1bfca842b0
* Move `Func` to its own file * Support `Func` imports with zero shims This commit extends the `Func` type in the `wasmtime` crate with static `wrap*` constructors. The goal of these constructors is to create a `Func` type which has zero shims associated with it, creating as small of a layer as possible between wasm code and calling imported Rust code. This is achieved by creating an `extern "C"` shim function which matches the ABI of what Cranelift will generate, and then the host function is passed directly into an `InstanceHandle` to get called later. This also enables enough inlining opportunities that LLVM will be able to see all functions and inline everything to the point where your function is called immediately from wasm, no questions asked.
51 lines
1.9 KiB
Rust
51 lines
1.9 KiB
Rust
//! Translation of hello example
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use anyhow::{ensure, Context as _, Result};
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use wasmtime::*;
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fn main() -> Result<()> {
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// Configure the initial compilation environment, creating the global
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// `Store` structure. Note that you can also tweak configuration settings
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// with a `Config` and an `Engine` if desired.
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println!("Initializing...");
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let store = Store::default();
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// Compile the wasm binary into an in-memory instance of a `Module`.
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println!("Compiling module...");
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let wat = r#"
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(module
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(func $hello (import "" "hello"))
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(func (export "run") (call $hello))
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)
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"#;
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let module = Module::new(&store, wat).context("> Error compiling module!")?;
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// Here we handle the imports of the module, which in this case is our
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// `HelloCallback` type and its associated implementation of `Callback.
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println!("Creating callback...");
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let hello_func = Func::wrap0(&store, || {
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println!("Calling back...");
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println!("> Hello World!");
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});
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// Once we've got that all set up we can then move to the instantiation
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// phase, pairing together a compiled module as well as a set of imports.
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// Note that this is where the wasm `start` function, if any, would run.
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println!("Instantiating module...");
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let imports = vec![hello_func.into()];
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let instance = Instance::new(&module, &imports).context("> Error instantiating module!")?;
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// Next we poke around a bit to extract the `run` function from the module.
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println!("Extracting export...");
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let exports = instance.exports();
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ensure!(!exports.is_empty(), "> Error accessing exports!");
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let run_func = exports[0].func().context("> Error accessing exports!")?;
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// And last but not least we can call it!
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println!("Calling export...");
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run_func.call(&[])?;
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println!("Done.");
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Ok(())
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}
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