BPF Linker π
bpf-linker aims to simplify building modern BPF programs while still supporting older, more restrictive kernels.
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 16. It can use the same LLVM used by the rust compiler, or it can use an external LLVM installation.
If your target is aarch64-unknown-linux-gnu (i.e. Linux on Apple Silicon) you
will have to use the external LLVM method.
Using LLVM provided by rustc
All you need to do is run:
cargo install bpf-linkerUsing external LLVM
On Debian based distributions you need to install the llvm-16-dev and
libclang-16-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 16 you can install the linker running:
cargo install bpf-linker --no-default-featuresIf 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:
cargo +nightly build --target=bpfel-unknown-none -Z build-std=core --releaseIf 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:
[build]
target = "bpfel-unknown-none"
[unstable]
build-std = ["core"]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 <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 <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: ]
--dump-module <path> Dump the final IR module to the given `path` before generating the code
--emit <emit> Output type. Can be one of `llvm-bc`, `asm`, `llvm-ir`, `obj` [default: obj]
--export <symbols>... Comma separated list of symbols to export. See also `--export-symbols`
--export-symbols <path> Export the symbols specified in the file `path`. The symbols must be separated by
new lines
-L <libs>... Add a directory to the library search path
--llvm-args <args>... Extra command line arguments to pass to LLVM
--log-file <path> Output logs to the given `path`
--log-level <level> Set the log level. Can be one of `off`, `info`, `warn`, `debug`, `trace`
-O <optimize>... Optimization level. 0-3, s, or z [default: 2]
-o, --output <output> Write output to <output>
--target <target> LLVM target triple. When not provided, the target is inferred from the inputs
ARGS:
<inputs>... Input files. Can be object files or static libraries
License
bpf-linker is licensed under either of
- Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)
at your option.