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Windows: Run compat_fn init before C++ init #97816

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Windows: Run compat_fn init before C++ init #97816

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18 changes: 13 additions & 5 deletions library/std/src/sys/windows/compat.rs
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Expand Up @@ -31,11 +31,16 @@
//! The mechanism of registering a static initializer with the CRT is
//! documented in
//! [CRT Initialization](https://docs.microsoft.com/en-us/cpp/c-runtime-library/crt-initialization?view=msvc-160).
//! It works by contributing a global symbol to the `.CRT$XCU` section.
//! It works by contributing a global symbol to the `.CRT$XIU` section.
//! The linker builds a table of all static initializer functions.
//! The CRT startup code then iterates that table, calling each
//! initializer function.
//!
//! This originally used the C++ initializer section `.CRT$XCU`. However, this
//! risks being run after user code that inserts their own initializers.
//! Instead the C initializer section `CRT$XIU` is used. Function placed here
//! are run earlier than the C++ initializers.
//!
//! # **WARNING!!*
//! The environment that a static initializer function runs in is highly
//! constrained. There are **many** restrictions on what static initializers
Expand All @@ -49,7 +54,7 @@
//! * call any Rust function or CRT function that touches any static
//! (global) state.

use crate::ffi::{c_void, CStr};
use crate::ffi::{c_int, c_void, CStr};
use crate::ptr::NonNull;
use crate::sys::c;

Expand Down Expand Up @@ -86,8 +91,8 @@ pub(crate) const fn const_cstr_from_bytes(bytes: &'static [u8]) -> &'static CStr
}

#[used]
#[link_section = ".CRT$XCU"]
static INIT_TABLE_ENTRY: unsafe extern "C" fn() = init;
#[link_section = ".CRT$XIU"]
static INIT_TABLE_ENTRY: unsafe extern "C" fn() -> c_int = init;

/// This is where the magic preloading of symbols happens.
///
Expand All @@ -96,7 +101,7 @@ static INIT_TABLE_ENTRY: unsafe extern "C" fn() = init;
///
/// Therefore, this is limited to `compat_fn_optional` functions which must be
/// preloaded and any functions which may be more time sensitive, even for the first call.
unsafe extern "C" fn init() {
unsafe extern "C" fn init() -> c_int {
// There is no locking here. This code is executed before main() is entered, and
// is guaranteed to be single-threaded.
//
Expand All @@ -116,6 +121,9 @@ unsafe extern "C" fn init() {
// Preloading this means getting a precise time will be as fast as possible.
c::GetSystemTimePreciseAsFileTime::preload(kernel32);
}

// Returns zero for success and non-zero for error.
0
}

/// Represents a loaded module.
Expand Down