From 6f813e887af44d74e9bcfdb207ecab407037a939 Mon Sep 17 00:00:00 2001
From: Reuben Cruise <reuben.cruise@arm.com>
Date: Mon, 1 Sep 2025 16:53:50 +0100
Subject: Adds AArch64 GCS support

- Adds option to rustc config to enable GCS
- Passes `guarded-control-stack` flag to llvm if enabled
---
 compiler/rustc_codegen_llvm/src/attributes.rs | 5 ++++-
 compiler/rustc_codegen_llvm/src/context.rs    | 9 ++++++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

(limited to 'compiler/rustc_codegen_llvm')

diff --git a/compiler/rustc_codegen_llvm/src/attributes.rs b/compiler/rustc_codegen_llvm/src/attributes.rs
index 573c51a9539..dcf6b945497 100644
--- a/compiler/rustc_codegen_llvm/src/attributes.rs
+++ b/compiler/rustc_codegen_llvm/src/attributes.rs
@@ -407,13 +407,16 @@ pub(crate) fn llfn_attrs_from_instance<'ll, 'tcx>(
         to_add.extend(sanitize_attrs(cx, codegen_fn_attrs.no_sanitize));
 
         // For non-naked functions, set branch protection attributes on aarch64.
-        if let Some(BranchProtection { bti, pac_ret }) =
+        if let Some(BranchProtection { bti, pac_ret, gcs }) =
             cx.sess().opts.unstable_opts.branch_protection
         {
             assert!(cx.sess().target.arch == "aarch64");
             if bti {
                 to_add.push(llvm::CreateAttrString(cx.llcx, "branch-target-enforcement"));
             }
+            if gcs {
+                to_add.push(llvm::CreateAttrString(cx.llcx, "guarded-control-stack"));
+            }
             if let Some(PacRet { leaf, pc, key }) = pac_ret {
                 if pc {
                     to_add.push(llvm::CreateAttrString(cx.llcx, "branch-protection-pauth-lr"));
diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs
index 4a8ea11a3a8..057f525c76f 100644
--- a/compiler/rustc_codegen_llvm/src/context.rs
+++ b/compiler/rustc_codegen_llvm/src/context.rs
@@ -370,7 +370,8 @@ pub(crate) unsafe fn create_module<'ll>(
         );
     }
 
-    if let Some(BranchProtection { bti, pac_ret }) = sess.opts.unstable_opts.branch_protection {
+    if let Some(BranchProtection { bti, pac_ret, gcs }) = sess.opts.unstable_opts.branch_protection
+    {
         if sess.target.arch == "aarch64" {
             llvm::add_module_flag_u32(
                 llmod,
@@ -403,6 +404,12 @@ pub(crate) unsafe fn create_module<'ll>(
                 "sign-return-address-with-bkey",
                 u32::from(pac_opts.key == PAuthKey::B),
             );
+            llvm::add_module_flag_u32(
+                llmod,
+                llvm::ModuleFlagMergeBehavior::Min,
+                "guarded-control-stack",
+                gcs.into(),
+            );
         } else {
             bug!(
                 "branch-protection used on non-AArch64 target; \
-- 
cgit 1.4.1-3-g733a5