std/sys/thread_local/destructors/
linux_like.rs

1//! Destructor registration for Linux-like systems.
2//!
3//! Since what appears to be version 2.18, glibc has shipped the
4//! `__cxa_thread_atexit_impl` symbol which GCC and clang both use to invoke
5//! destructors in C++ thread_local globals. This function does exactly what
6//! we want: it schedules a callback which will be run at thread exit with the
7//! provided argument.
8//!
9//! Unfortunately, our minimum supported glibc version (at the time of writing)
10//! is 2.17, so we can only link this symbol weakly and need to use the
11//! [`list`](super::list) destructor implementation as fallback.
12
13use crate::mem::transmute;
14
15pub unsafe fn register(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
16    /// This is necessary because the __cxa_thread_atexit_impl implementation
17    /// std links to by default may be a C or C++ implementation that was not
18    /// compiled using the Clang integer normalization option.
19    #[cfg(sanitizer_cfi_normalize_integers)]
20    use core::ffi::c_int;
21    #[cfg(not(sanitizer_cfi_normalize_integers))]
22    #[cfi_encoding = "i"]
23    #[repr(transparent)]
24    #[allow(non_camel_case_types)]
25    pub struct c_int(#[allow(dead_code)] pub core::ffi::c_int);
26
27    unsafe extern "C" {
28        #[linkage = "extern_weak"]
29        static __dso_handle: *mut u8;
30        #[linkage = "extern_weak"]
31        static __cxa_thread_atexit_impl: Option<
32            extern "C" fn(
33                unsafe extern "C" fn(*mut libc::c_void),
34                *mut libc::c_void,
35                *mut libc::c_void,
36            ) -> c_int,
37        >;
38    }
39
40    if let Some(f) = unsafe { __cxa_thread_atexit_impl } {
41        unsafe {
42            f(
43                transmute::<unsafe extern "C" fn(*mut u8), unsafe extern "C" fn(*mut libc::c_void)>(
44                    dtor,
45                ),
46                t.cast(),
47                (&raw const __dso_handle) as *mut _,
48            );
49        }
50    } else {
51        unsafe {
52            super::list::register(t, dtor);
53        }
54    }
55}
std/sys/thread_local/destructors/linux_like.rs

std/sys/thread_local/destructors/
linux_like.rs
