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 struct fork_info *fork_list;
  39 static int highest_fork_num;
  40
  41 /* Fork list data structure:  */
  42 struct fork_info
  43 {
  44   struct fork_info *next;
  45   ptid_t ptid;
  46   ptid_t parent_ptid;
  47   int num;                      /* Convenient handle (GDB fork id).  */
  48   readonly_detached_regcache *savedregs;        /* Convenient for info fork, saves
  49                                    having to actually switch contexts.  */
  50   CORE_ADDR pc;
  51   int clobber_regs;             /* True if we should restore saved regs.  */
  52   off_t *filepos;               /* Set of open file descriptors' offsets.  */
  53   int maxfd;
  54 };
  55
  56 /* Fork list methods:  */
  57
  58 int
  59 forks_exist_p (void)
  60 {
  61   return (fork_list != NULL);
  62 }
  63
  64 /* Return the last fork in the list.  */
  65
  66 static struct fork_info *
  67 find_last_fork (void)
  68 {
  69   struct fork_info *last;
  70
  71   if (fork_list == NULL)
  72     return NULL;
  73
  74   for (last = fork_list; last->next != NULL; last = last->next)
  75     ;
  76   return last;
  77 }
  78
  79 /* Add a fork to the internal fork list.  */
  80
  81 struct fork_info *
  82 add_fork (pid_t pid)
  83 {
  84   struct fork_info *fp;
  85
  86   if (fork_list == NULL && pid != inferior_ptid.pid ())
  87     {
  88       /* Special case -- if this is the first fork in the list
  89          (the list is hitherto empty), and if this new fork is
  90          NOT the current inferior_ptid, then add inferior_ptid
  91          first, as a special zeroeth fork id.  */
  92       highest_fork_num = -1;
  93       add_fork (inferior_ptid.pid ());  /* safe recursion */
  94     }
  95
  96   fp = XCNEW (struct fork_info);
  97   fp->ptid = ptid_t (pid, pid, 0);
  98   fp->num = ++highest_fork_num;
  99
 100   if (fork_list == NULL)
 101     fork_list = fp;
 102   else
 103     {
 104       struct fork_info *last = find_last_fork ();
 105
 106       last->next = fp;
 107     }
 108
 109   return fp;
 110 }
 111
 112 static void
 113 free_fork (struct fork_info *fp)
 114 {
 115   /* Notes on step-resume breakpoints: since this is a concern for
 116      threads, let's convince ourselves that it's not a concern for
 117      forks.  There are two ways for a fork_info to be created.  First,
 118      by the checkpoint command, in which case we're at a gdb prompt
 119      and there can't be any step-resume breakpoint.  Second, by a fork
 120      in the user program, in which case we *may* have stepped into the
 121      fork call, but regardless of whether we follow the parent or the
 122      child, we will return to the same place and the step-resume
 123      breakpoint, if any, will take care of itself as usual.  And
 124      unlike threads, we do not save a private copy of the step-resume
 125      breakpoint -- so we're OK.  */
 126
 127   if (fp)
 128     {
 129       if (fp->savedregs)
 130         delete fp->savedregs;
 131       if (fp->filepos)
 132         xfree (fp->filepos);
 133       xfree (fp);
 134     }
 135 }
 136
 137 static void
 138 delete_fork (ptid_t ptid)
 139 {
 140   struct fork_info *fp, *fpprev;
 141
 142   fpprev = NULL;
 143
 144   linux_target->low_forget_process (ptid.pid ());
 145
 146   for (fp = fork_list; fp; fpprev = fp, fp = fp->next)
 147     if (fp->ptid == ptid)
 148       break;
 149
 150   if (!fp)
 151     return;
 152
 153   if (fpprev)
 154     fpprev->next = fp->next;
 155   else
 156     fork_list = fp->next;
 157
 158   free_fork (fp);
 159
 160   /* Special case: if there is now only one process in the list,
 161      and if it is (hopefully!) the current inferior_ptid, then
 162      remove it, leaving the list empty -- we're now down to the
 163      default case of debugging a single process.  */
 164   if (fork_list != NULL && fork_list->next == NULL &&
 165       fork_list->ptid == inferior_ptid)
 166     {
 167       /* Last fork -- delete from list and handle as solo process
 168          (should be a safe recursion).  */
 169       delete_fork (inferior_ptid);
 170     }
 171 }
 172
 173 /* Find a fork_info by matching PTID.  */
 174 static struct fork_info *
 175 find_fork_ptid (ptid_t ptid)
 176 {
 177   struct fork_info *fp;
 178
 179   for (fp = fork_list; fp; fp = fp->next)
 180     if (fp->ptid == ptid)
 181       return fp;
 182
 183   return NULL;
 184 }
 185
 186 /* Find a fork_info by matching ID.  */
 187 static struct fork_info *
 188 find_fork_id (int num)
 189 {
 190   struct fork_info *fp;
 191
 192   for (fp = fork_list; fp; fp = fp->next)
 193     if (fp->num == num)
 194       return fp;
 195
 196   return NULL;
 197 }
 198
 199 /* Find a fork_info by matching pid.  */
 200 extern struct fork_info *
 201 find_fork_pid (pid_t pid)
 202 {
 203   struct fork_info *fp;
 204
 205   for (fp = fork_list; fp; fp = fp->next)
 206     if (pid == fp->ptid.pid ())
 207       return fp;
 208
 209   return NULL;
 210 }
 211
 212 static ptid_t
 213 fork_id_to_ptid (int num)
 214 {
 215   struct fork_info *fork = find_fork_id (num);
 216   if (fork)
 217     return fork->ptid;
 218   else
 219     return ptid_t (-1);
 220 }
 221
 222 static void
 223 init_fork_list (void)
 224 {
 225   struct fork_info *fp, *fpnext;
 226
 227   if (!fork_list)
 228     return;
 229
 230   for (fp = fork_list; fp; fp = fpnext)
 231     {
 232       fpnext = fp->next;
 233       free_fork (fp);
 234     }
 235
 236   fork_list = NULL;
 237 }
 238
 239 /* Fork list <-> gdb interface.  */
 240
 241 /* Utility function for fork_load/fork_save.
 242    Calls lseek in the (current) inferior process.  */
 243
 244 static off_t
 245 call_lseek (int fd, off_t offset, int whence)
 246 {
 247   char exp[80];
 248
 249   snprintf (&exp[0], sizeof (exp), "(long) lseek (%d, %ld, %d)",
 250             fd, (long) offset, whence);
 251   return (off_t) parse_and_eval_long (&exp[0]);
 252 }
 253
 254 /* Load infrun state for the fork PTID.  */
 255
 256 static void
 257 fork_load_infrun_state (struct fork_info *fp)
 258 {
 259   extern void nullify_last_target_wait_ptid ();
 260   int i;
 261
 262   linux_nat_switch_fork (fp->ptid);
 263
 264   if (fp->savedregs && fp->clobber_regs)
 265     get_current_regcache ()->restore (fp->savedregs);
 266
 267   registers_changed ();
 268   reinit_frame_cache ();
 269
 270   inferior_thread ()->suspend.stop_pc
 271     = regcache_read_pc (get_current_regcache ());
 272   nullify_last_target_wait_ptid ();
 273
 274   /* Now restore the file positions of open file descriptors.  */
 275   if (fp->filepos)
 276     {
 277       for (i = 0; i <= fp->maxfd; i++)
 278         if (fp->filepos[i] != (off_t) -1)
 279           call_lseek (i, fp->filepos[i], SEEK_SET);
 280       /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
 281          this is native-only.  If it ever has to be cross, we'll have
 282          to rethink this.  */
 283     }
 284 }
 285
 286 /* Save infrun state for the fork PTID.
 287    Exported for use by linux child_follow_fork.  */
 288
 289 static void
 290 fork_save_infrun_state (struct fork_info *fp, int clobber_regs)
 291 {
 292   char path[PATH_MAX];
 293   struct dirent *de;
 294   DIR *d;
 295
 296   if (fp->savedregs)
 297     delete fp->savedregs;
 298
 299   fp->savedregs = new readonly_detached_regcache (*get_current_regcache ());
 300   fp->pc = regcache_read_pc (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) fp->ptid.pid ());
 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 = fp->ptid.pid ();
 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 (inferior_ptid.pid (), &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 (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, inferior_ptid.pid (), 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 /* Temporarily switch to the infrun state stored on the fork_info
 441    identified by a given ptid_t.  When this object goes out of scope,
 442    restore the currently selected infrun state.   */
 443
 444 class scoped_switch_fork_info
 445 {
 446 public:
 447   /* Switch to the infrun state held on the fork_info identified by
 448      PPTID.  If PPTID is the current inferior then no switch is done.  */
 449   explicit scoped_switch_fork_info (ptid_t pptid)
 450     : m_oldfp (nullptr)
 451   {
 452     if (pptid != inferior_ptid)
 453       {
 454         struct fork_info *newfp = nullptr;
 455
 456         /* Switch to pptid.  */
 457         m_oldfp = find_fork_ptid (inferior_ptid);
 458         gdb_assert (m_oldfp != nullptr);
 459         newfp = find_fork_ptid (pptid);
 460         gdb_assert (newfp != nullptr);
 461         fork_save_infrun_state (m_oldfp, 1);
 462         remove_breakpoints ();
 463         fork_load_infrun_state (newfp);
 464         insert_breakpoints ();
 465       }
 466   }
 467
 468   /* Restore the previously selected infrun state.  If the constructor
 469      didn't need to switch states, then nothing is done here either.  */
 470   ~scoped_switch_fork_info ()
 471   {
 472     if (m_oldfp != nullptr)
 473       {
 474         /* Switch back to inferior_ptid.  */
 475         TRY
 476           {
 477             remove_breakpoints ();
 478             fork_load_infrun_state (m_oldfp);
 479             insert_breakpoints ();
 480           }
 481         CATCH (ex, RETURN_MASK_ALL)
 482           {
 483             warning (_("Couldn't restore checkpoint state in %s: %s"),
 484                      target_pid_to_str (m_oldfp->ptid), ex.message);
 485           }
 486         END_CATCH
 487       }
 488   }
 489
 490   DISABLE_COPY_AND_ASSIGN (scoped_switch_fork_info);
 491
 492 private:
 493   /* The fork_info for the previously selected infrun state, or nullptr if
 494      we were already in the desired state, and nothing needs to be
 495      restored.  */
 496   struct fork_info *m_oldfp;
 497 };
 498
 499 static int
 500 inferior_call_waitpid (ptid_t pptid, int pid)
 501 {
 502   struct objfile *waitpid_objf;
 503   struct value *waitpid_fn = NULL;
 504   int ret = -1;
 505
 506   scoped_switch_fork_info switch_fork_info (pptid);
 507
 508   /* Get the waitpid_fn.  */
 509   if (lookup_minimal_symbol ("waitpid", NULL, NULL).minsym != NULL)
 510     waitpid_fn = find_function_in_inferior ("waitpid", &waitpid_objf);
 511   if (!waitpid_fn
 512       && lookup_minimal_symbol ("_waitpid", NULL, NULL).minsym != NULL)
 513     waitpid_fn = find_function_in_inferior ("_waitpid", &waitpid_objf);
 514   if (waitpid_fn != nullptr)
 515     {
 516       struct gdbarch *gdbarch = get_current_arch ();
 517       struct value *argv[3], *retv;
 518
 519       /* Get the argv.  */
 520       argv[0] = value_from_longest (builtin_type (gdbarch)->builtin_int, pid);
 521       argv[1] = value_from_pointer (builtin_type (gdbarch)->builtin_data_ptr, 0);
 522       argv[2] = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 523
 524       retv = call_function_by_hand (waitpid_fn, NULL, argv);
 525
 526       if (value_as_long (retv) >= 0)
 527         ret = 0;
 528     }
 529
 530   return ret;
 531 }
 532
 533 /* Fork list <-> user interface.  */
 534
 535 static void
 536 delete_checkpoint_command (const char *args, int from_tty)
 537 {
 538   ptid_t ptid, pptid;
 539   struct fork_info *fi;
 540
 541   if (!args || !*args)
 542     error (_("Requires argument (checkpoint id to delete)"));
 543
 544   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 545   if (ptid == minus_one_ptid)
 546     error (_("No such checkpoint id, %s"), args);
 547
 548   if (ptid == inferior_ptid)
 549     error (_("\
 550 Please switch to another checkpoint before deleting the current one"));
 551
 552   if (ptrace (PTRACE_KILL, ptid.pid (), 0, 0))
 553     error (_("Unable to kill pid %s"), target_pid_to_str (ptid));
 554
 555   fi = find_fork_ptid (ptid);
 556   gdb_assert (fi);
 557   pptid = fi->parent_ptid;
 558
 559   if (from_tty)
 560     printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid));
 561
 562   delete_fork (ptid);
 563
 564   /* If fi->parent_ptid is not a part of lwp but it's a part of checkpoint
 565      list, waitpid the ptid.
 566      If fi->parent_ptid is a part of lwp and it is stopped, waitpid the
 567      ptid.  */
 568   thread_info *parent = find_thread_ptid (pptid);
 569   if ((parent == NULL && find_fork_ptid (pptid))
 570       || (parent != NULL && parent->state == THREAD_STOPPED))
 571     {
 572       if (inferior_call_waitpid (pptid, ptid.pid ()))
 573         warning (_("Unable to wait pid %s"), target_pid_to_str (ptid));
 574     }
 575 }
 576
 577 static void
 578 detach_checkpoint_command (const char *args, int from_tty)
 579 {
 580   ptid_t ptid;
 581
 582   if (!args || !*args)
 583     error (_("Requires argument (checkpoint id to detach)"));
 584
 585   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 586   if (ptid == minus_one_ptid)
 587     error (_("No such checkpoint id, %s"), args);
 588
 589   if (ptid == inferior_ptid)
 590     error (_("\
 591 Please switch to another checkpoint before detaching the current one"));
 592
 593   if (ptrace (PTRACE_DETACH, ptid.pid (), 0, 0))
 594     error (_("Unable to detach %s"), target_pid_to_str (ptid));
 595
 596   if (from_tty)
 597     printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid));
 598
 599   delete_fork (ptid);
 600 }
 601
 602 /* Print information about currently known checkpoints.  */
 603
 604 static void
 605 info_checkpoints_command (const char *arg, int from_tty)
 606 {
 607   struct gdbarch *gdbarch = get_current_arch ();
 608   struct symtab_and_line sal;
 609   struct fork_info *fp;
 610   ULONGEST pc;
 611   int requested = -1;
 612   struct fork_info *printed = NULL;
 613
 614   if (arg && *arg)
 615     requested = (int) parse_and_eval_long (arg);
 616
 617   for (fp = fork_list; fp; fp = fp->next)
 618     {
 619       if (requested > 0 && fp->num != requested)
 620         continue;
 621
 622       printed = fp;
 623       if (fp->ptid == inferior_ptid)
 624         printf_filtered ("* ");
 625       else
 626         printf_filtered ("  ");
 627
 628       pc = fp->pc;
 629       printf_filtered ("%d %s", fp->num, target_pid_to_str (fp->ptid));
 630       if (fp->num == 0)
 631         printf_filtered (_(" (main process)"));
 632       printf_filtered (_(" at "));
 633       fputs_filtered (paddress (gdbarch, pc), gdb_stdout);
 634
 635       sal = find_pc_line (pc, 0);
 636       if (sal.symtab)
 637         printf_filtered (_(", file %s"),
 638                          symtab_to_filename_for_display (sal.symtab));
 639       if (sal.line)
 640         printf_filtered (_(", line %d"), sal.line);
 641       if (!sal.symtab && !sal.line)
 642         {
 643           struct bound_minimal_symbol msym;
 644
 645           msym = lookup_minimal_symbol_by_pc (pc);
 646           if (msym.minsym)
 647             printf_filtered (", <%s>", MSYMBOL_LINKAGE_NAME (msym.minsym));
 648         }
 649
 650       putchar_filtered ('\n');
 651     }
 652   if (printed == NULL)
 653     {
 654       if (requested > 0)
 655         printf_filtered (_("No checkpoint number %d.\n"), requested);
 656       else
 657         printf_filtered (_("No checkpoints.\n"));
 658     }
 659 }
 660
 661 /* The PID of the process we're checkpointing.  */
 662 static int checkpointing_pid = 0;
 663
 664 int
 665 linux_fork_checkpointing_p (int pid)
 666 {
 667   return (checkpointing_pid == pid);
 668 }
 669
 670 /* Callback for iterate over threads.  Used to check whether
 671    the current inferior is multi-threaded.  Returns true as soon
 672    as it sees the second thread of the current inferior.  */
 673
 674 static int
 675 inf_has_multiple_thread_cb (struct thread_info *tp, void *data)
 676 {
 677   int *count_p = (int *) data;
 678
 679   if (current_inferior ()->pid == tp->ptid.pid ())
 680     (*count_p)++;
 681
 682   /* Stop the iteration if multiple threads have been detected.  */
 683   return *count_p > 1;
 684 }
 685
 686 /* Return true if the current inferior is multi-threaded.  */
 687
 688 static int
 689 inf_has_multiple_threads (void)
 690 {
 691   int count = 0;
 692
 693   iterate_over_threads (inf_has_multiple_thread_cb, &count);
 694   return (count > 1);
 695 }
 696
 697 static void
 698 checkpoint_command (const char *args, int from_tty)
 699 {
 700   struct objfile *fork_objf;
 701   struct gdbarch *gdbarch;
 702   struct target_waitstatus last_target_waitstatus;
 703   ptid_t last_target_ptid;
 704   struct value *fork_fn = NULL, *ret;
 705   struct fork_info *fp;
 706   pid_t retpid;
 707
 708   if (!target_has_execution)
 709     error (_("The program is not being run."));
 710
 711   /* Ensure that the inferior is not multithreaded.  */
 712   update_thread_list ();
 713   if (inf_has_multiple_threads ())
 714     error (_("checkpoint: can't checkpoint multiple threads."));
 715
 716   /* Make the inferior fork, record its (and gdb's) state.  */
 717
 718   if (lookup_minimal_symbol ("fork", NULL, NULL).minsym != NULL)
 719     fork_fn = find_function_in_inferior ("fork", &fork_objf);
 720   if (!fork_fn)
 721     if (lookup_minimal_symbol ("_fork", NULL, NULL).minsym != NULL)
 722       fork_fn = find_function_in_inferior ("fork", &fork_objf);
 723   if (!fork_fn)
 724     error (_("checkpoint: can't find fork function in inferior."));
 725
 726   gdbarch = get_objfile_arch (fork_objf);
 727   ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 728
 729   /* Tell linux-nat.c that we're checkpointing this inferior.  */
 730   {
 731     scoped_restore save_pid
 732       = make_scoped_restore (&checkpointing_pid, inferior_ptid.pid ());
 733
 734     ret = call_function_by_hand (fork_fn, NULL, {});
 735   }
 736
 737   if (!ret)     /* Probably can't happen.  */
 738     error (_("checkpoint: call_function_by_hand returned null."));
 739
 740   retpid = value_as_long (ret);
 741   get_last_target_status (&last_target_ptid, &last_target_waitstatus);
 742
 743   fp = find_fork_pid (retpid);
 744
 745   if (from_tty)
 746     {
 747       int parent_pid;
 748
 749       printf_filtered (_("checkpoint %d: fork returned pid %ld.\n"),
 750                        fp != NULL ? fp->num : -1, (long) retpid);
 751       if (info_verbose)
 752         {
 753           parent_pid = last_target_ptid.lwp ();
 754           if (parent_pid == 0)
 755             parent_pid = last_target_ptid.pid ();
 756           printf_filtered (_("   gdb says parent = %ld.\n"),
 757                            (long) parent_pid);
 758         }
 759     }
 760
 761   if (!fp)
 762     error (_("Failed to find new fork"));
 763   fork_save_infrun_state (fp, 1);
 764   fp->parent_ptid = last_target_ptid;
 765 }
 766
 767 static void
 768 linux_fork_context (struct fork_info *newfp, int from_tty)
 769 {
 770   /* Now we attempt to switch processes.  */
 771   struct fork_info *oldfp;
 772
 773   gdb_assert (newfp != NULL);
 774
 775   oldfp = find_fork_ptid (inferior_ptid);
 776   gdb_assert (oldfp != NULL);
 777
 778   fork_save_infrun_state (oldfp, 1);
 779   remove_breakpoints ();
 780   fork_load_infrun_state (newfp);
 781   insert_breakpoints ();
 782
 783   printf_filtered (_("Switching to %s\n"),
 784                    target_pid_to_str (inferior_ptid));
 785
 786   print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC, 1);
 787 }
 788
 789 /* Switch inferior process (checkpoint) context, by checkpoint id.  */
 790 static void
 791 restart_command (const char *args, int from_tty)
 792 {
 793   struct fork_info *fp;
 794
 795   if (!args || !*args)
 796     error (_("Requires argument (checkpoint id to restart)"));
 797
 798   if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
 799     error (_("Not found: checkpoint id %s"), args);
 800
 801   linux_fork_context (fp, from_tty);
 802 }
 803
 804 void
 805 _initialize_linux_fork (void)
 806 {
 807   init_fork_list ();
 808
 809   /* Checkpoint command: create a fork of the inferior process
 810      and set it aside for later debugging.  */
 811
 812   add_com ("checkpoint", class_obscure, checkpoint_command, _("\
 813 Fork a duplicate process (experimental)."));
 814
 815   /* Restart command: restore the context of a specified checkpoint
 816      process.  */
 817
 818   add_com ("restart", class_obscure, restart_command, _("\
 819 restart N: restore program context from a checkpoint.\n\
 820 Argument N is checkpoint ID, as displayed by 'info checkpoints'."));
 821
 822   /* Delete checkpoint command: kill the process and remove it from
 823      the fork list.  */
 824
 825   add_cmd ("checkpoint", class_obscure, delete_checkpoint_command, _("\
 826 Delete a checkpoint (experimental)."),
 827            &deletelist);
 828
 829   /* Detach checkpoint command: release the process to run independently,
 830      and remove it from the fork list.  */
 831
 832   add_cmd ("checkpoint", class_obscure, detach_checkpoint_command, _("\
 833 Detach from a checkpoint (experimental)."),
 834            &detachlist);
 835
 836   /* Info checkpoints command: list all forks/checkpoints
 837      currently under gdb's control.  */
 838
 839   add_info ("checkpoints", info_checkpoints_command,
 840             _("IDs of currently known checkpoints."));
 841 }