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   extern void nullify_last_target_wait_ptid ();
 219   int i;
 220
 221   linux_nat_switch_fork (fp->ptid);
 222
 223   if (fp->savedregs)
 224     get_current_regcache ()->restore (fp->savedregs);
 225
 226   registers_changed ();
 227   reinit_frame_cache ();
 228
 229   inferior_thread ()->suspend.stop_pc
 230     = regcache_read_pc (get_current_regcache ());
 231   nullify_last_target_wait_ptid ();
 232
 233   /* Now restore the file positions of open file descriptors.  */
 234   if (fp->filepos)
 235     {
 236       for (i = 0; i <= fp->maxfd; i++)
 237         if (fp->filepos[i] != (off_t) -1)
 238           call_lseek (i, fp->filepos[i], SEEK_SET);
 239       /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
 240          this is native-only.  If it ever has to be cross, we'll have
 241          to rethink this.  */
 242     }
 243 }
 244
 245 /* Save infrun state for the fork FP.  */
 246
 247 static void
 248 fork_save_infrun_state (struct fork_info *fp)
 249 {
 250   char path[PATH_MAX];
 251   struct dirent *de;
 252   DIR *d;
 253
 254   if (fp->savedregs)
 255     delete fp->savedregs;
 256
 257   fp->savedregs = new readonly_detached_regcache (*get_current_regcache ());
 258   fp->pc = regcache_read_pc (get_current_regcache ());
 259
 260   /* Now save the 'state' (file position) of all open file descriptors.
 261      Unfortunately fork does not take care of that for us...  */
 262   snprintf (path, PATH_MAX, "/proc/%ld/fd", (long) fp->ptid.pid ());
 263   if ((d = opendir (path)) != NULL)
 264     {
 265       long tmp;
 266
 267       fp->maxfd = 0;
 268       while ((de = readdir (d)) != NULL)
 269         {
 270           /* Count open file descriptors (actually find highest
 271              numbered).  */
 272           tmp = strtol (&de->d_name[0], NULL, 10);
 273           if (fp->maxfd < tmp)
 274             fp->maxfd = tmp;
 275         }
 276       /* Allocate array of file positions.  */
 277       fp->filepos = XRESIZEVEC (off_t, fp->filepos, fp->maxfd + 1);
 278
 279       /* Initialize to -1 (invalid).  */
 280       for (tmp = 0; tmp <= fp->maxfd; tmp++)
 281         fp->filepos[tmp] = -1;
 282
 283       /* Now find actual file positions.  */
 284       rewinddir (d);
 285       while ((de = readdir (d)) != NULL)
 286         if (isdigit (de->d_name[0]))
 287           {
 288             tmp = strtol (&de->d_name[0], NULL, 10);
 289             fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
 290           }
 291       closedir (d);
 292     }
 293 }
 294
 295 /* Kill 'em all, let God sort 'em out...  */
 296
 297 void
 298 linux_fork_killall (void)
 299 {
 300   /* Walk list and kill every pid.  No need to treat the
 301      current inferior_ptid as special (we do not return a
 302      status for it) -- however any process may be a child
 303      or a parent, so may get a SIGCHLD from a previously
 304      killed child.  Wait them all out.  */
 305
 306   for (fork_info &fi : fork_list)
 307     {
 308       pid_t pid = fi.ptid.pid ();
 309       int status;
 310       pid_t ret;
 311       do {
 312         /* Use SIGKILL instead of PTRACE_KILL because the former works even
 313            if the thread is running, while the later doesn't.  */
 314         kill (pid, SIGKILL);
 315         ret = waitpid (pid, &status, 0);
 316         /* We might get a SIGCHLD instead of an exit status.  This is
 317          aggravated by the first kill above - a child has just
 318          died.  MVS comment cut-and-pasted from linux-nat.  */
 319       } while (ret == pid && WIFSTOPPED (status));
 320     }
 321
 322   /* Clear list, prepare to start fresh.  */
 323   fork_list.clear ();
 324 }
 325
 326 /* The current inferior_ptid has exited, but there are other viable
 327    forks to debug.  Delete the exiting one and context-switch to the
 328    first available.  */
 329
 330 void
 331 linux_fork_mourn_inferior (void)
 332 {
 333   struct fork_info *last;
 334   int status;
 335
 336   /* Wait just one more time to collect the inferior's exit status.
 337      Do not check whether this succeeds though, since we may be
 338      dealing with a process that we attached to.  Such a process will
 339      only report its exit status to its original parent.  */
 340   waitpid (inferior_ptid.pid (), &status, 0);
 341
 342   /* OK, presumably inferior_ptid is the one who has exited.
 343      We need to delete that one from the fork_list, and switch
 344      to the next available fork.  */
 345   delete_fork (inferior_ptid);
 346
 347   /* There should still be a fork - if there's only one left,
 348      delete_fork won't remove it, because we haven't updated
 349      inferior_ptid yet.  */
 350   gdb_assert (!fork_list.empty ());
 351
 352   last = find_last_fork ();
 353   fork_load_infrun_state (last);
 354   printf_filtered (_("[Switching to %s]\n"),
 355                    target_pid_to_str (inferior_ptid).c_str ());
 356
 357   /* If there's only one fork, switch back to non-fork mode.  */
 358   if (one_fork_p ())
 359     delete_fork (inferior_ptid);
 360 }
 361
 362 /* The current inferior_ptid is being detached, but there are other
 363    viable forks to debug.  Detach and delete it and context-switch to
 364    the first available.  */
 365
 366 void
 367 linux_fork_detach (int from_tty)
 368 {
 369   /* OK, inferior_ptid is the one we are detaching from.  We need to
 370      delete it from the fork_list, and switch to the next available
 371      fork.  */
 372
 373   if (ptrace (PTRACE_DETACH, inferior_ptid.pid (), 0, 0))
 374     error (_("Unable to detach %s"),
 375            target_pid_to_str (inferior_ptid).c_str ());
 376
 377   delete_fork (inferior_ptid);
 378
 379   /* There should still be a fork - if there's only one left,
 380      delete_fork won't remove it, because we haven't updated
 381      inferior_ptid yet.  */
 382   gdb_assert (!fork_list.empty ());
 383
 384   fork_load_infrun_state (&fork_list.front ());
 385
 386   if (from_tty)
 387     printf_filtered (_("[Switching to %s]\n"),
 388                      target_pid_to_str (inferior_ptid).c_str ());
 389
 390   /* If there's only one fork, switch back to non-fork mode.  */
 391   if (one_fork_p ())
 392     delete_fork (inferior_ptid);
 393 }
 394
 395 /* Temporarily switch to the infrun state stored on the fork_info
 396    identified by a given ptid_t.  When this object goes out of scope,
 397    restore the currently selected infrun state.   */
 398
 399 class scoped_switch_fork_info
 400 {
 401 public:
 402   /* Switch to the infrun state held on the fork_info identified by
 403      PPTID.  If PPTID is the current inferior then no switch is done.  */
 404   explicit scoped_switch_fork_info (ptid_t pptid)
 405     : m_oldfp (nullptr)
 406   {
 407     if (pptid != inferior_ptid)
 408       {
 409         struct fork_info *newfp = nullptr;
 410
 411         /* Switch to pptid.  */
 412         m_oldfp = find_fork_ptid (inferior_ptid);
 413         gdb_assert (m_oldfp != nullptr);
 414         newfp = find_fork_ptid (pptid);
 415         gdb_assert (newfp != nullptr);
 416         fork_save_infrun_state (m_oldfp);
 417         remove_breakpoints ();
 418         fork_load_infrun_state (newfp);
 419         insert_breakpoints ();
 420       }
 421   }
 422
 423   /* Restore the previously selected infrun state.  If the constructor
 424      didn't need to switch states, then nothing is done here either.  */
 425   ~scoped_switch_fork_info ()
 426   {
 427     if (m_oldfp != nullptr)
 428       {
 429         /* Switch back to inferior_ptid.  */
 430         try
 431           {
 432             remove_breakpoints ();
 433             fork_load_infrun_state (m_oldfp);
 434             insert_breakpoints ();
 435           }
 436         catch (const gdb_exception &ex)
 437           {
 438             warning (_("Couldn't restore checkpoint state in %s: %s"),
 439                      target_pid_to_str (m_oldfp->ptid).c_str (),
 440                      ex.what ());
 441           }
 442       }
 443   }
 444
 445   DISABLE_COPY_AND_ASSIGN (scoped_switch_fork_info);
 446
 447 private:
 448   /* The fork_info for the previously selected infrun state, or nullptr if
 449      we were already in the desired state, and nothing needs to be
 450      restored.  */
 451   struct fork_info *m_oldfp;
 452 };
 453
 454 static int
 455 inferior_call_waitpid (ptid_t pptid, int pid)
 456 {
 457   struct objfile *waitpid_objf;
 458   struct value *waitpid_fn = NULL;
 459   int ret = -1;
 460
 461   scoped_switch_fork_info switch_fork_info (pptid);
 462
 463   /* Get the waitpid_fn.  */
 464   if (lookup_minimal_symbol ("waitpid", NULL, NULL).minsym != NULL)
 465     waitpid_fn = find_function_in_inferior ("waitpid", &waitpid_objf);
 466   if (!waitpid_fn
 467       && lookup_minimal_symbol ("_waitpid", NULL, NULL).minsym != NULL)
 468     waitpid_fn = find_function_in_inferior ("_waitpid", &waitpid_objf);
 469   if (waitpid_fn != nullptr)
 470     {
 471       struct gdbarch *gdbarch = get_current_arch ();
 472       struct value *argv[3], *retv;
 473
 474       /* Get the argv.  */
 475       argv[0] = value_from_longest (builtin_type (gdbarch)->builtin_int, pid);
 476       argv[1] = value_from_pointer (builtin_type (gdbarch)->builtin_data_ptr, 0);
 477       argv[2] = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 478
 479       retv = call_function_by_hand (waitpid_fn, NULL, argv);
 480
 481       if (value_as_long (retv) >= 0)
 482         ret = 0;
 483     }
 484
 485   return ret;
 486 }
 487
 488 /* Fork list <-> user interface.  */
 489
 490 static void
 491 delete_checkpoint_command (const char *args, int from_tty)
 492 {
 493   ptid_t ptid, pptid;
 494   struct fork_info *fi;
 495
 496   if (!args || !*args)
 497     error (_("Requires argument (checkpoint id to delete)"));
 498
 499   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 500   if (ptid == minus_one_ptid)
 501     error (_("No such checkpoint id, %s"), args);
 502
 503   if (ptid == inferior_ptid)
 504     error (_("\
 505 Please switch to another checkpoint before deleting the current one"));
 506
 507   if (ptrace (PTRACE_KILL, ptid.pid (), 0, 0))
 508     error (_("Unable to kill pid %s"), target_pid_to_str (ptid).c_str ());
 509
 510   fi = find_fork_ptid (ptid);
 511   gdb_assert (fi);
 512   pptid = fi->parent_ptid;
 513
 514   if (from_tty)
 515     printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid).c_str ());
 516
 517   delete_fork (ptid);
 518
 519   /* If fi->parent_ptid is not a part of lwp but it's a part of checkpoint
 520      list, waitpid the ptid.
 521      If fi->parent_ptid is a part of lwp and it is stopped, waitpid the
 522      ptid.  */
 523   thread_info *parent = find_thread_ptid (pptid);
 524   if ((parent == NULL && find_fork_ptid (pptid))
 525       || (parent != NULL && parent->state == THREAD_STOPPED))
 526     {
 527       if (inferior_call_waitpid (pptid, ptid.pid ()))
 528         warning (_("Unable to wait pid %s"),
 529                  target_pid_to_str (ptid).c_str ());
 530     }
 531 }
 532
 533 static void
 534 detach_checkpoint_command (const char *args, int from_tty)
 535 {
 536   ptid_t ptid;
 537
 538   if (!args || !*args)
 539     error (_("Requires argument (checkpoint id to detach)"));
 540
 541   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 542   if (ptid == minus_one_ptid)
 543     error (_("No such checkpoint id, %s"), args);
 544
 545   if (ptid == inferior_ptid)
 546     error (_("\
 547 Please switch to another checkpoint before detaching the current one"));
 548
 549   if (ptrace (PTRACE_DETACH, ptid.pid (), 0, 0))
 550     error (_("Unable to detach %s"), target_pid_to_str (ptid).c_str ());
 551
 552   if (from_tty)
 553     printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid).c_str ());
 554
 555   delete_fork (ptid);
 556 }
 557
 558 /* Print information about currently known checkpoints.  */
 559
 560 static void
 561 info_checkpoints_command (const char *arg, int from_tty)
 562 {
 563   struct gdbarch *gdbarch = get_current_arch ();
 564   int requested = -1;
 565   const fork_info *printed = NULL;
 566
 567   if (arg && *arg)
 568     requested = (int) parse_and_eval_long (arg);
 569
 570   for (const fork_info &fi : fork_list)
 571     {
 572       if (requested > 0 && fi.num != requested)
 573         continue;
 574
 575       printed = &fi;
 576       if (fi.ptid == inferior_ptid)
 577         printf_filtered ("* ");
 578       else
 579         printf_filtered ("  ");
 580
 581       ULONGEST pc = fi.pc;
 582       printf_filtered ("%d %s", fi.num, target_pid_to_str (fi.ptid).c_str ());
 583       if (fi.num == 0)
 584         printf_filtered (_(" (main process)"));
 585       printf_filtered (_(" at "));
 586       fputs_filtered (paddress (gdbarch, pc), gdb_stdout);
 587
 588       symtab_and_line sal = find_pc_line (pc, 0);
 589       if (sal.symtab)
 590         printf_filtered (_(", file %s"),
 591                          symtab_to_filename_for_display (sal.symtab));
 592       if (sal.line)
 593         printf_filtered (_(", line %d"), sal.line);
 594       if (!sal.symtab && !sal.line)
 595         {
 596           struct bound_minimal_symbol msym;
 597
 598           msym = lookup_minimal_symbol_by_pc (pc);
 599           if (msym.minsym)
 600             printf_filtered (", <%s>", msym.minsym->linkage_name ());
 601         }
 602
 603       putchar_filtered ('\n');
 604     }
 605   if (printed == NULL)
 606     {
 607       if (requested > 0)
 608         printf_filtered (_("No checkpoint number %d.\n"), requested);
 609       else
 610         printf_filtered (_("No checkpoints.\n"));
 611     }
 612 }
 613
 614 /* The PID of the process we're checkpointing.  */
 615 static int checkpointing_pid = 0;
 616
 617 int
 618 linux_fork_checkpointing_p (int pid)
 619 {
 620   return (checkpointing_pid == pid);
 621 }
 622
 623 /* Return true if the current inferior is multi-threaded.  */
 624
 625 static bool
 626 inf_has_multiple_threads ()
 627 {
 628   int count = 0;
 629
 630   /* Return true as soon as we see the second thread of the current
 631      inferior.  */
 632   for (thread_info *tp ATTRIBUTE_UNUSED : current_inferior ()->threads ())
 633     if (++count > 1)
 634       return true;
 635
 636   return false;
 637 }
 638
 639 static void
 640 checkpoint_command (const char *args, int from_tty)
 641 {
 642   struct objfile *fork_objf;
 643   struct gdbarch *gdbarch;
 644   struct target_waitstatus last_target_waitstatus;
 645   ptid_t last_target_ptid;
 646   struct value *fork_fn = NULL, *ret;
 647   struct fork_info *fp;
 648   pid_t retpid;
 649
 650   if (!target_has_execution)
 651     error (_("The program is not being run."));
 652
 653   /* Ensure that the inferior is not multithreaded.  */
 654   update_thread_list ();
 655   if (inf_has_multiple_threads ())
 656     error (_("checkpoint: can't checkpoint multiple threads."));
 657
 658   /* Make the inferior fork, record its (and gdb's) state.  */
 659
 660   if (lookup_minimal_symbol ("fork", NULL, NULL).minsym != NULL)
 661     fork_fn = find_function_in_inferior ("fork", &fork_objf);
 662   if (!fork_fn)
 663     if (lookup_minimal_symbol ("_fork", NULL, NULL).minsym != NULL)
 664       fork_fn = find_function_in_inferior ("fork", &fork_objf);
 665   if (!fork_fn)
 666     error (_("checkpoint: can't find fork function in inferior."));
 667
 668   gdbarch = get_objfile_arch (fork_objf);
 669   ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 670
 671   /* Tell linux-nat.c that we're checkpointing this inferior.  */
 672   {
 673     scoped_restore save_pid
 674       = make_scoped_restore (&checkpointing_pid, inferior_ptid.pid ());
 675
 676     ret = call_function_by_hand (fork_fn, NULL, {});
 677   }
 678
 679   if (!ret)     /* Probably can't happen.  */
 680     error (_("checkpoint: call_function_by_hand returned null."));
 681
 682   retpid = value_as_long (ret);
 683   get_last_target_status (&last_target_ptid, &last_target_waitstatus);
 684
 685   fp = find_fork_pid (retpid);
 686
 687   if (from_tty)
 688     {
 689       int parent_pid;
 690
 691       printf_filtered (_("checkpoint %d: fork returned pid %ld.\n"),
 692                        fp != NULL ? fp->num : -1, (long) retpid);
 693       if (info_verbose)
 694         {
 695           parent_pid = last_target_ptid.lwp ();
 696           if (parent_pid == 0)
 697             parent_pid = last_target_ptid.pid ();
 698           printf_filtered (_("   gdb says parent = %ld.\n"),
 699                            (long) parent_pid);
 700         }
 701     }
 702
 703   if (!fp)
 704     error (_("Failed to find new fork"));
 705
 706   if (one_fork_p ())
 707     {
 708       /* Special case -- if this is the first fork in the list (the
 709          list was hitherto empty), then add inferior_ptid first, as a
 710          special zeroeth fork id.  */
 711       fork_list.emplace_front (inferior_ptid.pid ());
 712     }
 713
 714   fork_save_infrun_state (fp);
 715   fp->parent_ptid = last_target_ptid;
 716 }
 717
 718 static void
 719 linux_fork_context (struct fork_info *newfp, int from_tty)
 720 {
 721   /* Now we attempt to switch processes.  */
 722   struct fork_info *oldfp;
 723
 724   gdb_assert (newfp != NULL);
 725
 726   oldfp = find_fork_ptid (inferior_ptid);
 727   gdb_assert (oldfp != NULL);
 728
 729   fork_save_infrun_state (oldfp);
 730   remove_breakpoints ();
 731   fork_load_infrun_state (newfp);
 732   insert_breakpoints ();
 733
 734   printf_filtered (_("Switching to %s\n"),
 735                    target_pid_to_str (inferior_ptid).c_str ());
 736
 737   print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC, 1);
 738 }
 739
 740 /* Switch inferior process (checkpoint) context, by checkpoint id.  */
 741 static void
 742 restart_command (const char *args, int from_tty)
 743 {
 744   struct fork_info *fp;
 745
 746   if (!args || !*args)
 747     error (_("Requires argument (checkpoint id to restart)"));
 748
 749   if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
 750     error (_("Not found: checkpoint id %s"), args);
 751
 752   linux_fork_context (fp, from_tty);
 753 }
 754
 755 void
 756 _initialize_linux_fork (void)
 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 Restore program context from a checkpoint.\n\
 769 Usage: restart N\n\
 770 Argument N is checkpoint ID, as displayed by 'info checkpoints'."));
 771
 772   /* Delete checkpoint command: kill the process and remove it from
 773      the fork list.  */
 774
 775   add_cmd ("checkpoint", class_obscure, delete_checkpoint_command, _("\
 776 Delete a checkpoint (experimental)."),
 777            &deletelist);
 778
 779   /* Detach checkpoint command: release the process to run independently,
 780      and remove it from the fork list.  */
 781
 782   add_cmd ("checkpoint", class_obscure, detach_checkpoint_command, _("\
 783 Detach from a checkpoint (experimental)."),
 784            &detachlist);
 785
 786   /* Info checkpoints command: list all forks/checkpoints
 787      currently under gdb's control.  */
 788
 789   add_info ("checkpoints", info_checkpoints_command,
 790             _("IDs of currently known checkpoints."));
 791 }