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}
56