[Clang][ARM][AArch64] Add branch protection attributes to the defaults.

[DanielKristofKiss]

These attributes are no longer inherited from the module flags, therefore need to be added for synthetic functions.

[llvmbot]

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-codegen

Author: Dani (DanielKristofKiss)

Changes

These attributes are no longer inherited from the module flags, therefore need to be added for synthetic functions.

---

Full diff: https://github.com/llvm/llvm-project/pull/83277.diff

2 Files Affected:

• (modified) clang/lib/CodeGen/CGCall.cpp (+16)
• (added) clang/test/CodeGenCXX/arm64-generated-fn-attr.cpp (+30)

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index d05cf1c6e1814e..d677a2e64be77e 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -2022,6 +2022,22 @@ static void getTrivialDefaultFunctionAttributes(
     std::tie(Var, Value) = Attr.split('=');
     FuncAttrs.addAttribute(Var, Value);
   }
+
+  TargetInfo::BranchProtectionInfo BPI(LangOpts);
+
+  if (BPI.SignReturnAddr != LangOptions::SignReturnAddressScopeKind::None) {
+    FuncAttrs.addAttribute("sign-return-address", BPI.getSignReturnAddrStr());
+    FuncAttrs.addAttribute(
+        "sign-return-address-key",
+        BPI.SignKey == LangOptions::SignReturnAddressKeyKind::AKey ? "a_key"
+                                                                   : "b_key");
+  }
+  if (BPI.BranchTargetEnforcement)
+    FuncAttrs.addAttribute("branch-target-enforcement", "true");
+  if (BPI.BranchProtectionPAuthLR)
+    FuncAttrs.addAttribute("branch-protection-pauth-lr", "true");
+  if (BPI.GuardedControlStack)
+    FuncAttrs.addAttribute("guarded-control-stack", "true");
 }
 
 /// Merges `target-features` from \TargetOpts and \F, and sets the result in
diff --git a/clang/test/CodeGenCXX/arm64-generated-fn-attr.cpp b/clang/test/CodeGenCXX/arm64-generated-fn-attr.cpp
new file mode 100644
index 00000000000000..8daf44abd4f91c
--- /dev/null
+++ b/clang/test/CodeGenCXX/arm64-generated-fn-attr.cpp
@@ -0,0 +1,30 @@
+// RUN: %clang_cc1 -triple aarch64-none-none -mbranch-target-enforce -msign-return-address=all -fcxx-exceptions -fexceptions -emit-llvm %s -o - | FileCheck %s --check-prefixes=CHECK
+
+// Check that functions generated by clang have the correct attributes
+
+class Example {
+public:
+  Example();
+  int fn();
+};
+
+// Initialization of var1 causes __cxx_global_var_init and __tls_init to be generated
+thread_local Example var1;
+extern thread_local Example var2;
+extern void fn();
+
+int testfn() noexcept {
+  // Calling fn in a noexcept function causes __clang_call_terminate to be generated
+  fn();
+  // Use of var1 and var2 causes TLS wrapper functions to be generated
+  return var1.fn() + var2.fn();
+}
+
+// CHECK: define {{.*}} @__cxx_global_var_init() [[ATTR1:#[0-9]+]]
+// CHECK: define {{.*}} @__clang_call_terminate({{.*}}) [[ATTR2:#[0-9]+]]
+// CHECK: define {{.*}} @_ZTW4var1() [[ATTR1]]
+// CHECK: define {{.*}} @_ZTW4var2() [[ATTR1]]
+// CHECK: define {{.*}} @__tls_init() [[ATTR1]]
+
+// CHECK: attributes [[ATTR1]] = { {{.*}}"branch-target-enforcement"="true"{{.*}}"sign-return-address"="all" "sign-return-address-key"="a_key"
+// CHECK: attributes [[ATTR2]] = { {{.*}}"branch-target-enforcement"="true"{{.*}}"sign-return-address"="all" "sign-return-address-key"="a_key"

[tmatheson-arm]

LGTM

[DanielKristofKiss]

Thanks.
I'm planning to land once all related patches are ready to land and in this order:
#82819 #83277 #83153 #83154

[DanielKristofKiss]

after #82819 lands, this can be 2 lines

Suggested change

	TargetInfo::BranchProtectionInfo BPI(LangOpts);
	BPI.setFnAttributes(FuncAttrs);

[MaskRay]

perhaps it's time to add CodeGenCXX/AArch64/ ? We have more target-specific directories under CodeGen.

Then the weird arm64- prefix (not recommended for ELF/Arm official) can be removed.

You can remove -fcxx-exceptions -fexceptions since they are unused. -triple aarch64-none-nonecan just be-triple aarch64`.

[DanielKristofKiss]

perhaps it's time to add CodeGenCXX/AArch64/ ? We have more target-specific directories under CodeGen.
Then the weird arm64- prefix (not recommended for ELF/Arm official) can be removed.

I'll create a NFC patch that cleans all of these up. (also in CodeGen where we have directories and prefixed files too.)

You can remove -fcxx-exceptions -fexceptions since they are unused

__clang_call_terminate is only generated when the exceptions are enabled. Clang generates the definition for it too and the test checks the right attributes for it.

-triple aarch64-none-nonecan just be-triple aarch64`.

ack

[DanielKristofKiss]

Sorry for the force push, need to be rebased. NFC since last review round.