gdb/linux-fork.c

   1 /* GNU/Linux native-dependent code for debugging multiple forks.
   2
   3    Copyright (C) 2005-2019 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 "common/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   /* True if we should restore saved regs.  */
  81   int clobber_regs = 0;
  82
  83   /* Set of open file descriptors' offsets.  */
  84   off_t *filepos = nullptr;
  85
  86   int maxfd = 0;
  87 };
  88
  89 static std::list<fork_info> fork_list;
  90 static int highest_fork_num;
  91
  92 /* Fork list methods:  */
  93
  94 int
  95 forks_exist_p (void)
  96 {
  97   return !fork_list.empty ();
  98 }
  99
 100 /* Return the last fork in the list.  */
 101
 102 static struct fork_info *
 103 find_last_fork (void)
 104 {
 105   if (fork_list.empty ())
 106     return NULL;
 107
 108   return &fork_list.back ();
 109 }
 110
 111 /* Return true iff there's one fork in the list.  */
 112
 113 static bool
 114 one_fork_p ()
 115 {
 116   return (!fork_list.empty ()
 117           && &fork_list.front () == &fork_list.back ());
 118 }
 119
 120 /* Add a new fork to the internal fork list.  */
 121
 122 void
 123 add_fork (pid_t pid)
 124 {
 125   fork_list.emplace_back (pid);
 126
 127   if (one_fork_p ())
 128     highest_fork_num = 0;
 129
 130   fork_info *fp = &fork_list.back ();
 131   fp->num = ++highest_fork_num;
 132 }
 133
 134 static void
 135 delete_fork (ptid_t ptid)
 136 {
 137   linux_target->low_forget_process (ptid.pid ());
 138
 139   for (auto it = fork_list.begin (); it != fork_list.end (); ++it)
 140     if (it->ptid == ptid)
 141       {
 142         fork_list.erase (it);
 143
 144         /* Special case: if there is now only one process in the list,
 145            and if it is (hopefully!) the current inferior_ptid, then
 146            remove it, leaving the list empty -- we're now down to the
 147            default case of debugging a single process.  */
 148         if (one_fork_p () && fork_list.front ().ptid == inferior_ptid)
 149           {
 150             /* Last fork -- delete from list and handle as solo
 151                process (should be a safe recursion).  */
 152             delete_fork (inferior_ptid);
 153           }
 154         return;
 155       }
 156 }
 157
 158 /* Find a fork_info by matching PTID.  */
 159 static struct fork_info *
 160 find_fork_ptid (ptid_t ptid)
 161 {
 162   for (fork_info &fi : fork_list)
 163     if (fi.ptid == ptid)
 164       return &fi;
 165
 166   return NULL;
 167 }
 168
 169 /* Find a fork_info by matching ID.  */
 170 static struct fork_info *
 171 find_fork_id (int num)
 172 {
 173   for (fork_info &fi : fork_list)
 174     if (fi.num == num)
 175       return &fi;
 176
 177   return NULL;
 178 }
 179
 180 /* Find a fork_info by matching pid.  */
 181 extern struct fork_info *
 182 find_fork_pid (pid_t pid)
 183 {
 184   for (fork_info &fi : fork_list)
 185     if (pid == fi.ptid.pid ())
 186       return &fi;
 187
 188   return NULL;
 189 }
 190
 191 static ptid_t
 192 fork_id_to_ptid (int num)
 193 {
 194   struct fork_info *fork = find_fork_id (num);
 195   if (fork)
 196     return fork->ptid;
 197   else
 198     return ptid_t (-1);
 199 }
 200
 201 /* Fork list <-> gdb interface.  */
 202
 203 /* Utility function for fork_load/fork_save.
 204    Calls lseek in the (current) inferior process.  */
 205
 206 static off_t
 207 call_lseek (int fd, off_t offset, int whence)
 208 {
 209   char exp[80];
 210
 211   snprintf (&exp[0], sizeof (exp), "(long) lseek (%d, %ld, %d)",
 212             fd, (long) offset, whence);
 213   return (off_t) parse_and_eval_long (&exp[0]);
 214 }
 215
 216 /* Load infrun state for the fork PTID.  */
 217
 218 static void
 219 fork_load_infrun_state (struct fork_info *fp)
 220 {
 221   extern void nullify_last_target_wait_ptid ();
 222   int i;
 223
 224   linux_nat_switch_fork (fp->ptid);
 225
 226   if (fp->savedregs && fp->clobber_regs)
 227     get_current_regcache ()->restore (fp->savedregs);
 228
 229   registers_changed ();
 230   reinit_frame_cache ();
 231
 232   inferior_thread ()->suspend.stop_pc
 233     = regcache_read_pc (get_current_regcache ());
 234   nullify_last_target_wait_ptid ();
 235
 236   /* Now restore the file positions of open file descriptors.  */
 237   if (fp->filepos)
 238     {
 239       for (i = 0; i <= fp->maxfd; i++)
 240         if (fp->filepos[i] != (off_t) -1)
 241           call_lseek (i, fp->filepos[i], SEEK_SET);
 242       /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
 243          this is native-only.  If it ever has to be cross, we'll have
 244          to rethink this.  */
 245     }
 246 }
 247
 248 /* Save infrun state for the fork PTID.
 249    Exported for use by linux child_follow_fork.  */
 250
 251 static void
 252 fork_save_infrun_state (struct fork_info *fp, int clobber_regs)
 253 {
 254   char path[PATH_MAX];
 255   struct dirent *de;
 256   DIR *d;
 257
 258   if (fp->savedregs)
 259     delete fp->savedregs;
 260
 261   fp->savedregs = new readonly_detached_regcache (*get_current_regcache ());
 262   fp->pc = regcache_read_pc (get_current_regcache ());
 263   fp->clobber_regs = clobber_regs;
 264
 265   if (clobber_regs)
 266     {
 267       /* Now save the 'state' (file position) of all open file descriptors.
 268          Unfortunately fork does not take care of that for us...  */
 269       snprintf (path, PATH_MAX, "/proc/%ld/fd",
 270                 (long) fp->ptid.pid ());
 271       if ((d = opendir (path)) != NULL)
 272         {
 273           long tmp;
 274
 275           fp->maxfd = 0;
 276           while ((de = readdir (d)) != NULL)
 277             {
 278               /* Count open file descriptors (actually find highest
 279                  numbered).  */
 280               tmp = strtol (&de->d_name[0], NULL, 10);
 281               if (fp->maxfd < tmp)
 282                 fp->maxfd = tmp;
 283             }
 284           /* Allocate array of file positions.  */
 285           fp->filepos = XRESIZEVEC (off_t, fp->filepos, fp->maxfd + 1);
 286
 287           /* Initialize to -1 (invalid).  */
 288           for (tmp = 0; tmp <= fp->maxfd; tmp++)
 289             fp->filepos[tmp] = -1;
 290
 291           /* Now find actual file positions.  */
 292           rewinddir (d);
 293           while ((de = readdir (d)) != NULL)
 294             if (isdigit (de->d_name[0]))
 295               {
 296                 tmp = strtol (&de->d_name[0], NULL, 10);
 297                 fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
 298               }
 299           closedir (d);
 300         }
 301     }
 302 }
 303
 304 /* Kill 'em all, let God sort 'em out...  */
 305
 306 void
 307 linux_fork_killall (void)
 308 {
 309   /* Walk list and kill every pid.  No need to treat the
 310      current inferior_ptid as special (we do not return a
 311      status for it) -- however any process may be a child
 312      or a parent, so may get a SIGCHLD from a previously
 313      killed child.  Wait them all out.  */
 314
 315   for (fork_info &fi : fork_list)
 316     {
 317       pid_t pid = fi.ptid.pid ();
 318       int status;
 319       pid_t ret;
 320       do {
 321         /* Use SIGKILL instead of PTRACE_KILL because the former works even
 322            if the thread is running, while the later doesn't.  */
 323         kill (pid, SIGKILL);
 324         ret = waitpid (pid, &status, 0);
 325         /* We might get a SIGCHLD instead of an exit status.  This is
 326          aggravated by the first kill above - a child has just
 327          died.  MVS comment cut-and-pasted from linux-nat.  */
 328       } while (ret == pid && WIFSTOPPED (status));
 329     }
 330
 331   /* Clear list, prepare to start fresh.  */
 332   fork_list.clear ();
 333 }
 334
 335 /* The current inferior_ptid has exited, but there are other viable
 336    forks to debug.  Delete the exiting one and context-switch to the
 337    first available.  */
 338
 339 void
 340 linux_fork_mourn_inferior (void)
 341 {
 342   struct fork_info *last;
 343   int status;
 344
 345   /* Wait just one more time to collect the inferior's exit status.
 346      Do not check whether this succeeds though, since we may be
 347      dealing with a process that we attached to.  Such a process will
 348      only report its exit status to its original parent.  */
 349   waitpid (inferior_ptid.pid (), &status, 0);
 350
 351   /* OK, presumably inferior_ptid is the one who has exited.
 352      We need to delete that one from the fork_list, and switch
 353      to the next available fork.  */
 354   delete_fork (inferior_ptid);
 355
 356   /* There should still be a fork - if there's only one left,
 357      delete_fork won't remove it, because we haven't updated
 358      inferior_ptid yet.  */
 359   gdb_assert (!fork_list.empty ());
 360
 361   last = find_last_fork ();
 362   fork_load_infrun_state (last);
 363   printf_filtered (_("[Switching to %s]\n"),
 364                    target_pid_to_str (inferior_ptid));
 365
 366   /* If there's only one fork, switch back to non-fork mode.  */
 367   if (one_fork_p ())
 368     delete_fork (inferior_ptid);
 369 }
 370
 371 /* The current inferior_ptid is being detached, but there are other
 372    viable forks to debug.  Detach and delete it and context-switch to
 373    the first available.  */
 374
 375 void
 376 linux_fork_detach (int from_tty)
 377 {
 378   /* OK, inferior_ptid is the one we are detaching from.  We need to
 379      delete it from the fork_list, and switch to the next available
 380      fork.  */
 381
 382   if (ptrace (PTRACE_DETACH, inferior_ptid.pid (), 0, 0))
 383     error (_("Unable to detach %s"), target_pid_to_str (inferior_ptid));
 384
 385   delete_fork (inferior_ptid);
 386
 387   /* There should still be a fork - if there's only one left,
 388      delete_fork won't remove it, because we haven't updated
 389      inferior_ptid yet.  */
 390   gdb_assert (!fork_list.empty ());
 391
 392   fork_load_infrun_state (&fork_list.front ());
 393
 394   if (from_tty)
 395     printf_filtered (_("[Switching to %s]\n"),
 396                      target_pid_to_str (inferior_ptid));
 397
 398   /* If there's only one fork, switch back to non-fork mode.  */
 399   if (one_fork_p ())
 400     delete_fork (inferior_ptid);
 401 }
 402
 403 /* Temporarily switch to the infrun state stored on the fork_info
 404    identified by a given ptid_t.  When this object goes out of scope,
 405    restore the currently selected infrun state.   */
 406
 407 class scoped_switch_fork_info
 408 {
 409 public:
 410   /* Switch to the infrun state held on the fork_info identified by
 411      PPTID.  If PPTID is the current inferior then no switch is done.  */
 412   explicit scoped_switch_fork_info (ptid_t pptid)
 413     : m_oldfp (nullptr)
 414   {
 415     if (pptid != inferior_ptid)
 416       {
 417         struct fork_info *newfp = nullptr;
 418
 419         /* Switch to pptid.  */
 420         m_oldfp = find_fork_ptid (inferior_ptid);
 421         gdb_assert (m_oldfp != nullptr);
 422         newfp = find_fork_ptid (pptid);
 423         gdb_assert (newfp != nullptr);
 424         fork_save_infrun_state (m_oldfp, 1);
 425         remove_breakpoints ();
 426         fork_load_infrun_state (newfp);
 427         insert_breakpoints ();
 428       }
 429   }
 430
 431   /* Restore the previously selected infrun state.  If the constructor
 432      didn't need to switch states, then nothing is done here either.  */
 433   ~scoped_switch_fork_info ()
 434   {
 435     if (m_oldfp != nullptr)
 436       {
 437         /* Switch back to inferior_ptid.  */
 438         TRY
 439           {
 440             remove_breakpoints ();
 441             fork_load_infrun_state (m_oldfp);
 442             insert_breakpoints ();
 443           }
 444         CATCH (ex, RETURN_MASK_ALL)
 445           {
 446             warning (_("Couldn't restore checkpoint state in %s: %s"),
 447                      target_pid_to_str (m_oldfp->ptid), ex.message);
 448           }
 449         END_CATCH
 450       }
 451   }
 452
 453   DISABLE_COPY_AND_ASSIGN (scoped_switch_fork_info);
 454
 455 private:
 456   /* The fork_info for the previously selected infrun state, or nullptr if
 457      we were already in the desired state, and nothing needs to be
 458      restored.  */
 459   struct fork_info *m_oldfp;
 460 };
 461
 462 static int
 463 inferior_call_waitpid (ptid_t pptid, int pid)
 464 {
 465   struct objfile *waitpid_objf;
 466   struct value *waitpid_fn = NULL;
 467   int ret = -1;
 468
 469   scoped_switch_fork_info switch_fork_info (pptid);
 470
 471   /* Get the waitpid_fn.  */
 472   if (lookup_minimal_symbol ("waitpid", NULL, NULL).minsym != NULL)
 473     waitpid_fn = find_function_in_inferior ("waitpid", &waitpid_objf);
 474   if (!waitpid_fn
 475       && lookup_minimal_symbol ("_waitpid", NULL, NULL).minsym != NULL)
 476     waitpid_fn = find_function_in_inferior ("_waitpid", &waitpid_objf);
 477   if (waitpid_fn != nullptr)
 478     {
 479       struct gdbarch *gdbarch = get_current_arch ();
 480       struct value *argv[3], *retv;
 481
 482       /* Get the argv.  */
 483       argv[0] = value_from_longest (builtin_type (gdbarch)->builtin_int, pid);
 484       argv[1] = value_from_pointer (builtin_type (gdbarch)->builtin_data_ptr, 0);
 485       argv[2] = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 486
 487       retv = call_function_by_hand (waitpid_fn, NULL, argv);
 488
 489       if (value_as_long (retv) >= 0)
 490         ret = 0;
 491     }
 492
 493   return ret;
 494 }
 495
 496 /* Fork list <-> user interface.  */
 497
 498 static void
 499 delete_checkpoint_command (const char *args, int from_tty)
 500 {
 501   ptid_t ptid, pptid;
 502   struct fork_info *fi;
 503
 504   if (!args || !*args)
 505     error (_("Requires argument (checkpoint id to delete)"));
 506
 507   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 508   if (ptid == minus_one_ptid)
 509     error (_("No such checkpoint id, %s"), args);
 510
 511   if (ptid == inferior_ptid)
 512     error (_("\
 513 Please switch to another checkpoint before deleting the current one"));
 514
 515   if (ptrace (PTRACE_KILL, ptid.pid (), 0, 0))
 516     error (_("Unable to kill pid %s"), target_pid_to_str (ptid));
 517
 518   fi = find_fork_ptid (ptid);
 519   gdb_assert (fi);
 520   pptid = fi->parent_ptid;
 521
 522   if (from_tty)
 523     printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid));
 524
 525   delete_fork (ptid);
 526
 527   /* If fi->parent_ptid is not a part of lwp but it's a part of checkpoint
 528      list, waitpid the ptid.
 529      If fi->parent_ptid is a part of lwp and it is stopped, waitpid the
 530      ptid.  */
 531   thread_info *parent = find_thread_ptid (pptid);
 532   if ((parent == NULL && find_fork_ptid (pptid))
 533       || (parent != NULL && parent->state == THREAD_STOPPED))
 534     {
 535       if (inferior_call_waitpid (pptid, ptid.pid ()))
 536         warning (_("Unable to wait pid %s"), target_pid_to_str (ptid));
 537     }
 538 }
 539
 540 static void
 541 detach_checkpoint_command (const char *args, int from_tty)
 542 {
 543   ptid_t ptid;
 544
 545   if (!args || !*args)
 546     error (_("Requires argument (checkpoint id to detach)"));
 547
 548   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 549   if (ptid == minus_one_ptid)
 550     error (_("No such checkpoint id, %s"), args);
 551
 552   if (ptid == inferior_ptid)
 553     error (_("\
 554 Please switch to another checkpoint before detaching the current one"));
 555
 556   if (ptrace (PTRACE_DETACH, ptid.pid (), 0, 0))
 557     error (_("Unable to detach %s"), target_pid_to_str (ptid));
 558
 559   if (from_tty)
 560     printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid));
 561
 562   delete_fork (ptid);
 563 }
 564
 565 /* Print information about currently known checkpoints.  */
 566
 567 static void
 568 info_checkpoints_command (const char *arg, int from_tty)
 569 {
 570   struct gdbarch *gdbarch = get_current_arch ();
 571   int requested = -1;
 572   const fork_info *printed = NULL;
 573
 574   if (arg && *arg)
 575     requested = (int) parse_and_eval_long (arg);
 576
 577   for (const fork_info &fi : fork_list)
 578     {
 579       if (requested > 0 && fi.num != requested)
 580         continue;
 581
 582       printed = &fi;
 583       if (fi.ptid == inferior_ptid)
 584         printf_filtered ("* ");
 585       else
 586         printf_filtered ("  ");
 587
 588       ULONGEST pc = fi.pc;
 589       printf_filtered ("%d %s", fi.num, target_pid_to_str (fi.ptid));
 590       if (fi.num == 0)
 591         printf_filtered (_(" (main process)"));
 592       printf_filtered (_(" at "));
 593       fputs_filtered (paddress (gdbarch, pc), gdb_stdout);
 594
 595       symtab_and_line sal = find_pc_line (pc, 0);
 596       if (sal.symtab)
 597         printf_filtered (_(", file %s"),
 598                          symtab_to_filename_for_display (sal.symtab));
 599       if (sal.line)
 600         printf_filtered (_(", line %d"), sal.line);
 601       if (!sal.symtab && !sal.line)
 602         {
 603           struct bound_minimal_symbol msym;
 604
 605           msym = lookup_minimal_symbol_by_pc (pc);
 606           if (msym.minsym)
 607             printf_filtered (", <%s>", MSYMBOL_LINKAGE_NAME (msym.minsym));
 608         }
 609
 610       putchar_filtered ('\n');
 611     }
 612   if (printed == NULL)
 613     {
 614       if (requested > 0)
 615         printf_filtered (_("No checkpoint number %d.\n"), requested);
 616       else
 617         printf_filtered (_("No checkpoints.\n"));
 618     }
 619 }
 620
 621 /* The PID of the process we're checkpointing.  */
 622 static int checkpointing_pid = 0;
 623
 624 int
 625 linux_fork_checkpointing_p (int pid)
 626 {
 627   return (checkpointing_pid == pid);
 628 }
 629
 630 /* Return true if the current inferior is multi-threaded.  */
 631
 632 static bool
 633 inf_has_multiple_threads ()
 634 {
 635   int count = 0;
 636
 637   /* Return true as soon as we see the second thread of the current
 638      inferior.  */
 639   for (thread_info *tp ATTRIBUTE_UNUSED : current_inferior ()->threads ())
 640     if (++count > 1)
 641       return true;
 642
 643   return false;
 644 }
 645
 646 static void
 647 checkpoint_command (const char *args, int from_tty)
 648 {
 649   struct objfile *fork_objf;
 650   struct gdbarch *gdbarch;
 651   struct target_waitstatus last_target_waitstatus;
 652   ptid_t last_target_ptid;
 653   struct value *fork_fn = NULL, *ret;
 654   struct fork_info *fp;
 655   pid_t retpid;
 656
 657   if (!target_has_execution)
 658     error (_("The program is not being run."));
 659
 660   /* Ensure that the inferior is not multithreaded.  */
 661   update_thread_list ();
 662   if (inf_has_multiple_threads ())
 663     error (_("checkpoint: can't checkpoint multiple threads."));
 664
 665   /* Make the inferior fork, record its (and gdb's) state.  */
 666
 667   if (lookup_minimal_symbol ("fork", NULL, NULL).minsym != NULL)
 668     fork_fn = find_function_in_inferior ("fork", &fork_objf);
 669   if (!fork_fn)
 670     if (lookup_minimal_symbol ("_fork", NULL, NULL).minsym != NULL)
 671       fork_fn = find_function_in_inferior ("fork", &fork_objf);
 672   if (!fork_fn)
 673     error (_("checkpoint: can't find fork function in inferior."));
 674
 675   gdbarch = get_objfile_arch (fork_objf);
 676   ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 677
 678   /* Tell linux-nat.c that we're checkpointing this inferior.  */
 679   {
 680     scoped_restore save_pid
 681       = make_scoped_restore (&checkpointing_pid, inferior_ptid.pid ());
 682
 683     ret = call_function_by_hand (fork_fn, NULL, {});
 684   }
 685
 686   if (!ret)     /* Probably can't happen.  */
 687     error (_("checkpoint: call_function_by_hand returned null."));
 688
 689   retpid = value_as_long (ret);
 690   get_last_target_status (&last_target_ptid, &last_target_waitstatus);
 691
 692   fp = find_fork_pid (retpid);
 693
 694   if (from_tty)
 695     {
 696       int parent_pid;
 697
 698       printf_filtered (_("checkpoint %d: fork returned pid %ld.\n"),
 699                        fp != NULL ? fp->num : -1, (long) retpid);
 700       if (info_verbose)
 701         {
 702           parent_pid = last_target_ptid.lwp ();
 703           if (parent_pid == 0)
 704             parent_pid = last_target_ptid.pid ();
 705           printf_filtered (_("   gdb says parent = %ld.\n"),
 706                            (long) parent_pid);
 707         }
 708     }
 709
 710   if (!fp)
 711     error (_("Failed to find new fork"));
 712
 713   if (one_fork_p ())
 714     {
 715       /* Special case -- if this is the first fork in the list (the
 716          list was hitherto empty), then add inferior_ptid first, as a
 717          special zeroeth fork id.  */
 718       fork_list.emplace_front (inferior_ptid.pid ());
 719     }
 720
 721   fork_save_infrun_state (fp, 1);
 722   fp->parent_ptid = last_target_ptid;
 723 }
 724
 725 static void
 726 linux_fork_context (struct fork_info *newfp, int from_tty)
 727 {
 728   /* Now we attempt to switch processes.  */
 729   struct fork_info *oldfp;
 730
 731   gdb_assert (newfp != NULL);
 732
 733   oldfp = find_fork_ptid (inferior_ptid);
 734   gdb_assert (oldfp != NULL);
 735
 736   fork_save_infrun_state (oldfp, 1);
 737   remove_breakpoints ();
 738   fork_load_infrun_state (newfp);
 739   insert_breakpoints ();
 740
 741   printf_filtered (_("Switching to %s\n"),
 742                    target_pid_to_str (inferior_ptid));
 743
 744   print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC, 1);
 745 }
 746
 747 /* Switch inferior process (checkpoint) context, by checkpoint id.  */
 748 static void
 749 restart_command (const char *args, int from_tty)
 750 {
 751   struct fork_info *fp;
 752
 753   if (!args || !*args)
 754     error (_("Requires argument (checkpoint id to restart)"));
 755
 756   if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
 757     error (_("Not found: checkpoint id %s"), args);
 758
 759   linux_fork_context (fp, from_tty);
 760 }
 761
 762 void
 763 _initialize_linux_fork (void)
 764 {
 765   /* Checkpoint command: create a fork of the inferior process
 766      and set it aside for later debugging.  */
 767
 768   add_com ("checkpoint", class_obscure, checkpoint_command, _("\
 769 Fork a duplicate process (experimental)."));
 770
 771   /* Restart command: restore the context of a specified checkpoint
 772      process.  */
 773
 774   add_com ("restart", class_obscure, restart_command, _("\
 775 restart N: restore program context from a checkpoint.\n\
 776 Argument N is checkpoint ID, as displayed by 'info checkpoints'."));
 777
 778   /* Delete checkpoint command: kill the process and remove it from
 779      the fork list.  */
 780
 781   add_cmd ("checkpoint", class_obscure, delete_checkpoint_command, _("\
 782 Delete a checkpoint (experimental)."),
 783            &deletelist);
 784
 785   /* Detach checkpoint command: release the process to run independently,
 786      and remove it from the fork list.  */
 787
 788   add_cmd ("checkpoint", class_obscure, detach_checkpoint_command, _("\
 789 Detach from a checkpoint (experimental)."),
 790            &detachlist);
 791
 792   /* Info checkpoints command: list all forks/checkpoints
 793      currently under gdb's control.  */
 794
 795   add_info ("checkpoints", info_checkpoints_command,
 796             _("IDs of currently known checkpoints."));
 797 }