gdb/linux-fork.c

   1 /* GNU/Linux native-dependent code for debugging multiple forks.
   2
   3    Copyright (C) 2005-2013 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 "arch-utils.h"
  22 #include "inferior.h"
  23 #include "regcache.h"
  24 #include "gdbcmd.h"
  25 #include "infcall.h"
  26 #include "objfiles.h"
  27 #include "gdb_assert.h"
  28 #include "gdb_string.h"
  29 #include "linux-fork.h"
  30 #include "linux-nat.h"
  31 #include "gdbthread.h"
  32 #include "source.h"
  33
  34 #include <sys/ptrace.h>
  35 #include "gdb_wait.h"
  36 #include "gdb_dirent.h"
  37 #include <ctype.h>
  38
  39 struct fork_info *fork_list;
  40 static int highest_fork_num;
  41
  42 /* Prevent warning from -Wmissing-prototypes.  */
  43 extern void _initialize_linux_fork (void);
  44
  45 /* Fork list data structure:  */
  46 struct fork_info
  47 {
  48   struct fork_info *next;
  49   ptid_t ptid;
  50   ptid_t parent_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   off_t *filepos;               /* Set of open file descriptors' offsets.  */
  56   int maxfd;
  57 };
  58
  59 /* Fork list methods:  */
  60
  61 int
  62 forks_exist_p (void)
  63 {
  64   return (fork_list != NULL);
  65 }
  66
  67 /* Add a fork to the internal fork list.  */
  68
  69 struct fork_info *
  70 add_fork (pid_t pid)
  71 {
  72   struct fork_info *fp;
  73
  74   if (fork_list == NULL && pid != ptid_get_pid (inferior_ptid))
  75     {
  76       /* Special case -- if this is the first fork in the list
  77          (the list is hitherto empty), and if this new fork is
  78          NOT the current inferior_ptid, then add inferior_ptid
  79          first, as a special zeroeth fork id.  */
  80       highest_fork_num = -1;
  81       add_fork (ptid_get_pid (inferior_ptid));  /* safe recursion */
  82     }
  83
  84   fp = XZALLOC (struct fork_info);
  85   fp->ptid = ptid_build (pid, pid, 0);
  86   fp->num = ++highest_fork_num;
  87   fp->next = fork_list;
  88   fork_list = fp;
  89   return fp;
  90 }
  91
  92 static void
  93 free_fork (struct fork_info *fp)
  94 {
  95   /* Notes on step-resume breakpoints: since this is a concern for
  96      threads, let's convince ourselves that it's not a concern for
  97      forks.  There are two ways for a fork_info to be created.  First,
  98      by the checkpoint command, in which case we're at a gdb prompt
  99      and there can't be any step-resume breakpoint.  Second, by a fork
 100      in the user program, in which case we *may* have stepped into the
 101      fork call, but regardless of whether we follow the parent or the
 102      child, we will return to the same place and the step-resume
 103      breakpoint, if any, will take care of itself as usual.  And
 104      unlike threads, we do not save a private copy of the step-resume
 105      breakpoint -- so we're OK.  */
 106
 107   if (fp)
 108     {
 109       if (fp->savedregs)
 110         regcache_xfree (fp->savedregs);
 111       if (fp->filepos)
 112         xfree (fp->filepos);
 113       xfree (fp);
 114     }
 115 }
 116
 117 static void
 118 delete_fork (ptid_t ptid)
 119 {
 120   struct fork_info *fp, *fpprev;
 121
 122   fpprev = NULL;
 123
 124   linux_nat_forget_process (ptid_get_pid (ptid));
 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       free_fork (fp);
 214     }
 215
 216   fork_list = NULL;
 217 }
 218
 219 /* Fork list <-> gdb interface.  */
 220
 221 /* Utility function for fork_load/fork_save.
 222    Calls lseek in the (current) inferior process.  */
 223
 224 static off_t
 225 call_lseek (int fd, off_t offset, int whence)
 226 {
 227   char exp[80];
 228
 229   snprintf (&exp[0], sizeof (exp), "lseek (%d, %ld, %d)",
 230             fd, (long) offset, whence);
 231   return (off_t) parse_and_eval_long (&exp[0]);
 232 }
 233
 234 /* Load infrun state for the fork PTID.  */
 235
 236 static void
 237 fork_load_infrun_state (struct fork_info *fp)
 238 {
 239   extern void nullify_last_target_wait_ptid ();
 240   int i;
 241
 242   linux_nat_switch_fork (fp->ptid);
 243
 244   if (fp->savedregs && fp->clobber_regs)
 245     regcache_cpy (get_current_regcache (), fp->savedregs);
 246
 247   registers_changed ();
 248   reinit_frame_cache ();
 249
 250   stop_pc = regcache_read_pc (get_current_regcache ());
 251   nullify_last_target_wait_ptid ();
 252
 253   /* Now restore the file positions of open file descriptors.  */
 254   if (fp->filepos)
 255     {
 256       for (i = 0; i <= fp->maxfd; i++)
 257         if (fp->filepos[i] != (off_t) -1)
 258           call_lseek (i, fp->filepos[i], SEEK_SET);
 259       /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
 260          this is native-only.  If it ever has to be cross, we'll have
 261          to rethink this.  */
 262     }
 263 }
 264
 265 /* Save infrun state for the fork PTID.
 266    Exported for use by linux child_follow_fork.  */
 267
 268 static void
 269 fork_save_infrun_state (struct fork_info *fp, int clobber_regs)
 270 {
 271   char path[PATH_MAX];
 272   struct dirent *de;
 273   DIR *d;
 274
 275   if (fp->savedregs)
 276     regcache_xfree (fp->savedregs);
 277
 278   fp->savedregs = regcache_dup (get_current_regcache ());
 279   fp->clobber_regs = clobber_regs;
 280
 281   if (clobber_regs)
 282     {
 283       /* Now save the 'state' (file position) of all open file descriptors.
 284          Unfortunately fork does not take care of that for us...  */
 285       snprintf (path, PATH_MAX, "/proc/%ld/fd",
 286                 (long) ptid_get_pid (fp->ptid));
 287       if ((d = opendir (path)) != NULL)
 288         {
 289           long tmp;
 290
 291           fp->maxfd = 0;
 292           while ((de = readdir (d)) != NULL)
 293             {
 294               /* Count open file descriptors (actually find highest
 295                  numbered).  */
 296               tmp = strtol (&de->d_name[0], NULL, 10);
 297               if (fp->maxfd < tmp)
 298                 fp->maxfd = tmp;
 299             }
 300           /* Allocate array of file positions.  */
 301           fp->filepos = xrealloc (fp->filepos,
 302                                   (fp->maxfd + 1) * sizeof (*fp->filepos));
 303
 304           /* Initialize to -1 (invalid).  */
 305           for (tmp = 0; tmp <= fp->maxfd; tmp++)
 306             fp->filepos[tmp] = -1;
 307
 308           /* Now find actual file positions.  */
 309           rewinddir (d);
 310           while ((de = readdir (d)) != NULL)
 311             if (isdigit (de->d_name[0]))
 312               {
 313                 tmp = strtol (&de->d_name[0], NULL, 10);
 314                 fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
 315               }
 316           closedir (d);
 317         }
 318     }
 319 }
 320
 321 /* Kill 'em all, let God sort 'em out...  */
 322
 323 void
 324 linux_fork_killall (void)
 325 {
 326   /* Walk list and kill every pid.  No need to treat the
 327      current inferior_ptid as special (we do not return a
 328      status for it) -- however any process may be a child
 329      or a parent, so may get a SIGCHLD from a previously
 330      killed child.  Wait them all out.  */
 331   struct fork_info *fp;
 332   pid_t pid, ret;
 333   int status;
 334
 335   for (fp = fork_list; fp; fp = fp->next)
 336     {
 337       pid = ptid_get_pid (fp->ptid);
 338       do {
 339         /* Use SIGKILL instead of PTRACE_KILL because the former works even
 340            if the thread is running, while the later doesn't.  */
 341         kill (pid, SIGKILL);
 342         ret = waitpid (pid, &status, 0);
 343         /* We might get a SIGCHLD instead of an exit status.  This is
 344          aggravated by the first kill above - a child has just
 345          died.  MVS comment cut-and-pasted from linux-nat.  */
 346       } while (ret == pid && WIFSTOPPED (status));
 347     }
 348   init_fork_list ();    /* Clear list, prepare to start fresh.  */
 349 }
 350
 351 /* The current inferior_ptid has exited, but there are other viable
 352    forks to debug.  Delete the exiting one and context-switch to the
 353    first available.  */
 354
 355 void
 356 linux_fork_mourn_inferior (void)
 357 {
 358   /* Wait just one more time to collect the inferior's exit status.
 359      Do not check whether this succeeds though, since we may be
 360      dealing with a process that we attached to.  Such a process will
 361      only report its exit status to its original parent.  */
 362   int status;
 363
 364   waitpid (ptid_get_pid (inferior_ptid), &status, 0);
 365
 366   /* OK, presumably inferior_ptid is the one who has exited.
 367      We need to delete that one from the fork_list, and switch
 368      to the next available fork.  */
 369   delete_fork (inferior_ptid);
 370
 371   /* There should still be a fork - if there's only one left,
 372      delete_fork won't remove it, because we haven't updated
 373      inferior_ptid yet.  */
 374   gdb_assert (fork_list);
 375
 376   fork_load_infrun_state (fork_list);
 377   printf_filtered (_("[Switching to %s]\n"),
 378                    target_pid_to_str (inferior_ptid));
 379
 380   /* If there's only one fork, switch back to non-fork mode.  */
 381   if (fork_list->next == NULL)
 382     delete_fork (inferior_ptid);
 383 }
 384
 385 /* The current inferior_ptid is being detached, but there are other
 386    viable forks to debug.  Detach and delete it and context-switch to
 387    the first available.  */
 388
 389 void
 390 linux_fork_detach (char *args, int from_tty)
 391 {
 392   /* OK, inferior_ptid is the one we are detaching from.  We need to
 393      delete it from the fork_list, and switch to the next available
 394      fork.  */
 395
 396   if (ptrace (PTRACE_DETACH, ptid_get_pid (inferior_ptid), 0, 0))
 397     error (_("Unable to detach %s"), target_pid_to_str (inferior_ptid));
 398
 399   delete_fork (inferior_ptid);
 400
 401   /* There should still be a fork - if there's only one left,
 402      delete_fork won't remove it, because we haven't updated
 403      inferior_ptid yet.  */
 404   gdb_assert (fork_list);
 405
 406   fork_load_infrun_state (fork_list);
 407
 408   if (from_tty)
 409     printf_filtered (_("[Switching to %s]\n"),
 410                      target_pid_to_str (inferior_ptid));
 411
 412   /* If there's only one fork, switch back to non-fork mode.  */
 413   if (fork_list->next == NULL)
 414     delete_fork (inferior_ptid);
 415 }
 416
 417 static void
 418 inferior_call_waitpid_cleanup (void *fp)
 419 {
 420   struct fork_info *oldfp = fp;
 421
 422   if (oldfp)
 423     {
 424       /* Switch back to inferior_ptid.  */
 425       remove_breakpoints ();
 426       fork_load_infrun_state (oldfp);
 427       insert_breakpoints ();
 428     }
 429 }
 430
 431 static int
 432 inferior_call_waitpid (ptid_t pptid, int pid)
 433 {
 434   struct objfile *waitpid_objf;
 435   struct value *waitpid_fn = NULL;
 436   struct value *argv[4], *retv;
 437   struct gdbarch *gdbarch = get_current_arch ();
 438   struct fork_info *oldfp = NULL, *newfp = NULL;
 439   struct cleanup *old_cleanup;
 440   int ret = -1;
 441
 442   if (!ptid_equal (pptid, inferior_ptid))
 443     {
 444       /* Switch to pptid.  */
 445       oldfp = find_fork_ptid (inferior_ptid);
 446       gdb_assert (oldfp != NULL);
 447       newfp = find_fork_ptid (pptid);
 448       gdb_assert (newfp != NULL);
 449       fork_save_infrun_state (oldfp, 1);
 450       remove_breakpoints ();
 451       fork_load_infrun_state (newfp);
 452       insert_breakpoints ();
 453     }
 454
 455   old_cleanup = make_cleanup (inferior_call_waitpid_cleanup, oldfp);
 456
 457   /* Get the waitpid_fn.  */
 458   if (lookup_minimal_symbol ("waitpid", NULL, NULL) != NULL)
 459     waitpid_fn = find_function_in_inferior ("waitpid", &waitpid_objf);
 460   if (!waitpid_fn && lookup_minimal_symbol ("_waitpid", NULL, NULL) != NULL)
 461     waitpid_fn = find_function_in_inferior ("_waitpid", &waitpid_objf);
 462   if (!waitpid_fn)
 463     goto out;
 464
 465   /* Get the argv.  */
 466   argv[0] = value_from_longest (builtin_type (gdbarch)->builtin_int, pid);
 467   argv[1] = value_from_pointer (builtin_type (gdbarch)->builtin_data_ptr, 0);
 468   argv[2] = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 469   argv[3] = 0;
 470
 471   retv = call_function_by_hand (waitpid_fn, 3, argv);
 472   if (value_as_long (retv) < 0)
 473     goto out;
 474
 475   ret = 0;
 476
 477 out:
 478   do_cleanups (old_cleanup);
 479   return ret;
 480 }
 481
 482 /* Fork list <-> user interface.  */
 483
 484 static void
 485 delete_checkpoint_command (char *args, int from_tty)
 486 {
 487   ptid_t ptid, pptid;
 488   struct fork_info *fi;
 489
 490   if (!args || !*args)
 491     error (_("Requires argument (checkpoint id to delete)"));
 492
 493   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 494   if (ptid_equal (ptid, minus_one_ptid))
 495     error (_("No such checkpoint id, %s"), args);
 496
 497   if (ptid_equal (ptid, inferior_ptid))
 498     error (_("\
 499 Please switch to another checkpoint before deleting the current one"));
 500
 501   if (ptrace (PTRACE_KILL, ptid_get_pid (ptid), 0, 0))
 502     error (_("Unable to kill pid %s"), target_pid_to_str (ptid));
 503
 504   fi = find_fork_ptid (ptid);
 505   gdb_assert (fi);
 506   pptid = fi->parent_ptid;
 507
 508   if (from_tty)
 509     printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid));
 510
 511   delete_fork (ptid);
 512
 513   /* If fi->parent_ptid is not a part of lwp but it's a part of checkpoint
 514      list, waitpid the ptid.
 515      If fi->parent_ptid is a part of lwp and it is stoped, waitpid the
 516      ptid.  */
 517   if ((!find_thread_ptid (pptid) && find_fork_ptid (pptid))
 518       || (find_thread_ptid (pptid) && is_stopped (pptid)))
 519     {
 520       if (inferior_call_waitpid (pptid, ptid_get_pid (ptid)))
 521         warning (_("Unable to wait pid %s"), target_pid_to_str (ptid));
 522     }
 523 }
 524
 525 static void
 526 detach_checkpoint_command (char *args, int from_tty)
 527 {
 528   ptid_t ptid;
 529
 530   if (!args || !*args)
 531     error (_("Requires argument (checkpoint id to detach)"));
 532
 533   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 534   if (ptid_equal (ptid, minus_one_ptid))
 535     error (_("No such checkpoint id, %s"), args);
 536
 537   if (ptid_equal (ptid, inferior_ptid))
 538     error (_("\
 539 Please switch to another checkpoint before detaching the current one"));
 540
 541   if (ptrace (PTRACE_DETACH, ptid_get_pid (ptid), 0, 0))
 542     error (_("Unable to detach %s"), target_pid_to_str (ptid));
 543
 544   if (from_tty)
 545     printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid));
 546
 547   delete_fork (ptid);
 548 }
 549
 550 /* Print information about currently known checkpoints.  */
 551
 552 static void
 553 info_checkpoints_command (char *arg, int from_tty)
 554 {
 555   struct gdbarch *gdbarch = get_current_arch ();
 556   struct symtab_and_line sal;
 557   struct fork_info *fp;
 558   ULONGEST pc;
 559   int requested = -1;
 560   struct fork_info *printed = NULL;
 561
 562   if (arg && *arg)
 563     requested = (int) parse_and_eval_long (arg);
 564
 565   for (fp = fork_list; fp; fp = fp->next)
 566     {
 567       if (requested > 0 && fp->num != requested)
 568         continue;
 569
 570       printed = fp;
 571       if (ptid_equal (fp->ptid, inferior_ptid))
 572         {
 573           printf_filtered ("* ");
 574           pc = regcache_read_pc (get_current_regcache ());
 575         }
 576       else
 577         {
 578           printf_filtered ("  ");
 579           pc = regcache_read_pc (fp->savedregs);
 580         }
 581       printf_filtered ("%d %s", fp->num, target_pid_to_str (fp->ptid));
 582       if (fp->num == 0)
 583         printf_filtered (_(" (main process)"));
 584       printf_filtered (_(" at "));
 585       fputs_filtered (paddress (gdbarch, pc), gdb_stdout);
 586
 587       sal = find_pc_line (pc, 0);
 588       if (sal.symtab)
 589         printf_filtered (_(", file %s"),
 590                          symtab_to_filename_for_display (sal.symtab));
 591       if (sal.line)
 592         printf_filtered (_(", line %d"), sal.line);
 593       if (!sal.symtab && !sal.line)
 594         {
 595           struct bound_minimal_symbol msym;
 596
 597           msym = lookup_minimal_symbol_by_pc (pc);
 598           if (msym.minsym)
 599             printf_filtered (", <%s>", SYMBOL_LINKAGE_NAME (msym.minsym));
 600         }
 601
 602       putchar_filtered ('\n');
 603     }
 604   if (printed == NULL)
 605     {
 606       if (requested > 0)
 607         printf_filtered (_("No checkpoint number %d.\n"), requested);
 608       else
 609         printf_filtered (_("No checkpoints.\n"));
 610     }
 611 }
 612
 613 /* The PID of the process we're checkpointing.  */
 614 static int checkpointing_pid = 0;
 615
 616 int
 617 linux_fork_checkpointing_p (int pid)
 618 {
 619   return (checkpointing_pid == pid);
 620 }
 621
 622 /* Callback for iterate over threads.  Used to check whether
 623    the current inferior is multi-threaded.  Returns true as soon
 624    as it sees the second thread of the current inferior.  */
 625
 626 static int
 627 inf_has_multiple_thread_cb (struct thread_info *tp, void *data)
 628 {
 629   int *count_p = (int *) data;
 630
 631   if (current_inferior ()->pid == ptid_get_pid (tp->ptid))
 632     (*count_p)++;
 633
 634   /* Stop the iteration if multiple threads have been detected.  */
 635   return *count_p > 1;
 636 }
 637
 638 /* Return true if the current inferior is multi-threaded.  */
 639
 640 static int
 641 inf_has_multiple_threads (void)
 642 {
 643   int count = 0;
 644
 645   iterate_over_threads (inf_has_multiple_thread_cb, &count);
 646   return (count > 1);
 647 }
 648
 649 static void
 650 checkpoint_command (char *args, int from_tty)
 651 {
 652   struct objfile *fork_objf;
 653   struct gdbarch *gdbarch;
 654   struct target_waitstatus last_target_waitstatus;
 655   ptid_t last_target_ptid;
 656   struct value *fork_fn = NULL, *ret;
 657   struct fork_info *fp;
 658   pid_t retpid;
 659   struct cleanup *old_chain;
 660
 661   if (!target_has_execution)
 662     error (_("The program is not being run."));
 663
 664   /* Ensure that the inferior is not multithreaded.  */
 665   update_thread_list ();
 666   if (inf_has_multiple_threads ())
 667     error (_("checkpoint: can't checkpoint multiple threads."));
 668
 669   /* Make the inferior fork, record its (and gdb's) state.  */
 670
 671   if (lookup_minimal_symbol ("fork", NULL, NULL) != NULL)
 672     fork_fn = find_function_in_inferior ("fork", &fork_objf);
 673   if (!fork_fn)
 674     if (lookup_minimal_symbol ("_fork", NULL, NULL) != NULL)
 675       fork_fn = find_function_in_inferior ("fork", &fork_objf);
 676   if (!fork_fn)
 677     error (_("checkpoint: can't find fork function in inferior."));
 678
 679   gdbarch = get_objfile_arch (fork_objf);
 680   ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 681
 682   /* Tell linux-nat.c that we're checkpointing this inferior.  */
 683   old_chain = make_cleanup_restore_integer (&checkpointing_pid);
 684   checkpointing_pid = ptid_get_pid (inferior_ptid);
 685
 686   ret = call_function_by_hand (fork_fn, 0, &ret);
 687   do_cleanups (old_chain);
 688   if (!ret)     /* Probably can't happen.  */
 689     error (_("checkpoint: call_function_by_hand returned null."));
 690
 691   retpid = value_as_long (ret);
 692   get_last_target_status (&last_target_ptid, &last_target_waitstatus);
 693   if (from_tty)
 694     {
 695       int parent_pid;
 696
 697       printf_filtered (_("checkpoint: fork returned pid %ld.\n"),
 698                        (long) retpid);
 699       if (info_verbose)
 700         {
 701           parent_pid = ptid_get_lwp (last_target_ptid);
 702           if (parent_pid == 0)
 703             parent_pid = ptid_get_pid (last_target_ptid);
 704           printf_filtered (_("   gdb says parent = %ld.\n"),
 705                            (long) parent_pid);
 706         }
 707     }
 708
 709   fp = find_fork_pid (retpid);
 710   if (!fp)
 711     error (_("Failed to find new fork"));
 712   fork_save_infrun_state (fp, 1);
 713   fp->parent_ptid = last_target_ptid;
 714 }
 715
 716 static void
 717 linux_fork_context (struct fork_info *newfp, int from_tty)
 718 {
 719   /* Now we attempt to switch processes.  */
 720   struct fork_info *oldfp;
 721
 722   gdb_assert (newfp != NULL);
 723
 724   oldfp = find_fork_ptid (inferior_ptid);
 725   gdb_assert (oldfp != NULL);
 726
 727   fork_save_infrun_state (oldfp, 1);
 728   remove_breakpoints ();
 729   fork_load_infrun_state (newfp);
 730   insert_breakpoints ();
 731
 732   printf_filtered (_("Switching to %s\n"),
 733                    target_pid_to_str (inferior_ptid));
 734
 735   print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC, 1);
 736 }
 737
 738 /* Switch inferior process (checkpoint) context, by checkpoint id.  */
 739 static void
 740 restart_command (char *args, int from_tty)
 741 {
 742   struct fork_info *fp;
 743
 744   if (!args || !*args)
 745     error (_("Requires argument (checkpoint id to restart)"));
 746
 747   if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
 748     error (_("Not found: checkpoint id %s"), args);
 749
 750   linux_fork_context (fp, from_tty);
 751 }
 752
 753 void
 754 _initialize_linux_fork (void)
 755 {
 756   init_fork_list ();
 757
 758   /* Checkpoint command: create a fork of the inferior process
 759      and set it aside for later debugging.  */
 760
 761   add_com ("checkpoint", class_obscure, checkpoint_command, _("\
 762 Fork a duplicate process (experimental)."));
 763
 764   /* Restart command: restore the context of a specified checkpoint
 765      process.  */
 766
 767   add_com ("restart", class_obscure, restart_command, _("\
 768 restart <n>: restore program context from a checkpoint.\n\
 769 Argument 'n' is checkpoint ID, as displayed by 'info checkpoints'."));
 770
 771   /* Delete checkpoint command: kill the process and remove it from
 772      the fork list.  */
 773
 774   add_cmd ("checkpoint", class_obscure, delete_checkpoint_command, _("\
 775 Delete a checkpoint (experimental)."),
 776            &deletelist);
 777
 778   /* Detach checkpoint command: release the process to run independently,
 779      and remove it from the fork list.  */
 780
 781   add_cmd ("checkpoint", class_obscure, detach_checkpoint_command, _("\
 782 Detach from a checkpoint (experimental)."),
 783            &detachlist);
 784
 785   /* Info checkpoints command: list all forks/checkpoints
 786      currently under gdb's control.  */
 787
 788   add_info ("checkpoints", info_checkpoints_command,
 789             _("IDs of currently known checkpoints."));
 790 }