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In order to keep the `ExternalName` enum small, the `TestcaseName` struct was limited to 17 bytes: a 1 byte length and a 16 byte buffer. Due to alignment, that made `ExternalName` 20 bytes. That fixed-size buffer means that the names of functions in Cranelift filetests are truncated to fit, which limits our ability to give tests meaningful names. And I think meaningful names are important in tests. This patch replaces the inline `TestcaseName` buffer with a heap-allocated slice. We don't care about performance for test names, so an indirection out to the heap is fine in that case. But we do care somewhat about the size of `ExternalName` when it's used during compiles. On 64-bit systems, `Box<[u8]>` is 16 bytes, so `TestcaseName` gets one byte smaller. Unfortunately, its alignment is 8 bytes, so `ExternalName` grows from 20 to 24 bytes. According to `valgrind --tool=dhat`, this change has very little effect on compiler performance. Building wasmtime with `--no-default-features --release`, and compiling the pulldown-cmark benchmark from Sightglass, I measured these differences between `main` and this patch: - total number of allocations didn't change (`ExternalName::TestCase` is not used in normal compiles) - 592 more bytes allocated over the process lifetime, out of 171.5MiB - 320 more bytes allocated at peak heap size, out of 12MiB - 0.24% more instructions executed - 16,987 more bytes written - 12,120 _fewer_ bytes read
wasmtime
A standalone runtime for WebAssembly
A Bytecode Alliance project
Guide | Contributing | Website | Chat
Installation
The Wasmtime CLI can be installed on Linux and macOS with a small install script:
curl https://wasmtime.dev/install.sh -sSf | bash
Windows or otherwise interested users can download installers and binaries directly from the GitHub Releases page.
Example
If you've got the Rust compiler installed then you can take some Rust source code:
fn main() {
println!("Hello, world!");
}
and compile/run it with:
$ rustup target add wasm32-wasi
$ rustc hello.rs --target wasm32-wasi
$ wasmtime hello.wasm
Hello, world!
Features
-
Fast. Wasmtime is built on the optimizing Cranelift code generator to quickly generate high-quality machine code either at runtime or ahead-of-time. Wasmtime is optimized for efficient instantiation, low-overhead calls between the embedder and wasm, and scalability of concurrent instances.
-
Secure. Wasmtime's development is strongly focused on correctness and security. Building on top of Rust's runtime safety guarantees, each Wasmtime feature goes through careful review and consideration via an RFC process. Once features are designed and implemented, they undergo 24/7 fuzzing donated by Google's OSS Fuzz. As features stabilize they become part of a release, and when things go wrong we have a well-defined security policy in place to quickly mitigate and patch any issues. We follow best practices for defense-in-depth and integrate protections and mitigations for issues like Spectre. Finally, we're working to push the state-of-the-art by collaborating with academic researchers to formally verify critical parts of Wasmtime and Cranelift.
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Configurable. Wasmtime uses sensible defaults, but can also be configured to provide more fine-grained control over things like CPU and memory consumption. Whether you want to run Wasmtime in a tiny environment or on massive servers with many concurrent instances, we've got you covered.
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WASI. Wasmtime supports a rich set of APIs for interacting with the host environment through the WASI standard.
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Standards Compliant. Wasmtime passes the official WebAssembly test suite, implements the official C API of wasm, and implements future proposals to WebAssembly as well. Wasmtime developers are intimately engaged with the WebAssembly standards process all along the way too.
Language Support
You can use Wasmtime from a variety of different languages through embeddings of the implementation:
- Rust - the
wasmtimecrate - C - the
wasm.h,wasi.h, andwasmtime.hheaders, CMake orwasmtimeConan package - C++ - the
wasmtime-cpprepository or usewasmtime-cppConan package - Python - the
wasmtimePyPI package - .NET - the
WasmtimeNuGet package - Go - the
wasmtime-gorepository
Documentation
📚 Read the Wasmtime guide here! 📚
The wasmtime guide is the best starting point to learn about what Wasmtime can do for you or help answer your questions about Wasmtime. If you're curious in contributing to Wasmtime, it can also help you do that!
It's Wasmtime.