arch/sh/kernel/ftrace.c - maze/linux - Git at Google

 /*
  * Copyright (C) 2008 Matt Fleming <matt@console-pimps.org>
  * Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org>
  *
  * 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/uaccess.h>
 #include <linux/ftrace.h>
 #include <linux/string.h>
 #include <linux/init.h>
 #include <linux/io.h>
 #include <linux/kernel.h>
 #include <asm/ftrace.h>
 #include <asm/cacheflush.h>
 #include <asm/unistd.h>
 #include <trace/syscall.h>

 #ifdef CONFIG_DYNAMIC_FTRACE
 static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];

 static unsigned char ftrace_nop[4];
 /*
  * If we're trying to nop out a call to a function, we instead
  * place a call to the address after the memory table.
  *
  * 8c011060 <a>:
  * 8c011060:       02 d1           mov.l   8c01106c <a+0xc>,r1
  * 8c011062:       22 4f           sts.l   pr,@-r15
  * 8c011064:       02 c7           mova    8c011070 <a+0x10>,r0
  * 8c011066:       2b 41           jmp     @r1
  * 8c011068:       2a 40           lds     r0,pr
  * 8c01106a:       09 00           nop
  * 8c01106c:       68 24           .word 0x2468     <--- ip
  * 8c01106e:       1d 8c           .word 0x8c1d
  * 8c011070:       26 4f           lds.l   @r15+,pr <--- ip + MCOUNT_INSN_SIZE
  *
  * We write 0x8c011070 to 0x8c01106c so that on entry to a() we branch
  * past the _mcount call and continue executing code like normal.
  */
 static unsigned char *ftrace_nop_replace(unsigned long ip)
 {
 	__raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop);
 	return ftrace_nop;
 }

 static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
 {
 	/* Place the address in the memory table. */
 	__raw_writel(addr, ftrace_replaced_code);

 	/*
 	 * No locking needed, this must be called via kstop_machine
 	 * which in essence is like running on a uniprocessor machine.
 	 */
 	return ftrace_replaced_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) Wait for any running NMIs to finish and set a flag that says
  *    we are modifying code, it is done in an atomic operation.
  * 3) Write the code
  * 4) clear the flag.
  * 5) 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.
  */
 #define MOD_CODE_WRITE_FLAG (1 << 31)	/* set when NMI should do the write */
 static atomic_t nmi_running = ATOMIC_INIT(0);
 static int mod_code_status;		/* holds return value of text 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 clear_mod_flag(void)
 {
 	int old = atomic_read(&nmi_running);

 	for (;;) {
 		int new = old & ~MOD_CODE_WRITE_FLAG;

 		if (old == new)
 			break;

 		old = atomic_cmpxchg(&nmi_running, old, new);
 	}
 }

 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);

 	/* if we fail, then kill any new writers */
 	if (mod_code_status)
 		clear_mod_flag();
 }

 void ftrace_nmi_enter(void)
 {
 	if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
 		smp_rmb();
 		ftrace_mod_code();
 		atomic_inc(&nmi_update_count);
 	}
 	/* Must have previous changes seen before executions */
 	smp_mb();
 }

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

 static void wait_for_nmi_and_set_mod_flag(void)
 {
 	if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG))
 		return;

 	do {
 		cpu_relax();
 	} while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));

 	nmi_wait_count++;
 }

 static void wait_for_nmi(void)
 {
 	if (!atomic_read(&nmi_running))
 		return;

 	do {
 		cpu_relax();
 	} while (atomic_read(&nmi_running));

 	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_mb();

 	wait_for_nmi_and_set_mod_flag();

 	/* 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_mb();

 	clear_mod_flag();
 	wait_for_nmi();

 	return mod_code_status;
 }

 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;

 	flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);

 	return 0;
 }

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

 	memcpy(old, (unsigned char *)ip, MCOUNT_INSN_SIZE);
 	new = ftrace_call_replace(ip, (unsigned long)func);

 	return ftrace_modify_code(ip, old, new);
 }

 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(ip);

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

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

 int __init ftrace_dyn_arch_init(void)
 {
 	return 0;
 }
 #endif /* CONFIG_DYNAMIC_FTRACE */

 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 #ifdef CONFIG_DYNAMIC_FTRACE
 extern void ftrace_graph_call(void);

 static int ftrace_mod(unsigned long ip, unsigned long old_addr,
 		      unsigned long new_addr)
 {
 	unsigned char code[MCOUNT_INSN_SIZE];

 	if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
 		return -EFAULT;

 	if (old_addr != __raw_readl((unsigned long *)code))
 		return -EINVAL;

 	__raw_writel(new_addr, ip);
 	return 0;
 }

 int ftrace_enable_ftrace_graph_caller(void)
 {
 	unsigned long ip, old_addr, new_addr;

 	ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
 	old_addr = (unsigned long)(&skip_trace);
 	new_addr = (unsigned long)(&ftrace_graph_caller);

 	return ftrace_mod(ip, old_addr, new_addr);
 }

 int ftrace_disable_ftrace_graph_caller(void)
 {
 	unsigned long ip, old_addr, new_addr;

 	ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
 	old_addr = (unsigned long)(&ftrace_graph_caller);
 	new_addr = (unsigned long)(&skip_trace);

 	return ftrace_mod(ip, old_addr, new_addr);
 }
 #endif /* CONFIG_DYNAMIC_FTRACE */

 /*
  * Hook the return address and push it in the stack of return addrs
  * in the current thread info.
  *
  * This is the main routine for the function graph tracer. The function
  * graph tracer essentially works like this:
  *
  * parent is the stack address containing self_addr's return address.
  * We pull the real return address out of parent and store it in
  * current's ret_stack. Then, we replace the return address on the stack
  * with the address of return_to_handler. self_addr is the function that
  * called mcount.
  *
  * When self_addr returns, it will jump to return_to_handler which calls
  * ftrace_return_to_handler. ftrace_return_to_handler will pull the real
  * return address off of current's ret_stack and jump to it.
  */
 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
 {
 	unsigned long old;
 	int faulted, err;
 	struct ftrace_graph_ent trace;
 	unsigned long return_hooker = (unsigned long)&return_to_handler;

 	if (unlikely(atomic_read(&current->tracing_graph_pause)))
 		return;

 	/*
 	 * Protect against fault, even if it shouldn't
 	 * happen. This tool is too much intrusive to
 	 * ignore such a protection.
 	 */
 	__asm__ __volatile__(
 		"1:						\n\t"
 		"mov.l		@%2, %0				\n\t"
 		"2:						\n\t"
 		"mov.l		%3, @%2				\n\t"
 		"mov		#0, %1				\n\t"
 		"3:						\n\t"
 		".section .fixup, \"ax\"			\n\t"
 		"4:						\n\t"
 		"mov.l		5f, %0				\n\t"
 		"jmp		@%0				\n\t"
 		" mov		#1, %1				\n\t"
 		".balign 4					\n\t"
 		"5:	.long 3b				\n\t"
 		".previous					\n\t"
 		".section __ex_table,\"a\"			\n\t"
 		".long 1b, 4b					\n\t"
 		".long 2b, 4b					\n\t"
 		".previous					\n\t"
 		: "=&r" (old), "=r" (faulted)
 		: "r" (parent), "r" (return_hooker)
 	);

 	if (unlikely(faulted)) {
 		ftrace_graph_stop();
 		WARN_ON(1);
 		return;
 	}

 	err = ftrace_push_return_trace(old, self_addr, &trace.depth, 0);
 	if (err == -EBUSY) {
 		__raw_writel(old, parent);
 		return;
 	}

 	trace.func = self_addr;

 	/* Only trace if the calling function expects to */
 	if (!ftrace_graph_entry(&trace)) {
 		current->curr_ret_stack--;
 		__raw_writel(old, parent);
 	}
 }
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
	/*
	* Copyright (C) 2008 Matt Fleming <matt@console-pimps.org>
	* Copyright (C) 2008 Paul Mundt <lethal@linux-sh.org>
	*
	* 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/uaccess.h>
	#include <linux/ftrace.h>
	#include <linux/string.h>
	#include <linux/init.h>
	#include <linux/io.h>
	#include <linux/kernel.h>
	#include <asm/ftrace.h>
	#include <asm/cacheflush.h>
	#include <asm/unistd.h>
	#include <trace/syscall.h>

	#ifdef CONFIG_DYNAMIC_FTRACE
	static unsigned char ftrace_replaced_code[MCOUNT_INSN_SIZE];

	static unsigned char ftrace_nop[4];
	/*
	* If we're trying to nop out a call to a function, we instead
	* place a call to the address after the memory table.
	*
	* 8c011060 <a>:
	* 8c011060: 02 d1 mov.l 8c01106c <a+0xc>,r1
	* 8c011062: 22 4f sts.l pr,@-r15
	* 8c011064: 02 c7 mova 8c011070 <a+0x10>,r0
	* 8c011066: 2b 41 jmp @r1
	* 8c011068: 2a 40 lds r0,pr
	* 8c01106a: 09 00 nop
	* 8c01106c: 68 24 .word 0x2468 <--- ip
	* 8c01106e: 1d 8c .word 0x8c1d
	* 8c011070: 26 4f lds.l @r15+,pr <--- ip + MCOUNT_INSN_SIZE
	*
	* We write 0x8c011070 to 0x8c01106c so that on entry to a() we branch
	* past the _mcount call and continue executing code like normal.
	*/
	static unsigned char *ftrace_nop_replace(unsigned long ip)
	{
	__raw_writel(ip + MCOUNT_INSN_SIZE, ftrace_nop);
	return ftrace_nop;
	}

	static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
	{
	/* Place the address in the memory table. */
	__raw_writel(addr, ftrace_replaced_code);

	/*
	* No locking needed, this must be called via kstop_machine
	* which in essence is like running on a uniprocessor machine.
	*/
	return ftrace_replaced_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) Wait for any running NMIs to finish and set a flag that says
	* we are modifying code, it is done in an atomic operation.
	* 3) Write the code
	* 4) clear the flag.
	* 5) 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.
	*/
	#define MOD_CODE_WRITE_FLAG (1 << 31) /* set when NMI should do the write */
	static atomic_t nmi_running = ATOMIC_INIT(0);
	static int mod_code_status; /* holds return value of text 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 clear_mod_flag(void)
	{
	int old = atomic_read(&nmi_running);

	for (;;) {
	int new = old & ~MOD_CODE_WRITE_FLAG;

	if (old == new)
	break;

	old = atomic_cmpxchg(&nmi_running, old, new);
	}
	}

	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);

	/* if we fail, then kill any new writers */
	if (mod_code_status)
	clear_mod_flag();
	}

	void ftrace_nmi_enter(void)
	{
	if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
	smp_rmb();
	ftrace_mod_code();
	atomic_inc(&nmi_update_count);
	}
	/* Must have previous changes seen before executions */
	smp_mb();
	}

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

	static void wait_for_nmi_and_set_mod_flag(void)
	{
	if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG))
	return;

	do {
	cpu_relax();
	} while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));

	nmi_wait_count++;
	}

	static void wait_for_nmi(void)
	{
	if (!atomic_read(&nmi_running))
	return;

	do {
	cpu_relax();
	} while (atomic_read(&nmi_running));

	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_mb();

	wait_for_nmi_and_set_mod_flag();

	/* 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_mb();

	clear_mod_flag();
	wait_for_nmi();

	return mod_code_status;
	}

	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;

	flush_icache_range(ip, ip + MCOUNT_INSN_SIZE);

	return 0;
	}

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

	memcpy(old, (unsigned char *)ip, MCOUNT_INSN_SIZE);
	new = ftrace_call_replace(ip, (unsigned long)func);

	return ftrace_modify_code(ip, old, new);
	}

	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(ip);

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

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

	int __init ftrace_dyn_arch_init(void)
	{
	return 0;
	}
	#endif /* CONFIG_DYNAMIC_FTRACE */

	#ifdef CONFIG_FUNCTION_GRAPH_TRACER
	#ifdef CONFIG_DYNAMIC_FTRACE
	extern void ftrace_graph_call(void);

	static int ftrace_mod(unsigned long ip, unsigned long old_addr,
	unsigned long new_addr)
	{
	unsigned char code[MCOUNT_INSN_SIZE];

	if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
	return -EFAULT;

	if (old_addr != __raw_readl((unsigned long *)code))
	return -EINVAL;

	__raw_writel(new_addr, ip);
	return 0;
	}

	int ftrace_enable_ftrace_graph_caller(void)
	{
	unsigned long ip, old_addr, new_addr;

	ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
	old_addr = (unsigned long)(&skip_trace);
	new_addr = (unsigned long)(&ftrace_graph_caller);

	return ftrace_mod(ip, old_addr, new_addr);
	}

	int ftrace_disable_ftrace_graph_caller(void)
	{
	unsigned long ip, old_addr, new_addr;

	ip = (unsigned long)(&ftrace_graph_call) + GRAPH_INSN_OFFSET;
	old_addr = (unsigned long)(&ftrace_graph_caller);
	new_addr = (unsigned long)(&skip_trace);

	return ftrace_mod(ip, old_addr, new_addr);
	}
	#endif /* CONFIG_DYNAMIC_FTRACE */

	/*
	* Hook the return address and push it in the stack of return addrs
	* in the current thread info.
	*
	* This is the main routine for the function graph tracer. The function
	* graph tracer essentially works like this:
	*
	* parent is the stack address containing self_addr's return address.
	* We pull the real return address out of parent and store it in
	* current's ret_stack. Then, we replace the return address on the stack
	* with the address of return_to_handler. self_addr is the function that
	* called mcount.
	*
	* When self_addr returns, it will jump to return_to_handler which calls
	* ftrace_return_to_handler. ftrace_return_to_handler will pull the real
	* return address off of current's ret_stack and jump to it.
	*/
	void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
	{
	unsigned long old;
	int faulted, err;
	struct ftrace_graph_ent trace;
	unsigned long return_hooker = (unsigned long)&return_to_handler;

	if (unlikely(atomic_read(&current->tracing_graph_pause)))
	return;

	/*
	* Protect against fault, even if it shouldn't
	* happen. This tool is too much intrusive to
	* ignore such a protection.
	*/
	__asm__ __volatile__(
	"1: \n\t"
	"mov.l @%2, %0 \n\t"
	"2: \n\t"
	"mov.l %3, @%2 \n\t"
	"mov #0, %1 \n\t"
	"3: \n\t"
	".section .fixup, \"ax\" \n\t"
	"4: \n\t"
	"mov.l 5f, %0 \n\t"
	"jmp @%0 \n\t"
	" mov #1, %1 \n\t"
	".balign 4 \n\t"
	"5: .long 3b \n\t"
	".previous \n\t"
	".section __ex_table,\"a\" \n\t"
	".long 1b, 4b \n\t"
	".long 2b, 4b \n\t"
	".previous \n\t"
	: "=&r" (old), "=r" (faulted)
	: "r" (parent), "r" (return_hooker)
	);

	if (unlikely(faulted)) {
	ftrace_graph_stop();
	WARN_ON(1);
	return;
	}

	err = ftrace_push_return_trace(old, self_addr, &trace.depth, 0);
	if (err == -EBUSY) {
	__raw_writel(old, parent);
	return;
	}

	trace.func = self_addr;

	/* Only trace if the calling function expects to */
	if (!ftrace_graph_entry(&trace)) {
	current->curr_ret_stack--;
	__raw_writel(old, parent);
	}
	}
	#endif /* CONFIG_FUNCTION_GRAPH_TRACER */