/*
   * x86 single-step support code, common to 32-bit and 64-bit.
   */
  #include <linux/sched.h>
  #include <linux/mm.h>
  #include <linux/ptrace.h>

  #include <asm/desc.h>

  unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs)

  {
  	unsigned long addr, seg;

  	addr = regs->ip;

  	seg = regs->cs & 0xffff;

  	if (v8086_mode(regs)) {

  		addr = (addr & 0xffff) + (seg << 4);
  		return addr;
  	}

  
  	/*
  	 * We'll assume that the code segments in the GDT
  	 * are all zero-based. That is largely true: the
  	 * TLS segments are used for data, and the PNPBIOS
  	 * and APM bios ones we just ignore here.
  	 */

  	if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) {

  		struct desc_struct *desc;

  		unsigned long base;
  
  		seg &= ~7UL;
  
  		mutex_lock(&child->mm->context.lock);
  		if (unlikely((seg >> 3) >= child->mm->context.size))
  			addr = -1L; /* bogus selector, access would fault */
  		else {
  			desc = child->mm->context.ldt + seg;

  			base = get_desc_base(desc);

  
  			/* 16-bit code segment? */

  			if (!desc->d)

  				addr &= 0xffff;
  			addr += base;
  		}
  		mutex_unlock(&child->mm->context.lock);
  	}
  
  	return addr;
  }
  
  static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
  {
  	int i, copied;
  	unsigned char opcode[15];

  	unsigned long addr = convert_ip_to_linear(child, regs);

  
  	copied = access_process_vm(child, addr, opcode, sizeof(opcode), 0);
  	for (i = 0; i < copied; i++) {
  		switch (opcode[i]) {
  		/* popf and iret */
  		case 0x9d: case 0xcf:
  			return 1;
  
  			/* CHECKME: 64 65 */
  
  		/* opcode and address size prefixes */
  		case 0x66: case 0x67:
  			continue;
  		/* irrelevant prefixes (segment overrides and repeats) */
  		case 0x26: case 0x2e:
  		case 0x36: case 0x3e:
  		case 0x64: case 0x65:

  		case 0xf0: case 0xf2: case 0xf3:

  			continue;

  #ifdef CONFIG_X86_64

  		case 0x40 ... 0x4f:

  			if (!user_64bit_mode(regs))

  				/* 32-bit mode: register increment */
  				return 0;
  			/* 64-bit mode: REX prefix */
  			continue;

  #endif

  
  			/* CHECKME: f2, f3 */
  
  		/*
  		 * pushf: NOTE! We should probably not let
  		 * the user see the TF bit being set. But
  		 * it's more pain than it's worth to avoid
  		 * it, and a debugger could emulate this
  		 * all in user space if it _really_ cares.
  		 */
  		case 0x9c:
  		default:
  			return 0;
  		}
  	}
  	return 0;
  }

  /*
   * Enable single-stepping.  Return nonzero if user mode is not using TF itself.
   */
  static int enable_single_step(struct task_struct *child)

  {
  	struct pt_regs *regs = task_pt_regs(child);

  	unsigned long oflags;

  
  	/*

  	 * If we stepped into a sysenter/syscall insn, it trapped in
  	 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
  	 * If user-mode had set TF itself, then it's still clear from
  	 * do_debug() and we need to set it again to restore the user
  	 * state so we don't wrongly set TIF_FORCED_TF below.
  	 * If enable_single_step() was used last and that is what
  	 * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are
  	 * already set and our bookkeeping is fine.
  	 */
  	if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP)))
  		regs->flags |= X86_EFLAGS_TF;
  
  	/*

  	 * Always set TIF_SINGLESTEP - this guarantees that
  	 * we single-step system calls etc..  This will also
  	 * cause us to set TF when returning to user mode.
  	 */
  	set_tsk_thread_flag(child, TIF_SINGLESTEP);

  	oflags = regs->flags;

  
  	/* Set TF on the kernel stack.. */

  	regs->flags |= X86_EFLAGS_TF;

  
  	/*
  	 * ..but if TF is changed by the instruction we will trace,
  	 * don't mark it as being "us" that set it, so that we
  	 * won't clear it by hand later.

  	 *
  	 * Note that if we don't actually execute the popf because
  	 * of a signal arriving right now or suchlike, we will lose
  	 * track of the fact that it really was "us" that set it.

  	 */

  	if (is_setting_trap_flag(child, regs)) {
  		clear_tsk_thread_flag(child, TIF_FORCED_TF);

  		return 0;

  	}
  
  	/*
  	 * If TF was already set, check whether it was us who set it.
  	 * If not, we should never attempt a block step.
  	 */
  	if (oflags & X86_EFLAGS_TF)
  		return test_tsk_thread_flag(child, TIF_FORCED_TF);

  	set_tsk_thread_flag(child, TIF_FORCED_TF);

  
  	return 1;
  }
  
  /*

   * Enable single or block step.
   */
  static void enable_step(struct task_struct *child, bool block)
  {
  	/*
  	 * Make sure block stepping (BTF) is not enabled unless it should be.
  	 * Note that we don't try to worry about any is_setting_trap_flag()
  	 * instructions after the first when using block stepping.

  	 * So no one should try to use debugger block stepping in a program

  	 * that uses user-mode single stepping itself.
  	 */

  	if (enable_single_step(child) && block) {
  		unsigned long debugctl = get_debugctlmsr();
  
  		debugctl |= DEBUGCTLMSR_BTF;
  		update_debugctlmsr(debugctl);
  		set_tsk_thread_flag(child, TIF_BLOCKSTEP);
  	} else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) {
  		unsigned long debugctl = get_debugctlmsr();
  
  		debugctl &= ~DEBUGCTLMSR_BTF;
  		update_debugctlmsr(debugctl);
  		clear_tsk_thread_flag(child, TIF_BLOCKSTEP);
  	}

  }
  
  void user_enable_single_step(struct task_struct *child)
  {
  	enable_step(child, 0);
  }
  
  void user_enable_block_step(struct task_struct *child)
  {
  	enable_step(child, 1);

  }
  
  void user_disable_single_step(struct task_struct *child)
  {

  	/*
  	 * Make sure block stepping (BTF) is disabled.
  	 */

  	if (test_tsk_thread_flag(child, TIF_BLOCKSTEP)) {
  		unsigned long debugctl = get_debugctlmsr();
  
  		debugctl &= ~DEBUGCTLMSR_BTF;
  		update_debugctlmsr(debugctl);
  		clear_tsk_thread_flag(child, TIF_BLOCKSTEP);
  	}

  	/* Always clear TIF_SINGLESTEP... */
  	clear_tsk_thread_flag(child, TIF_SINGLESTEP);
  
  	/* But touch TF only if it was set by us.. */

  	if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))

  		task_pt_regs(child)->flags &= ~X86_EFLAGS_TF;

  }