gdb/linux-fork.c

   1 /* GNU/Linux native-dependent code for debugging multiple forks.
   2
   3    Copyright (C) 2005, 2006, 2007, 2008, 2009 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 "regcache.h"
  24 #include "gdbcmd.h"
  25 #include "infcall.h"
  26 #include "objfiles.h"
  27 #include "gdb_assert.h"
  28 #include "gdb_string.h"
  29 #include "linux-fork.h"
  30 #include "linux-nat.h"
  31
  32 #include <sys/ptrace.h>
  33 #include "gdb_wait.h"
  34 #include <sys/param.h>
  35 #include "gdb_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 int detach_fork = 1;            /* Default behavior is to detach
  45                                    newly forked processes (legacy).  */
  46
  47 /* Fork list data structure:  */
  48 struct fork_info
  49 {
  50   struct fork_info *next;
  51   ptid_t ptid;
  52   int num;                      /* Convenient handle (GDB fork id) */
  53   struct regcache *savedregs;   /* Convenient for info fork, saves
  54                                    having to actually switch contexts.  */
  55   int clobber_regs;             /* True if we should restore saved regs.  */
  56   off_t *filepos;               /* Set of open file descriptors' offsets.  */
  57   int maxfd;
  58 };
  59
  60 /* Fork list methods:  */
  61
  62 int
  63 forks_exist_p (void)
  64 {
  65   return (fork_list != NULL);
  66 }
  67
  68 /* Add a fork to the internal fork list.  */
  69
  70 struct fork_info *
  71 add_fork (pid_t pid)
  72 {
  73   struct fork_info *fp;
  74
  75   if (fork_list == NULL && pid != PIDGET (inferior_ptid))
  76     {
  77       /* Special case -- if this is the first fork in the list
  78          (the list is hitherto empty), and if this new fork is
  79          NOT the current inferior_ptid, then add inferior_ptid
  80          first, as a special zeroeth fork id.  */
  81       highest_fork_num = -1;
  82       add_fork (PIDGET (inferior_ptid));        /* safe recursion */
  83     }
  84
  85   fp = XZALLOC (struct fork_info);
  86   fp->ptid = ptid_build (pid, pid, 0);
  87   fp->num = ++highest_fork_num;
  88   fp->next = fork_list;
  89   fork_list = fp;
  90   return fp;
  91 }
  92
  93 static void
  94 free_fork (struct fork_info *fp)
  95 {
  96   /* Notes on step-resume breakpoints: since this is a concern for
  97      threads, let's convince ourselves that it's not a concern for
  98      forks.  There are two ways for a fork_info to be created.  First,
  99      by the checkpoint command, in which case we're at a gdb prompt
 100      and there can't be any step-resume breakpoint.  Second, by a fork
 101      in the user program, in which case we *may* have stepped into the
 102      fork call, but regardless of whether we follow the parent or the
 103      child, we will return to the same place and the step-resume
 104      breakpoint, if any, will take care of itself as usual.  And
 105      unlike threads, we do not save a private copy of the step-resume
 106      breakpoint -- so we're OK.  */
 107
 108   if (fp)
 109     {
 110       if (fp->savedregs)
 111         regcache_xfree (fp->savedregs);
 112       if (fp->filepos)
 113         xfree (fp->filepos);
 114       xfree (fp);
 115     }
 116 }
 117
 118 static void
 119 delete_fork (ptid_t ptid)
 120 {
 121   struct fork_info *fp, *fpprev;
 122
 123   fpprev = NULL;
 124
 125   for (fp = fork_list; fp; fpprev = fp, fp = fp->next)
 126     if (ptid_equal (fp->ptid, ptid))
 127       break;
 128
 129   if (!fp)
 130     return;
 131
 132   if (fpprev)
 133     fpprev->next = fp->next;
 134   else
 135     fork_list = fp->next;
 136
 137   free_fork (fp);
 138
 139   /* Special case: if there is now only one process in the list,
 140      and if it is (hopefully!) the current inferior_ptid, then
 141      remove it, leaving the list empty -- we're now down to the
 142      default case of debugging a single process.  */
 143   if (fork_list != NULL && fork_list->next == NULL &&
 144       ptid_equal (fork_list->ptid, inferior_ptid))
 145     {
 146       /* Last fork -- delete from list and handle as solo process
 147          (should be a safe recursion).  */
 148       delete_fork (inferior_ptid);
 149     }
 150 }
 151
 152 /* Find a fork_info by matching PTID.  */
 153 static struct fork_info *
 154 find_fork_ptid (ptid_t ptid)
 155 {
 156   struct fork_info *fp;
 157
 158   for (fp = fork_list; fp; fp = fp->next)
 159     if (ptid_equal (fp->ptid, ptid))
 160       return fp;
 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   struct fork_info *fp;
 170
 171   for (fp = fork_list; fp; fp = fp->next)
 172     if (fp->num == num)
 173       return fp;
 174
 175   return NULL;
 176 }
 177
 178 /* Find a fork_info by matching pid.  */
 179 extern struct fork_info *
 180 find_fork_pid (pid_t pid)
 181 {
 182   struct fork_info *fp;
 183
 184   for (fp = fork_list; fp; fp = fp->next)
 185     if (pid == ptid_get_pid (fp->ptid))
 186       return fp;
 187
 188   return NULL;
 189 }
 190
 191 static ptid_t
 192 fork_id_to_ptid (int num)
 193 {
 194   struct fork_info *fork = find_fork_id (num);
 195   if (fork)
 196     return fork->ptid;
 197   else
 198     return pid_to_ptid (-1);
 199 }
 200
 201 static void
 202 init_fork_list (void)
 203 {
 204   struct fork_info *fp, *fpnext;
 205
 206   if (!fork_list)
 207     return;
 208
 209   for (fp = fork_list; fp; fp = fpnext)
 210     {
 211       fpnext = fp->next;
 212       free_fork (fp);
 213     }
 214
 215   fork_list = NULL;
 216 }
 217
 218 /* Fork list <-> gdb interface.  */
 219
 220 /* Utility function for fork_load/fork_save.
 221    Calls lseek in the (current) inferior process.  */
 222
 223 static off_t
 224 call_lseek (int fd, off_t offset, int whence)
 225 {
 226   char exp[80];
 227
 228   snprintf (&exp[0], sizeof (exp), "lseek (%d, %ld, %d)",
 229             fd, (long) offset, whence);
 230   return (off_t) parse_and_eval_long (&exp[0]);
 231 }
 232
 233 /* Load infrun state for the fork PTID.  */
 234
 235 static void
 236 fork_load_infrun_state (struct fork_info *fp)
 237 {
 238   extern void nullify_last_target_wait_ptid ();
 239   int i;
 240
 241   linux_nat_switch_fork (fp->ptid);
 242
 243   if (fp->savedregs && fp->clobber_regs)
 244     regcache_cpy (get_current_regcache (), fp->savedregs);
 245
 246   registers_changed ();
 247   reinit_frame_cache ();
 248
 249   stop_pc = regcache_read_pc (get_current_regcache ());
 250   nullify_last_target_wait_ptid ();
 251
 252   /* Now restore the file positions of open file descriptors.  */
 253   if (fp->filepos)
 254     {
 255       for (i = 0; i <= fp->maxfd; i++)
 256         if (fp->filepos[i] != (off_t) -1)
 257           call_lseek (i, fp->filepos[i], SEEK_SET);
 258       /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
 259          this is native-only.  If it ever has to be cross, we'll have
 260          to rethink this.  */
 261     }
 262 }
 263
 264 /* Save infrun state for the fork PTID.
 265    Exported for use by linux child_follow_fork.  */
 266
 267 static void
 268 fork_save_infrun_state (struct fork_info *fp, int clobber_regs)
 269 {
 270   char path[MAXPATHLEN];
 271   struct dirent *de;
 272   DIR *d;
 273
 274   if (fp->savedregs)
 275     regcache_xfree (fp->savedregs);
 276
 277   fp->savedregs = regcache_dup (get_current_regcache ());
 278   fp->clobber_regs = clobber_regs;
 279
 280   if (clobber_regs)
 281     {
 282       /* Now save the 'state' (file position) of all open file descriptors.
 283          Unfortunately fork does not take care of that for us...  */
 284       snprintf (path, MAXPATHLEN, "/proc/%ld/fd", (long) PIDGET (fp->ptid));
 285       if ((d = opendir (path)) != NULL)
 286         {
 287           long tmp;
 288
 289           fp->maxfd = 0;
 290           while ((de = readdir (d)) != NULL)
 291             {
 292               /* Count open file descriptors (actually find highest
 293                  numbered).  */
 294               tmp = strtol (&de->d_name[0], NULL, 10);
 295               if (fp->maxfd < tmp)
 296                 fp->maxfd = tmp;
 297             }
 298           /* Allocate array of file positions.  */
 299           fp->filepos = xrealloc (fp->filepos,
 300                                   (fp->maxfd + 1) * sizeof (*fp->filepos));
 301
 302           /* Initialize to -1 (invalid).  */
 303           for (tmp = 0; tmp <= fp->maxfd; tmp++)
 304             fp->filepos[tmp] = -1;
 305
 306           /* Now find actual file positions.  */
 307           rewinddir (d);
 308           while ((de = readdir (d)) != NULL)
 309             if (isdigit (de->d_name[0]))
 310               {
 311                 tmp = strtol (&de->d_name[0], NULL, 10);
 312                 fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
 313               }
 314           closedir (d);
 315         }
 316     }
 317 }
 318
 319 /* Kill 'em all, let God sort 'em out...  */
 320
 321 void
 322 linux_fork_killall (void)
 323 {
 324   /* Walk list and kill every pid.  No need to treat the
 325      current inferior_ptid as special (we do not return a
 326      status for it) -- however any process may be a child
 327      or a parent, so may get a SIGCHLD from a previously
 328      killed child.  Wait them all out.  */
 329   struct fork_info *fp;
 330   pid_t pid, ret;
 331   int status;
 332
 333   for (fp = fork_list; fp; fp = fp->next)
 334     {
 335       pid = PIDGET (fp->ptid);
 336       do {
 337         /* Use SIGKILL instead of PTRACE_KILL because the former works even
 338            if the thread is running, while the later doesn't.  */
 339         kill (pid, SIGKILL);
 340         ret = waitpid (pid, &status, 0);
 341         /* We might get a SIGCHLD instead of an exit status.  This is
 342          aggravated by the first kill above - a child has just
 343          died.  MVS comment cut-and-pasted from linux-nat.  */
 344       } while (ret == pid && WIFSTOPPED (status));
 345     }
 346   init_fork_list ();    /* Clear list, prepare to start fresh.  */
 347 }
 348
 349 /* The current inferior_ptid has exited, but there are other viable
 350    forks to debug.  Delete the exiting one and context-switch to the
 351    first available.  */
 352
 353 void
 354 linux_fork_mourn_inferior (void)
 355 {
 356   /* Wait just one more time to collect the inferior's exit status.
 357      Do not check whether this succeeds though, since we may be
 358      dealing with a process that we attached to.  Such a process will
 359      only report its exit status to its original parent.  */
 360   int status;
 361
 362   waitpid (ptid_get_pid (inferior_ptid), &status, 0);
 363
 364   /* OK, presumably inferior_ptid is the one who has exited.
 365      We need to delete that one from the fork_list, and switch
 366      to the next available fork.  */
 367   delete_fork (inferior_ptid);
 368
 369   /* There should still be a fork - if there's only one left,
 370      delete_fork won't remove it, because we haven't updated
 371      inferior_ptid yet.  */
 372   gdb_assert (fork_list);
 373
 374   fork_load_infrun_state (fork_list);
 375   printf_filtered (_("[Switching to %s]\n"),
 376                    target_pid_to_str (inferior_ptid));
 377
 378   /* If there's only one fork, switch back to non-fork mode.  */
 379   if (fork_list->next == NULL)
 380     delete_fork (inferior_ptid);
 381 }
 382
 383 /* The current inferior_ptid is being detached, but there are other
 384    viable forks to debug.  Detach and delete it and context-switch to
 385    the first available.  */
 386
 387 void
 388 linux_fork_detach (char *args, int from_tty)
 389 {
 390   /* OK, inferior_ptid is the one we are detaching from.  We need to
 391      delete it from the fork_list, and switch to the next available
 392      fork.  */
 393
 394   if (ptrace (PTRACE_DETACH, PIDGET (inferior_ptid), 0, 0))
 395     error (_("Unable to detach %s"), target_pid_to_str (inferior_ptid));
 396
 397   delete_fork (inferior_ptid);
 398
 399   /* There should still be a fork - if there's only one left,
 400      delete_fork won't remove it, because we haven't updated
 401      inferior_ptid yet.  */
 402   gdb_assert (fork_list);
 403
 404   fork_load_infrun_state (fork_list);
 405
 406   if (from_tty)
 407     printf_filtered (_("[Switching to %s]\n"),
 408                      target_pid_to_str (inferior_ptid));
 409
 410   /* If there's only one fork, switch back to non-fork mode.  */
 411   if (fork_list->next == NULL)
 412     delete_fork (inferior_ptid);
 413 }
 414
 415 /* Fork list <-> user interface.  */
 416
 417 static void
 418 delete_checkpoint_command (char *args, int from_tty)
 419 {
 420   ptid_t ptid;
 421
 422   if (!args || !*args)
 423     error (_("Requires argument (checkpoint id to delete)"));
 424
 425   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 426   if (ptid_equal (ptid, minus_one_ptid))
 427     error (_("No such checkpoint id, %s"), args);
 428
 429   if (ptid_equal (ptid, inferior_ptid))
 430     error (_("\
 431 Please switch to another checkpoint before deleting the current one"));
 432
 433   if (ptrace (PTRACE_KILL, PIDGET (ptid), 0, 0))
 434     error (_("Unable to kill pid %s"), target_pid_to_str (ptid));
 435
 436   if (from_tty)
 437     printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid));
 438
 439   delete_fork (ptid);
 440 }
 441
 442 static void
 443 detach_checkpoint_command (char *args, int from_tty)
 444 {
 445   ptid_t ptid;
 446
 447   if (!args || !*args)
 448     error (_("Requires argument (checkpoint id to detach)"));
 449
 450   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 451   if (ptid_equal (ptid, minus_one_ptid))
 452     error (_("No such checkpoint id, %s"), args);
 453
 454   if (ptid_equal (ptid, inferior_ptid))
 455     error (_("\
 456 Please switch to another checkpoint before detaching the current one"));
 457
 458   if (ptrace (PTRACE_DETACH, PIDGET (ptid), 0, 0))
 459     error (_("Unable to detach %s"), target_pid_to_str (ptid));
 460
 461   if (from_tty)
 462     printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid));
 463
 464   delete_fork (ptid);
 465 }
 466
 467 /* Print information about currently known checkpoints.  */
 468
 469 static void
 470 info_checkpoints_command (char *arg, int from_tty)
 471 {
 472   struct gdbarch *gdbarch = get_current_arch ();
 473   struct frame_info *cur_frame;
 474   struct symtab_and_line sal;
 475   struct symtab *cur_symtab;
 476   struct fork_info *fp;
 477   int cur_line;
 478   ULONGEST pc;
 479   int requested = -1;
 480   struct fork_info *printed = NULL;
 481
 482   if (arg && *arg)
 483     requested = (int) parse_and_eval_long (arg);
 484
 485   for (fp = fork_list; fp; fp = fp->next)
 486     {
 487       if (requested > 0 && fp->num != requested)
 488         continue;
 489
 490       printed = fp;
 491       if (ptid_equal (fp->ptid, inferior_ptid))
 492         {
 493           printf_filtered ("* ");
 494           pc = regcache_read_pc (get_current_regcache ());
 495         }
 496       else
 497         {
 498           printf_filtered ("  ");
 499           pc = regcache_read_pc (fp->savedregs);
 500         }
 501       printf_filtered ("%d %s", fp->num, target_pid_to_str (fp->ptid));
 502       if (fp->num == 0)
 503         printf_filtered (_(" (main process)"));
 504       printf_filtered (_(" at "));
 505       fputs_filtered (paddress (gdbarch, pc), gdb_stdout);
 506
 507       sal = find_pc_line (pc, 0);
 508       if (sal.symtab)
 509         {
 510           char *tmp = strrchr (sal.symtab->filename, '/');
 511
 512           if (tmp)
 513             printf_filtered (_(", file %s"), tmp + 1);
 514           else
 515             printf_filtered (_(", file %s"), sal.symtab->filename);
 516         }
 517       if (sal.line)
 518         printf_filtered (_(", line %d"), sal.line);
 519       if (!sal.symtab && !sal.line)
 520         {
 521           struct minimal_symbol *msym;
 522
 523           msym = lookup_minimal_symbol_by_pc (pc);
 524           if (msym)
 525             printf_filtered (", <%s>", SYMBOL_LINKAGE_NAME (msym));
 526         }
 527
 528       putchar_filtered ('\n');
 529     }
 530   if (printed == NULL)
 531     {
 532       if (requested > 0)
 533         printf_filtered (_("No checkpoint number %d.\n"), requested);
 534       else
 535         printf_filtered (_("No checkpoints.\n"));
 536     }
 537 }
 538
 539 /* The PID of the process we're checkpointing.  */
 540 static int checkpointing_pid = 0;
 541
 542 int
 543 linux_fork_checkpointing_p (int pid)
 544 {
 545   return (checkpointing_pid == pid);
 546 }
 547
 548 static void
 549 checkpoint_command (char *args, int from_tty)
 550 {
 551   struct objfile *fork_objf;
 552   struct gdbarch *gdbarch;
 553   struct target_waitstatus last_target_waitstatus;
 554   ptid_t last_target_ptid;
 555   struct value *fork_fn = NULL, *ret;
 556   struct fork_info *fp;
 557   pid_t retpid;
 558   struct cleanup *old_chain;
 559   long i;
 560
 561   /* Make the inferior fork, record its (and gdb's) state.  */
 562
 563   if (lookup_minimal_symbol ("fork", NULL, NULL) != NULL)
 564     fork_fn = find_function_in_inferior ("fork", &fork_objf);
 565   if (!fork_fn)
 566     if (lookup_minimal_symbol ("_fork", NULL, NULL) != NULL)
 567       fork_fn = find_function_in_inferior ("fork", &fork_objf);
 568   if (!fork_fn)
 569     error (_("checkpoint: can't find fork function in inferior."));
 570
 571   gdbarch = get_objfile_arch (fork_objf);
 572   ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 573
 574   /* Tell linux-nat.c that we're checkpointing this inferior.  */
 575   old_chain = make_cleanup_restore_integer (&checkpointing_pid);
 576   checkpointing_pid = PIDGET (inferior_ptid);
 577
 578   ret = call_function_by_hand (fork_fn, 0, &ret);
 579   do_cleanups (old_chain);
 580   if (!ret)     /* Probably can't happen.  */
 581     error (_("checkpoint: call_function_by_hand returned null."));
 582
 583   retpid = value_as_long (ret);
 584   get_last_target_status (&last_target_ptid, &last_target_waitstatus);
 585   if (from_tty)
 586     {
 587       int parent_pid;
 588
 589       printf_filtered (_("checkpoint: fork returned pid %ld.\n"),
 590                        (long) retpid);
 591       if (info_verbose)
 592         {
 593           parent_pid = ptid_get_lwp (last_target_ptid);
 594           if (parent_pid == 0)
 595             parent_pid = ptid_get_pid (last_target_ptid);
 596           printf_filtered (_("   gdb says parent = %ld.\n"),
 597                            (long) parent_pid);
 598         }
 599     }
 600
 601   fp = find_fork_pid (retpid);
 602   if (!fp)
 603     error (_("Failed to find new fork"));
 604   fork_save_infrun_state (fp, 1);
 605 }
 606
 607 static void
 608 linux_fork_context (struct fork_info *newfp, int from_tty)
 609 {
 610   /* Now we attempt to switch processes.  */
 611   struct fork_info *oldfp;
 612   ptid_t ptid;
 613   int id, i;
 614
 615   gdb_assert (newfp != NULL);
 616
 617   oldfp = find_fork_ptid (inferior_ptid);
 618   gdb_assert (oldfp != NULL);
 619
 620   fork_save_infrun_state (oldfp, 1);
 621   remove_breakpoints ();
 622   fork_load_infrun_state (newfp);
 623   insert_breakpoints ();
 624
 625   printf_filtered (_("Switching to %s\n"),
 626                    target_pid_to_str (inferior_ptid));
 627
 628   print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC);
 629 }
 630
 631 /* Switch inferior process (checkpoint) context, by checkpoint id.  */
 632 static void
 633 restart_command (char *args, int from_tty)
 634 {
 635   struct fork_info *fp;
 636
 637   if (!args || !*args)
 638     error (_("Requires argument (checkpoint id to restart)"));
 639
 640   if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
 641     error (_("Not found: checkpoint id %s"), args);
 642
 643   linux_fork_context (fp, from_tty);
 644 }
 645
 646 void
 647 _initialize_linux_fork (void)
 648 {
 649   init_fork_list ();
 650
 651   /* Set/show detach-on-fork: user-settable mode.  */
 652
 653   add_setshow_boolean_cmd ("detach-on-fork", class_obscure, &detach_fork, _("\
 654 Set whether gdb will detach the child of a fork."), _("\
 655 Show whether gdb will detach the child of a fork."), _("\
 656 Tells gdb whether to detach the child of a fork."),
 657                            NULL, NULL, &setlist, &showlist);
 658
 659   /* Checkpoint command: create a fork of the inferior process
 660      and set it aside for later debugging.  */
 661
 662   add_com ("checkpoint", class_obscure, checkpoint_command, _("\
 663 Fork a duplicate process (experimental)."));
 664
 665   /* Restart command: restore the context of a specified checkpoint
 666      process.  */
 667
 668   add_com ("restart", class_obscure, restart_command, _("\
 669 restart <n>: restore program context from a checkpoint.\n\
 670 Argument 'n' is checkpoint ID, as displayed by 'info checkpoints'."));
 671
 672   /* Delete checkpoint command: kill the process and remove it from
 673      the fork list.  */
 674
 675   add_cmd ("checkpoint", class_obscure, delete_checkpoint_command, _("\
 676 Delete a checkpoint (experimental)."),
 677            &deletelist);
 678
 679   /* Detach checkpoint command: release the process to run independently,
 680      and remove it from the fork list.  */
 681
 682   add_cmd ("checkpoint", class_obscure, detach_checkpoint_command, _("\
 683 Detach from a checkpoint (experimental)."),
 684            &detachlist);
 685
 686   /* Info checkpoints command: list all forks/checkpoints
 687      currently under gdb's control.  */
 688
 689   add_info ("checkpoints", info_checkpoints_command,
 690             _("IDs of currently known checkpoints."));
 691 }