v4.19.13 snapshot.
diff --git a/arch/arc/kernel/ctx_sw.c b/arch/arc/kernel/ctx_sw.c
new file mode 100644
index 0000000..9e1ae9d
--- /dev/null
+++ b/arch/arc/kernel/ctx_sw.c
@@ -0,0 +1,128 @@
+/*
+ * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Vineetg: Aug 2009
+ * -"C" version of lowest level context switch asm macro called by schedular
+ * gcc doesn't generate the dward CFI info for hand written asm, hence can't
+ * backtrace out of it (e.g. tasks sleeping in kernel).
+ * So we cheat a bit by writing almost similar code in inline-asm.
+ * -This is a hacky way of doing things, but there is no other simple way.
+ * I don't want/intend to extend unwinding code to understand raw asm
+ */
+
+#include <asm/asm-offsets.h>
+#include <linux/sched.h>
+#include <linux/sched/debug.h>
+#ifdef CONFIG_ARC_PLAT_EZNPS
+#include <plat/ctop.h>
+#endif
+
+#define KSP_WORD_OFF ((TASK_THREAD + THREAD_KSP) / 4)
+
+struct task_struct *__sched
+__switch_to(struct task_struct *prev_task, struct task_struct *next_task)
+{
+ unsigned int tmp;
+ unsigned int prev = (unsigned int)prev_task;
+ unsigned int next = (unsigned int)next_task;
+
+ __asm__ __volatile__(
+ /* FP/BLINK save generated by gcc (standard function prologue */
+ "st.a r13, [sp, -4] \n\t"
+ "st.a r14, [sp, -4] \n\t"
+ "st.a r15, [sp, -4] \n\t"
+ "st.a r16, [sp, -4] \n\t"
+ "st.a r17, [sp, -4] \n\t"
+ "st.a r18, [sp, -4] \n\t"
+ "st.a r19, [sp, -4] \n\t"
+ "st.a r20, [sp, -4] \n\t"
+ "st.a r21, [sp, -4] \n\t"
+ "st.a r22, [sp, -4] \n\t"
+ "st.a r23, [sp, -4] \n\t"
+ "st.a r24, [sp, -4] \n\t"
+#ifndef CONFIG_ARC_CURR_IN_REG
+ "st.a r25, [sp, -4] \n\t"
+#else
+ "sub sp, sp, 4 \n\t" /* usual r25 placeholder */
+#endif
+
+ /* set ksp of outgoing task in tsk->thread.ksp */
+#if KSP_WORD_OFF <= 255
+ "st.as sp, [%3, %1] \n\t"
+#else
+ /*
+ * Workaround for NR_CPUS=4k
+ * %1 is bigger than 255 (S9 offset for st.as)
+ */
+ "add2 r24, %3, %1 \n\t"
+ "st sp, [r24] \n\t"
+#endif
+
+ /*
+ * setup _current_task with incoming tsk.
+ * optionally, set r25 to that as well
+ * For SMP extra work to get to &_current_task[cpu]
+ * (open coded SET_CURR_TASK_ON_CPU)
+ */
+#ifndef CONFIG_SMP
+ "st %2, [@_current_task] \n\t"
+#else
+#ifdef CONFIG_ARC_PLAT_EZNPS
+ "lr r24, [%4] \n\t"
+#ifndef CONFIG_EZNPS_MTM_EXT
+ "lsr r24, r24, 4 \n\t"
+#endif
+#else
+ "lr r24, [identity] \n\t"
+ "lsr r24, r24, 8 \n\t"
+ "bmsk r24, r24, 7 \n\t"
+#endif
+ "add2 r24, @_current_task, r24 \n\t"
+ "st %2, [r24] \n\t"
+#endif
+#ifdef CONFIG_ARC_CURR_IN_REG
+ "mov r25, %2 \n\t"
+#endif
+
+ /* get ksp of incoming task from tsk->thread.ksp */
+ "ld.as sp, [%2, %1] \n\t"
+
+ /* start loading it's CALLEE reg file */
+
+#ifndef CONFIG_ARC_CURR_IN_REG
+ "ld.ab r25, [sp, 4] \n\t"
+#else
+ "add sp, sp, 4 \n\t"
+#endif
+ "ld.ab r24, [sp, 4] \n\t"
+ "ld.ab r23, [sp, 4] \n\t"
+ "ld.ab r22, [sp, 4] \n\t"
+ "ld.ab r21, [sp, 4] \n\t"
+ "ld.ab r20, [sp, 4] \n\t"
+ "ld.ab r19, [sp, 4] \n\t"
+ "ld.ab r18, [sp, 4] \n\t"
+ "ld.ab r17, [sp, 4] \n\t"
+ "ld.ab r16, [sp, 4] \n\t"
+ "ld.ab r15, [sp, 4] \n\t"
+ "ld.ab r14, [sp, 4] \n\t"
+ "ld.ab r13, [sp, 4] \n\t"
+
+ /* last (ret value) = prev : although for ARC it mov r0, r0 */
+ "mov %0, %3 \n\t"
+
+ /* FP/BLINK restore generated by gcc (standard func epilogue */
+
+ : "=r"(tmp)
+ : "n"(KSP_WORD_OFF), "r"(next), "r"(prev)
+#ifdef CONFIG_ARC_PLAT_EZNPS
+ , "i"(CTOP_AUX_LOGIC_GLOBAL_ID)
+#endif
+ : "blink"
+ );
+
+ return (struct task_struct *)tmp;
+}