1 // Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 #![cfg(target_thread_local)]
12 #![unstable(feature = "thread_local_internals", issue = "0")]
14 // Since what appears to be glibc 2.18 this symbol has been shipped which
15 // GCC and clang both use to invoke destructors in thread_local globals, so
18 // Note, however, that we run on lots older linuxes, as well as cross
19 // compiling from a newer linux to an older linux, so we also have a
20 // fallback implementation to use as well.
22 // Due to rust-lang/rust#18804, make sure this is not generic!
23 #[cfg(target_os = "linux")]
24 pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern fn(*mut u8)) {
27 use sys_common::thread_local::register_dtor_fallback;
30 #[linkage = "extern_weak"]
31 static __dso_handle: *mut u8;
32 #[linkage = "extern_weak"]
33 static __cxa_thread_atexit_impl: *const libc::c_void;
35 if !__cxa_thread_atexit_impl.is_null() {
36 type F = unsafe extern fn(dtor: unsafe extern fn(*mut u8),
38 dso_handle: *mut u8) -> libc::c_int;
39 mem::transmute::<*const libc::c_void, F>(__cxa_thread_atexit_impl)
40 (dtor, t, &__dso_handle as *const _ as *mut _);
43 register_dtor_fallback(t, dtor);
46 // macOS's analog of the above linux function is this _tlv_atexit function.
47 // The disassembly of thread_local globals in C++ (at least produced by
48 // clang) will have this show up in the output.
49 #[cfg(target_os = "macos")]
50 pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern fn(*mut u8)) {
52 fn _tlv_atexit(dtor: unsafe extern fn(*mut u8),
58 // Just use the thread_local fallback implementation, at least until there's
59 // a more direct implementation.
60 #[cfg(target_os = "fuchsia")]
61 pub use sys_common::thread_local::register_dtor_fallback as register_dtor;
63 pub fn requires_move_before_drop() -> bool {
64 // The macOS implementation of TLS apparently had an odd aspect to it
65 // where the pointer we have may be overwritten while this destructor
66 // is running. Specifically if a TLS destructor re-accesses TLS it may
67 // trigger a re-initialization of all TLS variables, paving over at
68 // least some destroyed ones with initial values.
70 // This means that if we drop a TLS value in place on macOS that we could
71 // revert the value to its original state halfway through the
72 // destructor, which would be bad!
74 // Hence, we use `ptr::read` on macOS (to move to a "safe" location)
75 // instead of drop_in_place.
76 cfg!(target_os = "macos")