Changes from last revision:

Remove the mention of SME support routines and __builtin_cpu_supports
as there is no obligation that they use __aarch64_cpu_features. Instead
say that the variable can only be placed in RELRO if it is only accessed
by FMV resolvers. Otherwise, if used by compiler generated code or the
runtime library then it requires constructor init and cannot be in RELRO.

Author: labrinea

sysvabi64/sysvabi64.rst

@@ -1716,23 +1716,19 @@ The variable may contain the following fields:
     +-------------------+----------+
 
 Implementing FMV using ``__aarch64_cpu_features`` is not required.
-Accessing this variable from outside a FMV resolver function is
-not well defined. The variable may be placed in the
-`Relocation Read Only (RELRO)`_ program segment to prevent it
-from being modified after the FMV resolvers have run. The
-variable must be defined as DSO-local with its symbol visibility
-set to ``STV_HIDDEN``.
+Accessing this variable from outside a FMV resolver function is not
+well defined. If the variable is only accessed by the FMV resolvers,
+then it may be placed in the `Relocation Read Only (RELRO)`_ program
+segment to prevent it from being modified after the FMV resolvers
+have run. The variable must be defined as DSO-local with its symbol
+visibility set to ``STV_HIDDEN``.
 
 .. note::
 
-   Both the SME support routines (see AAPCS64_ for more information)
-   and the compiler built-in function ``__builtin_cpu_supports`` rely
-   on the ``__aarch64_cpu_features`` variable for detecting CPU features.
-   Therefore the runtime library must ensure that the variable is
-   initialized prior to their usage. FMV support is not required for
-   using the SME support routines or the ``__builtin_cpu_supports``
-   function. The ``__aarch64_cpu_features`` variable should not be
-   placed in ``RELRO`` if no FMV resolver has run.
+   The ``__aarch64_cpu_features`` variable may be used by the runtime
+   library or by compiler generated code besides FMV. In that case the
+   runtime library must ensure that the variable is initialized via a
+   constructor function and cannot be placed in the ``RELRO`` segment.
 
 The ``__init_cpu_features_resolver`` function has the following
 prototype: