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[Bug-fix] Fix-the-backtrcae-problem-Ftrace is enable

To: ralf@linux-mips.org, paulmck@linux.vnet.ibm.com, fweisbec@gmail.com, paul.gortmaker@windriver.com, josh@joshtriplett.org, gergely@homejinni.com, akhipatel@gmail.com
Subject: [Bug-fix] Fix-the-backtrcae-problem-Ftrace is enable
From: Akhilesh Kumar <akhilesh.lxr@gmail.com>
Date: Fri, 4 May 2012 19:40:43 +0530
Cc: linux-mips@linux-mips.org, linux-kernel@vger.kernel.org
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Sender: linux-mips-bounce@linux-mips.org
Hi All, 
 
Please find the bug fix patch when HAVE_FUNCTION_TRACER is enable. 
 
Thanks, 
Akhilesh 
  
From 89004f88a1f8399be7a856b43b475f06c3d5bb30 Mon Sep 17 00:00:00 2001
From:  Akhilesh Kumar <akhilesh.lxr@gmail.com>
Date: Fri, 4 May 2012 18:52:46 +0530
Subject: [PATCH 1/1] Patch fix the backtrcae  problem using unwind_stack())

When ftrace is used, unwind_stack() is unable to retrieve the frame info
and call-trace doesn't work.

test module
----------------
static struct timer_list backtrace_timer;
static void backtrace_test_timer(unsigned long data)
{
        printk("Testing a backtrace from irq context.\n");
        printk("The following trace is a kernel self test and not a
bug!\n");
        dump_stack();
}
static int backtrace_regression_test(void)
{
        printk("====[ backtrace testing ]===========\n");
        printk("Testing a backtrace from process context.\n");
        printk("The following trace is a kernel self test and not a
bug!\n");
        dump_stack();

        init_timer(&backtrace_timer);
        backtrace_timer.function = backtrace_test_timer;
        mod_timer(&backtrace_timer, jiffies + 10);

        msleep(10);
        printk("====[ end of backtrace testing ]====\n");
        return 0;
}
static void exitf(void)
{
}
module_init(backtrace_regression_test);
module_exit(exitf);
MODULE_LICENSE("GPL");
---------------------------------------------------------------------
out put when HAVE_FUNCTION_TRACER is disable

====[ backtrace testing ]===========
Testing a backtrace from process context.
The following trace is a kernel self test and not a bug!
Testing a backtrace.
The following trace is a kernel self test and not a bug!
Call Trace:
[<80295134>] dump_stack+0x8/0x34
[<c0946060>] backtrace_regression_test+0x60/0x94 [sisc_backtrcae]
[<800004f0>] do_one_initcall+0xf0/0x1d0
[<80060954>] sys_init_module+0x19c8/0x1c60
[<8000a418>] stack_done+0x20/0x40

output befor patch when HAVE_FUNCTION_TRACER is enable
---------------------------------------------------------------------
VDLinux#> insmod sisc_backtrcae.ko
====[ backtrace testing ]===========
Testing a backtrace from process context.
The following trace is a kernel self test and not a bug!
Testing a backtrace.
The following trace is a kernel self test and not a bug!
Call Trace:
[<802e5164>] dump_stack+0x1c/0x50
[<802e5164>] dump_stack+0x1c/0x50
====[ end of backtrace testing ]====
------------------------------------------------------
above shows the wrong back trcae

output after patch when HAVE_FUNCTION_TRACER is enable
----------------------------------------------------------------------
====[ backtrace testing ]===========
Testing a backtrace from process context.
The following trace is a kernel self test and not a bug!
Testing a backtrace.
The following trace is a kernel self test and not a bug!
Call Trace:
[<802eb1a4>] dump_stack+0x20/0x54
[<c003405c>] backtrace_test_timer+0x5c/0x74 [sisc_backtrcae]
[<c00340dc>] init_module+0x68/0xa0 [sisc_backtrcae]
[<80000508>] do_one_initcall+0x108/0x1f0
[<8006d4c4>] sys_init_module+0x1a10/0x1c74
[<8000b038>] stack_done+0x20/0x40
------------------------------------------------------------------

get_frame_info() is used to fetch the frame information from the
function.
However,
1. this function just considers the first stack adjustment for frame
size.
2. On finding the save_lr instruction, it returns.
It doesn't handle the ftrace condition.

If Dynamic Frace "CONFIG_DYNAMIC_FTRACE" is enabled, the instrumentation code is:
 - jal <ftrace_caller>
 - addiu sp,sp,-8
Thus, the current Frame Size of function is increased by 8 for Ftrace.

Signed-off-by: Akhilesh Kumar <akhilesh.lxr@gmail.com>
Signed-off-by: Himanshu Maithani <hmaithani@gmail.com>
---
 arch/mips/kernel/process.c |   67 ++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 67 insertions(+), 0 deletions(-)

diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index 7955409..df72738 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -290,12 +290,45 @@ static inline int is_sp_move_ins(union mips_instruction *ip)
  return 0;
 }
 
+#ifdef CONFIG_DYNAMIC_FTRACE
+/*
+ * To create the jal <> instruction from mcount.
+ * taken from:
+ * - arch/mips/kernel/ftrace.c
+ */
+#define ADDR_MASK 0x03ffffff    /*  op_code|addr : 31...26|25 ....0 */
+#define JAL 0x0c000000      /* jump & link: ip --> ra, jump to target */
+#define INSN_JAL(addr)  \
+      ((unsigned int)(JAL | (((addr) >> 2) & ADDR_MASK)))
+
+/*
+ * We assume jal <mcount>/<ftrace_caller> to be present in
+ * first JAL_MAX_OFFSET instructions.
+ * Increment this, if its otherwise
+ */
+#define JAL_MAX_OFFSET 16U
+#define MCOUNT_STACK_INST 0x27bdfff8 /* addiu   sp,sp,-8 */
+
+/*
+ * If Dynamic Ftrace is enabled, ftrace_caller is the trace function.
+ * Otherwise its - mcount
+ */
+extern void  ftrace_caller(void);
+#endif /* CONFIG_DYNAMIC_FTRACE */
+
 static int get_frame_info(struct mips_frame_info *info)
 {
  union mips_instruction *ip = info->func;
  unsigned max_insns = info->func_size / sizeof(union mips_instruction);
  unsigned i;
 
+#ifdef CONFIG_DYNAMIC_FTRACE
+ unsigned max_prolog_inst = max_insns;
+ int jal_found = 0;
+ /* instruction corresponding to jal <_mcount>/<ftrace_caller> */
+ int jal_mcount = 0;
+#endif
+
  info->pc_offset = -1;
  info->frame_size = 0;
 
@@ -306,6 +339,28 @@ static int get_frame_info(struct mips_frame_info *info)
   max_insns = 128U; /* unknown function size */
  max_insns = min(128U, max_insns);
 
+#ifdef CONFIG_DYNAMIC_FTRACE
+ max_prolog_inst = min(JAL_MAX_OFFSET, max_prolog_inst);
+ jal_mcount = INSN_JAL((unsigned)&ftrace_caller);
+
+ for (i = 0; i < max_prolog_inst; i++, ip++) {
+  if ((*(int *)ip == jal_mcount) ||
+    /*
+     * for dyn ftrace, the code initially has 0.
+     * so we check whether the next instruction is
+     * addiu   sp,sp,-8
+     */
+    (!(*(int *)ip) &&
+     (*(int *)(ip + 1) == MCOUNT_STACK_INST))
+     ) {
+   jal_found = 1;
+   break;
+  }
+ }
+ /* restore the ip to start of function */
+ ip = info->func;
+#endif
+
  for (i = 0; i < max_insns; i++, ip++) {
 
   if (is_jal_jalr_jr_ins(ip))
@@ -321,6 +376,18 @@ static int get_frame_info(struct mips_frame_info *info)
    break;
   }
  }
+#ifdef CONFIG_DYNAMIC_FTRACE
+ /*
+  * to offset the effect of:
+  * addiu   sp,sp,-8
+  */
+ if (jal_found) {
+  if (info->frame_size)
+   info->frame_size += 8;
+  if (info->pc_offset >= 0)
+   info->pc_offset += 8 / sizeof(long);
+ }
+#endif
  if (info->frame_size && info->pc_offset >= 0) /* nested */
   return 0;
  if (info->pc_offset < 0) /* leaf */
--
1.7.8.4

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