xtensa: add trap_set_handler function

trap_set_handler sets new C-handler in the exception table and returns
previous handler.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>

arch/xtensa/include/asm/traps.h

+/*
+ * arch/xtensa/include/asm/traps.h
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2012 Tensilica Inc.
+ */
+#ifndef _XTENSA_TRAPS_H
+#define _XTENSA_TRAPS_H
+
+#include <asm/ptrace.h>
+
+/*
+ * handler must be either of the following:
+ *  void (*)(struct pt_regs *regs);
+ *  void (*)(struct pt_regs *regs, unsigned long exccause);
+ */
+extern void * __init trap_set_handler(int cause, void *handler);
+extern void do_unhandled(struct pt_regs *regs, unsigned long exccause);
+
+#endif /* _XTENSA_TRAPS_H */

arch/xtensa/kernel/traps.c

@@ -293,6 +293,17 @@ do_debug(struct pt_regs *regs)
 }
 
 
+/* Set exception C handler - for temporary use when probing exceptions */
+
+void * __init trap_set_handler(int cause, void *handler)
+{
+	unsigned long *entry = &exc_table[EXC_TABLE_DEFAULT / 4 + cause];
+	void *previous = (void *)*entry;
+	*entry = (unsigned long)handler;
+	return previous;
+}
+
+
 /*
  * Initialize dispatch tables.
  *