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</pre><pre class="rust ">
<span class="comment">// Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT</span>
<span class="comment">// file at the top-level directory of this distribution and at</span>
<span class="comment">// http://rust-lang.org/COPYRIGHT.</span>
<span class="comment">//</span>
<span class="comment">// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or</span>
<span class="comment">// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license</span>
<span class="comment">// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your</span>
<span class="comment">// option. This file may not be copied, modified, or distributed</span>
<span class="comment">// except according to those terms.</span>
<span class="attribute">#![<span class="ident">cfg</span>(<span class="ident">target_thread_local</span>)]</span>
<span class="attribute">#![<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"thread_local_internals"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"0"</span>)]</span>
<span class="comment">// Since what appears to be glibc 2.18 this symbol has been shipped which</span>
<span class="comment">// GCC and clang both use to invoke destructors in thread_local globals, so</span>
<span class="comment">// let's do the same!</span>
<span class="comment">//</span>
<span class="comment">// Note, however, that we run on lots older linuxes, as well as cross</span>
<span class="comment">// compiling from a newer linux to an older linux, so we also have a</span>
<span class="comment">// fallback implementation to use as well.</span>
<span class="comment">//</span>
<span class="comment">// Due to rust-lang/rust#18804, make sure this is not generic!</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">"linux"</span>)]</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">register_dtor</span>(<span class="ident">t</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>, <span class="ident">dtor</span>: <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>)) {
<span class="kw">use</span> <span class="ident">libc</span>;
<span class="kw">use</span> <span class="ident">mem</span>;
<span class="kw">use</span> <span class="ident">sys_common</span>::<span class="ident">thread_local</span>::<span class="ident">register_dtor_fallback</span>;
<span class="kw">extern</span> {
<span class="attribute">#[<span class="ident">linkage</span> <span class="op">=</span> <span class="string">"extern_weak"</span>]</span>
<span class="kw">static</span> <span class="ident">__dso_handle</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>;
<span class="attribute">#[<span class="ident">linkage</span> <span class="op">=</span> <span class="string">"extern_weak"</span>]</span>
<span class="kw">static</span> <span class="ident">__cxa_thread_atexit_impl</span>: <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">libc</span>::<span class="ident">c_void</span>;
}
<span class="kw">if</span> <span class="op">!</span><span class="ident">__cxa_thread_atexit_impl</span>.<span class="ident">is_null</span>() {
<span class="kw">type</span> <span class="ident">F</span> <span class="op">=</span> <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="ident">dtor</span>: <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>),
<span class="ident">arg</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>,
<span class="ident">dso_handle</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>) <span class="op">-></span> <span class="ident">libc</span>::<span class="ident">c_int</span>;
<span class="ident">mem</span>::<span class="ident">transmute</span>::<span class="op"><</span><span class="kw-2">*</span><span class="kw">const</span> <span class="ident">libc</span>::<span class="ident">c_void</span>, <span class="ident">F</span><span class="op">></span>(<span class="ident">__cxa_thread_atexit_impl</span>)
(<span class="ident">dtor</span>, <span class="ident">t</span>, <span class="kw-2">&</span><span class="ident">__dso_handle</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> _ <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> _);
<span class="kw">return</span>
}
<span class="ident">register_dtor_fallback</span>(<span class="ident">t</span>, <span class="ident">dtor</span>);
}
<span class="comment">// macOS's analog of the above linux function is this _tlv_atexit function.</span>
<span class="comment">// The disassembly of thread_local globals in C++ (at least produced by</span>
<span class="comment">// clang) will have this show up in the output.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">"macos"</span>)]</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">register_dtor</span>(<span class="ident">t</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>, <span class="ident">dtor</span>: <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>)) {
<span class="kw">extern</span> {
<span class="kw">fn</span> <span class="ident">_tlv_atexit</span>(<span class="ident">dtor</span>: <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>),
<span class="ident">arg</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>);
}
<span class="ident">_tlv_atexit</span>(<span class="ident">dtor</span>, <span class="ident">t</span>);
}
<span class="comment">// Just use the thread_local fallback implementation, at least until there's</span>
<span class="comment">// a more direct implementation.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">"fuchsia"</span>)]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">sys_common</span>::<span class="ident">thread_local</span>::<span class="ident">register_dtor_fallback</span> <span class="kw">as</span> <span class="ident">register_dtor</span>;
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">requires_move_before_drop</span>() <span class="op">-></span> <span class="ident">bool</span> {
<span class="comment">// The macOS implementation of TLS apparently had an odd aspect to it</span>
<span class="comment">// where the pointer we have may be overwritten while this destructor</span>
<span class="comment">// is running. Specifically if a TLS destructor re-accesses TLS it may</span>
<span class="comment">// trigger a re-initialization of all TLS variables, paving over at</span>
<span class="comment">// least some destroyed ones with initial values.</span>
<span class="comment">//</span>
<span class="comment">// This means that if we drop a TLS value in place on macOS that we could</span>
<span class="comment">// revert the value to its original state halfway through the</span>
<span class="comment">// destructor, which would be bad!</span>
<span class="comment">//</span>
<span class="comment">// Hence, we use `ptr::read` on macOS (to move to a "safe" location)</span>
<span class="comment">// instead of drop_in_place.</span>
<span class="macro">cfg</span><span class="macro">!</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">"macos"</span>)
}
</pre>
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