[clang] Implement type/address discrimination of type_info vtable. (#99726)

We want to be able to support full type and address discrimination of
type_info on targets that don't have existing ABI compatibility
constraints.

This patch does not enable such behavior on any platform, it just adds
the necessary machinery.

In clang we add a new commandline argument to control the type_info
vtable ABI:
  -fptrauth-type-info-vtable-pointer-discrimination

and a feature flag to allow source level detection of the ABI:
  __has_feature(ptrauth_type_info_vtable_pointer_discrimination)

Co-authored-by: Oliver Hunt <oliver@apple.com>

1 files changed, 15 insertions, 2 deletions

diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index bf57add..424fe53 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1488,8 +1488,15 @@ void CompilerInvocation::setDefaultPointerAuthOptions(
         Key::ASDA, LangOpts.PointerAuthVTPtrAddressDiscrimination,
         LangOpts.PointerAuthVTPtrTypeDiscrimination ? Discrimination::Type
                                                     : Discrimination::None);
-    Opts.CXXTypeInfoVTablePointer =
-        PointerAuthSchema(Key::ASDA, false, Discrimination::None);
+
+    if (LangOpts.PointerAuthTypeInfoVTPtrDiscrimination)
+      Opts.CXXTypeInfoVTablePointer =
+          PointerAuthSchema(Key::ASDA, true, Discrimination::Constant,
+                            StdTypeInfoVTablePointerConstantDiscrimination);
+    else
+      Opts.CXXTypeInfoVTablePointer =
+          PointerAuthSchema(Key::ASDA, false, Discrimination::None);
+
     Opts.CXXVTTVTablePointers =
         PointerAuthSchema(Key::ASDA, false, Discrimination::None);
     Opts.CXXVirtualFunctionPointers = Opts.CXXVirtualVariadicFunctionPointers =
@@ -3411,6 +3418,9 @@ static void GeneratePointerAuthArgs(const LangOptions &Opts,
     GenerateArg(Consumer, OPT_fptrauth_vtable_pointer_address_discrimination);
   if (Opts.PointerAuthVTPtrTypeDiscrimination)
     GenerateArg(Consumer, OPT_fptrauth_vtable_pointer_type_discrimination);
+  if (Opts.PointerAuthTypeInfoVTPtrDiscrimination)
+    GenerateArg(Consumer, OPT_fptrauth_type_info_vtable_pointer_discrimination);
+
   if (Opts.PointerAuthInitFini)
     GenerateArg(Consumer, OPT_fptrauth_init_fini);
   if (Opts.PointerAuthFunctionTypeDiscrimination)
@@ -3427,6 +3437,9 @@ static void ParsePointerAuthArgs(LangOptions &Opts, ArgList &Args,
       Args.hasArg(OPT_fptrauth_vtable_pointer_address_discrimination);
   Opts.PointerAuthVTPtrTypeDiscrimination =
       Args.hasArg(OPT_fptrauth_vtable_pointer_type_discrimination);
+  Opts.PointerAuthTypeInfoVTPtrDiscrimination =
+      Args.hasArg(OPT_fptrauth_type_info_vtable_pointer_discrimination);
+
   Opts.PointerAuthInitFini = Args.hasArg(OPT_fptrauth_init_fini);
   Opts.PointerAuthFunctionTypeDiscrimination =
       Args.hasArg(OPT_fptrauth_function_pointer_type_discrimination);