BPF Linker 🔗

bpf-linker aims to simplify building modern BPF programs while still supporting older, more restrictive kernels.

Build

Overview

bpf-linker can be used to statically link multiple BPF object files together and optionally perform optimizations needed to target older kernels. It operates on LLVM bitcode, so the inputs must be bitcode files (.bc) or object files with embedded bitcode (.o), optionally stored inside ar archives (.a).

Installation

The linker requires LLVM 12. It can use the same LLVM used by the rust compiler, or it can use an external LLVM installation.

Using LLVM provided by rustc

All you need to do is run:

sh cargo install bpf-linker

Using external LLVM

On Debian based distributions you need to install the llvm-12-dev and libclang-12-dev packages. If your distro doesn't have them you can get them from the official LLVM repo at https://apt.llvm.org.

On rpm based distribution you need the llvm-devel and clang-devel packages. If your distro doesn't have them you can get them from Fedora Rawhide.

Once you have installed LLVM 12 you can install the linker running:

sh cargo install --git https://github.com/aya-rs/bpf-linker --tag v0.9.2 --no-default-features --features system-llvm -- bpf-linker

If you don't have cargo you can get it from https://rustup.rs or from your distro's package manager.

Usage

Rust

Nightly

To compile your eBPF crate just run:

sh cargo +nightly build --target=bpfel-unknown-none -Z build-std=core --release

If you don't want to have to pass the target and build-std options every time, you can put them in .cargo/config.toml under the crate's root folder:

```toml [build] target = "bpfel-unknown-none"

[unstable] build-std = ["core"] ```

Stable (not recommended)

If for whatever reason you can't use rust nightly to build your project, you can still compile your eBPF crate with:

```sh $ cargo rustc --release -- \ -C linker-plugin-lto \ -C linker-flavor=wasm-ld -C linker=bpf-linker \ -C link-arg=--target=bpf Compiling bpf-log-clone v0.1.0 (/home/alessandro/bpf-log-clone) Finished release [optimized] target(s) in 0.86s

$ file target/release/libbpflogclone.so target/release/libbpflogclone.so: ELF 64-bit LSB relocatable, eBPF, version 1 (SYSV), not stripped ```

Clang

For a simple example of how to use the linker with clang see this gist. In the example lib.c is compiled as a static library which is then linked by program.c. The Makefile shows how to compile the C code and then link it.

Usage

``` bpf-linker

USAGE: bpf-linker [FLAGS] [OPTIONS] --output [--] [inputs]...

FLAGS: --disable-expand-memcpy-in-order Disable passing --bpf-expand-memcpy-in-order to LLVM --disable-memory-builtins Disble exporting memcpy, memmove, memset, memcmp and bcmp. Exporting those is commonly needed when LLVM does not manage to expand memory intrinsics to a sequence of loads and stores -h, --help Prints help information --ignore-inline-never Ignore noinline/#[inline(never)]. Useful when targeting kernels that don't support function calls --unroll-loops Try hard to unroll loops. Useful when targeting kernels that don't support loops -V, --version Prints version information

OPTIONS: --cpu Target BPF processor. Can be one of generic, probe, v1, v2, v3 [default: generic] --cpu-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: ] --dump-module Dump the final IR module to the given path before generating the code --emit Output type. Can be one of llvm-bc, asm, llvm-ir, obj [default: obj] --export ... Comma separated list of symbols to export. See also --export-symbols --export-symbols Export the symbols specified in the file path. The symbols must be separated by new lines -L ... Add a directory to the library search path --llvm-args ... Extra command line arguments to pass to LLVM --log-file Output logs to the given path --log-level Set the log level. Can be one of off, info, warn, debug, trace -O ... Optimization level. 0-3, s, or z [default: 2] -o, --output Write output to --target LLVM target triple. When not provided, the target is inferred from the inputs

ARGS: ... Input files. Can be object files or static libraries ```

License

bpf-linker is licensed under either of

at your option.