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.empty ()
 114           && &fork_list.front () == &fork_list.back ());
 115 }
 116
 117 /* Add a new fork to the internal fork list.  */
 118
 119 void
 120 add_fork (pid_t pid)
 121 {
 122   fork_list.emplace_back (pid);
 123
 124   if (one_fork_p ())
 125     highest_fork_num = 0;
 126
 127   fork_info *fp = &fork_list.back ();
 128   fp->num = ++highest_fork_num;
 129 }
 130
 131 static void
 132 delete_fork (ptid_t ptid)
 133 {
 134   linux_target->low_forget_process (ptid.pid ());
 135
 136   for (auto it = fork_list.begin (); it != fork_list.end (); ++it)
 137     if (it->ptid == ptid)
 138       {
 139         fork_list.erase (it);
 140
 141         /* Special case: if there is now only one process in the list,
 142            and if it is (hopefully!) the current inferior_ptid, then
 143            remove it, leaving the list empty -- we're now down to the
 144            default case of debugging a single process.  */
 145         if (one_fork_p () && fork_list.front ().ptid == inferior_ptid)
 146           {
 147             /* Last fork -- delete from list and handle as solo
 148                process (should be a safe recursion).  */
 149             delete_fork (inferior_ptid);
 150           }
 151         return;
 152       }
 153 }
 154
 155 /* Find a fork_info by matching PTID.  */
 156 static struct fork_info *
 157 find_fork_ptid (ptid_t ptid)
 158 {
 159   for (fork_info &fi : fork_list)
 160     if (fi.ptid == ptid)
 161       return &fi;
 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   for (fork_info &fi : fork_list)
 171     if (fi.num == num)
 172       return &fi;
 173
 174   return NULL;
 175 }
 176
 177 /* Find a fork_info by matching pid.  */
 178 extern struct fork_info *
 179 find_fork_pid (pid_t pid)
 180 {
 181   for (fork_info &fi : fork_list)
 182     if (pid == fi.ptid.pid ())
 183       return &fi;
 184
 185   return NULL;
 186 }
 187
 188 static ptid_t
 189 fork_id_to_ptid (int num)
 190 {
 191   struct fork_info *fork = find_fork_id (num);
 192   if (fork)
 193     return fork->ptid;
 194   else
 195     return ptid_t (-1);
 196 }
 197
 198 /* Fork list <-> gdb interface.  */
 199
 200 /* Utility function for fork_load/fork_save.
 201    Calls lseek in the (current) inferior process.  */
 202
 203 static off_t
 204 call_lseek (int fd, off_t offset, int whence)
 205 {
 206   char exp[80];
 207
 208   snprintf (&exp[0], sizeof (exp), "(long) lseek (%d, %ld, %d)",
 209             fd, (long) offset, whence);
 210   return (off_t) parse_and_eval_long (&exp[0]);
 211 }
 212
 213 /* Load infrun state for the fork PTID.  */
 214
 215 static void
 216 fork_load_infrun_state (struct fork_info *fp)
 217 {
 218   int i;
 219
 220   linux_nat_switch_fork (fp->ptid);
 221
 222   if (fp->savedregs)
 223     get_current_regcache ()->restore (fp->savedregs);
 224
 225   registers_changed ();
 226   reinit_frame_cache ();
 227
 228   inferior_thread ()->suspend.stop_pc
 229     = regcache_read_pc (get_current_regcache ());
 230   nullify_last_target_wait_ptid ();
 231
 232   /* Now restore the file positions of open file descriptors.  */
 233   if (fp->filepos)
 234     {
 235       for (i = 0; i <= fp->maxfd; i++)
 236         if (fp->filepos[i] != (off_t) -1)
 237           call_lseek (i, fp->filepos[i], SEEK_SET);
 238       /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
 239          this is native-only.  If it ever has to be cross, we'll have
 240          to rethink this.  */
 241     }
 242 }
 243
 244 /* Save infrun state for the fork FP.  */
 245
 246 static void
 247 fork_save_infrun_state (struct fork_info *fp)
 248 {
 249   char path[PATH_MAX];
 250   struct dirent *de;
 251   DIR *d;
 252
 253   if (fp->savedregs)
 254     delete fp->savedregs;
 255
 256   fp->savedregs = new readonly_detached_regcache (*get_current_regcache ());
 257   fp->pc = regcache_read_pc (get_current_regcache ());
 258
 259   /* Now save the 'state' (file position) of all open file descriptors.
 260      Unfortunately fork does not take care of that for us...  */
 261   snprintf (path, PATH_MAX, "/proc/%ld/fd", (long) fp->ptid.pid ());
 262   if ((d = opendir (path)) != NULL)
 263     {
 264       long tmp;
 265
 266       fp->maxfd = 0;
 267       while ((de = readdir (d)) != NULL)
 268         {
 269           /* Count open file descriptors (actually find highest
 270              numbered).  */
 271           tmp = strtol (&de->d_name[0], NULL, 10);
 272           if (fp->maxfd < tmp)
 273             fp->maxfd = tmp;
 274         }
 275       /* Allocate array of file positions.  */
 276       fp->filepos = XRESIZEVEC (off_t, fp->filepos, fp->maxfd + 1);
 277
 278       /* Initialize to -1 (invalid).  */
 279       for (tmp = 0; tmp <= fp->maxfd; tmp++)
 280         fp->filepos[tmp] = -1;
 281
 282       /* Now find actual file positions.  */
 283       rewinddir (d);
 284       while ((de = readdir (d)) != NULL)
 285         if (isdigit (de->d_name[0]))
 286           {
 287             tmp = strtol (&de->d_name[0], NULL, 10);
 288             fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
 289           }
 290       closedir (d);
 291     }
 292 }
 293
 294 /* Kill 'em all, let God sort 'em out...  */
 295
 296 void
 297 linux_fork_killall (void)
 298 {
 299   /* Walk list and kill every pid.  No need to treat the
 300      current inferior_ptid as special (we do not return a
 301      status for it) -- however any process may be a child
 302      or a parent, so may get a SIGCHLD from a previously
 303      killed child.  Wait them all out.  */
 304
 305   for (fork_info &fi : fork_list)
 306     {
 307       pid_t pid = fi.ptid.pid ();
 308       int status;
 309       pid_t ret;
 310       do {
 311         /* Use SIGKILL instead of PTRACE_KILL because the former works even
 312            if the thread is running, while the later doesn't.  */
 313         kill (pid, SIGKILL);
 314         ret = waitpid (pid, &status, 0);
 315         /* We might get a SIGCHLD instead of an exit status.  This is
 316          aggravated by the first kill above - a child has just
 317          died.  MVS comment cut-and-pasted from linux-nat.  */
 318       } while (ret == pid && WIFSTOPPED (status));
 319     }
 320
 321   /* Clear list, prepare to start fresh.  */
 322   fork_list.clear ();
 323 }
 324
 325 /* The current inferior_ptid has exited, but there are other viable
 326    forks to debug.  Delete the exiting one and context-switch to the
 327    first available.  */
 328
 329 void
 330 linux_fork_mourn_inferior (void)
 331 {
 332   struct fork_info *last;
 333   int status;
 334
 335   /* Wait just one more time to collect the inferior's exit status.
 336      Do not check whether this succeeds though, since we may be
 337      dealing with a process that we attached to.  Such a process will
 338      only report its exit status to its original parent.  */
 339   waitpid (inferior_ptid.pid (), &status, 0);
 340
 341   /* OK, presumably inferior_ptid is the one who has exited.
 342      We need to delete that one from the fork_list, and switch
 343      to the next available fork.  */
 344   delete_fork (inferior_ptid);
 345
 346   /* There should still be a fork - if there's only one left,
 347      delete_fork won't remove it, because we haven't updated
 348      inferior_ptid yet.  */
 349   gdb_assert (!fork_list.empty ());
 350
 351   last = find_last_fork ();
 352   fork_load_infrun_state (last);
 353   printf_filtered (_("[Switching to %s]\n"),
 354                    target_pid_to_str (inferior_ptid).c_str ());
 355
 356   /* If there's only one fork, switch back to non-fork mode.  */
 357   if (one_fork_p ())
 358     delete_fork (inferior_ptid);
 359 }
 360
 361 /* The current inferior_ptid is being detached, but there are other
 362    viable forks to debug.  Detach and delete it and context-switch to
 363    the first available.  */
 364
 365 void
 366 linux_fork_detach (int from_tty)
 367 {
 368   /* OK, inferior_ptid is the one we are detaching from.  We need to
 369      delete it from the fork_list, and switch to the next available
 370      fork.  */
 371
 372   if (ptrace (PTRACE_DETACH, inferior_ptid.pid (), 0, 0))
 373     error (_("Unable to detach %s"),
 374            target_pid_to_str (inferior_ptid).c_str ());
 375
 376   delete_fork (inferior_ptid);
 377
 378   /* There should still be a fork - if there's only one left,
 379      delete_fork won't remove it, because we haven't updated
 380      inferior_ptid yet.  */
 381   gdb_assert (!fork_list.empty ());
 382
 383   fork_load_infrun_state (&fork_list.front ());
 384
 385   if (from_tty)
 386     printf_filtered (_("[Switching to %s]\n"),
 387                      target_pid_to_str (inferior_ptid).c_str ());
 388
 389   /* If there's only one fork, switch back to non-fork mode.  */
 390   if (one_fork_p ())
 391     delete_fork (inferior_ptid);
 392 }
 393
 394 /* Temporarily switch to the infrun state stored on the fork_info
 395    identified by a given ptid_t.  When this object goes out of scope,
 396    restore the currently selected infrun state.   */
 397
 398 class scoped_switch_fork_info
 399 {
 400 public:
 401   /* Switch to the infrun state held on the fork_info identified by
 402      PPTID.  If PPTID is the current inferior then no switch is done.  */
 403   explicit scoped_switch_fork_info (ptid_t pptid)
 404     : m_oldfp (nullptr)
 405   {
 406     if (pptid != inferior_ptid)
 407       {
 408         struct fork_info *newfp = nullptr;
 409
 410         /* Switch to pptid.  */
 411         m_oldfp = find_fork_ptid (inferior_ptid);
 412         gdb_assert (m_oldfp != nullptr);
 413         newfp = find_fork_ptid (pptid);
 414         gdb_assert (newfp != nullptr);
 415         fork_save_infrun_state (m_oldfp);
 416         remove_breakpoints ();
 417         fork_load_infrun_state (newfp);
 418         insert_breakpoints ();
 419       }
 420   }
 421
 422   /* Restore the previously selected infrun state.  If the constructor
 423      didn't need to switch states, then nothing is done here either.  */
 424   ~scoped_switch_fork_info ()
 425   {
 426     if (m_oldfp != nullptr)
 427       {
 428         /* Switch back to inferior_ptid.  */
 429         try
 430           {
 431             remove_breakpoints ();
 432             fork_load_infrun_state (m_oldfp);
 433             insert_breakpoints ();
 434           }
 435         catch (const gdb_exception &ex)
 436           {
 437             warning (_("Couldn't restore checkpoint state in %s: %s"),
 438                      target_pid_to_str (m_oldfp->ptid).c_str (),
 439                      ex.what ());
 440           }
 441       }
 442   }
 443
 444   DISABLE_COPY_AND_ASSIGN (scoped_switch_fork_info);
 445
 446 private:
 447   /* The fork_info for the previously selected infrun state, or nullptr if
 448      we were already in the desired state, and nothing needs to be
 449      restored.  */
 450   struct fork_info *m_oldfp;
 451 };
 452
 453 static int
 454 inferior_call_waitpid (ptid_t pptid, int pid)
 455 {
 456   struct objfile *waitpid_objf;
 457   struct value *waitpid_fn = NULL;
 458   int ret = -1;
 459
 460   scoped_switch_fork_info switch_fork_info (pptid);
 461
 462   /* Get the waitpid_fn.  */
 463   if (lookup_minimal_symbol ("waitpid", NULL, NULL).minsym != NULL)
 464     waitpid_fn = find_function_in_inferior ("waitpid", &waitpid_objf);
 465   if (!waitpid_fn
 466       && lookup_minimal_symbol ("_waitpid", NULL, NULL).minsym != NULL)
 467     waitpid_fn = find_function_in_inferior ("_waitpid", &waitpid_objf);
 468   if (waitpid_fn != nullptr)
 469     {
 470       struct gdbarch *gdbarch = get_current_arch ();
 471       struct value *argv[3], *retv;
 472
 473       /* Get the argv.  */
 474       argv[0] = value_from_longest (builtin_type (gdbarch)->builtin_int, pid);
 475       argv[1] = value_from_pointer (builtin_type (gdbarch)->builtin_data_ptr, 0);
 476       argv[2] = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 477
 478       retv = call_function_by_hand (waitpid_fn, NULL, argv);
 479
 480       if (value_as_long (retv) >= 0)
 481         ret = 0;
 482     }
 483
 484   return ret;
 485 }
 486
 487 /* Fork list <-> user interface.  */
 488
 489 static void
 490 delete_checkpoint_command (const char *args, int from_tty)
 491 {
 492   ptid_t ptid, pptid;
 493   struct fork_info *fi;
 494
 495   if (!args || !*args)
 496     error (_("Requires argument (checkpoint id to delete)"));
 497
 498   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 499   if (ptid == minus_one_ptid)
 500     error (_("No such checkpoint id, %s"), args);
 501
 502   if (ptid == inferior_ptid)
 503     error (_("\
 504 Please switch to another checkpoint before deleting the current one"));
 505
 506   if (ptrace (PTRACE_KILL, ptid.pid (), 0, 0))
 507     error (_("Unable to kill pid %s"), target_pid_to_str (ptid).c_str ());
 508
 509   fi = find_fork_ptid (ptid);
 510   gdb_assert (fi);
 511   pptid = fi->parent_ptid;
 512
 513   if (from_tty)
 514     printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid).c_str ());
 515
 516   delete_fork (ptid);
 517
 518   /* If fi->parent_ptid is not a part of lwp but it's a part of checkpoint
 519      list, waitpid the ptid.
 520      If fi->parent_ptid is a part of lwp and it is stopped, waitpid the
 521      ptid.  */
 522   thread_info *parent = find_thread_ptid (pptid);
 523   if ((parent == NULL && find_fork_ptid (pptid))
 524       || (parent != NULL && parent->state == THREAD_STOPPED))
 525     {
 526       if (inferior_call_waitpid (pptid, ptid.pid ()))
 527         warning (_("Unable to wait pid %s"),
 528                  target_pid_to_str (ptid).c_str ());
 529     }
 530 }
 531
 532 static void
 533 detach_checkpoint_command (const char *args, int from_tty)
 534 {
 535   ptid_t ptid;
 536
 537   if (!args || !*args)
 538     error (_("Requires argument (checkpoint id to detach)"));
 539
 540   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 541   if (ptid == minus_one_ptid)
 542     error (_("No such checkpoint id, %s"), args);
 543
 544   if (ptid == inferior_ptid)
 545     error (_("\
 546 Please switch to another checkpoint before detaching the current one"));
 547
 548   if (ptrace (PTRACE_DETACH, ptid.pid (), 0, 0))
 549     error (_("Unable to detach %s"), target_pid_to_str (ptid).c_str ());
 550
 551   if (from_tty)
 552     printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid).c_str ());
 553
 554   delete_fork (ptid);
 555 }
 556
 557 /* Print information about currently known checkpoints.  */
 558
 559 static void
 560 info_checkpoints_command (const char *arg, int from_tty)
 561 {
 562   struct gdbarch *gdbarch = get_current_arch ();
 563   int requested = -1;
 564   const fork_info *printed = NULL;
 565
 566   if (arg && *arg)
 567     requested = (int) parse_and_eval_long (arg);
 568
 569   for (const fork_info &fi : fork_list)
 570     {
 571       if (requested > 0 && fi.num != requested)
 572         continue;
 573
 574       printed = &fi;
 575       if (fi.ptid == inferior_ptid)
 576         printf_filtered ("* ");
 577       else
 578         printf_filtered ("  ");
 579
 580       ULONGEST pc = fi.pc;
 581       printf_filtered ("%d %s", fi.num, target_pid_to_str (fi.ptid).c_str ());
 582       if (fi.num == 0)
 583         printf_filtered (_(" (main process)"));
 584       printf_filtered (_(" at "));
 585       fputs_filtered (paddress (gdbarch, pc), gdb_stdout);
 586
 587       symtab_and_line 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>", msym.minsym->linkage_name ());
 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 /* Return true if the current inferior is multi-threaded.  */
 623
 624 static bool
 625 inf_has_multiple_threads ()
 626 {
 627   int count = 0;
 628
 629   /* Return true as soon as we see the second thread of the current
 630      inferior.  */
 631   for (thread_info *tp ATTRIBUTE_UNUSED : current_inferior ()->threads ())
 632     if (++count > 1)
 633       return true;
 634
 635   return false;
 636 }
 637
 638 static void
 639 checkpoint_command (const char *args, int from_tty)
 640 {
 641   struct objfile *fork_objf;
 642   struct gdbarch *gdbarch;
 643   struct target_waitstatus last_target_waitstatus;
 644   ptid_t last_target_ptid;
 645   struct value *fork_fn = NULL, *ret;
 646   struct fork_info *fp;
 647   pid_t retpid;
 648
 649   if (!target_has_execution)
 650     error (_("The program is not being run."));
 651
 652   /* Ensure that the inferior is not multithreaded.  */
 653   update_thread_list ();
 654   if (inf_has_multiple_threads ())
 655     error (_("checkpoint: can't checkpoint multiple threads."));
 656
 657   /* Make the inferior fork, record its (and gdb's) state.  */
 658
 659   if (lookup_minimal_symbol ("fork", NULL, NULL).minsym != NULL)
 660     fork_fn = find_function_in_inferior ("fork", &fork_objf);
 661   if (!fork_fn)
 662     if (lookup_minimal_symbol ("_fork", NULL, NULL).minsym != NULL)
 663       fork_fn = find_function_in_inferior ("fork", &fork_objf);
 664   if (!fork_fn)
 665     error (_("checkpoint: can't find fork function in inferior."));
 666
 667   gdbarch = get_objfile_arch (fork_objf);
 668   ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 669
 670   /* Tell linux-nat.c that we're checkpointing this inferior.  */
 671   {
 672     scoped_restore save_pid
 673       = make_scoped_restore (&checkpointing_pid, inferior_ptid.pid ());
 674
 675     ret = call_function_by_hand (fork_fn, NULL, {});
 676   }
 677
 678   if (!ret)     /* Probably can't happen.  */
 679     error (_("checkpoint: call_function_by_hand returned null."));
 680
 681   retpid = value_as_long (ret);
 682   get_last_target_status (&last_target_ptid, &last_target_waitstatus);
 683
 684   fp = find_fork_pid (retpid);
 685
 686   if (from_tty)
 687     {
 688       int parent_pid;
 689
 690       printf_filtered (_("checkpoint %d: fork returned pid %ld.\n"),
 691                        fp != NULL ? fp->num : -1, (long) retpid);
 692       if (info_verbose)
 693         {
 694           parent_pid = last_target_ptid.lwp ();
 695           if (parent_pid == 0)
 696             parent_pid = last_target_ptid.pid ();
 697           printf_filtered (_("   gdb says parent = %ld.\n"),
 698                            (long) parent_pid);
 699         }
 700     }
 701
 702   if (!fp)
 703     error (_("Failed to find new fork"));
 704
 705   if (one_fork_p ())
 706     {
 707       /* Special case -- if this is the first fork in the list (the
 708          list was hitherto empty), then add inferior_ptid first, as a
 709          special zeroeth fork id.  */
 710       fork_list.emplace_front (inferior_ptid.pid ());
 711     }
 712
 713   fork_save_infrun_state (fp);
 714   fp->parent_ptid = last_target_ptid;
 715 }
 716
 717 static void
 718 linux_fork_context (struct fork_info *newfp, int from_tty)
 719 {
 720   /* Now we attempt to switch processes.  */
 721   struct fork_info *oldfp;
 722
 723   gdb_assert (newfp != NULL);
 724
 725   oldfp = find_fork_ptid (inferior_ptid);
 726   gdb_assert (oldfp != NULL);
 727
 728   fork_save_infrun_state (oldfp);
 729   remove_breakpoints ();
 730   fork_load_infrun_state (newfp);
 731   insert_breakpoints ();
 732
 733   printf_filtered (_("Switching to %s\n"),
 734                    target_pid_to_str (inferior_ptid).c_str ());
 735
 736   print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC, 1);
 737 }
 738
 739 /* Switch inferior process (checkpoint) context, by checkpoint id.  */
 740 static void
 741 restart_command (const char *args, int from_tty)
 742 {
 743   struct fork_info *fp;
 744
 745   if (!args || !*args)
 746     error (_("Requires argument (checkpoint id to restart)"));
 747
 748   if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
 749     error (_("Not found: checkpoint id %s"), args);
 750
 751   linux_fork_context (fp, from_tty);
 752 }
 753
 754 void
 755 _initialize_linux_fork (void)
 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 }