mpapierski / c2rust

Migrate C code to Rust

C2Rust

C2Rust helps you migrate C99-compliant code to Rust. The translator (or transpiler), c2rust transpile, produces unsafe Rust code that closely mirrors the input C code. The primary goal of the translator is to preserve functionality; test suites should continue to pass after translation.

Generating safe and idiomatic Rust code from C ultimately requires manual effort. We are currently working on analysis to automate some of the effort required to lift unsafe Rust into safe Rust types. This work is still in the early stages; please get in touch if you're interested! We previously maintained a scriptable refactoring tool, c2rust refactor, that reduces the tedium of refactoring, but this tool is now deprecated so that we can move forward with a recent Rust toolchain.

Here's the big picture:

To learn more, check out our RustConf'18 talk on YouTube and try the C2Rust translator online at c2rust.com.

Documentation

To learn more about using and developing C2Rust, check out the manual. The manual is still a work-in-progress, so if you can't find something please let us know.

Installation

Prerequisites

C2Rust requires LLVM 7 or later with its corresponding clang compiler and libraries. Python 3.6 or later, CMake 3.4.3 or later, and openssl (1.0) are also required. These prerequisites may be installed with the following commands, depending on your platform:

• Ubuntu 18.04, Debian 10, and later:

  apt install build-essential llvm clang libclang-dev cmake libssl-dev pkg-config python3

Depending on the LLVM distribution, the llvm-dev package may also be required. For example, the official LLVM packages from apt.llvm.org require llvm-dev to be installed.

• Arch Linux:

  pacman -S base-devel llvm clang cmake openssl python

• NixOS / nix:

  nix-shell

• macOS: Xcode command-line tools and recent LLVM (we recommend the Homebrew version) are required.

  xcode-select --install
  brew install llvm python3 cmake openssl

The C2Rust transpiler now builds using a stable Rust compiler. If you are developing other features, you may need to install the correct nightly compiler version.

Installing from crates.io

cargo install c2rust

You can also set the LLVM version explicitly if you have multiple installed, like this, for example:

LLVM_CONFIG_PATH=llvm-config-14 cargo install c2rust

On macOS with Homebrew LLVM, you need to point the build system at the LLVM installation. The path for the installation is architecture dependent:

• Intel Macs:

  LLVM_CONFIG_PATH=/usr/local/opt/llvm/bin/llvm-config cargo install c2rust

• Apple Silicon Macs:

  LLVM_CONFIG_PATH=/opt/homebrew/opt/llvm/bin/llvm-config cargo install c2rust

On Linux with Linuxbrew LLVM, you need to point the build system at the LLVM installation as follows:

LLVM_CONFIG_PATH=/home/linuxbrew/.linuxbrew/opt/llvm/bin/llvm-config cargo install c2rust

Note: adjust LLVM_CONFIG_PATH accordingly if Linuxbrew was installed to your home directory.

On Gentoo, you need to point the build system to the location of libclang.so and llvm-config as follows:

LLVM_CONFIG_PATH=/path/to/llvm-config LIBCLANG_PATH=/path/to/libclang.so cargo install c2rust

If you have trouble with building and installing, or want to build from the latest master, the developer docs provide more details on the build system.

Installing from Git

If you'd like to check our recently developed features or you urgently require a bugfixed version of c2rust, you can install it directly from Git:

cargo install --git https://github.com/immunant/c2rust.git c2rust

Please note that the master branch is under constant development and you may experience issues or crashes.

You should also set LLVM_CONFIG_PATH accordingly if required as described above.

Translating C to Rust

To translate C files specified in compile_commands.json (see below), run the c2rust tool with the transpile subcommand:

c2rust transpile compile_commands.json

(The c2rust refactor tool was also available for refactoring Rust code, see refactoring, but is now being replaced by a more robust way to refactor.)

The translator requires the exact compiler commands used to build the C code. This information is provided via a compilation database file named compile_commands.json. (Read more about compilation databases here). Many build systems can automatically generate this file; we show a few examples below.

Once you have a compile_commands.json file describing the C build, translate the C code to Rust with the following command:

c2rust transpile path/to/compile_commands.json

To generate a Cargo.toml template for a Rust library, add the -e option:

c2rust transpile --emit-build-files path/to/compile_commands.json

To generate a Cargo.toml template for a Rust binary, do this:

c2rust transpile --binary myprog path/to/compile_commands.json

Where --binary myprog tells the transpiler to use the main function from myprog.rs as the entry point for a binary.

The translated Rust files will not depend directly on each other like normal Rust modules. They will export and import functions through the C API. These modules can be compiled together into a single static Rust library or binary.

There are several known limitations in this translator. The translator will emit a warning and attempt to skip function definitions that cannot be translated.

Generating compile_commands.json Files

The compile_commands.json file can be automatically created using either cmake, intercept-build, or bear.

It may be a good idea to remove optimizations (-OX) from the compilation database, as there are optimization builtins which we do not support translating.

... with cmake

When creating the initial build directory with cmake, specify -DCMAKE_EXPORT_COMPILE_COMMANDS=1. This only works on projects configured to be built by cmake. This works on Linux and MacOS.

cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=1 ...

... with intercept-build

intercept-build (part of the scan-build tool) is recommended for non-cmake projects. intercept-build is bundled with clang under tools/scan-build-py, but a standalone version can be easily installed via pip with:

pip install scan-build

Usage:

intercept-build <build command>

You can also use intercept-build to generate a compilation database for compiling a single C file. For example:

intercept-build sh -c "cc program.c"

... with bear (Linux only)

If you have bear installed, it can be used similarly to intercept-build:

bear <build command>

... with compiledb

The compiledb package can also be used for makefile projects if the other tools don't work. Install via pip with:

pip install compiledb

Usage:

# After running
./autogen.sh && ./configure # etc.
# Run
compiledb make

Contact

To report issues with translation or refactoring, please use our Issue Tracker.

To reach the development team, join our discord channel or email us at [e-mail].

FAQ

I translated code on platform X, but it didn't work correctly on platform Y.

We run the C preprocessor before translation to Rust. This specializes the code to the host platform. For this reason, we do not support cross compiling translated code at the moment.

What platforms can C2Rust be run on?

The translator and refactoring tool support both macOS and Linux. Other features, such as cross checking the functionality between C and Rust code, are currently limited to Linux hosts.

Acknowledgements and Licensing

This material is available under the BSD-3 style license as found in the LICENSE file.

The C2Rust translator is inspired by Jamey Sharp's Corrode translator. We rely on Emscripten's Relooper algorithm to translate arbitrary C control flows.

This material is based upon work supported by the United States Air Force and DARPA under Contract No. FA8750-15-C-0124. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the United States Air Force and DARPA. Distribution Statement A, "Approved for Public Release, Distribution Unlimited."