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