[PAC] Define __builtin_ptrauth_type_discriminator (llvm#100204)

The builtin computes the discriminator for a type, which can be used to
sign/authenticate function pointers and member function pointers.

If the type passed to the builtin is a C++ member function pointer type,
the result is the discriminator used to signed member function pointers
of that type. If the type is a function, function pointer, or function
reference type, the result is the discriminator used to sign functions
of that type. It is ill-formed to use this builtin with any other type.

A call to this function is an integer constant expression.

Co-Authored-By: John McCall [email protected]

Author: ahatanak

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -942,6 +942,9 @@ def warn_ptrauth_auth_null_pointer :
   InGroup<PtrAuthNullPointers>;
 def err_ptrauth_string_not_literal : Error<
   "argument must be a string literal%select{| of char type}0">;
+def err_ptrauth_type_disc_undiscriminated : Error<
+  "cannot pass undiscriminated type %0 to "
+  "'__builtin_ptrauth_type_discriminator'">;
 
 def note_ptrauth_virtual_function_pointer_incomplete_arg_ret :
   Note<"cannot take an address of a virtual member function if its return or "

clang/include/clang/Basic/TokenKinds.def

@@ -596,6 +596,8 @@ ALIAS("__is_same_as", __is_same, KEYCXX)
 KEYWORD(__private_extern__          , KEYALL)
 KEYWORD(__module_private__          , KEYALL)
 
+UNARY_EXPR_OR_TYPE_TRAIT(__builtin_ptrauth_type_discriminator, PtrAuthTypeDiscriminator, KEYALL)
+
 // Extension that will be enabled for Microsoft, Borland and PS4, but can be
 // disabled via '-fno-declspec'.
 KEYWORD(__declspec                  , 0)

clang/include/clang/Parse/Parser.h

@@ -3890,6 +3890,8 @@ class Parser : public CodeCompletionHandler {
   ExprResult ParseArrayTypeTrait();
   ExprResult ParseExpressionTrait();
 
+  ExprResult ParseBuiltinPtrauthTypeDiscriminator();
+
   //===--------------------------------------------------------------------===//
   // Preprocessor code-completion pass-through
   void CodeCompleteDirective(bool InConditional) override;

clang/include/clang/Sema/Sema.h

@@ -3456,6 +3456,8 @@ class Sema final : public SemaBase {
                                     TemplateIdAnnotation *TemplateId,
                                     bool IsMemberSpecialization);
 
+  bool checkPointerAuthEnabled(SourceLocation Loc, SourceRange Range);
+
   bool checkConstantPointerAuthKey(Expr *keyExpr, unsigned &key);
 
   /// Diagnose function specifiers on a declaration of an identifier that

clang/lib/AST/ExprConstant.cpp

@@ -14058,6 +14058,12 @@ bool IntExprEvaluator::VisitUnaryExprOrTypeTraitExpr(
                      E);
   }
 
+  case UETT_PtrAuthTypeDiscriminator: {
+    if (E->getArgumentType()->isDependentType())
+      return false;
+    return Success(
+        Info.Ctx.getPointerAuthTypeDiscriminator(E->getArgumentType()), E);
+  }
   case UETT_VecStep: {
     QualType Ty = E->getTypeOfArgument();
 

clang/lib/AST/ItaniumMangle.cpp

@@ -5179,6 +5179,14 @@ void CXXNameMangler::mangleExpression(const Expr *E, unsigned Arity,
       Diags.Report(DiagID);
       return;
     }
+    case UETT_PtrAuthTypeDiscriminator: {
+      DiagnosticsEngine &Diags = Context.getDiags();
+      unsigned DiagID = Diags.getCustomDiagID(
+          DiagnosticsEngine::Error,
+          "cannot yet mangle __builtin_ptrauth_type_discriminator expression");
+      Diags.Report(E->getExprLoc(), DiagID);
+      return;
+    }
     case UETT_VecStep: {
       DiagnosticsEngine &Diags = Context.getDiags();
       unsigned DiagID = Diags.getCustomDiagID(DiagnosticsEngine::Error,

clang/lib/Headers/ptrauth.h

@@ -202,6 +202,23 @@ typedef __UINTPTR_TYPE__ ptrauth_generic_signature_t;
 #define ptrauth_string_discriminator(__string)                                 \
   __builtin_ptrauth_string_discriminator(__string)
 
+/* Compute a constant discriminator from the given type.
+
+   The result can be used as the second argument to
+   ptrauth_blend_discriminator or the third argument to the
+   __ptrauth qualifier.  It has type size_t.
+
+   If the type is a C++ member function pointer type, the result is
+   the discriminator used to signed member function pointers of that
+   type.  If the type is a function, function pointer, or function
+   reference type, the result is the discriminator used to sign
+   functions of that type.  It is ill-formed to use this macro with any
+   other type.
+
+   A call to this function is an integer constant expression. */
+#define ptrauth_type_discriminator(__type)                                     \
+  __builtin_ptrauth_type_discriminator(__type)
+
 /* Compute a signature for the given pair of pointer-sized values.
    The order of the arguments is significant.
 
@@ -289,6 +306,8 @@ typedef __UINTPTR_TYPE__ ptrauth_generic_signature_t;
     ((ptrauth_extra_data_t)0);                                                 \
   })
 
+#define ptrauth_type_discriminator(__type) ((ptrauth_extra_data_t)0)
+
 #define ptrauth_sign_generic_data(__value, __data)                             \
   ({                                                                           \
     (void)__value;                                                             \

clang/lib/Parse/ParseExpr.cpp

@@ -841,6 +841,26 @@ bool Parser::isRevertibleTypeTrait(const IdentifierInfo *II,
   return false;
 }
 
+ExprResult Parser::ParseBuiltinPtrauthTypeDiscriminator() {
+  SourceLocation Loc = ConsumeToken();
+
+  BalancedDelimiterTracker T(*this, tok::l_paren);
+  if (T.expectAndConsume())
+    return ExprError();
+
+  TypeResult Ty = ParseTypeName();
+  if (Ty.isInvalid()) {
+    SkipUntil(tok::r_paren, StopAtSemi);
+    return ExprError();
+  }
+
+  SourceLocation EndLoc = Tok.getLocation();
+  T.consumeClose();
+  return Actions.ActOnUnaryExprOrTypeTraitExpr(
+      Loc, UETT_PtrAuthTypeDiscriminator,
+      /*isType=*/true, Ty.get().getAsOpaquePtr(), SourceRange(Loc, EndLoc));
+}
+
 /// Parse a cast-expression, or, if \pisUnaryExpression is true, parse
 /// a unary-expression.
 ///
@@ -1806,6 +1826,9 @@ ExprResult Parser::ParseCastExpression(CastParseKind ParseKind,
     Res = ParseArrayTypeTrait();
     break;
 
+  case tok::kw___builtin_ptrauth_type_discriminator:
+    return ParseBuiltinPtrauthTypeDiscriminator();
+
   case tok::kw___is_lvalue_expr:
   case tok::kw___is_rvalue_expr:
     if (NotPrimaryExpression)

clang/lib/Sema/SemaChecking.cpp

@@ -1489,14 +1489,18 @@ enum PointerAuthOpKind {
 };
 }
 
-static bool checkPointerAuthEnabled(Sema &S, Expr *E) {
-  if (S.getLangOpts().PointerAuthIntrinsics)
+bool Sema::checkPointerAuthEnabled(SourceLocation Loc, SourceRange Range) {
+  if (getLangOpts().PointerAuthIntrinsics)
     return false;
 
-  S.Diag(E->getExprLoc(), diag::err_ptrauth_disabled) << E->getSourceRange();
+  Diag(Loc, diag::err_ptrauth_disabled) << Range;
   return true;
 }
 
+static bool checkPointerAuthEnabled(Sema &S, Expr *E) {
+  return S.checkPointerAuthEnabled(E->getExprLoc(), E->getSourceRange());
+}
+
 static bool checkPointerAuthKey(Sema &S, Expr *&Arg) {
   // Convert it to type 'int'.
   if (convertArgumentToType(S, Arg, S.Context.IntTy))

clang/lib/Sema/SemaExpr.cpp

@@ -4117,6 +4117,21 @@ static bool CheckVectorElementsTraitOperandType(Sema &S, QualType T,
   return false;
 }
 
+static bool checkPtrAuthTypeDiscriminatorOperandType(Sema &S, QualType T,
+                                                     SourceLocation Loc,
+                                                     SourceRange ArgRange) {
+  if (S.checkPointerAuthEnabled(Loc, ArgRange))
+    return true;
+
+  if (!T->isFunctionType() && !T->isFunctionPointerType() &&
+      !T->isFunctionReferenceType() && !T->isMemberFunctionPointerType()) {
+    S.Diag(Loc, diag::err_ptrauth_type_disc_undiscriminated) << T << ArgRange;
+    return true;
+  }
+
+  return false;
+}
+
 static bool CheckExtensionTraitOperandType(Sema &S, QualType T,
                                            SourceLocation Loc,
                                            SourceRange ArgRange,
@@ -4511,6 +4526,10 @@ bool Sema::CheckUnaryExprOrTypeTraitOperand(QualType ExprType,
     return CheckVectorElementsTraitOperandType(*this, ExprType, OpLoc,
                                                ExprRange);
 
+  if (ExprKind == UETT_PtrAuthTypeDiscriminator)
+    return checkPtrAuthTypeDiscriminatorOperandType(*this, ExprType, OpLoc,
+                                                    ExprRange);
+
   // Explicitly list some types as extensions.
   if (!CheckExtensionTraitOperandType(*this, ExprType, OpLoc, ExprRange,
                                       ExprKind))