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