[clang] [clang][PAC][NFC] Provide addition support macros to ptrauth.h (PR #161027)
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Sat Sep 27 16:26:32 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-x86
Author: Oliver Hunt (ojhunt)
<details>
<summary>Changes</summary>
This introduces a number of additional macros to support the use of manual pointer authentication.
---
Full diff: https://github.com/llvm/llvm-project/pull/161027.diff
2 Files Affected:
- (modified) clang/docs/PointerAuthentication.rst (+34)
- (modified) clang/lib/Headers/ptrauth.h (+73)
``````````diff
diff --git a/clang/docs/PointerAuthentication.rst b/clang/docs/PointerAuthentication.rst
index 96eb498bc48b6..eb4eaf08b854e 100644
--- a/clang/docs/PointerAuthentication.rst
+++ b/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
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Headers/ptrauth.h b/clang/lib/Headers/ptrauth.h
index f902ca1e3bbd3..1544456e189b4 100644
--- a/clang/lib/Headers/ptrauth.h
+++ b/clang/lib/Headers/ptrauth.h
@@ -199,6 +199,23 @@ 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 +258,18 @@ 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 +292,33 @@ 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 +427,10 @@ 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 +443,23 @@ 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__) */
``````````
</details>
https://github.com/llvm/llvm-project/pull/161027
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