1 files changed, 106 insertions, 0 deletions

diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
index 5459a7838370..65a3f8a89927 100644
--- a/arch/mips/kernel/ftrace.c
+++ b/arch/mips/kernel/ftrace.c
@@ -13,6 +13,8 @@
 #include <linux/ftrace.h>
 
 #include <asm/cacheflush.h>
+#include <asm/asm.h>
+#include <asm/asm-offsets.h>
 
 #ifdef CONFIG_DYNAMIC_FTRACE
 
@@ -110,3 +112,107 @@ int __init ftrace_dyn_arch_init(void *data)
         return 0;
 }
 #endif                          /* CONFIG_DYNAMIC_FTRACE */
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+
+#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 */
+
+unsigned long ftrace_get_parent_addr(unsigned long self_addr,
+                                     unsigned long parent,
+                                     unsigned long parent_addr,
+                                     unsigned long fp)
+{
+        unsigned long sp, ip, ra;
+        unsigned int code;
+
+        /* in module or kernel? */
+        if (self_addr & 0x40000000) {
+                /* module: move to the instruction "lui v1, HI_16BIT_OF_MCOUNT" */
+                ip = self_addr - 20;
+        } else {
+                /* kernel: move to the instruction "move ra, at" */
+                ip = self_addr - 12;
+        }
+
+        /* search the text until finding the non-store instruction or "s{d,w}
+         * ra, offset(sp)" instruction */
+        do {
+                ip -= 4;
+
+                /* get the code at "ip" */
+                code = *(unsigned int *)ip;
+
+                /* If we hit the non-store instruction before finding where the
+                 * ra is stored, then this is a leaf function and it does not
+                 * store the ra on the stack. */
+                if ((code & S_R_SP) != S_R_SP)
+                        return parent_addr;
+
+        } while (((code & S_RA_SP) != S_RA_SP));
+
+        sp = fp + (code & OFFSET_MASK);
+        ra = *(unsigned long *)sp;
+
+        if (ra == parent)
+                return sp;
+
+        return 0;
+}
+
+/*
+ * Hook the return address and push it in the stack of return addrs
+ * in current thread info.
+ */
+void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
+                           unsigned long fp)
+{
+        unsigned long old;
+        struct ftrace_graph_ent trace;
+        unsigned long return_hooker = (unsigned long)
+            &return_to_handler;
+
+        if (unlikely(atomic_read(&current->tracing_graph_pause)))
+                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,
+         * ftrace_get_parent_addr() does it!
+         */
+
+        old = *parent;
+
+        parent = (unsigned long *)ftrace_get_parent_addr(self_addr, old,
+                                                         (unsigned long)parent,
+                                                         fp);
+
+        /* If fails when getting the stack address of the non-leaf function's
+         * ra, stop function graph tracer and return */
+        if (parent == 0) {
+                ftrace_graph_stop();
+                WARN_ON(1);
+                return;
+        }
+
+        *parent = return_hooker;
+
+        if (ftrace_push_return_trace(old, self_addr, &trace.depth, fp) ==
+            -EBUSY) {
+                *parent = old;
+                return;
+        }
+
+        trace.func = self_addr;
+
+        /* Only trace if the calling function expects to */
+        if (!ftrace_graph_entry(&trace)) {
+                current->curr_ret_stack--;
+                *parent = old;
+        }
+}
+#endif                          /* CONFIG_FUNCTION_GRAPH_TRACER */