ARC: Make arc_unwind_core accessible externally

The arc unwinder can also be used for perf callchains.
Signed-off-by: Mischa Jonker <mjonker@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/include/asm/stacktrace.h

+/*
+ * Copyright (C) 2014-15 Synopsys, Inc. (www.synopsys.com)
+ * Copyright (C) 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.
+ */
+
+#ifndef __ASM_STACKTRACE_H
+#define __ASM_STACKTRACE_H
+
+#include <linux/sched.h>
+
+/**
+ * arc_unwind_core - Unwind the kernel mode stack for an execution context
+ * @tsk:		NULL for current task, specific task otherwise
+ * @regs:		pt_regs used to seed the unwinder {SP, FP, BLINK, PC}
+ * 			If NULL, use pt_regs of @tsk (if !NULL) otherwise
+ * 			use the current values of {SP, FP, BLINK, PC}
+ * @consumer_fn:	Callback invoked for each frame unwound
+ * 			Returns 0 to continue unwinding, -1 to stop
+ * @arg:		Arg to callback
+ *
+ * Returns the address of first function in stack
+ *
+ * Semantics:
+ *  - synchronous unwinding (e.g. dump_stack): @tsk  NULL, @regs  NULL
+ *  - Asynchronous unwinding of sleeping task: @tsk !NULL, @regs  NULL
+ *  - Asynchronous unwinding of intr/excp etc: @tsk !NULL, @regs !NULL
+ */
+notrace noinline unsigned int arc_unwind_core(
+	struct task_struct *tsk, struct pt_regs *regs,
+	int (*consumer_fn) (unsigned int, void *),
+	void *arg);
+
+#endif /* __ASM_STACKTRACE_H */

arch/arc/kernel/stacktrace.c

@@ -43,6 +43,10 @@ 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;
@@ -61,6 +65,11 @@ static void seed_unwind_frame_info(struct task_struct *tsk,
 		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;
 
@@ -83,6 +92,10 @@ static void seed_unwind_frame_info(struct task_struct *tsk,
 		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;
@@ -95,7 +108,7 @@ static void seed_unwind_frame_info(struct task_struct *tsk,
 
 #endif
 
-static noinline unsigned int
+notrace noinline unsigned int
 arc_unwind_core(struct task_struct *tsk, struct pt_regs *regs,
 		int (*consumer_fn) (unsigned int, void *), void *arg)
 {