[clang] [Clang][RISCV] Support -fcf-protection=return for RISC-V (PR #112477)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Jesse Huang (jaidTw)

<details>
<summary>Changes</summary>

This patches add a string attribute "hw-shadow-stack" to every function if `-fcf-protection=return` is set on RISC-V

---
Full diff: https://github.com/llvm/llvm-project/pull/112477.diff


2 Files Affected:

- (modified) clang/lib/Basic/Targets/RISCV.h (+6) 
- (modified) clang/lib/CodeGen/CodeGenFunction.cpp (+4) 


``````````diff
diff --git a/clang/lib/Basic/Targets/RISCV.h b/clang/lib/Basic/Targets/RISCV.h
index bf40edb8683b3e..3165623593fdf7 100644
--- a/clang/lib/Basic/Targets/RISCV.h
+++ b/clang/lib/Basic/Targets/RISCV.h
@@ -141,6 +141,12 @@ class RISCVTargetInfo : public TargetInfo {
     return true;
   }
 
+  bool checkCFProtectionReturnSupported(DiagnosticsEngine &Diags) const override {
+    if (ISAInfo->hasExtension("zimop"))
+      return true;
+    return TargetInfo::checkCFProtectionReturnSupported(Diags);
+  }
+
   CFBranchLabelSchemeKind getDefaultCFBranchLabelScheme() const override {
     return CFBranchLabelSchemeKind::FuncSig;
   }
diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 2306043c90f406..d8f0f7c14f6b40 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -899,6 +899,10 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
   if (CodeGenOpts.PointerAuth.IndirectGotos)
     Fn->addFnAttr("ptrauth-indirect-gotos");
 
+  // Add return control flow integrity attributes.
+  if (CodeGenOpts.CFProtectionReturn)
+    Fn->addFnAttr("hw-shadow-stack");
+
   // Apply xray attributes to the function (as a string, for now)
   bool AlwaysXRayAttr = false;
   if (const auto *XRayAttr = D ? D->getAttr<XRayInstrumentAttr>() : nullptr) {

``````````

</details>


https://github.com/llvm/llvm-project/pull/112477