xtensa: provide custom CALLER_ADDR* implementations

Definition of CALLER_ADDR* through __builtin_return_address makes
compiler insert calls to __xtensa_libgcc_window_spill, which in turn
makes fast_syscall_spill_registers syscall that clobbers registers when
called from the kernel mode, leading to invalid opcode exceptions on
return to userspace.

Provide definition for CALLER_ADDR0 as MAKE_PC_FROM_RA(a0, a1) and in
case CONFIG_FRAME_POINTER is enabled extract CALLER_ADDR{1-3} from
stack.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>

arch/xtensa/include/asm/ftrace.h

@@ -1 +1,33 @@
-/* empty */
+/*
+ * arch/xtensa/include/asm/ftrace.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) 2013 Tensilica Inc.
+ */
+#ifndef _XTENSA_FTRACE_H
+#define _XTENSA_FTRACE_H
+
+#include <asm/processor.h>
+
+#define HAVE_ARCH_CALLER_ADDR
+#define CALLER_ADDR0 ({ unsigned long a0, a1; \
+		__asm__ __volatile__ ( \
+			"mov %0, a0\n" \
+			"mov %1, a1\n" \
+			: "=r"(a0), "=r"(a1) : : ); \
+		MAKE_PC_FROM_RA(a0, a1); })
+#ifdef CONFIG_FRAME_POINTER
+extern unsigned long return_address(unsigned level);
+#define CALLER_ADDR1 return_address(1)
+#define CALLER_ADDR2 return_address(2)
+#define CALLER_ADDR3 return_address(3)
+#else
+#define CALLER_ADDR1 (0)
+#define CALLER_ADDR2 (0)
+#define CALLER_ADDR3 (0)
+#endif
+
+#endif /* _XTENSA_FTRACE_H */