sh: Setup the frame register in asm code

In order to use DWARF unwinder info the frame register has to contain a
valid value. Whilst GCC takes care of this for C code, we have to do it
ourselves for assembly.
Signed-off-by: Matt Fleming <matt@console-pimps.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/include/asm/entry-macros.S

@@ -108,3 +108,15 @@
 #else
 # define PREF(x)	nop
 #endif
+
+	/*
+	 * Macro for use within assembly. Because the DWARF unwinder
+	 * needs to use the frame register to unwind the stack, we
+	 * need to setup r14 with the value of the stack pointer as
+	 * the return address is usually on the stack somewhere.
+	 */
+	.macro	setup_frame_reg
+#ifdef CONFIG_DWARF_UNWINDER
+	mov	r15, r14
+#endif
+	.endm

arch/sh/kernel/cpu/sh3/entry.S

@@ -137,6 +137,7 @@ ENTRY(tlb_protection_violation_store)
 	 mov	#1, r5
 
 call_dpf:
+	setup_frame_reg
 	mov.l	1f, r0
 	mov	r5, r8
 	mov.l	@r0, r6

arch/sh/kernel/entry-common.S

@@ -285,6 +285,7 @@ ret_from_fork:
  * system calls and debug traps through their respective jump tables.
  */
 ENTRY(system_call)
+	setup_frame_reg
 #if !defined(CONFIG_CPU_SH2)
 	mov.l	1f, r9
 	mov.l	@r9, r8		! Read from TRA (Trap Address) Register