MIPS: Tracing: Cleanup of function graph tracer

Cleans up comments and ftrace_get_parent_addr() of function graph tracer.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips <linux-mips@linux-mips.org>
Cc: David Daney <david.s.daney@gmail.com>
Patchwork: http://patchwork.linux-mips.org/patch/1231/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 26 insertions, 22 deletions

diff --git a/arch/mips/kernel/ftrace.c b/arch/mips/kernel/ftrace.c
index c4042cad836e..628e90b992d1 100644
--- a/arch/mips/kernel/ftrace.c
+++ b/arch/mips/kernel/ftrace.c
@@ -146,7 +146,7 @@ int __init ftrace_dyn_arch_init(void *data)
 
         return 0;
 }
-#endif                          /* CONFIG_DYNAMIC_FTRACE */
+#endif  /* CONFIG_DYNAMIC_FTRACE */
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 
@@ -166,9 +166,10 @@ int ftrace_disable_ftrace_graph_caller(void)
         return ftrace_modify_code(FTRACE_GRAPH_CALL_IP, INSN_NOP);
 }
 
-#endif                          /* !CONFIG_DYNAMIC_FTRACE */
+#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 */
@@ -182,17 +183,17 @@ unsigned long ftrace_get_parent_addr(unsigned long self_addr,
         unsigned int code;
         int faulted;
 
-        /* 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;
-        }
+        /*
+         * For module, move the ip from calling site of mcount to the
+         * instruction "lui v1, hi_16bit_of_mcount"(offset is 20), but for
+         * kernel, move to the instruction "move ra, at"(offset is 12)
+         */
+        ip = self_addr - ((self_addr & 0x40000000) ? 20 : 12);
 
-        /* search the text until finding the non-store instruction or "s{d,w}
-         * ra, offset(sp)" instruction */
+        /*
+         * search the text until finding the non-store instruction or "s{d,w}
+         * ra, offset(sp)" instruction
+         */
         do {
                 ip -= 4;
 
@@ -201,10 +202,11 @@ unsigned long ftrace_get_parent_addr(unsigned long self_addr,
 
                 if (unlikely(faulted))
                         return 0;
-
-                /* If we hit the non-store instruction before finding where the
+                /*
+                 * 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. */
+                 * store the ra on the stack
+                 */
                 if ((code & S_R_SP) != S_R_SP)
                         return parent_addr;
 
@@ -222,7 +224,7 @@ unsigned long ftrace_get_parent_addr(unsigned long self_addr,
         return 0;
 }
 
-#endif
+#endif  /* !KBUILD_MCOUNT_RA_ADDRESS */
 
 /*
  * Hook the return address and push it in the stack of return addrs
@@ -240,7 +242,8 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
         if (unlikely(atomic_read(&current->tracing_graph_pause)))
                 return;
 
-        /* "parent" is the stack address saved the return address of the caller
+        /*
+         * "parent" is the stack address saved the return address of the caller
          * of _mcount.
          *
          * if the gcc < 4.5, a leaf function does not save the return address
@@ -262,10 +265,11 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
                 goto out;
 #ifndef KBUILD_MCOUNT_RA_ADDRESS
         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 */
+                        (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)
                 goto out;
 #endif
@@ -292,4 +296,4 @@ out:
         ftrace_graph_stop();
         WARN_ON(1);
 }
-#endif                          /* CONFIG_FUNCTION_GRAPH_TRACER */
+#endif  /* CONFIG_FUNCTION_GRAPH_TRACER */