Allow pauthabi+bti and disallow other combinations with pauthabi

Author: kovdan01

clang/test/Driver/aarch64-ptrauth.c

@@ -37,3 +37,13 @@
 // RUN: not %clang -### -c --target=x86_64 -mbranch-protection=pauthabi %s 2>&1 | \
 // RUN:   FileCheck %s --check-prefix=ERR2
 // ERR2: error: unsupported option '-mbranch-protection=' for target 'x86_64'
+
+// RUN: not %clang -### -c --target=aarch64 -mbranch-protection=pauthabi+pac-ret %s 2>&1 | \
+// RUN:   FileCheck %s --check-prefix=ERR3
+// ERR3: error: unsupported argument 'pauthabi+pac-ret' to option '-mbranch-protection='
+
+// RUN: not %clang -### -c --target=aarch64 -mbranch-protection=gcs+pauthabi %s 2>&1 | \
+// RUN:   FileCheck %s --check-prefix=ERR4
+// ERR4: error: unsupported argument 'pauthabi+gcs' to option '-mbranch-protection='
+
+// RUN: %clang -### -c --target=aarch64 -mbranch-protection=bti+pauthabi %s 2>&1

llvm/lib/TargetParser/ARMTargetParserCommon.cpp

@@ -190,5 +190,17 @@ bool ARM::parseBranchProtection(StringRef Spec, ParsedBranchProtection &PBP,
     return false;
   }
 
+  if (!PBP.HasPauthABI)
+    return true;
+
+  if (PBP.Scope != "none") {
+    Err = "pauthabi+pac-ret";
+    return false;
+  }
+  if (PBP.GuardedControlStack) {
+    Err = "pauthabi+gcs";
+    return false;
+  }
+
   return true;
 }