riscv: 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-riscv@lists.infradead.org
Cc: <stable@vger.kernel.org> # 5.3.x
Link: https://lore.kernel.org/r/20200102172413.654385-6-amanieu@gmail.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

arch/riscv/Kconfig

@@ -65,6 +65,7 @@ config RISCV
 	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
 	select HAVE_ARCH_MMAP_RND_BITS if MMU
 	select ARCH_HAS_GCOV_PROFILE_ALL
+	select HAVE_COPY_THREAD_TLS
 
 config ARCH_MMAP_RND_BITS_MIN
 	default 18 if 64BIT

arch/riscv/kernel/process.c

@@ -99,8 +99,8 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 	return 0;
 }
 
-int copy_thread(unsigned long clone_flags, unsigned long usp,
-	unsigned long arg, struct task_struct *p)
+int copy_thread_tls(unsigned long clone_flags, unsigned long usp,
+	unsigned long arg, struct task_struct *p, unsigned long tls)
 {
 	struct pt_regs *childregs = task_pt_regs(p);
 
@@ -121,7 +121,7 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
 		if (usp) /* User fork */
 			childregs->sp = usp;
 		if (clone_flags & CLONE_SETTLS)
-			childregs->tp = childregs->a5;
+			childregs->tp = tls;
 		childregs->a0 = 0; /* Return value of fork() */
 		p->thread.ra = (unsigned long)ret_from_fork;
 	}