MIPS: Tracing: Reserve $12(t0) for mcount-ra-address of gcc 4.5

A new option -mmcount-ra-address for gcc 4.5 have been sent by David
Daney <ddaney@caviumnetworks.com> in the thread "MIPS: Add option to
pass return address location to _mcount", which help to record the
location of the return address(ra) for the function graph tracer of MIPS
to hijack the return address easier and safer. that option used the
$12(t0) register by default, so, we reserve it for it, and use t1,t2,t3
instead of t0,t1,t2.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Nicholas Mc Guire <der.herr@hofr.at>
Cc: zhangfx@lemote.com
Cc: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/680/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/mcount.S

@@ -65,8 +65,8 @@ NESTED(ftrace_caller, PT_SIZE, ra)
 _mcount:
 	b	ftrace_stub
 	 nop
-	lw	t0, function_trace_stop
-	bnez	t0, ftrace_stub
+	lw	t1, function_trace_stop
+	bnez	t1, ftrace_stub
 	 nop
 
 	MCOUNT_SAVE_REGS
@@ -93,21 +93,21 @@ ftrace_stub:
 #else	/* ! CONFIG_DYNAMIC_FTRACE */
 
 NESTED(_mcount, PT_SIZE, ra)
-	lw	t0, function_trace_stop
-	bnez	t0, ftrace_stub
+	lw	t1, function_trace_stop
+	bnez	t1, ftrace_stub
 	 nop
-	PTR_LA	t0, ftrace_stub
-	PTR_L	t1, ftrace_trace_function /* Prepare t1 for (1) */
-	bne	t0, t1, static_trace
+	PTR_LA	t1, ftrace_stub
+	PTR_L	t2, ftrace_trace_function /* Prepare t2 for (1) */
+	bne	t1, t2, static_trace
 	 nop
 
 #ifdef	CONFIG_FUNCTION_GRAPH_TRACER
-	PTR_L	t2, ftrace_graph_return
-	bne	t0, t2, ftrace_graph_caller
+	PTR_L	t3, ftrace_graph_return
+	bne	t1, t3, ftrace_graph_caller
 	 nop
-	PTR_LA	t0, ftrace_graph_entry_stub
-	PTR_L	t2, ftrace_graph_entry
-	bne	t0, t2, ftrace_graph_caller
+	PTR_LA	t1, ftrace_graph_entry_stub
+	PTR_L	t3, ftrace_graph_entry
+	bne	t1, t3, ftrace_graph_caller
 	 nop
 #endif
 	b	ftrace_stub
@@ -117,7 +117,7 @@ static_trace:
 	MCOUNT_SAVE_REGS
 
 	move	a0, ra		/* arg1: next ip, selfaddr */
-	jalr	t1	/* (1) call *ftrace_trace_function */
+	jalr	t2		/* (1) call *ftrace_trace_function */
 	 move	a1, AT		/* arg2: the caller's next ip, parent */
 
 	MCOUNT_RESTORE_REGS