From: Akhilesh Kumar <akhilesh.lxr@xxxxxxxxx>
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@xxxxxxxxx>
Signed-off-by: Himanshu Maithani <hmaithani@xxxxxxxxx>
---
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
Attachment:
0001-Patch-fix-the-backtrcae-problem-using-unwind_stack.patch
Description: Binary data
