arm64: Make some stacktrace functions private

Now that open-coded stack unwinds have been converted to
arch_stack_walk(), we no longer need to expose any of unwind_frame(),
walk_stackframe(), or start_backtrace() outside of stacktrace.c.

Make those functions private to stacktrace.c, removing their prototypes
from <asm/stacktrace.h> and marking them static.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Cc: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
Link: https://lore.kernel.org/r/20211129142849.3056714-10-mark.rutland@arm.comSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/stacktrace.h

@@ -63,9 +63,6 @@ struct stackframe {
 #endif
 };
 
-extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame);
-extern void walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
-			    bool (*fn)(void *, unsigned long), void *data);
 extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
 			   const char *loglvl);
 
@@ -150,7 +147,4 @@ static inline bool on_accessible_stack(const struct task_struct *tsk,
 	return false;
 }
 
-void start_backtrace(struct stackframe *frame, unsigned long fp,
-		     unsigned long pc);
-
 #endif	/* __ASM_STACKTRACE_H */

arch/arm64/kernel/stacktrace.c

@@ -33,8 +33,8 @@
  */
 
 
-void start_backtrace(struct stackframe *frame, unsigned long fp,
-		     unsigned long pc)
+static void start_backtrace(struct stackframe *frame, unsigned long fp,
+			    unsigned long pc)
 {
 	frame->fp = fp;
 	frame->pc = pc;
@@ -63,7 +63,8 @@ void start_backtrace(struct stackframe *frame, unsigned long fp,
  * records (e.g. a cycle), determined based on the location and fp value of A
  * and the location (but not the fp value) of B.
  */
-int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
+static int notrace unwind_frame(struct task_struct *tsk,
+				struct stackframe *frame)
 {
 	unsigned long fp = frame->fp;
 	struct stack_info info;
@@ -141,8 +142,9 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
 }
 NOKPROBE_SYMBOL(unwind_frame);
 
-void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
-			     bool (*fn)(void *, unsigned long), void *data)
+static void notrace walk_stackframe(struct task_struct *tsk,
+				    struct stackframe *frame,
+				    bool (*fn)(void *, unsigned long), void *data)
 {
 	while (1) {
 		int ret;