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>

2 files changed, 33 insertions, 2 deletions

diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
index 65a3f8a89927..e981a497c98f 100644
--- a/arch/mips/kernel/ftrace.c
+++ b/arch/mips/kernel/ftrace.c
@@ -115,6 +115,27 @@ int __init ftrace_dyn_arch_init(void *data)
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 
+#ifdef CONFIG_DYNAMIC_FTRACE
+
+extern void ftrace_graph_call(void);
+#define JMP     0x08000000      /* jump to target directly */
+#define CALL_FTRACE_GRAPH_CALLER \
+        jump_insn_encode(JMP, (unsigned long)(&ftrace_graph_caller))
+#define FTRACE_GRAPH_CALL_IP    ((unsigned long)(&ftrace_graph_call))
+
+int ftrace_enable_ftrace_graph_caller(void)
+{
+        return ftrace_modify_code(FTRACE_GRAPH_CALL_IP,
+                                  CALL_FTRACE_GRAPH_CALLER);
+}
+
+int ftrace_disable_ftrace_graph_caller(void)
+{
+        return ftrace_modify_code(FTRACE_GRAPH_CALL_IP, ftrace_nop);
+}
+
+#endif                          /* !CONFIG_DYNAMIC_FTRACE */
+
 #define S_RA_SP (0xafbf << 16)  /* s{d,w} ra, offset(sp) */
 #define S_R_SP  (0xafb0 << 16)  /* s{d,w} R, offset(sp) */
 #define OFFSET_MASK     0xffff  /* stack offset range: 0 ~ PT_SIZE */
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 */