gdb/linux-fork.c

   1 /* GNU/Linux native-dependent code for debugging multiple forks.
   2
   3    Copyright (C) 2005-2022 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)
  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
  65     xfree (filepos);
  66   }
  67
  68   ptid_t ptid = null_ptid;
  69   ptid_t parent_ptid = null_ptid;
  70
  71   /* Convenient handle (GDB fork id).  */
  72   int num = 0;
  73
  74   /* Convenient for info fork, saves having to actually switch
  75      contexts.  */
  76   readonly_detached_regcache *savedregs = nullptr;
  77
  78   CORE_ADDR pc = 0;
  79
  80   /* Set of open file descriptors' offsets.  */
  81   off_t *filepos = nullptr;
  82
  83   int maxfd = 0;
  84 };
  85
  86 static std::list<fork_info> fork_list;
  87 static int highest_fork_num;
  88
  89 /* Fork list methods:  */
  90
  91 int
  92 forks_exist_p (void)
  93 {
  94   return !fork_list.empty ();
  95 }
  96
  97 /* Return the last fork in the list.  */
  98
  99 static struct fork_info *
 100 find_last_fork (void)
 101 {
 102   if (fork_list.empty ())
 103     return NULL;
 104
 105   return &fork_list.back ();
 106 }
 107
 108 /* Return true iff there's one fork in the list.  */
 109
 110 static bool
 111 one_fork_p ()
 112 {
 113   return fork_list.size () == 1;
 114 }
 115
 116 /* Add a new fork to the internal fork list.  */
 117
 118 void
 119 add_fork (pid_t pid)
 120 {
 121   fork_list.emplace_back (pid);
 122
 123   if (one_fork_p ())
 124     highest_fork_num = 0;
 125
 126   fork_info *fp = &fork_list.back ();
 127   fp->num = ++highest_fork_num;
 128 }
 129
 130 static void
 131 delete_fork (ptid_t ptid)
 132 {
 133   linux_target->low_forget_process (ptid.pid ());
 134
 135   for (auto it = fork_list.begin (); it != fork_list.end (); ++it)
 136     if (it->ptid == ptid)
 137       {
 138         fork_list.erase (it);
 139
 140         /* Special case: if there is now only one process in the list,
 141            and if it is (hopefully!) the current inferior_ptid, then
 142            remove it, leaving the list empty -- we're now down to the
 143            default case of debugging a single process.  */
 144         if (one_fork_p () && fork_list.front ().ptid == inferior_ptid)
 145           {
 146             /* Last fork -- delete from list and handle as solo
 147                process (should be a safe recursion).  */
 148             delete_fork (inferior_ptid);
 149           }
 150         return;
 151       }
 152 }
 153
 154 /* Find a fork_info by matching PTID.  */
 155 static struct fork_info *
 156 find_fork_ptid (ptid_t ptid)
 157 {
 158   for (fork_info &fi : fork_list)
 159     if (fi.ptid == ptid)
 160       return &fi;
 161
 162   return NULL;
 163 }
 164
 165 /* Find a fork_info by matching ID.  */
 166 static struct fork_info *
 167 find_fork_id (int num)
 168 {
 169   for (fork_info &fi : fork_list)
 170     if (fi.num == num)
 171       return &fi;
 172
 173   return NULL;
 174 }
 175
 176 /* Find a fork_info by matching pid.  */
 177 extern struct fork_info *
 178 find_fork_pid (pid_t pid)
 179 {
 180   for (fork_info &fi : fork_list)
 181     if (pid == fi.ptid.pid ())
 182       return &fi;
 183
 184   return NULL;
 185 }
 186
 187 static ptid_t
 188 fork_id_to_ptid (int num)
 189 {
 190   struct fork_info *fork = find_fork_id (num);
 191   if (fork)
 192     return fork->ptid;
 193   else
 194     return ptid_t (-1);
 195 }
 196
 197 /* Fork list <-> gdb interface.  */
 198
 199 /* Utility function for fork_load/fork_save.
 200    Calls lseek in the (current) inferior process.  */
 201
 202 static off_t
 203 call_lseek (int fd, off_t offset, int whence)
 204 {
 205   char exp[80];
 206
 207   snprintf (&exp[0], sizeof (exp), "(long) lseek (%d, %ld, %d)",
 208             fd, (long) offset, whence);
 209   return (off_t) parse_and_eval_long (&exp[0]);
 210 }
 211
 212 /* Load infrun state for the fork PTID.  */
 213
 214 static void
 215 fork_load_infrun_state (struct fork_info *fp)
 216 {
 217   int i;
 218
 219   linux_nat_switch_fork (fp->ptid);
 220
 221   if (fp->savedregs)
 222     get_current_regcache ()->restore (fp->savedregs);
 223
 224   registers_changed ();
 225   reinit_frame_cache ();
 226
 227   inferior_thread ()->set_stop_pc (regcache_read_pc (get_current_regcache ()));
 228   nullify_last_target_wait_ptid ();
 229
 230   /* Now restore the file positions of open file descriptors.  */
 231   if (fp->filepos)
 232     {
 233       for (i = 0; i <= fp->maxfd; i++)
 234         if (fp->filepos[i] != (off_t) -1)
 235           call_lseek (i, fp->filepos[i], SEEK_SET);
 236       /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
 237          this is native-only.  If it ever has to be cross, we'll have
 238          to rethink this.  */
 239     }
 240 }
 241
 242 /* Save infrun state for the fork FP.  */
 243
 244 static void
 245 fork_save_infrun_state (struct fork_info *fp)
 246 {
 247   char path[PATH_MAX];
 248   struct dirent *de;
 249   DIR *d;
 250
 251   if (fp->savedregs)
 252     delete fp->savedregs;
 253
 254   fp->savedregs = new readonly_detached_regcache (*get_current_regcache ());
 255   fp->pc = regcache_read_pc (get_current_regcache ());
 256
 257   /* Now save the 'state' (file position) of all open file descriptors.
 258      Unfortunately fork does not take care of that for us...  */
 259   snprintf (path, PATH_MAX, "/proc/%ld/fd", (long) fp->ptid.pid ());
 260   if ((d = opendir (path)) != NULL)
 261     {
 262       long tmp;
 263
 264       fp->maxfd = 0;
 265       while ((de = readdir (d)) != NULL)
 266         {
 267           /* Count open file descriptors (actually find highest
 268              numbered).  */
 269           tmp = strtol (&de->d_name[0], NULL, 10);
 270           if (fp->maxfd < tmp)
 271             fp->maxfd = tmp;
 272         }
 273       /* Allocate array of file positions.  */
 274       fp->filepos = XRESIZEVEC (off_t, fp->filepos, fp->maxfd + 1);
 275
 276       /* Initialize to -1 (invalid).  */
 277       for (tmp = 0; tmp <= fp->maxfd; tmp++)
 278         fp->filepos[tmp] = -1;
 279
 280       /* Now find actual file positions.  */
 281       rewinddir (d);
 282       while ((de = readdir (d)) != NULL)
 283         if (isdigit (de->d_name[0]))
 284           {
 285             tmp = strtol (&de->d_name[0], NULL, 10);
 286             fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
 287           }
 288       closedir (d);
 289     }
 290 }
 291
 292 /* Kill 'em all, let God sort 'em out...  */
 293
 294 void
 295 linux_fork_killall (void)
 296 {
 297   /* Walk list and kill every pid.  No need to treat the
 298      current inferior_ptid as special (we do not return a
 299      status for it) -- however any process may be a child
 300      or a parent, so may get a SIGCHLD from a previously
 301      killed child.  Wait them all out.  */
 302
 303   for (fork_info &fi : fork_list)
 304     {
 305       pid_t pid = fi.ptid.pid ();
 306       int status;
 307       pid_t ret;
 308       do {
 309         /* Use SIGKILL instead of PTRACE_KILL because the former works even
 310            if the thread is running, while the later doesn't.  */
 311         kill (pid, SIGKILL);
 312         ret = waitpid (pid, &status, 0);
 313         /* We might get a SIGCHLD instead of an exit status.  This is
 314          aggravated by the first kill above - a child has just
 315          died.  MVS comment cut-and-pasted from linux-nat.  */
 316       } while (ret == pid && WIFSTOPPED (status));
 317     }
 318
 319   /* Clear list, prepare to start fresh.  */
 320   fork_list.clear ();
 321 }
 322
 323 /* The current inferior_ptid has exited, but there are other viable
 324    forks to debug.  Delete the exiting one and context-switch to the
 325    first available.  */
 326
 327 void
 328 linux_fork_mourn_inferior (void)
 329 {
 330   struct fork_info *last;
 331   int status;
 332
 333   /* Wait just one more time to collect the inferior's exit status.
 334      Do not check whether this succeeds though, since we may be
 335      dealing with a process that we attached to.  Such a process will
 336      only report its exit status to its original parent.  */
 337   waitpid (inferior_ptid.pid (), &status, 0);
 338
 339   /* OK, presumably inferior_ptid is the one who has exited.
 340      We need to delete that one from the fork_list, and switch
 341      to the next available fork.  */
 342   delete_fork (inferior_ptid);
 343
 344   /* There should still be a fork - if there's only one left,
 345      delete_fork won't remove it, because we haven't updated
 346      inferior_ptid yet.  */
 347   gdb_assert (!fork_list.empty ());
 348
 349   last = find_last_fork ();
 350   fork_load_infrun_state (last);
 351   printf_filtered (_("[Switching to %s]\n"),
 352                    target_pid_to_str (inferior_ptid).c_str ());
 353
 354   /* If there's only one fork, switch back to non-fork mode.  */
 355   if (one_fork_p ())
 356     delete_fork (inferior_ptid);
 357 }
 358
 359 /* The current inferior_ptid is being detached, but there are other
 360    viable forks to debug.  Detach and delete it and context-switch to
 361    the first available.  */
 362
 363 void
 364 linux_fork_detach (int from_tty)
 365 {
 366   /* OK, inferior_ptid is the one we are detaching from.  We need to
 367      delete it from the fork_list, and switch to the next available
 368      fork.  */
 369
 370   if (ptrace (PTRACE_DETACH, inferior_ptid.pid (), 0, 0))
 371     error (_("Unable to detach %s"),
 372            target_pid_to_str (inferior_ptid).c_str ());
 373
 374   delete_fork (inferior_ptid);
 375
 376   /* There should still be a fork - if there's only one left,
 377      delete_fork won't remove it, because we haven't updated
 378      inferior_ptid yet.  */
 379   gdb_assert (!fork_list.empty ());
 380
 381   fork_load_infrun_state (&fork_list.front ());
 382
 383   if (from_tty)
 384     printf_filtered (_("[Switching to %s]\n"),
 385                      target_pid_to_str (inferior_ptid).c_str ());
 386
 387   /* If there's only one fork, switch back to non-fork mode.  */
 388   if (one_fork_p ())
 389     delete_fork (inferior_ptid);
 390 }
 391
 392 /* Temporarily switch to the infrun state stored on the fork_info
 393    identified by a given ptid_t.  When this object goes out of scope,
 394    restore the currently selected infrun state.   */
 395
 396 class scoped_switch_fork_info
 397 {
 398 public:
 399   /* Switch to the infrun state held on the fork_info identified by
 400      PPTID.  If PPTID is the current inferior then no switch is done.  */
 401   explicit scoped_switch_fork_info (ptid_t pptid)
 402     : m_oldfp (nullptr)
 403   {
 404     if (pptid != inferior_ptid)
 405       {
 406         struct fork_info *newfp = nullptr;
 407
 408         /* Switch to pptid.  */
 409         m_oldfp = find_fork_ptid (inferior_ptid);
 410         gdb_assert (m_oldfp != nullptr);
 411         newfp = find_fork_ptid (pptid);
 412         gdb_assert (newfp != nullptr);
 413         fork_save_infrun_state (m_oldfp);
 414         remove_breakpoints ();
 415         fork_load_infrun_state (newfp);
 416         insert_breakpoints ();
 417       }
 418   }
 419
 420   /* Restore the previously selected infrun state.  If the constructor
 421      didn't need to switch states, then nothing is done here either.  */
 422   ~scoped_switch_fork_info ()
 423   {
 424     if (m_oldfp != nullptr)
 425       {
 426         /* Switch back to inferior_ptid.  */
 427         try
 428           {
 429             remove_breakpoints ();
 430             fork_load_infrun_state (m_oldfp);
 431             insert_breakpoints ();
 432           }
 433         catch (const gdb_exception &ex)
 434           {
 435             warning (_("Couldn't restore checkpoint state in %s: %s"),
 436                      target_pid_to_str (m_oldfp->ptid).c_str (),
 437                      ex.what ());
 438           }
 439       }
 440   }
 441
 442   DISABLE_COPY_AND_ASSIGN (scoped_switch_fork_info);
 443
 444 private:
 445   /* The fork_info for the previously selected infrun state, or nullptr if
 446      we were already in the desired state, and nothing needs to be
 447      restored.  */
 448   struct fork_info *m_oldfp;
 449 };
 450
 451 static int
 452 inferior_call_waitpid (ptid_t pptid, int pid)
 453 {
 454   struct objfile *waitpid_objf;
 455   struct value *waitpid_fn = NULL;
 456   int ret = -1;
 457
 458   scoped_switch_fork_info switch_fork_info (pptid);
 459
 460   /* Get the waitpid_fn.  */
 461   if (lookup_minimal_symbol ("waitpid", NULL, NULL).minsym != NULL)
 462     waitpid_fn = find_function_in_inferior ("waitpid", &waitpid_objf);
 463   if (!waitpid_fn
 464       && lookup_minimal_symbol ("_waitpid", NULL, NULL).minsym != NULL)
 465     waitpid_fn = find_function_in_inferior ("_waitpid", &waitpid_objf);
 466   if (waitpid_fn != nullptr)
 467     {
 468       struct gdbarch *gdbarch = get_current_arch ();
 469       struct value *argv[3], *retv;
 470
 471       /* Get the argv.  */
 472       argv[0] = value_from_longest (builtin_type (gdbarch)->builtin_int, pid);
 473       argv[1] = value_from_pointer (builtin_type (gdbarch)->builtin_data_ptr, 0);
 474       argv[2] = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 475
 476       retv = call_function_by_hand (waitpid_fn, NULL, argv);
 477
 478       if (value_as_long (retv) >= 0)
 479         ret = 0;
 480     }
 481
 482   return ret;
 483 }
 484
 485 /* Fork list <-> user interface.  */
 486
 487 static void
 488 delete_checkpoint_command (const char *args, int from_tty)
 489 {
 490   ptid_t ptid, pptid;
 491   struct fork_info *fi;
 492
 493   if (!args || !*args)
 494     error (_("Requires argument (checkpoint id to delete)"));
 495
 496   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 497   if (ptid == minus_one_ptid)
 498     error (_("No such checkpoint id, %s"), args);
 499
 500   if (ptid == inferior_ptid)
 501     error (_("\
 502 Please switch to another checkpoint before deleting the current one"));
 503
 504   if (ptrace (PTRACE_KILL, ptid.pid (), 0, 0))
 505     error (_("Unable to kill pid %s"), target_pid_to_str (ptid).c_str ());
 506
 507   fi = find_fork_ptid (ptid);
 508   gdb_assert (fi);
 509   pptid = fi->parent_ptid;
 510
 511   if (from_tty)
 512     printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid).c_str ());
 513
 514   delete_fork (ptid);
 515
 516   /* If fi->parent_ptid is not a part of lwp but it's a part of checkpoint
 517      list, waitpid the ptid.
 518      If fi->parent_ptid is a part of lwp and it is stopped, waitpid the
 519      ptid.  */
 520   thread_info *parent = find_thread_ptid (linux_target, pptid);
 521   if ((parent == NULL && find_fork_ptid (pptid))
 522       || (parent != NULL && parent->state == THREAD_STOPPED))
 523     {
 524       if (inferior_call_waitpid (pptid, ptid.pid ()))
 525         warning (_("Unable to wait pid %s"),
 526                  target_pid_to_str (ptid).c_str ());
 527     }
 528 }
 529
 530 static void
 531 detach_checkpoint_command (const char *args, int from_tty)
 532 {
 533   ptid_t ptid;
 534
 535   if (!args || !*args)
 536     error (_("Requires argument (checkpoint id to detach)"));
 537
 538   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 539   if (ptid == minus_one_ptid)
 540     error (_("No such checkpoint id, %s"), args);
 541
 542   if (ptid == inferior_ptid)
 543     error (_("\
 544 Please switch to another checkpoint before detaching the current one"));
 545
 546   if (ptrace (PTRACE_DETACH, ptid.pid (), 0, 0))
 547     error (_("Unable to detach %s"), target_pid_to_str (ptid).c_str ());
 548
 549   if (from_tty)
 550     printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid).c_str ());
 551
 552   delete_fork (ptid);
 553 }
 554
 555 /* Print information about currently known checkpoints.  */
 556
 557 static void
 558 info_checkpoints_command (const char *arg, int from_tty)
 559 {
 560   struct gdbarch *gdbarch = get_current_arch ();
 561   int requested = -1;
 562   const fork_info *printed = NULL;
 563
 564   if (arg && *arg)
 565     requested = (int) parse_and_eval_long (arg);
 566
 567   for (const fork_info &fi : fork_list)
 568     {
 569       if (requested > 0 && fi.num != requested)
 570         continue;
 571
 572       printed = &fi;
 573       if (fi.ptid == inferior_ptid)
 574         printf_filtered ("* ");
 575       else
 576         printf_filtered ("  ");
 577
 578       ULONGEST pc = fi.pc;
 579       printf_filtered ("%d %s", fi.num, target_pid_to_str (fi.ptid).c_str ());
 580       if (fi.num == 0)
 581         printf_filtered (_(" (main process)"));
 582       printf_filtered (_(" at "));
 583       fputs_filtered (paddress (gdbarch, pc), gdb_stdout);
 584
 585       symtab_and_line sal = find_pc_line (pc, 0);
 586       if (sal.symtab)
 587         printf_filtered (_(", file %s"),
 588                          symtab_to_filename_for_display (sal.symtab));
 589       if (sal.line)
 590         printf_filtered (_(", line %d"), sal.line);
 591       if (!sal.symtab && !sal.line)
 592         {
 593           struct bound_minimal_symbol msym;
 594
 595           msym = lookup_minimal_symbol_by_pc (pc);
 596           if (msym.minsym)
 597             printf_filtered (", <%s>", msym.minsym->linkage_name ());
 598         }
 599
 600       putchar_filtered ('\n');
 601     }
 602   if (printed == NULL)
 603     {
 604       if (requested > 0)
 605         printf_filtered (_("No checkpoint number %d.\n"), requested);
 606       else
 607         printf_filtered (_("No checkpoints.\n"));
 608     }
 609 }
 610
 611 /* The PID of the process we're checkpointing.  */
 612 static int checkpointing_pid = 0;
 613
 614 int
 615 linux_fork_checkpointing_p (int pid)
 616 {
 617   return (checkpointing_pid == pid);
 618 }
 619
 620 /* Return true if the current inferior is multi-threaded.  */
 621
 622 static bool
 623 inf_has_multiple_threads ()
 624 {
 625   int count = 0;
 626
 627   /* Return true as soon as we see the second thread of the current
 628      inferior.  */
 629   for (thread_info *tp ATTRIBUTE_UNUSED : current_inferior ()->threads ())
 630     if (++count > 1)
 631       return true;
 632
 633   return false;
 634 }
 635
 636 static void
 637 checkpoint_command (const char *args, int from_tty)
 638 {
 639   struct objfile *fork_objf;
 640   struct gdbarch *gdbarch;
 641   struct target_waitstatus last_target_waitstatus;
 642   ptid_t last_target_ptid;
 643   struct value *fork_fn = NULL, *ret;
 644   struct fork_info *fp;
 645   pid_t retpid;
 646
 647   if (!target_has_execution ())
 648     error (_("The program is not being run."));
 649
 650   /* Ensure that the inferior is not multithreaded.  */
 651   update_thread_list ();
 652   if (inf_has_multiple_threads ())
 653     error (_("checkpoint: can't checkpoint multiple threads."));
 654
 655   /* Make the inferior fork, record its (and gdb's) state.  */
 656
 657   if (lookup_minimal_symbol ("fork", NULL, NULL).minsym != NULL)
 658     fork_fn = find_function_in_inferior ("fork", &fork_objf);
 659   if (!fork_fn)
 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     error (_("checkpoint: can't find fork function in inferior."));
 664
 665   gdbarch = fork_objf->arch ();
 666   ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 667
 668   /* Tell linux-nat.c that we're checkpointing this inferior.  */
 669   {
 670     scoped_restore save_pid
 671       = make_scoped_restore (&checkpointing_pid, inferior_ptid.pid ());
 672
 673     ret = call_function_by_hand (fork_fn, NULL, {});
 674   }
 675
 676   if (!ret)     /* Probably can't happen.  */
 677     error (_("checkpoint: call_function_by_hand returned null."));
 678
 679   retpid = value_as_long (ret);
 680   get_last_target_status (nullptr, &last_target_ptid, &last_target_waitstatus);
 681
 682   fp = find_fork_pid (retpid);
 683
 684   if (from_tty)
 685     {
 686       int parent_pid;
 687
 688       printf_filtered (_("checkpoint %d: fork returned pid %ld.\n"),
 689                        fp != NULL ? fp->num : -1, (long) retpid);
 690       if (info_verbose)
 691         {
 692           parent_pid = last_target_ptid.lwp ();
 693           if (parent_pid == 0)
 694             parent_pid = last_target_ptid.pid ();
 695           printf_filtered (_("   gdb says parent = %ld.\n"),
 696                            (long) parent_pid);
 697         }
 698     }
 699
 700   if (!fp)
 701     error (_("Failed to find new fork"));
 702
 703   if (one_fork_p ())
 704     {
 705       /* Special case -- if this is the first fork in the list (the
 706          list was hitherto empty), then add inferior_ptid first, as a
 707          special zeroeth fork id.  */
 708       fork_list.emplace_front (inferior_ptid.pid ());
 709     }
 710
 711   fork_save_infrun_state (fp);
 712   fp->parent_ptid = last_target_ptid;
 713 }
 714
 715 static void
 716 linux_fork_context (struct fork_info *newfp, int from_tty)
 717 {
 718   /* Now we attempt to switch processes.  */
 719   struct fork_info *oldfp;
 720
 721   gdb_assert (newfp != NULL);
 722
 723   oldfp = find_fork_ptid (inferior_ptid);
 724   gdb_assert (oldfp != NULL);
 725
 726   fork_save_infrun_state (oldfp);
 727   remove_breakpoints ();
 728   fork_load_infrun_state (newfp);
 729   insert_breakpoints ();
 730
 731   printf_filtered (_("Switching to %s\n"),
 732                    target_pid_to_str (inferior_ptid).c_str ());
 733
 734   print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC, 1);
 735 }
 736
 737 /* Switch inferior process (checkpoint) context, by checkpoint id.  */
 738 static void
 739 restart_command (const char *args, int from_tty)
 740 {
 741   struct fork_info *fp;
 742
 743   if (!args || !*args)
 744     error (_("Requires argument (checkpoint id to restart)"));
 745
 746   if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
 747     error (_("Not found: checkpoint id %s"), args);
 748
 749   linux_fork_context (fp, from_tty);
 750 }
 751
 752 void _initialize_linux_fork ();
 753 void
 754 _initialize_linux_fork ()
 755 {
 756   /* Checkpoint command: create a fork of the inferior process
 757      and set it aside for later debugging.  */
 758
 759   add_com ("checkpoint", class_obscure, checkpoint_command, _("\
 760 Fork a duplicate process (experimental)."));
 761
 762   /* Restart command: restore the context of a specified checkpoint
 763      process.  */
 764
 765   add_com ("restart", class_obscure, restart_command, _("\
 766 Restore program context from a checkpoint.\n\
 767 Usage: restart N\n\
 768 Argument N is checkpoint ID, as displayed by 'info checkpoints'."));
 769
 770   /* Delete checkpoint command: kill the process and remove it from
 771      the fork list.  */
 772
 773   add_cmd ("checkpoint", class_obscure, delete_checkpoint_command, _("\
 774 Delete a checkpoint (experimental)."),
 775            &deletelist);
 776
 777   /* Detach checkpoint command: release the process to run independently,
 778      and remove it from the fork list.  */
 779
 780   add_cmd ("checkpoint", class_obscure, detach_checkpoint_command, _("\
 781 Detach from a checkpoint (experimental)."),
 782            &detachlist);
 783
 784   /* Info checkpoints command: list all forks/checkpoints
 785      currently under gdb's control.  */
 786
 787   add_info ("checkpoints", info_checkpoints_command,
 788             _("IDs of currently known checkpoints."));
 789 }