of the software stack; use kernel probes for core subsystems and add user‑space probes only where needed.

Avoid tracing high‑frequency user‑space functions with uprobes, as they can introduce noticeable overhead.

Leverage existing libraries (libbpf, libbpfgo, bcc) to handle map management, program loading, and attachment boilerplate.

Validate map types and helper availability on the target kernel with bpftool feature probe | grep map_type and bpftool feature probe | grep helper.

Conclusion

eBPF provides a full‑coverage, non‑intrusive, programmable framework for kernel and user‑space observability. Its effectiveness hinges on a solid understanding of the software stack to select appropriate probe points and on using the verifier‑approved helper set and map infrastructure for safe, high‑performance instrumentation.