gdb/linux-fork.c

   1 /* GNU/Linux native-dependent code for debugging multiple forks.
   2
   3    Copyright (C) 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 #include "defs.h"
  21 #include "inferior.h"
  22 #include "regcache.h"
  23 #include "gdbcmd.h"
  24 #include "infcall.h"
  25 #include "objfiles.h"
  26 #include "gdb_assert.h"
  27 #include "gdb_string.h"
  28 #include "linux-fork.h"
  29 #include "linux-nat.h"
  30
  31 #include <sys/ptrace.h>
  32 #include "gdb_wait.h"
  33 #include <sys/param.h>
  34 #include "gdb_dirent.h"
  35 #include <ctype.h>
  36
  37 struct fork_info *fork_list;
  38 static int highest_fork_num;
  39
  40 /* Prevent warning from -Wmissing-prototypes.  */
  41 extern void _initialize_linux_fork (void);
  42
  43 int detach_fork = 1;            /* Default behavior is to detach
  44                                    newly forked processes (legacy).  */
  45
  46 /* Fork list data structure:  */
  47 struct fork_info
  48 {
  49   struct fork_info *next;
  50   ptid_t ptid;
  51   int num;                      /* Convenient handle (GDB fork id) */
  52   struct regcache *savedregs;   /* Convenient for info fork, saves
  53                                    having to actually switch contexts.  */
  54   int clobber_regs;             /* True if we should restore saved regs.  */
  55   ULONGEST pc;                  /* PC for info fork.  */
  56   off_t *filepos;               /* Set of open file descriptors' offsets.  */
  57   int maxfd;
  58 };
  59
  60 /* Fork list methods:  */
  61
  62 extern int
  63 forks_exist_p (void)
  64 {
  65   return (fork_list != NULL);
  66 }
  67
  68 /* Add a fork to internal fork list.
  69    Called from linux child_follow_fork.  */
  70
  71 extern struct fork_info *
  72 add_fork (pid_t pid)
  73 {
  74   struct fork_info *fp;
  75
  76   if (fork_list == NULL && pid != PIDGET (inferior_ptid))
  77     {
  78       /* Special case -- if this is the first fork in the list
  79          (the list is hitherto empty), and if this new fork is
  80          NOT the current inferior_ptid, then add inferior_ptid
  81          first, as a special zeroeth fork id.  */
  82       highest_fork_num = -1;
  83       add_fork (PIDGET (inferior_ptid));        /* safe recursion */
  84     }
  85
  86   fp = XZALLOC (struct fork_info);
  87   fp->ptid = ptid_build (pid, pid, 0);
  88   fp->num = ++highest_fork_num;
  89   fp->next = fork_list;
  90   fork_list = fp;
  91   return fp;
  92 }
  93
  94 static void
  95 free_fork (struct fork_info *fp)
  96 {
  97   /* Notes on step-resume breakpoints: since this is a concern for
  98      threads, let's convince ourselves that it's not a concern for
  99      forks.  There are two ways for a fork_info to be created.  First,
 100      by the checkpoint command, in which case we're at a gdb prompt
 101      and there can't be any step-resume breakpoint.  Second, by a fork
 102      in the user program, in which case we *may* have stepped into the
 103      fork call, but regardless of whether we follow the parent or the
 104      child, we will return to the same place and the step-resume
 105      breakpoint, if any, will take care of itself as usual.  And
 106      unlike threads, we do not save a private copy of the step-resume
 107      breakpoint -- so we're OK.  */
 108
 109   if (fp)
 110     {
 111       if (fp->savedregs)
 112         regcache_xfree (fp->savedregs);
 113       if (fp->filepos)
 114         xfree (fp->filepos);
 115       xfree (fp);
 116     }
 117 }
 118
 119 static void
 120 delete_fork (ptid_t ptid)
 121 {
 122   struct fork_info *fp, *fpprev;
 123
 124   fpprev = NULL;
 125
 126   for (fp = fork_list; fp; fpprev = fp, fp = fp->next)
 127     if (ptid_equal (fp->ptid, ptid))
 128       break;
 129
 130   if (!fp)
 131     return;
 132
 133   if (fpprev)
 134     fpprev->next = fp->next;
 135   else
 136     fork_list = fp->next;
 137
 138   free_fork (fp);
 139
 140   /* Special case: if there is now only one process in the list,
 141      and if it is (hopefully!) the current inferior_ptid, then
 142      remove it, leaving the list empty -- we're now down to the
 143      default case of debugging a single process.  */
 144   if (fork_list != NULL && fork_list->next == NULL &&
 145       ptid_equal (fork_list->ptid, inferior_ptid))
 146     {
 147       /* Last fork -- delete from list and handle as solo process
 148          (should be a safe recursion).  */
 149       delete_fork (inferior_ptid);
 150     }
 151 }
 152
 153 /* Find a fork_info by matching PTID.  */
 154 static struct fork_info *
 155 find_fork_ptid (ptid_t ptid)
 156 {
 157   struct fork_info *fp;
 158
 159   for (fp = fork_list; fp; fp = fp->next)
 160     if (ptid_equal (fp->ptid, ptid))
 161       return fp;
 162
 163   return NULL;
 164 }
 165
 166 /* Find a fork_info by matching ID.  */
 167 static struct fork_info *
 168 find_fork_id (int num)
 169 {
 170   struct fork_info *fp;
 171
 172   for (fp = fork_list; fp; fp = fp->next)
 173     if (fp->num == num)
 174       return fp;
 175
 176   return NULL;
 177 }
 178
 179 /* Find a fork_info by matching pid.  */
 180 extern struct fork_info *
 181 find_fork_pid (pid_t pid)
 182 {
 183   struct fork_info *fp;
 184
 185   for (fp = fork_list; fp; fp = fp->next)
 186     if (pid == ptid_get_pid (fp->ptid))
 187       return fp;
 188
 189   return NULL;
 190 }
 191
 192 static ptid_t
 193 fork_id_to_ptid (int num)
 194 {
 195   struct fork_info *fork = find_fork_id (num);
 196   if (fork)
 197     return fork->ptid;
 198   else
 199     return pid_to_ptid (-1);
 200 }
 201
 202 static void
 203 init_fork_list (void)
 204 {
 205   struct fork_info *fp, *fpnext;
 206
 207   if (!fork_list)
 208     return;
 209
 210   for (fp = fork_list; fp; fp = fpnext)
 211     {
 212       fpnext = fp->next;
 213       delete_inferior (ptid_get_pid (fp->ptid));
 214       free_fork (fp);
 215     }
 216
 217   fork_list = NULL;
 218 }
 219
 220 /* Fork list <-> gdb interface.  */
 221
 222 /* Utility function for fork_load/fork_save.
 223    Calls lseek in the (current) inferior process.  */
 224
 225 static off_t
 226 call_lseek (int fd, off_t offset, int whence)
 227 {
 228   char exp[80];
 229
 230   snprintf (&exp[0], sizeof (exp), "lseek (%d, %ld, %d)",
 231             fd, (long) offset, whence);
 232   return (off_t) parse_and_eval_long (&exp[0]);
 233 }
 234
 235 /* Load infrun state for the fork PTID.  */
 236
 237 static void
 238 fork_load_infrun_state (struct fork_info *fp)
 239 {
 240   extern void nullify_last_target_wait_ptid ();
 241   int i;
 242
 243   inferior_ptid = fp->ptid;
 244
 245   linux_nat_switch_fork (inferior_ptid);
 246
 247   if (fp->savedregs && fp->clobber_regs)
 248     regcache_cpy (get_current_regcache (), fp->savedregs);
 249
 250   registers_changed ();
 251   reinit_frame_cache ();
 252
 253   stop_pc = read_pc ();
 254   nullify_last_target_wait_ptid ();
 255
 256   /* Now restore the file positions of open file descriptors.  */
 257   if (fp->filepos)
 258     {
 259       for (i = 0; i <= fp->maxfd; i++)
 260         if (fp->filepos[i] != (off_t) -1)
 261           call_lseek (i, fp->filepos[i], SEEK_SET);
 262       /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
 263          this is native-only.  If it ever has to be cross, we'll have
 264          to rethink this.  */
 265     }
 266 }
 267
 268 /* Save infrun state for the fork PTID.
 269    Exported for use by linux child_follow_fork.  */
 270
 271 extern void
 272 fork_save_infrun_state (struct fork_info *fp, int clobber_regs)
 273 {
 274   char path[MAXPATHLEN];
 275   struct dirent *de;
 276   DIR *d;
 277
 278   if (fp->savedregs)
 279     regcache_xfree (fp->savedregs);
 280
 281   fp->savedregs = regcache_dup (get_current_regcache ());
 282   fp->clobber_regs = clobber_regs;
 283   fp->pc = read_pc ();
 284
 285   if (clobber_regs)
 286     {
 287       /* Now save the 'state' (file position) of all open file descriptors.
 288          Unfortunately fork does not take care of that for us...  */
 289       snprintf (path, MAXPATHLEN, "/proc/%ld/fd", (long) PIDGET (fp->ptid));
 290       if ((d = opendir (path)) != NULL)
 291         {
 292           long tmp;
 293
 294           fp->maxfd = 0;
 295           while ((de = readdir (d)) != NULL)
 296             {
 297               /* Count open file descriptors (actually find highest
 298                  numbered).  */
 299               tmp = strtol (&de->d_name[0], NULL, 10);
 300               if (fp->maxfd < tmp)
 301                 fp->maxfd = tmp;
 302             }
 303           /* Allocate array of file positions.  */
 304           fp->filepos = xrealloc (fp->filepos,
 305                                   (fp->maxfd + 1) * sizeof (*fp->filepos));
 306
 307           /* Initialize to -1 (invalid).  */
 308           for (tmp = 0; tmp <= fp->maxfd; tmp++)
 309             fp->filepos[tmp] = -1;
 310
 311           /* Now find actual file positions.  */
 312           rewinddir (d);
 313           while ((de = readdir (d)) != NULL)
 314             if (isdigit (de->d_name[0]))
 315               {
 316                 tmp = strtol (&de->d_name[0], NULL, 10);
 317                 fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
 318               }
 319           closedir (d);
 320         }
 321     }
 322 }
 323
 324 /* Kill 'em all, let God sort 'em out...  */
 325
 326 extern void
 327 linux_fork_killall (void)
 328 {
 329   /* Walk list and kill every pid.  No need to treat the
 330      current inferior_ptid as special (we do not return a
 331      status for it) -- however any process may be a child
 332      or a parent, so may get a SIGCHLD from a previously
 333      killed child.  Wait them all out.  */
 334   struct fork_info *fp;
 335   pid_t pid, ret;
 336   int status;
 337
 338   for (fp = fork_list; fp; fp = fp->next)
 339     {
 340       pid = PIDGET (fp->ptid);
 341       do {
 342         /* Use SIGKILL instead of PTRACE_KILL because the former works even
 343            if the thread is running, while the later doesn't.  */
 344         kill (pid, SIGKILL);
 345         ret = waitpid (pid, &status, 0);
 346         /* We might get a SIGCHLD instead of an exit status.  This is
 347          aggravated by the first kill above - a child has just
 348          died.  MVS comment cut-and-pasted from linux-nat.  */
 349       } while (ret == pid && WIFSTOPPED (status));
 350     }
 351   init_fork_list ();    /* Clear list, prepare to start fresh.  */
 352 }
 353
 354 /* The current inferior_ptid has exited, but there are other viable
 355    forks to debug.  Delete the exiting one and context-switch to the
 356    first available.  */
 357
 358 extern void
 359 linux_fork_mourn_inferior (void)
 360 {
 361   /* Wait just one more time to collect the inferior's exit status.
 362      Do not check whether this succeeds though, since we may be
 363      dealing with a process that we attached to.  Such a process will
 364      only report its exit status to its original parent.  */
 365   int status;
 366
 367   waitpid (ptid_get_pid (inferior_ptid), &status, 0);
 368
 369   /* OK, presumably inferior_ptid is the one who has exited.
 370      We need to delete that one from the fork_list, and switch
 371      to the next available fork.  */
 372   delete_fork (inferior_ptid);
 373   /* Delete process from GDB's inferior list.  */
 374   delete_inferior (ptid_get_pid (inferior_ptid));
 375
 376   /* There should still be a fork - if there's only one left,
 377      delete_fork won't remove it, because we haven't updated
 378      inferior_ptid yet.  */
 379   gdb_assert (fork_list);
 380
 381   fork_load_infrun_state (fork_list);
 382   printf_filtered (_("[Switching to %s]\n"),
 383                    target_pid_to_str (inferior_ptid));
 384
 385   /* If there's only one fork, switch back to non-fork mode.  */
 386   if (fork_list->next == NULL)
 387     delete_fork (inferior_ptid);
 388 }
 389
 390 /* Fork list <-> user interface.  */
 391
 392 static void
 393 delete_fork_command (char *args, int from_tty)
 394 {
 395   ptid_t ptid;
 396
 397   if (!args || !*args)
 398     error (_("Requires argument (fork/checkpoint id to delete)"));
 399
 400   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 401   if (ptid_equal (ptid, minus_one_ptid))
 402     error (_("No such fork/checkpoint id, %s"), args);
 403
 404   if (ptid_equal (ptid, inferior_ptid))
 405     error (_("Please switch to another fork/checkpoint before deleting the current one"));
 406
 407   if (ptrace (PTRACE_KILL, PIDGET (ptid), 0, 0))
 408     error (_("Unable to kill pid %s"), target_tid_to_str (ptid));
 409
 410   if (from_tty)
 411     printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid));
 412
 413   delete_fork (ptid);
 414   /* Delete process from GDB's inferior list.  */
 415   delete_inferior (ptid_get_pid (ptid));
 416 }
 417
 418 static void
 419 detach_fork_command (char *args, int from_tty)
 420 {
 421   ptid_t ptid;
 422
 423   if (!args || !*args)
 424     error (_("Requires argument (fork id to detach)"));
 425
 426   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 427   if (ptid_equal (ptid, minus_one_ptid))
 428     error (_("No such fork id, %s"), args);
 429
 430   if (ptid_equal (ptid, inferior_ptid))
 431     error (_("Please switch to another fork before detaching the current one"));
 432
 433   if (ptrace (PTRACE_DETACH, PIDGET (ptid), 0, 0))
 434     error (_("Unable to detach %s"), target_pid_to_str (ptid));
 435
 436   if (from_tty)
 437     printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid));
 438
 439   delete_fork (ptid);
 440   /* Delete process from GDB's process table.  */
 441   detach_inferior (ptid_get_pid (ptid));
 442 }
 443
 444 /* Print information about currently known forks.  */
 445
 446 static void
 447 info_forks_command (char *arg, int from_tty)
 448 {
 449   struct frame_info *cur_frame;
 450   struct symtab_and_line sal;
 451   struct symtab *cur_symtab;
 452   struct fork_info *fp;
 453   int cur_line;
 454   ULONGEST pc;
 455   int requested = -1;
 456   struct fork_info *printed = NULL;
 457
 458   if (arg && *arg)
 459     requested = (int) parse_and_eval_long (arg);
 460
 461   for (fp = fork_list; fp; fp = fp->next)
 462     {
 463       if (requested > 0 && fp->num != requested)
 464         continue;
 465
 466       printed = fp;
 467       if (ptid_equal (fp->ptid, inferior_ptid))
 468         {
 469           printf_filtered ("* ");
 470           pc = read_pc ();
 471         }
 472       else
 473         {
 474           printf_filtered ("  ");
 475           pc = fp->pc;
 476         }
 477       printf_filtered ("%d %s", fp->num, target_pid_to_str (fp->ptid));
 478       if (fp->num == 0)
 479         printf_filtered (_(" (main process)"));
 480       printf_filtered (_(" at "));
 481       fputs_filtered (paddress (pc), gdb_stdout);
 482
 483       sal = find_pc_line (pc, 0);
 484       if (sal.symtab)
 485         {
 486           char *tmp = strrchr (sal.symtab->filename, '/');
 487
 488           if (tmp)
 489             printf_filtered (_(", file %s"), tmp + 1);
 490           else
 491             printf_filtered (_(", file %s"), sal.symtab->filename);
 492         }
 493       if (sal.line)
 494         printf_filtered (_(", line %d"), sal.line);
 495       if (!sal.symtab && !sal.line)
 496         {
 497           struct minimal_symbol *msym;
 498
 499           msym = lookup_minimal_symbol_by_pc (pc);
 500           if (msym)
 501             printf_filtered (", <%s>", SYMBOL_LINKAGE_NAME (msym));
 502         }
 503
 504       putchar_filtered ('\n');
 505     }
 506   if (printed == NULL)
 507     {
 508       if (requested > 0)
 509         printf_filtered (_("No fork number %d.\n"), requested);
 510       else
 511         printf_filtered (_("No forks.\n"));
 512     }
 513 }
 514
 515 /* Save/restore mode variable 'detach_fork':
 516    We need to temporarily take over this mode variable, while
 517    preserving the user-specified state, and make sure that it
 518    gets restored in case of error.
 519
 520    The int pointer that we use comes from the caller, so we can
 521    be called more than once (even though currently we don't need to).  */
 522
 523 static void
 524 restore_detach_fork (void *arg)
 525 {
 526   detach_fork = *(int *) arg;
 527 }
 528
 529 static struct cleanup *
 530 save_detach_fork (int *saved_val)
 531 {
 532   *saved_val = detach_fork;
 533   return make_cleanup (restore_detach_fork, (void *) saved_val);
 534 }
 535
 536 static void
 537 checkpoint_command (char *args, int from_tty)
 538 {
 539   struct objfile *fork_objf;
 540   struct gdbarch *gdbarch;
 541   struct target_waitstatus last_target_waitstatus;
 542   ptid_t last_target_ptid;
 543   struct value *fork_fn = NULL, *ret;
 544   struct fork_info *fp;
 545   pid_t retpid;
 546   struct cleanup *old_chain;
 547   long i;
 548   /* Make this temp var static, 'cause it's used in the error context.  */
 549   static int temp_detach_fork;
 550
 551   /* Remove breakpoints, so that they are not inserted
 552      in the forked process.  */
 553   remove_breakpoints ();
 554
 555   /* Make the inferior fork, record its (and gdb's) state.  */
 556
 557   if (lookup_minimal_symbol ("fork", NULL, NULL) != NULL)
 558     fork_fn = find_function_in_inferior ("fork", &fork_objf);
 559   if (!fork_fn)
 560     if (lookup_minimal_symbol ("_fork", NULL, NULL) != NULL)
 561       fork_fn = find_function_in_inferior ("fork", &fork_objf);
 562   if (!fork_fn)
 563     error (_("checkpoint: can't find fork function in inferior."));
 564
 565   gdbarch = get_objfile_arch (fork_objf);
 566   ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 567   old_chain = save_detach_fork (&temp_detach_fork);
 568   detach_fork = 0;
 569   ret = call_function_by_hand (fork_fn, 0, &ret);
 570   do_cleanups (old_chain);
 571   if (!ret)     /* Probably can't happen.  */
 572     error (_("checkpoint: call_function_by_hand returned null."));
 573
 574   retpid = value_as_long (ret);
 575   get_last_target_status (&last_target_ptid, &last_target_waitstatus);
 576   if (from_tty)
 577     {
 578       int parent_pid;
 579
 580       printf_filtered (_("checkpoint: fork returned pid %ld.\n"),
 581                        (long) retpid);
 582       if (info_verbose)
 583         {
 584           parent_pid = ptid_get_lwp (last_target_ptid);
 585           if (parent_pid == 0)
 586             parent_pid = ptid_get_pid (last_target_ptid);
 587           printf_filtered (_("   gdb says parent = %ld.\n"),
 588                            (long) parent_pid);
 589         }
 590     }
 591
 592   fp = find_fork_pid (retpid);
 593   if (!fp)
 594     error (_("Failed to find new fork"));
 595   fork_save_infrun_state (fp, 1);
 596   insert_breakpoints ();
 597 }
 598
 599 static void
 600 linux_fork_context (struct fork_info *newfp, int from_tty)
 601 {
 602   /* Now we attempt to switch processes.  */
 603   struct fork_info *oldfp;
 604   ptid_t ptid;
 605   int id, i;
 606
 607   gdb_assert (newfp != NULL);
 608
 609   oldfp = find_fork_ptid (inferior_ptid);
 610   gdb_assert (oldfp != NULL);
 611
 612   fork_save_infrun_state (oldfp, 1);
 613   remove_breakpoints ();
 614   fork_load_infrun_state (newfp);
 615   insert_breakpoints ();
 616
 617   printf_filtered (_("Switching to %s\n"),
 618                    target_pid_to_str (inferior_ptid));
 619
 620   print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC);
 621 }
 622
 623 /* Switch inferior process (fork) context, by process id.  */
 624 static void
 625 process_command (char *args, int from_tty)
 626 {
 627   struct fork_info *fp;
 628
 629   if (!args || !*args)
 630     error (_("Requires argument (process id to switch to)"));
 631
 632   if ((fp = find_fork_pid (parse_and_eval_long (args))) == NULL)
 633     error (_("Not found: process id %s"), args);
 634
 635   linux_fork_context (fp, from_tty);
 636 }
 637
 638 /* Switch inferior process (fork) context, by fork id.  */
 639 static void
 640 fork_command (char *args, int from_tty)
 641 {
 642   struct fork_info *fp;
 643
 644   if (!args || !*args)
 645     error (_("Requires argument (fork id to switch to)"));
 646
 647   if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
 648     error (_("Not found: fork id %s"), args);
 649
 650   linux_fork_context (fp, from_tty);
 651 }
 652
 653 /* Switch inferior process (fork) context, by checkpoint id.  */
 654 static void
 655 restart_command (char *args, int from_tty)
 656 {
 657   struct fork_info *fp;
 658
 659   if (!args || !*args)
 660     error (_("Requires argument (checkpoint id to restart)"));
 661
 662   if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
 663     error (_("Not found: checkpoint id %s"), args);
 664
 665   linux_fork_context (fp, from_tty);
 666 }
 667
 668 void
 669 _initialize_linux_fork (void)
 670 {
 671   init_fork_list ();
 672
 673   /* Set/show detach-on-fork: user-settable mode.  */
 674
 675   add_setshow_boolean_cmd ("detach-on-fork", class_obscure, &detach_fork, _("\
 676 Set whether gdb will detach the child of a fork."), _("\
 677 Show whether gdb will detach the child of a fork."), _("\
 678 Tells gdb whether to detach the child of a fork."),
 679                            NULL, NULL, &setlist, &showlist);
 680
 681   /* Set/show restart-auto-finish: user-settable count.  Causes the
 682      first "restart" of a fork to do some number of "finish" commands
 683      before returning to user.
 684
 685      Useful because otherwise the virgin fork process will be stopped
 686      somewhere in the un-interesting fork system call.  */
 687
 688   /* Checkpoint command: create a fork of the inferior process
 689      and set it aside for later debugging.  */
 690
 691   add_com ("checkpoint", class_obscure, checkpoint_command, _("\
 692 Fork a duplicate process (experimental)."));
 693
 694   /* Restart command: restore the context of a specified fork
 695      process.  May be used for "program forks" as well as for
 696      "debugger forks" (checkpoints).  */
 697
 698   add_com ("restart", class_obscure, restart_command, _("\
 699 restart <n>: restore program context from a checkpoint.\n\
 700 Argument 'n' is checkpoint ID, as displayed by 'info checkpoints'."));
 701
 702   /* Delete checkpoint command: kill the process and remove it from
 703      fork list.  */
 704
 705   add_cmd ("checkpoint", class_obscure, delete_fork_command, _("\
 706 Delete a fork/checkpoint (experimental)."),
 707            &deletelist);
 708
 709   /* Detach checkpoint command: release the process to run independently,
 710      and remove it from the fork list.  */
 711
 712   add_cmd ("checkpoint", class_obscure, detach_fork_command, _("\
 713 Detach from a fork/checkpoint (experimental)."),
 714            &detachlist);
 715
 716   /* Info checkpoints command: list all forks/checkpoints
 717      currently under gdb's control.  */
 718
 719   add_info ("checkpoints", info_forks_command,
 720             _("IDs of currently known forks/checkpoints."));
 721
 722   /* Command aliases (let "fork" and "checkpoint" be used
 723      interchangeably).  */
 724
 725   add_alias_cmd ("fork", "checkpoint", class_obscure, 1, &deletelist);
 726   add_alias_cmd ("fork", "checkpoint", class_obscure, 1, &detachlist);
 727   add_info_alias ("forks", "checkpoints", 0);
 728
 729   /* "fork <n>" (by analogy to "thread <n>").  */
 730   add_com ("fork", class_obscure, fork_command, _("\
 731 fork <n>: Switch between forked processes.\n\
 732 Argument 'n' is fork ID, as displayed by 'info forks'."));
 733
 734   /* "process <proc id>" as opposed to "fork <fork id>".  */
 735   add_com ("process", class_obscure, process_command, _("\
 736 process <pid>: Switch between forked processes.\n\
 737 Argument 'pid' is process ID, as displayed by 'info forks' or 'shell ps'."));
 738 }