alpha: switch to copy_thread_tls()

Use the copy_thread_tls() calling convention which passes tls through a
register. This is required so we can remove the copy_thread{_tls}() split
and remove the HAVE_COPY_THREAD_TLS macro.

Cc: linux-alpha@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

arch/alpha/Kconfig

@@ -38,6 +38,7 @@ config ALPHA
 	select OLD_SIGSUSPEND
 	select CPU_NO_EFFICIENT_FFS if !ALPHA_EV67
 	select MMU_GATHER_NO_RANGE
+	select HAVE_COPY_THREAD_TLS
 	help
 	  The Alpha is a 64-bit general-purpose processor designed and
 	  marketed by the Digital Equipment Corporation of blessed memory,

arch/alpha/kernel/process.c

@@ -233,10 +233,9 @@ release_thread(struct task_struct *dead_task)
 /*
  * Copy architecture-specific thread state
  */
-int
-copy_thread(unsigned long clone_flags, unsigned long usp,
-	    unsigned long kthread_arg,
-	    struct task_struct *p)
+int copy_thread_tls(unsigned long clone_flags, unsigned long usp,
+		    unsigned long kthread_arg, struct task_struct *p,
+		    unsigned long tls)
 {
 	extern void ret_from_fork(void);
 	extern void ret_from_kernel_thread(void);
@@ -267,7 +266,7 @@ copy_thread(unsigned long clone_flags, unsigned long usp,
 	   required for proper operation in the case of a threaded
 	   application calling fork.  */
 	if (clone_flags & CLONE_SETTLS)
-		childti->pcb.unique = regs->r20;
+		childti->pcb.unique = tls;
 	else
 		regs->r20 = 0;	/* OSF/1 has some strange fork() semantics.  */
 	childti->pcb.usp = usp ?: rdusp();