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
15// FIXME: The Rust compiler currently omits weakly function definitions (i.e.,
16// __cxa_thread_atexit_impl) and its metadata from LLVM IR.
17#[no_sanitize(cfi, kcfi)]
18pub unsafe fn register(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
19 /// This is necessary because the __cxa_thread_atexit_impl implementation
20 /// std links to by default may be a C or C++ implementation that was not
21 /// compiled using the Clang integer normalization option.
22 #[cfg(sanitizer_cfi_normalize_integers)]
23 use core::ffi::c_int;
24 #[cfg(not(sanitizer_cfi_normalize_integers))]
25 #[cfi_encoding = "i"]
26 #[repr(transparent)]
27 #[allow(non_camel_case_types)]
28 pub struct c_int(#[allow(dead_code)] pub core::ffi::c_int);
29
30 unsafe extern "C" {
31 #[linkage = "extern_weak"]
32 static __dso_handle: *mut u8;
33 #[linkage = "extern_weak"]
34 static __cxa_thread_atexit_impl: Option<
35 extern "C" fn(
36 unsafe extern "C" fn(*mut libc::c_void),
37 *mut libc::c_void,
38 *mut libc::c_void,
39 ) -> c_int,
40 >;
41 }
42
43 if let Some(f) = unsafe { __cxa_thread_atexit_impl } {
44 unsafe {
45 f(
46 transmute::<unsafe extern "C" fn(*mut u8), unsafe extern "C" fn(*mut libc::c_void)>(
47 dtor,
48 ),
49 t.cast(),
50 (&raw const __dso_handle) as *mut _,
51 );
52 }
53 } else {
54 unsafe {
55 super::list::register(t, dtor);
56 }
57 }
58}
59