[AArch64][PAC][clang][ELF] Support PAuth ABI compatibility tag

Emit PAuth ABI compatibility tag values as llvm module flags:
- `aarch64-elf-pauthabi-platform`
- `aarch64-elf-pauthabi-version`

Author: kovdan01

clang/lib/CodeGen/CodeGenModule.cpp

@@ -51,6 +51,7 @@
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/BinaryFormat/ELF.h"
 #include "llvm/Frontend/OpenMP/OMPIRBuilder.h"
 #include "llvm/IR/AttributeMask.h"
 #include "llvm/IR/CallingConv.h"
@@ -1075,6 +1076,23 @@ void CodeGenModule::Release() {
     if (!LangOpts.isSignReturnAddressWithAKey())
       getModule().addModuleFlag(llvm::Module::Min,
                                 "sign-return-address-with-bkey", 1);
+
+    if (getTriple().isOSLinux() && getTriple().isOSBinFormatELF()) {
+      uint64_t PAuthABIVersion =
+          (LangOpts.PointerAuthCalls << 0) |
+          (LangOpts.PointerAuthReturns << 1) |
+          (LangOpts.PointerAuthVTPtrAddressDiscrimination << 2) |
+          (LangOpts.PointerAuthVTPtrTypeDiscrimination << 3) |
+          (LangOpts.PointerAuthInitFini << 4);
+      if (PAuthABIVersion != 0) {
+        getModule().addModuleFlag(
+            llvm::Module::Error, "aarch64-elf-pauthabi-platform",
+            llvm::ELF::GNU_PROPERTY_AARCH64_FEATURE_PAUTH_PLATFORM_LINUX);
+        getModule().addModuleFlag(llvm::Module::Error,
+                                  "aarch64-elf-pauthabi-version",
+                                  PAuthABIVersion);
+      }
+    }
   }
 
   if (!CodeGenOpts.MemoryProfileOutput.empty()) {

clang/test/CodeGen/aarch64-elf-pauthabi.c

@@ -0,0 +1,28 @@
+// RUN: %clang -target aarch64-linux -S -emit-llvm -o - -mbranch-protection=pauthabi %s                                    | FileCheck %s --check-prefix=ALL
+// RUN: %clang -target aarch64-linux -S -emit-llvm -o - -fptrauth-returns %s                                               | FileCheck %s --check-prefix=RET
+// RUN: %clang -target aarch64-linux -S -emit-llvm -o - -fptrauth-calls %s                                                 | FileCheck %s --check-prefix=CALL
+// RUN: %clang -target aarch64-linux -S -emit-llvm -o - -fptrauth-calls -fptrauth-vtable-pointer-address-discrimination %s | FileCheck %s --check-prefix=VPTRADDR
+// RUN: %clang -target aarch64-linux -S -emit-llvm -o - -fptrauth-calls -fptrauth-vtable-pointer-type-discrimination %s    | FileCheck %s --check-prefix=VPTRTYPE
+// RUN: %clang -target aarch64-linux -S -emit-llvm -o - -fptrauth-calls -fptrauth-init-fini %s                             | FileCheck %s --check-prefix=INITFINI
+
+// REQUIRES: aarch64-registered-target
+
+// ALL: !{i32 1, !"aarch64-elf-pauthabi-platform", i32 2}
+// ALL: !{i32 1, !"aarch64-elf-pauthabi-version", i32 31}
+
+// RET: !{i32 1, !"aarch64-elf-pauthabi-platform", i32 2}
+// RET: !{i32 1, !"aarch64-elf-pauthabi-version", i32 2}
+
+// CALL: !{i32 1, !"aarch64-elf-pauthabi-platform", i32 2}
+// CALL: !{i32 1, !"aarch64-elf-pauthabi-version", i32 1}
+
+// VPTRADDR: !{i32 1, !"aarch64-elf-pauthabi-platform", i32 2}
+// VPTRADDR: !{i32 1, !"aarch64-elf-pauthabi-version", i32 5}
+
+// VPTRTYPE: !{i32 1, !"aarch64-elf-pauthabi-platform", i32 2}
+// VPTRTYPE: !{i32 1, !"aarch64-elf-pauthabi-version", i32 9}
+
+// INITFINI: !{i32 1, !"aarch64-elf-pauthabi-platform", i32 2}
+// INITFINI: !{i32 1, !"aarch64-elf-pauthabi-version", i32 17}
+
+void foo() {}