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Dan Gohman
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cranelift/README.md
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Cranelift Code Generator
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========================
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Cranelift is a low-level retargetable code generator. It translates a
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[target-independent intermediate
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representation](https://cranelift.readthedocs.io/en/latest/langref.html)
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into executable machine code.
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[](https://cranelift.readthedocs.io/en/latest/?badge=latest)
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[](https://travis-ci.org/CraneStation/cranelift)
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[](https://gitter.im/CraneStation/Lobby/~chat)
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For more information, see [the
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documentation](https://cranelift.readthedocs.io/en/latest/?badge=latest).
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Status
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------
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Cranelift currently supports enough functionality to run a wide variety
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of programs, including all the functionality needed to execute
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WebAssembly MVP functions, although it needs to be used within an
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external WebAssembly embedding to be part of a complete WebAssembly
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implementation.
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The x86-64 backend is currently the most complete and stable; other
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architectures are in various stages of development. Cranelift currently
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supports the System V AMD64 ABI calling convention used on many
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platforms, but does not yet support the Windows x64 calling convention.
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The performance of code produced by Cranelift is not yet impressive,
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though we have plans to fix that.
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The core codegen crates have minimal dependencies, support
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[no\_std](#building-with-no-std) mode, and do not require any host
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floating-point support.
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Cranelift does not yet perform mitigations for Spectre or related
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security issues, though it may do so in the future. It does not
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currently make any security-relevant instruction timing guarantees. It
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has seen a fair amount of testing and fuzzing, although more work is
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needed before it would be ready for a production use case.
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Cranelift's APIs are not yet stable.
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Cranelift currently supports Rust 1.22.1 and later. We intend to always
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support the latest *stable* Rust. And, we currently support the version
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of Rust in the latest Ubuntu LTS, although whether we will always do so
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is not yet determined. Cranelift requires Python 2.7 or Python 3 to
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build.
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Planned uses
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------------
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Cranelift is designed to be a code generator for WebAssembly, but it is
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general enough to be useful elsewhere too. The initial planned uses that
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affected its design are:
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1. [WebAssembly compiler for the SpiderMonkey engine in
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Firefox](spidermonkey.md#phase-1-webassembly).
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2. [Backend for the IonMonkey JavaScript JIT compiler in
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Firefox](spidermonkey.md#phase-2-ionmonkey).
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3. [Debug build backend for the Rust compiler](rustc.md).
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Building Cranelift
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------------------
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Cranelift uses a [conventional Cargo build
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process](https://doc.rust-lang.org/cargo/guide/working-on-an-existing-project.html).
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Cranelift consists of a collection of crates, and uses a [Cargo
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Workspace](https://doc.rust-lang.org/book/second-edition/ch14-03-cargo-workspaces.html),
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so for some cargo commands, such as `cargo test`, the `--all` is needed
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to tell cargo to visit all of the crates.
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`test-all.sh` at the top level is a script which runs all the cargo
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tests and also performs code format, lint, and documentation checks.
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Building with no\_std
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---------------------
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The following crates support \`no\_std\`:
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- cranelift-entity
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- cranelift-codegen
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- cranelift-frontend
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- cranelift-native
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- cranelift-wasm
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- cranelift-module
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- cranelift-simplejit
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- cranelift
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To use no\_std mode, disable the std feature and enable the core
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feature. This currently requires nightly rust.
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For example, to build \`cranelift-codegen\`:
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``` {.sourceCode .sh}
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cd lib/codegen
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cargo build --no-default-features --features core
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```
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Or, when using cranelift-codegen as a dependency (in Cargo.toml):
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``` {.sourceCode .}
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[dependency.cranelift-codegen]
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...
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default-features = false
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features = ["core"]
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```
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no\_std support is currently "best effort". We won't try to break it,
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and we'll accept patches fixing problems, however we don't expect all
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developers to build and test no\_std when submitting patches.
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Accordingly, the ./test-all.sh script does not test no\_std.
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There is a separate ./test-no\_std.sh script that tests the no\_std
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support in packages which support it.
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It's important to note that cranelift still needs liballoc to compile.
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Thus, whatever environment is used must implement an allocator.
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Also, to allow the use of HashMaps with no\_std, an external crate
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called hashmap\_core is pulled in (via the core feature). This is mostly
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the same as std::collections::HashMap, except that it doesn't have DOS
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protection. Just something to think about.
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Building the documentation
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--------------------------
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To build the Cranelift documentation, you need the [Sphinx documentation
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generator](https://www.sphinx-doc.org/):
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$ pip install sphinx sphinx-autobuild sphinx_rtd_theme
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$ cd cranelift/docs
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$ make html
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$ open _build/html/index.html
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We don't support Sphinx versions before 1.4 since the format of index
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tuples has changed.
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