Reverse Engineeringbpflinkerllvmbitcodekerneloptimization

bpf-linker

bpf-linker simplifies building modern BPF programs by statically linking multiple BPF object files together and optionally performing optimizations for older kernels. It operates on LLVM bitcode from .bc, .o, or .a files.

Description

bpf-linker is a tool designed to streamline the development of Berkeley Packet Filter (BPF) programs, particularly those used in modern Linux kernel contexts like eBPF. It enables developers to combine multiple BPF object files or static libraries into a single output, making it easier to manage complex BPF applications.

Use cases include building optimized BPF programs for kernel probing, networking, or tracing where compatibility with older kernels is required. By handling LLVM bitcode inputs, it supports the typical workflow of BPF development tools like clang/LLVM.

The tool is particularly useful in cybersecurity and system programming scenarios where custom kernel-level filters or observers need to be deployed across diverse environments.

How It Works

bpf-linker processes LLVM bitcode from input files (.bc object files, .o with embedded bitcode, or .a archives). It performs static linking of multiple inputs and applies optimizations based on specified levels and target CPU features to ensure compatibility with older kernels. Outputs can be in formats like object files, assembly, LLVM IR, or bitcode, with optional BTF emission for kernel loading.

Installation

bash
sudo apt install bpf-linker

Flags

--target <TARGET>LLVM target triple. When not provided, the target is inferred from the inputs
--cpu <CPU>Target BPF processor. Can be one of `generic`, `probe`, `v1`, `v2`, `v3` [default: generic]
--cpu-features <features>Enable or disable CPU features. The available features are: alu32, dummy, dwarfris. Use +feature to enable a feature, or -feature to disable it. For example --cpu-features=+alu32,-dwarfris [default: ]
-o, --output <OUTPUT>Write output to <output>
--emit <EMIT>Output type. Can be one of `llvm-bc`, `asm`, `llvm-ir`, `obj` [default: obj]
--btfEmit BTF information
-L <LIBS>Add a directory to the library search path
-O <OPTIMIZE>Optimization level. 0-3, s, or z [default: 2]

Examples

Display help and usage information for bpf-linker
bpf-linker -h
Link two object files into a single output object file using default settings
bpf-linker --output output.o input1.o input2.o
Link a bitcode file specifying the LLVM target triple and output as bitcode
bpf-linker --target bpf-pc-linux input.bc --output linked.bc
Link targeting BPF v2 CPU with alu32 feature enabled
bpf-linker --cpu v2 --cpu-features=+alu32 input.o -o optimized.o
Link from archive, emit assembly with BTF information
bpf-linker --emit asm --btf inputs.a -o program.s
Link with optimization level 3 and custom library search path
bpf-linker -O 3 -L /path/to/libs input1.o input2.o -o fast.o
Target probe CPU, disable dwarfris feature for specific kernel compatibility
bpf-linker --cpu probe --cpu-features=-dwarfris multi.bc -o probe.o
Updated 2026-04-16kali.org ↗