arch/arm64: disable fork support in protected build mode

Modify ARM64 architecture configuration to disable fork support in protected
build mode (BUILD_PROTECTED). Update ARCH_HAVE_FORK condition from
"!BUILD_KERNEL" to "!BUILD_KERNEL && !BUILD_PROTECTED", ensuring fork is
only available in flat/monolithic builds, not in protected kernel builds.

Signed-off-by: hujun5 <hujun5@xiaomi.com>

Documentation/reference/user/01_task_control.rst

@@ -358,7 +358,9 @@ Functions
      NOTE: ``vfork()`` is not an independent NuttX feature, but is
      implemented in architecture-specific logic (using only helper
      functions from the NuttX core logic). As a result, ``vfork()`` may
-     not be available on all architectures.
+     not be available on all architectures. The current implementation in
+     NuttX arm64 only guarantees that ``vfork()`` works when
+     CONFIG_BUILD_FLAT=y.
 
   :return: Upon successful completion, ``vfork()`` returns 0 to
     the child process and returns the process ID of the child process to the

arch/Kconfig

@@ -29,7 +29,7 @@ config ARCH_ARM64
 	select ARCH_64BIT
 	select ARCH_HAVE_BACKTRACE
 	select ARCH_HAVE_INTERRUPTSTACK
-	select ARCH_HAVE_FORK if !BUILD_KERNEL
+	select ARCH_HAVE_FORK if !BUILD_KERNEL && !BUILD_PROTECTED
 	select ARCH_HAVE_STACKCHECK
 	select ARCH_HAVE_CUSTOMOPT
 	select ARCH_HAVE_STDARG_H