std: Run TLS destructors in a statically linked binary

Running TLS destructors for a MSVC Windows binary requires the linker doesn't
elide the `_tls_used` or `__tls_used` symbols (depending on the architecture).
This is currently achieved via a `#[link_args]` hack but this only works for
dynamically linked binaries because the link arguments aren't propagated to
statically linked binaries.

This commit alters the strategy to instead emit a volatile load from those
symbols so LLVM can't elide it, forcing the reference to the symbol to stay
alive as long as the callback function stays alive (which we've made sure of
with the `#[linkage]` attribute).

Closes #28111

2 files changed, 39 insertions, 0 deletions

diff --git a/src/test/run-pass/down-with-thread-dtors.rs b/src/test/run-pass/down-with-thread-dtors.rs
index ee835785cbe..5c449d511d5 100644
--- a/src/test/run-pass/down-with-thread-dtors.rs
+++ b/src/test/run-pass/down-with-thread-dtors.rs
@@ -12,6 +12,8 @@ thread_local!(static FOO: Foo = Foo);
 thread_local!(static BAR: Bar = Bar(1));
 thread_local!(static BAZ: Baz = Baz);
 
+static mut HIT: bool = false;
+
 struct Foo;
 struct Bar(i32);
 struct Baz;
@@ -31,8 +33,15 @@ impl Drop for Bar {
     }
 }
 
+impl Drop for Baz {
+    fn drop(&mut self) {
+        unsafe { HIT = true; }
+    }
+}
+
 fn main() {
     std::thread::spawn(|| {
         FOO.with(|_| {});
     }).join().unwrap();
+    assert!(unsafe { HIT });
 }
diff --git a/src/test/run-pass/tls-dtors-are-run-in-a-static-binary.rs b/src/test/run-pass/tls-dtors-are-run-in-a-static-binary.rs
new file mode 100644
index 00000000000..da30100f67f
--- /dev/null
+++ b/src/test/run-pass/tls-dtors-are-run-in-a-static-binary.rs
@@ -0,0 +1,30 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// no-prefer-dynamic
+
+static mut HIT: bool = false;
+
+struct Foo;
+
+impl Drop for Foo {
+    fn drop(&mut self) {
+        unsafe { HIT = true; }
+    }
+}
+
+thread_local!(static FOO: Foo = Foo);
+
+fn main() {
+    std::thread::spawn(|| {
+        FOO.with(|_| {});
+    }).join().unwrap();
+    assert!(unsafe { HIT });
+}