eBPF (Extended Berkeley Packet Filter)
eBPF (Extended Berkeley Packet Filter) is a Linux kernel subsystem, its modern form dating to kernel 3.18 (2014), that allows user-authored programs to run inside the kernel with near-native performance, subject to safety guarantees enforced at load time by a verifier. The name is historical: the original BPF (Berkeley Packet Filter, 1992) was a narrow packet filtering mechanism for tools like tcpdump. eBPF extended the instruction set, registers, and capabilities far beyond packet filtering into a general-purpose in-kernel programmability platform. The central design constraint is that eBPF programs must be provably safe: they cannot crash the kernel, loop infinitely, or access memory out of bounds. The verifier statically analyses every program at load time, checking that all memory accesses are bounds-checked, all loops are bounded or unrolled, and all pointer dereferences are preceded by null checks. Only programs that pass verification are accepted; once accepted, the kernel JIT-compiles the eBPF bytecode to native machine code for the host architecture — x86-64, ARM64, RISC-V — so eBPF programs run at the same speed as compiled kernel code, not as an interpreter.