[Clang][RISCV] Support -fcf-protection=return for RISC-V

[jaidTw]

This patches enables the support of -fcf-protection=return on RISC-V, and add a string attribute "hw-shadow-stack" to every function if the option is set on RISC-V

[llvmbot]

@llvm/pr-subscribers-backend-risc-v
@llvm/pr-subscribers-clang-codegen

@llvm/pr-subscribers-clang

Author: Jesse Huang (jaidTw)

Changes

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 --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) {

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[mylai-mtk]

LGTM, but please wait for others. I'm too junior to this community that I'm not sure if my words are enough 😂

[kito-cheng]

Test?

[jaidTw]

Addressed comments

[kito-cheng]

LGTM

[jaidTw]

After a meeting with Kito, we decided to use Zicfiss as the requirement in this patch.
I will change the requirement of both patches (this and 112478) to Zicfis.s
And after taking a look at other tests, I think -triple=riscv64/32 is sufficient for the tuples so I also changed it

[jaidTw]

@mylai-mtk could you take a look at the latest version?
I'm gonna merge it if it looks good to you too

[mylai-mtk]

LGTM. Thanks.