kernel/debug/debug_core.c

   1 /*
   2  * Kernel Debug Core
   3  *
   4  * Maintainer: Jason Wessel <jason.wessel@windriver.com>
   5  *
   6  * Copyright (C) 2000-2001 VERITAS Software Corporation.
   7  * Copyright (C) 2002-2004 Timesys Corporation
   8  * Copyright (C) 2003-2004 Amit S. Kale <amitkale@linsyssoft.com>
   9  * Copyright (C) 2004 Pavel Machek <pavel@ucw.cz>
  10  * Copyright (C) 2004-2006 Tom Rini <trini@kernel.crashing.org>
  11  * Copyright (C) 2004-2006 LinSysSoft Technologies Pvt. Ltd.
  12  * Copyright (C) 2005-2009 Wind River Systems, Inc.
  13  * Copyright (C) 2007 MontaVista Software, Inc.
  14  * Copyright (C) 2008 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
  15  *
  16  * Contributors at various stages not listed above:
  17  *  Jason Wessel ( jason.wessel@windriver.com )
  18  *  George Anzinger <george@mvista.com>
  19  *  Anurekh Saxena (anurekh.saxena@timesys.com)
  20  *  Lake Stevens Instrument Division (Glenn Engel)
  21  *  Jim Kingdon, Cygnus Support.
  22  *
  23  * Original KGDB stub: David Grothe <dave@gcom.com>,
  24  * Tigran Aivazian <tigran@sco.com>
  25  *
  26  * This file is licensed under the terms of the GNU General Public License
  27  * version 2. This program is licensed "as is" without any warranty of any
  28  * kind, whether express or implied.
  29  */
  30 #include <linux/pid_namespace.h>
  31 #include <linux/clocksource.h>
  32 #include <linux/serial_core.h>
  33 #include <linux/interrupt.h>
  34 #include <linux/spinlock.h>
  35 #include <linux/console.h>
  36 #include <linux/threads.h>
  37 #include <linux/uaccess.h>
  38 #include <linux/kernel.h>
  39 #include <linux/module.h>
  40 #include <linux/ptrace.h>
  41 #include <linux/string.h>
  42 #include <linux/delay.h>
  43 #include <linux/sched.h>
  44 #include <linux/sysrq.h>
  45 #include <linux/reboot.h>
  46 #include <linux/init.h>
  47 #include <linux/kgdb.h>
  48 #include <linux/kdb.h>
  49 #include <linux/pid.h>
  50 #include <linux/smp.h>
  51 #include <linux/mm.h>
  52 #include <linux/vmacache.h>
  53 #include <linux/rcupdate.h>
  54
  55 #include <asm/cacheflush.h>
  56 #include <asm/byteorder.h>
  57 #include <linux/atomic.h>
  58
  59 #include "debug_core.h"
  60
  61 static int kgdb_break_asap;
  62
  63 struct debuggerinfo_struct kgdb_info[NR_CPUS];
  64
  65 /**
  66  * kgdb_connected - Is a host GDB connected to us?
  67  */
  68 int                             kgdb_connected;
  69 EXPORT_SYMBOL_GPL(kgdb_connected);
  70
  71 /* All the KGDB handlers are installed */
  72 int                     kgdb_io_module_registered;
  73
  74 /* Guard for recursive entry */
  75 static int                      exception_level;
  76
  77 struct kgdb_io          *dbg_io_ops;
  78 static DEFINE_SPINLOCK(kgdb_registration_lock);
  79
  80 /* Action for the reboot notifiter, a global allow kdb to change it */
  81 static int kgdbreboot;
  82 /* kgdb console driver is loaded */
  83 static int kgdb_con_registered;
  84 /* determine if kgdb console output should be used */
  85 static int kgdb_use_con;
  86 /* Flag for alternate operations for early debugging */
  87 bool dbg_is_early = true;
  88 /* Next cpu to become the master debug core */
  89 int dbg_switch_cpu;
  90
  91 /* Use kdb or gdbserver mode */
  92 int dbg_kdb_mode = 1;
  93
  94 static int __init opt_kgdb_con(char *str)
  95 {
  96         kgdb_use_con = 1;
  97         return 0;
  98 }
  99
 100 early_param("kgdbcon", opt_kgdb_con);
 101
 102 module_param(kgdb_use_con, int, 0644);
 103 module_param(kgdbreboot, int, 0644);
 104
 105 /*
 106  * Holds information about breakpoints in a kernel. These breakpoints are
 107  * added and removed by gdb.
 108  */
 109 static struct kgdb_bkpt         kgdb_break[KGDB_MAX_BREAKPOINTS] = {
 110         [0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
 111 };
 112
 113 /*
 114  * The CPU# of the active CPU, or -1 if none:
 115  */
 116 atomic_t                        kgdb_active = ATOMIC_INIT(-1);
 117 EXPORT_SYMBOL_GPL(kgdb_active);
 118 static DEFINE_RAW_SPINLOCK(dbg_master_lock);
 119 static DEFINE_RAW_SPINLOCK(dbg_slave_lock);
 120
 121 /*
 122  * We use NR_CPUs not PERCPU, in case kgdb is used to debug early
 123  * bootup code (which might not have percpu set up yet):
 124  */
 125 static atomic_t                 masters_in_kgdb;
 126 static atomic_t                 slaves_in_kgdb;
 127 static atomic_t                 kgdb_break_tasklet_var;
 128 atomic_t                        kgdb_setting_breakpoint;
 129
 130 struct task_struct              *kgdb_usethread;
 131 struct task_struct              *kgdb_contthread;
 132
 133 int                             kgdb_single_step;
 134 static pid_t                    kgdb_sstep_pid;
 135
 136 /* to keep track of the CPU which is doing the single stepping*/
 137 atomic_t                        kgdb_cpu_doing_single_step = ATOMIC_INIT(-1);
 138
 139 /*
 140  * If you are debugging a problem where roundup (the collection of
 141  * all other CPUs) is a problem [this should be extremely rare],
 142  * then use the nokgdbroundup option to avoid roundup. In that case
 143  * the other CPUs might interfere with your debugging context, so
 144  * use this with care:
 145  */
 146 static int kgdb_do_roundup = 1;
 147
 148 static int __init opt_nokgdbroundup(char *str)
 149 {
 150         kgdb_do_roundup = 0;
 151
 152         return 0;
 153 }
 154
 155 early_param("nokgdbroundup", opt_nokgdbroundup);
 156
 157 /*
 158  * Finally, some KGDB code :-)
 159  */
 160
 161 /*
 162  * Weak aliases for breakpoint management,
 163  * can be overriden by architectures when needed:
 164  */
 165 int __weak kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
 166 {
 167         int err;
 168
 169         err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr,
 170                                 BREAK_INSTR_SIZE);
 171         if (err)
 172                 return err;
 173         err = probe_kernel_write((char *)bpt->bpt_addr,
 174                                  arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
 175         return err;
 176 }
 177
 178 int __weak kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 179 {
 180         return probe_kernel_write((char *)bpt->bpt_addr,
 181                                   (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
 182 }
 183
 184 int __weak kgdb_validate_break_address(unsigned long addr)
 185 {
 186         struct kgdb_bkpt tmp;
 187         int err;
 188         /* Validate setting the breakpoint and then removing it.  If the
 189          * remove fails, the kernel needs to emit a bad message because we
 190          * are deep trouble not being able to put things back the way we
 191          * found them.
 192          */
 193         tmp.bpt_addr = addr;
 194         err = kgdb_arch_set_breakpoint(&tmp);
 195         if (err)
 196                 return err;
 197         err = kgdb_arch_remove_breakpoint(&tmp);
 198         if (err)
 199                 printk(KERN_ERR "KGDB: Critical breakpoint error, kernel "
 200                    "memory destroyed at: %lx", addr);
 201         return err;
 202 }
 203
 204 unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
 205 {
 206         return instruction_pointer(regs);
 207 }
 208
 209 int __weak kgdb_arch_init(void)
 210 {
 211         return 0;
 212 }
 213
 214 int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
 215 {
 216         return 0;
 217 }
 218
 219 /*
 220  * Some architectures need cache flushes when we set/clear a
 221  * breakpoint:
 222  */
 223 static void kgdb_flush_swbreak_addr(unsigned long addr)
 224 {
 225         if (!CACHE_FLUSH_IS_SAFE)
 226                 return;
 227
 228         if (current->mm) {
 229                 int i;
 230
 231                 for (i = 0; i < VMACACHE_SIZE; i++) {
 232                         if (!current->vmacache[i])
 233                                 continue;
 234                         flush_cache_range(current->vmacache[i],
 235                                           addr, addr + BREAK_INSTR_SIZE);
 236                 }
 237         }
 238
 239         /* Force flush instruction cache if it was outside the mm */
 240         flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
 241 }
 242
 243 /*
 244  * SW breakpoint management:
 245  */
 246 int dbg_activate_sw_breakpoints(void)
 247 {
 248         int error;
 249         int ret = 0;
 250         int i;
 251
 252         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 253                 if (kgdb_break[i].state != BP_SET)
 254                         continue;
 255
 256                 error = kgdb_arch_set_breakpoint(&kgdb_break[i]);
 257                 if (error) {
 258                         ret = error;
 259                         printk(KERN_INFO "KGDB: BP install failed: %lx",
 260                                kgdb_break[i].bpt_addr);
 261                         continue;
 262                 }
 263
 264                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 265                 kgdb_break[i].state = BP_ACTIVE;
 266         }
 267         return ret;
 268 }
 269
 270 int dbg_set_sw_break(unsigned long addr)
 271 {
 272         int err = kgdb_validate_break_address(addr);
 273         int breakno = -1;
 274         int i;
 275
 276         if (err)
 277                 return err;
 278
 279         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 280                 if ((kgdb_break[i].state == BP_SET) &&
 281                                         (kgdb_break[i].bpt_addr == addr))
 282                         return -EEXIST;
 283         }
 284         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 285                 if (kgdb_break[i].state == BP_REMOVED &&
 286                                         kgdb_break[i].bpt_addr == addr) {
 287                         breakno = i;
 288                         break;
 289                 }
 290         }
 291
 292         if (breakno == -1) {
 293                 for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 294                         if (kgdb_break[i].state == BP_UNDEFINED) {
 295                                 breakno = i;
 296                                 break;
 297                         }
 298                 }
 299         }
 300
 301         if (breakno == -1)
 302                 return -E2BIG;
 303
 304         kgdb_break[breakno].state = BP_SET;
 305         kgdb_break[breakno].type = BP_BREAKPOINT;
 306         kgdb_break[breakno].bpt_addr = addr;
 307
 308         return 0;
 309 }
 310
 311 int dbg_deactivate_sw_breakpoints(void)
 312 {
 313         int error;
 314         int ret = 0;
 315         int i;
 316
 317         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 318                 if (kgdb_break[i].state != BP_ACTIVE)
 319                         continue;
 320                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 321                 if (error) {
 322                         printk(KERN_INFO "KGDB: BP remove failed: %lx\n",
 323                                kgdb_break[i].bpt_addr);
 324                         ret = error;
 325                 }
 326
 327                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
 328                 kgdb_break[i].state = BP_SET;
 329         }
 330         return ret;
 331 }
 332
 333 int dbg_remove_sw_break(unsigned long addr)
 334 {
 335         int i;
 336
 337         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 338                 if ((kgdb_break[i].state == BP_SET) &&
 339                                 (kgdb_break[i].bpt_addr == addr)) {
 340                         kgdb_break[i].state = BP_REMOVED;
 341                         return 0;
 342                 }
 343         }
 344         return -ENOENT;
 345 }
 346
 347 int kgdb_isremovedbreak(unsigned long addr)
 348 {
 349         int i;
 350
 351         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 352                 if ((kgdb_break[i].state == BP_REMOVED) &&
 353                                         (kgdb_break[i].bpt_addr == addr))
 354                         return 1;
 355         }
 356         return 0;
 357 }
 358
 359 int dbg_remove_all_break(void)
 360 {
 361         int error;
 362         int i;
 363
 364         /* Clear memory breakpoints. */
 365         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
 366                 if (kgdb_break[i].state != BP_ACTIVE)
 367                         goto setundefined;
 368                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
 369                 if (error)
 370                         printk(KERN_ERR "KGDB: breakpoint remove failed: %lx\n",
 371                                kgdb_break[i].bpt_addr);
 372 setundefined:
 373                 kgdb_break[i].state = BP_UNDEFINED;
 374         }
 375
 376         /* Clear hardware breakpoints. */
 377         if (arch_kgdb_ops.remove_all_hw_break)
 378                 arch_kgdb_ops.remove_all_hw_break();
 379
 380         return 0;
 381 }
 382
 383 /*
 384  * Return true if there is a valid kgdb I/O module.  Also if no
 385  * debugger is attached a message can be printed to the console about
 386  * waiting for the debugger to attach.
 387  *
 388  * The print_wait argument is only to be true when called from inside
 389  * the core kgdb_handle_exception, because it will wait for the
 390  * debugger to attach.
 391  */
 392 static int kgdb_io_ready(int print_wait)
 393 {
 394         if (!dbg_io_ops)
 395                 return 0;
 396         if (kgdb_connected)
 397                 return 1;
 398         if (atomic_read(&kgdb_setting_breakpoint))
 399                 return 1;
 400         if (print_wait) {
 401 #ifdef CONFIG_KGDB_KDB
 402                 if (!dbg_kdb_mode)
 403                         printk(KERN_CRIT "KGDB: waiting... or $3#33 for KDB\n");
 404 #else
 405                 printk(KERN_CRIT "KGDB: Waiting for remote debugger\n");
 406 #endif
 407         }
 408         return 1;
 409 }
 410
 411 static int kgdb_reenter_check(struct kgdb_state *ks)
 412 {
 413         unsigned long addr;
 414
 415         if (atomic_read(&kgdb_active) != raw_smp_processor_id())
 416                 return 0;
 417
 418         /* Panic on recursive debugger calls: */
 419         exception_level++;
 420         addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
 421         dbg_deactivate_sw_breakpoints();
 422
 423         /*
 424          * If the break point removed ok at the place exception
 425          * occurred, try to recover and print a warning to the end
 426          * user because the user planted a breakpoint in a place that
 427          * KGDB needs in order to function.
 428          */
 429         if (dbg_remove_sw_break(addr) == 0) {
 430                 exception_level = 0;
 431                 kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 432                 dbg_activate_sw_breakpoints();
 433                 printk(KERN_CRIT "KGDB: re-enter error: breakpoint removed %lx\n",
 434                         addr);
 435                 WARN_ON_ONCE(1);
 436
 437                 return 1;
 438         }
 439         dbg_remove_all_break();
 440         kgdb_skipexception(ks->ex_vector, ks->linux_regs);
 441
 442         if (exception_level > 1) {
 443                 dump_stack();
 444                 panic("Recursive entry to debugger");
 445         }
 446
 447         printk(KERN_CRIT "KGDB: re-enter exception: ALL breakpoints killed\n");
 448 #ifdef CONFIG_KGDB_KDB
 449         /* Allow kdb to debug itself one level */
 450         return 0;
 451 #endif
 452         dump_stack();
 453         panic("Recursive entry to debugger");
 454
 455         return 1;
 456 }
 457
 458 static void dbg_touch_watchdogs(void)
 459 {
 460         touch_softlockup_watchdog_sync();
 461         clocksource_touch_watchdog();
 462         rcu_cpu_stall_reset();
 463 }
 464
 465 static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
 466                 int exception_state)
 467 {
 468         unsigned long flags;
 469         int sstep_tries = 100;
 470         int error;
 471         int cpu;
 472         int trace_on = 0;
 473         int online_cpus = num_online_cpus();
 474
 475         kgdb_info[ks->cpu].enter_kgdb++;
 476         kgdb_info[ks->cpu].exception_state |= exception_state;
 477
 478         if (exception_state == DCPU_WANT_MASTER)
 479                 atomic_inc(&masters_in_kgdb);
 480         else
 481                 atomic_inc(&slaves_in_kgdb);
 482
 483         if (arch_kgdb_ops.disable_hw_break)
 484                 arch_kgdb_ops.disable_hw_break(regs);
 485
 486 acquirelock:
 487         /*
 488          * Interrupts will be restored by the 'trap return' code, except when
 489          * single stepping.
 490          */
 491         local_irq_save(flags);
 492
 493         cpu = ks->cpu;
 494         kgdb_info[cpu].debuggerinfo = regs;
 495         kgdb_info[cpu].task = current;
 496         kgdb_info[cpu].ret_state = 0;
 497         kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
 498
 499         /* Make sure the above info reaches the primary CPU */
 500         smp_mb();
 501
 502         if (exception_level == 1) {
 503                 if (raw_spin_trylock(&dbg_master_lock))
 504                         atomic_xchg(&kgdb_active, cpu);
 505                 goto cpu_master_loop;
 506         }
 507
 508         /*
 509          * CPU will loop if it is a slave or request to become a kgdb
 510          * master cpu and acquire the kgdb_active lock:
 511          */
 512         while (1) {
 513 cpu_loop:
 514                 if (kgdb_info[cpu].exception_state & DCPU_NEXT_MASTER) {
 515                         kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
 516                         goto cpu_master_loop;
 517                 } else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
 518                         if (raw_spin_trylock(&dbg_master_lock)) {
 519                                 atomic_xchg(&kgdb_active, cpu);
 520                                 break;
 521                         }
 522                 } else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
 523                         if (!raw_spin_is_locked(&dbg_slave_lock))
 524                                 goto return_normal;
 525                 } else {
 526 return_normal:
 527                         /* Return to normal operation by executing any
 528                          * hw breakpoint fixup.
 529                          */
 530                         if (arch_kgdb_ops.correct_hw_break)
 531                                 arch_kgdb_ops.correct_hw_break();
 532                         if (trace_on)
 533                                 tracing_on();
 534                         kgdb_info[cpu].exception_state &=
 535                                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 536                         kgdb_info[cpu].enter_kgdb--;
 537                         smp_mb__before_atomic_dec();
 538                         atomic_dec(&slaves_in_kgdb);
 539                         dbg_touch_watchdogs();
 540                         local_irq_restore(flags);
 541                         return 0;
 542                 }
 543                 cpu_relax();
 544         }
 545
 546         /*
 547          * For single stepping, try to only enter on the processor
 548          * that was single stepping.  To guard against a deadlock, the
 549          * kernel will only try for the value of sstep_tries before
 550          * giving up and continuing on.
 551          */
 552         if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
 553             (kgdb_info[cpu].task &&
 554              kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
 555                 atomic_set(&kgdb_active, -1);
 556                 raw_spin_unlock(&dbg_master_lock);
 557                 dbg_touch_watchdogs();
 558                 local_irq_restore(flags);
 559
 560                 goto acquirelock;
 561         }
 562
 563         if (!kgdb_io_ready(1)) {
 564                 kgdb_info[cpu].ret_state = 1;
 565                 goto kgdb_restore; /* No I/O connection, resume the system */
 566         }
 567
 568         /*
 569          * Don't enter if we have hit a removed breakpoint.
 570          */
 571         if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
 572                 goto kgdb_restore;
 573
 574         /* Call the I/O driver's pre_exception routine */
 575         if (dbg_io_ops->pre_exception)
 576                 dbg_io_ops->pre_exception();
 577
 578         /*
 579          * Get the passive CPU lock which will hold all the non-primary
 580          * CPU in a spin state while the debugger is active
 581          */
 582         if (!kgdb_single_step)
 583                 raw_spin_lock(&dbg_slave_lock);
 584
 585 #ifdef CONFIG_SMP
 586         /* If send_ready set, slaves are already waiting */
 587         if (ks->send_ready)
 588                 atomic_set(ks->send_ready, 1);
 589
 590         /* Signal the other CPUs to enter kgdb_wait() */
 591         else if ((!kgdb_single_step) && kgdb_do_roundup)
 592                 kgdb_roundup_cpus(flags);
 593 #endif
 594
 595         /*
 596          * Wait for the other CPUs to be notified and be waiting for us:
 597          */
 598         while (kgdb_do_roundup && (atomic_read(&masters_in_kgdb) +
 599                                 atomic_read(&slaves_in_kgdb)) != online_cpus)
 600                 cpu_relax();
 601
 602         /*
 603          * At this point the primary processor is completely
 604          * in the debugger and all secondary CPUs are quiescent
 605          */
 606         dbg_deactivate_sw_breakpoints();
 607         kgdb_single_step = 0;
 608         kgdb_contthread = current;
 609         exception_level = 0;
 610         trace_on = tracing_is_on();
 611         if (trace_on)
 612                 tracing_off();
 613
 614         while (1) {
 615 cpu_master_loop:
 616                 if (dbg_kdb_mode) {
 617                         kgdb_connected = 1;
 618                         error = kdb_stub(ks);
 619                         if (error == -1)
 620                                 continue;
 621                         kgdb_connected = 0;
 622                 } else {
 623                         error = gdb_serial_stub(ks);
 624                 }
 625
 626                 if (error == DBG_PASS_EVENT) {
 627                         dbg_kdb_mode = !dbg_kdb_mode;
 628                 } else if (error == DBG_SWITCH_CPU_EVENT) {
 629                         kgdb_info[dbg_switch_cpu].exception_state |=
 630                                 DCPU_NEXT_MASTER;
 631                         goto cpu_loop;
 632                 } else {
 633                         kgdb_info[cpu].ret_state = error;
 634                         break;
 635                 }
 636         }
 637
 638         /* Call the I/O driver's post_exception routine */
 639         if (dbg_io_ops->post_exception)
 640                 dbg_io_ops->post_exception();
 641
 642         if (!kgdb_single_step) {
 643                 raw_spin_unlock(&dbg_slave_lock);
 644                 /* Wait till all the CPUs have quit from the debugger. */
 645                 while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
 646                         cpu_relax();
 647         }
 648
 649 kgdb_restore:
 650         if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
 651                 int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
 652                 if (kgdb_info[sstep_cpu].task)
 653                         kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
 654                 else
 655                         kgdb_sstep_pid = 0;
 656         }
 657         if (arch_kgdb_ops.correct_hw_break)
 658                 arch_kgdb_ops.correct_hw_break();
 659         if (trace_on)
 660                 tracing_on();
 661
 662         kgdb_info[cpu].exception_state &=
 663                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
 664         kgdb_info[cpu].enter_kgdb--;
 665         smp_mb__before_atomic_dec();
 666         atomic_dec(&masters_in_kgdb);
 667         /* Free kgdb_active */
 668         atomic_set(&kgdb_active, -1);
 669         raw_spin_unlock(&dbg_master_lock);
 670         dbg_touch_watchdogs();
 671         local_irq_restore(flags);
 672
 673         return kgdb_info[cpu].ret_state;
 674 }
 675
 676 /*
 677  * kgdb_handle_exception() - main entry point from a kernel exception
 678  *
 679  * Locking hierarchy:
 680  *      interface locks, if any (begin_session)
 681  *      kgdb lock (kgdb_active)
 682  */
 683 int
 684 kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 685 {
 686         struct kgdb_state kgdb_var;
 687         struct kgdb_state *ks = &kgdb_var;
 688         int ret = 0;
 689
 690         if (arch_kgdb_ops.enable_nmi)
 691                 arch_kgdb_ops.enable_nmi(0);
 692
 693         memset(ks, 0, sizeof(struct kgdb_state));
 694         ks->cpu                 = raw_smp_processor_id();
 695         ks->ex_vector           = evector;
 696         ks->signo               = signo;
 697         ks->err_code            = ecode;
 698         ks->linux_regs          = regs;
 699
 700         if (kgdb_reenter_check(ks))
 701                 goto out; /* Ouch, double exception ! */
 702         if (kgdb_info[ks->cpu].enter_kgdb != 0)
 703                 goto out;
 704
 705         ret = kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 706 out:
 707         if (arch_kgdb_ops.enable_nmi)
 708                 arch_kgdb_ops.enable_nmi(1);
 709         return ret;
 710 }
 711
 712 /*
 713  * GDB places a breakpoint at this function to know dynamically
 714  * loaded objects. It's not defined static so that only one instance with this
 715  * name exists in the kernel.
 716  */
 717
 718 static int module_event(struct notifier_block *self, unsigned long val,
 719         void *data)
 720 {
 721         return 0;
 722 }
 723
 724 static struct notifier_block dbg_module_load_nb = {
 725         .notifier_call  = module_event,
 726 };
 727
 728 int kgdb_nmicallback(int cpu, void *regs)
 729 {
 730 #ifdef CONFIG_SMP
 731         struct kgdb_state kgdb_var;
 732         struct kgdb_state *ks = &kgdb_var;
 733
 734         memset(ks, 0, sizeof(struct kgdb_state));
 735         ks->cpu                 = cpu;
 736         ks->linux_regs          = regs;
 737
 738         if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
 739                         raw_spin_is_locked(&dbg_master_lock)) {
 740                 kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
 741                 return 0;
 742         }
 743 #endif
 744         return 1;
 745 }
 746
 747 int kgdb_nmicallin(int cpu, int trapnr, void *regs, int err_code,
 748                                                         atomic_t *send_ready)
 749 {
 750 #ifdef CONFIG_SMP
 751         if (!kgdb_io_ready(0) || !send_ready)
 752                 return 1;
 753
 754         if (kgdb_info[cpu].enter_kgdb == 0) {
 755                 struct kgdb_state kgdb_var;
 756                 struct kgdb_state *ks = &kgdb_var;
 757
 758                 memset(ks, 0, sizeof(struct kgdb_state));
 759                 ks->cpu                 = cpu;
 760                 ks->ex_vector           = trapnr;
 761                 ks->signo               = SIGTRAP;
 762                 ks->err_code            = err_code;
 763                 ks->linux_regs          = regs;
 764                 ks->send_ready          = send_ready;
 765                 kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 766                 return 0;
 767         }
 768 #endif
 769         return 1;
 770 }
 771
 772 static void kgdb_console_write(struct console *co, const char *s,
 773    unsigned count)
 774 {
 775         unsigned long flags;
 776
 777         /* If we're debugging, or KGDB has not connected, don't try
 778          * and print. */
 779         if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
 780                 return;
 781
 782         local_irq_save(flags);
 783         gdbstub_msg_write(s, count);
 784         local_irq_restore(flags);
 785 }
 786
 787 static struct console kgdbcons = {
 788         .name           = "kgdb",
 789         .write          = kgdb_console_write,
 790         .flags          = CON_PRINTBUFFER | CON_ENABLED,
 791         .index          = -1,
 792 };
 793
 794 #ifdef CONFIG_MAGIC_SYSRQ
 795 static void sysrq_handle_dbg(int key)
 796 {
 797         if (!dbg_io_ops) {
 798                 printk(KERN_CRIT "ERROR: No KGDB I/O module available\n");
 799                 return;
 800         }
 801         if (!kgdb_connected) {
 802 #ifdef CONFIG_KGDB_KDB
 803                 if (!dbg_kdb_mode)
 804                         printk(KERN_CRIT "KGDB or $3#33 for KDB\n");
 805 #else
 806                 printk(KERN_CRIT "Entering KGDB\n");
 807 #endif
 808         }
 809
 810         kgdb_breakpoint();
 811 }
 812
 813 static struct sysrq_key_op sysrq_dbg_op = {
 814         .handler        = sysrq_handle_dbg,
 815         .help_msg       = "debug(g)",
 816         .action_msg     = "DEBUG",
 817 };
 818 #endif
 819
 820 static int kgdb_panic_event(struct notifier_block *self,
 821                             unsigned long val,
 822                             void *data)
 823 {
 824         if (dbg_kdb_mode)
 825                 kdb_printf("PANIC: %s\n", (char *)data);
 826         kgdb_breakpoint();
 827         return NOTIFY_DONE;
 828 }
 829
 830 static struct notifier_block kgdb_panic_event_nb = {
 831        .notifier_call   = kgdb_panic_event,
 832        .priority        = INT_MAX,
 833 };
 834
 835 void __weak kgdb_arch_late(void)
 836 {
 837 }
 838
 839 void __init dbg_late_init(void)
 840 {
 841         dbg_is_early = false;
 842         if (kgdb_io_module_registered)
 843                 kgdb_arch_late();
 844         kdb_init(KDB_INIT_FULL);
 845 }
 846
 847 static int
 848 dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
 849 {
 850         /*
 851          * Take the following action on reboot notify depending on value:
 852          *    1 == Enter debugger
 853          *    0 == [the default] detatch debug client
 854          *   -1 == Do nothing... and use this until the board resets
 855          */
 856         switch (kgdbreboot) {
 857         case 1:
 858                 kgdb_breakpoint();
 859         case -1:
 860                 goto done;
 861         }
 862         if (!dbg_kdb_mode)
 863                 gdbstub_exit(code);
 864 done:
 865         return NOTIFY_DONE;
 866 }
 867
 868 static struct notifier_block dbg_reboot_notifier = {
 869         .notifier_call          = dbg_notify_reboot,
 870         .next                   = NULL,
 871         .priority               = INT_MAX,
 872 };
 873
 874 static void kgdb_register_callbacks(void)
 875 {
 876         if (!kgdb_io_module_registered) {
 877                 kgdb_io_module_registered = 1;
 878                 kgdb_arch_init();
 879                 if (!dbg_is_early)
 880                         kgdb_arch_late();
 881                 register_module_notifier(&dbg_module_load_nb);
 882                 register_reboot_notifier(&dbg_reboot_notifier);
 883                 atomic_notifier_chain_register(&panic_notifier_list,
 884                                                &kgdb_panic_event_nb);
 885 #ifdef CONFIG_MAGIC_SYSRQ
 886                 register_sysrq_key('g', &sysrq_dbg_op);
 887 #endif
 888                 if (kgdb_use_con && !kgdb_con_registered) {
 889                         register_console(&kgdbcons);
 890                         kgdb_con_registered = 1;
 891                 }
 892         }
 893 }
 894
 895 static void kgdb_unregister_callbacks(void)
 896 {
 897         /*
 898          * When this routine is called KGDB should unregister from the
 899          * panic handler and clean up, making sure it is not handling any
 900          * break exceptions at the time.
 901          */
 902         if (kgdb_io_module_registered) {
 903                 kgdb_io_module_registered = 0;
 904                 unregister_reboot_notifier(&dbg_reboot_notifier);
 905                 unregister_module_notifier(&dbg_module_load_nb);
 906                 atomic_notifier_chain_unregister(&panic_notifier_list,
 907                                                &kgdb_panic_event_nb);
 908                 kgdb_arch_exit();
 909 #ifdef CONFIG_MAGIC_SYSRQ
 910                 unregister_sysrq_key('g', &sysrq_dbg_op);
 911 #endif
 912                 if (kgdb_con_registered) {
 913                         unregister_console(&kgdbcons);
 914                         kgdb_con_registered = 0;
 915                 }
 916         }
 917 }
 918
 919 /*
 920  * There are times a tasklet needs to be used vs a compiled in
 921  * break point so as to cause an exception outside a kgdb I/O module,
 922  * such as is the case with kgdboe, where calling a breakpoint in the
 923  * I/O driver itself would be fatal.
 924  */
 925 static void kgdb_tasklet_bpt(unsigned long ing)
 926 {
 927         kgdb_breakpoint();
 928         atomic_set(&kgdb_break_tasklet_var, 0);
 929 }
 930
 931 static DECLARE_TASKLET(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt, 0);
 932
 933 void kgdb_schedule_breakpoint(void)
 934 {
 935         if (atomic_read(&kgdb_break_tasklet_var) ||
 936                 atomic_read(&kgdb_active) != -1 ||
 937                 atomic_read(&kgdb_setting_breakpoint))
 938                 return;
 939         atomic_inc(&kgdb_break_tasklet_var);
 940         tasklet_schedule(&kgdb_tasklet_breakpoint);
 941 }
 942 EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
 943
 944 static void kgdb_initial_breakpoint(void)
 945 {
 946         kgdb_break_asap = 0;
 947
 948         printk(KERN_CRIT "kgdb: Waiting for connection from remote gdb...\n");
 949         kgdb_breakpoint();
 950 }
 951
 952 /**
 953  *      kgdb_register_io_module - register KGDB IO module
 954  *      @new_dbg_io_ops: the io ops vector
 955  *
 956  *      Register it with the KGDB core.
 957  */
 958 int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
 959 {
 960         int err;
 961
 962         spin_lock(&kgdb_registration_lock);
 963
 964         if (dbg_io_ops) {
 965                 spin_unlock(&kgdb_registration_lock);
 966
 967                 printk(KERN_ERR "kgdb: Another I/O driver is already "
 968                                 "registered with KGDB.\n");
 969                 return -EBUSY;
 970         }
 971
 972         if (new_dbg_io_ops->init) {
 973                 err = new_dbg_io_ops->init();
 974                 if (err) {
 975                         spin_unlock(&kgdb_registration_lock);
 976                         return err;
 977                 }
 978         }
 979
 980         dbg_io_ops = new_dbg_io_ops;
 981
 982         spin_unlock(&kgdb_registration_lock);
 983
 984         printk(KERN_INFO "kgdb: Registered I/O driver %s.\n",
 985                new_dbg_io_ops->name);
 986
 987         /* Arm KGDB now. */
 988         kgdb_register_callbacks();
 989
 990         if (kgdb_break_asap)
 991                 kgdb_initial_breakpoint();
 992
 993         return 0;
 994 }
 995 EXPORT_SYMBOL_GPL(kgdb_register_io_module);
 996
 997 /**
 998  *      kkgdb_unregister_io_module - unregister KGDB IO module
 999  *      @old_dbg_io_ops: the io ops vector
1000  *
1001  *      Unregister it with the KGDB core.
1002  */
1003 void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
1004 {
1005         BUG_ON(kgdb_connected);
1006
1007         /*
1008          * KGDB is no longer able to communicate out, so
1009          * unregister our callbacks and reset state.
1010          */
1011         kgdb_unregister_callbacks();
1012
1013         spin_lock(&kgdb_registration_lock);
1014
1015         WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
1016         dbg_io_ops = NULL;
1017
1018         spin_unlock(&kgdb_registration_lock);
1019
1020         printk(KERN_INFO
1021                 "kgdb: Unregistered I/O driver %s, debugger disabled.\n",
1022                 old_dbg_io_ops->name);
1023 }
1024 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
1025
1026 int dbg_io_get_char(void)
1027 {
1028         int ret = dbg_io_ops->read_char();
1029         if (ret == NO_POLL_CHAR)
1030                 return -1;
1031         if (!dbg_kdb_mode)
1032                 return ret;
1033         if (ret == 127)
1034                 return 8;
1035         return ret;
1036 }
1037
1038 /**
1039  * kgdb_breakpoint - generate breakpoint exception
1040  *
1041  * This function will generate a breakpoint exception.  It is used at the
1042  * beginning of a program to sync up with a debugger and can be used
1043  * otherwise as a quick means to stop program execution and "break" into
1044  * the debugger.
1045  */
1046 void kgdb_breakpoint(void)
1047 {
1048         atomic_inc(&kgdb_setting_breakpoint);
1049         wmb(); /* Sync point before breakpoint */
1050         arch_kgdb_breakpoint();
1051         wmb(); /* Sync point after breakpoint */
1052         atomic_dec(&kgdb_setting_breakpoint);
1053 }
1054 EXPORT_SYMBOL_GPL(kgdb_breakpoint);
1055
1056 static int __init opt_kgdb_wait(char *str)
1057 {
1058         kgdb_break_asap = 1;
1059
1060         kdb_init(KDB_INIT_EARLY);
1061         if (kgdb_io_module_registered)
1062                 kgdb_initial_breakpoint();
1063
1064         return 0;
1065 }
1066
1067 early_param("kgdbwait", opt_kgdb_wait);