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Linux/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 
 31 #define pr_fmt(fmt) "KGDB: " fmt
 32 
 33 #include <linux/pid_namespace.h>
 34 #include <linux/clocksource.h>
 35 #include <linux/serial_core.h>
 36 #include <linux/interrupt.h>
 37 #include <linux/spinlock.h>
 38 #include <linux/console.h>
 39 #include <linux/threads.h>
 40 #include <linux/uaccess.h>
 41 #include <linux/kernel.h>
 42 #include <linux/module.h>
 43 #include <linux/ptrace.h>
 44 #include <linux/string.h>
 45 #include <linux/delay.h>
 46 #include <linux/sched.h>
 47 #include <linux/sysrq.h>
 48 #include <linux/reboot.h>
 49 #include <linux/init.h>
 50 #include <linux/kgdb.h>
 51 #include <linux/kdb.h>
 52 #include <linux/pid.h>
 53 #include <linux/smp.h>
 54 #include <linux/mm.h>
 55 #include <linux/vmacache.h>
 56 #include <linux/rcupdate.h>
 57 
 58 #include <asm/cacheflush.h>
 59 #include <asm/byteorder.h>
 60 #include <linux/atomic.h>
 61 
 62 #include "debug_core.h"
 63 
 64 static int kgdb_break_asap;
 65 
 66 struct debuggerinfo_struct kgdb_info[NR_CPUS];
 67 
 68 /**
 69  * kgdb_connected - Is a host GDB connected to us?
 70  */
 71 int                             kgdb_connected;
 72 EXPORT_SYMBOL_GPL(kgdb_connected);
 73 
 74 /* All the KGDB handlers are installed */
 75 int                     kgdb_io_module_registered;
 76 
 77 /* Guard for recursive entry */
 78 static int                      exception_level;
 79 
 80 struct kgdb_io          *dbg_io_ops;
 81 static DEFINE_SPINLOCK(kgdb_registration_lock);
 82 
 83 /* Action for the reboot notifiter, a global allow kdb to change it */
 84 static int kgdbreboot;
 85 /* kgdb console driver is loaded */
 86 static int kgdb_con_registered;
 87 /* determine if kgdb console output should be used */
 88 static int kgdb_use_con;
 89 /* Flag for alternate operations for early debugging */
 90 bool dbg_is_early = true;
 91 /* Next cpu to become the master debug core */
 92 int dbg_switch_cpu;
 93 
 94 /* Use kdb or gdbserver mode */
 95 int dbg_kdb_mode = 1;
 96 
 97 static int __init opt_kgdb_con(char *str)
 98 {
 99         kgdb_use_con = 1;
100         return 0;
101 }
102 
103 early_param("kgdbcon", opt_kgdb_con);
104 
105 module_param(kgdb_use_con, int, 0644);
106 module_param(kgdbreboot, int, 0644);
107 
108 /*
109  * Holds information about breakpoints in a kernel. These breakpoints are
110  * added and removed by gdb.
111  */
112 static struct kgdb_bkpt         kgdb_break[KGDB_MAX_BREAKPOINTS] = {
113         [0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
114 };
115 
116 /*
117  * The CPU# of the active CPU, or -1 if none:
118  */
119 atomic_t                        kgdb_active = ATOMIC_INIT(-1);
120 EXPORT_SYMBOL_GPL(kgdb_active);
121 static DEFINE_RAW_SPINLOCK(dbg_master_lock);
122 static DEFINE_RAW_SPINLOCK(dbg_slave_lock);
123 
124 /*
125  * We use NR_CPUs not PERCPU, in case kgdb is used to debug early
126  * bootup code (which might not have percpu set up yet):
127  */
128 static atomic_t                 masters_in_kgdb;
129 static atomic_t                 slaves_in_kgdb;
130 static atomic_t                 kgdb_break_tasklet_var;
131 atomic_t                        kgdb_setting_breakpoint;
132 
133 struct task_struct              *kgdb_usethread;
134 struct task_struct              *kgdb_contthread;
135 
136 int                             kgdb_single_step;
137 static pid_t                    kgdb_sstep_pid;
138 
139 /* to keep track of the CPU which is doing the single stepping*/
140 atomic_t                        kgdb_cpu_doing_single_step = ATOMIC_INIT(-1);
141 
142 /*
143  * If you are debugging a problem where roundup (the collection of
144  * all other CPUs) is a problem [this should be extremely rare],
145  * then use the nokgdbroundup option to avoid roundup. In that case
146  * the other CPUs might interfere with your debugging context, so
147  * use this with care:
148  */
149 static int kgdb_do_roundup = 1;
150 
151 static int __init opt_nokgdbroundup(char *str)
152 {
153         kgdb_do_roundup = 0;
154 
155         return 0;
156 }
157 
158 early_param("nokgdbroundup", opt_nokgdbroundup);
159 
160 /*
161  * Finally, some KGDB code :-)
162  */
163 
164 /*
165  * Weak aliases for breakpoint management,
166  * can be overriden by architectures when needed:
167  */
168 int __weak kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
169 {
170         int err;
171 
172         err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr,
173                                 BREAK_INSTR_SIZE);
174         if (err)
175                 return err;
176         err = probe_kernel_write((char *)bpt->bpt_addr,
177                                  arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
178         return err;
179 }
180 
181 int __weak kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
182 {
183         return probe_kernel_write((char *)bpt->bpt_addr,
184                                   (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
185 }
186 
187 int __weak kgdb_validate_break_address(unsigned long addr)
188 {
189         struct kgdb_bkpt tmp;
190         int err;
191         /* Validate setting the breakpoint and then removing it.  If the
192          * remove fails, the kernel needs to emit a bad message because we
193          * are deep trouble not being able to put things back the way we
194          * found them.
195          */
196         tmp.bpt_addr = addr;
197         err = kgdb_arch_set_breakpoint(&tmp);
198         if (err)
199                 return err;
200         err = kgdb_arch_remove_breakpoint(&tmp);
201         if (err)
202                 pr_err("Critical breakpoint error, kernel memory destroyed at: %lx\n",
203                        addr);
204         return err;
205 }
206 
207 unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
208 {
209         return instruction_pointer(regs);
210 }
211 
212 int __weak kgdb_arch_init(void)
213 {
214         return 0;
215 }
216 
217 int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
218 {
219         return 0;
220 }
221 
222 /*
223  * Some architectures need cache flushes when we set/clear a
224  * breakpoint:
225  */
226 static void kgdb_flush_swbreak_addr(unsigned long addr)
227 {
228         if (!CACHE_FLUSH_IS_SAFE)
229                 return;
230 
231         if (current->mm) {
232                 int i;
233 
234                 for (i = 0; i < VMACACHE_SIZE; i++) {
235                         if (!current->vmacache[i])
236                                 continue;
237                         flush_cache_range(current->vmacache[i],
238                                           addr, addr + BREAK_INSTR_SIZE);
239                 }
240         }
241 
242         /* Force flush instruction cache if it was outside the mm */
243         flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
244 }
245 
246 /*
247  * SW breakpoint management:
248  */
249 int dbg_activate_sw_breakpoints(void)
250 {
251         int error;
252         int ret = 0;
253         int i;
254 
255         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
256                 if (kgdb_break[i].state != BP_SET)
257                         continue;
258 
259                 error = kgdb_arch_set_breakpoint(&kgdb_break[i]);
260                 if (error) {
261                         ret = error;
262                         pr_info("BP install failed: %lx\n",
263                                 kgdb_break[i].bpt_addr);
264                         continue;
265                 }
266 
267                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
268                 kgdb_break[i].state = BP_ACTIVE;
269         }
270         return ret;
271 }
272 
273 int dbg_set_sw_break(unsigned long addr)
274 {
275         int err = kgdb_validate_break_address(addr);
276         int breakno = -1;
277         int i;
278 
279         if (err)
280                 return err;
281 
282         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
283                 if ((kgdb_break[i].state == BP_SET) &&
284                                         (kgdb_break[i].bpt_addr == addr))
285                         return -EEXIST;
286         }
287         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
288                 if (kgdb_break[i].state == BP_REMOVED &&
289                                         kgdb_break[i].bpt_addr == addr) {
290                         breakno = i;
291                         break;
292                 }
293         }
294 
295         if (breakno == -1) {
296                 for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
297                         if (kgdb_break[i].state == BP_UNDEFINED) {
298                                 breakno = i;
299                                 break;
300                         }
301                 }
302         }
303 
304         if (breakno == -1)
305                 return -E2BIG;
306 
307         kgdb_break[breakno].state = BP_SET;
308         kgdb_break[breakno].type = BP_BREAKPOINT;
309         kgdb_break[breakno].bpt_addr = addr;
310 
311         return 0;
312 }
313 
314 int dbg_deactivate_sw_breakpoints(void)
315 {
316         int error;
317         int ret = 0;
318         int i;
319 
320         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
321                 if (kgdb_break[i].state != BP_ACTIVE)
322                         continue;
323                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
324                 if (error) {
325                         pr_info("BP remove failed: %lx\n",
326                                 kgdb_break[i].bpt_addr);
327                         ret = error;
328                 }
329 
330                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
331                 kgdb_break[i].state = BP_SET;
332         }
333         return ret;
334 }
335 
336 int dbg_remove_sw_break(unsigned long addr)
337 {
338         int i;
339 
340         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
341                 if ((kgdb_break[i].state == BP_SET) &&
342                                 (kgdb_break[i].bpt_addr == addr)) {
343                         kgdb_break[i].state = BP_REMOVED;
344                         return 0;
345                 }
346         }
347         return -ENOENT;
348 }
349 
350 int kgdb_isremovedbreak(unsigned long addr)
351 {
352         int i;
353 
354         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
355                 if ((kgdb_break[i].state == BP_REMOVED) &&
356                                         (kgdb_break[i].bpt_addr == addr))
357                         return 1;
358         }
359         return 0;
360 }
361 
362 int dbg_remove_all_break(void)
363 {
364         int error;
365         int i;
366 
367         /* Clear memory breakpoints. */
368         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
369                 if (kgdb_break[i].state != BP_ACTIVE)
370                         goto setundefined;
371                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
372                 if (error)
373                         pr_err("breakpoint remove failed: %lx\n",
374                                kgdb_break[i].bpt_addr);
375 setundefined:
376                 kgdb_break[i].state = BP_UNDEFINED;
377         }
378 
379         /* Clear hardware breakpoints. */
380         if (arch_kgdb_ops.remove_all_hw_break)
381                 arch_kgdb_ops.remove_all_hw_break();
382 
383         return 0;
384 }
385 
386 /*
387  * Return true if there is a valid kgdb I/O module.  Also if no
388  * debugger is attached a message can be printed to the console about
389  * waiting for the debugger to attach.
390  *
391  * The print_wait argument is only to be true when called from inside
392  * the core kgdb_handle_exception, because it will wait for the
393  * debugger to attach.
394  */
395 static int kgdb_io_ready(int print_wait)
396 {
397         if (!dbg_io_ops)
398                 return 0;
399         if (kgdb_connected)
400                 return 1;
401         if (atomic_read(&kgdb_setting_breakpoint))
402                 return 1;
403         if (print_wait) {
404 #ifdef CONFIG_KGDB_KDB
405                 if (!dbg_kdb_mode)
406                         pr_crit("waiting... or $3#33 for KDB\n");
407 #else
408                 pr_crit("Waiting for remote debugger\n");
409 #endif
410         }
411         return 1;
412 }
413 
414 static int kgdb_reenter_check(struct kgdb_state *ks)
415 {
416         unsigned long addr;
417 
418         if (atomic_read(&kgdb_active) != raw_smp_processor_id())
419                 return 0;
420 
421         /* Panic on recursive debugger calls: */
422         exception_level++;
423         addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
424         dbg_deactivate_sw_breakpoints();
425 
426         /*
427          * If the break point removed ok at the place exception
428          * occurred, try to recover and print a warning to the end
429          * user because the user planted a breakpoint in a place that
430          * KGDB needs in order to function.
431          */
432         if (dbg_remove_sw_break(addr) == 0) {
433                 exception_level = 0;
434                 kgdb_skipexception(ks->ex_vector, ks->linux_regs);
435                 dbg_activate_sw_breakpoints();
436                 pr_crit("re-enter error: breakpoint removed %lx\n", 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         pr_crit("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_touch_watchdogs(void)
461 {
462         touch_softlockup_watchdog_sync();
463         clocksource_touch_watchdog();
464         rcu_cpu_stall_reset();
465 }
466 
467 static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
468                 int exception_state)
469 {
470         unsigned long flags;
471         int sstep_tries = 100;
472         int error;
473         int cpu;
474         int trace_on = 0;
475         int online_cpus = num_online_cpus();
476         u64 time_left;
477 
478         kgdb_info[ks->cpu].enter_kgdb++;
479         kgdb_info[ks->cpu].exception_state |= exception_state;
480 
481         if (exception_state == DCPU_WANT_MASTER)
482                 atomic_inc(&masters_in_kgdb);
483         else
484                 atomic_inc(&slaves_in_kgdb);
485 
486         if (arch_kgdb_ops.disable_hw_break)
487                 arch_kgdb_ops.disable_hw_break(regs);
488 
489 acquirelock:
490         /*
491          * Interrupts will be restored by the 'trap return' code, except when
492          * single stepping.
493          */
494         local_irq_save(flags);
495 
496         cpu = ks->cpu;
497         kgdb_info[cpu].debuggerinfo = regs;
498         kgdb_info[cpu].task = current;
499         kgdb_info[cpu].ret_state = 0;
500         kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
501 
502         /* Make sure the above info reaches the primary CPU */
503         smp_mb();
504 
505         if (exception_level == 1) {
506                 if (raw_spin_trylock(&dbg_master_lock))
507                         atomic_xchg(&kgdb_active, cpu);
508                 goto cpu_master_loop;
509         }
510 
511         /*
512          * CPU will loop if it is a slave or request to become a kgdb
513          * master cpu and acquire the kgdb_active lock:
514          */
515         while (1) {
516 cpu_loop:
517                 if (kgdb_info[cpu].exception_state & DCPU_NEXT_MASTER) {
518                         kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
519                         goto cpu_master_loop;
520                 } else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
521                         if (raw_spin_trylock(&dbg_master_lock)) {
522                                 atomic_xchg(&kgdb_active, cpu);
523                                 break;
524                         }
525                 } else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
526                         if (!raw_spin_is_locked(&dbg_slave_lock))
527                                 goto return_normal;
528                 } else {
529 return_normal:
530                         /* Return to normal operation by executing any
531                          * hw breakpoint fixup.
532                          */
533                         if (arch_kgdb_ops.correct_hw_break)
534                                 arch_kgdb_ops.correct_hw_break();
535                         if (trace_on)
536                                 tracing_on();
537                         kgdb_info[cpu].exception_state &=
538                                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
539                         kgdb_info[cpu].enter_kgdb--;
540                         smp_mb__before_atomic();
541                         atomic_dec(&slaves_in_kgdb);
542                         dbg_touch_watchdogs();
543                         local_irq_restore(flags);
544                         return 0;
545                 }
546                 cpu_relax();
547         }
548 
549         /*
550          * For single stepping, try to only enter on the processor
551          * that was single stepping.  To guard against a deadlock, the
552          * kernel will only try for the value of sstep_tries before
553          * giving up and continuing on.
554          */
555         if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
556             (kgdb_info[cpu].task &&
557              kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
558                 atomic_set(&kgdb_active, -1);
559                 raw_spin_unlock(&dbg_master_lock);
560                 dbg_touch_watchdogs();
561                 local_irq_restore(flags);
562 
563                 goto acquirelock;
564         }
565 
566         if (!kgdb_io_ready(1)) {
567                 kgdb_info[cpu].ret_state = 1;
568                 goto kgdb_restore; /* No I/O connection, resume the system */
569         }
570 
571         /*
572          * Don't enter if we have hit a removed breakpoint.
573          */
574         if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
575                 goto kgdb_restore;
576 
577         /* Call the I/O driver's pre_exception routine */
578         if (dbg_io_ops->pre_exception)
579                 dbg_io_ops->pre_exception();
580 
581         /*
582          * Get the passive CPU lock which will hold all the non-primary
583          * CPU in a spin state while the debugger is active
584          */
585         if (!kgdb_single_step)
586                 raw_spin_lock(&dbg_slave_lock);
587 
588 #ifdef CONFIG_SMP
589         /* If send_ready set, slaves are already waiting */
590         if (ks->send_ready)
591                 atomic_set(ks->send_ready, 1);
592 
593         /* Signal the other CPUs to enter kgdb_wait() */
594         else if ((!kgdb_single_step) && kgdb_do_roundup)
595                 kgdb_roundup_cpus(flags);
596 #endif
597 
598         /*
599          * Wait for the other CPUs to be notified and be waiting for us:
600          */
601         time_left = MSEC_PER_SEC;
602         while (kgdb_do_roundup && --time_left &&
603                (atomic_read(&masters_in_kgdb) + atomic_read(&slaves_in_kgdb)) !=
604                    online_cpus)
605                 udelay(1000);
606         if (!time_left)
607                 pr_crit("Timed out waiting for secondary CPUs.\n");
608 
609         /*
610          * At this point the primary processor is completely
611          * in the debugger and all secondary CPUs are quiescent
612          */
613         dbg_deactivate_sw_breakpoints();
614         kgdb_single_step = 0;
615         kgdb_contthread = current;
616         exception_level = 0;
617         trace_on = tracing_is_on();
618         if (trace_on)
619                 tracing_off();
620 
621         while (1) {
622 cpu_master_loop:
623                 if (dbg_kdb_mode) {
624                         kgdb_connected = 1;
625                         error = kdb_stub(ks);
626                         if (error == -1)
627                                 continue;
628                         kgdb_connected = 0;
629                 } else {
630                         error = gdb_serial_stub(ks);
631                 }
632 
633                 if (error == DBG_PASS_EVENT) {
634                         dbg_kdb_mode = !dbg_kdb_mode;
635                 } else if (error == DBG_SWITCH_CPU_EVENT) {
636                         kgdb_info[dbg_switch_cpu].exception_state |=
637                                 DCPU_NEXT_MASTER;
638                         goto cpu_loop;
639                 } else {
640                         kgdb_info[cpu].ret_state = error;
641                         break;
642                 }
643         }
644 
645         /* Call the I/O driver's post_exception routine */
646         if (dbg_io_ops->post_exception)
647                 dbg_io_ops->post_exception();
648 
649         if (!kgdb_single_step) {
650                 raw_spin_unlock(&dbg_slave_lock);
651                 /* Wait till all the CPUs have quit from the debugger. */
652                 while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
653                         cpu_relax();
654         }
655 
656 kgdb_restore:
657         if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
658                 int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
659                 if (kgdb_info[sstep_cpu].task)
660                         kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
661                 else
662                         kgdb_sstep_pid = 0;
663         }
664         if (arch_kgdb_ops.correct_hw_break)
665                 arch_kgdb_ops.correct_hw_break();
666         if (trace_on)
667                 tracing_on();
668 
669         kgdb_info[cpu].exception_state &=
670                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
671         kgdb_info[cpu].enter_kgdb--;
672         smp_mb__before_atomic();
673         atomic_dec(&masters_in_kgdb);
674         /* Free kgdb_active */
675         atomic_set(&kgdb_active, -1);
676         raw_spin_unlock(&dbg_master_lock);
677         dbg_touch_watchdogs();
678         local_irq_restore(flags);
679 
680         return kgdb_info[cpu].ret_state;
681 }
682 
683 /*
684  * kgdb_handle_exception() - main entry point from a kernel exception
685  *
686  * Locking hierarchy:
687  *      interface locks, if any (begin_session)
688  *      kgdb lock (kgdb_active)
689  */
690 int
691 kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
692 {
693         struct kgdb_state kgdb_var;
694         struct kgdb_state *ks = &kgdb_var;
695         int ret = 0;
696 
697         if (arch_kgdb_ops.enable_nmi)
698                 arch_kgdb_ops.enable_nmi(0);
699         /*
700          * Avoid entering the debugger if we were triggered due to an oops
701          * but panic_timeout indicates the system should automatically
702          * reboot on panic. We don't want to get stuck waiting for input
703          * on such systems, especially if its "just" an oops.
704          */
705         if (signo != SIGTRAP && panic_timeout)
706                 return 1;
707 
708         memset(ks, 0, sizeof(struct kgdb_state));
709         ks->cpu                 = raw_smp_processor_id();
710         ks->ex_vector           = evector;
711         ks->signo               = signo;
712         ks->err_code            = ecode;
713         ks->linux_regs          = regs;
714 
715         if (kgdb_reenter_check(ks))
716                 goto out; /* Ouch, double exception ! */
717         if (kgdb_info[ks->cpu].enter_kgdb != 0)
718                 goto out;
719 
720         ret = kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
721 out:
722         if (arch_kgdb_ops.enable_nmi)
723                 arch_kgdb_ops.enable_nmi(1);
724         return ret;
725 }
726 
727 /*
728  * GDB places a breakpoint at this function to know dynamically
729  * loaded objects. It's not defined static so that only one instance with this
730  * name exists in the kernel.
731  */
732 
733 static int module_event(struct notifier_block *self, unsigned long val,
734         void *data)
735 {
736         return 0;
737 }
738 
739 static struct notifier_block dbg_module_load_nb = {
740         .notifier_call  = module_event,
741 };
742 
743 int kgdb_nmicallback(int cpu, void *regs)
744 {
745 #ifdef CONFIG_SMP
746         struct kgdb_state kgdb_var;
747         struct kgdb_state *ks = &kgdb_var;
748 
749         memset(ks, 0, sizeof(struct kgdb_state));
750         ks->cpu                 = cpu;
751         ks->linux_regs          = regs;
752 
753         if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
754                         raw_spin_is_locked(&dbg_master_lock)) {
755                 kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
756                 return 0;
757         }
758 #endif
759         return 1;
760 }
761 
762 int kgdb_nmicallin(int cpu, int trapnr, void *regs, int err_code,
763                                                         atomic_t *send_ready)
764 {
765 #ifdef CONFIG_SMP
766         if (!kgdb_io_ready(0) || !send_ready)
767                 return 1;
768 
769         if (kgdb_info[cpu].enter_kgdb == 0) {
770                 struct kgdb_state kgdb_var;
771                 struct kgdb_state *ks = &kgdb_var;
772 
773                 memset(ks, 0, sizeof(struct kgdb_state));
774                 ks->cpu                 = cpu;
775                 ks->ex_vector           = trapnr;
776                 ks->signo               = SIGTRAP;
777                 ks->err_code            = err_code;
778                 ks->linux_regs          = regs;
779                 ks->send_ready          = send_ready;
780                 kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
781                 return 0;
782         }
783 #endif
784         return 1;
785 }
786 
787 static void kgdb_console_write(struct console *co, const char *s,
788    unsigned count)
789 {
790         unsigned long flags;
791 
792         /* If we're debugging, or KGDB has not connected, don't try
793          * and print. */
794         if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
795                 return;
796 
797         local_irq_save(flags);
798         gdbstub_msg_write(s, count);
799         local_irq_restore(flags);
800 }
801 
802 static struct console kgdbcons = {
803         .name           = "kgdb",
804         .write          = kgdb_console_write,
805         .flags          = CON_PRINTBUFFER | CON_ENABLED,
806         .index          = -1,
807 };
808 
809 #ifdef CONFIG_MAGIC_SYSRQ
810 static void sysrq_handle_dbg(int key)
811 {
812         if (!dbg_io_ops) {
813                 pr_crit("ERROR: No KGDB I/O module available\n");
814                 return;
815         }
816         if (!kgdb_connected) {
817 #ifdef CONFIG_KGDB_KDB
818                 if (!dbg_kdb_mode)
819                         pr_crit("KGDB or $3#33 for KDB\n");
820 #else
821                 pr_crit("Entering KGDB\n");
822 #endif
823         }
824 
825         kgdb_breakpoint();
826 }
827 
828 static struct sysrq_key_op sysrq_dbg_op = {
829         .handler        = sysrq_handle_dbg,
830         .help_msg       = "debug(g)",
831         .action_msg     = "DEBUG",
832 };
833 #endif
834 
835 static int kgdb_panic_event(struct notifier_block *self,
836                             unsigned long val,
837                             void *data)
838 {
839         /*
840          * Avoid entering the debugger if we were triggered due to a panic
841          * We don't want to get stuck waiting for input from user in such case.
842          * panic_timeout indicates the system should automatically
843          * reboot on panic.
844          */
845         if (panic_timeout)
846                 return NOTIFY_DONE;
847 
848         if (dbg_kdb_mode)
849                 kdb_printf("PANIC: %s\n", (char *)data);
850         kgdb_breakpoint();
851         return NOTIFY_DONE;
852 }
853 
854 static struct notifier_block kgdb_panic_event_nb = {
855        .notifier_call   = kgdb_panic_event,
856        .priority        = INT_MAX,
857 };
858 
859 void __weak kgdb_arch_late(void)
860 {
861 }
862 
863 void __init dbg_late_init(void)
864 {
865         dbg_is_early = false;
866         if (kgdb_io_module_registered)
867                 kgdb_arch_late();
868         kdb_init(KDB_INIT_FULL);
869 }
870 
871 static int
872 dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
873 {
874         /*
875          * Take the following action on reboot notify depending on value:
876          *    1 == Enter debugger
877          *    0 == [the default] detatch debug client
878          *   -1 == Do nothing... and use this until the board resets
879          */
880         switch (kgdbreboot) {
881         case 1:
882                 kgdb_breakpoint();
883         case -1:
884                 goto done;
885         }
886         if (!dbg_kdb_mode)
887                 gdbstub_exit(code);
888 done:
889         return NOTIFY_DONE;
890 }
891 
892 static struct notifier_block dbg_reboot_notifier = {
893         .notifier_call          = dbg_notify_reboot,
894         .next                   = NULL,
895         .priority               = INT_MAX,
896 };
897 
898 static void kgdb_register_callbacks(void)
899 {
900         if (!kgdb_io_module_registered) {
901                 kgdb_io_module_registered = 1;
902                 kgdb_arch_init();
903                 if (!dbg_is_early)
904                         kgdb_arch_late();
905                 register_module_notifier(&dbg_module_load_nb);
906                 register_reboot_notifier(&dbg_reboot_notifier);
907                 atomic_notifier_chain_register(&panic_notifier_list,
908                                                &kgdb_panic_event_nb);
909 #ifdef CONFIG_MAGIC_SYSRQ
910                 register_sysrq_key('g', &sysrq_dbg_op);
911 #endif
912                 if (kgdb_use_con && !kgdb_con_registered) {
913                         register_console(&kgdbcons);
914                         kgdb_con_registered = 1;
915                 }
916         }
917 }
918 
919 static void kgdb_unregister_callbacks(void)
920 {
921         /*
922          * When this routine is called KGDB should unregister from the
923          * panic handler and clean up, making sure it is not handling any
924          * break exceptions at the time.
925          */
926         if (kgdb_io_module_registered) {
927                 kgdb_io_module_registered = 0;
928                 unregister_reboot_notifier(&dbg_reboot_notifier);
929                 unregister_module_notifier(&dbg_module_load_nb);
930                 atomic_notifier_chain_unregister(&panic_notifier_list,
931                                                &kgdb_panic_event_nb);
932                 kgdb_arch_exit();
933 #ifdef CONFIG_MAGIC_SYSRQ
934                 unregister_sysrq_key('g', &sysrq_dbg_op);
935 #endif
936                 if (kgdb_con_registered) {
937                         unregister_console(&kgdbcons);
938                         kgdb_con_registered = 0;
939                 }
940         }
941 }
942 
943 /*
944  * There are times a tasklet needs to be used vs a compiled in
945  * break point so as to cause an exception outside a kgdb I/O module,
946  * such as is the case with kgdboe, where calling a breakpoint in the
947  * I/O driver itself would be fatal.
948  */
949 static void kgdb_tasklet_bpt(unsigned long ing)
950 {
951         kgdb_breakpoint();
952         atomic_set(&kgdb_break_tasklet_var, 0);
953 }
954 
955 static DECLARE_TASKLET(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt, 0);
956 
957 void kgdb_schedule_breakpoint(void)
958 {
959         if (atomic_read(&kgdb_break_tasklet_var) ||
960                 atomic_read(&kgdb_active) != -1 ||
961                 atomic_read(&kgdb_setting_breakpoint))
962                 return;
963         atomic_inc(&kgdb_break_tasklet_var);
964         tasklet_schedule(&kgdb_tasklet_breakpoint);
965 }
966 EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
967 
968 static void kgdb_initial_breakpoint(void)
969 {
970         kgdb_break_asap = 0;
971 
972         pr_crit("Waiting for connection from remote gdb...\n");
973         kgdb_breakpoint();
974 }
975 
976 /**
977  *      kgdb_register_io_module - register KGDB IO module
978  *      @new_dbg_io_ops: the io ops vector
979  *
980  *      Register it with the KGDB core.
981  */
982 int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
983 {
984         int err;
985 
986         spin_lock(&kgdb_registration_lock);
987 
988         if (dbg_io_ops) {
989                 spin_unlock(&kgdb_registration_lock);
990 
991                 pr_err("Another I/O driver is already registered with KGDB\n");
992                 return -EBUSY;
993         }
994 
995         if (new_dbg_io_ops->init) {
996                 err = new_dbg_io_ops->init();
997                 if (err) {
998                         spin_unlock(&kgdb_registration_lock);
999                         return err;
1000                 }
1001         }
1002 
1003         dbg_io_ops = new_dbg_io_ops;
1004 
1005         spin_unlock(&kgdb_registration_lock);
1006 
1007         pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
1008 
1009         /* Arm KGDB now. */
1010         kgdb_register_callbacks();
1011 
1012         if (kgdb_break_asap)
1013                 kgdb_initial_breakpoint();
1014 
1015         return 0;
1016 }
1017 EXPORT_SYMBOL_GPL(kgdb_register_io_module);
1018 
1019 /**
1020  *      kkgdb_unregister_io_module - unregister KGDB IO module
1021  *      @old_dbg_io_ops: the io ops vector
1022  *
1023  *      Unregister it with the KGDB core.
1024  */
1025 void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
1026 {
1027         BUG_ON(kgdb_connected);
1028 
1029         /*
1030          * KGDB is no longer able to communicate out, so
1031          * unregister our callbacks and reset state.
1032          */
1033         kgdb_unregister_callbacks();
1034 
1035         spin_lock(&kgdb_registration_lock);
1036 
1037         WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
1038         dbg_io_ops = NULL;
1039 
1040         spin_unlock(&kgdb_registration_lock);
1041 
1042         pr_info("Unregistered I/O driver %s, debugger disabled\n",
1043                 old_dbg_io_ops->name);
1044 }
1045 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
1046 
1047 int dbg_io_get_char(void)
1048 {
1049         int ret = dbg_io_ops->read_char();
1050         if (ret == NO_POLL_CHAR)
1051                 return -1;
1052         if (!dbg_kdb_mode)
1053                 return ret;
1054         if (ret == 127)
1055                 return 8;
1056         return ret;
1057 }
1058 
1059 /**
1060  * kgdb_breakpoint - generate breakpoint exception
1061  *
1062  * This function will generate a breakpoint exception.  It is used at the
1063  * beginning of a program to sync up with a debugger and can be used
1064  * otherwise as a quick means to stop program execution and "break" into
1065  * the debugger.
1066  */
1067 noinline void kgdb_breakpoint(void)
1068 {
1069         atomic_inc(&kgdb_setting_breakpoint);
1070         wmb(); /* Sync point before breakpoint */
1071         arch_kgdb_breakpoint();
1072         wmb(); /* Sync point after breakpoint */
1073         atomic_dec(&kgdb_setting_breakpoint);
1074 }
1075 EXPORT_SYMBOL_GPL(kgdb_breakpoint);
1076 
1077 static int __init opt_kgdb_wait(char *str)
1078 {
1079         kgdb_break_asap = 1;
1080 
1081         kdb_init(KDB_INIT_EARLY);
1082         if (kgdb_io_module_registered)
1083                 kgdb_initial_breakpoint();
1084 
1085         return 0;
1086 }
1087 
1088 early_param("kgdbwait", opt_kgdb_wait);
1089 

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