powerpc32, ftrace: port function graph tracer to ppc32, static only

This patch ports the function graph tracer for PowerPC, but only
for static function tracing.

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/Kconfig

@@ -111,7 +111,7 @@ config PPC
 	select HAVE_FTRACE_MCOUNT_RECORD
 	select HAVE_DYNAMIC_FTRACE
 	select HAVE_FUNCTION_TRACER
-	select HAVE_FUNCTION_GRAPH_TRACER if PPC64
+	select HAVE_FUNCTION_GRAPH_TRACER if PPC64 || !DYNAMIC_FTRACE
 	select ARCH_WANT_OPTIONAL_GPIOLIB
 	select HAVE_IDE
 	select HAVE_IOREMAP_PROT

arch/powerpc/kernel/entry_32.S

@@ -1199,9 +1199,11 @@ _GLOBAL(_mcount)
 
 	mtctr	r5
 	bctrl
-
 	nop
 
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	b	ftrace_graph_caller
+#endif
 	MCOUNT_RESTORE_FRAME
 
 	bctr
@@ -1210,4 +1212,43 @@ _GLOBAL(_mcount)
 _GLOBAL(ftrace_stub)
 	blr
 
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+_GLOBAL(ftrace_graph_caller)
+	/* load r4 with local address */
+	lwz	r4, 44(r1)
+	subi	r4, r4, MCOUNT_INSN_SIZE
+
+	/* get the parent address */
+	addi	r3, r1, 52
+
+	bl	prepare_ftrace_return
+	nop
+
+	MCOUNT_RESTORE_FRAME
+	/* old link register ends up in ctr reg */
+	bctr
+
+_GLOBAL(return_to_handler)
+	/* need to save return values */
+	stwu	r1, -32(r1)
+	stw	r3, 20(r1)
+	stw	r4, 16(r1)
+	stw	r31, 12(r1)
+	mr	r31, r1
+
+	bl	ftrace_return_to_handler
+	nop
+
+	/* return value has real return address */
+	mtlr	r3
+
+	lwz	r3, 20(r1)
+	lwz	r4, 16(r1)
+	lwz	r31,12(r1)
+	lwz	r1, 0(r1)
+
+	/* Jump back to real return address */
+	blr
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
 #endif /* CONFIG_MCOUNT */

arch/powerpc/kernel/ftrace.c

@@ -603,7 +603,7 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
 		"1: " PPC_LL "%[old], 0(%[parent])\n"
 		"2: " PPC_STL "%[return_hooker], 0(%[parent])\n"
 		"   li %[faulted], 0\n"
-		"3:"
+		"3:\n"
 
 		".section .fixup, \"ax\"\n"
 		"4: li %[faulted], 1\n"