[clang] Define ptrauth_string_discriminator builtin. (#93903)

This exposes the ABI-stable hash function that allows computing a 16-bit
discriminator from a constant string.

This allows manually matching the implicit string discriminators
computed in the ABI (e.g., from mangled names for vtable pointer/entry
signing), as well as enabling the use of interesting discriminators when
manually annotating specific pointers with the __ptrauth qualifier.

The argument must be a string literal of char character type.  The
result has type ptrauth_extra_data_t.
The result value is never zero and always within range for both the
__ptrauth qualifier and ptrauth_blend_discriminator.
This can be used in constant expressions.

Co-authored-by: John McCall <rjmccall@apple.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/clang/docs/PointerAuthentication.rst b/clang/docs/PointerAuthentication.rst
index 19b3384..130e657 100644
--- a/clang/docs/PointerAuthentication.rst
+++ b/clang/docs/PointerAuthentication.rst
@@ -328,6 +328,23 @@ be done in a single instruction with an immediate integer.
 ``pointer`` must have pointer type, and ``integer`` must have integer type. The
 result has type ``ptrauth_extra_data_t``.
 
+``ptrauth_string_discriminator``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: c
+
+  ptrauth_string_discriminator(string)
+
+Compute a constant discriminator from the given string.
+
+``string`` must be a string literal of ``char`` character type.  The result has
+type ``ptrauth_extra_data_t``.
+
+The result value is never zero and always within range for both the
+``__ptrauth`` qualifier and ``ptrauth_blend_discriminator``.
+
+This can be used in constant expressions.
+
 ``ptrauth_strip``
 ^^^^^^^^^^^^^^^^^