Wild linker

Wild is a linker with the goal of being very fast for iterative development.

The plan is to eventually make it incremental, however that isn't yet implemented. It is however already pretty fast even without incremental linking.

For production builds, its recommended to use a more mature linker like GNU ld or LLD.

During development, if you'd like faster warm build times, then you could give Wild a try. It's at the point now where it should be usable for development purposes provided you're developing on x86-64 Linux. If you hit any issues, please file a bug report.

Installation

To install a pre-built binary, you can copy and paste the command from the releases page. Alternatively, you can download the tarball and manually copy the wild binary somewhere on your path.

To build and install, you can run:

cargo install --locked --bin wild --git https://github.com/davidlattimore/wild.git wild

Using as your default linker

If you'd like to use Wild as your default linker for building Rust code, you can put the following in ~/.cargo/config.toml.

[target.x86_64-unknown-linux-gnu]
linker = "clang"
rustflags = ["-C", "link-arg=--ld-path=wild"]

Q&A

Why another linker?

Mold is already very fast, however it doesn't do incremental linking and the author has stated that they don't intend to. Wild doesn't do incremental linking yet, but that is the end-goal. By writing Wild in Rust, it's hoped that the complexity of incremental linking will be achievable.

What's working?

The following platforms / architectures are currently supported:

x86-64 on Linux

The following is working with the caveat that there may be bugs:

Output to statically linked, non-relocatable binaries
Output to statically linked, position-independent binaries (static-PIE)
Output to dynamically linked binaries
Output to shared objects (.so files)
Rust proc-macros, when linked with Wild work
Most of the top downloaded crates on crates.io have been tested with Wild and pass their tests
Debug info

What isn't yet supported?

Lots of stuff. Here are some of the larger things that aren't yet done, roughly sorted by current priority:

Incremental linking
Support for architectures other than x86-64
Support for a wider range of linker flags
Linker scripts
Mac support
Windows support
LTO

How can I verify that Wild was used to link a binary?

Install readelf, then run:

readelf  -p .comment my-executable

Look for a line like:

Linker: Wild version 0.1.0

Or if you don't want to install readelf, you can probably get away with:

strings my-executable | grep 'Linker:'

Where did the name come from?

It's somewhat of a tradition for linkers to end with the letters "ld". e.g. "GNU ld, "gold", "lld", "mold". Since the end-goal is for the linker to be incremental, an "I" is added. Let's say the "W" stands for "Wild", since recursive acronyms are popular in open-source projects.

Benchmarks

The goal of Wild is to eventually be very fast via incremental linking. However, we also want to be as fast as we can be for non-incremental linking and for the initial link when incremental linking is enabled.

These benchmark were run on David Lattimore's laptop (2020 model System76 Lemur pro), which has 4 cores (8 threads) and 42 GB of RAM.

The following times are for linking rustc-driver, which is a shared object that contains most of the code of the Rust compiler. Linking was done with with --strip-debug and --build-id=none.

Linker	Time (ms)	± Standard deviation (ms)
GNU ld (2.38)	20774	855
gold (2.38)	6796	58
lld (18.1.8)	1601	24
mold (2.34.1)	946	17
wild (2024-11-30)	486	19

The following times are for linking the C compiler, clang without debug info.

Linker	Time (ms)	± Standard deviation (ms)
GNU ld (2.38)	8784	42
gold (2.38)	2528	37
lld (18.1.8)	1679	23
mold (2.34.1)	429	2
wild (2024-11-30)	244	6

Next, let's add debug info (remove --strip-debug). First rustc-driver:

Linker	Time (ms)	± Standard deviation (ms)
GNU ld (2.38)	23224	1030
gold (2.38)	8840	879
lld (18.1.8)	2741	1403
mold (2.34.1)	3514	2102
wild (2024-11-30)	3158	1616

Now clang with debug info:

Linker	Time (ms)	± Standard deviation (ms)
GNU ld (2.38)	139985	9871
gold (2.38)	92147	7287
lld (18.1.8)	30549	9819
mold (2.34.1)	16933	5359
wild (2024-11-30)	31540	7133

So Wild performs pretty well without debug info, but with debug info, it's performing less well at the moment.

See BENCHMARKING.md for more details on benchmarking.

Linking Rust code

The following is a cargo test command-line that can be used to build and test a crate using Wild. This has been run successfully on a few popular crates (e.g. ripgrep, serde, tokio, rand, bitflags). It assumes that the "wild" binary is on your path. It also depends on the Clang compiler being installed, since GCC doesn't allow using an arbitrary linker.

RUSTFLAGS="-Clinker=clang -Clink-args=--ld-path=wild" cargo test

Contributing

For more information on contributing to wild see CONTRIBUTING.md

Sponsorship

If you'd like to sponsor this work, that would be very much appreciated. The more sponsorship I get the longer I can continue to work on this project full time.

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Wild by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.