arch/x86/kernel/ftrace.c - LeafOS-Devices/android_kernel_samsung_gta4xl - Gitiles

 /*
  * Code for replacing ftrace calls with jumps.
  *
  * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
  *
  * Thanks goes to Ingo Molnar, for suggesting the idea.
  * Mathieu Desnoyers, for suggesting postponing the modifications.
  * Arjan van de Ven, for keeping me straight, and explaining to me
  * the dangers of modifying code on the run.
  */

 #include <linux/spinlock.h>
 #include <linux/hardirq.h>
 #include <linux/uaccess.h>
 #include <linux/ftrace.h>
 #include <linux/percpu.h>
 #include <linux/sched.h>
 #include <linux/init.h>
 #include <linux/list.h>

 #include <asm/ftrace.h>
 #include <linux/ftrace.h>
 #include <asm/nops.h>
 #include <asm/nmi.h>


 #ifdef CONFIG_DYNAMIC_FTRACE

 union ftrace_code_union {
 	char code[MCOUNT_INSN_SIZE];
 	struct {
 		char e8;
 		int offset;
 	} __attribute__((packed));
 };

 static int ftrace_calc_offset(long ip, long addr)
 {
 	return (int)(addr - ip);
 }

 static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
 {
 	static union ftrace_code_union calc;

 	calc.e8		= 0xe8;
 	calc.offset	= ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr);

 	/*
 	 * No locking needed, this must be called via kstop_machine
 	 * which in essence is like running on a uniprocessor machine.
 	 */
 	return calc.code;
 }

 /*
  * Modifying code must take extra care. On an SMP machine, if
  * the code being modified is also being executed on another CPU
  * that CPU will have undefined results and possibly take a GPF.
  * We use kstop_machine to stop other CPUS from exectuing code.
  * But this does not stop NMIs from happening. We still need
  * to protect against that. We separate out the modification of
  * the code to take care of this.
  *
  * Two buffers are added: An IP buffer and a "code" buffer.
  *
  * 1) Put the instruction pointer into the IP buffer
  *    and the new code into the "code" buffer.
  * 2) Set a flag that says we are modifying code
  * 3) Wait for any running NMIs to finish.
  * 4) Write the code
  * 5) clear the flag.
  * 6) Wait for any running NMIs to finish.
  *
  * If an NMI is executed, the first thing it does is to call
  * "ftrace_nmi_enter". This will check if the flag is set to write
  * and if it is, it will write what is in the IP and "code" buffers.
  *
  * The trick is, it does not matter if everyone is writing the same
  * content to the code location. Also, if a CPU is executing code
  * it is OK to write to that code location if the contents being written
  * are the same as what exists.
  */

 static atomic_t in_nmi = ATOMIC_INIT(0);
 static int mod_code_status;		/* holds return value of text write */
 static int mod_code_write;		/* set when NMI should do the write */
 static void *mod_code_ip;		/* holds the IP to write to */
 static void *mod_code_newcode;		/* holds the text to write to the IP */

 static unsigned nmi_wait_count;
 static atomic_t nmi_update_count = ATOMIC_INIT(0);

 int ftrace_arch_read_dyn_info(char *buf, int size)
 {
 	int r;

 	r = snprintf(buf, size, "%u %u",
 		     nmi_wait_count,
 		     atomic_read(&nmi_update_count));
 	return r;
 }

 static void ftrace_mod_code(void)
 {
 	/*
 	 * Yes, more than one CPU process can be writing to mod_code_status.
 	 *    (and the code itself)
 	 * But if one were to fail, then they all should, and if one were
 	 * to succeed, then they all should.
 	 */
 	mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode,
 					     MCOUNT_INSN_SIZE);

 }

 void ftrace_nmi_enter(void)
 {
 	atomic_inc(&in_nmi);
 	/* Must have in_nmi seen before reading write flag */
 	smp_mb();
 	if (mod_code_write) {
 		ftrace_mod_code();
 		atomic_inc(&nmi_update_count);
 	}
 }

 void ftrace_nmi_exit(void)
 {
 	/* Finish all executions before clearing in_nmi */
 	smp_wmb();
 	atomic_dec(&in_nmi);
 }

 static void wait_for_nmi(void)
 {
 	int waited = 0;

 	while (atomic_read(&in_nmi)) {
 		waited = 1;
 		cpu_relax();
 	}

 	if (waited)
 		nmi_wait_count++;
 }

 static int
 do_ftrace_mod_code(unsigned long ip, void *new_code)
 {
 	mod_code_ip = (void *)ip;
 	mod_code_newcode = new_code;

 	/* The buffers need to be visible before we let NMIs write them */
 	smp_wmb();

 	mod_code_write = 1;

 	/* Make sure write bit is visible before we wait on NMIs */
 	smp_mb();

 	wait_for_nmi();

 	/* Make sure all running NMIs have finished before we write the code */
 	smp_mb();

 	ftrace_mod_code();

 	/* Make sure the write happens before clearing the bit */
 	smp_wmb();

 	mod_code_write = 0;

 	/* make sure NMIs see the cleared bit */
 	smp_mb();

 	wait_for_nmi();

 	return mod_code_status;
 }


 static unsigned char ftrace_nop[MCOUNT_INSN_SIZE];

 static unsigned char *ftrace_nop_replace(void)
 {
 	return ftrace_nop;
 }

 static int
 ftrace_modify_code(unsigned long ip, unsigned char *old_code,
 		   unsigned char *new_code)
 {
 	unsigned char replaced[MCOUNT_INSN_SIZE];

 	/*
 	 * Note: Due to modules and __init, code can
 	 *  disappear and change, we need to protect against faulting
 	 *  as well as code changing. We do this by using the
 	 *  probe_kernel_* functions.
 	 *
 	 * No real locking needed, this code is run through
 	 * kstop_machine, or before SMP starts.
 	 */

 	/* read the text we want to modify */
 	if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
 		return -EFAULT;

 	/* Make sure it is what we expect it to be */
 	if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
 		return -EINVAL;

 	/* replace the text with the new text */
 	if (do_ftrace_mod_code(ip, new_code))
 		return -EPERM;

 	sync_core();

 	return 0;
 }

 int ftrace_make_nop(struct module *mod,
 		    struct dyn_ftrace *rec, unsigned long addr)
 {
 	unsigned char *new, *old;
 	unsigned long ip = rec->ip;

 	old = ftrace_call_replace(ip, addr);
 	new = ftrace_nop_replace();

 	return ftrace_modify_code(rec->ip, old, new);
 }

 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
 	unsigned char *new, *old;
 	unsigned long ip = rec->ip;

 	old = ftrace_nop_replace();
 	new = ftrace_call_replace(ip, addr);

 	return ftrace_modify_code(rec->ip, old, new);
 }

 int ftrace_update_ftrace_func(ftrace_func_t func)
 {
 	unsigned long ip = (unsigned long)(&ftrace_call);
 	unsigned char old[MCOUNT_INSN_SIZE], *new;
 	int ret;

 	memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
 	new = ftrace_call_replace(ip, (unsigned long)func);
 	ret = ftrace_modify_code(ip, old, new);

 	return ret;
 }

 int __init ftrace_dyn_arch_init(void *data)
 {
 	extern const unsigned char ftrace_test_p6nop[];
 	extern const unsigned char ftrace_test_nop5[];
 	extern const unsigned char ftrace_test_jmp[];
 	int faulted = 0;

 	/*
 	 * There is no good nop for all x86 archs.
 	 * We will default to using the P6_NOP5, but first we
 	 * will test to make sure that the nop will actually
 	 * work on this CPU. If it faults, we will then
 	 * go to a lesser efficient 5 byte nop. If that fails
 	 * we then just use a jmp as our nop. This isn't the most
 	 * efficient nop, but we can not use a multi part nop
 	 * since we would then risk being preempted in the middle
 	 * of that nop, and if we enabled tracing then, it might
 	 * cause a system crash.
 	 *
 	 * TODO: check the cpuid to determine the best nop.
 	 */
 	asm volatile (
 		"ftrace_test_jmp:"
 		"jmp ftrace_test_p6nop\n"
 		"nop\n"
 		"nop\n"
 		"nop\n"  /* 2 byte jmp + 3 bytes */
 		"ftrace_test_p6nop:"
 		P6_NOP5
 		"jmp 1f\n"
 		"ftrace_test_nop5:"
 		".byte 0x66,0x66,0x66,0x66,0x90\n"
 		"1:"
 		".section .fixup, \"ax\"\n"
 		"2:	movl $1, %0\n"
 		"	jmp ftrace_test_nop5\n"
 		"3:	movl $2, %0\n"
 		"	jmp 1b\n"
 		".previous\n"
 		_ASM_EXTABLE(ftrace_test_p6nop, 2b)
 		_ASM_EXTABLE(ftrace_test_nop5, 3b)
 		: "=r"(faulted) : "0" (faulted));

 	switch (faulted) {
 	case 0:
 		pr_info("ftrace: converting mcount calls to 0f 1f 44 00 00\n");
 		memcpy(ftrace_nop, ftrace_test_p6nop, MCOUNT_INSN_SIZE);
 		break;
 	case 1:
 		pr_info("ftrace: converting mcount calls to 66 66 66 66 90\n");
 		memcpy(ftrace_nop, ftrace_test_nop5, MCOUNT_INSN_SIZE);
 		break;
 	case 2:
 		pr_info("ftrace: converting mcount calls to jmp . + 5\n");
 		memcpy(ftrace_nop, ftrace_test_jmp, MCOUNT_INSN_SIZE);
 		break;
 	}

 	/* The return code is retured via data */
 	*(unsigned long *)data = 0;

 	return 0;
 }
 #endif

 #ifdef CONFIG_FUNCTION_RET_TRACER

 #ifndef CONFIG_DYNAMIC_FTRACE

 /*
  * These functions are picked from those used on
  * this page for dynamic ftrace. They have been
  * simplified to ignore all traces in NMI context.
  */
 static atomic_t in_nmi;

 void ftrace_nmi_enter(void)
 {
 	atomic_inc(&in_nmi);
 }

 void ftrace_nmi_exit(void)
 {
 	atomic_dec(&in_nmi);
 }
 #endif /* !CONFIG_DYNAMIC_FTRACE */

 /* Add a function return address to the trace stack on thread info.*/
 static int push_return_trace(unsigned long ret, unsigned long long time,
 				unsigned long func)
 {
 	int index;
 	struct thread_info *ti = current_thread_info();

 	/* The return trace stack is full */
 	if (ti->curr_ret_stack == FTRACE_RET_STACK_SIZE - 1)
 		return -EBUSY;

 	index = ++ti->curr_ret_stack;
 	barrier();
 	ti->ret_stack[index].ret = ret;
 	ti->ret_stack[index].func = func;
 	ti->ret_stack[index].calltime = time;

 	return 0;
 }

 /* Retrieve a function return address to the trace stack on thread info.*/
 static void pop_return_trace(unsigned long *ret, unsigned long long *time,
 				unsigned long *func)
 {
 	int index;

 	struct thread_info *ti = current_thread_info();
 	index = ti->curr_ret_stack;
 	*ret = ti->ret_stack[index].ret;
 	*func = ti->ret_stack[index].func;
 	*time = ti->ret_stack[index].calltime;
 	ti->curr_ret_stack--;
 }

 /*
  * Send the trace to the ring-buffer.
  * @return the original return address.
  */
 unsigned long ftrace_return_to_handler(void)
 {
 	struct ftrace_retfunc trace;
 	pop_return_trace(&trace.ret, &trace.calltime, &trace.func);
 	trace.rettime = cpu_clock(raw_smp_processor_id());
 	ftrace_function_return(&trace);

 	return trace.ret;
 }

 /*
  * 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 old;
 	unsigned long long calltime;
 	int faulted;
 	unsigned long return_hooker = (unsigned long)
 				&return_to_handler;

 	/* Nmi's are currently unsupported */
 	if (atomic_read(&in_nmi))
 		return;

 	/*
 	 * Protect against fault, even if it shouldn't
 	 * happen. This tool is too much intrusive to
 	 * ignore such a protection.
 	 */
 	asm volatile(
 		"1: movl (%[parent_old]), %[old]\n"
 		"2: movl %[return_hooker], (%[parent_replaced])\n"
 		"   movl $0, %[faulted]\n"

 		".section .fixup, \"ax\"\n"
 		"3: movl $1, %[faulted]\n"
 		".previous\n"

 		".section __ex_table, \"a\"\n"
 		"   .long 1b, 3b\n"
 		"   .long 2b, 3b\n"
 		".previous\n"

 		: [parent_replaced] "=r" (parent), [old] "=r" (old),
 		  [faulted] "=r" (faulted)
 		: [parent_old] "0" (parent), [return_hooker] "r" (return_hooker)
 		: "memory"
 	);

 	if (WARN_ON(faulted)) {
 		unregister_ftrace_return();
 		return;
 	}

 	if (WARN_ON(!__kernel_text_address(old))) {
 		unregister_ftrace_return();
 		*parent = old;
 		return;
 	}

 	calltime = cpu_clock(raw_smp_processor_id());

 	if (push_return_trace(old, calltime, self_addr) == -EBUSY)
 		*parent = old;
 }

 #endif /* CONFIG_FUNCTION_RET_TRACER */
	/*
	* Code for replacing ftrace calls with jumps.
	*
	* Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
	*
	* Thanks goes to Ingo Molnar, for suggesting the idea.
	* Mathieu Desnoyers, for suggesting postponing the modifications.
	* Arjan van de Ven, for keeping me straight, and explaining to me
	* the dangers of modifying code on the run.
	*/

	#include <linux/spinlock.h>
	#include <linux/hardirq.h>
	#include <linux/uaccess.h>
	#include <linux/ftrace.h>
	#include <linux/percpu.h>
	#include <linux/sched.h>
	#include <linux/init.h>
	#include <linux/list.h>

	#include <asm/ftrace.h>
	#include <linux/ftrace.h>
	#include <asm/nops.h>
	#include <asm/nmi.h>


	#ifdef CONFIG_DYNAMIC_FTRACE

	union ftrace_code_union {
	char code[MCOUNT_INSN_SIZE];
	struct {
	char e8;
	int offset;
	} __attribute__((packed));
	};

	static int ftrace_calc_offset(long ip, long addr)
	{
	return (int)(addr - ip);
	}

	static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
	{
	static union ftrace_code_union calc;

	calc.e8 = 0xe8;
	calc.offset = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr);

	/*
	* No locking needed, this must be called via kstop_machine
	* which in essence is like running on a uniprocessor machine.
	*/
	return calc.code;
	}

	/*
	* Modifying code must take extra care. On an SMP machine, if
	* the code being modified is also being executed on another CPU
	* that CPU will have undefined results and possibly take a GPF.
	* We use kstop_machine to stop other CPUS from exectuing code.
	* But this does not stop NMIs from happening. We still need
	* to protect against that. We separate out the modification of
	* the code to take care of this.
	*
	* Two buffers are added: An IP buffer and a "code" buffer.
	*
	* 1) Put the instruction pointer into the IP buffer
	* and the new code into the "code" buffer.
	* 2) Set a flag that says we are modifying code
	* 3) Wait for any running NMIs to finish.
	* 4) Write the code
	* 5) clear the flag.
	* 6) Wait for any running NMIs to finish.
	*
	* If an NMI is executed, the first thing it does is to call
	* "ftrace_nmi_enter". This will check if the flag is set to write
	* and if it is, it will write what is in the IP and "code" buffers.
	*
	* The trick is, it does not matter if everyone is writing the same
	* content to the code location. Also, if a CPU is executing code
	* it is OK to write to that code location if the contents being written
	* are the same as what exists.
	*/

	static atomic_t in_nmi = ATOMIC_INIT(0);
	static int mod_code_status; /* holds return value of text write */
	static int mod_code_write; /* set when NMI should do the write */
	static void mod_code_ip; / holds the IP to write to */
	static void mod_code_newcode; / holds the text to write to the IP */

	static unsigned nmi_wait_count;
	static atomic_t nmi_update_count = ATOMIC_INIT(0);

	int ftrace_arch_read_dyn_info(char *buf, int size)
	{
	int r;

	r = snprintf(buf, size, "%u %u",
	nmi_wait_count,
	atomic_read(&nmi_update_count));
	return r;
	}

	static void ftrace_mod_code(void)
	{
	/*
	* Yes, more than one CPU process can be writing to mod_code_status.
	* (and the code itself)
	* But if one were to fail, then they all should, and if one were
	* to succeed, then they all should.
	*/
	mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode,
	MCOUNT_INSN_SIZE);

	}

	void ftrace_nmi_enter(void)
	{
	atomic_inc(&in_nmi);
	/* Must have in_nmi seen before reading write flag */
	smp_mb();
	if (mod_code_write) {
	ftrace_mod_code();
	atomic_inc(&nmi_update_count);
	}
	}

	void ftrace_nmi_exit(void)
	{
	/* Finish all executions before clearing in_nmi */
	smp_wmb();
	atomic_dec(&in_nmi);
	}

	static void wait_for_nmi(void)
	{
	int waited = 0;

	while (atomic_read(&in_nmi)) {
	waited = 1;
	cpu_relax();
	}

	if (waited)
	nmi_wait_count++;
	}

	static int
	do_ftrace_mod_code(unsigned long ip, void *new_code)
	{
	mod_code_ip = (void *)ip;
	mod_code_newcode = new_code;

	/* The buffers need to be visible before we let NMIs write them */
	smp_wmb();

	mod_code_write = 1;

	/* Make sure write bit is visible before we wait on NMIs */
	smp_mb();

	wait_for_nmi();

	/* Make sure all running NMIs have finished before we write the code */
	smp_mb();

	ftrace_mod_code();

	/* Make sure the write happens before clearing the bit */
	smp_wmb();

	mod_code_write = 0;

	/* make sure NMIs see the cleared bit */
	smp_mb();

	wait_for_nmi();

	return mod_code_status;
	}




	static unsigned char ftrace_nop[MCOUNT_INSN_SIZE];

	static unsigned char *ftrace_nop_replace(void)
	{
	return ftrace_nop;
	}

	static int
	ftrace_modify_code(unsigned long ip, unsigned char *old_code,
	unsigned char *new_code)
	{
	unsigned char replaced[MCOUNT_INSN_SIZE];

	/*
	* Note: Due to modules and __init, code can
	* disappear and change, we need to protect against faulting
	* as well as code changing. We do this by using the
	* probe_kernel_* functions.
	*
	* No real locking needed, this code is run through
	* kstop_machine, or before SMP starts.
	*/

	/* read the text we want to modify */
	if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
	return -EFAULT;

	/* Make sure it is what we expect it to be */
	if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
	return -EINVAL;

	/* replace the text with the new text */
	if (do_ftrace_mod_code(ip, new_code))
	return -EPERM;

	sync_core();

	return 0;
	}

	int ftrace_make_nop(struct module *mod,
	struct dyn_ftrace *rec, unsigned long addr)
	{
	unsigned char new, old;
	unsigned long ip = rec->ip;

	old = ftrace_call_replace(ip, addr);
	new = ftrace_nop_replace();

	return ftrace_modify_code(rec->ip, old, new);
	}

	int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
	{
	unsigned char new, old;
	unsigned long ip = rec->ip;

	old = ftrace_nop_replace();
	new = ftrace_call_replace(ip, addr);

	return ftrace_modify_code(rec->ip, old, new);
	}

	int ftrace_update_ftrace_func(ftrace_func_t func)
	{
	unsigned long ip = (unsigned long)(&ftrace_call);
	unsigned char old[MCOUNT_INSN_SIZE], *new;
	int ret;

	memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
	new = ftrace_call_replace(ip, (unsigned long)func);
	ret = ftrace_modify_code(ip, old, new);

	return ret;
	}

	int __init ftrace_dyn_arch_init(void *data)
	{
	extern const unsigned char ftrace_test_p6nop[];
	extern const unsigned char ftrace_test_nop5[];
	extern const unsigned char ftrace_test_jmp[];
	int faulted = 0;

	/*
	* There is no good nop for all x86 archs.
	* We will default to using the P6_NOP5, but first we
	* will test to make sure that the nop will actually
	* work on this CPU. If it faults, we will then
	* go to a lesser efficient 5 byte nop. If that fails
	* we then just use a jmp as our nop. This isn't the most
	* efficient nop, but we can not use a multi part nop
	* since we would then risk being preempted in the middle
	* of that nop, and if we enabled tracing then, it might
	* cause a system crash.
	*
	* TODO: check the cpuid to determine the best nop.
	*/
	asm volatile (
	"ftrace_test_jmp:"
	"jmp ftrace_test_p6nop\n"
	"nop\n"
	"nop\n"
	"nop\n" /* 2 byte jmp + 3 bytes */
	"ftrace_test_p6nop:"
	P6_NOP5
	"jmp 1f\n"
	"ftrace_test_nop5:"
	".byte 0x66,0x66,0x66,0x66,0x90\n"
	"1:"
	".section .fixup, \"ax\"\n"
	"2: movl $1, %0\n"
	" jmp ftrace_test_nop5\n"
	"3: movl $2, %0\n"
	" jmp 1b\n"
	".previous\n"
	_ASM_EXTABLE(ftrace_test_p6nop, 2b)
	_ASM_EXTABLE(ftrace_test_nop5, 3b)
	: "=r"(faulted) : "0" (faulted));

	switch (faulted) {
	case 0:
	pr_info("ftrace: converting mcount calls to 0f 1f 44 00 00\n");
	memcpy(ftrace_nop, ftrace_test_p6nop, MCOUNT_INSN_SIZE);
	break;
	case 1:
	pr_info("ftrace: converting mcount calls to 66 66 66 66 90\n");
	memcpy(ftrace_nop, ftrace_test_nop5, MCOUNT_INSN_SIZE);
	break;
	case 2:
	pr_info("ftrace: converting mcount calls to jmp . + 5\n");
	memcpy(ftrace_nop, ftrace_test_jmp, MCOUNT_INSN_SIZE);
	break;
	}

	/* The return code is retured via data */
	(unsigned long )data = 0;

	return 0;
	}
	#endif

	#ifdef CONFIG_FUNCTION_RET_TRACER

	#ifndef CONFIG_DYNAMIC_FTRACE

	/*
	* These functions are picked from those used on
	* this page for dynamic ftrace. They have been
	* simplified to ignore all traces in NMI context.
	*/
	static atomic_t in_nmi;

	void ftrace_nmi_enter(void)
	{
	atomic_inc(&in_nmi);
	}

	void ftrace_nmi_exit(void)
	{
	atomic_dec(&in_nmi);
	}
	#endif /* !CONFIG_DYNAMIC_FTRACE */

	/* Add a function return address to the trace stack on thread info.*/
	static int push_return_trace(unsigned long ret, unsigned long long time,
	unsigned long func)
	{
	int index;
	struct thread_info *ti = current_thread_info();

	/* The return trace stack is full */
	if (ti->curr_ret_stack == FTRACE_RET_STACK_SIZE - 1)
	return -EBUSY;

	index = ++ti->curr_ret_stack;
	barrier();
	ti->ret_stack[index].ret = ret;
	ti->ret_stack[index].func = func;
	ti->ret_stack[index].calltime = time;

	return 0;
	}

	/* Retrieve a function return address to the trace stack on thread info.*/
	static void pop_return_trace(unsigned long ret, unsigned long long time,
	unsigned long *func)
	{
	int index;

	struct thread_info *ti = current_thread_info();
	index = ti->curr_ret_stack;
	*ret = ti->ret_stack[index].ret;
	*func = ti->ret_stack[index].func;
	*time = ti->ret_stack[index].calltime;
	ti->curr_ret_stack--;
	}

	/*
	* Send the trace to the ring-buffer.
	* @return the original return address.
	*/
	unsigned long ftrace_return_to_handler(void)
	{
	struct ftrace_retfunc trace;
	pop_return_trace(&trace.ret, &trace.calltime, &trace.func);
	trace.rettime = cpu_clock(raw_smp_processor_id());
	ftrace_function_return(&trace);

	return trace.ret;
	}

	/*
	* 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 old;
	unsigned long long calltime;
	int faulted;
	unsigned long return_hooker = (unsigned long)
	&return_to_handler;

	/* Nmi's are currently unsupported */
	if (atomic_read(&in_nmi))
	return;

	/*
	* Protect against fault, even if it shouldn't
	* happen. This tool is too much intrusive to
	* ignore such a protection.
	*/
	asm volatile(
	"1: movl (%[parent_old]), %[old]\n"
	"2: movl %[return_hooker], (%[parent_replaced])\n"
	" movl $0, %[faulted]\n"

	".section .fixup, \"ax\"\n"
	"3: movl $1, %[faulted]\n"
	".previous\n"

	".section __ex_table, \"a\"\n"
	" .long 1b, 3b\n"
	" .long 2b, 3b\n"
	".previous\n"

	: [parent_replaced] "=r" (parent), [old] "=r" (old),
	[faulted] "=r" (faulted)
	: [parent_old] "0" (parent), [return_hooker] "r" (return_hooker)
	: "memory"
	);

	if (WARN_ON(faulted)) {
	unregister_ftrace_return();
	return;
	}

	if (WARN_ON(!__kernel_text_address(old))) {
	unregister_ftrace_return();
	*parent = old;
	return;
	}

	calltime = cpu_clock(raw_smp_processor_id());

	if (push_return_trace(old, calltime, self_addr) == -EBUSY)
	*parent = old;
	}

	#endif /* CONFIG_FUNCTION_RET_TRACER */