195bf0e29a
* Fully support multiple returns in Wasmtime For quite some time now Wasmtime has "supported" multiple return values, but only in the mose bare bones ways. Up until recently you couldn't get a typed version of functions with multiple return values, and never have you been able to use `Func::wrap` with functions that return multiple values. Even recently where `Func::typed` can call functions that return multiple values it uses a double-indirection by calling a trampoline which calls the real function. The underlying reason for this lack of support is that cranelift's ABI for returning multiple values is not possible to write in Rust. For example if a wasm function returns two `i32` values there is no Rust (or C!) function you can write to correspond to that. This commit, however fixes that. This commit adds two new ABIs to Cranelift: `WasmtimeSystemV` and `WasmtimeFastcall`. The intention is that these Wasmtime-specific ABIs match their corresponding ABI (e.g. `SystemV` or `WindowsFastcall`) for everything *except* how multiple values are returned. For multiple return values we simply define our own version of the ABI which Wasmtime implements, which is that for N return values the first is returned as if the function only returned that and the latter N-1 return values are returned via an out-ptr that's the last parameter to the function. These custom ABIs provides the ability for Wasmtime to bind these in Rust meaning that `Func::wrap` can now wrap functions that return multiple values and `Func::typed` no longer uses trampolines when calling functions that return multiple values. Although there's lots of internal changes there's no actual changes in the API surface area of Wasmtime, just a few more impls of more public traits which means that more types are supported in more places! Another change made with this PR is a consolidation of how the ABI of each function in a wasm module is selected. The native `SystemV` ABI, for example, is more efficient at returning multiple values than the wasmtime version of the ABI (since more things are in more registers). To continue to take advantage of this Wasmtime will now classify some functions in a wasm module with the "fast" ABI. Only functions that are not reachable externally from the module are classified with the fast ABI (e.g. those not exported, used in tables, or used with `ref.func`). This should enable purely internal functions of modules to have a faster calling convention than those which might be exposed to Wasmtime itself. Closes #1178 * Tweak some names and add docs * "fix" lightbeam compile * Fix TODO with dummy environ * Unwind info is a property of the target, not the ABI * Remove lightbeam unused imports * Attempt to fix arm64 * Document new ABIs aren't stable * Fix filetests to use the right target * Don't always do 64-bit stores with cranelift This was overwriting upper bits when 32-bit registers were being stored into return values, so fix the code inline to do a sized store instead of one-size-fits-all store. * At least get tests passing on the old backend * Fix a typo * Add some filetests with mixed abi calls * Get `multi` example working * Fix doctests on old x86 backend * Add a mixture of wasmtime/system_v tests
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
-
Lightweight. Wasmtime is a standalone runtime for WebAssembly that scales with your needs. It fits on tiny chips as well as makes use of huge servers. Wasmtime can be embedded into almost any application too.
-
Fast. Wasmtime is built on the optimizing Cranelift code generator to quickly generate high-quality machine code at runtime.
-
Configurable. Whether you need to precompile your wasm ahead of time, generate code blazingly fast with Lightbeam, or interpret it at runtime, Wasmtime has you covered for all your wasm-executing needs.
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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 - 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.