Mark CXX module initializer with PACBTI attributes

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.

Author: vhscampos

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();

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();