gdb/linux-fork.c

   1 /* GNU/Linux native-dependent code for debugging multiple forks.
   2
   3    Copyright (C) 2005-2017 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 "gdb_wait.h"
  35 #include <dirent.h>
  36 #include <ctype.h>
  37
  38 struct fork_info *fork_list;
  39 static int highest_fork_num;
  40
  41 /* Prevent warning from -Wmissing-prototypes.  */
  42 extern void _initialize_linux_fork (void);
  43
  44 /* Fork list data structure:  */
  45 struct fork_info
  46 {
  47   struct fork_info *next;
  48   ptid_t ptid;
  49   ptid_t parent_ptid;
  50   int num;                      /* Convenient handle (GDB fork id).  */
  51   struct regcache *savedregs;   /* Convenient for info fork, saves
  52                                    having to actually switch contexts.  */
  53   int clobber_regs;             /* True if we should restore saved regs.  */
  54   off_t *filepos;               /* Set of open file descriptors' offsets.  */
  55   int maxfd;
  56 };
  57
  58 /* Fork list methods:  */
  59
  60 int
  61 forks_exist_p (void)
  62 {
  63   return (fork_list != NULL);
  64 }
  65
  66 /* Return the last fork in the list.  */
  67
  68 static struct fork_info *
  69 find_last_fork (void)
  70 {
  71   struct fork_info *last;
  72
  73   if (fork_list == NULL)
  74     return NULL;
  75
  76   for (last = fork_list; last->next != NULL; last = last->next)
  77     ;
  78   return last;
  79 }
  80
  81 /* Add a fork to the internal fork list.  */
  82
  83 struct fork_info *
  84 add_fork (pid_t pid)
  85 {
  86   struct fork_info *fp;
  87
  88   if (fork_list == NULL && pid != ptid_get_pid (inferior_ptid))
  89     {
  90       /* Special case -- if this is the first fork in the list
  91          (the list is hitherto empty), and if this new fork is
  92          NOT the current inferior_ptid, then add inferior_ptid
  93          first, as a special zeroeth fork id.  */
  94       highest_fork_num = -1;
  95       add_fork (ptid_get_pid (inferior_ptid));  /* safe recursion */
  96     }
  97
  98   fp = XCNEW (struct fork_info);
  99   fp->ptid = ptid_build (pid, pid, 0);
 100   fp->num = ++highest_fork_num;
 101
 102   if (fork_list == NULL)
 103     fork_list = fp;
 104   else
 105     {
 106       struct fork_info *last = find_last_fork ();
 107
 108       last->next = fp;
 109     }
 110
 111   return fp;
 112 }
 113
 114 static void
 115 free_fork (struct fork_info *fp)
 116 {
 117   /* Notes on step-resume breakpoints: since this is a concern for
 118      threads, let's convince ourselves that it's not a concern for
 119      forks.  There are two ways for a fork_info to be created.  First,
 120      by the checkpoint command, in which case we're at a gdb prompt
 121      and there can't be any step-resume breakpoint.  Second, by a fork
 122      in the user program, in which case we *may* have stepped into the
 123      fork call, but regardless of whether we follow the parent or the
 124      child, we will return to the same place and the step-resume
 125      breakpoint, if any, will take care of itself as usual.  And
 126      unlike threads, we do not save a private copy of the step-resume
 127      breakpoint -- so we're OK.  */
 128
 129   if (fp)
 130     {
 131       if (fp->savedregs)
 132         regcache_xfree (fp->savedregs);
 133       if (fp->filepos)
 134         xfree (fp->filepos);
 135       xfree (fp);
 136     }
 137 }
 138
 139 static void
 140 delete_fork (ptid_t ptid)
 141 {
 142   struct fork_info *fp, *fpprev;
 143
 144   fpprev = NULL;
 145
 146   linux_nat_forget_process (ptid_get_pid (ptid));
 147
 148   for (fp = fork_list; fp; fpprev = fp, fp = fp->next)
 149     if (ptid_equal (fp->ptid, ptid))
 150       break;
 151
 152   if (!fp)
 153     return;
 154
 155   if (fpprev)
 156     fpprev->next = fp->next;
 157   else
 158     fork_list = fp->next;
 159
 160   free_fork (fp);
 161
 162   /* Special case: if there is now only one process in the list,
 163      and if it is (hopefully!) the current inferior_ptid, then
 164      remove it, leaving the list empty -- we're now down to the
 165      default case of debugging a single process.  */
 166   if (fork_list != NULL && fork_list->next == NULL &&
 167       ptid_equal (fork_list->ptid, inferior_ptid))
 168     {
 169       /* Last fork -- delete from list and handle as solo process
 170          (should be a safe recursion).  */
 171       delete_fork (inferior_ptid);
 172     }
 173 }
 174
 175 /* Find a fork_info by matching PTID.  */
 176 static struct fork_info *
 177 find_fork_ptid (ptid_t ptid)
 178 {
 179   struct fork_info *fp;
 180
 181   for (fp = fork_list; fp; fp = fp->next)
 182     if (ptid_equal (fp->ptid, ptid))
 183       return fp;
 184
 185   return NULL;
 186 }
 187
 188 /* Find a fork_info by matching ID.  */
 189 static struct fork_info *
 190 find_fork_id (int num)
 191 {
 192   struct fork_info *fp;
 193
 194   for (fp = fork_list; fp; fp = fp->next)
 195     if (fp->num == num)
 196       return fp;
 197
 198   return NULL;
 199 }
 200
 201 /* Find a fork_info by matching pid.  */
 202 extern struct fork_info *
 203 find_fork_pid (pid_t pid)
 204 {
 205   struct fork_info *fp;
 206
 207   for (fp = fork_list; fp; fp = fp->next)
 208     if (pid == ptid_get_pid (fp->ptid))
 209       return fp;
 210
 211   return NULL;
 212 }
 213
 214 static ptid_t
 215 fork_id_to_ptid (int num)
 216 {
 217   struct fork_info *fork = find_fork_id (num);
 218   if (fork)
 219     return fork->ptid;
 220   else
 221     return pid_to_ptid (-1);
 222 }
 223
 224 static void
 225 init_fork_list (void)
 226 {
 227   struct fork_info *fp, *fpnext;
 228
 229   if (!fork_list)
 230     return;
 231
 232   for (fp = fork_list; fp; fp = fpnext)
 233     {
 234       fpnext = fp->next;
 235       free_fork (fp);
 236     }
 237
 238   fork_list = NULL;
 239 }
 240
 241 /* Fork list <-> gdb interface.  */
 242
 243 /* Utility function for fork_load/fork_save.
 244    Calls lseek in the (current) inferior process.  */
 245
 246 static off_t
 247 call_lseek (int fd, off_t offset, int whence)
 248 {
 249   char exp[80];
 250
 251   snprintf (&exp[0], sizeof (exp), "(long) lseek (%d, %ld, %d)",
 252             fd, (long) offset, whence);
 253   return (off_t) parse_and_eval_long (&exp[0]);
 254 }
 255
 256 /* Load infrun state for the fork PTID.  */
 257
 258 static void
 259 fork_load_infrun_state (struct fork_info *fp)
 260 {
 261   extern void nullify_last_target_wait_ptid ();
 262   int i;
 263
 264   linux_nat_switch_fork (fp->ptid);
 265
 266   if (fp->savedregs && fp->clobber_regs)
 267     regcache_cpy (get_current_regcache (), fp->savedregs);
 268
 269   registers_changed ();
 270   reinit_frame_cache ();
 271
 272   stop_pc = regcache_read_pc (get_current_regcache ());
 273   nullify_last_target_wait_ptid ();
 274
 275   /* Now restore the file positions of open file descriptors.  */
 276   if (fp->filepos)
 277     {
 278       for (i = 0; i <= fp->maxfd; i++)
 279         if (fp->filepos[i] != (off_t) -1)
 280           call_lseek (i, fp->filepos[i], SEEK_SET);
 281       /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
 282          this is native-only.  If it ever has to be cross, we'll have
 283          to rethink this.  */
 284     }
 285 }
 286
 287 /* Save infrun state for the fork PTID.
 288    Exported for use by linux child_follow_fork.  */
 289
 290 static void
 291 fork_save_infrun_state (struct fork_info *fp, int clobber_regs)
 292 {
 293   char path[PATH_MAX];
 294   struct dirent *de;
 295   DIR *d;
 296
 297   if (fp->savedregs)
 298     regcache_xfree (fp->savedregs);
 299
 300   fp->savedregs = regcache_dup (get_current_regcache ());
 301   fp->clobber_regs = clobber_regs;
 302
 303   if (clobber_regs)
 304     {
 305       /* Now save the 'state' (file position) of all open file descriptors.
 306          Unfortunately fork does not take care of that for us...  */
 307       snprintf (path, PATH_MAX, "/proc/%ld/fd",
 308                 (long) ptid_get_pid (fp->ptid));
 309       if ((d = opendir (path)) != NULL)
 310         {
 311           long tmp;
 312
 313           fp->maxfd = 0;
 314           while ((de = readdir (d)) != NULL)
 315             {
 316               /* Count open file descriptors (actually find highest
 317                  numbered).  */
 318               tmp = strtol (&de->d_name[0], NULL, 10);
 319               if (fp->maxfd < tmp)
 320                 fp->maxfd = tmp;
 321             }
 322           /* Allocate array of file positions.  */
 323           fp->filepos = XRESIZEVEC (off_t, fp->filepos, fp->maxfd + 1);
 324
 325           /* Initialize to -1 (invalid).  */
 326           for (tmp = 0; tmp <= fp->maxfd; tmp++)
 327             fp->filepos[tmp] = -1;
 328
 329           /* Now find actual file positions.  */
 330           rewinddir (d);
 331           while ((de = readdir (d)) != NULL)
 332             if (isdigit (de->d_name[0]))
 333               {
 334                 tmp = strtol (&de->d_name[0], NULL, 10);
 335                 fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
 336               }
 337           closedir (d);
 338         }
 339     }
 340 }
 341
 342 /* Kill 'em all, let God sort 'em out...  */
 343
 344 void
 345 linux_fork_killall (void)
 346 {
 347   /* Walk list and kill every pid.  No need to treat the
 348      current inferior_ptid as special (we do not return a
 349      status for it) -- however any process may be a child
 350      or a parent, so may get a SIGCHLD from a previously
 351      killed child.  Wait them all out.  */
 352   struct fork_info *fp;
 353   pid_t pid, ret;
 354   int status;
 355
 356   for (fp = fork_list; fp; fp = fp->next)
 357     {
 358       pid = ptid_get_pid (fp->ptid);
 359       do {
 360         /* Use SIGKILL instead of PTRACE_KILL because the former works even
 361            if the thread is running, while the later doesn't.  */
 362         kill (pid, SIGKILL);
 363         ret = waitpid (pid, &status, 0);
 364         /* We might get a SIGCHLD instead of an exit status.  This is
 365          aggravated by the first kill above - a child has just
 366          died.  MVS comment cut-and-pasted from linux-nat.  */
 367       } while (ret == pid && WIFSTOPPED (status));
 368     }
 369   init_fork_list ();    /* Clear list, prepare to start fresh.  */
 370 }
 371
 372 /* The current inferior_ptid has exited, but there are other viable
 373    forks to debug.  Delete the exiting one and context-switch to the
 374    first available.  */
 375
 376 void
 377 linux_fork_mourn_inferior (void)
 378 {
 379   struct fork_info *last;
 380   int status;
 381
 382   /* Wait just one more time to collect the inferior's exit status.
 383      Do not check whether this succeeds though, since we may be
 384      dealing with a process that we attached to.  Such a process will
 385      only report its exit status to its original parent.  */
 386   waitpid (ptid_get_pid (inferior_ptid), &status, 0);
 387
 388   /* OK, presumably inferior_ptid is the one who has exited.
 389      We need to delete that one from the fork_list, and switch
 390      to the next available fork.  */
 391   delete_fork (inferior_ptid);
 392
 393   /* There should still be a fork - if there's only one left,
 394      delete_fork won't remove it, because we haven't updated
 395      inferior_ptid yet.  */
 396   gdb_assert (fork_list);
 397
 398   last = find_last_fork ();
 399   fork_load_infrun_state (last);
 400   printf_filtered (_("[Switching to %s]\n"),
 401                    target_pid_to_str (inferior_ptid));
 402
 403   /* If there's only one fork, switch back to non-fork mode.  */
 404   if (fork_list->next == NULL)
 405     delete_fork (inferior_ptid);
 406 }
 407
 408 /* The current inferior_ptid is being detached, but there are other
 409    viable forks to debug.  Detach and delete it and context-switch to
 410    the first available.  */
 411
 412 void
 413 linux_fork_detach (const char *args, int from_tty)
 414 {
 415   /* OK, inferior_ptid is the one we are detaching from.  We need to
 416      delete it from the fork_list, and switch to the next available
 417      fork.  */
 418
 419   if (ptrace (PTRACE_DETACH, ptid_get_pid (inferior_ptid), 0, 0))
 420     error (_("Unable to detach %s"), target_pid_to_str (inferior_ptid));
 421
 422   delete_fork (inferior_ptid);
 423
 424   /* There should still be a fork - if there's only one left,
 425      delete_fork won't remove it, because we haven't updated
 426      inferior_ptid yet.  */
 427   gdb_assert (fork_list);
 428
 429   fork_load_infrun_state (fork_list);
 430
 431   if (from_tty)
 432     printf_filtered (_("[Switching to %s]\n"),
 433                      target_pid_to_str (inferior_ptid));
 434
 435   /* If there's only one fork, switch back to non-fork mode.  */
 436   if (fork_list->next == NULL)
 437     delete_fork (inferior_ptid);
 438 }
 439
 440 static void
 441 inferior_call_waitpid_cleanup (void *fp)
 442 {
 443   struct fork_info *oldfp = (struct fork_info *) fp;
 444
 445   if (oldfp)
 446     {
 447       /* Switch back to inferior_ptid.  */
 448       remove_breakpoints ();
 449       fork_load_infrun_state (oldfp);
 450       insert_breakpoints ();
 451     }
 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   struct value *argv[4], *retv;
 460   struct gdbarch *gdbarch = get_current_arch ();
 461   struct fork_info *oldfp = NULL, *newfp = NULL;
 462   struct cleanup *old_cleanup;
 463   int ret = -1;
 464
 465   if (!ptid_equal (pptid, inferior_ptid))
 466     {
 467       /* Switch to pptid.  */
 468       oldfp = find_fork_ptid (inferior_ptid);
 469       gdb_assert (oldfp != NULL);
 470       newfp = find_fork_ptid (pptid);
 471       gdb_assert (newfp != NULL);
 472       fork_save_infrun_state (oldfp, 1);
 473       remove_breakpoints ();
 474       fork_load_infrun_state (newfp);
 475       insert_breakpoints ();
 476     }
 477
 478   old_cleanup = make_cleanup (inferior_call_waitpid_cleanup, oldfp);
 479
 480   /* Get the waitpid_fn.  */
 481   if (lookup_minimal_symbol ("waitpid", NULL, NULL).minsym != NULL)
 482     waitpid_fn = find_function_in_inferior ("waitpid", &waitpid_objf);
 483   if (!waitpid_fn
 484       && lookup_minimal_symbol ("_waitpid", NULL, NULL).minsym != NULL)
 485     waitpid_fn = find_function_in_inferior ("_waitpid", &waitpid_objf);
 486   if (!waitpid_fn)
 487     goto out;
 488
 489   /* Get the argv.  */
 490   argv[0] = value_from_longest (builtin_type (gdbarch)->builtin_int, pid);
 491   argv[1] = value_from_pointer (builtin_type (gdbarch)->builtin_data_ptr, 0);
 492   argv[2] = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 493   argv[3] = 0;
 494
 495   retv = call_function_by_hand (waitpid_fn, NULL, 3, argv);
 496   if (value_as_long (retv) < 0)
 497     goto out;
 498
 499   ret = 0;
 500
 501 out:
 502   do_cleanups (old_cleanup);
 503   return ret;
 504 }
 505
 506 /* Fork list <-> user interface.  */
 507
 508 static void
 509 delete_checkpoint_command (char *args, int from_tty)
 510 {
 511   ptid_t ptid, pptid;
 512   struct fork_info *fi;
 513
 514   if (!args || !*args)
 515     error (_("Requires argument (checkpoint id to delete)"));
 516
 517   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 518   if (ptid_equal (ptid, minus_one_ptid))
 519     error (_("No such checkpoint id, %s"), args);
 520
 521   if (ptid_equal (ptid, inferior_ptid))
 522     error (_("\
 523 Please switch to another checkpoint before deleting the current one"));
 524
 525   if (ptrace (PTRACE_KILL, ptid_get_pid (ptid), 0, 0))
 526     error (_("Unable to kill pid %s"), target_pid_to_str (ptid));
 527
 528   fi = find_fork_ptid (ptid);
 529   gdb_assert (fi);
 530   pptid = fi->parent_ptid;
 531
 532   if (from_tty)
 533     printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid));
 534
 535   delete_fork (ptid);
 536
 537   /* If fi->parent_ptid is not a part of lwp but it's a part of checkpoint
 538      list, waitpid the ptid.
 539      If fi->parent_ptid is a part of lwp and it is stoped, waitpid the
 540      ptid.  */
 541   if ((!find_thread_ptid (pptid) && find_fork_ptid (pptid))
 542       || (find_thread_ptid (pptid) && is_stopped (pptid)))
 543     {
 544       if (inferior_call_waitpid (pptid, ptid_get_pid (ptid)))
 545         warning (_("Unable to wait pid %s"), target_pid_to_str (ptid));
 546     }
 547 }
 548
 549 static void
 550 detach_checkpoint_command (char *args, int from_tty)
 551 {
 552   ptid_t ptid;
 553
 554   if (!args || !*args)
 555     error (_("Requires argument (checkpoint id to detach)"));
 556
 557   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 558   if (ptid_equal (ptid, minus_one_ptid))
 559     error (_("No such checkpoint id, %s"), args);
 560
 561   if (ptid_equal (ptid, inferior_ptid))
 562     error (_("\
 563 Please switch to another checkpoint before detaching the current one"));
 564
 565   if (ptrace (PTRACE_DETACH, ptid_get_pid (ptid), 0, 0))
 566     error (_("Unable to detach %s"), target_pid_to_str (ptid));
 567
 568   if (from_tty)
 569     printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid));
 570
 571   delete_fork (ptid);
 572 }
 573
 574 /* Print information about currently known checkpoints.  */
 575
 576 static void
 577 info_checkpoints_command (char *arg, int from_tty)
 578 {
 579   struct gdbarch *gdbarch = get_current_arch ();
 580   struct symtab_and_line sal;
 581   struct fork_info *fp;
 582   ULONGEST pc;
 583   int requested = -1;
 584   struct fork_info *printed = NULL;
 585
 586   if (arg && *arg)
 587     requested = (int) parse_and_eval_long (arg);
 588
 589   for (fp = fork_list; fp; fp = fp->next)
 590     {
 591       if (requested > 0 && fp->num != requested)
 592         continue;
 593
 594       printed = fp;
 595       if (ptid_equal (fp->ptid, inferior_ptid))
 596         {
 597           printf_filtered ("* ");
 598           pc = regcache_read_pc (get_current_regcache ());
 599         }
 600       else
 601         {
 602           printf_filtered ("  ");
 603           pc = regcache_read_pc (fp->savedregs);
 604         }
 605       printf_filtered ("%d %s", fp->num, target_pid_to_str (fp->ptid));
 606       if (fp->num == 0)
 607         printf_filtered (_(" (main process)"));
 608       printf_filtered (_(" at "));
 609       fputs_filtered (paddress (gdbarch, pc), gdb_stdout);
 610
 611       sal = find_pc_line (pc, 0);
 612       if (sal.symtab)
 613         printf_filtered (_(", file %s"),
 614                          symtab_to_filename_for_display (sal.symtab));
 615       if (sal.line)
 616         printf_filtered (_(", line %d"), sal.line);
 617       if (!sal.symtab && !sal.line)
 618         {
 619           struct bound_minimal_symbol msym;
 620
 621           msym = lookup_minimal_symbol_by_pc (pc);
 622           if (msym.minsym)
 623             printf_filtered (", <%s>", MSYMBOL_LINKAGE_NAME (msym.minsym));
 624         }
 625
 626       putchar_filtered ('\n');
 627     }
 628   if (printed == NULL)
 629     {
 630       if (requested > 0)
 631         printf_filtered (_("No checkpoint number %d.\n"), requested);
 632       else
 633         printf_filtered (_("No checkpoints.\n"));
 634     }
 635 }
 636
 637 /* The PID of the process we're checkpointing.  */
 638 static int checkpointing_pid = 0;
 639
 640 int
 641 linux_fork_checkpointing_p (int pid)
 642 {
 643   return (checkpointing_pid == pid);
 644 }
 645
 646 /* Callback for iterate over threads.  Used to check whether
 647    the current inferior is multi-threaded.  Returns true as soon
 648    as it sees the second thread of the current inferior.  */
 649
 650 static int
 651 inf_has_multiple_thread_cb (struct thread_info *tp, void *data)
 652 {
 653   int *count_p = (int *) data;
 654
 655   if (current_inferior ()->pid == ptid_get_pid (tp->ptid))
 656     (*count_p)++;
 657
 658   /* Stop the iteration if multiple threads have been detected.  */
 659   return *count_p > 1;
 660 }
 661
 662 /* Return true if the current inferior is multi-threaded.  */
 663
 664 static int
 665 inf_has_multiple_threads (void)
 666 {
 667   int count = 0;
 668
 669   iterate_over_threads (inf_has_multiple_thread_cb, &count);
 670   return (count > 1);
 671 }
 672
 673 static void
 674 checkpoint_command (char *args, int from_tty)
 675 {
 676   struct objfile *fork_objf;
 677   struct gdbarch *gdbarch;
 678   struct target_waitstatus last_target_waitstatus;
 679   ptid_t last_target_ptid;
 680   struct value *fork_fn = NULL, *ret;
 681   struct fork_info *fp;
 682   pid_t retpid;
 683
 684   if (!target_has_execution)
 685     error (_("The program is not being run."));
 686
 687   /* Ensure that the inferior is not multithreaded.  */
 688   update_thread_list ();
 689   if (inf_has_multiple_threads ())
 690     error (_("checkpoint: can't checkpoint multiple threads."));
 691
 692   /* Make the inferior fork, record its (and gdb's) state.  */
 693
 694   if (lookup_minimal_symbol ("fork", NULL, NULL).minsym != NULL)
 695     fork_fn = find_function_in_inferior ("fork", &fork_objf);
 696   if (!fork_fn)
 697     if (lookup_minimal_symbol ("_fork", NULL, NULL).minsym != NULL)
 698       fork_fn = find_function_in_inferior ("fork", &fork_objf);
 699   if (!fork_fn)
 700     error (_("checkpoint: can't find fork function in inferior."));
 701
 702   gdbarch = get_objfile_arch (fork_objf);
 703   ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 704
 705   /* Tell linux-nat.c that we're checkpointing this inferior.  */
 706   {
 707     scoped_restore save_pid
 708       = make_scoped_restore (&checkpointing_pid, ptid_get_pid (inferior_ptid));
 709
 710     ret = call_function_by_hand (fork_fn, NULL, 0, &ret);
 711   }
 712
 713   if (!ret)     /* Probably can't happen.  */
 714     error (_("checkpoint: call_function_by_hand returned null."));
 715
 716   retpid = value_as_long (ret);
 717   get_last_target_status (&last_target_ptid, &last_target_waitstatus);
 718
 719   fp = find_fork_pid (retpid);
 720
 721   if (from_tty)
 722     {
 723       int parent_pid;
 724
 725       printf_filtered (_("checkpoint %d: fork returned pid %ld.\n"),
 726                        fp != NULL ? fp->num : -1, (long) retpid);
 727       if (info_verbose)
 728         {
 729           parent_pid = ptid_get_lwp (last_target_ptid);
 730           if (parent_pid == 0)
 731             parent_pid = ptid_get_pid (last_target_ptid);
 732           printf_filtered (_("   gdb says parent = %ld.\n"),
 733                            (long) parent_pid);
 734         }
 735     }
 736
 737   if (!fp)
 738     error (_("Failed to find new fork"));
 739   fork_save_infrun_state (fp, 1);
 740   fp->parent_ptid = last_target_ptid;
 741 }
 742
 743 static void
 744 linux_fork_context (struct fork_info *newfp, int from_tty)
 745 {
 746   /* Now we attempt to switch processes.  */
 747   struct fork_info *oldfp;
 748
 749   gdb_assert (newfp != NULL);
 750
 751   oldfp = find_fork_ptid (inferior_ptid);
 752   gdb_assert (oldfp != NULL);
 753
 754   fork_save_infrun_state (oldfp, 1);
 755   remove_breakpoints ();
 756   fork_load_infrun_state (newfp);
 757   insert_breakpoints ();
 758
 759   printf_filtered (_("Switching to %s\n"),
 760                    target_pid_to_str (inferior_ptid));
 761
 762   print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC, 1);
 763 }
 764
 765 /* Switch inferior process (checkpoint) context, by checkpoint id.  */
 766 static void
 767 restart_command (char *args, int from_tty)
 768 {
 769   struct fork_info *fp;
 770
 771   if (!args || !*args)
 772     error (_("Requires argument (checkpoint id to restart)"));
 773
 774   if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
 775     error (_("Not found: checkpoint id %s"), args);
 776
 777   linux_fork_context (fp, from_tty);
 778 }
 779
 780 void
 781 _initialize_linux_fork (void)
 782 {
 783   init_fork_list ();
 784
 785   /* Checkpoint command: create a fork of the inferior process
 786      and set it aside for later debugging.  */
 787
 788   add_com ("checkpoint", class_obscure, checkpoint_command, _("\
 789 Fork a duplicate process (experimental)."));
 790
 791   /* Restart command: restore the context of a specified checkpoint
 792      process.  */
 793
 794   add_com ("restart", class_obscure, restart_command, _("\
 795 restart <n>: restore program context from a checkpoint.\n\
 796 Argument 'n' is checkpoint ID, as displayed by 'info checkpoints'."));
 797
 798   /* Delete checkpoint command: kill the process and remove it from
 799      the fork list.  */
 800
 801   add_cmd ("checkpoint", class_obscure, delete_checkpoint_command, _("\
 802 Delete a checkpoint (experimental)."),
 803            &deletelist);
 804
 805   /* Detach checkpoint command: release the process to run independently,
 806      and remove it from the fork list.  */
 807
 808   add_cmd ("checkpoint", class_obscure, detach_checkpoint_command, _("\
 809 Detach from a checkpoint (experimental)."),
 810            &detachlist);
 811
 812   /* Info checkpoints command: list all forks/checkpoints
 813      currently under gdb's control.  */
 814
 815   add_info ("checkpoints", info_checkpoints_command,
 816             _("IDs of currently known checkpoints."));
 817 }