[clang] [clang][PAC] Add ptrauth.h helpers for type diversity helpers (PR #163456)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: Oliver Hunt (ojhunt)

<details>
<summary>Changes</summary>

Adds an additional helper that had not been upstreamed, and adds documentation for both `ptrauth_type_discriminator` and `ptrauth_function_pointer_type_discriminator`

---
Full diff: https://github.com/llvm/llvm-project/pull/163456.diff


2 Files Affected:

- (modified) clang/docs/PointerAuthentication.rst (+30) 
- (modified) clang/lib/Headers/ptrauth.h (+12) 


``````````diff
diff --git a/clang/docs/PointerAuthentication.rst b/clang/docs/PointerAuthentication.rst
index 96eb498bc48b6..7e65f4b1b4915 100644
--- a/clang/docs/PointerAuthentication.rst
+++ b/clang/docs/PointerAuthentication.rst
@@ -592,6 +592,36 @@ The result value is never zero and always within range for both the
 
 This can be used in constant expressions.
 
+``ptrauth_type_discriminator``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c
+
+  ptrauth_type_discriminator(type)
+
+Compute the constant discriminator derived from the given type, as is computed
+for automatically type diversified schemas.
+
+``type`` must be a type. The result has the type ``ptrauth_extra_data_t``.
+
+This can be used in constant expressions.
+
+``ptrauth_function_pointer_type_discriminator``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c
+
+  ptrauth_function_pointer_type_discriminator(function_type)
+
+Compute the constant discriminator derived from the provided function type, for
+use in contexts where the default function authentication schema. If function
+pointer type diversity is enabled, this is equivalent to
+`ptrauth_type_discriminator(function_type)`, if it is not enabled this is `0`.
+
+``function_type`` must be a function type. The result has the type ``ptrauth_extra_data_t``.
+
+This can be used in constant expressions.
+
 ``ptrauth_strip``
 ^^^^^^^^^^^^^^^^^
 
diff --git a/clang/lib/Headers/ptrauth.h b/clang/lib/Headers/ptrauth.h
index f902ca1e3bbd3..1de8324e1ec6f 100644
--- a/clang/lib/Headers/ptrauth.h
+++ b/clang/lib/Headers/ptrauth.h
@@ -241,6 +241,17 @@ 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.
 
@@ -372,6 +383,7 @@ typedef __UINTPTR_TYPE__ ptrauth_generic_signature_t;
   })
 
 #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)                             \
   ({                                                                           \

``````````

</details>


https://github.com/llvm/llvm-project/pull/163456