arch/x86/kernel/ftrace.c - arm/linux-arm64-legacy - Git at Google

 /*
  * 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.
  */

 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

 #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 <linux/module.h>

 #include <trace/syscall.h>

 #include <asm/cacheflush.h>
 #include <asm/kprobes.h>
 #include <asm/ftrace.h>
 #include <asm/nops.h>

 #ifdef CONFIG_DYNAMIC_FTRACE

 int ftrace_arch_code_modify_prepare(void)
 {
 	set_kernel_text_rw();
 	set_all_modules_text_rw();
 	return 0;
 }

 int ftrace_arch_code_modify_post_process(void)
 {
 	set_all_modules_text_ro();
 	set_kernel_text_ro();
 	return 0;
 }

 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;
 }

 static inline int
 within(unsigned long addr, unsigned long start, unsigned long end)
 {
 	return addr >= start && addr < end;
 }

 static unsigned long text_ip_addr(unsigned long ip)
 {
 	/*
 	 * On x86_64, kernel text mappings are mapped read-only with
 	 * CONFIG_DEBUG_RODATA. So we use the kernel identity mapping instead
 	 * of the kernel text mapping to modify the kernel text.
 	 *
 	 * For 32bit kernels, these mappings are same and we can use
 	 * kernel identity mapping to modify code.
 	 */
 	if (within(ip, (unsigned long)_text, (unsigned long)_etext))
 		ip = (unsigned long)__va(__pa_symbol(ip));

 	return ip;
 }

 static const unsigned char *ftrace_nop_replace(void)
 {
 	return ideal_nops[NOP_ATOMIC5];
 }

 static int
 ftrace_modify_code_direct(unsigned long ip, unsigned const char *old_code,
 		   unsigned const 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;

 	ip = text_ip_addr(ip);

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

 	sync_core();

 	return 0;
 }

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

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

 	/*
 	 * On boot up, and when modules are loaded, the MCOUNT_ADDR
 	 * is converted to a nop, and will never become MCOUNT_ADDR
 	 * again. This code is either running before SMP (on boot up)
 	 * or before the code will ever be executed (module load).
 	 * We do not want to use the breakpoint version in this case,
 	 * just modify the code directly.
 	 */
 	if (addr == MCOUNT_ADDR)
 		return ftrace_modify_code_direct(rec->ip, old, new);

 	/* Normal cases use add_brk_on_nop */
 	WARN_ONCE(1, "invalid use of ftrace_make_nop");
 	return -EINVAL;
 }

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

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

 	/* Should only be called when module is loaded */
 	return ftrace_modify_code_direct(rec->ip, old, new);
 }

 /*
  * The modifying_ftrace_code is used to tell the breakpoint
  * handler to call ftrace_int3_handler(). If it fails to
  * call this handler for a breakpoint added by ftrace, then
  * the kernel may crash.
  *
  * As atomic_writes on x86 do not need a barrier, we do not
  * need to add smp_mb()s for this to work. It is also considered
  * that we can not read the modifying_ftrace_code before
  * executing the breakpoint. That would be quite remarkable if
  * it could do that. Here's the flow that is required:
  *
  *   CPU-0                          CPU-1
  *
  * atomic_inc(mfc);
  * write int3s
  *				<trap-int3> // implicit (r)mb
  *				if (atomic_read(mfc))
  *					call ftrace_int3_handler()
  *
  * Then when we are finished:
  *
  * atomic_dec(mfc);
  *
  * If we hit a breakpoint that was not set by ftrace, it does not
  * matter if ftrace_int3_handler() is called or not. It will
  * simply be ignored. But it is crucial that a ftrace nop/caller
  * breakpoint is handled. No other user should ever place a
  * breakpoint on an ftrace nop/caller location. It must only
  * be done by this code.
  */
 atomic_t modifying_ftrace_code __read_mostly;

 static int
 ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
 		   unsigned const char *new_code);

 /*
  * Should never be called:
  *  As it is only called by __ftrace_replace_code() which is called by
  *  ftrace_replace_code() that x86 overrides, and by ftrace_update_code()
  *  which is called to turn mcount into nops or nops into function calls
  *  but not to convert a function from not using regs to one that uses
  *  regs, which ftrace_modify_call() is for.
  */
 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 				 unsigned long addr)
 {
 	WARN_ON(1);
 	return -EINVAL;
 }

 static unsigned long ftrace_update_func;

 static int update_ftrace_func(unsigned long ip, void *new)
 {
 	unsigned char old[MCOUNT_INSN_SIZE];
 	int ret;

 	memcpy(old, (void *)ip, MCOUNT_INSN_SIZE);

 	ftrace_update_func = ip;
 	/* Make sure the breakpoints see the ftrace_update_func update */
 	smp_wmb();

 	/* See comment above by declaration of modifying_ftrace_code */
 	atomic_inc(&modifying_ftrace_code);

 	ret = ftrace_modify_code(ip, old, new);

 	atomic_dec(&modifying_ftrace_code);

 	return ret;
 }

 int ftrace_update_ftrace_func(ftrace_func_t func)
 {
 	unsigned long ip = (unsigned long)(&ftrace_call);
 	unsigned char *new;
 	int ret;

 	new = ftrace_call_replace(ip, (unsigned long)func);
 	ret = update_ftrace_func(ip, new);

 	/* Also update the regs callback function */
 	if (!ret) {
 		ip = (unsigned long)(&ftrace_regs_call);
 		new = ftrace_call_replace(ip, (unsigned long)func);
 		ret = update_ftrace_func(ip, new);
 	}

 	return ret;
 }

 static int is_ftrace_caller(unsigned long ip)
 {
 	if (ip == ftrace_update_func)
 		return 1;

 	return 0;
 }

 /*
  * A breakpoint was added to the code address we are about to
  * modify, and this is the handle that will just skip over it.
  * We are either changing a nop into a trace call, or a trace
  * call to a nop. While the change is taking place, we treat
  * it just like it was a nop.
  */
 int ftrace_int3_handler(struct pt_regs *regs)
 {
 	unsigned long ip;

 	if (WARN_ON_ONCE(!regs))
 		return 0;

 	ip = regs->ip - 1;
 	if (!ftrace_location(ip) && !is_ftrace_caller(ip))
 		return 0;

 	regs->ip += MCOUNT_INSN_SIZE - 1;

 	return 1;
 }

 static int ftrace_write(unsigned long ip, const char *val, int size)
 {
 	ip = text_ip_addr(ip);

 	if (probe_kernel_write((void *)ip, val, size))
 		return -EPERM;

 	return 0;
 }

 static int add_break(unsigned long ip, const char *old)
 {
 	unsigned char replaced[MCOUNT_INSN_SIZE];
 	unsigned char brk = BREAKPOINT_INSTRUCTION;

 	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, MCOUNT_INSN_SIZE) != 0)
 		return -EINVAL;

 	return ftrace_write(ip, &brk, 1);
 }

 static int add_brk_on_call(struct dyn_ftrace *rec, unsigned long addr)
 {
 	unsigned const char *old;
 	unsigned long ip = rec->ip;

 	old = ftrace_call_replace(ip, addr);

 	return add_break(rec->ip, old);
 }


 static int add_brk_on_nop(struct dyn_ftrace *rec)
 {
 	unsigned const char *old;

 	old = ftrace_nop_replace();

 	return add_break(rec->ip, old);
 }

 static int add_breakpoints(struct dyn_ftrace *rec, int enable)
 {
 	unsigned long ftrace_addr;
 	int ret;

 	ftrace_addr = ftrace_get_addr_curr(rec);

 	ret = ftrace_test_record(rec, enable);

 	switch (ret) {
 	case FTRACE_UPDATE_IGNORE:
 		return 0;

 	case FTRACE_UPDATE_MAKE_CALL:
 		/* converting nop to call */
 		return add_brk_on_nop(rec);

 	case FTRACE_UPDATE_MODIFY_CALL:
 	case FTRACE_UPDATE_MAKE_NOP:
 		/* converting a call to a nop */
 		return add_brk_on_call(rec, ftrace_addr);
 	}
 	return 0;
 }

 /*
  * On error, we need to remove breakpoints. This needs to
  * be done caefully. If the address does not currently have a
  * breakpoint, we know we are done. Otherwise, we look at the
  * remaining 4 bytes of the instruction. If it matches a nop
  * we replace the breakpoint with the nop. Otherwise we replace
  * it with the call instruction.
  */
 static int remove_breakpoint(struct dyn_ftrace *rec)
 {
 	unsigned char ins[MCOUNT_INSN_SIZE];
 	unsigned char brk = BREAKPOINT_INSTRUCTION;
 	const unsigned char *nop;
 	unsigned long ftrace_addr;
 	unsigned long ip = rec->ip;

 	/* If we fail the read, just give up */
 	if (probe_kernel_read(ins, (void *)ip, MCOUNT_INSN_SIZE))
 		return -EFAULT;

 	/* If this does not have a breakpoint, we are done */
 	if (ins[0] != brk)
 		return 0;

 	nop = ftrace_nop_replace();

 	/*
 	 * If the last 4 bytes of the instruction do not match
 	 * a nop, then we assume that this is a call to ftrace_addr.
 	 */
 	if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0) {
 		/*
 		 * For extra paranoidism, we check if the breakpoint is on
 		 * a call that would actually jump to the ftrace_addr.
 		 * If not, don't touch the breakpoint, we make just create
 		 * a disaster.
 		 */
 		ftrace_addr = ftrace_get_addr_new(rec);
 		nop = ftrace_call_replace(ip, ftrace_addr);

 		if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) == 0)
 			goto update;

 		/* Check both ftrace_addr and ftrace_old_addr */
 		ftrace_addr = ftrace_get_addr_curr(rec);
 		nop = ftrace_call_replace(ip, ftrace_addr);

 		if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0)
 			return -EINVAL;
 	}

  update:
 	return ftrace_write(ip, nop, 1);
 }

 static int add_update_code(unsigned long ip, unsigned const char *new)
 {
 	/* skip breakpoint */
 	ip++;
 	new++;
 	return ftrace_write(ip, new, MCOUNT_INSN_SIZE - 1);
 }

 static int add_update_call(struct dyn_ftrace *rec, unsigned long addr)
 {
 	unsigned long ip = rec->ip;
 	unsigned const char *new;

 	new = ftrace_call_replace(ip, addr);
 	return add_update_code(ip, new);
 }

 static int add_update_nop(struct dyn_ftrace *rec)
 {
 	unsigned long ip = rec->ip;
 	unsigned const char *new;

 	new = ftrace_nop_replace();
 	return add_update_code(ip, new);
 }

 static int add_update(struct dyn_ftrace *rec, int enable)
 {
 	unsigned long ftrace_addr;
 	int ret;

 	ret = ftrace_test_record(rec, enable);

 	ftrace_addr  = ftrace_get_addr_new(rec);

 	switch (ret) {
 	case FTRACE_UPDATE_IGNORE:
 		return 0;

 	case FTRACE_UPDATE_MODIFY_CALL:
 	case FTRACE_UPDATE_MAKE_CALL:
 		/* converting nop to call */
 		return add_update_call(rec, ftrace_addr);

 	case FTRACE_UPDATE_MAKE_NOP:
 		/* converting a call to a nop */
 		return add_update_nop(rec);
 	}

 	return 0;
 }

 static int finish_update_call(struct dyn_ftrace *rec, unsigned long addr)
 {
 	unsigned long ip = rec->ip;
 	unsigned const char *new;

 	new = ftrace_call_replace(ip, addr);

 	return ftrace_write(ip, new, 1);
 }

 static int finish_update_nop(struct dyn_ftrace *rec)
 {
 	unsigned long ip = rec->ip;
 	unsigned const char *new;

 	new = ftrace_nop_replace();

 	return ftrace_write(ip, new, 1);
 }

 static int finish_update(struct dyn_ftrace *rec, int enable)
 {
 	unsigned long ftrace_addr;
 	int ret;

 	ret = ftrace_update_record(rec, enable);

 	ftrace_addr = ftrace_get_addr_new(rec);

 	switch (ret) {
 	case FTRACE_UPDATE_IGNORE:
 		return 0;

 	case FTRACE_UPDATE_MODIFY_CALL:
 	case FTRACE_UPDATE_MAKE_CALL:
 		/* converting nop to call */
 		return finish_update_call(rec, ftrace_addr);

 	case FTRACE_UPDATE_MAKE_NOP:
 		/* converting a call to a nop */
 		return finish_update_nop(rec);
 	}

 	return 0;
 }

 static void do_sync_core(void *data)
 {
 	sync_core();
 }

 static void run_sync(void)
 {
 	int enable_irqs = irqs_disabled();

 	/* We may be called with interrupts disbled (on bootup). */
 	if (enable_irqs)
 		local_irq_enable();
 	on_each_cpu(do_sync_core, NULL, 1);
 	if (enable_irqs)
 		local_irq_disable();
 }

 void ftrace_replace_code(int enable)
 {
 	struct ftrace_rec_iter *iter;
 	struct dyn_ftrace *rec;
 	const char *report = "adding breakpoints";
 	int count = 0;
 	int ret;

 	for_ftrace_rec_iter(iter) {
 		rec = ftrace_rec_iter_record(iter);

 		ret = add_breakpoints(rec, enable);
 		if (ret)
 			goto remove_breakpoints;
 		count++;
 	}

 	run_sync();

 	report = "updating code";

 	for_ftrace_rec_iter(iter) {
 		rec = ftrace_rec_iter_record(iter);

 		ret = add_update(rec, enable);
 		if (ret)
 			goto remove_breakpoints;
 	}

 	run_sync();

 	report = "removing breakpoints";

 	for_ftrace_rec_iter(iter) {
 		rec = ftrace_rec_iter_record(iter);

 		ret = finish_update(rec, enable);
 		if (ret)
 			goto remove_breakpoints;
 	}

 	run_sync();

 	return;

  remove_breakpoints:
 	pr_warn("Failed on %s (%d):\n", report, count);
 	ftrace_bug(ret, rec ? rec->ip : 0);
 	for_ftrace_rec_iter(iter) {
 		rec = ftrace_rec_iter_record(iter);
 		/*
 		 * Breakpoints are handled only when this function is in
 		 * progress. The system could not work with them.
 		 */
 		if (remove_breakpoint(rec))
 			BUG();
 	}
 	run_sync();
 }

 static int
 ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
 		   unsigned const char *new_code)
 {
 	int ret;

 	ret = add_break(ip, old_code);
 	if (ret)
 		goto out;

 	run_sync();

 	ret = add_update_code(ip, new_code);
 	if (ret)
 		goto fail_update;

 	run_sync();

 	ret = ftrace_write(ip, new_code, 1);
 	/*
 	 * The breakpoint is handled only when this function is in progress.
 	 * The system could not work if we could not remove it.
 	 */
 	BUG_ON(ret);
  out:
 	run_sync();
 	return ret;

  fail_update:
 	/* Also here the system could not work with the breakpoint */
 	if (ftrace_write(ip, old_code, 1))
 		BUG();
 	goto out;
 }

 void arch_ftrace_update_code(int command)
 {
 	/* See comment above by declaration of modifying_ftrace_code */
 	atomic_inc(&modifying_ftrace_code);

 	ftrace_modify_all_code(command);

 	atomic_dec(&modifying_ftrace_code);
 }

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

 #ifdef CONFIG_FUNCTION_GRAPH_TRACER

 #ifdef CONFIG_DYNAMIC_FTRACE
 extern void ftrace_graph_call(void);

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

 	/* Jmp not a call (ignore the .e8) */
 	calc.e8		= 0xe9;
 	calc.offset	= ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr);

 	/*
 	 * ftrace external locks synchronize the access to the static variable.
 	 */
 	return calc.code;
 }

 static int ftrace_mod_jmp(unsigned long ip, void *func)
 {
 	unsigned char *new;

 	new = ftrace_jmp_replace(ip, (unsigned long)func);

 	return update_ftrace_func(ip, new);
 }

 int ftrace_enable_ftrace_graph_caller(void)
 {
 	unsigned long ip = (unsigned long)(&ftrace_graph_call);

 	return ftrace_mod_jmp(ip, &ftrace_graph_caller);
 }

 int ftrace_disable_ftrace_graph_caller(void)
 {
 	unsigned long ip = (unsigned long)(&ftrace_graph_call);

 	return ftrace_mod_jmp(ip, &ftrace_stub);
 }

 #endif /* !CONFIG_DYNAMIC_FTRACE */

 /*
  * 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 frame_pointer)
 {
 	unsigned long old;
 	int faulted;
 	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: " _ASM_MOV " (%[parent]), %[old]\n"
 		"2: " _ASM_MOV " %[return_hooker], (%[parent])\n"
 		"   movl $0, %[faulted]\n"
 		"3:\n"

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

 		_ASM_EXTABLE(1b, 4b)
 		_ASM_EXTABLE(2b, 4b)

 		: [old] "=&r" (old), [faulted] "=r" (faulted)
 		: [parent] "r" (parent), [return_hooker] "r" (return_hooker)
 		: "memory"
 	);

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

 	trace.func = self_addr;
 	trace.depth = current->curr_ret_stack + 1;

 	/* Only trace if the calling function expects to */
 	if (!ftrace_graph_entry(&trace)) {
 		*parent = old;
 		return;
 	}

 	if (ftrace_push_return_trace(old, self_addr, &trace.depth,
 		    frame_pointer) == -EBUSY) {
 		*parent = old;
 		return;
 	}
 }
 #endif /* CONFIG_FUNCTION_GRAPH_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.
	*/

	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

	#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 <linux/module.h>

	#include <trace/syscall.h>

	#include <asm/cacheflush.h>
	#include <asm/kprobes.h>
	#include <asm/ftrace.h>
	#include <asm/nops.h>

	#ifdef CONFIG_DYNAMIC_FTRACE

	int ftrace_arch_code_modify_prepare(void)
	{
	set_kernel_text_rw();
	set_all_modules_text_rw();
	return 0;
	}

	int ftrace_arch_code_modify_post_process(void)
	{
	set_all_modules_text_ro();
	set_kernel_text_ro();
	return 0;
	}

	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;
	}

	static inline int
	within(unsigned long addr, unsigned long start, unsigned long end)
	{
	return addr >= start && addr < end;
	}

	static unsigned long text_ip_addr(unsigned long ip)
	{
	/*
	* On x86_64, kernel text mappings are mapped read-only with
	* CONFIG_DEBUG_RODATA. So we use the kernel identity mapping instead
	* of the kernel text mapping to modify the kernel text.
	*
	* For 32bit kernels, these mappings are same and we can use
	* kernel identity mapping to modify code.
	*/
	if (within(ip, (unsigned long)_text, (unsigned long)_etext))
	ip = (unsigned long)__va(__pa_symbol(ip));

	return ip;
	}

	static const unsigned char *ftrace_nop_replace(void)
	{
	return ideal_nops[NOP_ATOMIC5];
	}

	static int
	ftrace_modify_code_direct(unsigned long ip, unsigned const char *old_code,
	unsigned const 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;

	ip = text_ip_addr(ip);

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

	sync_core();

	return 0;
	}

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

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

	/*
	* On boot up, and when modules are loaded, the MCOUNT_ADDR
	* is converted to a nop, and will never become MCOUNT_ADDR
	* again. This code is either running before SMP (on boot up)
	* or before the code will ever be executed (module load).
	* We do not want to use the breakpoint version in this case,
	* just modify the code directly.
	*/
	if (addr == MCOUNT_ADDR)
	return ftrace_modify_code_direct(rec->ip, old, new);

	/* Normal cases use add_brk_on_nop */
	WARN_ONCE(1, "invalid use of ftrace_make_nop");
	return -EINVAL;
	}

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

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

	/* Should only be called when module is loaded */
	return ftrace_modify_code_direct(rec->ip, old, new);
	}

	/*
	* The modifying_ftrace_code is used to tell the breakpoint
	* handler to call ftrace_int3_handler(). If it fails to
	* call this handler for a breakpoint added by ftrace, then
	* the kernel may crash.
	*
	* As atomic_writes on x86 do not need a barrier, we do not
	* need to add smp_mb()s for this to work. It is also considered
	* that we can not read the modifying_ftrace_code before
	* executing the breakpoint. That would be quite remarkable if
	* it could do that. Here's the flow that is required:
	*
	* CPU-0 CPU-1
	*
	* atomic_inc(mfc);
	* write int3s
	* <trap-int3> // implicit (r)mb
	* if (atomic_read(mfc))
	* call ftrace_int3_handler()
	*
	* Then when we are finished:
	*
	* atomic_dec(mfc);
	*
	* If we hit a breakpoint that was not set by ftrace, it does not
	* matter if ftrace_int3_handler() is called or not. It will
	* simply be ignored. But it is crucial that a ftrace nop/caller
	* breakpoint is handled. No other user should ever place a
	* breakpoint on an ftrace nop/caller location. It must only
	* be done by this code.
	*/
	atomic_t modifying_ftrace_code __read_mostly;

	static int
	ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
	unsigned const char *new_code);

	/*
	* Should never be called:
	* As it is only called by __ftrace_replace_code() which is called by
	* ftrace_replace_code() that x86 overrides, and by ftrace_update_code()
	* which is called to turn mcount into nops or nops into function calls
	* but not to convert a function from not using regs to one that uses
	* regs, which ftrace_modify_call() is for.
	*/
	int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
	unsigned long addr)
	{
	WARN_ON(1);
	return -EINVAL;
	}

	static unsigned long ftrace_update_func;

	static int update_ftrace_func(unsigned long ip, void *new)
	{
	unsigned char old[MCOUNT_INSN_SIZE];
	int ret;

	memcpy(old, (void *)ip, MCOUNT_INSN_SIZE);

	ftrace_update_func = ip;
	/* Make sure the breakpoints see the ftrace_update_func update */
	smp_wmb();

	/* See comment above by declaration of modifying_ftrace_code */
	atomic_inc(&modifying_ftrace_code);

	ret = ftrace_modify_code(ip, old, new);

	atomic_dec(&modifying_ftrace_code);

	return ret;
	}

	int ftrace_update_ftrace_func(ftrace_func_t func)
	{
	unsigned long ip = (unsigned long)(&ftrace_call);
	unsigned char *new;
	int ret;

	new = ftrace_call_replace(ip, (unsigned long)func);
	ret = update_ftrace_func(ip, new);

	/* Also update the regs callback function */
	if (!ret) {
	ip = (unsigned long)(&ftrace_regs_call);
	new = ftrace_call_replace(ip, (unsigned long)func);
	ret = update_ftrace_func(ip, new);
	}

	return ret;
	}

	static int is_ftrace_caller(unsigned long ip)
	{
	if (ip == ftrace_update_func)
	return 1;

	return 0;
	}

	/*
	* A breakpoint was added to the code address we are about to
	* modify, and this is the handle that will just skip over it.
	* We are either changing a nop into a trace call, or a trace
	* call to a nop. While the change is taking place, we treat
	* it just like it was a nop.
	*/
	int ftrace_int3_handler(struct pt_regs *regs)
	{
	unsigned long ip;

	if (WARN_ON_ONCE(!regs))
	return 0;

	ip = regs->ip - 1;
	if (!ftrace_location(ip) && !is_ftrace_caller(ip))
	return 0;

	regs->ip += MCOUNT_INSN_SIZE - 1;

	return 1;
	}

	static int ftrace_write(unsigned long ip, const char *val, int size)
	{
	ip = text_ip_addr(ip);

	if (probe_kernel_write((void *)ip, val, size))
	return -EPERM;

	return 0;
	}

	static int add_break(unsigned long ip, const char *old)
	{
	unsigned char replaced[MCOUNT_INSN_SIZE];
	unsigned char brk = BREAKPOINT_INSTRUCTION;

	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, MCOUNT_INSN_SIZE) != 0)
	return -EINVAL;

	return ftrace_write(ip, &brk, 1);
	}

	static int add_brk_on_call(struct dyn_ftrace *rec, unsigned long addr)
	{
	unsigned const char *old;
	unsigned long ip = rec->ip;

	old = ftrace_call_replace(ip, addr);

	return add_break(rec->ip, old);
	}


	static int add_brk_on_nop(struct dyn_ftrace *rec)
	{
	unsigned const char *old;

	old = ftrace_nop_replace();

	return add_break(rec->ip, old);
	}

	static int add_breakpoints(struct dyn_ftrace *rec, int enable)
	{
	unsigned long ftrace_addr;
	int ret;

	ftrace_addr = ftrace_get_addr_curr(rec);

	ret = ftrace_test_record(rec, enable);

	switch (ret) {
	case FTRACE_UPDATE_IGNORE:
	return 0;

	case FTRACE_UPDATE_MAKE_CALL:
	/* converting nop to call */
	return add_brk_on_nop(rec);

	case FTRACE_UPDATE_MODIFY_CALL:
	case FTRACE_UPDATE_MAKE_NOP:
	/* converting a call to a nop */
	return add_brk_on_call(rec, ftrace_addr);
	}
	return 0;
	}

	/*
	* On error, we need to remove breakpoints. This needs to
	* be done caefully. If the address does not currently have a
	* breakpoint, we know we are done. Otherwise, we look at the
	* remaining 4 bytes of the instruction. If it matches a nop
	* we replace the breakpoint with the nop. Otherwise we replace
	* it with the call instruction.
	*/
	static int remove_breakpoint(struct dyn_ftrace *rec)
	{
	unsigned char ins[MCOUNT_INSN_SIZE];
	unsigned char brk = BREAKPOINT_INSTRUCTION;
	const unsigned char *nop;
	unsigned long ftrace_addr;
	unsigned long ip = rec->ip;

	/* If we fail the read, just give up */
	if (probe_kernel_read(ins, (void *)ip, MCOUNT_INSN_SIZE))
	return -EFAULT;

	/* If this does not have a breakpoint, we are done */
	if (ins[0] != brk)
	return 0;

	nop = ftrace_nop_replace();

	/*
	* If the last 4 bytes of the instruction do not match
	* a nop, then we assume that this is a call to ftrace_addr.
	*/
	if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0) {
	/*
	* For extra paranoidism, we check if the breakpoint is on
	* a call that would actually jump to the ftrace_addr.
	* If not, don't touch the breakpoint, we make just create
	* a disaster.
	*/
	ftrace_addr = ftrace_get_addr_new(rec);
	nop = ftrace_call_replace(ip, ftrace_addr);

	if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) == 0)
	goto update;

	/* Check both ftrace_addr and ftrace_old_addr */
	ftrace_addr = ftrace_get_addr_curr(rec);
	nop = ftrace_call_replace(ip, ftrace_addr);

	if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0)
	return -EINVAL;
	}

	update:
	return ftrace_write(ip, nop, 1);
	}

	static int add_update_code(unsigned long ip, unsigned const char *new)
	{
	/* skip breakpoint */
	ip++;
	new++;
	return ftrace_write(ip, new, MCOUNT_INSN_SIZE - 1);
	}

	static int add_update_call(struct dyn_ftrace *rec, unsigned long addr)
	{
	unsigned long ip = rec->ip;
	unsigned const char *new;

	new = ftrace_call_replace(ip, addr);
	return add_update_code(ip, new);
	}

	static int add_update_nop(struct dyn_ftrace *rec)
	{
	unsigned long ip = rec->ip;
	unsigned const char *new;

	new = ftrace_nop_replace();
	return add_update_code(ip, new);
	}

	static int add_update(struct dyn_ftrace *rec, int enable)
	{
	unsigned long ftrace_addr;
	int ret;

	ret = ftrace_test_record(rec, enable);

	ftrace_addr = ftrace_get_addr_new(rec);

	switch (ret) {
	case FTRACE_UPDATE_IGNORE:
	return 0;

	case FTRACE_UPDATE_MODIFY_CALL:
	case FTRACE_UPDATE_MAKE_CALL:
	/* converting nop to call */
	return add_update_call(rec, ftrace_addr);

	case FTRACE_UPDATE_MAKE_NOP:
	/* converting a call to a nop */
	return add_update_nop(rec);
	}

	return 0;
	}

	static int finish_update_call(struct dyn_ftrace *rec, unsigned long addr)
	{
	unsigned long ip = rec->ip;
	unsigned const char *new;

	new = ftrace_call_replace(ip, addr);

	return ftrace_write(ip, new, 1);
	}

	static int finish_update_nop(struct dyn_ftrace *rec)
	{
	unsigned long ip = rec->ip;
	unsigned const char *new;

	new = ftrace_nop_replace();

	return ftrace_write(ip, new, 1);
	}

	static int finish_update(struct dyn_ftrace *rec, int enable)
	{
	unsigned long ftrace_addr;
	int ret;

	ret = ftrace_update_record(rec, enable);

	ftrace_addr = ftrace_get_addr_new(rec);

	switch (ret) {
	case FTRACE_UPDATE_IGNORE:
	return 0;

	case FTRACE_UPDATE_MODIFY_CALL:
	case FTRACE_UPDATE_MAKE_CALL:
	/* converting nop to call */
	return finish_update_call(rec, ftrace_addr);

	case FTRACE_UPDATE_MAKE_NOP:
	/* converting a call to a nop */
	return finish_update_nop(rec);
	}

	return 0;
	}

	static void do_sync_core(void *data)
	{
	sync_core();
	}

	static void run_sync(void)
	{
	int enable_irqs = irqs_disabled();

	/* We may be called with interrupts disbled (on bootup). */
	if (enable_irqs)
	local_irq_enable();
	on_each_cpu(do_sync_core, NULL, 1);
	if (enable_irqs)
	local_irq_disable();
	}

	void ftrace_replace_code(int enable)
	{
	struct ftrace_rec_iter *iter;
	struct dyn_ftrace *rec;
	const char *report = "adding breakpoints";
	int count = 0;
	int ret;

	for_ftrace_rec_iter(iter) {
	rec = ftrace_rec_iter_record(iter);

	ret = add_breakpoints(rec, enable);
	if (ret)
	goto remove_breakpoints;
	count++;
	}

	run_sync();

	report = "updating code";

	for_ftrace_rec_iter(iter) {
	rec = ftrace_rec_iter_record(iter);

	ret = add_update(rec, enable);
	if (ret)
	goto remove_breakpoints;
	}

	run_sync();

	report = "removing breakpoints";

	for_ftrace_rec_iter(iter) {
	rec = ftrace_rec_iter_record(iter);

	ret = finish_update(rec, enable);
	if (ret)
	goto remove_breakpoints;
	}

	run_sync();

	return;

	remove_breakpoints:
	pr_warn("Failed on %s (%d):\n", report, count);
	ftrace_bug(ret, rec ? rec->ip : 0);
	for_ftrace_rec_iter(iter) {
	rec = ftrace_rec_iter_record(iter);
	/*
	* Breakpoints are handled only when this function is in
	* progress. The system could not work with them.
	*/
	if (remove_breakpoint(rec))
	BUG();
	}
	run_sync();
	}

	static int
	ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
	unsigned const char *new_code)
	{
	int ret;

	ret = add_break(ip, old_code);
	if (ret)
	goto out;

	run_sync();

	ret = add_update_code(ip, new_code);
	if (ret)
	goto fail_update;

	run_sync();

	ret = ftrace_write(ip, new_code, 1);
	/*
	* The breakpoint is handled only when this function is in progress.
	* The system could not work if we could not remove it.
	*/
	BUG_ON(ret);
	out:
	run_sync();
	return ret;

	fail_update:
	/* Also here the system could not work with the breakpoint */
	if (ftrace_write(ip, old_code, 1))
	BUG();
	goto out;
	}

	void arch_ftrace_update_code(int command)
	{
	/* See comment above by declaration of modifying_ftrace_code */
	atomic_inc(&modifying_ftrace_code);

	ftrace_modify_all_code(command);

	atomic_dec(&modifying_ftrace_code);
	}

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

	#ifdef CONFIG_FUNCTION_GRAPH_TRACER

	#ifdef CONFIG_DYNAMIC_FTRACE
	extern void ftrace_graph_call(void);

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

	/* Jmp not a call (ignore the .e8) */
	calc.e8 = 0xe9;
	calc.offset = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr);

	/*
	* ftrace external locks synchronize the access to the static variable.
	*/
	return calc.code;
	}

	static int ftrace_mod_jmp(unsigned long ip, void *func)
	{
	unsigned char *new;

	new = ftrace_jmp_replace(ip, (unsigned long)func);

	return update_ftrace_func(ip, new);
	}

	int ftrace_enable_ftrace_graph_caller(void)
	{
	unsigned long ip = (unsigned long)(&ftrace_graph_call);

	return ftrace_mod_jmp(ip, &ftrace_graph_caller);
	}

	int ftrace_disable_ftrace_graph_caller(void)
	{
	unsigned long ip = (unsigned long)(&ftrace_graph_call);

	return ftrace_mod_jmp(ip, &ftrace_stub);
	}

	#endif /* !CONFIG_DYNAMIC_FTRACE */

	/*
	* 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 frame_pointer)
	{
	unsigned long old;
	int faulted;
	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: " _ASM_MOV " (%[parent]), %[old]\n"
	"2: " _ASM_MOV " %[return_hooker], (%[parent])\n"
	" movl $0, %[faulted]\n"
	"3:\n"

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

	_ASM_EXTABLE(1b, 4b)
	_ASM_EXTABLE(2b, 4b)

	: [old] "=&r" (old), [faulted] "=r" (faulted)
	: [parent] "r" (parent), [return_hooker] "r" (return_hooker)
	: "memory"
	);

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

	trace.func = self_addr;
	trace.depth = current->curr_ret_stack + 1;

	/* Only trace if the calling function expects to */
	if (!ftrace_graph_entry(&trace)) {
	*parent = old;
	return;
	}

	if (ftrace_push_return_trace(old, self_addr, &trace.depth,
	frame_pointer) == -EBUSY) {
	*parent = old;
	return;
	}
	}
	#endif /* CONFIG_FUNCTION_GRAPH_TRACER */