A Thorough Introduction to eBPF

Why I Read This

eBPF is fundamental to modern Linux observability and networking tooling. Understanding the verifier and map types is a prerequisite for writing anything non-trivial with libbpf.

Key Takeaways

• The eBPF verifier performs static analysis at load time — it rejects programs with unbounded loops, invalid memory accesses, and stack overflows before they ever run.
• BPF maps are the primary mechanism for sharing data between the kernel-space eBPF program and user space. Choosing the right map type (hash, array, ring buffer, LRU) has significant performance implications.
• JIT compilation means eBPF programs run at near-native speed — the interpreted fallback is only used on architectures without a JIT backend.
• Program types (kprobes, tracepoints, XDP, tc) determine what kernel hooks the program can attach to and what helper functions are available.

What I Found Surprising

The verifier tracks every possible code path and refuses programs where any path could lead to an unsafe state. This is stricter than most developers expect — even dead code that can never execute at runtime must pass verification.