wit_bindgen_rt/
lib.rs

1#![no_std]
2
3extern crate alloc;
4
5// Re-export `bitflags` so that we can reference it from macros.
6#[cfg(feature = "bitflags")]
7#[doc(hidden)]
8pub use bitflags;
9
10/// For more information about this see `./ci/rebuild-libcabi-realloc.sh`.
11#[cfg(not(target_env = "p2"))]
12mod cabi_realloc;
13
14/// This function is called from generated bindings and will be deleted by
15/// the linker. The purpose of this function is to force a reference to the
16/// symbol `cabi_realloc` to make its way through to the final linker
17/// command line. That way `wasm-ld` will pick it up, see it needs to be
18/// exported, and then export it.
19///
20/// For more information about this see `./ci/rebuild-libcabi-realloc.sh`.
21pub fn maybe_link_cabi_realloc() {
22    #[cfg(all(target_family = "wasm", not(target_env = "p2")))]
23    {
24        extern "C" {
25            fn cabi_realloc(
26                old_ptr: *mut u8,
27                old_len: usize,
28                align: usize,
29                new_len: usize,
30            ) -> *mut u8;
31        }
32        // Force the `cabi_realloc` symbol to be referenced from here. This
33        // is done with a `#[used]` Rust `static` to ensure that this
34        // reference makes it all the way to the linker before it's
35        // considered for garbage collection. When the linker sees it it'll
36        // remove this `static` here (due to it not actually being needed)
37        // but the linker will have at that point seen the `cabi_realloc`
38        // symbol and it should get exported.
39        #[used]
40        static _NAME_DOES_NOT_MATTER: unsafe extern "C" fn(
41            *mut u8,
42            usize,
43            usize,
44            usize,
45        ) -> *mut u8 = cabi_realloc;
46    }
47}
48
49/// NB: this function is called by a generated function in the
50/// `cabi_realloc` module above. It's otherwise never explicitly called.
51///
52/// For more information about this see `./ci/rebuild-libcabi-realloc.sh`.
53#[cfg(not(target_env = "p2"))]
54pub unsafe fn cabi_realloc(
55    old_ptr: *mut u8,
56    old_len: usize,
57    align: usize,
58    new_len: usize,
59) -> *mut u8 {
60    use self::alloc::alloc::{self, Layout};
61
62    let layout;
63    let ptr = if old_len == 0 {
64        if new_len == 0 {
65            return align as *mut u8;
66        }
67        layout = Layout::from_size_align_unchecked(new_len, align);
68        alloc::alloc(layout)
69    } else {
70        debug_assert_ne!(new_len, 0, "non-zero old_len requires non-zero new_len!");
71        layout = Layout::from_size_align_unchecked(old_len, align);
72        alloc::realloc(old_ptr, layout, new_len)
73    };
74    if ptr.is_null() {
75        // Print a nice message in debug mode, but in release mode don't
76        // pull in so many dependencies related to printing so just emit an
77        // `unreachable` instruction.
78        if cfg!(debug_assertions) {
79            alloc::handle_alloc_error(layout);
80        } else {
81            #[cfg(target_arch = "wasm32")]
82            core::arch::wasm32::unreachable();
83            #[cfg(not(target_arch = "wasm32"))]
84            unreachable!();
85        }
86    }
87    return ptr;
88}
89
90/// Provide a hook for generated export functions to run static constructors at
91/// most once.
92///
93/// wit-bindgen-rust generates a call to this function at the start of all
94/// component export functions. Importantly, it is not called as part of
95/// `cabi_realloc`, which is a *core* export func, but should not execute ctors.
96#[cfg(target_arch = "wasm32")]
97pub fn run_ctors_once() {
98    static mut RUN: bool = false;
99    unsafe {
100        if !RUN {
101            // This function is synthesized by `wasm-ld` to run all static
102            // constructors. wasm-ld will either provide an implementation
103            // of this symbol, or synthesize a wrapper around each
104            // exported function to (unconditionally) run ctors. By using
105            // this function, the linked module is opting into "manually"
106            // running ctors.
107            extern "C" {
108                fn __wasm_call_ctors();
109            }
110            __wasm_call_ctors();
111            RUN = true;
112        }
113    }
114}
115
116/// Support for using the Component Model Async ABI
117#[cfg(feature = "async")]
118pub mod async_support;
wit_bindgen_rt/lib.rs

wit_bindgen_rt/
lib.rs
