[clang] [Clang][ARM][AArch64] Alway emit protection attributes for functions. (PR #82819)

[Nick Desaulniers via cfe-commits]

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@@ -173,6 +167,13 @@ class ARMTargetCodeGenInfo : public TargetCodeGenInfo {
               diag::warn_target_unsupported_branch_protection_attribute)
               << Attr.CPU;
       }
+    } else if (CGM.getTarget().isBranchProtectionSupportedArch(
+                   CGM.getTarget().getTargetOpts().CPU)) {
+      TargetInfo::BranchProtectionInfo BPI(CGM.getLangOpts());
+      if (BPI.SignReturnAddr != LangOptions::SignReturnAddressScopeKind::None)
+        Fn->addFnAttr("sign-return-address", BPI.getSignReturnAddrStr());
+      if (BPI.BranchTargetEnforcement)
+        Fn->addFnAttr("branch-target-enforcement", "true");
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nickdesaulniers wrote:

On L157 this fn attr gets set to `false`.  Does that need to happen on this branch, too?

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Consider adding a `getBranchTargetEnforcementStr` method to `BranchProtectionInfo` to encapsulate this.  Perhaps the same for branch-protection-pauth-lr and guarded-control-stack (L129-L134 of clang/lib/CodeGen/Targets/AArch64.cpp).

---

I wonder if `BranchProtectionInfo` should just have one method that accepts an `llvm::Function` and sets all appropriate fn attrs there?  Then what looks somewhat like duplicated logic (between ARM.cpp and AArch64.cpp) to me could be shared there?

https://github.com/llvm/llvm-project/pull/82819