From 540e41f8b3822661d2f9d0768bbfe1dd3bb65e4d Mon Sep 17 00:00:00 2001
From: Alice Ryhl <aliceryhl@google.com>
Date: Wed, 25 Sep 2024 10:23:30 +0200
Subject: [PATCH] Add missing module flags for function-return=thunk-extern

---
 compiler/rustc_codegen_llvm/src/context.rs | 14 +++++++++++++-
 tests/codegen/function-return.rs           |  6 ++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs
index 2b8912d1db2..81b82840472 100644
--- a/compiler/rustc_codegen_llvm/src/context.rs
+++ b/compiler/rustc_codegen_llvm/src/context.rs
@@ -19,7 +19,7 @@
 use rustc_middle::{bug, span_bug};
 use rustc_session::Session;
 use rustc_session::config::{
-    BranchProtection, CFGuard, CFProtection, CrateType, DebugInfo, PAuthKey, PacRet,
+    BranchProtection, CFGuard, CFProtection, CrateType, DebugInfo, FunctionReturn, PAuthKey, PacRet,
 };
 use rustc_span::source_map::Spanned;
 use rustc_span::{DUMMY_SP, Span};
@@ -378,6 +378,18 @@ pub(crate) unsafe fn create_module<'ll>(
         }
     }
 
+    match sess.opts.unstable_opts.function_return {
+        FunctionReturn::Keep => {}
+        FunctionReturn::ThunkExtern => unsafe {
+            llvm::LLVMRustAddModuleFlagU32(
+                llmod,
+                llvm::LLVMModFlagBehavior::Override,
+                c"function_return_thunk_extern".as_ptr(),
+                1,
+            )
+        },
+    }
+
     match (sess.opts.unstable_opts.small_data_threshold, sess.target.small_data_threshold_support())
     {
         // Set up the small-data optimization limit for architectures that use
diff --git a/tests/codegen/function-return.rs b/tests/codegen/function-return.rs
index 0ca1a41ee86..2b9de4e1478 100644
--- a/tests/codegen/function-return.rs
+++ b/tests/codegen/function-return.rs
@@ -26,3 +26,9 @@ pub fn foo() {
     // keep-thunk-extern: attributes #0 = { {{.*}}fn_ret_thunk_extern{{.*}} }
     // thunk-extern-keep-NOT: fn_ret_thunk_extern
 }
+
+// unset-NOT: !{{[0-9]+}} = !{i32 4, !"function_return_thunk_extern", i32 1}
+// keep-NOT: !{{[0-9]+}} = !{i32 4, !"function_return_thunk_extern", i32 1}
+// thunk-extern: !{{[0-9]+}} = !{i32 4, !"function_return_thunk_extern", i32 1}
+// keep-thunk-extern: !{{[0-9]+}} = !{i32 4, !"function_return_thunk_extern", i32 1}
+// thunk-extern-keep-NOT: !{{[0-9]+}} = !{i32 4, !"function_return_thunk_extern", i32 1}