58062b5efe
The `fpcmp` helper in the x64 backend uses `put_in_xmm_mem` for one of its operands, which allows the compiler to merge a load with the compare instruction (`ucomiss` or `ucomisd`). Unfortunately, as we saw in #2576 for the integer-compare case, this does not work with our lowering algorithm because compares can be lowered more than once (unlike all other instructions) to reproduce the flags where needed. Merging a load into an op that executes more than once is invalid in general (the two loads may observe different values, which violates the original program semantics because there was only one load originally). This does not result in a miscompilation, but instead will cause a panic at regalloc time because the register that should have been defined by the separate load is never written (the load is never emitted separately). I think this (very subtle, easy to miss) condition was unfortunately not ported over when we moved the logic in #3682. The existing fcmp-of-load test in `cmp-mem-bug` (from #2576) does not seem to trigger it, for a reason I haven't fully deduced. I just added the verbatim function body (happens to come from `clang.wasm`) that triggers the bug as a test. Discovered while bringing up regalloc2 support. It's pretty unlikely to hit by chance, which is why I think none of our fuzzing has hit it yet.
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, 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 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.