830885383f
* Turn off probestack by default in Cranelift The probestack feature is not implemented for the aarch64 and s390x backends and currently the on-by-default status requires the aarch64 and s390x implementations to be a stub. Turning off probestack by default allows the s390x and aarch64 backends to panic with an error message to avoid providing a false sense of security. When the probestack option is implemented for all backends, however, it may be reasonable to re-enable. * aarch64: Improve codegen for AMode fallback Currently the final fallback for finalizing an `AMode` will generate both a constant-loading instruction as well as an `add` instruction to the base register into the same temporary. This commit improves the codegen by removing the `add` instruction and folding the final add into the finalized `AMode`. This changes the `extendop` used but both registers are 64-bit so shouldn't be affected by the extending operation. * aarch64: Implement inline stack probes This commit implements inline stack probes for the aarch64 backend in Cranelift. The support here is modeled after the x64 support where unrolled probes are used up to a particular threshold after which a loop is generated. The instructions here are similar in spirit to x64 except that unlike x64 the stack pointer isn't modified during the unrolled loop to avoid needing to re-adjust it back up at the end of the loop. * Enable inline probestack for AArch64 and Riscv64 This commit enables inline probestacks for the AArch64 and Riscv64 architectures in the same manner that x86_64 has it enabled now. Some more testing was additionally added since on Unix platforms we should be guaranteed that Rust's stack overflow message is now printed too. * Enable probestack for aarch64 in cranelift-fuzzgen * Address review comments * Remove implicit stack overflow traps from x64 backend This commit removes implicit `StackOverflow` traps inserted by the x64 backend for stack-based operations. This was historically required when stack overflow was detected with page faults but Wasmtime no longer requires that since it's not suitable for wasm modules which call host functions. Additionally no other backend implements this form of implicit trap-code additions so this is intended to synchronize the behavior of all the backends. This fixes a test added prior for aarch64 to properly abort the process instead of accidentally being caught by Wasmtime. * Fix a style issue
Cranelift Code Generator
A Bytecode Alliance project
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 JIT Demo, which implements a toy language.
For an example of how to use Cranelift to run WebAssembly code, see Wasmtime, which implements a standalone, embeddable, VM using Cranelift.
Status
Cranelift currently supports enough functionality to run a wide variety of programs, including all the functionality needed to execute WebAssembly (MVP and various extensions like SIMD), although it needs to be used within an external WebAssembly embedding such as Wasmtime to be part of a complete WebAssembly implementation. It is also usable as a backend for non-WebAssembly use cases: for example, there is an effort to build a Rust compiler backend using Cranelift.
Cranelift is production-ready, and is used in production in several places, all within the context of Wasmtime. It is carefully fuzzed as part of Wasmtime with differential comparison against V8 and the executable Wasm spec, and the register allocator is separately fuzzed with symbolic verification. There is an active effort to formally verify Cranelift's instruction-selection backends. We take security seriously and have a security policy as a part of Bytecode Alliance.
Cranelift has three backends: x86-64, aarch64 (aka ARM64), and s390x (aka IBM Z). All three backends fully support enough functionality for Wasm MVP, and x86-64 and aarch64 fully support SIMD as well. On x86-64, Cranelift supports both the System V AMD64 ABI calling convention used on many platforms and the Windows x64 calling convention. On aarch64, Cranelift supports the standard Linux calling convention and also has specific support for macOS (i.e., M1 / Apple Silicon).
Cranelift's code quality is within range of competitiveness to browser JIT engines' optimizing tiers. A recent paper includes third-party benchmarks of Cranelift, driven by Wasmtime, against V8 and an LLVM-based Wasm engine, WAVM (Fig 22). The speed of Cranelift's generated code is ~2% slower than that of V8 (TurboFan), and ~14% slower than WAVM (LLVM). Its compilation speed, in the same paper, is measured as approximately an order of magnitude faster than WAVM (LLVM). We continue to work to improve both measures.
The core codegen crates have minimal dependencies and are carefully written to handle malicious or arbitrary compiler input: in particular, they do not use callstack recursion.
Cranelift performs some basic mitigations for Spectre attacks on heap bounds checks, table bounds checks, and indirect branch bounds checks; see #1032 for more.
Cranelift's APIs are not yet considered stable, though we do follow semantic-versioning (semver) with minor-version patch releases.
Cranelift generally requires the latest stable Rust to build as a policy, and is tested as such, but we can incorporate fixes for compilation with older Rust versions on a best-effort basis.
Contributing
If you're interested in contributing to Cranelift: thank you! We have a contributing guide which will help you getting involved in the Cranelift project.
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 were:
- Wasmtime non-Web wasm engine.
- Debug build backend for the Rust compiler.
- WebAssembly compiler for the SpiderMonkey engine in Firefox (currently not planned anymore; SpiderMonkey team may re-assess in the future).
- Backend for the IonMonkey JavaScript JIT compiler in Firefox (currently not planned anymore; SpiderMonkey team may re-assess in the future).
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.
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"]
Editor Support
Editor support for working with Cranelift IR (clif) files: