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→About rui314/mold
rui314/mold is an open-source project on GitHub, mainly written in Rust. mold 🦠: A Modern Linker in Rust 🦀 It currently holds 17,187 stars and 558 forks with 185 open issues, and was last pushed on 2026-09-20 (repository created 2020-09-29).
Project Overview
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GitHub Repository Details
README
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
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
| Program (output size) | lld | wild | mold | wild/mold | lld/mold |-----------------------------------|--------|-------|-------|-----------|--------- | Blender 5.2 (2.46 GiB) | 4.72s | 1.98s | 0.86s | 2.3x | 5.5x | Chromium 145 (4.51 GiB) | 16.64s | 3.98s | 1.65s | 2.4x | 10.1x | Chromium 145 ARM64 (4.76 GiB) | 20.91s | N/A | 1.83s | N/A | 11.4x | Clang 21 (4.19 GiB) | 6.19s | 3.71s | 1.34s | 2.8x | 4.6x | ClickHouse 26.1 (5.58 GiB) | 6.62s | 4.40s | 0.98s | 4.5x | 6.7x | Firefox 149 (2.37 GiB) | 5.11s | N/A | 0.78s | N/A | 6.5x | Firefox 149 ARM64 (2.43 GiB) | 6.40s | N/A | 0.93s | N/A | 6.9x | Godot 4.6 (1.01 GiB) | 1.77s | 1.08s | 0.46s | 2.3x | 3.8x | LibreOffice 26.2 (0.98 GiB) | 3.46s | 1.41s | 0.44s | 3.2x | 7.9x | PyTorch 2.9 (3.51 GiB) | 4.35s | 2.48s | 0.80s | 3.1x | 5.4x | TensorFlow 2.21 (9.55 GiB) | 50.73s | N/A | 3.15s | N/A | 16.1x
AMD Ryzen Threadripper 7980X, release builds
| Program (output size) | lld | wild | mold | wild/mold | lld/mold |-----------------------------------|-------|-------|-------|-----------|--------- | Blender 5.2 (0.24 GiB) | 0.85s | 0.30s | 0.20s | 1.5x | 4.2x | Chromium 145 (0.58 GiB) | 6.48s | N/A | 0.64s | N/A | 10.2x | Chromium 145 ARM64 (0.60 GiB) | 7.91s | N/A | 0.73s | N/A | 10.8x | Clang 21 (0.21 GiB) | 0.53s | 0.23s | 0.11s | 2.2x | 5.0x | ClickHouse 26.1 (1.23 GiB) | 3.18s | 2.07s | 0.41s | 5.0x | 7.7x | Firefox 149 (0.22 GiB) | 1.01s | 0.41s | 0.21s | 2.0x | 4.9x | Godot 4.6 (0.15 GiB) | 0.44s | 0.21s | 0.08s | 2.7x | 5.8x | LibreOffice 26.2 (0.19 GiB) | 1.13s | 0.57s | 0.19s | 3.0x | 6.0x | PyTorch 2.9 (0.31 GiB) | 0.68s | 0.32s | 0.15s | 2.2x | 4.7x | TensorFlow 2.21 (0.73 GiB) | 9.62s | N/A | 0.70s | N/A | 13.7x
Apple M1 Ultra, debug builds
| Program (output size) | lld | wild | mold | wild/mold | lld/mold |-----------------------------------|--------|-------|-------|-----------|--------- | Blender 5.2 (2.46 GiB) | 3.21s | 1.81s | 1.56s | 1.2x | 2.1x | Chromium 145 (4.51 GiB) | 9.54s | 3.49s | 2.22s | 1.6x | 4.3x | Chromium 145 ARM64 (4.76 GiB) | 12.67s | N/A | 2.31s | N/A | 5.5x | Clang 21 (4.19 GiB) | 4.40s | 2.78s | 2.96s | 0.9x | 1.5x | ClickHouse 26.1 (5.58 GiB) | 4.92s | 3.50s | 1.71s | 2.1x | 2.9x | Firefox 149 (2.37 GiB) | 3.21s | N/A | 1.12s | N/A | 2.9x | Firefox 149 ARM64 (2.43 GiB) | 4.13s | N/A | 1.12s | N/A | 3.7x | Godot 4.6 (1.01 GiB) | 1.12s | 0.81s | 0.62s | 1.3x | 1.8x | LibreOffice 26.2 (0.98 GiB) | 2.08s | 0.94s | 0.63s | 1.5x | 3.3x | PyTorch 2.9 (3.51 GiB) | 3.07s | 2.10s | 1.45s | 1.4x | 2.1x | TensorFlow 2.21 (9.55 GiB) | 43.68s | N/A | 4.43s | N/A | 9.9x
Apple M1 Ultra, release builds
| Program (output size) | lld | wild | mold | wild/mold | lld/mold |-----------------------------------|-------|-------|-------|-----------|--------- | Blender 5.2 (0.24 GiB) | 0.56s | 0.20s | 0.25s | 0.8x | 2.3x | Chromium 145 (0.58 GiB) | 4.25s | N/A | 0.78s | N/A | 5.5x | Chromium 145 ARM64 (0.60 GiB) | 5.17s | N/A | 0.91s | N/A | 5.7x | Clang 21 (0.21 GiB) | 0.30s | 0.15s | 0.14s | 1.0x | 2.1x | ClickHouse 26.1 (1.23 GiB) | 1.94s | 0.95s | 0.55s | 1.7x | 3.5x | Firefox 149 (0.22 GiB) | 0.56s | 0.23s | 0.20s | 1.1x | 2.7x | Godot 4.6 (0.15 GiB) | 0.26s | 0.11s | 0.11s | 1.0x | 2.3x | LibreOffice 26.2 (0.19 GiB) | 0.62s | 0.30s | 0.23s | 1.3x | 2.7x | PyTorch 2.9 (0.31 GiB) | 0.43s | 0.22s | 0.17s | 1.3x | 2.5x | TensorFlow 2.21 (0.73 GiB) | 8.07s | N/A | 0.68s | N/A | 11.9x
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. Install the stable Rust 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 and its companion preload library are
target/release/mold and target/release/mold-wrapper.so.
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
A classic way to use mold
On Unix, the linker command (usually /usr/bin/ld) is indirectly invoked by
the compiler driver (typically cc, gcc, or clang), which is in turn
indirectly invoked by make or other build system commands.
If you can specify an additional command line option for your compiler driver
by modifying the build system's config files, add one of the following flags
to use mold instead of /usr/bin/ld:
- For Clang: pass
-fuse-ld=mold - For GCC 12.1.0 or later: pass
-fuse-ld=mold - For GCC before 12.1.0: the
-fuse-ldoption does not acceptmoldas a
-B option instead. The -B option
tells GCC where to look for external commands like ld.
If you installed mold using the script above, there is a directory named
/usr/local/libexec/mold, and the ld command there is a symlink to mold.
Pass -B/usr/local/libexec/mold to GCC. If you installed under another
prefix, use that prefix instead.
If you haven't installed ld.mold to any $PATH, you can still pass
-fuse-ld=/absolute/path/to/mold to clang to use mold. However, GCC does not
accept an absolute path as an argument for -fuse-ld.
If you are using Rust
Create .cargo/config.toml in your project directory with the following:
[target.'cfg(target_os = "linux")']
linker = "clang"
rustflags = ["-C", "link-arg=-fuse-ld=/path/to/mold"]
where /path/to/mold is an absolute path to the mold executable. In the
example above, we use clang as a linker driver since it always accepts the
-fuse-ld option. If your GCC is recent enough to recognize the option, you
may be able to remove the linker = "clang" line.
[target.'cfg(target_os = "linux")']
rustflags = ["-C", "link-arg=-fuse-ld=mold"]
If you want to use mold for all projects, add the above snippet to
~/.cargo/config.toml.
If you are using Nim
Create config.nims in your project directory with the following:
when findExe("mold").len > 0 and defined(linux):
switch("passL", "-fuse-ld=mold")
where mold must be included in the PATH environment variable. In this
example, gcc is used as the linker driver. Use the -fuse-ld option if your
GCC is recent enough to recognize this option.
If you want to use mold for all projects, add the above snippet to
~/.config/config.nims.
If you are using Conan package manager
You can configure Conan to download the latest
version of mold and use it as the linker when building your dependencies and
projects from source. Please see the instructions here.
mold -run
It is sometimes very hard to pass an appropriate command line option to cc
to specify an alternative linker. To address this situation, mold has a
feature to intercept all invocations of ld, ld.bfd, ld.lld, or ld.gold
and redirect them to itself. To use this feature, run make (or another build
command) as a subcommand of mold as follows:
mold -run make
Internally, mold invokes a given command with the LD_PRELOAD environment
variable set to its companion shared object file. The shared object file
intercepts all function calls to exec(3)-family functions to replace
argv[0] with mold if it is ld, ld.bfd, ld.gold, or ld.lld.
GitHub Actions
You can use our setup-mold GitHub Action to speed up GitHub-hosted continuous builds. Although GitHub Actions run on a 4 core machine, mold is still significantly faster than the default GNU linker, especially when linking large programs.
Verify that you are using mold
mold leaves its identification string in the .comment section of an output
file. You can print it out to verify that you are actually using mold.
$ readelf -p .comment
String dump of section '.comment':
[ 0] GCC: (Ubuntu 10.2.0-5ubuntu1~20.04) 10.2.0
[ 2b] mold 9a1679b47d9b22012ec7dfbda97c8983956716f7
If mold is present in the .comment section, the file was created by mold.
Online manual
Since mold is a drop-in replacement, you should be able to use it without
reading its manual. However, if you need it, mold's man page
is available online. You can read the same manual by running man mold.
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
Individual sponsors
GitHub Stars & Activity
17,187Stars
558Forks
185Open issues
RustLanguage
GitHub Popularity
GitHub stars17,187
Forks558
Open issues185
Primary languageRust
LicenseMIT
Stars gained today44
Created2020-09-29
Last pushed2026-09-20
Trending History
Daily boardrank #59 · ▲ 44 stars
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