diff --git a/executer/include/uprotocol.h b/executer/include/uprotocol.h
index dedfc373..dc2c037c 100644
--- a/executer/include/uprotocol.h
+++ b/executer/include/uprotocol.h
@@ -55,7 +55,7 @@
 #define MCEXEC_UP_SYS_UNSHARE    0x30a02916
 
 #define MCEXEC_UP_UTI_GET_CTX    0x30a02920
-#define MCEXEC_UP_UTI_SAVE_FS    0x30a02921
+#define MCEXEC_UP_UTI_SWITCH_CTX 0x30a02921
 #define MCEXEC_UP_SIG_THREAD     0x30a02922
 #define MCEXEC_UP_SYSCALL_THREAD 0x30a02924
 #define MCEXEC_UP_TERMINATE_THREAD 0x30a02925
diff --git a/executer/kernel/mcctrl/arch/arm64/archdeps.c b/executer/kernel/mcctrl/arch/arm64/archdeps.c
index 09a7c488..63189245 100644
--- a/executer/kernel/mcctrl/arch/arm64/archdeps.c
+++ b/executer/kernel/mcctrl/arch/arm64/archdeps.c
@@ -1,7 +1,12 @@
-/* archdeps.c COPYRIGHT FUJITSU LIMITED 2016 */
+/* archdeps.c COPYRIGHT FUJITSU LIMITED 2016-2019 */
 #include <linux/version.h>
 #include <linux/mm_types.h>
 #include <linux/kallsyms.h>
+#if KERNEL_VERSION(4, 11, 0) <= LINUX_VERSION_CODE
+#include <linux/sched/task_stack.h>
+#endif /* LINUX_VERSION_CODE >= KERNEL_VERSION(4, 11, 0) */
+#include <linux/ptrace.h>
+#include <linux/uaccess.h>
 #include <asm/vdso.h>
 #include "config.h"
 #include "../../mcctrl.h"
@@ -150,30 +155,11 @@ set_user_sp(void *usp)
 	/* TODO; skeleton for UTI */
 }
 
-/* TODO; skeleton for UTI */
 struct trans_uctx {
 	volatile int cond;
 	int fregsize;
-
-	unsigned long rax;
-	unsigned long rbx;
-	unsigned long rcx;
-	unsigned long rdx;
-	unsigned long rsi;
-	unsigned long rdi;
-	unsigned long rbp;
-	unsigned long r8;
-	unsigned long r9;
-	unsigned long r10;
-	unsigned long r11;
-	unsigned long r12;
-	unsigned long r13;
-	unsigned long r14;
-	unsigned long r15;
-	unsigned long rflags;
-	unsigned long rip;
-	unsigned long rsp;
-	unsigned long fs;
+	struct user_pt_regs regs;
+	unsigned long tls_baseaddr;
 };
 
 void
@@ -302,3 +288,38 @@ out:
 			error, rva, rpa, pgsize);
 	return error;
 }
+
+/*
+ * Assembler switch_ctx executes only ioctl.
+ * Context register save/load is done on Linux (get from current_pt_regs).
+ * Do TLS save/load and register host_thread with ioctl.
+ */
+long arch_switch_ctx(struct uti_save_fs_desc *desc)
+{
+	int rc = 0;
+	struct trans_uctx *__user rctx = NULL;
+	struct trans_uctx *__user lctx = NULL;
+	struct trans_uctx klctx = {
+		.regs = current_pt_regs()->user_regs,
+	};
+
+	rctx = desc->rctx;
+	lctx = desc->lctx;
+
+	if (copy_to_user(lctx, &klctx, sizeof(klctx))) {
+		pr_err("%s: Error: copy_to_user failed\n", __func__);
+		rc = -EFAULT;
+		goto out;
+	}
+
+	if (copy_from_user(&current_pt_regs()->user_regs,
+			   &rctx->regs, sizeof(rctx->regs))) {
+		pr_err("%s: Error: copy_from_user failed\n", __func__);
+		rc = -EFAULT;
+		goto out;
+	}
+	restore_fs(get_fs_ctx(rctx));
+
+out:
+	return rc;
+}
diff --git a/executer/kernel/mcctrl/arch/x86_64/archdeps.c b/executer/kernel/mcctrl/arch/x86_64/archdeps.c
index 88bbe312..06c60479 100644
--- a/executer/kernel/mcctrl/arch/x86_64/archdeps.c
+++ b/executer/kernel/mcctrl/arch/x86_64/archdeps.c
@@ -368,3 +368,11 @@ static inline bool pte_is_write_combined(pte_t pte)
 }
 #endif /* POSTK_DEBUG_ARCH_DEP_12 */
 
+/*
+ * The assembler switch_ctx is save/load registers in the context.
+ * Do FS save/load and register host_thread with ioctl.
+ */
+long arch_switch_ctx(struct uti_save_fs_desc *desc)
+{
+	return 0;
+}
diff --git a/executer/kernel/mcctrl/control.c b/executer/kernel/mcctrl/control.c
index 29cfa07e..d1539671 100644
--- a/executer/kernel/mcctrl/control.c
+++ b/executer/kernel/mcctrl/control.c
@@ -319,17 +319,6 @@ struct mcos_handler_info;
 static LIST_HEAD(host_threads); /* Used for FS switch */
 DEFINE_RWLOCK(host_thread_lock);
 
-/* Info of Linux counterpart of migrated-to-Linux thread */
-struct host_thread {
-	struct list_head list;
-	struct mcos_handler_info *handler;
-	int     pid;
-	int     tid;
-	unsigned long usp;
-	unsigned long lfs;
-	unsigned long rfs;
-};
-
 struct mcos_handler_info *new_mcos_handler_info(ihk_os_t os, struct file *file)
 {
 	struct mcos_handler_info *info;
@@ -2492,7 +2481,8 @@ long mcexec_uti_get_ctx(ihk_os_t os, struct uti_get_ctx_desc __user *udesc)
 	return rc;
 }
 
-long mcexec_uti_save_fs(ihk_os_t os, struct uti_save_fs_desc __user *udesc, struct file *file)
+long mcctrl_switch_ctx(ihk_os_t os, struct uti_save_fs_desc __user *udesc,
+		       struct file *file)
 {
 	int rc = 0;
 	void *usp = get_user_sp();
@@ -2509,12 +2499,17 @@ long mcexec_uti_save_fs(ihk_os_t os, struct uti_save_fs_desc __user *udesc, stru
 		goto out;
 	}
 
-	if(copy_from_user(&desc, udesc, sizeof(struct uti_save_fs_desc))) {
+	if (copy_from_user(&desc, udesc, sizeof(struct uti_save_fs_desc))) {
 		printk("%s: Error: copy_from_user failed\n", __FUNCTION__);
 		rc = -EFAULT;
 		goto out;
 	}
 
+	rc = arch_switch_ctx(&desc);
+	if (rc < 0) {
+		goto out;
+	}
+
 	save_fs_ctx(desc.lctx);
 	info = ihk_os_get_mcos_private_data(file);
 	thread = kmalloc(sizeof(struct host_thread), GFP_KERNEL);
@@ -3272,8 +3267,9 @@ long __mcctrl_control(ihk_os_t os, unsigned int req, unsigned long arg,
 	case MCEXEC_UP_UTI_GET_CTX:
 		return mcexec_uti_get_ctx(os, (struct uti_get_ctx_desc *)arg);
 
-	case MCEXEC_UP_UTI_SAVE_FS:
-		return mcexec_uti_save_fs(os, (struct uti_save_fs_desc *)arg, file);
+	case MCEXEC_UP_UTI_SWITCH_CTX:
+		return mcctrl_switch_ctx(os, (struct uti_save_fs_desc *)arg,
+					 file);
 
 	case MCEXEC_UP_SIG_THREAD:
 		return mcexec_sig_thread(os, arg, file);
diff --git a/executer/kernel/mcctrl/driver.c b/executer/kernel/mcctrl/driver.c
index d521074a..30588b30 100644
--- a/executer/kernel/mcctrl/driver.c
+++ b/executer/kernel/mcctrl/driver.c
@@ -86,7 +86,7 @@ static struct ihk_os_user_call_handler mcctrl_uchs[] = {
 	{ .request = MCEXEC_UP_SYS_UNSHARE, .func = mcctrl_ioctl },
 #endif // MCEXEC_BIND_MOUNT
 	{ .request = MCEXEC_UP_UTI_GET_CTX, .func = mcctrl_ioctl },
-	{ .request = MCEXEC_UP_UTI_SAVE_FS, .func = mcctrl_ioctl },
+	{ .request = MCEXEC_UP_UTI_SWITCH_CTX, .func = mcctrl_ioctl },
 	{ .request = MCEXEC_UP_SIG_THREAD, .func = mcctrl_ioctl },
 	{ .request = MCEXEC_UP_SYSCALL_THREAD, .func = mcctrl_ioctl },
 	{ .request = MCEXEC_UP_TERMINATE_THREAD, .func = mcctrl_ioctl },
diff --git a/executer/kernel/mcctrl/mcctrl.h b/executer/kernel/mcctrl/mcctrl.h
index ac2c0dcb..eca0604c 100644
--- a/executer/kernel/mcctrl/mcctrl.h
+++ b/executer/kernel/mcctrl/mcctrl.h
@@ -124,12 +124,6 @@ enum mcctrl_os_cpu_operation {
 	MCCTRL_OS_CPU_MAX_OP
 };
 
-/* Used to wake-up a Linux thread futex_wait()-ing */
-struct uti_futex_resp {
-	int done;
-	wait_queue_head_t wq;
-};
-
 struct ikc_scd_packet {
 	struct ihk_ikc_packet_header header;
 	int msg;
@@ -570,4 +564,24 @@ struct mcctrl_ioctl_getrusage_desc {
 	size_t size_rusage;
 };
 
+/* uti */
+long mcctrl_switch_ctx(ihk_os_t os, struct uti_save_fs_desc __user *desc,
+			struct file *file);
+long arch_switch_ctx(struct uti_save_fs_desc *desc);
+
+struct host_thread {
+	struct list_head list;
+	struct mcos_handler_info *handler;
+	int     pid;
+	int     tid;
+	unsigned long usp;
+	unsigned long lfs;
+	unsigned long rfs;
+};
+
+/* Used to wake-up a Linux thread futex_wait()-ing */
+struct uti_futex_resp {
+	int done;
+	wait_queue_head_t wq;
+};
 #endif
diff --git a/executer/user/arch/arm64/archdep.S b/executer/user/arch/arm64/archdep.S
index 57f19660..5e88dc1a 100644
--- a/executer/user/arch/arm64/archdep.S
+++ b/executer/user/arch/arm64/archdep.S
@@ -1,4 +1,4 @@
-/* archdep.S COPYRIGHT FUJITSU LIMITED 2017-2018 */
+/* archdep.S COPYRIGHT FUJITSU LIMITED 2017-2019 */
 
 #include <sys/syscall.h>
 
@@ -11,6 +11,8 @@
  *     x2 : void **param
  *     x3 : void *lctx
  *     x4 : void *rctx
+ *
+ * Save and switch the context including TLS.
  */
 .global switch_ctx
 switch_ctx:
diff --git a/executer/user/arch/x86_64/archdep.S b/executer/user/arch/x86_64/archdep.S
index 6cc5351d..5a26cd81 100644
--- a/executer/user/arch/x86_64/archdep.S
+++ b/executer/user/arch/x86_64/archdep.S
@@ -17,6 +17,8 @@ Syscam call convention:
   rdi:	 fd
   rsi:	cmd
   rdx:	param
+
+  Save and switch the context including FS.
 */
 
 .global switch_ctx
diff --git a/executer/user/mcexec.c b/executer/user/mcexec.c
index b893c672..97d5aba8 100644
--- a/executer/user/mcexec.c
+++ b/executer/user/mcexec.c
@@ -2894,7 +2894,8 @@ static long util_thread(struct thread_data_s *my_thread, unsigned long rp_rctx,
 	save_fs_desc.rctx = uti_desc->rctx;
 	save_fs_desc.lctx = uti_desc->lctx;
 
-	if ((rc = switch_ctx(fd, MCEXEC_UP_UTI_SAVE_FS, &save_fs_desc, uti_desc->lctx, uti_desc->rctx))
+	if ((rc = switch_ctx(fd, MCEXEC_UP_UTI_SWITCH_CTX, &save_fs_desc,
+			     uti_desc->lctx, uti_desc->rctx))
 	    < 0) {
 		fprintf(stderr, "%s: ERROR switch_ctx failed (%d)\n", __FUNCTION__, rc);
 		goto out;