wasmtime/runtime/vm/sys/
mod.rs

1//! OS-related abstractions required by Wasmtime.
2//!
3//! This module is intended to house all logic that's specific to either Unix
4//! or Windows, for example. The goal of this module is to be the "single
5//! module" to edit if Wasmtime is ported to a new platform. Ideally all that's
6//! needed is an extra block below and a new platform should be good to go after
7//! filling out the implementation.
8
9#![allow(
10    clippy::cast_sign_loss,
11    reason = "platforms too fiddly to worry about this"
12)]
13
14use crate::runtime::vm::SendSyncPtr;
15use core::ptr::{self, NonNull};
16
17/// What happens to a mapping after it is decommitted?
18#[derive(Clone, Copy, PartialEq, Eq, Debug)]
19pub enum DecommitBehavior {
20    /// The mapping is zeroed.
21    Zero,
22    /// The original mapping is restored. If it was zero, then it is zero again;
23    /// if it was a CoW mapping, then the original CoW mapping is restored;
24    /// etc...
25    RestoreOriginalMapping,
26}
27
28fn empty_mmap() -> SendSyncPtr<[u8]> {
29    // Callers of this API assume that `.as_ptr()` below returns something
30    // page-aligned and non-null. This is because the pointer returned from
31    // that location is casted to other types which reside at a higher
32    // alignment than a byte for example. Despite the length being zero we
33    // still need to ensure that the pointer is suitably aligned.
34    //
35    // To handle that do a bit of trickery here to get the compiler to
36    // generate an empty array to a high-alignment type (here 4k which is
37    // the min page size we work with today). Then use this empty array as
38    // the source pointer for an empty byte slice. It's a bit wonky but this
39    // makes it such that the returned length is always zero (so this is
40    // safe) but the pointer is always 4096 or suitably aligned.
41    #[repr(C, align(4096))]
42    struct PageAligned;
43    let empty_page_alloc: &mut [PageAligned] = &mut [];
44    let empty = NonNull::new(ptr::slice_from_raw_parts_mut(
45        empty_page_alloc.as_mut_ptr().cast(),
46        0,
47    ))
48    .unwrap();
49    SendSyncPtr::from(empty)
50}
51
52cfg_if::cfg_if! {
53    if #[cfg(miri)] {
54        mod miri;
55        pub use miri::*;
56    } else if #[cfg(not(feature = "std"))] {
57        mod custom;
58        pub use custom::*;
59    } else if #[cfg(windows)] {
60        mod windows;
61        pub use windows::*;
62    } else if #[cfg(unix)] {
63        mod unix;
64        pub use unix::*;
65    } else {
66        mod custom;
67        pub use custom::*;
68    }
69}
wasmtime/runtime/vm/sys/mod.rs

wasmtime/runtime/vm/sys/
mod.rs
