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Alignment on all memory instructions in wasm is currently best-effort and not actually required, meaning that whatever wasm actually uses as an address should work regardless of whether the address is aligned or not. This is theoretically tested in the fuzzers via wasm-smith-generated code, but wasm-smith doesn't today have too too high of a chance of generating an actual successful load/store. This commit adds a new configuration option to the `Config` generator for fuzzing which forces usage of a custom linear memory implementation which is backed by Rust's `Vec<u8>` and forces the base address of linear memory to be off-by-one relative to the base address of the `Vec<u8>` itself. This should theoretically force host addresses to almost always be unaligned, even if wasm addresses are otherwise aligned. The main interesting fuzz coverage here is likely to be in the existing `differential` target which compares running the same module in wasmtime with two different `Config` values to ensure the same results are produced. This probably won't increase coverage all that much in the near future due to wasm-smith rarely generating successful loads/stores, but in the meantime by hooking this up into `Config` it also means that we'll be running in comparison against v8 and also ensuring that all spec tests succeed if misalignment is forced at the hardware level. As a side effect this commit also cleans up the fuzzers slightly: * The `DifferentialConfig` struct is removed and folded into `Config` * The `init_hang_limit` processing is removed since we don't use `-ttf`-generated modules from binaryen any more. * Traps are now asserted to have the same trap code, otherwise differential fuzzing fails. * Some more debug logging was added to the differential fuzzer
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.
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Configurable. Whether you need to precompile your wasm ahead of time, 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 or usewasmtimeConan 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.