sparc32: make show_stack() acquire %fp if @_ksp is not specified

show_stack(current or NULL, NULL) is used by arch-independent code to dump
backtrace of the current task; however, sparc32 show_stack() doesn't
implement it and wouldn't print any backtrace when NULL @_ksp is specfied.

Make show_stack() acquire and use %fp if @tsk is NULL or current and @_ksp
is NULL.  This makes %fp fetching in dump_stack() unnecessary.  Make it
use NULL for @_ksp instead.

Only compile tested.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David S. Miller <davem@davemloft.net>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/sparc/kernel/process_32.c

@@ -142,11 +142,13 @@ void show_stack(struct task_struct *tsk, unsigned long *_ksp)
 	struct reg_window32 *rw;
 	int count = 0;
 
-	if (tsk != NULL)
-		task_base = (unsigned long) task_stack_page(tsk);
-	else
-		task_base = (unsigned long) current_thread_info();
+	if (!tsk)
+		tsk = current;
 
+	if (tsk == current && !_ksp)
+		__asm__ __volatile__("mov	%%fp, %0" : "=r" (_ksp));
+
+	task_base = (unsigned long) task_stack_page(tsk);
 	fp = (unsigned long) _ksp;
 	do {
 		/* Bogus frame pointer? */
@@ -164,11 +166,7 @@ void show_stack(struct task_struct *tsk, unsigned long *_ksp)
 
 void dump_stack(void)
 {
-	unsigned long *ksp;
-
-	__asm__ __volatile__("mov	%%fp, %0"
-			     : "=r" (ksp));
-	show_stack(current, ksp);
+	show_stack(current, NULL);
 }
 
 EXPORT_SYMBOL(dump_stack);