Auto merge of #108089 - Zoxc:windows-tls, r=bjorn3

Support TLS access into dylibs on Windows

This allows access to `#[thread_local]`  in upstream dylibs on Windows by introducing a MIR shim to return the address of the thread local. Accesses that go into an upstream dylib will call the MIR shim to get the address of it.

`convert_tls_rvalues` is introduced in `rustc_codegen_ssa` which rewrites MIR TLS accesses to dummy calls which are replaced with calls to the MIR shims when the dummy calls are lowered to backend calls.

A new `dll_tls_export` target option enables this behavior with a `false` value which is set for Windows platforms.

This fixes https://github.com/rust-lang/rust/issues/84933.

3 files changed, 51 insertions, 0 deletions

diff --git a/tests/ui/thread-local/auxiliary/tls-export.rs b/tests/ui/thread-local/auxiliary/tls-export.rs
new file mode 100644
index 00000000000..027213bc033
--- /dev/null
+++ b/tests/ui/thread-local/auxiliary/tls-export.rs
@@ -0,0 +1,17 @@
+#![crate_type = "dylib"]
+#![feature(thread_local)]
+#![feature(cfg_target_thread_local)]
+
+extern crate tls_rlib;
+
+pub use tls_rlib::*;
+
+#[cfg(target_thread_local)]
+#[thread_local]
+pub static FOO: bool = true;
+
+#[cfg(target_thread_local)]
+#[inline(never)]
+pub fn foo_addr() -> usize {
+    &FOO as *const bool as usize
+}
diff --git a/tests/ui/thread-local/auxiliary/tls-rlib.rs b/tests/ui/thread-local/auxiliary/tls-rlib.rs
new file mode 100644
index 00000000000..20bc998ec11
--- /dev/null
+++ b/tests/ui/thread-local/auxiliary/tls-rlib.rs
@@ -0,0 +1,15 @@
+// no-prefer-dynamic
+
+#![crate_type = "rlib"]
+#![feature(thread_local)]
+#![feature(cfg_target_thread_local)]
+
+#[cfg(target_thread_local)]
+#[thread_local]
+pub static BAR: bool = true;
+
+#[cfg(target_thread_local)]
+#[inline(never)]
+pub fn bar_addr() -> usize {
+    &BAR as *const bool as usize
+}
diff --git a/tests/ui/thread-local/tls-dylib-access.rs b/tests/ui/thread-local/tls-dylib-access.rs
new file mode 100644
index 00000000000..12c46113cea
--- /dev/null
+++ b/tests/ui/thread-local/tls-dylib-access.rs
@@ -0,0 +1,19 @@
+// aux-build: tls-rlib.rs
+// aux-build: tls-export.rs
+// run-pass
+
+#![feature(cfg_target_thread_local)]
+
+#[cfg(target_thread_local)]
+extern crate tls_export;
+
+fn main() {
+    #[cfg(target_thread_local)]
+    {
+        // Check that we get the real address of the `FOO` TLS in the dylib
+        assert_eq!(&tls_export::FOO as *const bool as usize, tls_export::foo_addr());
+
+        // Check that we get the real address of the `BAR` TLS in the rlib linked into the dylib
+        assert_eq!(&tls_export::BAR as *const bool as usize, tls_export::bar_addr());
+    }
+}