created_at2018-10-22 19:37:23.389733
updated_at2022-01-24 22:10:21.196708
descriptionSimply and Easily cross-compile the Rust sysroot crates.
Diana (DianaNites)



Cargo-sysroot maintenance-experimental

A simple tool to compile the sysroot crates for your no_std application, while using the standard cargo tools.

This is not a wrapper like cargo xbuild or xargo, this is a standalone tool you call once beforehand. This has the nice benefit of actually working with standard tools like Rust Analyzer, clippy, or even the simple cargo check. It accomplishes this by generating a .cargo/config for you.


  • The latest nightly compiler.
  • The rust-src component must be installed for the active toolchain.
  • Your Cargo.toml file MUST contain, where target is a target specification json file.
    • A built-in target also works!
  • OR Pass --target on the command line, ex cargo sysroot --target path/to/target.json

Example Cargo.toml

name = "My Project"
version = "0.1.0"
authors = ["Me <>"]

target = "my_custom_target.json" # This is relative to Cargo.toml

Getting Started

  • Run cargo install cargo-sysroot.
  • Run cargo sysroot in the working directory of your project.

This tool will generate a .cargo/config.toml for you that looks something like this. This can be disabled via the --no-config command-line option.

target = <>
rustflags = [
    "<project root>/target/sysroot",

The sysroot will be located at target/sysroot and the target directory for building it at target/sysroot/target.

Due to how the rust sysroot works, you can use multiple different target specifications at a time without rebuilding, by simply passing a different --target to cargo.

Note that this tool is currently quite simple, so it won't attempt to do anything if that file already exists. In this case you will have to edit it manually.

This will allow Cargo to properly build your project with the normal commands, such as cargo build.

You may wish to modify this file to make use of the target.$triple.runner key. See the Cargo Documentation for details. Note that the author experienced problems with the $triple variant not working, and you may experience better success with the cfg variant.

If you update your Rust nightly version you will need to run cargo-sysroot again, causing cargo to detect the update and rebuild the sysroot and your project.


If you have more complicated needs than can be satisfied by target.$triple.runner, which doesn't support complex-ish modifications of the command line.

The author recommends their own, cargo-runner to solve this, it allows specifying the command-line in Cargo.toml and applying a suffix to the path from Cargo.

Alternatives include cargo-make, which you can setup to run whatever you like, instead of using cargo run.

Use my other crate, cargo-image to build an image suitable for running in QEMU.


The sysroot crates are compiled with the --release switch. compiler_builtins is built with the mem and rustc-dep-of-std features, which provides memcpy and related.

The sysroot crates will share any profile information your crate specifies. Eg if you enable debug for release, the sysroot crates will have that too. This matches cargo-xbuild behavior and some crates, for example bootloader, require this to function.

You can pass custom rust sources through the --rust-src-dir flag.


  • Allow disabling the mem feature?


  • Q: Why did you write this over just using cargo-xbuild
  • A: It was easier and simpler than getting cargo-xbuild to work reliably or with any other standard tools.


Licensed under either of

at your option.


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

Commit count: 238

cargo fmt