From 6bbf734ecac35a5a1c3bcb680d20519dfd46da11 Mon Sep 17 00:00:00 2001
From: Anatoly Trosinenko <atrosinenko@accesssoftek.com>
Date: Wed, 17 Sep 2025 20:23:09 +0300
Subject: [FMV] Set default attributes on the resolver functions (#141573)

There is a number of attributes that is expected to be set on functions
by default. This patch implements setting more such attributes on the
FMV resolver functions generated by Clang. On AArch64, this makes the
resolver functions use the default PAC and BTI hardening settings.
---
 clang/lib/CodeGen/CodeGenModule.cpp | 34 +++++++++++++++++++++++++++-------
 1 file changed, 27 insertions(+), 7 deletions(-)

(limited to 'clang/lib/CodeGen/CodeGenModule.cpp')

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 0ebab141b187..0b660e3daaf8 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -4610,12 +4610,6 @@ void CodeGenModule::emitMultiVersionFunctions() {
     }
     llvm::Function *ResolverFunc = cast<llvm::Function>(ResolverConstant);
 
-    ResolverFunc->setLinkage(getMultiversionLinkage(*this, GD));
-
-    if (!ResolverFunc->hasLocalLinkage() && supportsCOMDAT())
-      ResolverFunc->setComdat(
-          getModule().getOrInsertComdat(ResolverFunc->getName()));
-
     const TargetInfo &TI = getTarget();
     llvm::stable_sort(
         Options, [&TI](const CodeGenFunction::FMVResolverOption &LHS,
@@ -4624,6 +4618,11 @@ void CodeGenModule::emitMultiVersionFunctions() {
         });
     CodeGenFunction CGF(*this);
     CGF.EmitMultiVersionResolver(ResolverFunc, Options);
+
+    setMultiVersionResolverAttributes(ResolverFunc, GD);
+    if (!ResolverFunc->hasLocalLinkage() && supportsCOMDAT())
+      ResolverFunc->setComdat(
+          getModule().getOrInsertComdat(ResolverFunc->getName()));
   }
 
   // Ensure that any additions to the deferred decls list caused by emitting a
@@ -4674,7 +4673,7 @@ void CodeGenModule::emitCPUDispatchDefinition(GlobalDecl GD) {
 
   auto *ResolverFunc = cast<llvm::Function>(GetOrCreateLLVMFunction(
       ResolverName, ResolverType, ResolverGD, /*ForVTable=*/false));
-  ResolverFunc->setLinkage(getMultiversionLinkage(*this, GD));
+
   if (supportsCOMDAT())
     ResolverFunc->setComdat(
         getModule().getOrInsertComdat(ResolverFunc->getName()));
@@ -4740,6 +4739,7 @@ void CodeGenModule::emitCPUDispatchDefinition(GlobalDecl GD) {
 
   CodeGenFunction CGF(*this);
   CGF.EmitMultiVersionResolver(ResolverFunc, Options);
+  setMultiVersionResolverAttributes(ResolverFunc, GD);
 
   if (getTarget().supportsIFunc()) {
     llvm::GlobalValue::LinkageTypes Linkage = getMultiversionLinkage(*this, GD);
@@ -4858,6 +4858,26 @@ llvm::Constant *CodeGenModule::GetOrCreateMultiVersionResolver(GlobalDecl GD) {
   return Resolver;
 }
 
+void CodeGenModule::setMultiVersionResolverAttributes(llvm::Function *Resolver,
+                                                      GlobalDecl GD) {
+  const NamedDecl *D = dyn_cast_or_null<NamedDecl>(GD.getDecl());
+  Resolver->setLinkage(getMultiversionLinkage(*this, GD));
+
+  // Function body has to be emitted before calling setGlobalVisibility
+  // for Resolver to be considered as definition.
+  setGlobalVisibility(Resolver, D);
+
+  setDSOLocal(Resolver);
+
+  // Set the default target-specific attributes, such as PAC and BTI ones on
+  // AArch64. Not passing Decl to prevent setting unrelated attributes,
+  // as Resolver can be shared by multiple declarations.
+  // FIXME Some targets may require a non-null D to set some attributes
+  //       (such as "stackrealign" on X86, even when it is requested via
+  //       "-mstackrealign" command line option).
+  getTargetCodeGenInfo().setTargetAttributes(/*D=*/nullptr, Resolver, *this);
+}
+
 bool CodeGenModule::shouldDropDLLAttribute(const Decl *D,
                                            const llvm::GlobalValue *GV) const {
   auto SC = GV->getDLLStorageClass();
-- 
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