xref: /linux/kernel/debug/debug_core.c (revision d39d0ed196aa1685bb24771e92f78633c66ac9cb)
1 /*
2  * Kernel Debug Core
3  *
4  * Maintainer: Jason Wessel <jason.wessel@windriver.com>
5  *
6  * Copyright (C) 2000-2001 VERITAS Software Corporation.
7  * Copyright (C) 2002-2004 Timesys Corporation
8  * Copyright (C) 2003-2004 Amit S. Kale <amitkale@linsyssoft.com>
9  * Copyright (C) 2004 Pavel Machek <pavel@ucw.cz>
10  * Copyright (C) 2004-2006 Tom Rini <trini@kernel.crashing.org>
11  * Copyright (C) 2004-2006 LinSysSoft Technologies Pvt. Ltd.
12  * Copyright (C) 2005-2009 Wind River Systems, Inc.
13  * Copyright (C) 2007 MontaVista Software, Inc.
14  * Copyright (C) 2008 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
15  *
16  * Contributors at various stages not listed above:
17  *  Jason Wessel ( jason.wessel@windriver.com )
18  *  George Anzinger <george@mvista.com>
19  *  Anurekh Saxena (anurekh.saxena@timesys.com)
20  *  Lake Stevens Instrument Division (Glenn Engel)
21  *  Jim Kingdon, Cygnus Support.
22  *
23  * Original KGDB stub: David Grothe <dave@gcom.com>,
24  * Tigran Aivazian <tigran@sco.com>
25  *
26  * This file is licensed under the terms of the GNU General Public License
27  * version 2. This program is licensed "as is" without any warranty of any
28  * kind, whether express or implied.
29  */
30 #include <linux/pid_namespace.h>
31 #include <linux/clocksource.h>
32 #include <linux/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 			if (error == -1)
609 				continue;
610 			kgdb_connected = 0;
611 		} else {
612 			error = gdb_serial_stub(ks);
613 		}
614 
615 		if (error == DBG_PASS_EVENT) {
616 			dbg_kdb_mode = !dbg_kdb_mode;
617 		} else if (error == DBG_SWITCH_CPU_EVENT) {
618 			dbg_cpu_switch(cpu, dbg_switch_cpu);
619 			goto cpu_loop;
620 		} else {
621 			kgdb_info[cpu].ret_state = error;
622 			break;
623 		}
624 	}
625 
626 	/* Call the I/O driver's post_exception routine */
627 	if (dbg_io_ops->post_exception)
628 		dbg_io_ops->post_exception();
629 
630 	atomic_dec(&cpu_in_kgdb[ks->cpu]);
631 
632 	if (!kgdb_single_step) {
633 		for (i = NR_CPUS-1; i >= 0; i--)
634 			atomic_dec(&passive_cpu_wait[i]);
635 		/*
636 		 * Wait till all the CPUs have quit from the debugger,
637 		 * but allow a CPU that hit an exception and is
638 		 * waiting to become the master to remain in the debug
639 		 * core.
640 		 */
641 		for_each_online_cpu(i) {
642 			while (kgdb_do_roundup &&
643 			       atomic_read(&cpu_in_kgdb[i]) &&
644 			       !(kgdb_info[i].exception_state &
645 				 DCPU_WANT_MASTER))
646 				cpu_relax();
647 		}
648 	}
649 
650 kgdb_restore:
651 	if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
652 		int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
653 		if (kgdb_info[sstep_cpu].task)
654 			kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
655 		else
656 			kgdb_sstep_pid = 0;
657 	}
658 	if (trace_on)
659 		tracing_on();
660 	/* Free kgdb_active */
661 	atomic_set(&kgdb_active, -1);
662 	touch_softlockup_watchdog_sync();
663 	clocksource_touch_watchdog();
664 	local_irq_restore(flags);
665 
666 	return kgdb_info[cpu].ret_state;
667 }
668 
669 /*
670  * kgdb_handle_exception() - main entry point from a kernel exception
671  *
672  * Locking hierarchy:
673  *	interface locks, if any (begin_session)
674  *	kgdb lock (kgdb_active)
675  */
676 int
677 kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
678 {
679 	struct kgdb_state kgdb_var;
680 	struct kgdb_state *ks = &kgdb_var;
681 	int ret;
682 
683 	ks->cpu			= raw_smp_processor_id();
684 	ks->ex_vector		= evector;
685 	ks->signo		= signo;
686 	ks->err_code		= ecode;
687 	ks->kgdb_usethreadid	= 0;
688 	ks->linux_regs		= regs;
689 
690 	if (kgdb_reenter_check(ks))
691 		return 0; /* Ouch, double exception ! */
692 	kgdb_info[ks->cpu].exception_state |= DCPU_WANT_MASTER;
693 	ret = kgdb_cpu_enter(ks, regs);
694 	kgdb_info[ks->cpu].exception_state &= ~(DCPU_WANT_MASTER |
695 						DCPU_IS_SLAVE);
696 	return ret;
697 }
698 
699 int kgdb_nmicallback(int cpu, void *regs)
700 {
701 #ifdef CONFIG_SMP
702 	struct kgdb_state kgdb_var;
703 	struct kgdb_state *ks = &kgdb_var;
704 
705 	memset(ks, 0, sizeof(struct kgdb_state));
706 	ks->cpu			= cpu;
707 	ks->linux_regs		= regs;
708 
709 	if (!atomic_read(&cpu_in_kgdb[cpu]) &&
710 	    atomic_read(&kgdb_active) != -1 &&
711 	    atomic_read(&kgdb_active) != cpu) {
712 		kgdb_info[cpu].exception_state |= DCPU_IS_SLAVE;
713 		kgdb_cpu_enter(ks, regs);
714 		kgdb_info[cpu].exception_state &= ~DCPU_IS_SLAVE;
715 		return 0;
716 	}
717 #endif
718 	return 1;
719 }
720 
721 static void kgdb_console_write(struct console *co, const char *s,
722    unsigned count)
723 {
724 	unsigned long flags;
725 
726 	/* If we're debugging, or KGDB has not connected, don't try
727 	 * and print. */
728 	if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
729 		return;
730 
731 	local_irq_save(flags);
732 	gdbstub_msg_write(s, count);
733 	local_irq_restore(flags);
734 }
735 
736 static struct console kgdbcons = {
737 	.name		= "kgdb",
738 	.write		= kgdb_console_write,
739 	.flags		= CON_PRINTBUFFER | CON_ENABLED,
740 	.index		= -1,
741 };
742 
743 #ifdef CONFIG_MAGIC_SYSRQ
744 static void sysrq_handle_dbg(int key, struct tty_struct *tty)
745 {
746 	if (!dbg_io_ops) {
747 		printk(KERN_CRIT "ERROR: No KGDB I/O module available\n");
748 		return;
749 	}
750 	if (!kgdb_connected) {
751 #ifdef CONFIG_KGDB_KDB
752 		if (!dbg_kdb_mode)
753 			printk(KERN_CRIT "KGDB or $3#33 for KDB\n");
754 #else
755 		printk(KERN_CRIT "Entering KGDB\n");
756 #endif
757 	}
758 
759 	kgdb_breakpoint();
760 }
761 
762 static struct sysrq_key_op sysrq_dbg_op = {
763 	.handler	= sysrq_handle_dbg,
764 	.help_msg	= "debug(G)",
765 	.action_msg	= "DEBUG",
766 };
767 #endif
768 
769 static int kgdb_panic_event(struct notifier_block *self,
770 			    unsigned long val,
771 			    void *data)
772 {
773 	if (dbg_kdb_mode)
774 		kdb_printf("PANIC: %s\n", (char *)data);
775 	kgdb_breakpoint();
776 	return NOTIFY_DONE;
777 }
778 
779 static struct notifier_block kgdb_panic_event_nb = {
780        .notifier_call	= kgdb_panic_event,
781        .priority	= INT_MAX,
782 };
783 
784 void __weak kgdb_arch_late(void)
785 {
786 }
787 
788 void __init dbg_late_init(void)
789 {
790 	dbg_is_early = false;
791 	if (kgdb_io_module_registered)
792 		kgdb_arch_late();
793 	kdb_init(KDB_INIT_FULL);
794 }
795 
796 static void kgdb_register_callbacks(void)
797 {
798 	if (!kgdb_io_module_registered) {
799 		kgdb_io_module_registered = 1;
800 		kgdb_arch_init();
801 		if (!dbg_is_early)
802 			kgdb_arch_late();
803 		atomic_notifier_chain_register(&panic_notifier_list,
804 					       &kgdb_panic_event_nb);
805 #ifdef CONFIG_MAGIC_SYSRQ
806 		register_sysrq_key('g', &sysrq_dbg_op);
807 #endif
808 		if (kgdb_use_con && !kgdb_con_registered) {
809 			register_console(&kgdbcons);
810 			kgdb_con_registered = 1;
811 		}
812 	}
813 }
814 
815 static void kgdb_unregister_callbacks(void)
816 {
817 	/*
818 	 * When this routine is called KGDB should unregister from the
819 	 * panic handler and clean up, making sure it is not handling any
820 	 * break exceptions at the time.
821 	 */
822 	if (kgdb_io_module_registered) {
823 		kgdb_io_module_registered = 0;
824 		atomic_notifier_chain_unregister(&panic_notifier_list,
825 					       &kgdb_panic_event_nb);
826 		kgdb_arch_exit();
827 #ifdef CONFIG_MAGIC_SYSRQ
828 		unregister_sysrq_key('g', &sysrq_dbg_op);
829 #endif
830 		if (kgdb_con_registered) {
831 			unregister_console(&kgdbcons);
832 			kgdb_con_registered = 0;
833 		}
834 	}
835 }
836 
837 /*
838  * There are times a tasklet needs to be used vs a compiled in
839  * break point so as to cause an exception outside a kgdb I/O module,
840  * such as is the case with kgdboe, where calling a breakpoint in the
841  * I/O driver itself would be fatal.
842  */
843 static void kgdb_tasklet_bpt(unsigned long ing)
844 {
845 	kgdb_breakpoint();
846 	atomic_set(&kgdb_break_tasklet_var, 0);
847 }
848 
849 static DECLARE_TASKLET(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt, 0);
850 
851 void kgdb_schedule_breakpoint(void)
852 {
853 	if (atomic_read(&kgdb_break_tasklet_var) ||
854 		atomic_read(&kgdb_active) != -1 ||
855 		atomic_read(&kgdb_setting_breakpoint))
856 		return;
857 	atomic_inc(&kgdb_break_tasklet_var);
858 	tasklet_schedule(&kgdb_tasklet_breakpoint);
859 }
860 EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
861 
862 static void kgdb_initial_breakpoint(void)
863 {
864 	kgdb_break_asap = 0;
865 
866 	printk(KERN_CRIT "kgdb: Waiting for connection from remote gdb...\n");
867 	kgdb_breakpoint();
868 }
869 
870 /**
871  *	kgdb_register_io_module - register KGDB IO module
872  *	@new_dbg_io_ops: the io ops vector
873  *
874  *	Register it with the KGDB core.
875  */
876 int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
877 {
878 	int err;
879 
880 	spin_lock(&kgdb_registration_lock);
881 
882 	if (dbg_io_ops) {
883 		spin_unlock(&kgdb_registration_lock);
884 
885 		printk(KERN_ERR "kgdb: Another I/O driver is already "
886 				"registered with KGDB.\n");
887 		return -EBUSY;
888 	}
889 
890 	if (new_dbg_io_ops->init) {
891 		err = new_dbg_io_ops->init();
892 		if (err) {
893 			spin_unlock(&kgdb_registration_lock);
894 			return err;
895 		}
896 	}
897 
898 	dbg_io_ops = new_dbg_io_ops;
899 
900 	spin_unlock(&kgdb_registration_lock);
901 
902 	printk(KERN_INFO "kgdb: Registered I/O driver %s.\n",
903 	       new_dbg_io_ops->name);
904 
905 	/* Arm KGDB now. */
906 	kgdb_register_callbacks();
907 
908 	if (kgdb_break_asap)
909 		kgdb_initial_breakpoint();
910 
911 	return 0;
912 }
913 EXPORT_SYMBOL_GPL(kgdb_register_io_module);
914 
915 /**
916  *	kkgdb_unregister_io_module - unregister KGDB IO module
917  *	@old_dbg_io_ops: the io ops vector
918  *
919  *	Unregister it with the KGDB core.
920  */
921 void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
922 {
923 	BUG_ON(kgdb_connected);
924 
925 	/*
926 	 * KGDB is no longer able to communicate out, so
927 	 * unregister our callbacks and reset state.
928 	 */
929 	kgdb_unregister_callbacks();
930 
931 	spin_lock(&kgdb_registration_lock);
932 
933 	WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
934 	dbg_io_ops = NULL;
935 
936 	spin_unlock(&kgdb_registration_lock);
937 
938 	printk(KERN_INFO
939 		"kgdb: Unregistered I/O driver %s, debugger disabled.\n",
940 		old_dbg_io_ops->name);
941 }
942 EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
943 
944 int dbg_io_get_char(void)
945 {
946 	int ret = dbg_io_ops->read_char();
947 	if (ret == NO_POLL_CHAR)
948 		return -1;
949 	if (!dbg_kdb_mode)
950 		return ret;
951 	if (ret == 127)
952 		return 8;
953 	return ret;
954 }
955 
956 /**
957  * kgdb_breakpoint - generate breakpoint exception
958  *
959  * This function will generate a breakpoint exception.  It is used at the
960  * beginning of a program to sync up with a debugger and can be used
961  * otherwise as a quick means to stop program execution and "break" into
962  * the debugger.
963  */
964 void kgdb_breakpoint(void)
965 {
966 	atomic_inc(&kgdb_setting_breakpoint);
967 	wmb(); /* Sync point before breakpoint */
968 	arch_kgdb_breakpoint();
969 	wmb(); /* Sync point after breakpoint */
970 	atomic_dec(&kgdb_setting_breakpoint);
971 }
972 EXPORT_SYMBOL_GPL(kgdb_breakpoint);
973 
974 static int __init opt_kgdb_wait(char *str)
975 {
976 	kgdb_break_asap = 1;
977 
978 	kdb_init(KDB_INIT_EARLY);
979 	if (kgdb_io_module_registered)
980 		kgdb_initial_breakpoint();
981 
982 	return 0;
983 }
984 
985 early_param("kgdbwait", opt_kgdb_wait);
986