sh: dwarf unwinder support.

This is a first cut at a generic DWARF unwinder for the kernel. It's
still lacking DWARF64 support and the DWARF expression support hasn't
been tested very well but it is generating proper stacktraces on SH for
WARN_ON() and NULL dereferences.

Signed-off-by: Matt Fleming <matt@console-pimps.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/Kconfig.debug

@@ -110,6 +110,14 @@ config DUMP_CODE
 
 	  Those looking for more verbose debugging output should say Y.
 
+config DWARF_UNWINDER
+	bool "Enable the DWARF unwinder for stacktraces"
+	select FRAME_POINTER
+	default n
+	help
+	  Enabling this option will make stacktraces more accurate, at
+	  the cost of an increase in overall kernel size.
+
 config SH_NO_BSS_INIT
 	bool "Avoid zeroing BSS (to speed-up startup on suitable platforms)"
 	depends on DEBUG_KERNEL

arch/sh/Makefile

@@ -191,6 +191,10 @@ ifeq ($(CONFIG_MCOUNT),y)
   KBUILD_CFLAGS += -pg
 endif
 
+ifeq ($(CONFIG_DWARF_UNWINDER),y)
+  KBUILD_CFLAGS += -fasynchronous-unwind-tables
+endif
+
 libs-$(CONFIG_SUPERH32)		:= arch/sh/lib/	$(libs-y)
 libs-$(CONFIG_SUPERH64)		:= arch/sh/lib64/ $(libs-y)