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TOMOYO Linux Cross Reference
Linux/kernel/debug/debug_core.c

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  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/nmi.h>
 53 #include <linux/pid.h>
 54 #include <linux/smp.h>
 55 #include <linux/mm.h>
 56 #include <linux/vmacache.h>
 57 #include <linux/rcupdate.h>
 58 #include <linux/irq.h>
 59 
 60 #include <asm/cacheflush.h>
 61 #include <asm/byteorder.h>
 62 #include <linux/atomic.h>
 63 
 64 #include "debug_core.h"
 65 
 66 static int kgdb_break_asap;
 67 
 68 struct debuggerinfo_struct kgdb_info[NR_CPUS];
 69 
 70 /**
 71  * kgdb_connected - Is a host GDB connected to us?
 72  */
 73 int                             kgdb_connected;
 74 EXPORT_SYMBOL_GPL(kgdb_connected);
 75 
 76 /* All the KGDB handlers are installed */
 77 int                     kgdb_io_module_registered;
 78 
 79 /* Guard for recursive entry */
 80 static int                      exception_level;
 81 
 82 struct kgdb_io          *dbg_io_ops;
 83 static DEFINE_SPINLOCK(kgdb_registration_lock);
 84 
 85 /* Action for the reboot notifiter, a global allow kdb to change it */
 86 static int kgdbreboot;
 87 /* kgdb console driver is loaded */
 88 static int kgdb_con_registered;
 89 /* determine if kgdb console output should be used */
 90 static int kgdb_use_con;
 91 /* Flag for alternate operations for early debugging */
 92 bool dbg_is_early = true;
 93 /* Next cpu to become the master debug core */
 94 int dbg_switch_cpu;
 95 
 96 /* Use kdb or gdbserver mode */
 97 int dbg_kdb_mode = 1;
 98 
 99 static int __init opt_kgdb_con(char *str)
100 {
101         kgdb_use_con = 1;
102         return 0;
103 }
104 
105 early_param("kgdbcon", opt_kgdb_con);
106 
107 module_param(kgdb_use_con, int, 0644);
108 module_param(kgdbreboot, int, 0644);
109 
110 /*
111  * Holds information about breakpoints in a kernel. These breakpoints are
112  * added and removed by gdb.
113  */
114 static struct kgdb_bkpt         kgdb_break[KGDB_MAX_BREAKPOINTS] = {
115         [0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
116 };
117 
118 /*
119  * The CPU# of the active CPU, or -1 if none:
120  */
121 atomic_t                        kgdb_active = ATOMIC_INIT(-1);
122 EXPORT_SYMBOL_GPL(kgdb_active);
123 static DEFINE_RAW_SPINLOCK(dbg_master_lock);
124 static DEFINE_RAW_SPINLOCK(dbg_slave_lock);
125 
126 /*
127  * We use NR_CPUs not PERCPU, in case kgdb is used to debug early
128  * bootup code (which might not have percpu set up yet):
129  */
130 static atomic_t                 masters_in_kgdb;
131 static atomic_t                 slaves_in_kgdb;
132 static atomic_t                 kgdb_break_tasklet_var;
133 atomic_t                        kgdb_setting_breakpoint;
134 
135 struct task_struct              *kgdb_usethread;
136 struct task_struct              *kgdb_contthread;
137 
138 int                             kgdb_single_step;
139 static pid_t                    kgdb_sstep_pid;
140 
141 /* to keep track of the CPU which is doing the single stepping*/
142 atomic_t                        kgdb_cpu_doing_single_step = ATOMIC_INIT(-1);
143 
144 /*
145  * If you are debugging a problem where roundup (the collection of
146  * all other CPUs) is a problem [this should be extremely rare],
147  * then use the nokgdbroundup option to avoid roundup. In that case
148  * the other CPUs might interfere with your debugging context, so
149  * use this with care:
150  */
151 static int kgdb_do_roundup = 1;
152 
153 static int __init opt_nokgdbroundup(char *str)
154 {
155         kgdb_do_roundup = 0;
156 
157         return 0;
158 }
159 
160 early_param("nokgdbroundup", opt_nokgdbroundup);
161 
162 /*
163  * Finally, some KGDB code :-)
164  */
165 
166 /*
167  * Weak aliases for breakpoint management,
168  * can be overriden by architectures when needed:
169  */
170 int __weak kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
171 {
172         int err;
173 
174         err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr,
175                                 BREAK_INSTR_SIZE);
176         if (err)
177                 return err;
178         err = probe_kernel_write((char *)bpt->bpt_addr,
179                                  arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
180         return err;
181 }
182 
183 int __weak kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
184 {
185         return probe_kernel_write((char *)bpt->bpt_addr,
186                                   (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
187 }
188 
189 int __weak kgdb_validate_break_address(unsigned long addr)
190 {
191         struct kgdb_bkpt tmp;
192         int err;
193         /* Validate setting the breakpoint and then removing it.  If the
194          * remove fails, the kernel needs to emit a bad message because we
195          * are deep trouble not being able to put things back the way we
196          * found them.
197          */
198         tmp.bpt_addr = addr;
199         err = kgdb_arch_set_breakpoint(&tmp);
200         if (err)
201                 return err;
202         err = kgdb_arch_remove_breakpoint(&tmp);
203         if (err)
204                 pr_err("Critical breakpoint error, kernel memory destroyed at: %lx\n",
205                        addr);
206         return err;
207 }
208 
209 unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
210 {
211         return instruction_pointer(regs);
212 }
213 
214 int __weak kgdb_arch_init(void)
215 {
216         return 0;
217 }
218 
219 int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
220 {
221         return 0;
222 }
223 
224 #ifdef CONFIG_SMP
225 
226 /*
227  * Default (weak) implementation for kgdb_roundup_cpus
228  */
229 
230 static DEFINE_PER_CPU(call_single_data_t, kgdb_roundup_csd);
231 
232 void __weak kgdb_call_nmi_hook(void *ignored)
233 {
234         /*
235          * NOTE: get_irq_regs() is supposed to get the registers from
236          * before the IPI interrupt happened and so is supposed to
237          * show where the processor was.  In some situations it's
238          * possible we might be called without an IPI, so it might be
239          * safer to figure out how to make kgdb_breakpoint() work
240          * properly here.
241          */
242         kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
243 }
244 
245 void __weak kgdb_roundup_cpus(void)
246 {
247         call_single_data_t *csd;
248         int this_cpu = raw_smp_processor_id();
249         int cpu;
250         int ret;
251 
252         for_each_online_cpu(cpu) {
253                 /* No need to roundup ourselves */
254                 if (cpu == this_cpu)
255                         continue;
256 
257                 csd = &per_cpu(kgdb_roundup_csd, cpu);
258 
259                 /*
260                  * If it didn't round up last time, don't try again
261                  * since smp_call_function_single_async() will block.
262                  *
263                  * If rounding_up is false then we know that the
264                  * previous call must have at least started and that
265                  * means smp_call_function_single_async() won't block.
266                  */
267                 if (kgdb_info[cpu].rounding_up)
268                         continue;
269                 kgdb_info[cpu].rounding_up = true;
270 
271                 csd->func = kgdb_call_nmi_hook;
272                 ret = smp_call_function_single_async(cpu, csd);
273                 if (ret)
274                         kgdb_info[cpu].rounding_up = false;
275         }
276 }
277 
278 #endif
279 
280 /*
281  * Some architectures need cache flushes when we set/clear a
282  * breakpoint:
283  */
284 static void kgdb_flush_swbreak_addr(unsigned long addr)
285 {
286         if (!CACHE_FLUSH_IS_SAFE)
287                 return;
288 
289         if (current->mm) {
290                 int i;
291 
292                 for (i = 0; i < VMACACHE_SIZE; i++) {
293                         if (!current->vmacache.vmas[i])
294                                 continue;
295                         flush_cache_range(current->vmacache.vmas[i],
296                                           addr, addr + BREAK_INSTR_SIZE);
297                 }
298         }
299 
300         /* Force flush instruction cache if it was outside the mm */
301         flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
302 }
303 
304 /*
305  * SW breakpoint management:
306  */
307 int dbg_activate_sw_breakpoints(void)
308 {
309         int error;
310         int ret = 0;
311         int i;
312 
313         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
314                 if (kgdb_break[i].state != BP_SET)
315                         continue;
316 
317                 error = kgdb_arch_set_breakpoint(&kgdb_break[i]);
318                 if (error) {
319                         ret = error;
320                         pr_info("BP install failed: %lx\n",
321                                 kgdb_break[i].bpt_addr);
322                         continue;
323                 }
324 
325                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
326                 kgdb_break[i].state = BP_ACTIVE;
327         }
328         return ret;
329 }
330 
331 int dbg_set_sw_break(unsigned long addr)
332 {
333         int err = kgdb_validate_break_address(addr);
334         int breakno = -1;
335         int i;
336 
337         if (err)
338                 return err;
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                         return -EEXIST;
344         }
345         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
346                 if (kgdb_break[i].state == BP_REMOVED &&
347                                         kgdb_break[i].bpt_addr == addr) {
348                         breakno = i;
349                         break;
350                 }
351         }
352 
353         if (breakno == -1) {
354                 for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
355                         if (kgdb_break[i].state == BP_UNDEFINED) {
356                                 breakno = i;
357                                 break;
358                         }
359                 }
360         }
361 
362         if (breakno == -1)
363                 return -E2BIG;
364 
365         kgdb_break[breakno].state = BP_SET;
366         kgdb_break[breakno].type = BP_BREAKPOINT;
367         kgdb_break[breakno].bpt_addr = addr;
368 
369         return 0;
370 }
371 
372 int dbg_deactivate_sw_breakpoints(void)
373 {
374         int error;
375         int ret = 0;
376         int i;
377 
378         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
379                 if (kgdb_break[i].state != BP_ACTIVE)
380                         continue;
381                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
382                 if (error) {
383                         pr_info("BP remove failed: %lx\n",
384                                 kgdb_break[i].bpt_addr);
385                         ret = error;
386                 }
387 
388                 kgdb_flush_swbreak_addr(kgdb_break[i].bpt_addr);
389                 kgdb_break[i].state = BP_SET;
390         }
391         return ret;
392 }
393 
394 int dbg_remove_sw_break(unsigned long addr)
395 {
396         int i;
397 
398         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
399                 if ((kgdb_break[i].state == BP_SET) &&
400                                 (kgdb_break[i].bpt_addr == addr)) {
401                         kgdb_break[i].state = BP_REMOVED;
402                         return 0;
403                 }
404         }
405         return -ENOENT;
406 }
407 
408 int kgdb_isremovedbreak(unsigned long addr)
409 {
410         int i;
411 
412         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
413                 if ((kgdb_break[i].state == BP_REMOVED) &&
414                                         (kgdb_break[i].bpt_addr == addr))
415                         return 1;
416         }
417         return 0;
418 }
419 
420 int dbg_remove_all_break(void)
421 {
422         int error;
423         int i;
424 
425         /* Clear memory breakpoints. */
426         for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
427                 if (kgdb_break[i].state != BP_ACTIVE)
428                         goto setundefined;
429                 error = kgdb_arch_remove_breakpoint(&kgdb_break[i]);
430                 if (error)
431                         pr_err("breakpoint remove failed: %lx\n",
432                                kgdb_break[i].bpt_addr);
433 setundefined:
434                 kgdb_break[i].state = BP_UNDEFINED;
435         }
436 
437         /* Clear hardware breakpoints. */
438         if (arch_kgdb_ops.remove_all_hw_break)
439                 arch_kgdb_ops.remove_all_hw_break();
440 
441         return 0;
442 }
443 
444 /*
445  * Return true if there is a valid kgdb I/O module.  Also if no
446  * debugger is attached a message can be printed to the console about
447  * waiting for the debugger to attach.
448  *
449  * The print_wait argument is only to be true when called from inside
450  * the core kgdb_handle_exception, because it will wait for the
451  * debugger to attach.
452  */
453 static int kgdb_io_ready(int print_wait)
454 {
455         if (!dbg_io_ops)
456                 return 0;
457         if (kgdb_connected)
458                 return 1;
459         if (atomic_read(&kgdb_setting_breakpoint))
460                 return 1;
461         if (print_wait) {
462 #ifdef CONFIG_KGDB_KDB
463                 if (!dbg_kdb_mode)
464                         pr_crit("waiting... or $3#33 for KDB\n");
465 #else
466                 pr_crit("Waiting for remote debugger\n");
467 #endif
468         }
469         return 1;
470 }
471 
472 static int kgdb_reenter_check(struct kgdb_state *ks)
473 {
474         unsigned long addr;
475 
476         if (atomic_read(&kgdb_active) != raw_smp_processor_id())
477                 return 0;
478 
479         /* Panic on recursive debugger calls: */
480         exception_level++;
481         addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
482         dbg_deactivate_sw_breakpoints();
483 
484         /*
485          * If the break point removed ok at the place exception
486          * occurred, try to recover and print a warning to the end
487          * user because the user planted a breakpoint in a place that
488          * KGDB needs in order to function.
489          */
490         if (dbg_remove_sw_break(addr) == 0) {
491                 exception_level = 0;
492                 kgdb_skipexception(ks->ex_vector, ks->linux_regs);
493                 dbg_activate_sw_breakpoints();
494                 pr_crit("re-enter error: breakpoint removed %lx\n", addr);
495                 WARN_ON_ONCE(1);
496 
497                 return 1;
498         }
499         dbg_remove_all_break();
500         kgdb_skipexception(ks->ex_vector, ks->linux_regs);
501 
502         if (exception_level > 1) {
503                 dump_stack();
504                 panic("Recursive entry to debugger");
505         }
506 
507         pr_crit("re-enter exception: ALL breakpoints killed\n");
508 #ifdef CONFIG_KGDB_KDB
509         /* Allow kdb to debug itself one level */
510         return 0;
511 #endif
512         dump_stack();
513         panic("Recursive entry to debugger");
514 
515         return 1;
516 }
517 
518 static void dbg_touch_watchdogs(void)
519 {
520         touch_softlockup_watchdog_sync();
521         clocksource_touch_watchdog();
522         rcu_cpu_stall_reset();
523 }
524 
525 static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
526                 int exception_state)
527 {
528         unsigned long flags;
529         int sstep_tries = 100;
530         int error;
531         int cpu;
532         int trace_on = 0;
533         int online_cpus = num_online_cpus();
534         u64 time_left;
535 
536         kgdb_info[ks->cpu].enter_kgdb++;
537         kgdb_info[ks->cpu].exception_state |= exception_state;
538 
539         if (exception_state == DCPU_WANT_MASTER)
540                 atomic_inc(&masters_in_kgdb);
541         else
542                 atomic_inc(&slaves_in_kgdb);
543 
544         if (arch_kgdb_ops.disable_hw_break)
545                 arch_kgdb_ops.disable_hw_break(regs);
546 
547 acquirelock:
548         /*
549          * Interrupts will be restored by the 'trap return' code, except when
550          * single stepping.
551          */
552         local_irq_save(flags);
553 
554         cpu = ks->cpu;
555         kgdb_info[cpu].debuggerinfo = regs;
556         kgdb_info[cpu].task = current;
557         kgdb_info[cpu].ret_state = 0;
558         kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
559 
560         /* Make sure the above info reaches the primary CPU */
561         smp_mb();
562 
563         if (exception_level == 1) {
564                 if (raw_spin_trylock(&dbg_master_lock))
565                         atomic_xchg(&kgdb_active, cpu);
566                 goto cpu_master_loop;
567         }
568 
569         /*
570          * CPU will loop if it is a slave or request to become a kgdb
571          * master cpu and acquire the kgdb_active lock:
572          */
573         while (1) {
574 cpu_loop:
575                 if (kgdb_info[cpu].exception_state & DCPU_NEXT_MASTER) {
576                         kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
577                         goto cpu_master_loop;
578                 } else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
579                         if (raw_spin_trylock(&dbg_master_lock)) {
580                                 atomic_xchg(&kgdb_active, cpu);
581                                 break;
582                         }
583                 } else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
584                         if (!raw_spin_is_locked(&dbg_slave_lock))
585                                 goto return_normal;
586                 } else {
587 return_normal:
588                         /* Return to normal operation by executing any
589                          * hw breakpoint fixup.
590                          */
591                         if (arch_kgdb_ops.correct_hw_break)
592                                 arch_kgdb_ops.correct_hw_break();
593                         if (trace_on)
594                                 tracing_on();
595                         kgdb_info[cpu].debuggerinfo = NULL;
596                         kgdb_info[cpu].task = NULL;
597                         kgdb_info[cpu].exception_state &=
598                                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
599                         kgdb_info[cpu].enter_kgdb--;
600                         smp_mb__before_atomic();
601                         atomic_dec(&slaves_in_kgdb);
602                         dbg_touch_watchdogs();
603                         local_irq_restore(flags);
604                         return 0;
605                 }
606                 cpu_relax();
607         }
608 
609         /*
610          * For single stepping, try to only enter on the processor
611          * that was single stepping.  To guard against a deadlock, the
612          * kernel will only try for the value of sstep_tries before
613          * giving up and continuing on.
614          */
615         if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
616             (kgdb_info[cpu].task &&
617              kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
618                 atomic_set(&kgdb_active, -1);
619                 raw_spin_unlock(&dbg_master_lock);
620                 dbg_touch_watchdogs();
621                 local_irq_restore(flags);
622 
623                 goto acquirelock;
624         }
625 
626         if (!kgdb_io_ready(1)) {
627                 kgdb_info[cpu].ret_state = 1;
628                 goto kgdb_restore; /* No I/O connection, resume the system */
629         }
630 
631         /*
632          * Don't enter if we have hit a removed breakpoint.
633          */
634         if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
635                 goto kgdb_restore;
636 
637         /* Call the I/O driver's pre_exception routine */
638         if (dbg_io_ops->pre_exception)
639                 dbg_io_ops->pre_exception();
640 
641         /*
642          * Get the passive CPU lock which will hold all the non-primary
643          * CPU in a spin state while the debugger is active
644          */
645         if (!kgdb_single_step)
646                 raw_spin_lock(&dbg_slave_lock);
647 
648 #ifdef CONFIG_SMP
649         /* If send_ready set, slaves are already waiting */
650         if (ks->send_ready)
651                 atomic_set(ks->send_ready, 1);
652 
653         /* Signal the other CPUs to enter kgdb_wait() */
654         else if ((!kgdb_single_step) && kgdb_do_roundup)
655                 kgdb_roundup_cpus();
656 #endif
657 
658         /*
659          * Wait for the other CPUs to be notified and be waiting for us:
660          */
661         time_left = MSEC_PER_SEC;
662         while (kgdb_do_roundup && --time_left &&
663                (atomic_read(&masters_in_kgdb) + atomic_read(&slaves_in_kgdb)) !=
664                    online_cpus)
665                 udelay(1000);
666         if (!time_left)
667                 pr_crit("Timed out waiting for secondary CPUs.\n");
668 
669         /*
670          * At this point the primary processor is completely
671          * in the debugger and all secondary CPUs are quiescent
672          */
673         dbg_deactivate_sw_breakpoints();
674         kgdb_single_step = 0;
675         kgdb_contthread = current;
676         exception_level = 0;
677         trace_on = tracing_is_on();
678         if (trace_on)
679                 tracing_off();
680 
681         while (1) {
682 cpu_master_loop:
683                 if (dbg_kdb_mode) {
684                         kgdb_connected = 1;
685                         error = kdb_stub(ks);
686                         if (error == -1)
687                                 continue;
688                         kgdb_connected = 0;
689                 } else {
690                         error = gdb_serial_stub(ks);
691                 }
692 
693                 if (error == DBG_PASS_EVENT) {
694                         dbg_kdb_mode = !dbg_kdb_mode;
695                 } else if (error == DBG_SWITCH_CPU_EVENT) {
696                         kgdb_info[dbg_switch_cpu].exception_state |=
697                                 DCPU_NEXT_MASTER;
698                         goto cpu_loop;
699                 } else {
700                         kgdb_info[cpu].ret_state = error;
701                         break;
702                 }
703         }
704 
705         /* Call the I/O driver's post_exception routine */
706         if (dbg_io_ops->post_exception)
707                 dbg_io_ops->post_exception();
708 
709         if (!kgdb_single_step) {
710                 raw_spin_unlock(&dbg_slave_lock);
711                 /* Wait till all the CPUs have quit from the debugger. */
712                 while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
713                         cpu_relax();
714         }
715 
716 kgdb_restore:
717         if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
718                 int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
719                 if (kgdb_info[sstep_cpu].task)
720                         kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
721                 else
722                         kgdb_sstep_pid = 0;
723         }
724         if (arch_kgdb_ops.correct_hw_break)
725                 arch_kgdb_ops.correct_hw_break();
726         if (trace_on)
727                 tracing_on();
728 
729         kgdb_info[cpu].debuggerinfo = NULL;
730         kgdb_info[cpu].task = NULL;
731         kgdb_info[cpu].exception_state &=
732                 ~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
733         kgdb_info[cpu].enter_kgdb--;
734         smp_mb__before_atomic();
735         atomic_dec(&masters_in_kgdb);
736         /* Free kgdb_active */
737         atomic_set(&kgdb_active, -1);
738         raw_spin_unlock(&dbg_master_lock);
739         dbg_touch_watchdogs();
740         local_irq_restore(flags);
741 
742         return kgdb_info[cpu].ret_state;
743 }
744 
745 /*
746  * kgdb_handle_exception() - main entry point from a kernel exception
747  *
748  * Locking hierarchy:
749  *      interface locks, if any (begin_session)
750  *      kgdb lock (kgdb_active)
751  */
752 int
753 kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
754 {
755         struct kgdb_state kgdb_var;
756         struct kgdb_state *ks = &kgdb_var;
757         int ret = 0;
758 
759         if (arch_kgdb_ops.enable_nmi)
760                 arch_kgdb_ops.enable_nmi(0);
761         /*
762          * Avoid entering the debugger if we were triggered due to an oops
763          * but panic_timeout indicates the system should automatically
764          * reboot on panic. We don't want to get stuck waiting for input
765          * on such systems, especially if its "just" an oops.
766          */
767         if (signo != SIGTRAP && panic_timeout)
768                 return 1;
769 
770         memset(ks, 0, sizeof(struct kgdb_state));
771         ks->cpu                 = raw_smp_processor_id();
772         ks->ex_vector           = evector;
773         ks->signo               = signo;
774         ks->err_code            = ecode;
775         ks->linux_regs          = regs;
776 
777         if (kgdb_reenter_check(ks))
778                 goto out; /* Ouch, double exception ! */
779         if (kgdb_info[ks->cpu].enter_kgdb != 0)
780                 goto out;
781 
782         ret = kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
783 out:
784         if (arch_kgdb_ops.enable_nmi)
785                 arch_kgdb_ops.enable_nmi(1);
786         return ret;
787 }
788 
789 /*
790  * GDB places a breakpoint at this function to know dynamically
791  * loaded objects. It's not defined static so that only one instance with this
792  * name exists in the kernel.
793  */
794 
795 static int module_event(struct notifier_block *self, unsigned long val,
796         void *data)
797 {
798         return 0;
799 }
800 
801 static struct notifier_block dbg_module_load_nb = {
802         .notifier_call  = module_event,
803 };
804 
805 int kgdb_nmicallback(int cpu, void *regs)
806 {
807 #ifdef CONFIG_SMP
808         struct kgdb_state kgdb_var;
809         struct kgdb_state *ks = &kgdb_var;
810 
811         kgdb_info[cpu].rounding_up = false;
812 
813         memset(ks, 0, sizeof(struct kgdb_state));
814         ks->cpu                 = cpu;
815         ks->linux_regs          = regs;
816 
817         if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
818                         raw_spin_is_locked(&dbg_master_lock)) {
819                 kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
820                 return 0;
821         }
822 #endif
823         return 1;
824 }
825 
826 int kgdb_nmicallin(int cpu, int trapnr, void *regs, int err_code,
827                                                         atomic_t *send_ready)
828 {
829 #ifdef CONFIG_SMP
830         if (!kgdb_io_ready(0) || !send_ready)
831                 return 1;
832 
833         if (kgdb_info[cpu].enter_kgdb == 0) {
834                 struct kgdb_state kgdb_var;
835                 struct kgdb_state *ks = &kgdb_var;
836 
837                 memset(ks, 0, sizeof(struct kgdb_state));
838                 ks->cpu                 = cpu;
839                 ks->ex_vector           = trapnr;
840                 ks->signo               = SIGTRAP;
841                 ks->err_code            = err_code;
842                 ks->linux_regs          = regs;
843                 ks->send_ready          = send_ready;
844                 kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
845                 return 0;
846         }
847 #endif
848         return 1;
849 }
850 
851 static void kgdb_console_write(struct console *co, const char *s,
852    unsigned count)
853 {
854         unsigned long flags;
855 
856         /* If we're debugging, or KGDB has not connected, don't try
857          * and print. */
858         if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
859                 return;
860 
861         local_irq_save(flags);
862         gdbstub_msg_write(s, count);
863         local_irq_restore(flags);
864 }
865 
866 static struct console kgdbcons = {
867         .name           = "kgdb",
868         .write          = kgdb_console_write,
869         .flags          = CON_PRINTBUFFER | CON_ENABLED,
870         .index          = -1,
871 };
872 
873 #ifdef CONFIG_MAGIC_SYSRQ
874 static void sysrq_handle_dbg(int key)
875 {
876         if (!dbg_io_ops) {
877                 pr_crit("ERROR: No KGDB I/O module available\n");
878                 return;
879         }
880         if (!kgdb_connected) {
881 #ifdef CONFIG_KGDB_KDB
882                 if (!dbg_kdb_mode)
883                         pr_crit("KGDB or $3#33 for KDB\n");
884 #else
885                 pr_crit("Entering KGDB\n");
886 #endif
887         }
888 
889         kgdb_breakpoint();
890 }
891 
892 static struct sysrq_key_op sysrq_dbg_op = {
893         .handler        = sysrq_handle_dbg,
894         .help_msg       = "debug(g)",
895         .action_msg     = "DEBUG",
896 };
897 #endif
898 
899 static int kgdb_panic_event(struct notifier_block *self,
900                             unsigned long val,
901                             void *data)
902 {
903         /*
904          * Avoid entering the debugger if we were triggered due to a panic
905          * We don't want to get stuck waiting for input from user in such case.
906          * panic_timeout indicates the system should automatically
907          * reboot on panic.
908          */
909         if (panic_timeout)
910                 return NOTIFY_DONE;
911 
912         if (dbg_kdb_mode)
913                 kdb_printf("PANIC: %s\n", (char *)data);
914         kgdb_breakpoint();
915         return NOTIFY_DONE;
916 }
917 
918 static struct notifier_block kgdb_panic_event_nb = {
919        .notifier_call   = kgdb_panic_event,
920        .priority        = INT_MAX,
921 };
922 
923 void __weak kgdb_arch_late(void)
924 {
925 }
926 
927 void __init dbg_late_init(void)
928 {
929         dbg_is_early = false;
930         if (kgdb_io_module_registered)
931                 kgdb_arch_late();
932         kdb_init(KDB_INIT_FULL);
933 }
934 
935 static int
936 dbg_notify_reboot(struct notifier_block *this, unsigned long code, void *x)
937 {
938         /*
939          * Take the following action on reboot notify depending on value:
940          *    1 == Enter debugger
941          *    0 == [the default] detatch debug client
942          *   -1 == Do nothing... and use this until the board resets
943          */
944         switch (kgdbreboot) {
945         case 1:
946                 kgdb_breakpoint();
947         case -1:
948                 goto done;
949         }
950         if (!dbg_kdb_mode)
951                 gdbstub_exit(code);
952 done:
953         return NOTIFY_DONE;
954 }
955 
956 static struct notifier_block dbg_reboot_notifier = {
957         .notifier_call          = dbg_notify_reboot,
958         .next                   = NULL,
959         .priority               = INT_MAX,
960 };
961 
962 static void kgdb_register_callbacks(void)
963 {
964         if (!kgdb_io_module_registered) {
965                 kgdb_io_module_registered = 1;
966                 kgdb_arch_init();
967                 if (!dbg_is_early)
968                         kgdb_arch_late();
969                 register_module_notifier(&dbg_module_load_nb);
970                 register_reboot_notifier(&dbg_reboot_notifier);
971                 atomic_notifier_chain_register(&panic_notifier_list,
972                                                &kgdb_panic_event_nb);
973 #ifdef CONFIG_MAGIC_SYSRQ
974                 register_sysrq_key('g', &sysrq_dbg_op);
975 #endif
976                 if (kgdb_use_con && !kgdb_con_registered) {
977                         register_console(&kgdbcons);
978                         kgdb_con_registered = 1;
979                 }
980         }
981 }
982 
983 static void kgdb_unregister_callbacks(void)
984 {
985         /*
986          * When this routine is called KGDB should unregister from the
987          * panic handler and clean up, making sure it is not handling any
988          * break exceptions at the time.
989          */
990         if (kgdb_io_module_registered) {
991                 kgdb_io_module_registered = 0;
992                 unregister_reboot_notifier(&dbg_reboot_notifier);
993                 unregister_module_notifier(&dbg_module_load_nb);
994                 atomic_notifier_chain_unregister(&panic_notifier_list,
995                                                &kgdb_panic_event_nb);
996                 kgdb_arch_exit();
997 #ifdef CONFIG_MAGIC_SYSRQ
998                 unregister_sysrq_key('g', &sysrq_dbg_op);
999 #endif
1000                 if (kgdb_con_registered) {
1001                         unregister_console(&kgdbcons);
1002                         kgdb_con_registered = 0;
1003                 }
1004         }
1005 }
1006 
1007 /*
1008  * There are times a tasklet needs to be used vs a compiled in
1009  * break point so as to cause an exception outside a kgdb I/O module,
1010  * such as is the case with kgdboe, where calling a breakpoint in the
1011  * I/O driver itself would be fatal.
1012  */
1013 static void kgdb_tasklet_bpt(unsigned long ing)
1014 {
1015         kgdb_breakpoint();
1016         atomic_set(&kgdb_break_tasklet_var, 0);
1017 }
1018 
1019 static DECLARE_TASKLET(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt, 0);
1020 
1021 void kgdb_schedule_breakpoint(void)
1022 {
1023         if (atomic_read(&kgdb_break_tasklet_var) ||
1024                 atomic_read(&kgdb_active) != -1 ||
1025                 atomic_read(&kgdb_setting_breakpoint))
1026                 return;
1027         atomic_inc(&kgdb_break_tasklet_var);
1028         tasklet_schedule(&kgdb_tasklet_breakpoint);
1029 }
1030 EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
1031 
1032 static void kgdb_initial_breakpoint(void)
1033 {
1034         kgdb_break_asap = 0;
1035 
1036         pr_crit("Waiting for connection from remote gdb...\n");
1037         kgdb_breakpoint();
1038 }
1039 
1040 /**
1041  *      kgdb_register_io_module - register KGDB IO module
1042  *      @new_dbg_io_ops: the io ops vector
1043  *
1044  *      Register it with the KGDB core.
1045  */
1046 int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
1047 {
1048         int err;
1049 
1050         spin_lock(&kgdb_registration_lock);
1051 
1052         if (dbg_io_ops) {
1053                 spin_unlock(&kgdb_registration_lock);
1054 
1055                 pr_err("Another I/O driver is already registered with KGDB\n");
1056                 return -EBUSY;
1057         }
1058 
1059         if (new_dbg_io_ops->init) {
1060                 err = new_dbg_io_ops->init();
1061                 if (err) {
1062                         spin_unlock(&kgdb_registration_lock);
1063                         return err;
1064                 }
1065         }
1066 
1067         dbg_io_ops = new_dbg_io_ops;
1068 
1069         spin_unlock(&kgdb_registration_lock);
1070 
1071         pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);
1072 
1073         /* Arm KGDB now. */
1074         kgdb_register_callbacks();
1075 
1076         if (kgdb_break_asap)
1077                 kgdb_initial_breakpoint();
1078 
1079         return 0;
1080 }
1081 EXPORT_SYMBOL_GPL(kgdb_register_io_module);
1082 
1083 /**
1084  *      kkgdb_unregister_io_module - unregister KGDB IO module
1085  *      @old_dbg_io_ops: the io ops vector
1086  *
1087  *      Unregister it with the KGDB core.
1088  */
1089 void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
1090 {
1091         BUG_ON(kgdb_connected);
1092 
1093         /*
1094          * KGDB is no longer able to communicate out, so
1095          * unregister our callbacks and reset state.
1096          */
1097         kgdb_unregister_callbacks();
1098 
1099         spin_lock(&kgdb_registration_lock);
1100 
1101         WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
1102         dbg_io_ops = NULL;
1103 
1104         spin_unlock(&kgdb_registration_lock);
1105 
1106         pr_info("Unregistered I/O driver %s, debugger disabled\n",
1107                 old_dbg_io_ops->name);
1108 }
1109 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
1110 
1111 int dbg_io_get_char(void)
1112 {
1113         int ret = dbg_io_ops->read_char();
1114         if (ret == NO_POLL_CHAR)
1115                 return -1;
1116         if (!dbg_kdb_mode)
1117                 return ret;
1118         if (ret == 127)
1119                 return 8;
1120         return ret;
1121 }
1122 
1123 /**
1124  * kgdb_breakpoint - generate breakpoint exception
1125  *
1126  * This function will generate a breakpoint exception.  It is used at the
1127  * beginning of a program to sync up with a debugger and can be used
1128  * otherwise as a quick means to stop program execution and "break" into
1129  * the debugger.
1130  */
1131 noinline void kgdb_breakpoint(void)
1132 {
1133         atomic_inc(&kgdb_setting_breakpoint);
1134         wmb(); /* Sync point before breakpoint */
1135         arch_kgdb_breakpoint();
1136         wmb(); /* Sync point after breakpoint */
1137         atomic_dec(&kgdb_setting_breakpoint);
1138 }
1139 EXPORT_SYMBOL_GPL(kgdb_breakpoint);
1140 
1141 static int __init opt_kgdb_wait(char *str)
1142 {
1143         kgdb_break_asap = 1;
1144 
1145         kdb_init(KDB_INIT_EARLY);
1146         if (kgdb_io_module_registered)
1147                 kgdb_initial_breakpoint();
1148 
1149         return 0;
1150 }
1151 
1152 early_param("kgdbwait", opt_kgdb_wait);
1153 

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