[libunwind] [libunwind][AArch64] Protect PC within libunwind's context. (PR #113368)

[John Brawn via cfe-commits]

================
@@ -1823,9 +1823,48 @@ extern "C" void *__libunwind_cet_get_jump_target() {
 #endif
 
 class _LIBUNWIND_HIDDEN Registers_arm64 {
+protected:
+  /// The program counter is used effectively as a return address
+  /// when the context is restored therefore protect it with PAC.
+  /// The base address of the context is used with the A key for
+  /// authentication and signing. Return address authentication is
+  /// still managed according to the unwind info.
+  inline uint64_t getAuthSalt() const {
+    return reinterpret_cast<uint64_t>(this);
+  }
+#if defined(_LIBUNWIND_IS_NATIVE_ONLY)
+  // Authenticate the given pointer and return with the raw value
+  // if the authentication is succeeded.
----------------
john-brawn-arm wrote:

"authentication is succeeded" should be either "authentication succeeded" or "authentication is successful".

https://github.com/llvm/llvm-project/pull/113368