6632c45c01
As a subtle consequence of the recent load-op fusion, popcnt of a value that came from a load.i32 was compiling into a 64-bit load. This is a result of the way in which x86 infers the width of loads: it is a consequence of the instruction containing the memory reference, not the memory reference itself. So the `input_to_reg_mem()` helper (convert an instruction input into a register or memory reference) was providing the appropriate memory reference for the result of a load.i32, but never encoded the assumption that it would only be used in a 32-bit instruction. It turns out that popcnt.i32 uses a 64-bit instruction to load this RM op, hence widening a 32-bit to 64-bit load (which is problematic when the offset is (memory_length - 4)). Separately, popcnt was using the RM operand twice, resulting in two loads if we merged a load. This isn't a correctness bug in practice because only a racy sequence (store interleaving between the loads) would produce incorrect results, but we decided earlier to treat loads as effectful for now, neither reordering nor duplicating them, to deliberately reduce complexity. Because of the second issue, the fix is just to force the operand into a register always, so any source load will not be merged. Discovered via fuzzing with oss-fuzz.
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.
-
WASI. Wasmtime supports a rich set of APIs for interacting with the host environment through the WASI standard.
-
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.