sh: Generalize CALLER_ADDRx support.

This splits out the unwinder implementation and adds a new
return_address() abstraction modelled after the ARM code. The DWARF
unwinder is tied in to this, returning NULL otherwise in the case of
being unable to support arbitrary depths.

This enables us to get correct behaviour with the unwinder enabled,
as well as disabling the arbitrary depth support when frame pointers are
enabled, as arbitrary depths with __builtin_return_address() are not
supported regardless.

With this abstraction it's also possible to layer on a simplified
implementation with frame pointers in the event that the unwinder isn't
enabled, although this is left as a future exercise.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/include/asm/dwarf.h

@@ -194,6 +194,11 @@
 #define DWARF_ARCH_RA_REG	17
 
 #ifndef __ASSEMBLY__
+
+#include <linux/compiler.h>
+#include <linux/bug.h>
+#include <linux/list.h>
+
 /*
  * Read either the frame pointer (r14) or the stack pointer (r15).
  * NOTE: this MUST be inlined.

arch/sh/include/asm/ftrace.h

@@ -32,52 +32,18 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
 	return addr;
 }
 
-
-#ifdef CONFIG_DWARF_UNWINDER
-#include <asm/dwarf.h>
+/* arch/sh/kernel/return_address.c */
+extern void *return_address(unsigned int);
 
 #define HAVE_ARCH_CALLER_ADDR
 
-static inline unsigned long dwarf_return_address(int depth)
-{
-	struct dwarf_frame *frame;
-	unsigned long ra;
-	int i;
-
-	for (i = 0, frame = NULL, ra = 0; i <= depth; i++) {
-		struct dwarf_frame *tmp;
-
-		tmp = dwarf_unwind_stack(ra, frame);
-
-		if (frame)
-			dwarf_free_frame(frame);
-
-		frame = tmp;
-
-		if (!frame || !frame->return_addr)
-			break;
-
-		ra = frame->return_addr;
-	}
-
-	/* Failed to unwind the stack to the specified depth. */
-	WARN_ON(i != depth + 1);
-
-	if (frame)
-		dwarf_free_frame(frame);
-
-	return ra;
-}
-
 #define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0))
-#define CALLER_ADDR1 dwarf_return_address(1)
-#define CALLER_ADDR2 dwarf_return_address(2)
-#define CALLER_ADDR3 dwarf_return_address(3)
-#define CALLER_ADDR4 dwarf_return_address(4)
-#define CALLER_ADDR5 dwarf_return_address(5)
-#define CALLER_ADDR6 dwarf_return_address(6)
-
-#endif /* CONFIG_DWARF_UNWINDER */
+#define CALLER_ADDR1 ((unsigned long)return_address(1))
+#define CALLER_ADDR2 ((unsigned long)return_address(2))
+#define CALLER_ADDR3 ((unsigned long)return_address(3))
+#define CALLER_ADDR4 ((unsigned long)return_address(4))
+#define CALLER_ADDR5 ((unsigned long)return_address(5))
+#define CALLER_ADDR6 ((unsigned long)return_address(6))
 
 #endif /* __ASSEMBLY__ */
 #endif /* CONFIG_FUNCTION_TRACER */

arch/sh/kernel/Makefile

@@ -11,6 +11,7 @@ endif
 
 obj-y	:= debugtraps.o dumpstack.o idle.o io.o io_generic.o irq.o	\
 	   machvec.o nmi_debug.o process_$(BITS).o ptrace_$(BITS).o	\
+	   return_address.o						\
 	   setup.o signal_$(BITS).o sys_sh.o sys_sh$(BITS).o		\
 	   syscalls_$(BITS).o time.o topology.o traps.o			\
 	   traps_$(BITS).o unwinder.o

arch/sh/kernel/return_address.c

@@ -0,0 +1,54 @@
+/*
+ * arch/sh/kernel/return_address.c
+ *
+ * Copyright (C) 2009  Matt Fleming
+ * Copyright (C) 2009  Paul Mundt
+ *
+ * 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.
+ */
+#include <linux/kernel.h>
+#include <asm/dwarf.h>
+
+#ifdef CONFIG_DWARF_UNWINDER
+
+void *return_address(unsigned int depth)
+{
+	struct dwarf_frame *frame;
+	unsigned long ra;
+	int i;
+
+	for (i = 0, frame = NULL, ra = 0; i <= depth; i++) {
+		struct dwarf_frame *tmp;
+
+		tmp = dwarf_unwind_stack(ra, frame);
+
+		if (frame)
+			dwarf_free_frame(frame);
+
+		frame = tmp;
+
+		if (!frame || !frame->return_addr)
+			break;
+
+		ra = frame->return_addr;
+	}
+
+	/* Failed to unwind the stack to the specified depth. */
+	WARN_ON(i != depth + 1);
+
+	if (frame)
+		dwarf_free_frame(frame);
+
+	return (void *)ra;
+}
+
+#else
+
+void *return_address(unsigned int depth)
+{
+	return NULL;
+}
+
+#endif