434fbf2b27
* Refactor metadata storage in AOT artifacts This commit is a reorganization of how metadata is stored in Wasmtime's compiled artifacts. Currently Wasmtime's ELF artifacts have data appended after them to contain metadata about the `Engine` as well as type information for the module itself. This extra data at the end of the file is ignored by ELF-related utilities generally and is assembled during the module serialization process. In working on AOT-compiling components, though, I've discovered a number of issues with this: * Primarily it's possible to mistakenly change an artifact if it's deserialized and then serialized again. This issue is probably theoretical but the deserialized artifact records the `Engine` configuration at time of creation but when re-serializing that it serializes the current `Engine` state, not the original `Engine` state. * Additionally the serialization strategy here is tightly coupled to `Module` and its serialization format. While this makes sense it is not conducive for future refactorings to use a similar serialization format for components. The engine metadata, for example, does not necessarily need to be tied up with type information. * The storage for this extra metadata is a bit wonky by shoving it at the end of the ELF file. The original reason for this was to have a compiled artifact be multiple objects concatenated with each other to support serializing module-linking-using modules. Module linking is no longer a thing and I have since decided that for the component model all compilation artifacts will go into one object file to assist debugability. This means that the extra stick-it-at-the-end is no longer necessary. To solve these issues this commit splits up the `module/serialization.rs` file in two, mostly moving the logic to `engine/serialization.rs`. The engine serialization logic now handles everything related to `Engine` compatibility such as targets, compiler flags, wasm features, etc. The module serialization logic is now exclusively interested in type information. The engine metadata and serialized type information additionally live in sections of the final file now instead of at the end. This means that there are three primary `bincode`-encoded sections that are parsed on deserializing a file: 1. The `Engine`-specific metadata. This will be the same for both modules and components. 2. The `CompiledModuleInfo` structure. For core wasm there's just one of these but for the component model there will be multiple, one per core wasm module. 3. The type information. For core wasm this is a `ModuleTypes` but for a component this will be a `ComponentTypes`. No true functional change is expected from this commit. Binary artifacts might get inflated by a small handful of bytes due to using ELF sections to represent this now. A related change I made during this commit as well was the plumbing of the `is_branch_protection_enabled` flag. This is technically `Engine`-level metadata but I didn't want to plumb it all over the place as was done now, so instead a new section was added to the final binary just for this bti information. This means that it no longer needs to be a parameter to `CodeMemory::publish` and additionally is more amenable to a `Component`-is-just-one-object world where no single module owns this piece of metadata. * Exclude some functions in a cranelift-less build
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
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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.
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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.
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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.
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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, 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.