aboutsummaryrefslogtreecommitdiff
path: root/gdb/linux-fork.c
blob: 51e8fddbc2351cde5ca879a1df3882f10f6f44c0 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
/* GNU/Linux native-dependent code for debugging multiple forks.

   Copyright (C) 2005-2019 Free Software Foundation, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include "defs.h"
#include "arch-utils.h"
#include "inferior.h"
#include "infrun.h"
#include "regcache.h"
#include "gdbcmd.h"
#include "infcall.h"
#include "objfiles.h"
#include "linux-fork.h"
#include "linux-nat.h"
#include "gdbthread.h"
#include "source.h"

#include "nat/gdb_ptrace.h"
#include "common/gdb_wait.h"
#include <dirent.h>
#include <ctype.h>

#include <list>

/* Fork list data structure:  */
struct fork_info
{
  explicit fork_info (pid_t pid)
    : ptid (pid, pid, 0)
  {
  }

  ~fork_info ()
  {
    /* Notes on step-resume breakpoints: since this is a concern for
       threads, let's convince ourselves that it's not a concern for
       forks.  There are two ways for a fork_info to be created.
       First, by the checkpoint command, in which case we're at a gdb
       prompt and there can't be any step-resume breakpoint.  Second,
       by a fork in the user program, in which case we *may* have
       stepped into the fork call, but regardless of whether we follow
       the parent or the child, we will return to the same place and
       the step-resume breakpoint, if any, will take care of itself as
       usual.  And unlike threads, we do not save a private copy of
       the step-resume breakpoint -- so we're OK.  */

    if (savedregs)
      delete savedregs;
    if (filepos)
      xfree (filepos);
  }

  ptid_t ptid = null_ptid;
  ptid_t parent_ptid = null_ptid;

  /* Convenient handle (GDB fork id).  */
  int num = 0;

  /* Convenient for info fork, saves having to actually switch
     contexts.  */
  readonly_detached_regcache *savedregs = nullptr;

  CORE_ADDR pc = 0;

  /* Set of open file descriptors' offsets.  */
  off_t *filepos = nullptr;

  int maxfd = 0;
};

static std::list<fork_info> fork_list;
static int highest_fork_num;

/* Fork list methods:  */

int
forks_exist_p (void)
{
  return !fork_list.empty ();
}

/* Return the last fork in the list.  */

static struct fork_info *
find_last_fork (void)
{
  if (fork_list.empty ())
    return NULL;

  return &fork_list.back ();
}

/* Return true iff there's one fork in the list.  */

static bool
one_fork_p ()
{
  return (!fork_list.empty ()
	  && &fork_list.front () == &fork_list.back ());
}

/* Add a new fork to the internal fork list.  */

void
add_fork (pid_t pid)
{
  fork_list.emplace_back (pid);

  if (one_fork_p ())
    highest_fork_num = 0;

  fork_info *fp = &fork_list.back ();
  fp->num = ++highest_fork_num;
}

static void
delete_fork (ptid_t ptid)
{
  linux_target->low_forget_process (ptid.pid ());

  for (auto it = fork_list.begin (); it != fork_list.end (); ++it)
    if (it->ptid == ptid)
      {
	fork_list.erase (it);

	/* Special case: if there is now only one process in the list,
	   and if it is (hopefully!) the current inferior_ptid, then
	   remove it, leaving the list empty -- we're now down to the
	   default case of debugging a single process.  */
	if (one_fork_p () && fork_list.front ().ptid == inferior_ptid)
	  {
	    /* Last fork -- delete from list and handle as solo
	       process (should be a safe recursion).  */
	    delete_fork (inferior_ptid);
	  }
	return;
      }
}

/* Find a fork_info by matching PTID.  */
static struct fork_info *
find_fork_ptid (ptid_t ptid)
{
  for (fork_info &fi : fork_list)
    if (fi.ptid == ptid)
      return &fi;

  return NULL;
}

/* Find a fork_info by matching ID.  */
static struct fork_info *
find_fork_id (int num)
{
  for (fork_info &fi : fork_list)
    if (fi.num == num)
      return &fi;

  return NULL;
}

/* Find a fork_info by matching pid.  */
extern struct fork_info *
find_fork_pid (pid_t pid)
{
  for (fork_info &fi : fork_list)
    if (pid == fi.ptid.pid ())
      return &fi;

  return NULL;
}

static ptid_t
fork_id_to_ptid (int num)
{
  struct fork_info *fork = find_fork_id (num);
  if (fork)
    return fork->ptid;
  else
    return ptid_t (-1);
}

/* Fork list <-> gdb interface.  */

/* Utility function for fork_load/fork_save.
   Calls lseek in the (current) inferior process.  */

static off_t
call_lseek (int fd, off_t offset, int whence)
{
  char exp[80];

  snprintf (&exp[0], sizeof (exp), "(long) lseek (%d, %ld, %d)",
	    fd, (long) offset, whence);
  return (off_t) parse_and_eval_long (&exp[0]);
}

/* Load infrun state for the fork PTID.  */

static void
fork_load_infrun_state (struct fork_info *fp)
{
  extern void nullify_last_target_wait_ptid ();
  int i;

  linux_nat_switch_fork (fp->ptid);

  if (fp->savedregs)
    get_current_regcache ()->restore (fp->savedregs);

  registers_changed ();
  reinit_frame_cache ();

  inferior_thread ()->suspend.stop_pc
    = regcache_read_pc (get_current_regcache ());
  nullify_last_target_wait_ptid ();

  /* Now restore the file positions of open file descriptors.  */
  if (fp->filepos)
    {
      for (i = 0; i <= fp->maxfd; i++)
	if (fp->filepos[i] != (off_t) -1)
	  call_lseek (i, fp->filepos[i], SEEK_SET);
      /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
	 this is native-only.  If it ever has to be cross, we'll have
	 to rethink this.  */
    }
}

/* Save infrun state for the fork FP.  */

static void
fork_save_infrun_state (struct fork_info *fp)
{
  char path[PATH_MAX];
  struct dirent *de;
  DIR *d;

  if (fp->savedregs)
    delete fp->savedregs;

  fp->savedregs = new readonly_detached_regcache (*get_current_regcache ());
  fp->pc = regcache_read_pc (get_current_regcache ());

  /* Now save the 'state' (file position) of all open file descriptors.
     Unfortunately fork does not take care of that for us...  */
  snprintf (path, PATH_MAX, "/proc/%ld/fd", (long) fp->ptid.pid ());
  if ((d = opendir (path)) != NULL)
    {
      long tmp;

      fp->maxfd = 0;
      while ((de = readdir (d)) != NULL)
	{
	  /* Count open file descriptors (actually find highest
	     numbered).  */
	  tmp = strtol (&de->d_name[0], NULL, 10);
	  if (fp->maxfd < tmp)
	    fp->maxfd = tmp;
	}
      /* Allocate array of file positions.  */
      fp->filepos = XRESIZEVEC (off_t, fp->filepos, fp->maxfd + 1);

      /* Initialize to -1 (invalid).  */
      for (tmp = 0; tmp <= fp->maxfd; tmp++)
	fp->filepos[tmp] = -1;

      /* Now find actual file positions.  */
      rewinddir (d);
      while ((de = readdir (d)) != NULL)
	if (isdigit (de->d_name[0]))
	  {
	    tmp = strtol (&de->d_name[0], NULL, 10);
	    fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
	  }
      closedir (d);
    }
}

/* Kill 'em all, let God sort 'em out...  */

void
linux_fork_killall (void)
{
  /* Walk list and kill every pid.  No need to treat the
     current inferior_ptid as special (we do not return a
     status for it) -- however any process may be a child
     or a parent, so may get a SIGCHLD from a previously
     killed child.  Wait them all out.  */

  for (fork_info &fi : fork_list)
    {
      pid_t pid = fi.ptid.pid ();
      int status;
      pid_t ret;
      do {
	/* Use SIGKILL instead of PTRACE_KILL because the former works even
	   if the thread is running, while the later doesn't.  */
	kill (pid, SIGKILL);
	ret = waitpid (pid, &status, 0);
	/* We might get a SIGCHLD instead of an exit status.  This is
	 aggravated by the first kill above - a child has just
	 died.  MVS comment cut-and-pasted from linux-nat.  */
      } while (ret == pid && WIFSTOPPED (status));
    }

  /* Clear list, prepare to start fresh.  */
  fork_list.clear ();
}

/* The current inferior_ptid has exited, but there are other viable
   forks to debug.  Delete the exiting one and context-switch to the
   first available.  */

void
linux_fork_mourn_inferior (void)
{
  struct fork_info *last;
  int status;

  /* Wait just one more time to collect the inferior's exit status.
     Do not check whether this succeeds though, since we may be
     dealing with a process that we attached to.  Such a process will
     only report its exit status to its original parent.  */
  waitpid (inferior_ptid.pid (), &status, 0);

  /* OK, presumably inferior_ptid is the one who has exited.
     We need to delete that one from the fork_list, and switch
     to the next available fork.  */
  delete_fork (inferior_ptid);

  /* There should still be a fork - if there's only one left,
     delete_fork won't remove it, because we haven't updated
     inferior_ptid yet.  */
  gdb_assert (!fork_list.empty ());

  last = find_last_fork ();
  fork_load_infrun_state (last);
  printf_filtered (_("[Switching to %s]\n"),
		   target_pid_to_str (inferior_ptid));

  /* If there's only one fork, switch back to non-fork mode.  */
  if (one_fork_p ())
    delete_fork (inferior_ptid);
}

/* The current inferior_ptid is being detached, but there are other
   viable forks to debug.  Detach and delete it and context-switch to
   the first available.  */

void
linux_fork_detach (int from_tty)
{
  /* OK, inferior_ptid is the one we are detaching from.  We need to
     delete it from the fork_list, and switch to the next available
     fork.  */

  if (ptrace (PTRACE_DETACH, inferior_ptid.pid (), 0, 0))
    error (_("Unable to detach %s"), target_pid_to_str (inferior_ptid));

  delete_fork (inferior_ptid);

  /* There should still be a fork - if there's only one left,
     delete_fork won't remove it, because we haven't updated
     inferior_ptid yet.  */
  gdb_assert (!fork_list.empty ());

  fork_load_infrun_state (&fork_list.front ());

  if (from_tty)
    printf_filtered (_("[Switching to %s]\n"),
		     target_pid_to_str (inferior_ptid));

  /* If there's only one fork, switch back to non-fork mode.  */
  if (one_fork_p ())
    delete_fork (inferior_ptid);
}

/* Temporarily switch to the infrun state stored on the fork_info
   identified by a given ptid_t.  When this object goes out of scope,
   restore the currently selected infrun state.   */

class scoped_switch_fork_info
{
public:
  /* Switch to the infrun state held on the fork_info identified by
     PPTID.  If PPTID is the current inferior then no switch is done.  */
  explicit scoped_switch_fork_info (ptid_t pptid)
    : m_oldfp (nullptr)
  {
    if (pptid != inferior_ptid)
      {
	struct fork_info *newfp = nullptr;

	/* Switch to pptid.  */
	m_oldfp = find_fork_ptid (inferior_ptid);
	gdb_assert (m_oldfp != nullptr);
	newfp = find_fork_ptid (pptid);
	gdb_assert (newfp != nullptr);
	fork_save_infrun_state (m_oldfp);
	remove_breakpoints ();
	fork_load_infrun_state (newfp);
	insert_breakpoints ();
      }
  }

  /* Restore the previously selected infrun state.  If the constructor
     didn't need to switch states, then nothing is done here either.  */
  ~scoped_switch_fork_info ()
  {
    if (m_oldfp != nullptr)
      {
	/* Switch back to inferior_ptid.  */
	TRY
	  {
	    remove_breakpoints ();
	    fork_load_infrun_state (m_oldfp);
	    insert_breakpoints ();
	  }
	CATCH (ex, RETURN_MASK_ALL)
	  {
	    warning (_("Couldn't restore checkpoint state in %s: %s"),
		     target_pid_to_str (m_oldfp->ptid), ex.message);
	  }
	END_CATCH
      }
  }

  DISABLE_COPY_AND_ASSIGN (scoped_switch_fork_info);

private:
  /* The fork_info for the previously selected infrun state, or nullptr if
     we were already in the desired state, and nothing needs to be
     restored.  */
  struct fork_info *m_oldfp;
};

static int
inferior_call_waitpid (ptid_t pptid, int pid)
{
  struct objfile *waitpid_objf;
  struct value *waitpid_fn = NULL;
  int ret = -1;

  scoped_switch_fork_info switch_fork_info (pptid);

  /* Get the waitpid_fn.  */
  if (lookup_minimal_symbol ("waitpid", NULL, NULL).minsym != NULL)
    waitpid_fn = find_function_in_inferior ("waitpid", &waitpid_objf);
  if (!waitpid_fn
      && lookup_minimal_symbol ("_waitpid", NULL, NULL).minsym != NULL)
    waitpid_fn = find_function_in_inferior ("_waitpid", &waitpid_objf);
  if (waitpid_fn != nullptr)
    {
      struct gdbarch *gdbarch = get_current_arch ();
      struct value *argv[3], *retv;

      /* Get the argv.  */
      argv[0] = value_from_longest (builtin_type (gdbarch)->builtin_int, pid);
      argv[1] = value_from_pointer (builtin_type (gdbarch)->builtin_data_ptr, 0);
      argv[2] = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);

      retv = call_function_by_hand (waitpid_fn, NULL, argv);

      if (value_as_long (retv) >= 0)
	ret = 0;
    }

  return ret;
}

/* Fork list <-> user interface.  */

static void
delete_checkpoint_command (const char *args, int from_tty)
{
  ptid_t ptid, pptid;
  struct fork_info *fi;

  if (!args || !*args)
    error (_("Requires argument (checkpoint id to delete)"));

  ptid = fork_id_to_ptid (parse_and_eval_long (args));
  if (ptid == minus_one_ptid)
    error (_("No such checkpoint id, %s"), args);

  if (ptid == inferior_ptid)
    error (_("\
Please switch to another checkpoint before deleting the current one"));

  if (ptrace (PTRACE_KILL, ptid.pid (), 0, 0))
    error (_("Unable to kill pid %s"), target_pid_to_str (ptid));

  fi = find_fork_ptid (ptid);
  gdb_assert (fi);
  pptid = fi->parent_ptid;

  if (from_tty)
    printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid));

  delete_fork (ptid);

  /* If fi->parent_ptid is not a part of lwp but it's a part of checkpoint
     list, waitpid the ptid.
     If fi->parent_ptid is a part of lwp and it is stopped, waitpid the
     ptid.  */
  thread_info *parent = find_thread_ptid (pptid);
  if ((parent == NULL && find_fork_ptid (pptid))
      || (parent != NULL && parent->state == THREAD_STOPPED))
    {
      if (inferior_call_waitpid (pptid, ptid.pid ()))
        warning (_("Unable to wait pid %s"), target_pid_to_str (ptid));
    }
}

static void
detach_checkpoint_command (const char *args, int from_tty)
{
  ptid_t ptid;

  if (!args || !*args)
    error (_("Requires argument (checkpoint id to detach)"));

  ptid = fork_id_to_ptid (parse_and_eval_long (args));
  if (ptid == minus_one_ptid)
    error (_("No such checkpoint id, %s"), args);

  if (ptid == inferior_ptid)
    error (_("\
Please switch to another checkpoint before detaching the current one"));

  if (ptrace (PTRACE_DETACH, ptid.pid (), 0, 0))
    error (_("Unable to detach %s"), target_pid_to_str (ptid));

  if (from_tty)
    printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid));

  delete_fork (ptid);
}

/* Print information about currently known checkpoints.  */

static void
info_checkpoints_command (const char *arg, int from_tty)
{
  struct gdbarch *gdbarch = get_current_arch ();
  int requested = -1;
  const fork_info *printed = NULL;

  if (arg && *arg)
    requested = (int) parse_and_eval_long (arg);

  for (const fork_info &fi : fork_list)
    {
      if (requested > 0 && fi.num != requested)
	continue;

      printed = &fi;
      if (fi.ptid == inferior_ptid)
	printf_filtered ("* ");
      else
	printf_filtered ("  ");

      ULONGEST pc = fi.pc;
      printf_filtered ("%d %s", fi.num, target_pid_to_str (fi.ptid));
      if (fi.num == 0)
	printf_filtered (_(" (main process)"));
      printf_filtered (_(" at "));
      fputs_filtered (paddress (gdbarch, pc), gdb_stdout);

      symtab_and_line sal = find_pc_line (pc, 0);
      if (sal.symtab)
	printf_filtered (_(", file %s"),
			 symtab_to_filename_for_display (sal.symtab));
      if (sal.line)
	printf_filtered (_(", line %d"), sal.line);
      if (!sal.symtab && !sal.line)
	{
	  struct bound_minimal_symbol msym;

	  msym = lookup_minimal_symbol_by_pc (pc);
	  if (msym.minsym)
	    printf_filtered (", <%s>", MSYMBOL_LINKAGE_NAME (msym.minsym));
	}

      putchar_filtered ('\n');
    }
  if (printed == NULL)
    {
      if (requested > 0)
	printf_filtered (_("No checkpoint number %d.\n"), requested);
      else
	printf_filtered (_("No checkpoints.\n"));
    }
}

/* The PID of the process we're checkpointing.  */
static int checkpointing_pid = 0;

int
linux_fork_checkpointing_p (int pid)
{
  return (checkpointing_pid == pid);
}

/* Return true if the current inferior is multi-threaded.  */

static bool
inf_has_multiple_threads ()
{
  int count = 0;

  /* Return true as soon as we see the second thread of the current
     inferior.  */
  for (thread_info *tp ATTRIBUTE_UNUSED : current_inferior ()->threads ())
    if (++count > 1)
      return true;

  return false;
}

static void
checkpoint_command (const char *args, int from_tty)
{
  struct objfile *fork_objf;
  struct gdbarch *gdbarch;
  struct target_waitstatus last_target_waitstatus;
  ptid_t last_target_ptid;
  struct value *fork_fn = NULL, *ret;
  struct fork_info *fp;
  pid_t retpid;

  if (!target_has_execution) 
    error (_("The program is not being run."));

  /* Ensure that the inferior is not multithreaded.  */
  update_thread_list ();
  if (inf_has_multiple_threads ())
    error (_("checkpoint: can't checkpoint multiple threads."));
  
  /* Make the inferior fork, record its (and gdb's) state.  */

  if (lookup_minimal_symbol ("fork", NULL, NULL).minsym != NULL)
    fork_fn = find_function_in_inferior ("fork", &fork_objf);
  if (!fork_fn)
    if (lookup_minimal_symbol ("_fork", NULL, NULL).minsym != NULL)
      fork_fn = find_function_in_inferior ("fork", &fork_objf);
  if (!fork_fn)
    error (_("checkpoint: can't find fork function in inferior."));

  gdbarch = get_objfile_arch (fork_objf);
  ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);

  /* Tell linux-nat.c that we're checkpointing this inferior.  */
  {
    scoped_restore save_pid
      = make_scoped_restore (&checkpointing_pid, inferior_ptid.pid ());

    ret = call_function_by_hand (fork_fn, NULL, {});
  }

  if (!ret)	/* Probably can't happen.  */
    error (_("checkpoint: call_function_by_hand returned null."));

  retpid = value_as_long (ret);
  get_last_target_status (&last_target_ptid, &last_target_waitstatus);

  fp = find_fork_pid (retpid);

  if (from_tty)
    {
      int parent_pid;

      printf_filtered (_("checkpoint %d: fork returned pid %ld.\n"),
		       fp != NULL ? fp->num : -1, (long) retpid);
      if (info_verbose)
	{
	  parent_pid = last_target_ptid.lwp ();
	  if (parent_pid == 0)
	    parent_pid = last_target_ptid.pid ();
	  printf_filtered (_("   gdb says parent = %ld.\n"),
			   (long) parent_pid);
	}
    }

  if (!fp)
    error (_("Failed to find new fork"));

  if (one_fork_p ())
    {
      /* Special case -- if this is the first fork in the list (the
	 list was hitherto empty), then add inferior_ptid first, as a
	 special zeroeth fork id.  */
      fork_list.emplace_front (inferior_ptid.pid ());
    }

  fork_save_infrun_state (fp);
  fp->parent_ptid = last_target_ptid;
}

static void
linux_fork_context (struct fork_info *newfp, int from_tty)
{
  /* Now we attempt to switch processes.  */
  struct fork_info *oldfp;

  gdb_assert (newfp != NULL);

  oldfp = find_fork_ptid (inferior_ptid);
  gdb_assert (oldfp != NULL);

  fork_save_infrun_state (oldfp);
  remove_breakpoints ();
  fork_load_infrun_state (newfp);
  insert_breakpoints ();

  printf_filtered (_("Switching to %s\n"),
		   target_pid_to_str (inferior_ptid));

  print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC, 1);
}

/* Switch inferior process (checkpoint) context, by checkpoint id.  */
static void
restart_command (const char *args, int from_tty)
{
  struct fork_info *fp;

  if (!args || !*args)
    error (_("Requires argument (checkpoint id to restart)"));

  if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
    error (_("Not found: checkpoint id %s"), args);

  linux_fork_context (fp, from_tty);
}

void
_initialize_linux_fork (void)
{
  /* Checkpoint command: create a fork of the inferior process
     and set it aside for later debugging.  */

  add_com ("checkpoint", class_obscure, checkpoint_command, _("\
Fork a duplicate process (experimental)."));

  /* Restart command: restore the context of a specified checkpoint
     process.  */

  add_com ("restart", class_obscure, restart_command, _("\
restart N: restore program context from a checkpoint.\n\
Argument N is checkpoint ID, as displayed by 'info checkpoints'."));

  /* Delete checkpoint command: kill the process and remove it from
     the fork list.  */

  add_cmd ("checkpoint", class_obscure, delete_checkpoint_command, _("\
Delete a checkpoint (experimental)."),
	   &deletelist);

  /* Detach checkpoint command: release the process to run independently,
     and remove it from the fork list.  */

  add_cmd ("checkpoint", class_obscure, detach_checkpoint_command, _("\
Detach from a checkpoint (experimental)."),
	   &detachlist);

  /* Info checkpoints command: list all forks/checkpoints
     currently under gdb's control.  */

  add_info ("checkpoints", info_checkpoints_command,
	    _("IDs of currently known checkpoints."));
}