gdb/linux-fork.c

   1 /* GNU/Linux native-dependent code for debugging multiple forks.
   2
   3    Copyright (C) 2005-2024 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 "arch-utils.h"
  21 #include "event-top.h"
  22 #include "inferior.h"
  23 #include "infrun.h"
  24 #include "regcache.h"
  25 #include "cli/cli-cmds.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 "target/waitstatus.h"
  36 #include <dirent.h>
  37 #include <ctype.h>
  38
  39 #include <list>
  40
  41 /* Fork list data structure:  */
  42 struct fork_info
  43 {
  44   explicit fork_info (pid_t pid)
  45     : ptid (pid, pid)
  46   {
  47   }
  48
  49   ~fork_info ()
  50   {
  51     /* Notes on step-resume breakpoints: since this is a concern for
  52        threads, let's convince ourselves that it's not a concern for
  53        forks.  There are two ways for a fork_info to be created.
  54        First, by the checkpoint command, in which case we're at a gdb
  55        prompt and there can't be any step-resume breakpoint.  Second,
  56        by a fork in the user program, in which case we *may* have
  57        stepped into the fork call, but regardless of whether we follow
  58        the parent or the child, we will return to the same place and
  59        the step-resume breakpoint, if any, will take care of itself as
  60        usual.  And unlike threads, we do not save a private copy of
  61        the step-resume breakpoint -- so we're OK.  */
  62
  63     if (savedregs)
  64       delete savedregs;
  65
  66     xfree (filepos);
  67   }
  68
  69   ptid_t ptid = null_ptid;
  70   ptid_t parent_ptid = null_ptid;
  71
  72   /* Convenient handle (GDB fork id).  */
  73   int num = 0;
  74
  75   /* Convenient for info fork, saves having to actually switch
  76      contexts.  */
  77   readonly_detached_regcache *savedregs = nullptr;
  78
  79   CORE_ADDR pc = 0;
  80
  81   /* Set of open file descriptors' offsets.  */
  82   off_t *filepos = nullptr;
  83
  84   int maxfd = 0;
  85 };
  86
  87 static std::list<fork_info> fork_list;
  88 static int highest_fork_num;
  89
  90 /* Fork list methods:  */
  91
  92 int
  93 forks_exist_p (void)
  94 {
  95   return !fork_list.empty ();
  96 }
  97
  98 /* Return the last fork in the list.  */
  99
 100 static struct fork_info *
 101 find_last_fork (void)
 102 {
 103   if (fork_list.empty ())
 104     return NULL;
 105
 106   return &fork_list.back ();
 107 }
 108
 109 /* Return true iff there's one fork in the list.  */
 110
 111 static bool
 112 one_fork_p ()
 113 {
 114   return fork_list.size () == 1;
 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_thread_regcache (inferior_thread ())->restore (fp->savedregs);
 224
 225   registers_changed ();
 226   reinit_frame_cache ();
 227
 228   inferior_thread ()->set_stop_pc
 229     (regcache_read_pc (get_thread_regcache (inferior_thread ())));
 230   inferior_thread ()->set_executing (false);
 231   inferior_thread ()->set_resumed (false);
 232   nullify_last_target_wait_ptid ();
 233
 234   /* Now restore the file positions of open file descriptors.  */
 235   if (fp->filepos)
 236     {
 237       for (i = 0; i <= fp->maxfd; i++)
 238         if (fp->filepos[i] != (off_t) -1)
 239           call_lseek (i, fp->filepos[i], SEEK_SET);
 240       /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
 241          this is native-only.  If it ever has to be cross, we'll have
 242          to rethink this.  */
 243     }
 244 }
 245
 246 /* Save infrun state for the fork FP.  */
 247
 248 static void
 249 fork_save_infrun_state (struct fork_info *fp)
 250 {
 251   char path[PATH_MAX];
 252   struct dirent *de;
 253   DIR *d;
 254
 255   if (fp->savedregs)
 256     delete fp->savedregs;
 257
 258   fp->savedregs = new readonly_detached_regcache
 259     (*get_thread_regcache (inferior_thread ()));
 260   fp->pc = regcache_read_pc (get_thread_regcache (inferior_thread ()));
 261
 262   /* Now save the 'state' (file position) of all open file descriptors.
 263      Unfortunately fork does not take care of that for us...  */
 264   snprintf (path, PATH_MAX, "/proc/%ld/fd", (long) fp->ptid.pid ());
 265   if ((d = opendir (path)) != NULL)
 266     {
 267       long tmp;
 268
 269       fp->maxfd = 0;
 270       while ((de = readdir (d)) != NULL)
 271         {
 272           /* Count open file descriptors (actually find highest
 273              numbered).  */
 274           tmp = strtol (&de->d_name[0], NULL, 10);
 275           if (fp->maxfd < tmp)
 276             fp->maxfd = tmp;
 277         }
 278       /* Allocate array of file positions.  */
 279       fp->filepos = XRESIZEVEC (off_t, fp->filepos, fp->maxfd + 1);
 280
 281       /* Initialize to -1 (invalid).  */
 282       for (tmp = 0; tmp <= fp->maxfd; tmp++)
 283         fp->filepos[tmp] = -1;
 284
 285       /* Now find actual file positions.  */
 286       rewinddir (d);
 287       while ((de = readdir (d)) != NULL)
 288         if (isdigit (de->d_name[0]))
 289           {
 290             tmp = strtol (&de->d_name[0], NULL, 10);
 291             fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
 292           }
 293       closedir (d);
 294     }
 295 }
 296
 297 /* Kill 'em all, let God sort 'em out...  */
 298
 299 void
 300 linux_fork_killall (void)
 301 {
 302   /* Walk list and kill every pid.  No need to treat the
 303      current inferior_ptid as special (we do not return a
 304      status for it) -- however any process may be a child
 305      or a parent, so may get a SIGCHLD from a previously
 306      killed child.  Wait them all out.  */
 307
 308   for (fork_info &fi : fork_list)
 309     {
 310       pid_t pid = fi.ptid.pid ();
 311       int status;
 312       pid_t ret;
 313       do {
 314         /* Use SIGKILL instead of PTRACE_KILL because the former works even
 315            if the thread is running, while the later doesn't.  */
 316         kill (pid, SIGKILL);
 317         ret = waitpid (pid, &status, 0);
 318         /* We might get a SIGCHLD instead of an exit status.  This is
 319          aggravated by the first kill above - a child has just
 320          died.  MVS comment cut-and-pasted from linux-nat.  */
 321       } while (ret == pid && WIFSTOPPED (status));
 322     }
 323
 324   /* Clear list, prepare to start fresh.  */
 325   fork_list.clear ();
 326 }
 327
 328 /* The current inferior_ptid has exited, but there are other viable
 329    forks to debug.  Delete the exiting one and context-switch to the
 330    first available.  */
 331
 332 void
 333 linux_fork_mourn_inferior (void)
 334 {
 335   struct fork_info *last;
 336   int status;
 337
 338   /* Wait just one more time to collect the inferior's exit status.
 339      Do not check whether this succeeds though, since we may be
 340      dealing with a process that we attached to.  Such a process will
 341      only report its exit status to its original parent.  */
 342   waitpid (inferior_ptid.pid (), &status, 0);
 343
 344   /* OK, presumably inferior_ptid is the one who has exited.
 345      We need to delete that one from the fork_list, and switch
 346      to the next available fork.  */
 347   delete_fork (inferior_ptid);
 348
 349   /* There should still be a fork - if there's only one left,
 350      delete_fork won't remove it, because we haven't updated
 351      inferior_ptid yet.  */
 352   gdb_assert (!fork_list.empty ());
 353
 354   last = find_last_fork ();
 355   fork_load_infrun_state (last);
 356   gdb_printf (_("[Switching to %s]\n"),
 357               target_pid_to_str (inferior_ptid).c_str ());
 358
 359   /* If there's only one fork, switch back to non-fork mode.  */
 360   if (one_fork_p ())
 361     delete_fork (inferior_ptid);
 362 }
 363
 364 /* The current inferior_ptid is being detached, but there are other
 365    viable forks to debug.  Detach and delete it and context-switch to
 366    the first available.  */
 367
 368 void
 369 linux_fork_detach (int from_tty, lwp_info *lp)
 370 {
 371   gdb_assert (lp != nullptr);
 372   gdb_assert (lp->ptid == inferior_ptid);
 373
 374   /* OK, inferior_ptid is the one we are detaching from.  We need to
 375      delete it from the fork_list, and switch to the next available
 376      fork.  But before doing the detach, do make sure that the lwp
 377      hasn't exited or been terminated first.  */
 378
 379   if (lp->waitstatus.kind () != TARGET_WAITKIND_EXITED
 380       && lp->waitstatus.kind () != TARGET_WAITKIND_THREAD_EXITED
 381       && lp->waitstatus.kind () != TARGET_WAITKIND_SIGNALLED)
 382     {
 383       if (ptrace (PTRACE_DETACH, inferior_ptid.pid (), 0, 0))
 384         error (_("Unable to detach %s"),
 385                target_pid_to_str (inferior_ptid).c_str ());
 386     }
 387
 388   delete_fork (inferior_ptid);
 389
 390   /* There should still be a fork - if there's only one left,
 391      delete_fork won't remove it, because we haven't updated
 392      inferior_ptid yet.  */
 393   gdb_assert (!fork_list.empty ());
 394
 395   fork_load_infrun_state (&fork_list.front ());
 396
 397   if (from_tty)
 398     gdb_printf (_("[Switching to %s]\n"),
 399                 target_pid_to_str (inferior_ptid).c_str ());
 400
 401   /* If there's only one fork, switch back to non-fork mode.  */
 402   if (one_fork_p ())
 403     delete_fork (inferior_ptid);
 404 }
 405
 406 /* Temporarily switch to the infrun state stored on the fork_info
 407    identified by a given ptid_t.  When this object goes out of scope,
 408    restore the currently selected infrun state.   */
 409
 410 class scoped_switch_fork_info
 411 {
 412 public:
 413   /* Switch to the infrun state held on the fork_info identified by
 414      PPTID.  If PPTID is the current inferior then no switch is done.  */
 415   explicit scoped_switch_fork_info (ptid_t pptid)
 416     : m_oldfp (nullptr)
 417   {
 418     if (pptid != inferior_ptid)
 419       {
 420         struct fork_info *newfp = nullptr;
 421
 422         /* Switch to pptid.  */
 423         m_oldfp = find_fork_ptid (inferior_ptid);
 424         gdb_assert (m_oldfp != nullptr);
 425         newfp = find_fork_ptid (pptid);
 426         gdb_assert (newfp != nullptr);
 427         fork_save_infrun_state (m_oldfp);
 428         remove_breakpoints ();
 429         fork_load_infrun_state (newfp);
 430         insert_breakpoints ();
 431       }
 432   }
 433
 434   /* Restore the previously selected infrun state.  If the constructor
 435      didn't need to switch states, then nothing is done here either.  */
 436   ~scoped_switch_fork_info ()
 437   {
 438     if (m_oldfp != nullptr)
 439       {
 440         /* Switch back to inferior_ptid.  */
 441         try
 442           {
 443             remove_breakpoints ();
 444             fork_load_infrun_state (m_oldfp);
 445             insert_breakpoints ();
 446           }
 447         catch (const gdb_exception_quit &ex)
 448           {
 449             /* We can't throw from a destructor, so re-set the quit flag
 450               for later QUIT checking.  */
 451             set_quit_flag ();
 452           }
 453         catch (const gdb_exception_forced_quit &ex)
 454           {
 455             /* Like above, but (eventually) cause GDB to terminate by
 456                setting sync_quit_force_run.  */
 457             set_force_quit_flag ();
 458           }
 459         catch (const gdb_exception &ex)
 460           {
 461             warning (_("Couldn't restore checkpoint state in %s: %s"),
 462                      target_pid_to_str (m_oldfp->ptid).c_str (),
 463                      ex.what ());
 464           }
 465       }
 466   }
 467
 468   DISABLE_COPY_AND_ASSIGN (scoped_switch_fork_info);
 469
 470 private:
 471   /* The fork_info for the previously selected infrun state, or nullptr if
 472      we were already in the desired state, and nothing needs to be
 473      restored.  */
 474   struct fork_info *m_oldfp;
 475 };
 476
 477 static int
 478 inferior_call_waitpid (ptid_t pptid, int pid)
 479 {
 480   struct objfile *waitpid_objf;
 481   struct value *waitpid_fn = NULL;
 482   int ret = -1;
 483
 484   scoped_switch_fork_info switch_fork_info (pptid);
 485
 486   /* Get the waitpid_fn.  */
 487   if (lookup_minimal_symbol ("waitpid", NULL, NULL).minsym != NULL)
 488     waitpid_fn = find_function_in_inferior ("waitpid", &waitpid_objf);
 489   if (!waitpid_fn
 490       && lookup_minimal_symbol ("_waitpid", NULL, NULL).minsym != NULL)
 491     waitpid_fn = find_function_in_inferior ("_waitpid", &waitpid_objf);
 492   if (waitpid_fn != nullptr)
 493     {
 494       struct gdbarch *gdbarch = get_current_arch ();
 495       struct value *argv[3], *retv;
 496
 497       /* Get the argv.  */
 498       argv[0] = value_from_longest (builtin_type (gdbarch)->builtin_int, pid);
 499       argv[1] = value_from_pointer (builtin_type (gdbarch)->builtin_data_ptr, 0);
 500       argv[2] = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 501
 502       retv = call_function_by_hand (waitpid_fn, NULL, argv);
 503
 504       if (value_as_long (retv) >= 0)
 505         ret = 0;
 506     }
 507
 508   return ret;
 509 }
 510
 511 /* Fork list <-> user interface.  */
 512
 513 static void
 514 delete_checkpoint_command (const char *args, int from_tty)
 515 {
 516   ptid_t ptid, pptid;
 517   struct fork_info *fi;
 518
 519   if (!args || !*args)
 520     error (_("Requires argument (checkpoint id to delete)"));
 521
 522   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 523   if (ptid == minus_one_ptid)
 524     error (_("No such checkpoint id, %s"), args);
 525
 526   if (ptid == inferior_ptid)
 527     error (_("\
 528 Please switch to another checkpoint before deleting the current one"));
 529
 530   if (ptrace (PTRACE_KILL, ptid.pid (), 0, 0))
 531     error (_("Unable to kill pid %s"), target_pid_to_str (ptid).c_str ());
 532
 533   fi = find_fork_ptid (ptid);
 534   gdb_assert (fi);
 535   pptid = fi->parent_ptid;
 536
 537   if (from_tty)
 538     gdb_printf (_("Killed %s\n"), target_pid_to_str (ptid).c_str ());
 539
 540   delete_fork (ptid);
 541
 542   if (pptid == null_ptid)
 543     {
 544       int status;
 545       /* Wait to collect the inferior's exit status.  Do not check whether
 546          this succeeds though, since we may be dealing with a process that we
 547          attached to.  Such a process will only report its exit status to its
 548          original parent.  */
 549       waitpid (ptid.pid (), &status, 0);
 550       return;
 551     }
 552
 553   /* If fi->parent_ptid is not a part of lwp but it's a part of checkpoint
 554      list, waitpid the ptid.
 555      If fi->parent_ptid is a part of lwp and it is stopped, waitpid the
 556      ptid.  */
 557   thread_info *parent = linux_target->find_thread (pptid);
 558   if ((parent == NULL && find_fork_ptid (pptid))
 559       || (parent != NULL && parent->state == THREAD_STOPPED))
 560     {
 561       if (inferior_call_waitpid (pptid, ptid.pid ()))
 562         warning (_("Unable to wait pid %s"),
 563                  target_pid_to_str (ptid).c_str ());
 564     }
 565 }
 566
 567 static void
 568 detach_checkpoint_command (const char *args, int from_tty)
 569 {
 570   ptid_t ptid;
 571
 572   if (!args || !*args)
 573     error (_("Requires argument (checkpoint id to detach)"));
 574
 575   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 576   if (ptid == minus_one_ptid)
 577     error (_("No such checkpoint id, %s"), args);
 578
 579   if (ptid == inferior_ptid)
 580     error (_("\
 581 Please switch to another checkpoint before detaching the current one"));
 582
 583   if (ptrace (PTRACE_DETACH, ptid.pid (), 0, 0))
 584     error (_("Unable to detach %s"), target_pid_to_str (ptid).c_str ());
 585
 586   if (from_tty)
 587     gdb_printf (_("Detached %s\n"), target_pid_to_str (ptid).c_str ());
 588
 589   delete_fork (ptid);
 590 }
 591
 592 /* Print information about currently known checkpoints.  */
 593
 594 static void
 595 info_checkpoints_command (const char *arg, int from_tty)
 596 {
 597   struct gdbarch *gdbarch = get_current_arch ();
 598   int requested = -1;
 599   bool printed = false;
 600
 601   if (arg && *arg)
 602     requested = (int) parse_and_eval_long (arg);
 603
 604   for (const fork_info &fi : fork_list)
 605     {
 606       if (requested > 0 && fi.num != requested)
 607         continue;
 608       printed = true;
 609
 610       bool is_current = fi.ptid == inferior_ptid;
 611       if (is_current)
 612         gdb_printf ("* ");
 613       else
 614         gdb_printf ("  ");
 615
 616       gdb_printf ("%d %s", fi.num, target_pid_to_str (fi.ptid).c_str ());
 617       if (fi.num == 0)
 618         gdb_printf (_(" (main process)"));
 619
 620       if (is_current && inferior_thread ()->state == THREAD_RUNNING)
 621         {
 622           gdb_printf (_(" <running>\n"));
 623           continue;
 624         }
 625
 626       gdb_printf (_(" at "));
 627       ULONGEST pc
 628         = (is_current
 629            ? regcache_read_pc (get_thread_regcache (inferior_thread ()))
 630            : fi.pc);
 631       gdb_puts (paddress (gdbarch, pc));
 632
 633       symtab_and_line sal = find_pc_line (pc, 0);
 634       if (sal.symtab)
 635         gdb_printf (_(", file %s"),
 636                     symtab_to_filename_for_display (sal.symtab));
 637       if (sal.line)
 638         gdb_printf (_(", line %d"), sal.line);
 639       if (!sal.symtab && !sal.line)
 640         {
 641           struct bound_minimal_symbol msym;
 642
 643           msym = lookup_minimal_symbol_by_pc (pc);
 644           if (msym.minsym)
 645             gdb_printf (", <%s>", msym.minsym->linkage_name ());
 646         }
 647
 648       gdb_putc ('\n');
 649     }
 650
 651   if (!printed)
 652     {
 653       if (requested > 0)
 654         gdb_printf (_("No checkpoint number %d.\n"), requested);
 655       else
 656         gdb_printf (_("No checkpoints.\n"));
 657     }
 658 }
 659
 660 /* The PID of the process we're checkpointing.  */
 661 static int checkpointing_pid = 0;
 662
 663 int
 664 linux_fork_checkpointing_p (int pid)
 665 {
 666   return (checkpointing_pid == pid);
 667 }
 668
 669 /* Return true if the current inferior is multi-threaded.  */
 670
 671 static bool
 672 inf_has_multiple_threads ()
 673 {
 674   int count = 0;
 675
 676   /* Return true as soon as we see the second thread of the current
 677      inferior.  */
 678   for (thread_info *tp ATTRIBUTE_UNUSED : current_inferior ()->threads ())
 679     if (++count > 1)
 680       return true;
 681
 682   return false;
 683 }
 684
 685 static void
 686 checkpoint_command (const char *args, int from_tty)
 687 {
 688   struct objfile *fork_objf;
 689   struct gdbarch *gdbarch;
 690   struct target_waitstatus last_target_waitstatus;
 691   ptid_t last_target_ptid;
 692   struct value *fork_fn = NULL, *ret;
 693   struct fork_info *fp;
 694   pid_t retpid;
 695
 696   if (!target_has_execution ())
 697     error (_("The program is not being run."));
 698
 699   /* Ensure that the inferior is not multithreaded.  */
 700   update_thread_list ();
 701   if (inf_has_multiple_threads ())
 702     error (_("checkpoint: can't checkpoint multiple threads."));
 703
 704   /* Make the inferior fork, record its (and gdb's) state.  */
 705
 706   if (lookup_minimal_symbol ("fork", NULL, NULL).minsym != NULL)
 707     fork_fn = find_function_in_inferior ("fork", &fork_objf);
 708   if (!fork_fn)
 709     if (lookup_minimal_symbol ("_fork", NULL, NULL).minsym != NULL)
 710       fork_fn = find_function_in_inferior ("fork", &fork_objf);
 711   if (!fork_fn)
 712     error (_("checkpoint: can't find fork function in inferior."));
 713
 714   gdbarch = fork_objf->arch ();
 715   ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 716
 717   /* Tell linux-nat.c that we're checkpointing this inferior.  */
 718   {
 719     scoped_restore save_pid
 720       = make_scoped_restore (&checkpointing_pid, inferior_ptid.pid ());
 721
 722     ret = call_function_by_hand (fork_fn, NULL, {});
 723   }
 724
 725   if (!ret)     /* Probably can't happen.  */
 726     error (_("checkpoint: call_function_by_hand returned null."));
 727
 728   retpid = value_as_long (ret);
 729   get_last_target_status (nullptr, &last_target_ptid, &last_target_waitstatus);
 730
 731   fp = find_fork_pid (retpid);
 732
 733   if (from_tty)
 734     {
 735       int parent_pid;
 736
 737       gdb_printf (_("checkpoint %d: fork returned pid %ld.\n"),
 738                   fp != NULL ? fp->num : -1, (long) retpid);
 739       if (info_verbose)
 740         {
 741           parent_pid = last_target_ptid.lwp ();
 742           if (parent_pid == 0)
 743             parent_pid = last_target_ptid.pid ();
 744           gdb_printf (_("   gdb says parent = %ld.\n"),
 745                       (long) parent_pid);
 746         }
 747     }
 748
 749   if (!fp)
 750     error (_("Failed to find new fork"));
 751
 752   if (one_fork_p ())
 753     {
 754       /* Special case -- if this is the first fork in the list (the
 755          list was hitherto empty), then add inferior_ptid first, as a
 756          special zeroeth fork id.  */
 757       fork_list.emplace_front (inferior_ptid.pid ());
 758     }
 759
 760   fork_save_infrun_state (fp);
 761   fp->parent_ptid = last_target_ptid;
 762 }
 763
 764 static void
 765 linux_fork_context (struct fork_info *newfp, int from_tty)
 766 {
 767   /* Now we attempt to switch processes.  */
 768   struct fork_info *oldfp;
 769
 770   gdb_assert (newfp != NULL);
 771
 772   oldfp = find_fork_ptid (inferior_ptid);
 773   gdb_assert (oldfp != NULL);
 774
 775   fork_save_infrun_state (oldfp);
 776   remove_breakpoints ();
 777   fork_load_infrun_state (newfp);
 778   insert_breakpoints ();
 779
 780   gdb_printf (_("Switching to %s\n"),
 781               target_pid_to_str (inferior_ptid).c_str ());
 782
 783   print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC, 1);
 784 }
 785
 786 /* Switch inferior process (checkpoint) context, by checkpoint id.  */
 787 static void
 788 restart_command (const char *args, int from_tty)
 789 {
 790   struct fork_info *fp;
 791
 792   if (!args || !*args)
 793     error (_("Requires argument (checkpoint id to restart)"));
 794
 795   if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
 796     error (_("Not found: checkpoint id %s"), args);
 797
 798   linux_fork_context (fp, from_tty);
 799 }
 800
 801 void _initialize_linux_fork ();
 802 void
 803 _initialize_linux_fork ()
 804 {
 805   /* Checkpoint command: create a fork of the inferior process
 806      and set it aside for later debugging.  */
 807
 808   add_com ("checkpoint", class_obscure, checkpoint_command, _("\
 809 Fork a duplicate process (experimental)."));
 810
 811   /* Restart command: restore the context of a specified checkpoint
 812      process.  */
 813
 814   add_com ("restart", class_obscure, restart_command, _("\
 815 Restore program context from a checkpoint.\n\
 816 Usage: restart N\n\
 817 Argument N is checkpoint ID, as displayed by 'info checkpoints'."));
 818
 819   /* Delete checkpoint command: kill the process and remove it from
 820      the fork list.  */
 821
 822   add_cmd ("checkpoint", class_obscure, delete_checkpoint_command, _("\
 823 Delete a checkpoint (experimental)."),
 824            &deletelist);
 825
 826   /* Detach checkpoint command: release the process to run independently,
 827      and remove it from the fork list.  */
 828
 829   add_cmd ("checkpoint", class_obscure, detach_checkpoint_command, _("\
 830 Detach from a checkpoint (experimental)."),
 831            &detachlist);
 832
 833   /* Info checkpoints command: list all forks/checkpoints
 834      currently under gdb's control.  */
 835
 836   add_info ("checkpoints", info_checkpoints_command,
 837             _("IDs of currently known checkpoints."));
 838 }