/*
   * 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/ftrace.h>

  #include <asm/nops.h>

  #include <asm/nmi.h>

  #ifdef CONFIG_DYNAMIC_FTRACE

  /*
   * modifying_code is set to notify NMIs that they need to use
   * memory barriers when entering or exiting. But we don't want
   * to burden NMIs with unnecessary memory barriers when code
   * modification is not being done (which is most of the time).
   *
   * A mutex is already held when ftrace_arch_code_modify_prepare
   * and post_process are called. No locks need to be taken here.
   *
   * Stop machine will make sure currently running NMIs are done
   * and new NMIs will see the updated variable before we need
   * to worry about NMIs doing memory barriers.
   */
  static int modifying_code __read_mostly;
  static DEFINE_PER_CPU(int, save_modifying_code);

  int ftrace_arch_code_modify_prepare(void)
  {
  	set_kernel_text_rw();

  	set_all_modules_text_rw();

  	modifying_code = 1;

  	return 0;
  }
  
  int ftrace_arch_code_modify_post_process(void)
  {

  	modifying_code = 0;

  	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;

  }

  /*
   * 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 const 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)

  {

  	__this_cpu_write(save_modifying_code, modifying_code);

  	if (!__this_cpu_read(save_modifying_code))

  		return;

  	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)

  {

  	if (!__this_cpu_read(save_modifying_code))

  		return;

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

  static int

  do_ftrace_mod_code(unsigned long ip, const void *new_code)

  {

  	/*
  	 * 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(ip));

  	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 const unsigned char *ftrace_nop_replace(void)

  {

  	return ideal_nops[NOP_ATOMIC5];

  }

  static int

  ftrace_modify_code(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;

  	/* 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 const 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 const 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)

  {

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

  	return 0;
  }

  #endif

  #ifdef CONFIG_FUNCTION_GRAPH_TRACER

  #ifdef CONFIG_DYNAMIC_FTRACE
  extern void ftrace_graph_call(void);
  
  static int ftrace_mod_jmp(unsigned long ip,
  			  int old_offset, int new_offset)
  {
  	unsigned char code[MCOUNT_INSN_SIZE];
  
  	if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
  		return -EFAULT;
  
  	if (code[0] != 0xe9 || old_offset != *(int *)(&code[1]))
  		return -EINVAL;
  
  	*(int *)(&code[1]) = new_offset;
  
  	if (do_ftrace_mod_code(ip, &code))
  		return -EPERM;
  
  	return 0;
  }
  
  int ftrace_enable_ftrace_graph_caller(void)
  {
  	unsigned long ip = (unsigned long)(&ftrace_graph_call);
  	int old_offset, new_offset;
  
  	old_offset = (unsigned long)(&ftrace_stub) - (ip + MCOUNT_INSN_SIZE);
  	new_offset = (unsigned long)(&ftrace_graph_caller) - (ip + MCOUNT_INSN_SIZE);
  
  	return ftrace_mod_jmp(ip, old_offset, new_offset);
  }
  
  int ftrace_disable_ftrace_graph_caller(void)
  {
  	unsigned long ip = (unsigned long)(&ftrace_graph_call);
  	int old_offset, new_offset;
  
  	old_offset = (unsigned long)(&ftrace_graph_caller) - (ip + MCOUNT_INSN_SIZE);
  	new_offset = (unsigned long)(&ftrace_stub) - (ip + MCOUNT_INSN_SIZE);
  
  	return ftrace_mod_jmp(ip, old_offset, new_offset);
  }

  #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]
  "
  		"2: " _ASM_MOV " %[return_hooker], (%[parent])
  "

  		"   movl $0, %[faulted]
  "

  		"3:
  "

  
  		".section .fixup, \"ax\"
  "

  		"4: movl $1, %[faulted]
  "
  		"   jmp 3b
  "

  		".previous
  "

  		_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 */