Cranelift Code Generator

Cranelift is a low-level retargetable code generator. It translates a target-independent intermediate representation into executable machine code.

For more information, see the documentation.

For an example of how to use the JIT, see the SimpleJIT Demo, which implements a toy language.

Status

Cranelift currently supports enough functionality to run a wide variety of programs, including all the functionality needed to execute WebAssembly MVP functions, although it needs to be used within an external WebAssembly embedding to be part of a complete WebAssembly implementation.

The x86-64 backend is currently the most complete and stable; other architectures are in various stages of development. Cranelift currently supports both the System V AMD64 ABI calling convention used on many platforms and the Windows x64 calling convention. The performance of code produced by Cranelift is not yet impressive, though we have plans to fix that.

The core codegen crates have minimal dependencies, support no_std mode (see below), and do not require any host floating-point support, and do not use callstack recursion.

Cranelift does not yet perform mitigations for Spectre or related security issues, though it may do so in the future. It does not currently make any security-relevant instruction timing guarantees. It has seen a fair amount of testing and fuzzing, although more work is needed before it would be ready for a production use case.

Cranelift's APIs are not yet stable.

Cranelift currently supports Rust 1.25.0 and later. We intend to always support the latest stable Rust. And, we currently support the version of Rust in the latest Ubuntu LTS, although whether we will always do so is not yet determined. Cranelift requires Python 2.7 or Python 3 to build.

Planned uses

Cranelift is designed to be a code generator for WebAssembly, but it is general enough to be useful elsewhere too. The initial planned uses that affected its design are:

• WebAssembly compiler for the SpiderMonkey engine in Firefox.
• Backend for the IonMonkey JavaScript JIT compiler in Firefox.
• Debug build backend for the Rust compiler.

Building Cranelift

Cranelift uses a conventional Cargo build process.

Cranelift consists of a collection of crates, and uses a Cargo Workspace, so for some cargo commands, such as cargo test, the --all is needed to tell cargo to visit all of the crates.

test-all.sh at the top level is a script which runs all the cargo tests and also performs code format, lint, and documentation checks.

Building with no_std

The following crates support `no_std`, although they do depend on liballoc:

• cranelift-entity
• cranelift-bforest
• cranelift-codegen
• cranelift-frontend
• cranelift-native
• cranelift-wasm
• cranelift-module
• cranelift-simplejit
• cranelift

To use no_std mode, disable the std feature and enable the core feature. This currently requires nightly rust.

For example, to build `cranelift-codegen`:

cd lib/codegen
cargo build --no-default-features --features core

Or, when using cranelift-codegen as a dependency (in Cargo.toml):

[dependency.cranelift-codegen]
...
default-features = false
features = ["core"]

no_std support is currently "best effort". We won't try to break it, and we'll accept patches fixing problems, however we don't expect all developers to build and test no_std when submitting patches. Accordingly, the ./test-all.sh script does not test no_std.

There is a separate ./test-no_std.sh script that tests the no_std support in packages which support it.

It's important to note that cranelift still needs liballoc to compile. Thus, whatever environment is used must implement an allocator.

Also, to allow the use of HashMaps with no_std, an external crate called hashmap_core is pulled in (via the core feature). This is mostly the same as std::collections::HashMap, except that it doesn't have DOS protection. Just something to think about.

Log configuration

Cranelift uses the log crate to log messages at various levels. It doesn't specify any maximal logging level, so embedders can choose what it should be; however, this can have an impact of Cranelift's code size. You can use log features to reduce the maximum logging level. For instance if you want to limit the level of logging to warn messages and above in release mode:

[dependency.log]
...
features = ["release_max_level_warn"]

Building the documentation

Cranelift's documentation is published online.

To build the documentation locally, you need the Sphinx documentation generator as well as Python 3::

$ pip install sphinx sphinx-autobuild sphinx_rtd_theme
$ cd cranelift/docs
$ make html
$ open _build/html/index.html