v4.19.13 snapshot.
diff --git a/arch/arc/kernel/stacktrace.c b/arch/arc/kernel/stacktrace.c
new file mode 100644
index 0000000..bf40e06
--- /dev/null
+++ b/arch/arc/kernel/stacktrace.c
@@ -0,0 +1,263 @@
+/*
+ * stacktrace.c : stacktracing APIs needed by rest of kernel
+ * (wrappers over ARC dwarf based unwinder)
+ *
+ * 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
+ * -Implemented CONFIG_STACKTRACE APIs, primarily save_stack_trace_tsk( )
+ * for displaying task's kernel mode call stack in /proc/<pid>/stack
+ * -Iterator based approach to have single copy of unwinding core and APIs
+ * needing unwinding, implement the logic in iterator regarding:
+ * = which frame onwards to start capture
+ * = which frame to stop capturing (wchan)
+ * = specifics of data structs where trace is saved(CONFIG_STACKTRACE etc)
+ *
+ * vineetg: March 2009
+ * -Implemented correct versions of thread_saved_pc() and get_wchan()
+ *
+ * rajeshwarr: 2008
+ * -Initial implementation
+ */
+
+#include <linux/ptrace.h>
+#include <linux/export.h>
+#include <linux/stacktrace.h>
+#include <linux/kallsyms.h>
+#include <linux/sched/debug.h>
+
+#include <asm/arcregs.h>
+#include <asm/unwind.h>
+#include <asm/switch_to.h>
+
+/*-------------------------------------------------------------------------
+ * Unwinder Iterator
+ *-------------------------------------------------------------------------
+ */
+
+#ifdef CONFIG_ARC_DW2_UNWIND
+
+static void seed_unwind_frame_info(struct task_struct *tsk,
+ struct pt_regs *regs,
+ struct unwind_frame_info *frame_info)
+{
+ /*
+ * synchronous unwinding (e.g. dump_stack)
+ * - uses current values of SP and friends
+ */
+ if (tsk == NULL && regs == NULL) {
+ unsigned long fp, sp, blink, ret;
+ frame_info->task = current;
+
+ __asm__ __volatile__(
+ "mov %0,r27\n\t"
+ "mov %1,r28\n\t"
+ "mov %2,r31\n\t"
+ "mov %3,r63\n\t"
+ : "=r"(fp), "=r"(sp), "=r"(blink), "=r"(ret)
+ );
+
+ frame_info->regs.r27 = fp;
+ frame_info->regs.r28 = sp;
+ frame_info->regs.r31 = blink;
+ frame_info->regs.r63 = ret;
+ frame_info->call_frame = 0;
+ } else if (regs == NULL) {
+ /*
+ * Asynchronous unwinding of sleeping task
+ * - Gets SP etc from task's pt_regs (saved bottom of kernel
+ * mode stack of task)
+ */
+
+ frame_info->task = tsk;
+
+ frame_info->regs.r27 = TSK_K_FP(tsk);
+ frame_info->regs.r28 = TSK_K_ESP(tsk);
+ frame_info->regs.r31 = TSK_K_BLINK(tsk);
+ frame_info->regs.r63 = (unsigned int)__switch_to;
+
+ /* In the prologue of __switch_to, first FP is saved on stack
+ * and then SP is copied to FP. Dwarf assumes cfa as FP based
+ * but we didn't save FP. The value retrieved above is FP's
+ * state in previous frame.
+ * As a work around for this, we unwind from __switch_to start
+ * and adjust SP accordingly. The other limitation is that
+ * __switch_to macro is dwarf rules are not generated for inline
+ * assembly code
+ */
+ frame_info->regs.r27 = 0;
+ frame_info->regs.r28 += 60;
+ frame_info->call_frame = 0;
+
+ } else {
+ /*
+ * Asynchronous unwinding of intr/exception
+ * - Just uses the pt_regs passed
+ */
+ frame_info->task = tsk;
+
+ frame_info->regs.r27 = regs->fp;
+ frame_info->regs.r28 = regs->sp;
+ frame_info->regs.r31 = regs->blink;
+ frame_info->regs.r63 = regs->ret;
+ frame_info->call_frame = 0;
+ }
+}
+
+#endif
+
+notrace noinline unsigned int
+arc_unwind_core(struct task_struct *tsk, struct pt_regs *regs,
+ int (*consumer_fn) (unsigned int, void *), void *arg)
+{
+#ifdef CONFIG_ARC_DW2_UNWIND
+ int ret = 0;
+ unsigned int address;
+ struct unwind_frame_info frame_info;
+
+ seed_unwind_frame_info(tsk, regs, &frame_info);
+
+ while (1) {
+ address = UNW_PC(&frame_info);
+
+ if (!address || !__kernel_text_address(address))
+ break;
+
+ if (consumer_fn(address, arg) == -1)
+ break;
+
+ ret = arc_unwind(&frame_info);
+ if (ret)
+ break;
+
+ frame_info.regs.r63 = frame_info.regs.r31;
+ }
+
+ return address; /* return the last address it saw */
+#else
+ /* On ARC, only Dward based unwinder works. fp based backtracing is
+ * not possible (-fno-omit-frame-pointer) because of the way function
+ * prelogue is setup (callee regs saved and then fp set and not other
+ * way around
+ */
+ pr_warn_once("CONFIG_ARC_DW2_UNWIND needs to be enabled\n");
+ return 0;
+
+#endif
+}
+
+/*-------------------------------------------------------------------------
+ * callbacks called by unwinder iterator to implement kernel APIs
+ *
+ * The callback can return -1 to force the iterator to stop, which by default
+ * keeps going till the bottom-most frame.
+ *-------------------------------------------------------------------------
+ */
+
+/* Call-back which plugs into unwinding core to dump the stack in
+ * case of panic/OOPs/BUG etc
+ */
+static int __print_sym(unsigned int address, void *unused)
+{
+ printk(" %pS\n", (void *)address);
+ return 0;
+}
+
+#ifdef CONFIG_STACKTRACE
+
+/* Call-back which plugs into unwinding core to capture the
+ * traces needed by kernel on /proc/<pid>/stack
+ */
+static int __collect_all(unsigned int address, void *arg)
+{
+ struct stack_trace *trace = arg;
+
+ if (trace->skip > 0)
+ trace->skip--;
+ else
+ trace->entries[trace->nr_entries++] = address;
+
+ if (trace->nr_entries >= trace->max_entries)
+ return -1;
+
+ return 0;
+}
+
+static int __collect_all_but_sched(unsigned int address, void *arg)
+{
+ struct stack_trace *trace = arg;
+
+ if (in_sched_functions(address))
+ return 0;
+
+ if (trace->skip > 0)
+ trace->skip--;
+ else
+ trace->entries[trace->nr_entries++] = address;
+
+ if (trace->nr_entries >= trace->max_entries)
+ return -1;
+
+ return 0;
+}
+
+#endif
+
+static int __get_first_nonsched(unsigned int address, void *unused)
+{
+ if (in_sched_functions(address))
+ return 0;
+
+ return -1;
+}
+
+/*-------------------------------------------------------------------------
+ * APIs expected by various kernel sub-systems
+ *-------------------------------------------------------------------------
+ */
+
+noinline void show_stacktrace(struct task_struct *tsk, struct pt_regs *regs)
+{
+ pr_info("\nStack Trace:\n");
+ arc_unwind_core(tsk, regs, __print_sym, NULL);
+}
+EXPORT_SYMBOL(show_stacktrace);
+
+/* Expected by sched Code */
+void show_stack(struct task_struct *tsk, unsigned long *sp)
+{
+ show_stacktrace(tsk, NULL);
+}
+
+/* Another API expected by schedular, shows up in "ps" as Wait Channel
+ * Of course just returning schedule( ) would be pointless so unwind until
+ * the function is not in schedular code
+ */
+unsigned int get_wchan(struct task_struct *tsk)
+{
+ return arc_unwind_core(tsk, NULL, __get_first_nonsched, NULL);
+}
+
+#ifdef CONFIG_STACKTRACE
+
+/*
+ * API required by CONFIG_STACKTRACE, CONFIG_LATENCYTOP.
+ * A typical use is when /proc/<pid>/stack is queried by userland
+ */
+void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
+{
+ /* Assumes @tsk is sleeping so unwinds from __switch_to */
+ arc_unwind_core(tsk, NULL, __collect_all_but_sched, trace);
+}
+
+void save_stack_trace(struct stack_trace *trace)
+{
+ /* Pass NULL for task so it unwinds the current call frame */
+ arc_unwind_core(NULL, NULL, __collect_all, trace);
+}
+EXPORT_SYMBOL_GPL(save_stack_trace);
+#endif