[clang][PAC][NFC] Provide addition support macros to ptrauth.h

This introduces a number of additional macros to support the
use of manual pointer authentication.

Author: ojhunt

clang/docs/PointerAuthentication.rst

@@ -722,6 +722,40 @@ type.  Implementations are not required to make all bits of the result equally
 significant; in particular, some implementations are known to not leave
 meaningful data in the low bits.
 
+``ptrauth_nop_cast``
+^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c
+
+  ptrauth_nop_cast(__type, __value)
+
+Cast a pointer to the given type without changing any signature.
+
+This operation can be used to convert a value from one type to another without
+attempting to re-sign the value. This makes it possible to view a signed value
+of one type as another type signed with the same schema. This can be used to
+convert implicit schemas to explicit schemas, to convert to or from opaque
+types, or simply to change the effective underlying type of a signed value.
+
+The `__type` must be a pointer sized value compatible with the `__ptrauth`
+qualifier. The authentication schema must not include address diversity.
+
+The result is a bitwise identical value with the type passed as the `__type`
+argument.
+
+``ptrauth_function_pointer_type_discriminator``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c
+
+  ptrauth_function_pointer_type_discriminator(__type)
+
+Compute the constant discriminator used by Clang to sign pointers with the
+given C function pointer type.
+
+A call to this function is an integer constant expression.
+
+
 Standard ``__ptrauth`` qualifiers
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

clang/lib/Headers/ptrauth.h

@@ -199,6 +199,25 @@ typedef __UINTPTR_TYPE__ ptrauth_generic_signature_t;
   ptrauth_auth_and_resign(__value, __old_key, __old_data,                      \
                           ptrauth_key_function_pointer, 0)
 
+/* Cast a value to the given type without changing any signature.
+
+   The type must be a pointer sized type compatible with the __ptrauth
+   qualifier.
+   The value must be an expression with a non-address diversified pointer
+   authentication schema, and will be converted to an rvalue prior to the cast.
+   The result has type given by the first argument.
+
+   The result has an identical bit-pattern to the input pointer. */
+#define ptrauth_nop_cast(__type, __value)                                      \
+  ({                                                                           \
+    union {                                                                    \
+      typeof(*(__value)) *__fptr;                                              \
+      typeof(__type) __opaque;                                                 \
+    } __storage;                                                               \
+    __storage.__fptr = (__value);                                              \
+    __storage.__opaque;                                                        \
+  })
+
 /* Authenticate a data pointer.
 
    The value must be an expression of non-function pointer type.
@@ -241,6 +260,18 @@ typedef __UINTPTR_TYPE__ ptrauth_generic_signature_t;
 #define ptrauth_type_discriminator(__type)                                     \
   __builtin_ptrauth_type_discriminator(__type)
 
+/* Compute the constant discriminator used by Clang to sign pointers with the
+   given C function pointer type.
+
+   A call to this function is an integer constant expression. */
+#if __has_feature(ptrauth_function_pointer_type_discrimination)
+#define ptrauth_function_pointer_type_discriminator(__type)                    \
+  __builtin_ptrauth_type_discriminator(__type)
+#else
+#define ptrauth_function_pointer_type_discriminator(__type)                    \
+  ((ptrauth_extra_data_t)0)
+#endif
+
 /* Compute a signature for the given pair of pointer-sized values.
    The order of the arguments is significant.
 
@@ -263,6 +294,32 @@ typedef __UINTPTR_TYPE__ ptrauth_generic_signature_t;
 #define ptrauth_sign_generic_data(__value, __data)                             \
   __builtin_ptrauth_sign_generic_data(__value, __data)
 
+/* Define some standard __ptrauth qualifiers used in the ABI. */
+#define __ptrauth_function_pointer(__typekey)                                  \
+  __ptrauth(ptrauth_key_function_pointer, 0, __typekey)
+#define __ptrauth_return_address __ptrauth(ptrauth_key_return_address, 1, 0)
+#define __ptrauth_block_invocation_pointer                                     \
+  __ptrauth(ptrauth_key_function_pointer, 1, 0)
+#define __ptrauth_block_copy_helper                                            \
+  __ptrauth(ptrauth_key_function_pointer, 1, 0)
+#define __ptrauth_block_destroy_helper                                         \
+  __ptrauth(ptrauth_key_function_pointer, 1, 0)
+#define __ptrauth_block_byref_copy_helper                                      \
+  __ptrauth(ptrauth_key_function_pointer, 1, 0)
+#define __ptrauth_block_byref_destroy_helper                                   \
+  __ptrauth(ptrauth_key_function_pointer, 1, 0)
+#if __has_feature(ptrauth_signed_block_descriptors)
+#define __ptrauth_block_descriptor_pointer                                     \
+  __ptrauth(ptrauth_key_block_descriptor_pointer, 1, 0xC0BB)
+#else
+#define __ptrauth_block_descriptor_pointer
+#endif
+
+#define __ptrauth_cxx_vtable_pointer                                           \
+  __ptrauth(ptrauth_key_cxx_vtable_pointer, 0, 0)
+#define __ptrauth_cxx_vtt_vtable_pointer                                       \
+  __ptrauth(ptrauth_key_cxx_vtable_pointer, 0, 0)
+
 /* C++ vtable pointer signing class attribute */
 #define ptrauth_cxx_vtable_pointer(key, address_discrimination,                \
                                    extra_discrimination...)                    \
@@ -371,7 +428,10 @@ typedef __UINTPTR_TYPE__ ptrauth_generic_signature_t;
     ((ptrauth_extra_data_t)0);                                                 \
   })
 
+#define ptrauth_nop_cast(__type, __value) (__type)(__value)
 #define ptrauth_type_discriminator(__type) ((ptrauth_extra_data_t)0)
+#define ptrauth_function_pointer_type_discriminator(__type)                    \
+  ((ptrauth_extra_data_t)0)
 
 #define ptrauth_sign_generic_data(__value, __data)                             \
   ({                                                                           \
@@ -384,9 +444,23 @@ typedef __UINTPTR_TYPE__ ptrauth_generic_signature_t;
 #define ptrauth_cxx_vtable_pointer(key, address_discrimination,                \
                                    extra_discrimination...)
 
+#define __ptrauth_function_pointer(__typekey)
+#define __ptrauth_return_address
+#define __ptrauth_block_invocation_pointer
+#define __ptrauth_block_copy_helper
+#define __ptrauth_block_destroy_helper
+#define __ptrauth_block_byref_copy_helper
+#define __ptrauth_block_byref_destroy_helper
+#define __ptrauth_block_descriptor_pointer
+#define __ptrauth_objc_method_list_imp
+#define __ptrauth_objc_method_list_pointer
 #define __ptrauth_objc_isa_pointer
 #define __ptrauth_objc_isa_uintptr
 #define __ptrauth_objc_super_pointer
+#define __ptrauth_cxx_vtable_pointer
+#define __ptrauth_cxx_vtt_vtable_pointer
+#define __ptrauth_objc_sel
+#define __ptrauth_objc_class_ro
 
 #endif /* __has_feature(ptrauth_intrinsics) || defined(__PTRAUTH__) */