7717d8fa55
* wiggle: adapt Wiggle guest slices for `unsafe` shared use When multiple threads can concurrently modify a WebAssembly shared memory, the underlying data for a Wiggle `GuestSlice` and `GuestSliceMut` could change due to access from other threads. This breaks Rust guarantees when `&[T]` and `&mut [T]` slices are handed out. This change modifies `GuestPtr` to make `as_slice` and `as_slice_mut` return an `Option` which is `None` when the underlying WebAssembly memory is shared. But WASI implementations still need access to the underlying WebAssembly memory, both to read to it and write from it. This change adds new APIs: - `GuestPtr::to_vec` copies the bytes from WebAssembly memory (from which we can safely take a `&[T]`) - `GuestPtr::as_unsafe_slice_mut` returns a wrapper `struct` from which we can `unsafe`-ly return a mutable slice (users must accept the unsafety of concurrently modifying a `&mut [T]`) This approach allows us to maintain Wiggle's borrow-checking infrastructure, which enforces the guarantee that Wiggle will not modify overlapping regions, e.g. This is important because the underlying system calls may expect this. Though other threads may modify the same underlying region, this is impossible to prevent; at least Wiggle will not be able to do so. Finally, the changes to Wiggle's API are propagated to all WASI implementations in Wasmtime. For now, code locations that attempt to get a guest slice will panic if the underlying memory is shared. Note that Wiggle is not enabled for shared memory (that will come later in something like #5054), but when it is, these panics will be clear indicators of locations that must be re-implemented in a thread-safe way. * review: remove double cast * review: refactor to include more logic in 'UnsafeGuestSlice' * review: add reference to #4203 * review: link all thread-safe WASI fixups to #5235 * fix: consume 'UnsafeGuestSlice' during conversion to safe versions * review: remove 'as_slice' and 'as_slice_mut' * review: use 'as_unsafe_slice_mut' in 'to_vec' * review: add `UnsafeBorrowResult`
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.
-
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.
-
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.