3 files changed, 38 insertions, 7 deletions

diff --git a/arch/mips/Makefile b/arch/mips/Makefile
index 3725ee923d05..d2c39fdcdfeb 100644
--- a/arch/mips/Makefile
+++ b/arch/mips/Makefile
@@ -51,6 +51,13 @@ endif
 ifndef CONFIG_FUNCTION_TRACER
 cflags-y := -ffunction-sections
 endif
+ifdef CONFIG_FUNCTION_GRAPH_TRACER
+  ifndef KBUILD_MCOUNT_RA_ADDRESS
+    ifeq ($(call cc-option-yn,-mmcount-ra-address), y)
+      cflags-y += -mmcount-ra-address -DKBUILD_MCOUNT_RA_ADDRESS
+    endif
+  endif
+endif
 cflags-y += $(call cc-option, -mno-check-zero-division)
 
 ifdef CONFIG_32BIT
diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
index e363fc69aabd..68b067040d8b 100644
--- a/arch/mips/kernel/ftrace.c
+++ b/arch/mips/kernel/ftrace.c
@@ -148,6 +148,7 @@ int ftrace_disable_ftrace_graph_caller(void)
 
 #endif                          /* !CONFIG_DYNAMIC_FTRACE */
 
+#ifndef KBUILD_MCOUNT_RA_ADDRESS
 #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 */
@@ -201,6 +202,8 @@ unsigned long ftrace_get_parent_addr(unsigned long self_addr,
         return 0;
 }
 
+#endif
+
 /*
  * Hook the return address and push it in the stack of return addrs
  * in current thread info.
@@ -218,19 +221,26 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
                 return;
 
         /* "parent" is the stack address saved the return address of the caller
-         * of _mcount, for a leaf function not save the return address in the
-         * stack address, so, we "emulate" one in _mcount's stack space, and
-         * hijack it directly, but for a non-leaf function, it will save the
-         * return address to the its stack space, so, we can not hijack the
-         * "parent" directly, but need to find the real stack address,
+         * of _mcount.
+         *
+         * if the gcc < 4.5, a leaf function does not save the return address
+         * in the stack address, so, we "emulate" one in _mcount's stack space,
+         * and hijack it directly, but for a non-leaf function, it save the
+         * return address to the its own stack space, we can not hijack it
+         * directly, but need to find the real stack address,
          * ftrace_get_parent_addr() does it!
+         *
+         * if gcc>= 4.5, with the new -mmcount-ra-address option, for a
+         * non-leaf function, the location of the return address will be saved
+         * to $12 for us, and for a leaf function, only put a zero into $12. we
+         * do it in ftrace_graph_caller of mcount.S.
          */
 
         /* old = *parent; */
         safe_load_stack(old, parent, faulted);
         if (unlikely(faulted))
                 goto out;
-
+#ifndef KBUILD_MCOUNT_RA_ADDRESS
         parent = (unsigned long *)ftrace_get_parent_addr(self_addr, old,
                                                          (unsigned long)parent,
                                                          fp);
@@ -238,7 +248,7 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
          * ra, stop function graph tracer and return */
         if (parent == 0)
                 goto out;
-
+#endif
         /* *parent = return_hooker; */
         safe_store_stack(return_hooker, parent, faulted);
         if (unlikely(faulted))
diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S
index 522e91c688fc..0a9cfdb271dd 100644
--- a/arch/mips/kernel/mcount.S
+++ b/arch/mips/kernel/mcount.S
@@ -70,6 +70,9 @@ _mcount:
          nop
 
         MCOUNT_SAVE_REGS
+#ifdef KBUILD_MCOUNT_RA_ADDRESS
+        PTR_S   t0, PT_R12(sp)  /* t0 saved the location of the return address(at) by -mmcount-ra-address */
+#endif
 
         move    a0, ra          /* arg1: next ip, selfaddr */
         .globl ftrace_call
@@ -133,11 +136,22 @@ ftrace_stub:
 NESTED(ftrace_graph_caller, PT_SIZE, ra)
 #ifdef CONFIG_DYNAMIC_FTRACE
         PTR_L   a1, PT_R31(sp)  /* load the original ra from the stack */
+#ifdef KBUILD_MCOUNT_RA_ADDRESS
+        PTR_L   t0, PT_R12(sp)  /* load the original t0 from the stack */
+#endif
 #else
         MCOUNT_SAVE_REGS
         move    a1, ra          /* arg2: next ip, selfaddr */
 #endif
+
+#ifdef KBUILD_MCOUNT_RA_ADDRESS
+        bnez    t0, 1f          /* non-leaf func: t0 saved the location of the return address */
+         nop
+        PTR_LA  t0, PT_R1(sp)   /* leaf func: get the location of at(old ra) from our own stack */
+1:      move    a0, t0          /* arg1: the location of the return address */
+#else
         PTR_LA  a0, PT_R1(sp)   /* arg1: &AT -> a0 */
+#endif
         jal     prepare_ftrace_return
 #ifdef CONFIG_FRAME_POINTER
          move   a2, fp          /* arg3: frame pointer */