mold: A Modern Linker

mold is a high-performance drop-in replacement for existing Unix linkers, designed to speed up builds. In our August 2026 benchmarks, it links 4.9x faster than LLVM lld and 1.9x faster than wild at the median; see Benchmark for the full results.

mold is written by the original developer of LLVM lld, the linker that Android, Chrome, FreeBSD, PlayStation, Nintendo Switch, and other production systems are built with. mold started as an effort to build an even faster linker from scratch, free of the architectural limits its author had run into while optimizing lld. It has been in production use since 2021, and today it is the default linker of many large open-source projects and is used internally by many companies.

mold supports x86-64, i386, ARM 32/64, RISC-V 32/64, PowerPC 32/64, s390x, LoongArch 32/64, SPARC64, m68k, and SH-4.

Why does linking speed matter?

If you are using a compiled language such as C, C++, or Rust, a build consists of two phases. In the first phase, a compiler compiles source files into object files (.o files). In the second phase, a linker takes all object files and combines them into a single executable or shared library file.

The second phase can be time-consuming if your build output is large. mold can speed up this process, saving you time and preventing distractions while waiting for a lengthy build to finish. The difference is most noticeable during rapid debug-edit-rebuild cycles.

Benchmark

Here is a performance comparison of lld, wild, and mold when linking nine large programs on two machines:

• AMD Ryzen Threadripper 7980X (64 cores) running Ubuntu 24.04
• Apple M1 Ultra (16 performance cores and 4 efficiency cores) running Fedora Asahi Remix 42; the benchmark is restricted to the performance cores

The Threadripper represents many-core workstation and server processors, and the M1 Ultra represents high-performance desktop processors.

All three linkers were built from source in release configuration as of 2026-08-28 and ran with their default options. Times are wall-clock times as seen by the caller, the median of three runs after a warm-up. The ARM64 rows are the ARM64 builds of the same programs. The benchmark suite, including all linker inputs, is available on Zenodo.

AMD Ryzen Threadripper 7980X, debug builds

AMD Ryzen Threadripper 7980X, release builds

Apple M1 Ultra, debug builds

Apple M1 Ultra, release builds

N/A indicates that the linker cannot link that program. wild's Chromium release links are also marked N/A because wild does not implement --icf=all and links without identical code folding.

Why is mold so fast?

mold owes its speed to pervasive parallelism and to efficient data structures and algorithms. For details, read our paper "mold: A Massively Parallel Linker" (ASPLOS 2027), available at https://arxiv.org/abs/2608.23228.

Installation

Binary packages for the following systems are currently available:

Prebuilt binaries for Linux on x86-64, ARM64, ARM32, RISC-V, PPC64LE, s390x, and LoongArch are also attached to each GitHub release.

How to Build

mold is written in Rust and built with Cargo. It requires Rust 1.95 or later; if your system's Rust is older, install the stable toolchain with rustup. You also need Git and a C compiler such as GCC or Clang, which you can install with your system's package manager.

Compile mold

git clone https://github.com/rui314/mold.git
cd mold
cargo build --release

The executable is target/release/mold.

Install mold

Run sudo ./install-mold.sh to install mold under /usr/local. To install it under a different prefix, set PREFIX, as in sudo PREFIX=/usr ./install-mold.sh.

You can also run target/release/mold directly without installing it.

How to use

[target.'cfg(target_os = "linux")']
linker = "clang"
rustflags = ["-C", "link-arg=-fuse-ld=/path/to/mold"]

[target.'cfg(target_os = "linux")']
rustflags = ["-C", "link-arg=-fuse-ld=mold"]

when findExe("mold").len > 0 and defined(linux):
  switch("passL", "-fuse-ld=mold")

mold -run make <make-options-if-any>

$ readelf -p .comment <executable-file>

String dump of section '.comment':
  [     0]  GCC: (Ubuntu 10.2.0-5ubuntu1~20.04) 10.2.0
  [    2b]  mold 9a1679b47d9b22012ec7dfbda97c8983956716f7

Stability

mold has been developed in the open since 2020 and has more than 140 contributors. Its test suite, which covers every linker feature, runs in CI for all supported target CPU architectures, natively or under QEMU, and under ASAN and TSAN. Before each release, we try to build all of Gentoo Linux's roughly 19,000 packages with mold, using GNU ld as a control, to find regressions before they reach a release.

Sponsors

mold is free to use, but keeping it maintained is continuous work: supporting new architectures and toolchain features, keeping up with the projects that depend on it, and making it faster. That work is funded by sponsors. If mold saves you or your company time, please consider becoming a GitHub sponsor.

We thank everyone who sponsors the project. In particular, we'd like to acknowledge the following people and organizations who have sponsored $128/month or more:

Corporate sponsors

• G-Research
• Signal Slot Inc.
• GlareDB

Individual sponsors

• Wei Wu
• kyle-elliott
• Bryant Biggs
• kraptor23
• Jinkyu Yi
• Pedro Navarro