wasmtime_runtime/
trampolines.rs

1//! Trampolines for calling into Wasm from the host and calling the host from
2//! Wasm.
3
4use crate::VMContext;
5use std::mem;
6
7/// Given a Wasm function pointer and a `vmctx`, prepare the `vmctx` for calling
8/// into that Wasm function, and return the host-to-Wasm entry trampoline.
9///
10/// Callers must never call Wasm function pointers directly. Callers must
11/// instead call this function and then enter Wasm through the returned
12/// host-to-Wasm trampoline.
13///
14/// # Unsafety
15///
16/// The `vmctx` argument must be valid.
17///
18/// The generic type `T` must be a function pointer type and `func` must be a
19/// pointer to a Wasm function of that signature.
20///
21/// After calling this function, you may not mess with the vmctx or any other
22/// Wasm state until after you've called the trampoline returned by this
23/// function.
24#[inline]
25pub unsafe fn prepare_host_to_wasm_trampoline<T>(vmctx: *mut VMContext, func: T) -> T {
26    assert_eq!(mem::size_of::<T>(), mem::size_of::<usize>());
27
28    // Save the callee in the `vmctx`. The trampoline will read this function
29    // pointer and tail call to it.
30    (*vmctx)
31        .instance_mut()
32        .set_callee(Some(mem::transmute_copy(&func)));
33
34    // Give callers the trampoline, transmuted into their desired function
35    // signature (the trampoline is variadic and works with all signatures).
36    mem::transmute_copy(&(host_to_wasm_trampoline as usize))
37}
38
39extern "C" {
40    fn host_to_wasm_trampoline();
41    pub(crate) fn wasm_to_host_trampoline();
42}
43
44cfg_if::cfg_if! {
45    if #[cfg(target_arch = "x86_64")] {
46        #[macro_use]
47        mod x86_64;
48    } else if #[cfg(target_arch = "aarch64")] {
49        #[macro_use]
50        mod aarch64;
51    } else if #[cfg(target_arch = "s390x")] {
52        #[macro_use]
53        mod s390x;
54    }else if #[cfg(target_arch = "riscv64")] {
55        #[macro_use]
56        mod riscv64;
57    } else {
58        compile_error!("unsupported architecture");
59    }
60}
wasmtime_runtime/trampolines.rs

wasmtime_runtime/
trampolines.rs
