MIPS: Tracing: Add dynamic function graph tracer for MIPS

This patch make function graph tracer work with dynamic function tracer.

To share the source code of dynamic function tracer(MCOUNT_SAVE_REGS),
and avoid restoring the whole saved registers, we need to restore the ra
register from the stack.

(NOTE: This not work with 32bit! need to ensure why!)

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/678/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 12 insertions, 2 deletions

diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S
index b50e38d828c4..98d469032506 100644
--- a/arch/mips/kernel/mcount.S
+++ b/arch/mips/kernel/mcount.S
@@ -77,6 +77,13 @@ ftrace_call:
         nop     /* a placeholder for the call to a real tracing function */
          move   a1, AT          /* arg2: the caller's next ip, parent */
 
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+        .globl ftrace_graph_call
+ftrace_graph_call:
+        nop
+         nop
+#endif
+
         MCOUNT_RESTORE_REGS
         .globl ftrace_stub
 ftrace_stub:
@@ -124,10 +131,13 @@ ftrace_stub:
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 
 NESTED(ftrace_graph_caller, PT_SIZE, ra)
+#ifdef CONFIG_DYNAMIC_FTRACE
+        PTR_L   a1, PT_R31(sp)  /* load the original ra from the stack */
+#else
         MCOUNT_SAVE_REGS
-
-        PTR_LA  a0, PT_R1(sp)   /* arg1: &AT -> a0 */
         move    a1, ra          /* arg2: next ip, selfaddr */
+#endif
+        PTR_LA  a0, PT_R1(sp)   /* arg1: &AT -> a0 */
         jal     prepare_ftrace_return
          move   a2, fp          /* arg3: frame pointer */