xtensa: Implement copy_thread_tls

This is required for clone3 which passes the TLS value through a
struct rather than a register.

Signed-off-by: Amanieu d'Antras <amanieu@gmail.com>
Cc: linux-xtensa@linux-xtensa.org
Cc: <stable@vger.kernel.org> # 5.3.x
Link: https://lore.kernel.org/r/20200102172413.654385-7-amanieu@gmail.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Author: Amanieu

arch/xtensa/Kconfig

@@ -24,6 +24,7 @@ config XTENSA
 	select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL
 	select HAVE_ARCH_KASAN if MMU && !XIP_KERNEL
 	select HAVE_ARCH_TRACEHOOK
+	select HAVE_COPY_THREAD_TLS
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DMA_CONTIGUOUS
 	select HAVE_EXIT_THREAD

arch/xtensa/kernel/process.c

@@ -202,8 +202,9 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
  * involved.  Much simpler to just not copy those live frames across.
  */
 
-int copy_thread(unsigned long clone_flags, unsigned long usp_thread_fn,
-		unsigned long thread_fn_arg, struct task_struct *p)
+int copy_thread_tls(unsigned long clone_flags, unsigned long usp_thread_fn,
+		unsigned long thread_fn_arg, struct task_struct *p,
+		unsigned long tls)
 {
 	struct pt_regs *childregs = task_pt_regs(p);
 
@@ -266,9 +267,8 @@ int copy_thread(unsigned long clone_flags, unsigned long usp_thread_fn,
 
 		childregs->syscall = regs->syscall;
 
-		/* The thread pointer is passed in the '4th argument' (= a5) */
 		if (clone_flags & CLONE_SETTLS)
-			childregs->threadptr = childregs->areg[5];
+			childregs->threadptr = tls;
 	} else {
 		p->thread.ra = MAKE_RA_FOR_CALL(
 				(unsigned long)ret_from_kernel_thread, 1);