text: /*
   * Kernel Debug Core
   *
   * Maintainer: Jason Wessel <jason.wessel@windriver.com>
   *
   * Copyright (C) 2000-2001 VERITAS Software Corporation.
   * Copyright (C) 2002-2004 Timesys Corporation
   * Copyright (C) 2003-2004 Amit S. Kale <amitkale@linsyssoft.com>
   * Copyright (C) 2004 Pavel Machek <pavel@ucw.cz>
   * Copyright (C) 2004-2006 Tom Rini <trini@kernel.crashing.org>
   * Copyright (C) 2004-2006 LinSysSoft Technologies Pvt. Ltd.
   * Copyright (C) 2005-2009 Wind River Systems, Inc.
   * Copyright (C) 2007 MontaVista Software, Inc.
   * Copyright (C) 2008 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   *
   * Contributors at various stages not listed above:
   *  Jason Wessel ( jason.wessel@windriver.com )
   *  George Anzinger <george@mvista.com>
   *  Anurekh Saxena (anurekh.saxena@timesys.com)
   *  Lake Stevens Instrument Division (Glenn Engel)
   *  Jim Kingdon, Cygnus Support.
   *
   * Original KGDB stub: David Grothe <dave@gcom.com>,
   * Tigran Aivazian <tigran@sco.com>
   *
   * This file is licensed under the terms of the GNU General Public License
   * version 2. This program is licensed "as is" without any warranty of any
   * kind, whether express or implied.
   */
  #include <linux/pid_namespace.h>
  #include <linux/clocksource.h>
  #include <linux/interrupt.h>
  #include <linux/spinlock.h>
  #include <linux/console.h>
  #include <linux/threads.h>
  #include <linux/uaccess.h>
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/ptrace.h>
  #include <linux/string.h>
  #include <linux/delay.h>
  #include <linux/sched.h>
  #include <linux/sysrq.h>
  #include <linux/reboot.h>
  #include <linux/init.h>
  #include <linux/kgdb.h>
  #include <linux/kdb.h>
  #include <linux/pid.h>
  #include <linux/smp.h>
  #include <linux/mm.h>
  #include <linux/rcupdate.h>
  
  #include <asm/cacheflush.h>
  #include <asm/byteorder.h>
  #include <linux/atomic.h>
  
  #include "debug_core.h"
  
  static int kgdb_break_asap;
  
  struct debuggerinfo_struct kgdb_info[NR_CPUS];
  
  /**
   * kgdb_connected - Is a host GDB connected to us?
   */
  int				kgdb_connected;
  EXPORT_SYMBOL_GPL(kgdb_connected);
  
  /* All the KGDB handlers are installed */
  int			kgdb_io_module_registered;
  
  /* Guard for recursive entry */
  static int			exception_level;
  
  struct kgdb_io		*dbg_io_ops;
  static DEFINE_SPINLOCK(kgdb_registration_lock);
  
  /* Action for the reboot notifiter, a global allow kdb to change it */
  static int kgdbreboot;
  /* kgdb console driver is loaded */
  static int kgdb_con_registered;
  /* determine if kgdb console output should be used */
  static int kgdb_use_con;
  /* Flag for alternate operations for early debugging */
  bool dbg_is_early = true;
  /* Next cpu to become the master debug core */
  int dbg_switch_cpu;
  /* Flag for entering kdb when a panic occurs */
  static bool break_on_panic = true;
  /* Flag for entering kdb when an exception occurs */
  static bool break_on_exception = true;
  
  /* Use kdb or gdbserver mode */
  int dbg_kdb_mode = 1;
  
  static int __init opt_kgdb_con(char *str)
  {
  	kgdb_use_con = 1;
  	return 0;
  }
  
  early_param("kgdbcon", opt_kgdb_con);
  
  module_param(kgdb_use_con, int, 0644);
  module_param(kgdbreboot, int, 0644);
  module_param(break_on_panic, bool, 0644);
  module_param(break_on_exception, bool, 0644);
  
  /*
   * Holds information about breakpoints in a kernel. These breakpoints are
   * added and removed by gdb.
   */
  static struct kgdb_bkpt		kgdb_break[KGDB_MAX_BREAKPOINTS] = {
  	[0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
  };
  
  /*
   * The CPU# of the active CPU, or -1 if none:
   */
  atomic_t			kgdb_active = ATOMIC_INIT(-1);
  EXPORT_SYMBOL_GPL(kgdb_active);
  static DEFINE_RAW_SPINLOCK(dbg_master_lock);
  static DEFINE_RAW_SPINLOCK(dbg_slave_lock);
  
  /*
   * We use NR_CPUs not PERCPU, in case kgdb is used to debug early
   * bootup code (which might not have percpu set up yet):
   */
  static atomic_t			masters_in_kgdb;
  static atomic_t			slaves_in_kgdb;
  static atomic_t			kgdb_break_tasklet_var;
  atomic_t			kgdb_setting_breakpoint;
  
  struct task_struct		*kgdb_usethread;
  struct task_struct		*kgdb_contthread;
  
  int				kgdb_single_step;
  static pid_t			kgdb_sstep_pid;
  
  /* to keep track of the CPU which is doing the single stepping*/
  atomic_t			kgdb_cpu_doing_single_step = ATOMIC_INIT(-1);
  
  /*
   * If you are debugging a problem where roundup (the collection of
   * all other CPUs) is a problem [this should be extremely rare],
   * then use the nokgdbroundup option to avoid roundup. In that case
   * the other CPUs might interfere with your debugging context, so
   * use this with care:
   */
  static int kgdb_do_roundup = 1;
  
  static int __init opt_nokgdbroundup(char *str)
  {
  	kgdb_do_roundup = 0;
  
  	return 0;
  }
  
  early_param("nokgdbroundup", opt_nokgdbroundup);
  
  /*
   * Finally, some KGDB code :-)
   */
  
  /*
   * Weak aliases for breakpoint management,
   * can be overriden by architectures when needed:
   */
  int __weak kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
  {
  	int err;
  
  	err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr,
  				BREAK_INSTR_SIZE);
  	if (err)
  		return err;
  	err = probe_kernel_write((char *)bpt->bpt_addr,
  				 arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
  	return err;
  }
  
  int __weak kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
  {
  	return probe_kernel_write((char *)bpt->bpt_addr,
  				  (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
  }
  
  int __weak kgdb_validate_break_address(unsigned long addr)
  {
  	struct kgdb_bkpt tmp;
  	int err;
  	/* Validate setting the breakpoint and then removing it.  If the
  	 * remove fails, the kernel needs to emit a bad message because we
  	 * are deep trouble not being able to put things back the way we
  	 * found them.
  	 */
  	tmp.bpt_addr = addr;
  	err = kgdb_arch_set_breakpoint(&tmp);
  	if (err)
  		return err;
  	err = kgdb_arch_remove_breakpoint(&tmp);
  	if (err)
  		printk(KERN_ERR "KGDB: Critical breakpoint error, kernel "
  		   "memory destroyed at: %lx", addr);
  	return err;
  }
  
  unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
  {
  	return instruction_pointer(regs);
  }
  
  int __weak kgdb_arch_init(void)
  {
  	return 0;
  }
  
  int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
  {
  	return 0;
  }
  
  /*
   * Some architectures need cache flushes when we set/clear a
   * breakpoint:
   */
  static void kgdb_flush_swbreak_addr(unsigned long addr)
  {
  	if (!CACHE_FLUSH_IS_SAFE)
  		return;
  
  	if (current->mm && current->mm->mmap_cache) {
  		flush_cache_range(current->mm->mmap_cache,
  				  addr, addr + BREAK_INSTR_SIZE);
  	}
  	/* Force flush instruction cache if it was outside the mm */
  	flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
  }
  
  /*
   * SW breakpoint management:
   */
  int dbg_activate_sw_breakpoints(void)
  {
  	int error;
  	int ret = 0;
  	int i;
  
  	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
  		if (kgdb_break[i].state != BP_SET)
  			continue;
  
  		error = kgdb_arch_set_breakpoint(&kgdb_break[i]);
  		if (error) {
  			ret = error;
  			printk(KERN_INFO "KGDB: BP install failed: %lx",
  			       kgdb_break[i].bpt_addr);
  			continue;
  		}
  
  		kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
  		kgdb_break[i].state = BP_ACTIVE;
  	}
  	return ret;
  }
  
  int dbg_set_sw_break(unsigned long addr)
  {
  	int err = kgdb_validate_break_address(addr);
  	int breakno = -1;
  	int i;
  
  	if (err)
  		return err;
  
  	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
  		if ((kgdb_break[i].state == BP_SET) &&
  					(kgdb_break[i].bpt_addr == addr))
  			return -EEXIST;
  	}
  	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
  		if (kgdb_break[i].state == BP_REMOVED &&
  					kgdb_break[i].bpt_addr == addr) {
  			breakno = i;
  			break;
  		}
  	}
  
  	if (breakno == -1) {
  		for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
  			if (kgdb_break[i].state == BP_UNDEFINED) {
  				breakno = i;
  				break;
  			}
  		}
  	}
  
  	if (breakno == -1)
  		return -E2BIG;
  
  	kgdb_break[breakno].state = BP_SET;
  	kgdb_break[breakno].type = BP_BREAKPOINT;
  	kgdb_break[breakno].bpt_addr = addr;
  
  	return 0;
  }
  
  int dbg_deactivate_sw_breakpoints(void)
  {
  	int error;
  	int ret = 0;
  	int i;
  
  	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
  		if (kgdb_break[i].state != BP_ACTIVE)
  			continue;
  		error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
  		if (error) {
  			printk(KERN_INFO "KGDB: BP remove failed: %lx\n",
  			       kgdb_break[i].bpt_addr);
  			ret = error;
  		}
  
  		kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
  		kgdb_break[i].state = BP_SET;
  	}
  	return ret;
  }
  
  int dbg_remove_sw_break(unsigned long addr)
  {
  	int i;
  
  	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
  		if ((kgdb_break[i].state == BP_SET) &&
  				(kgdb_break[i].bpt_addr == addr)) {
  			kgdb_break[i].state = BP_REMOVED;
  			return 0;
  		}
  	}
  	return -ENOENT;
  }
  
  int kgdb_isremovedbreak(unsigned long addr)
  {
  	int i;
  
  	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
  		if ((kgdb_break[i].state == BP_REMOVED) &&
  					(kgdb_break[i].bpt_addr == addr))
  			return 1;
  	}
  	return 0;
  }
  
  int dbg_remove_all_break(void)
  {
  	int error;
  	int i;
  
  	/* Clear memory breakpoints. */
  	for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
  		if (kgdb_break[i].state != BP_ACTIVE)
  			goto setundefined;
  		error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
  		if (error)
  			printk(KERN_ERR "KGDB: breakpoint remove failed: %lx\n",
  			       kgdb_break[i].bpt_addr);
  setundefined:
  		kgdb_break[i].state = BP_UNDEFINED;
  	}
  
  	/* Clear hardware breakpoints. */
  	if (arch_kgdb_ops.remove_all_hw_break)
  		arch_kgdb_ops.remove_all_hw_break();
  
  	return 0;
  }
  
  /*
   * Return true if there is a valid kgdb I/O module.  Also if no
   * debugger is attached a message can be printed to the console about
   * waiting for the debugger to attach.
   *
   * The print_wait argument is only to be true when called from inside
   * the core kgdb_handle_exception, because it will wait for the
   * debugger to attach.
   */
  static int kgdb_io_ready(int print_wait)
  {
  	if (!dbg_io_ops)
  		return 0;
  	if (kgdb_connected)
  		return 1;
  	if (atomic_read(&kgdb_setting_breakpoint))
  		return 1;
  	if (print_wait) {
  #ifdef CONFIG_KGDB_KDB
  		if (!dbg_kdb_mode)
  			printk(KERN_CRIT "KGDB: waiting... or $3#33 for KDB\n");
  #else
  		printk(KERN_CRIT "KGDB: Waiting for remote debugger\n");
  #endif
  	}
  	return 1;
  }
  
  static int kgdb_reenter_check(struct kgdb_state *ks)
  {
  	unsigned long addr;
  
  	if (atomic_read(&kgdb_active) != raw_smp_processor_id())
  		return 0;
  
  	/* Panic on recursive debugger calls: */
  	exception_level++;
  	addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
  	dbg_deactivate_sw_breakpoints();
  
  	/*
  	 * If the break point removed ok at the place exception
  	 * occurred, try to recover and print a warning to the end
  	 * user because the user planted a breakpoint in a place that
  	 * KGDB needs in order to function.
  	 */
  	if (dbg_remove_sw_break(addr) == 0) {
  		exception_level = 0;
  		kgdb_skipexception(ks->ex_vector, ks->linux_regs);
  		dbg_activate_sw_breakpoints();
  		printk(KERN_CRIT "KGDB: re-enter error: breakpoint removed %lx\n",
  			addr);
  		WARN_ON_ONCE(1);
  
  		return 1;
  	}
  	dbg_remove_all_break();
  	kgdb_skipexception(ks->ex_vector, ks->linux_regs);
  
  	if (exception_level > 1) {
  		dump_stack();
  		panic("Recursive entry to debugger");
  	}
  
  	printk(KERN_CRIT "KGDB: re-enter exception: ALL breakpoints killed\n");
  #ifdef CONFIG_KGDB_KDB
  	/* Allow kdb to debug itself one level */
  	return 0;
  #endif
  	dump_stack();
  	panic("Recursive entry to debugger");
  
  	return 1;
  }
  
  static void dbg_touch_watchdogs(void)
  {
  	touch_softlockup_watchdog_sync();
  	clocksource_touch_watchdog();
  	rcu_cpu_stall_reset();
  }
  
  static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
  		int exception_state)
  {
  	unsigned long flags;
  	int sstep_tries = 100;
  	int error;
  	int cpu;
  	int trace_on = 0;
  	int online_cpus = num_online_cpus();
  
  	kgdb_info[ks->cpu].enter_kgdb++;
  	kgdb_info[ks->cpu].exception_state |= exception_state;
  
  	if (exception_state == DCPU_WANT_MASTER)
  		atomic_inc(&masters_in_kgdb);
  	else
  		atomic_inc(&slaves_in_kgdb);
  
  	if (arch_kgdb_ops.disable_hw_break)
  		arch_kgdb_ops.disable_hw_break(regs);
  
  acquirelock:
  	/*
  	 * Interrupts will be restored by the 'trap return' code, except when
  	 * single stepping.
  	 */
  	local_irq_save(flags);
  
  	cpu = ks->cpu;
  	kgdb_info[cpu].debuggerinfo = regs;
  	kgdb_info[cpu].task = current;
  	kgdb_info[cpu].ret_state = 0;
  	kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
  
  	/* Make sure the above info reaches the primary CPU */
  	smp_mb();
  
  	if (exception_level == 1) {
  		if (raw_spin_trylock(&dbg_master_lock))
  			atomic_xchg(&kgdb_active, cpu);
  		goto cpu_master_loop;
  	}
  
  	/*
  	 * CPU will loop if it is a slave or request to become a kgdb
  	 * master cpu and acquire the kgdb_active lock:
  	 */
  	while (1) {
  cpu_loop:
  		if (kgdb_info[cpu].exception_state & DCPU_NEXT_MASTER) {
  			kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
  			goto cpu_master_loop;
  		} else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
  			if (raw_spin_trylock(&dbg_master_lock)) {
  				atomic_xchg(&kgdb_active, cpu);
  				break;
  			}
  		} else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
  			if (!raw_spin_is_locked(&dbg_slave_lock))
  				goto return_normal;
  		} else {
  return_normal:
  			/* Return to normal operation by executing any
  			 * hw breakpoint fixup.
  			 */
  			if (arch_kgdb_ops.correct_hw_break)
  				arch_kgdb_ops.correct_hw_break();
  			if (trace_on)
  				tracing_on();
  			kgdb_info[cpu].exception_state &=
  				~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
  			kgdb_info[cpu].enter_kgdb--;
  			smp_mb__before_atomic_dec();
  			atomic_dec(&slaves_in_kgdb);
  			dbg_touch_watchdogs();
  			local_irq_restore(flags);
  			return 0;
  		}
  		cpu_relax();
  	}
  
  	/*
  	 * For single stepping, try to only enter on the processor
  	 * that was single stepping.  To guard against a deadlock, the
  	 * kernel will only try for the value of sstep_tries before
  	 * giving up and continuing on.
  	 */
  	if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
  	    (kgdb_info[cpu].task &&
  	     kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
  		atomic_set(&kgdb_active, -1);
  		raw_spin_unlock(&dbg_master_lock);
  		dbg_touch_watchdogs();
  		local_irq_restore(flags);
  
  		goto acquirelock;
  	}
  
  	if (!kgdb_io_ready(1)) {
  		kgdb_info[cpu].ret_state = 1;
  		goto kgdb_restore; /* No I/O connection, resume the system */
  	}
  
  	/*
  	 * Don't enter if we have hit a removed breakpoint.
  	 */
  	if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
  		goto kgdb_restore;
  
  	/* Call the I/O driver's pre_exception routine */
  	if (dbg_io_ops->pre_exception)
  		dbg_io_ops->pre_exception();
  
  	/*
  	 * Get the passive CPU lock which will hold all the non-primary
  	 * CPU in a spin state while the debugger is active
  	 */
  	if (!kgdb_single_step)
  		raw_spin_lock(&dbg_slave_lock);
  
  #ifdef CONFIG_SMP
  	/* Signal the other CPUs to enter kgdb_wait() */
  	if ((!kgdb_single_step) && kgdb_do_roundup)
  		kgdb_roundup_cpus(flags);
  #endif
  
  	/*
  	 * Wait for the other CPUs to be notified and be waiting for us:
  	 */
  	while (kgdb_do_roundup && (atomic_read(&masters_in_kgdb) +
  				atomic_read(&slaves_in_kgdb)) != online_cpus)
  		cpu_relax();
  
  	/*
  	 * At this point the primary processor is completely
  	 * in the debugger and all secondary CPUs are quiescent
  	 */
  	dbg_deactivate_sw_breakpoints();
  	kgdb_single_step = 0;
  	kgdb_contthread = current;
  	exception_level = 0;
  	trace_on = tracing_is_on();
  	if (trace_on)
  		tracing_off();
  
  	while (1) {
  cpu_master_loop:
  		if (dbg_kdb_mode) {
  			kgdb_connected = 1;
  			error = kdb_stub(ks);
  			if (error == -1)
  				continue;
  			kgdb_connected = 0;
  		} else {
  			error = gdb_serial_stub(ks);
  		}
  
  		if (error == DBG_PASS_EVENT) {
  			dbg_kdb_mode = !dbg_kdb_mode;
  		} else if (error == DBG_SWITCH_CPU_EVENT) {
  			kgdb_info[dbg_switch_cpu].exception_state |=
  				DCPU_NEXT_MASTER;
  			goto cpu_loop;
  		} else {
  			kgdb_info[cpu].ret_state = error;
  			break;
  		}
  	}
  
  	/* Call the I/O driver's post_exception routine */
  	if (dbg_io_ops->post_exception)
  		dbg_io_ops->post_exception();
  
  	if (!kgdb_single_step) {
  		raw_spin_unlock(&dbg_slave_lock);
  		/* Wait till all the CPUs have quit from the debugger. */
  		while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
  			cpu_relax();
  	}
  
  kgdb_restore:
  	if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
  		int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
  		if (kgdb_info[sstep_cpu].task)
  			kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
  		else
  			kgdb_sstep_pid = 0;
  	}
  	if (arch_kgdb_ops.correct_hw_break)
  		arch_kgdb_ops.correct_hw_break();
  	if (trace_on)
  		tracing_on();
  
  	kgdb_info[cpu].exception_state &=
  		~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
  	kgdb_info[cpu].enter_kgdb--;
  	smp_mb__before_atomic_dec();
  	atomic_dec(&masters_in_kgdb);
  	/* Free kgdb_active */
  	atomic_set(&kgdb_active, -1);
  	raw_spin_unlock(&dbg_master_lock);
  	dbg_touch_watchdogs();
  	local_irq_restore(flags);
  
  	return kgdb_info[cpu].ret_state;
  }
  
  /*
   * kgdb_handle_exception() - main entry point from a kernel exception
   *
   * Locking hierarchy:
   *	interface locks, if any (begin_session)
   *	kgdb lock (kgdb_active)
   */
  int
  kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
  {
  	struct kgdb_state kgdb_var;
  	struct kgdb_state *ks = &kgdb_var;
  
  	if (unlikely(signo != SIGTRAP && !break_on_exception))
  		return 1;
  
  	ks->cpu			= raw_smp_processor_id();
  	ks->ex_vector		= evector;
  	ks->signo		= signo;
  	ks->err_code		= ecode;
  	ks->kgdb_usethreadid	= 0;
  	ks->linux_regs		= regs;
  
  	if (kgdb_reenter_check(ks))
  		return 0; /* Ouch, double exception ! */
  	if (kgdb_info[ks->cpu].enter_kgdb != 0)
  		return 0;
  
  	return kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
  }
  
  int kgdb_nmicallback(int cpu, void *regs)
  {
  #ifdef CONFIG_SMP
  	struct kgdb_state kgdb_var;
  	struct kgdb_state *ks = &kgdb_var;
  
  	memset(ks, 0, sizeof(struct kgdb_state));
  	ks->cpu			= cpu;
  	ks->linux_regs		= regs;
  
  	if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
  			raw_spin_is_locked(&dbg_master_lock)) {
  		kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
  		return 0;
  	}
  #endif
  	return 1;
  }
  
  static void kgdb_console_write(struct console *co, const char *s,
     unsigned count)
  {
  	unsigned long flags;
  
  	/* If we're debugging, or KGDB has not connected, don't try
  	 * and print. */
  	if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
  		return;
  
  	local_irq_save(flags);
  	gdbstub_msg_write(s, count);
  	local_irq_restore(flags);
  }
  
  static struct console kgdbcons = {
  	.name		= "kgdb",
  	.write		= kgdb_console_write,
  	.flags		= CON_PRINTBUFFER | CON_ENABLED,
  	.index		= -1,
  };
  
  #ifdef CONFIG_MAGIC_SYSRQ
  static void sysrq_handle_dbg(int key)
  {
  	if (!dbg_io_ops) {
  		printk(KERN_CRIT "ERROR: No KGDB I/O module available\n");
  		return;
  	}
  	if (!kgdb_connected) {
  #ifdef CONFIG_KGDB_KDB
  		if (!dbg_kdb_mode)
  			printk(KERN_CRIT "KGDB or $3#33 for KDB\n");
  #else
  		printk(KERN_CRIT "Entering KGDB\n");
  #endif
  	}
  
  	kgdb_breakpoint();
  }
  
  static struct sysrq_key_op sysrq_dbg_op = {
  	.handler	= sysrq_handle_dbg,
  	.help_msg	= "debug(G)",
  	.action_msg	= "DEBUG",
  };
  #endif
  
  static int kgdb_panic_event(struct notifier_block *self,
  			    unsigned long val,
  			    void *data)
  {
  	if (!break_on_panic)
  		return NOTIFY_DONE;
  
  	if (dbg_kdb_mode)
  		kdb_printf("PANIC: %s\n", (char *)data);
  	kgdb_breakpoint();
  	return NOTIFY_DONE;
  }
  
  static struct notifier_block kgdb_panic_event_nb = {
         .notifier_call	= kgdb_panic_event,
         .priority	= INT_MAX,
  };
  
  void __weak kgdb_arch_late(void)
  {
  }
  
  void __init dbg_late_init(void)
  {
  	dbg_is_early = false;
  	if (kgdb_io_module_registered)
  		kgdb_arch_late();
  	kdb_init(KDB_INIT_FULL);
  }
  
  static int
  dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
  {
  	/*
  	 * Take the following action on reboot notify depending on value:
  	 *    1 == Enter debugger
  	 *    0 == [the default] detatch debug client
  	 *   -1 == Do nothing... and use this until the board resets
  	 */
  	switch (kgdbreboot) {
  	case 1:
  		kgdb_breakpoint();
  	case -1:
  		goto done;
  	}
  	if (!dbg_kdb_mode)
  		gdbstub_exit(code);
  done:
  	return NOTIFY_DONE;
  }
  
  static struct notifier_block dbg_reboot_notifier = {
  	.notifier_call		= dbg_notify_reboot,
  	.next			= NULL,
  	.priority		= INT_MAX,
  };
  
  static void kgdb_register_callbacks(void)
  {
  	if (!kgdb_io_module_registered) {
  		kgdb_io_module_registered = 1;
  		kgdb_arch_init();
  		if (!dbg_is_early)
  			kgdb_arch_late();
  		register_reboot_notifier(&dbg_reboot_notifier);
  		atomic_notifier_chain_register(&panic_notifier_list,
  					       &kgdb_panic_event_nb);
  #ifdef CONFIG_MAGIC_SYSRQ
  		register_sysrq_key('g', &sysrq_dbg_op);
  #endif
  		if (kgdb_use_con && !kgdb_con_registered) {
  			register_console(&kgdbcons);
  			kgdb_con_registered = 1;
  		}
  	}
  }
  
  static void kgdb_unregister_callbacks(void)
  {
  	/*
  	 * When this routine is called KGDB should unregister from the
  	 * panic handler and clean up, making sure it is not handling any
  	 * break exceptions at the time.
  	 */
  	if (kgdb_io_module_registered) {
  		kgdb_io_module_registered = 0;
  		unregister_reboot_notifier(&dbg_reboot_notifier);
  		atomic_notifier_chain_unregister(&panic_notifier_list,
  					       &kgdb_panic_event_nb);
  		kgdb_arch_exit();
  #ifdef CONFIG_MAGIC_SYSRQ
  		unregister_sysrq_key('g', &sysrq_dbg_op);
  #endif
  		if (kgdb_con_registered) {
  			unregister_console(&kgdbcons);
  			kgdb_con_registered = 0;
  		}
  	}
  }
  
  /*
   * There are times a tasklet needs to be used vs a compiled in
   * break point so as to cause an exception outside a kgdb I/O module,
   * such as is the case with kgdboe, where calling a breakpoint in the
   * I/O driver itself would be fatal.
   */
  static void kgdb_tasklet_bpt(unsigned long ing)
  {
  	kgdb_breakpoint();
  	atomic_set(&kgdb_break_tasklet_var, 0);
  }
  
  static DECLARE_TASKLET(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt, 0);
  
  void kgdb_schedule_breakpoint(void)
  {
  	if (atomic_read(&kgdb_break_tasklet_var) ||
  		atomic_read(&kgdb_active) != -1 ||
  		atomic_read(&kgdb_setting_breakpoint))
  		return;
  	atomic_inc(&kgdb_break_tasklet_var);
  	tasklet_schedule(&kgdb_tasklet_breakpoint);
  }
  EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
  
  static void kgdb_initial_breakpoint(void)
  {
  	kgdb_break_asap = 0;
  
  	printk(KERN_CRIT "kgdb: Waiting for connection from remote gdb...\n");
  	kgdb_breakpoint();
  }
  
  /**
   *	kgdb_register_io_module - register KGDB IO module
   *	@new_dbg_io_ops: the io ops vector
   *
   *	Register it with the KGDB core.
   */
  int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
  {
  	int err;
  
  	spin_lock(&kgdb_registration_lock);
  
  	if (dbg_io_ops) {
  		spin_unlock(&kgdb_registration_lock);
  
  		printk(KERN_ERR "kgdb: Another I/O driver is already "
  				"registered with KGDB.\n");
  		return -EBUSY;
  	}
  
  	if (new_dbg_io_ops->init) {
  		err = new_dbg_io_ops->init();
  		if (err) {
  			spin_unlock(&kgdb_registration_lock);
  			return err;
  		}
  	}
  
  	dbg_io_ops = new_dbg_io_ops;
  
  	spin_unlock(&kgdb_registration_lock);
  
  	printk(KERN_INFO "kgdb: Registered I/O driver %s.\n",
  	       new_dbg_io_ops->name);
  
  	/* Arm KGDB now. */
  	kgdb_register_callbacks();
  
  	if (kgdb_break_asap)
  		kgdb_initial_breakpoint();
  
  	return 0;
  }
  EXPORT_SYMBOL_GPL(kgdb_register_io_module);
  
  /**
   *	kkgdb_unregister_io_module - unregister KGDB IO module
   *	@old_dbg_io_ops: the io ops vector
   *
   *	Unregister it with the KGDB core.
   */
  void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
  {
  	BUG_ON(kgdb_connected);
  
  	/*
  	 * KGDB is no longer able to communicate out, so
  	 * unregister our callbacks and reset state.
  	 */
  	kgdb_unregister_callbacks();
  
  	spin_lock(&kgdb_registration_lock);
  
  	WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
  	dbg_io_ops = NULL;
  
  	spin_unlock(&kgdb_registration_lock);
  
  	printk(KERN_INFO
  		"kgdb: Unregistered I/O driver %s, debugger disabled.\n",
  		old_dbg_io_ops->name);
  }
  EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
  
  int dbg_io_get_char(void)
  {
  	int ret = dbg_io_ops->read_char();
  	if (ret == NO_POLL_CHAR)
  		return -1;
  	if (!dbg_kdb_mode)
  		return ret;
  	if (ret == 127)
  		return 8;
  	return ret;
  }
  
  /**
   * kgdb_breakpoint - generate breakpoint exception
   *
   * This function will generate a breakpoint exception.  It is used at the
   * beginning of a program to sync up with a debugger and can be used
   * otherwise as a quick means to stop program execution and "break" into
   * the debugger.
   */
  void kgdb_breakpoint(void)
  {
  	atomic_inc(&kgdb_setting_breakpoint);
  	wmb(); /* Sync point before breakpoint */
  	arch_kgdb_breakpoint();
  	wmb(); /* Sync point after breakpoint */
  	atomic_dec(&kgdb_setting_breakpoint);
  }
  EXPORT_SYMBOL_GPL(kgdb_breakpoint);
  
  static int __init opt_kgdb_wait(char *str)
  {
  	kgdb_break_asap = 1;
  
  	kdb_init(KDB_INIT_EARLY);
  	if (kgdb_io_module_registered)
  		kgdb_initial_breakpoint();
  
  	return 0;
  }
  
  early_param("kgdbwait", opt_kgdb_wait);
  