dd09865611
When one branch target label in a MachBuffer is redirected to another, we eventually fix up branches targetting the first to refer to the redirected target instead. Separately, we have a branch-folding optimization that, when an unconditional branch occurs as the only instruction in a block (right at a label) and the previous instruction is also an unconditional branch (hence no fallthrough), we can elide that block entirely and redirect the label. Finally, we prevented infinite loops when resolving label aliases by chasing only one alias deep. Unfortunately, these three facts interacted poorly, and this is a result of our correctness arguments assuming a fully-general "redirect" that was not limited to one indirection level. In particular, we could have some label A that redirected to B, then remove the block at B because it is just a single branch to C, redirecting B to C. A would still redirect to B, though, without chasing to C, and hence a branch to B would fall through to the unrelated block that came after block B. Thanks to @bnjbvr for finding this bug while debugging the x64 backend and reducing a failure to the function in issue #2082. (This is a very subtle bug and it seems to have been quite difficult to chase; my apologies!) The fix is to (i) chase redirects arbitrarily deep, but also (ii) ensure that we do not form a cycle of redirects. The latter is done by very carefully checking the existing fully-resolved target of the label we are about to redirect *to*; if it resolves back to the branch that is causing this redirect, then we avoid making the alias. The comments in this patch make a slightly more detailed argument why this should be correct. Unfortunately we cannot directly test the CLIF that @bnjbvr reduced because we don't have a way to assert anything about the machine-code that comes after the branch folding and emission. However, the dedicated unit tests in this patch replicate an equivalent folding case, and also test that we handle branch cycles properly (as argued above). Fixes #2082.
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.