gdb/linux-fork.c

   1 /* GNU/Linux native-dependent code for debugging multiple forks.
   2
   3    Copyright (C) 2005-2020 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 "infrun.h"
  24 #include "regcache.h"
  25 #include "gdbcmd.h"
  26 #include "infcall.h"
  27 #include "objfiles.h"
  28 #include "linux-fork.h"
  29 #include "linux-nat.h"
  30 #include "gdbthread.h"
  31 #include "source.h"
  32
  33 #include "nat/gdb_ptrace.h"
  34 #include "gdbsupport/gdb_wait.h"
  35 #include <dirent.h>
  36 #include <ctype.h>
  37
  38 #include <list>
  39
  40 /* Fork list data structure:  */
  41 struct fork_info
  42 {
  43   explicit fork_info (pid_t pid)
  44     : ptid (pid, pid, 0)
  45   {
  46   }
  47
  48   ~fork_info ()
  49   {
  50     /* Notes on step-resume breakpoints: since this is a concern for
  51        threads, let's convince ourselves that it's not a concern for
  52        forks.  There are two ways for a fork_info to be created.
  53        First, by the checkpoint command, in which case we're at a gdb
  54        prompt and there can't be any step-resume breakpoint.  Second,
  55        by a fork in the user program, in which case we *may* have
  56        stepped into the fork call, but regardless of whether we follow
  57        the parent or the child, we will return to the same place and
  58        the step-resume breakpoint, if any, will take care of itself as
  59        usual.  And unlike threads, we do not save a private copy of
  60        the step-resume breakpoint -- so we're OK.  */
  61
  62     if (savedregs)
  63       delete savedregs;
  64     if (filepos)
  65       xfree (filepos);
  66   }
  67
  68   ptid_t ptid = null_ptid;
  69   ptid_t parent_ptid = null_ptid;
  70
  71   /* Convenient handle (GDB fork id).  */
  72   int num = 0;
  73
  74   /* Convenient for info fork, saves having to actually switch
  75      contexts.  */
  76   readonly_detached_regcache *savedregs = nullptr;
  77
  78   CORE_ADDR pc = 0;
  79
  80   /* Set of open file descriptors' offsets.  */
  81   off_t *filepos = nullptr;
  82
  83   int maxfd = 0;
  84 };
  85
  86 static std::list<fork_info> fork_list;
  87 static int highest_fork_num;
  88
  89 /* Fork list methods:  */
  90
  91 int
  92 forks_exist_p (void)
  93 {
  94   return !fork_list.empty ();
  95 }
  96
  97 /* Return the last fork in the list.  */
  98
  99 static struct fork_info *
 100 find_last_fork (void)
 101 {
 102   if (fork_list.empty ())
 103     return NULL;
 104
 105   return &fork_list.back ();
 106 }
 107
 108 /* Return true iff there's one fork in the list.  */
 109
 110 static bool
 111 one_fork_p ()
 112 {
 113   return fork_list.size () == 1;
 114 }
 115
 116 /* Add a new fork to the internal fork list.  */
 117
 118 void
 119 add_fork (pid_t pid)
 120 {
 121   fork_list.emplace_back (pid);
 122
 123   if (one_fork_p ())
 124     highest_fork_num = 0;
 125
 126   fork_info *fp = &fork_list.back ();
 127   fp->num = ++highest_fork_num;
 128 }
 129
 130 static void
 131 delete_fork (ptid_t ptid)
 132 {
 133   linux_target->low_forget_process (ptid.pid ());
 134
 135   for (auto it = fork_list.begin (); it != fork_list.end (); ++it)
 136     if (it->ptid == ptid)
 137       {
 138         fork_list.erase (it);
 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 (one_fork_p () && fork_list.front ().ptid == inferior_ptid)
 145           {
 146             /* Last fork -- delete from list and handle as solo
 147                process (should be a safe recursion).  */
 148             delete_fork (inferior_ptid);
 149           }
 150         return;
 151       }
 152 }
 153
 154 /* Find a fork_info by matching PTID.  */
 155 static struct fork_info *
 156 find_fork_ptid (ptid_t ptid)
 157 {
 158   for (fork_info &fi : fork_list)
 159     if (fi.ptid == ptid)
 160       return &fi;
 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   for (fork_info &fi : fork_list)
 170     if (fi.num == num)
 171       return &fi;
 172
 173   return NULL;
 174 }
 175
 176 /* Find a fork_info by matching pid.  */
 177 extern struct fork_info *
 178 find_fork_pid (pid_t pid)
 179 {
 180   for (fork_info &fi : fork_list)
 181     if (pid == fi.ptid.pid ())
 182       return &fi;
 183
 184   return NULL;
 185 }
 186
 187 static ptid_t
 188 fork_id_to_ptid (int num)
 189 {
 190   struct fork_info *fork = find_fork_id (num);
 191   if (fork)
 192     return fork->ptid;
 193   else
 194     return ptid_t (-1);
 195 }
 196
 197 /* Fork list <-> gdb interface.  */
 198
 199 /* Utility function for fork_load/fork_save.
 200    Calls lseek in the (current) inferior process.  */
 201
 202 static off_t
 203 call_lseek (int fd, off_t offset, int whence)
 204 {
 205   char exp[80];
 206
 207   snprintf (&exp[0], sizeof (exp), "(long) lseek (%d, %ld, %d)",
 208             fd, (long) offset, whence);
 209   return (off_t) parse_and_eval_long (&exp[0]);
 210 }
 211
 212 /* Load infrun state for the fork PTID.  */
 213
 214 static void
 215 fork_load_infrun_state (struct fork_info *fp)
 216 {
 217   int i;
 218
 219   linux_nat_switch_fork (fp->ptid);
 220
 221   if (fp->savedregs)
 222     get_current_regcache ()->restore (fp->savedregs);
 223
 224   registers_changed ();
 225   reinit_frame_cache ();
 226
 227   inferior_thread ()->suspend.stop_pc
 228     = regcache_read_pc (get_current_regcache ());
 229   nullify_last_target_wait_ptid ();
 230
 231   /* Now restore the file positions of open file descriptors.  */
 232   if (fp->filepos)
 233     {
 234       for (i = 0; i <= fp->maxfd; i++)
 235         if (fp->filepos[i] != (off_t) -1)
 236           call_lseek (i, fp->filepos[i], SEEK_SET);
 237       /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
 238          this is native-only.  If it ever has to be cross, we'll have
 239          to rethink this.  */
 240     }
 241 }
 242
 243 /* Save infrun state for the fork FP.  */
 244
 245 static void
 246 fork_save_infrun_state (struct fork_info *fp)
 247 {
 248   char path[PATH_MAX];
 249   struct dirent *de;
 250   DIR *d;
 251
 252   if (fp->savedregs)
 253     delete fp->savedregs;
 254
 255   fp->savedregs = new readonly_detached_regcache (*get_current_regcache ());
 256   fp->pc = regcache_read_pc (get_current_regcache ());
 257
 258   /* Now save the 'state' (file position) of all open file descriptors.
 259      Unfortunately fork does not take care of that for us...  */
 260   snprintf (path, PATH_MAX, "/proc/%ld/fd", (long) fp->ptid.pid ());
 261   if ((d = opendir (path)) != NULL)
 262     {
 263       long tmp;
 264
 265       fp->maxfd = 0;
 266       while ((de = readdir (d)) != NULL)
 267         {
 268           /* Count open file descriptors (actually find highest
 269              numbered).  */
 270           tmp = strtol (&de->d_name[0], NULL, 10);
 271           if (fp->maxfd < tmp)
 272             fp->maxfd = tmp;
 273         }
 274       /* Allocate array of file positions.  */
 275       fp->filepos = XRESIZEVEC (off_t, fp->filepos, fp->maxfd + 1);
 276
 277       /* Initialize to -1 (invalid).  */
 278       for (tmp = 0; tmp <= fp->maxfd; tmp++)
 279         fp->filepos[tmp] = -1;
 280
 281       /* Now find actual file positions.  */
 282       rewinddir (d);
 283       while ((de = readdir (d)) != NULL)
 284         if (isdigit (de->d_name[0]))
 285           {
 286             tmp = strtol (&de->d_name[0], NULL, 10);
 287             fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
 288           }
 289       closedir (d);
 290     }
 291 }
 292
 293 /* Kill 'em all, let God sort 'em out...  */
 294
 295 void
 296 linux_fork_killall (void)
 297 {
 298   /* Walk list and kill every pid.  No need to treat the
 299      current inferior_ptid as special (we do not return a
 300      status for it) -- however any process may be a child
 301      or a parent, so may get a SIGCHLD from a previously
 302      killed child.  Wait them all out.  */
 303
 304   for (fork_info &fi : fork_list)
 305     {
 306       pid_t pid = fi.ptid.pid ();
 307       int status;
 308       pid_t ret;
 309       do {
 310         /* Use SIGKILL instead of PTRACE_KILL because the former works even
 311            if the thread is running, while the later doesn't.  */
 312         kill (pid, SIGKILL);
 313         ret = waitpid (pid, &status, 0);
 314         /* We might get a SIGCHLD instead of an exit status.  This is
 315          aggravated by the first kill above - a child has just
 316          died.  MVS comment cut-and-pasted from linux-nat.  */
 317       } while (ret == pid && WIFSTOPPED (status));
 318     }
 319
 320   /* Clear list, prepare to start fresh.  */
 321   fork_list.clear ();
 322 }
 323
 324 /* The current inferior_ptid has exited, but there are other viable
 325    forks to debug.  Delete the exiting one and context-switch to the
 326    first available.  */
 327
 328 void
 329 linux_fork_mourn_inferior (void)
 330 {
 331   struct fork_info *last;
 332   int status;
 333
 334   /* Wait just one more time to collect the inferior's exit status.
 335      Do not check whether this succeeds though, since we may be
 336      dealing with a process that we attached to.  Such a process will
 337      only report its exit status to its original parent.  */
 338   waitpid (inferior_ptid.pid (), &status, 0);
 339
 340   /* OK, presumably inferior_ptid is the one who has exited.
 341      We need to delete that one from the fork_list, and switch
 342      to the next available fork.  */
 343   delete_fork (inferior_ptid);
 344
 345   /* There should still be a fork - if there's only one left,
 346      delete_fork won't remove it, because we haven't updated
 347      inferior_ptid yet.  */
 348   gdb_assert (!fork_list.empty ());
 349
 350   last = find_last_fork ();
 351   fork_load_infrun_state (last);
 352   printf_filtered (_("[Switching to %s]\n"),
 353                    target_pid_to_str (inferior_ptid).c_str ());
 354
 355   /* If there's only one fork, switch back to non-fork mode.  */
 356   if (one_fork_p ())
 357     delete_fork (inferior_ptid);
 358 }
 359
 360 /* The current inferior_ptid is being detached, but there are other
 361    viable forks to debug.  Detach and delete it and context-switch to
 362    the first available.  */
 363
 364 void
 365 linux_fork_detach (int from_tty)
 366 {
 367   /* OK, inferior_ptid is the one we are detaching from.  We need to
 368      delete it from the fork_list, and switch to the next available
 369      fork.  */
 370
 371   if (ptrace (PTRACE_DETACH, inferior_ptid.pid (), 0, 0))
 372     error (_("Unable to detach %s"),
 373            target_pid_to_str (inferior_ptid).c_str ());
 374
 375   delete_fork (inferior_ptid);
 376
 377   /* There should still be a fork - if there's only one left,
 378      delete_fork won't remove it, because we haven't updated
 379      inferior_ptid yet.  */
 380   gdb_assert (!fork_list.empty ());
 381
 382   fork_load_infrun_state (&fork_list.front ());
 383
 384   if (from_tty)
 385     printf_filtered (_("[Switching to %s]\n"),
 386                      target_pid_to_str (inferior_ptid).c_str ());
 387
 388   /* If there's only one fork, switch back to non-fork mode.  */
 389   if (one_fork_p ())
 390     delete_fork (inferior_ptid);
 391 }
 392
 393 /* Temporarily switch to the infrun state stored on the fork_info
 394    identified by a given ptid_t.  When this object goes out of scope,
 395    restore the currently selected infrun state.   */
 396
 397 class scoped_switch_fork_info
 398 {
 399 public:
 400   /* Switch to the infrun state held on the fork_info identified by
 401      PPTID.  If PPTID is the current inferior then no switch is done.  */
 402   explicit scoped_switch_fork_info (ptid_t pptid)
 403     : m_oldfp (nullptr)
 404   {
 405     if (pptid != inferior_ptid)
 406       {
 407         struct fork_info *newfp = nullptr;
 408
 409         /* Switch to pptid.  */
 410         m_oldfp = find_fork_ptid (inferior_ptid);
 411         gdb_assert (m_oldfp != nullptr);
 412         newfp = find_fork_ptid (pptid);
 413         gdb_assert (newfp != nullptr);
 414         fork_save_infrun_state (m_oldfp);
 415         remove_breakpoints ();
 416         fork_load_infrun_state (newfp);
 417         insert_breakpoints ();
 418       }
 419   }
 420
 421   /* Restore the previously selected infrun state.  If the constructor
 422      didn't need to switch states, then nothing is done here either.  */
 423   ~scoped_switch_fork_info ()
 424   {
 425     if (m_oldfp != nullptr)
 426       {
 427         /* Switch back to inferior_ptid.  */
 428         try
 429           {
 430             remove_breakpoints ();
 431             fork_load_infrun_state (m_oldfp);
 432             insert_breakpoints ();
 433           }
 434         catch (const gdb_exception &ex)
 435           {
 436             warning (_("Couldn't restore checkpoint state in %s: %s"),
 437                      target_pid_to_str (m_oldfp->ptid).c_str (),
 438                      ex.what ());
 439           }
 440       }
 441   }
 442
 443   DISABLE_COPY_AND_ASSIGN (scoped_switch_fork_info);
 444
 445 private:
 446   /* The fork_info for the previously selected infrun state, or nullptr if
 447      we were already in the desired state, and nothing needs to be
 448      restored.  */
 449   struct fork_info *m_oldfp;
 450 };
 451
 452 static int
 453 inferior_call_waitpid (ptid_t pptid, int pid)
 454 {
 455   struct objfile *waitpid_objf;
 456   struct value *waitpid_fn = NULL;
 457   int ret = -1;
 458
 459   scoped_switch_fork_info switch_fork_info (pptid);
 460
 461   /* Get the waitpid_fn.  */
 462   if (lookup_minimal_symbol ("waitpid", NULL, NULL).minsym != NULL)
 463     waitpid_fn = find_function_in_inferior ("waitpid", &waitpid_objf);
 464   if (!waitpid_fn
 465       && lookup_minimal_symbol ("_waitpid", NULL, NULL).minsym != NULL)
 466     waitpid_fn = find_function_in_inferior ("_waitpid", &waitpid_objf);
 467   if (waitpid_fn != nullptr)
 468     {
 469       struct gdbarch *gdbarch = get_current_arch ();
 470       struct value *argv[3], *retv;
 471
 472       /* Get the argv.  */
 473       argv[0] = value_from_longest (builtin_type (gdbarch)->builtin_int, pid);
 474       argv[1] = value_from_pointer (builtin_type (gdbarch)->builtin_data_ptr, 0);
 475       argv[2] = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 476
 477       retv = call_function_by_hand (waitpid_fn, NULL, argv);
 478
 479       if (value_as_long (retv) >= 0)
 480         ret = 0;
 481     }
 482
 483   return ret;
 484 }
 485
 486 /* Fork list <-> user interface.  */
 487
 488 static void
 489 delete_checkpoint_command (const char *args, int from_tty)
 490 {
 491   ptid_t ptid, pptid;
 492   struct fork_info *fi;
 493
 494   if (!args || !*args)
 495     error (_("Requires argument (checkpoint id to delete)"));
 496
 497   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 498   if (ptid == minus_one_ptid)
 499     error (_("No such checkpoint id, %s"), args);
 500
 501   if (ptid == inferior_ptid)
 502     error (_("\
 503 Please switch to another checkpoint before deleting the current one"));
 504
 505   if (ptrace (PTRACE_KILL, ptid.pid (), 0, 0))
 506     error (_("Unable to kill pid %s"), target_pid_to_str (ptid).c_str ());
 507
 508   fi = find_fork_ptid (ptid);
 509   gdb_assert (fi);
 510   pptid = fi->parent_ptid;
 511
 512   if (from_tty)
 513     printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid).c_str ());
 514
 515   delete_fork (ptid);
 516
 517   /* If fi->parent_ptid is not a part of lwp but it's a part of checkpoint
 518      list, waitpid the ptid.
 519      If fi->parent_ptid is a part of lwp and it is stopped, waitpid the
 520      ptid.  */
 521   thread_info *parent = find_thread_ptid (linux_target, pptid);
 522   if ((parent == NULL && find_fork_ptid (pptid))
 523       || (parent != NULL && parent->state == THREAD_STOPPED))
 524     {
 525       if (inferior_call_waitpid (pptid, ptid.pid ()))
 526         warning (_("Unable to wait pid %s"),
 527                  target_pid_to_str (ptid).c_str ());
 528     }
 529 }
 530
 531 static void
 532 detach_checkpoint_command (const char *args, int from_tty)
 533 {
 534   ptid_t ptid;
 535
 536   if (!args || !*args)
 537     error (_("Requires argument (checkpoint id to detach)"));
 538
 539   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 540   if (ptid == minus_one_ptid)
 541     error (_("No such checkpoint id, %s"), args);
 542
 543   if (ptid == inferior_ptid)
 544     error (_("\
 545 Please switch to another checkpoint before detaching the current one"));
 546
 547   if (ptrace (PTRACE_DETACH, ptid.pid (), 0, 0))
 548     error (_("Unable to detach %s"), target_pid_to_str (ptid).c_str ());
 549
 550   if (from_tty)
 551     printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid).c_str ());
 552
 553   delete_fork (ptid);
 554 }
 555
 556 /* Print information about currently known checkpoints.  */
 557
 558 static void
 559 info_checkpoints_command (const char *arg, int from_tty)
 560 {
 561   struct gdbarch *gdbarch = get_current_arch ();
 562   int requested = -1;
 563   const fork_info *printed = NULL;
 564
 565   if (arg && *arg)
 566     requested = (int) parse_and_eval_long (arg);
 567
 568   for (const fork_info &fi : fork_list)
 569     {
 570       if (requested > 0 && fi.num != requested)
 571         continue;
 572
 573       printed = &fi;
 574       if (fi.ptid == inferior_ptid)
 575         printf_filtered ("* ");
 576       else
 577         printf_filtered ("  ");
 578
 579       ULONGEST pc = fi.pc;
 580       printf_filtered ("%d %s", fi.num, target_pid_to_str (fi.ptid).c_str ());
 581       if (fi.num == 0)
 582         printf_filtered (_(" (main process)"));
 583       printf_filtered (_(" at "));
 584       fputs_filtered (paddress (gdbarch, pc), gdb_stdout);
 585
 586       symtab_and_line sal = find_pc_line (pc, 0);
 587       if (sal.symtab)
 588         printf_filtered (_(", file %s"),
 589                          symtab_to_filename_for_display (sal.symtab));
 590       if (sal.line)
 591         printf_filtered (_(", line %d"), sal.line);
 592       if (!sal.symtab && !sal.line)
 593         {
 594           struct bound_minimal_symbol msym;
 595
 596           msym = lookup_minimal_symbol_by_pc (pc);
 597           if (msym.minsym)
 598             printf_filtered (", <%s>", msym.minsym->linkage_name ());
 599         }
 600
 601       putchar_filtered ('\n');
 602     }
 603   if (printed == NULL)
 604     {
 605       if (requested > 0)
 606         printf_filtered (_("No checkpoint number %d.\n"), requested);
 607       else
 608         printf_filtered (_("No checkpoints.\n"));
 609     }
 610 }
 611
 612 /* The PID of the process we're checkpointing.  */
 613 static int checkpointing_pid = 0;
 614
 615 int
 616 linux_fork_checkpointing_p (int pid)
 617 {
 618   return (checkpointing_pid == pid);
 619 }
 620
 621 /* Return true if the current inferior is multi-threaded.  */
 622
 623 static bool
 624 inf_has_multiple_threads ()
 625 {
 626   int count = 0;
 627
 628   /* Return true as soon as we see the second thread of the current
 629      inferior.  */
 630   for (thread_info *tp ATTRIBUTE_UNUSED : current_inferior ()->threads ())
 631     if (++count > 1)
 632       return true;
 633
 634   return false;
 635 }
 636
 637 static void
 638 checkpoint_command (const char *args, int from_tty)
 639 {
 640   struct objfile *fork_objf;
 641   struct gdbarch *gdbarch;
 642   struct target_waitstatus last_target_waitstatus;
 643   ptid_t last_target_ptid;
 644   struct value *fork_fn = NULL, *ret;
 645   struct fork_info *fp;
 646   pid_t retpid;
 647
 648   if (!target_has_execution)
 649     error (_("The program is not being run."));
 650
 651   /* Ensure that the inferior is not multithreaded.  */
 652   update_thread_list ();
 653   if (inf_has_multiple_threads ())
 654     error (_("checkpoint: can't checkpoint multiple threads."));
 655
 656   /* Make the inferior fork, record its (and gdb's) state.  */
 657
 658   if (lookup_minimal_symbol ("fork", NULL, NULL).minsym != NULL)
 659     fork_fn = find_function_in_inferior ("fork", &fork_objf);
 660   if (!fork_fn)
 661     if (lookup_minimal_symbol ("_fork", NULL, NULL).minsym != NULL)
 662       fork_fn = find_function_in_inferior ("fork", &fork_objf);
 663   if (!fork_fn)
 664     error (_("checkpoint: can't find fork function in inferior."));
 665
 666   gdbarch = get_objfile_arch (fork_objf);
 667   ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 668
 669   /* Tell linux-nat.c that we're checkpointing this inferior.  */
 670   {
 671     scoped_restore save_pid
 672       = make_scoped_restore (&checkpointing_pid, inferior_ptid.pid ());
 673
 674     ret = call_function_by_hand (fork_fn, NULL, {});
 675   }
 676
 677   if (!ret)     /* Probably can't happen.  */
 678     error (_("checkpoint: call_function_by_hand returned null."));
 679
 680   retpid = value_as_long (ret);
 681   get_last_target_status (nullptr, &last_target_ptid, &last_target_waitstatus);
 682
 683   fp = find_fork_pid (retpid);
 684
 685   if (from_tty)
 686     {
 687       int parent_pid;
 688
 689       printf_filtered (_("checkpoint %d: fork returned pid %ld.\n"),
 690                        fp != NULL ? fp->num : -1, (long) retpid);
 691       if (info_verbose)
 692         {
 693           parent_pid = last_target_ptid.lwp ();
 694           if (parent_pid == 0)
 695             parent_pid = last_target_ptid.pid ();
 696           printf_filtered (_("   gdb says parent = %ld.\n"),
 697                            (long) parent_pid);
 698         }
 699     }
 700
 701   if (!fp)
 702     error (_("Failed to find new fork"));
 703
 704   if (one_fork_p ())
 705     {
 706       /* Special case -- if this is the first fork in the list (the
 707          list was hitherto empty), then add inferior_ptid first, as a
 708          special zeroeth fork id.  */
 709       fork_list.emplace_front (inferior_ptid.pid ());
 710     }
 711
 712   fork_save_infrun_state (fp);
 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);
 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).c_str ());
 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 (const 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 _initialize_linux_fork ();
 754 void
 755 _initialize_linux_fork ()
 756 {
 757   /* Checkpoint command: create a fork of the inferior process
 758      and set it aside for later debugging.  */
 759
 760   add_com ("checkpoint", class_obscure, checkpoint_command, _("\
 761 Fork a duplicate process (experimental)."));
 762
 763   /* Restart command: restore the context of a specified checkpoint
 764      process.  */
 765
 766   add_com ("restart", class_obscure, restart_command, _("\
 767 Restore program context from a checkpoint.\n\
 768 Usage: restart N\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 }