Managed linkers

The default system selection preserves Cargo's linker. Change it when you want to try another linker or share a pinned choice across a workspace. Every selection other than system links through clang, so it requires clang on PATH. Keep system on Windows, where mbx does not support rust-lld selection.

Try a linker

On Linux, try a pinned mold release for one build:

MBX_LINKER=mold@2.42.0 mbx build

This is an example version, not an automatically updated recommendation.

On Linux or macOS, rust-lld uses the active Rust toolchain's bundled LLD without a download:

MBX_LINKER=rust-lld mbx build

mbx includes the selected linker executable in the cache key for native links (see Native linking is cached only where the linker can be described). Changing the linker can therefore change cache keys, so compare equivalent builds when you measure a linker's effect.

Selectors

mbx selects a linker by Cargo profile and target triple and routes native Rust links through it. For mold and Wild, it installs the exact version you name, downloading it from the linker's official GitHub releases.

Selector	Linker	Downloads
system	Cargo's own linker selection, unchanged	No
rust-lld or lld	The LLD shipped with the active Rust toolchain	No
mold@<version> or wild@<version>	The named mold or Wild release, checked against GitHub's SHA-256 digest	Yes
path:<executable>	A linker mbx does not install	No

The mold and Wild selectors require an exact version, not latest. mbx installs each download once beneath <cache_dir>/tools, and concurrent builds wait on the same installation lock. When GITHUB_TOKEN is set, mbx sends it with its GitHub API and download requests.

mbx installs mold and Wild only on Linux. On an unsupported host, the build fails before Cargo starts rather than silently changing the linker.

Choose a linker by profile and target

Store persistent selections in your global configuration or in the workspace policy. Workspace policy, which the repository owns, cannot use the path: selector.

[linker]
default = "system"

[linker.profiles.dev]
x86_64-unknown-linux-gnu = "mold@2.42.0"
aarch64-unknown-linux-gnu = "wild@0.10.0"

[linker.profiles.release]
default = "rust-lld"

Within a profile table, an exact target triple wins over default. The top-level linker.default applies when the active profile has no matching entry. mbx reads the active profile from the Cargo command:

Cargo command or flag	Profile
--profile <name>	<name>
--release	release
cargo bench	bench
cargo install	release
cargo install --debug	debug
Any other command	dev

From Cargo 1.99, cargo install --debug builds with the debug profile. When linker.profiles.debug is absent, mbx uses the dev table instead.

MBX_LINKER overrides the global configuration and workspace policy for one invocation:

MBX_LINKER=mold@2.42.0 cargo build
MBX_LINKER=system cargo build --release