[clang] Mark CXX module initializer with PACBTI attributes (PR #133716)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-codegen

Author: Victor Campos (vhscampos)

<details>
<summary>Changes</summary>

The CXX module initializer function, which is called at program startup, needs to be tagged with Pointer Authentication and Branch Target Identification marks whenever relevant.

Before this patch, in CPUs set up for PACBTI execution, the function wasn't protected with return address signing and no BTI instruction was inserted at the start of it, thus leading to an execution fault.

This patch fixes the issue by marking the function with the function attributes related to PAC and BTI if relevant.

---
Full diff: https://github.com/llvm/llvm-project/pull/133716.diff


2 Files Affected:

- (modified) clang/lib/CodeGen/CGDeclCXX.cpp (+6) 
- (added) clang/test/CodeGenCXX/cxx20-module-initializer-pacbti.cpp (+32) 


``````````diff
diff --git a/clang/lib/CodeGen/CGDeclCXX.cpp b/clang/lib/CodeGen/CGDeclCXX.cpp
index a01fa157c2b26..0366e3977b812 100644
--- a/clang/lib/CodeGen/CGDeclCXX.cpp
+++ b/clang/lib/CodeGen/CGDeclCXX.cpp
@@ -818,6 +818,12 @@ void CodeGenModule::EmitCXXModuleInitFunc(Module *Primary) {
     Fn->addFnAttr("device-init");
   }
 
+  if (getTarget().isBranchProtectionSupportedArch(
+          getTarget().getTargetOpts().CPU)) {
+    TargetInfo::BranchProtectionInfo BPI(getLangOpts());
+    getTargetCodeGenInfo().setBranchProtectionFnAttributes(BPI, (*Fn));
+  }
+
   // We are done with the inits.
   AllImports.clear();
   PrioritizedCXXGlobalInits.clear();
diff --git a/clang/test/CodeGenCXX/cxx20-module-initializer-pacbti.cpp b/clang/test/CodeGenCXX/cxx20-module-initializer-pacbti.cpp
new file mode 100644
index 0000000000000..7ebaa5e8f349e
--- /dev/null
+++ b/clang/test/CodeGenCXX/cxx20-module-initializer-pacbti.cpp
@@ -0,0 +1,32 @@
+// RUN: %clang_cc1 -triple thumbv8.1m.main-unknown-none-eabi -emit-module-interface -target-feature +pacbti -mbranch-target-enforce -std=c++20 %s -o %t.pcm
+// RUN: %clang_cc1 -triple thumbv8.1m.main-unknown-none-eabi -std=c++20 %t.pcm -emit-llvm -o - | \
+// RUN: FileCheck --check-prefixes=CHECK,CHECK-BTI %s
+
+// RUN: %clang_cc1 -triple thumbv8.1m.main-unknown-none-eabi -emit-module-interface -target-feature +pacbti -msign-return-address=non-leaf -std=c++20 %s -o %t.pcm
+// RUN: %clang_cc1 -triple thumbv8.1m.main-unknown-none-eabi -std=c++20 %t.pcm -emit-llvm -o - | \
+// RUN: FileCheck --check-prefixes=CHECK,CHECK-PAC %s
+
+// RUN: %clang_cc1 -triple thumbv8.1m.main-unknown-none-eabi -emit-module-interface -target-feature +pacbti -msign-return-address=all -std=c++20 %s -o %t.pcm
+// RUN: %clang_cc1 -triple thumbv8.1m.main-unknown-none-eabi -std=c++20 %t.pcm -emit-llvm -o - | \
+// RUN: FileCheck --check-prefixes=CHECK,CHECK-PAC-ALL %s
+
+// RUN: %clang_cc1 -triple thumbv8.1m.main-unknown-none-eabi -emit-module-interface -target-feature +pacbti -msign-return-address=non-leaf -mbranch-target-enforce -std=c++20 %s -o %t.pcm
+// RUN: %clang_cc1 -triple thumbv8.1m.main-unknown-none-eabi -std=c++20 %t.pcm -emit-llvm -o - | \
+// RUN: FileCheck --check-prefixes=CHECK,CHECK-PAC-BTI %s
+
+// RUN: %clang_cc1 -triple thumbv8.1m.main-unknown-none-eabi -emit-module-interface -target-feature +pacbti -msign-return-address=all -mbranch-target-enforce -std=c++20 %s -o %t.pcm
+// RUN: %clang_cc1 -triple thumbv8.1m.main-unknown-none-eabi -std=c++20 %t.pcm -emit-llvm -o - | \
+// RUN: FileCheck --check-prefixes=CHECK,CHECK-PAC-BTI-ALL %s
+
+// CHECK: define void @_ZGIW3foo() #0
+// CHECK-BTI: attributes #0 = { nounwind "branch-target-enforcement" }
+// CHECK-PAC: attributes #0 = { nounwind "sign-return-address"="non-leaf" "sign-return-address-key"="a_key" }
+// CHECK-PAC-ALL: attributes #0 = { nounwind "sign-return-address"="all" "sign-return-address-key"="a_key" }
+// CHECK-PAC-BTI: attributes #0 = { nounwind "branch-target-enforcement" "sign-return-address"="non-leaf" "sign-return-address-key"="a_key" }
+// CHECK-PAC-BTI-ALL: attributes #0 = { nounwind "branch-target-enforcement" "sign-return-address"="all" "sign-return-address-key"="a_key" }
+
+module;
+
+export module foo;
+
+export void func();

``````````

</details>


https://github.com/llvm/llvm-project/pull/133716