fd28d94352
This commit fixes #4600 in a somewhat roundabout fashion. Currently the `main` branch of Wasmtime exhibits unusual behavior: * If `./ci/run-tests.sh` is run then the `cache_accounts_for_opt_level` test does not fail. * If `cargo test -p wasmtime --lib` is run, however, then the test fails. This test is indeed being run as part of `./ci/run-tests.sh` and it's also passing in CI. The exact failure is that part of the debuginfo support we have takes an existing ELF image, copies it, and then appends some information to inform profilers/gdb about the image. This code is all quite old at this point and not 100% optimal, but that's at least where we're at. The problem is that the appended `ProgramHeader64` is not aligned correctly during `cargo test -p wasmtime --lib`, which is the panic that happens causing the test to fail. The reason, however, that this test passes with `./ci/run-tests.sh` is that the alignment of `ProgramHeader64` is 1 instead of 8. The reason for that is that the `object` crate has an `unaligned` feature which forcibly unaligns all primitives to 1 byte instead of their natural alignment. During `cargo test -p wasmtime --lib` this feature is not enabled but during `./ci/run-tests.sh` this feature is enabled. The feature is currently enabled through inclusion of the `backtrace` crate which only happens for some tests in some crates. The alignment issue explains why the test fails on a single crate test but fails on the whole workspace tests. The next issue I investigated was if this test ever passed. It turns out that on v0.39.0 this test passed, and the regression to main was introduced during #4571. That PR, however, has nothing to do with any of this! The reason that this showed up as causing a "regression" however is because it changed cranelift settings which changed the size of serialized metadata at the end of a Wasmtime cache object. Wasmtime compiled artifacts are ELF images with Wasmtime-specific metadata appended after them. This appended metadata was making its way all the way through to the gdbjit image itself which mean that while the end of the ELF file itself was properly aligned the space after the Wasmtime metadata was not aligned. This metadata changes in size over time as Cranelift settings change which explains why #4571 was the "source" of the regression. The fix in this commit is to discard the extra Wasmtime metadata when creating an `MmapVec` representing the underlying ELF image. This is already supported with `MmapVec::drain` so it was relatively easy to insert that. This means that the gdbjit image starts with just the ELF file itself which is always aligned at the end, which gets the test passing with/without the `unaligned` feature in the `object` crate.
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
-
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's runtime is also optimized for cases such as efficient instantiation, low-overhead transitions between the embedder and wasm, and scalability of concurrent instances.
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Secure. Wasmtime's development is strongly focused on the correctness of its implementation with 24/7 fuzzing donated by Google's OSS Fuzz, leveraging Rust's API and runtime safety guarantees, careful design of features and APIs through an RFC process, a security policy in place for when things go wrong, and a release policy for patching older versions as well. We follow best practices for defense-in-depth and known 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. Wastime supports a rich set of APIs and build time configuration to provide many options such as further means of restricting WebAssembly beyond its basic guarantees such as its CPU and Memory consumption. Wasmtime also runs in tiny environments all the way up to massive servers with many concurrent instances.
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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.