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 extern int
  63 forks_exist_p (void)
  64 {
  65   return (fork_list != NULL);
  66 }
  67
  68 /* Add a fork to internal fork list.
  69    Called from linux child_follow_fork.  */
  70
  71 extern struct fork_info *
  72 add_fork (pid_t pid)
  73 {
  74   struct fork_info *fp;
  75
  76   if (fork_list == NULL && pid != PIDGET (inferior_ptid))
  77     {
  78       /* Special case -- if this is the first fork in the list
  79          (the list is hitherto empty), and if this new fork is
  80          NOT the current inferior_ptid, then add inferior_ptid
  81          first, as a special zeroeth fork id.  */
  82       highest_fork_num = -1;
  83       add_fork (PIDGET (inferior_ptid));        /* safe recursion */
  84     }
  85
  86   fp = XZALLOC (struct fork_info);
  87   fp->ptid = ptid_build (pid, pid, 0);
  88   fp->num = ++highest_fork_num;
  89   fp->next = fork_list;
  90   fork_list = fp;
  91   return fp;
  92 }
  93
  94 static void
  95 free_fork (struct fork_info *fp)
  96 {
  97   /* Notes on step-resume breakpoints: since this is a concern for
  98      threads, let's convince ourselves that it's not a concern for
  99      forks.  There are two ways for a fork_info to be created.  First,
 100      by the checkpoint command, in which case we're at a gdb prompt
 101      and there can't be any step-resume breakpoint.  Second, by a fork
 102      in the user program, in which case we *may* have stepped into the
 103      fork call, but regardless of whether we follow the parent or the
 104      child, we will return to the same place and the step-resume
 105      breakpoint, if any, will take care of itself as usual.  And
 106      unlike threads, we do not save a private copy of the step-resume
 107      breakpoint -- so we're OK.  */
 108
 109   if (fp)
 110     {
 111       if (fp->savedregs)
 112         regcache_xfree (fp->savedregs);
 113       if (fp->filepos)
 114         xfree (fp->filepos);
 115       xfree (fp);
 116     }
 117 }
 118
 119 static void
 120 delete_fork (ptid_t ptid)
 121 {
 122   struct fork_info *fp, *fpprev;
 123
 124   fpprev = NULL;
 125
 126   for (fp = fork_list; fp; fpprev = fp, fp = fp->next)
 127     if (ptid_equal (fp->ptid, ptid))
 128       break;
 129
 130   if (!fp)
 131     return;
 132
 133   if (fpprev)
 134     fpprev->next = fp->next;
 135   else
 136     fork_list = fp->next;
 137
 138   free_fork (fp);
 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 (fork_list != NULL && fork_list->next == NULL &&
 145       ptid_equal (fork_list->ptid, inferior_ptid))
 146     {
 147       /* Last fork -- delete from list and handle as solo process
 148          (should be a safe recursion).  */
 149       delete_fork (inferior_ptid);
 150     }
 151 }
 152
 153 /* Find a fork_info by matching PTID.  */
 154 static struct fork_info *
 155 find_fork_ptid (ptid_t ptid)
 156 {
 157   struct fork_info *fp;
 158
 159   for (fp = fork_list; fp; fp = fp->next)
 160     if (ptid_equal (fp->ptid, ptid))
 161       return fp;
 162
 163   return NULL;
 164 }
 165
 166 /* Find a fork_info by matching ID.  */
 167 static struct fork_info *
 168 find_fork_id (int num)
 169 {
 170   struct fork_info *fp;
 171
 172   for (fp = fork_list; fp; fp = fp->next)
 173     if (fp->num == num)
 174       return fp;
 175
 176   return NULL;
 177 }
 178
 179 /* Find a fork_info by matching pid.  */
 180 extern struct fork_info *
 181 find_fork_pid (pid_t pid)
 182 {
 183   struct fork_info *fp;
 184
 185   for (fp = fork_list; fp; fp = fp->next)
 186     if (pid == ptid_get_pid (fp->ptid))
 187       return fp;
 188
 189   return NULL;
 190 }
 191
 192 static ptid_t
 193 fork_id_to_ptid (int num)
 194 {
 195   struct fork_info *fork = find_fork_id (num);
 196   if (fork)
 197     return fork->ptid;
 198   else
 199     return pid_to_ptid (-1);
 200 }
 201
 202 static void
 203 init_fork_list (void)
 204 {
 205   struct fork_info *fp, *fpnext;
 206
 207   if (!fork_list)
 208     return;
 209
 210   for (fp = fork_list; fp; fp = fpnext)
 211     {
 212       fpnext = fp->next;
 213       free_fork (fp);
 214     }
 215
 216   fork_list = NULL;
 217 }
 218
 219 /* Fork list <-> gdb interface.  */
 220
 221 /* Utility function for fork_load/fork_save.
 222    Calls lseek in the (current) inferior process.  */
 223
 224 static off_t
 225 call_lseek (int fd, off_t offset, int whence)
 226 {
 227   char exp[80];
 228
 229   snprintf (&exp[0], sizeof (exp), "lseek (%d, %ld, %d)",
 230             fd, (long) offset, whence);
 231   return (off_t) parse_and_eval_long (&exp[0]);
 232 }
 233
 234 /* Load infrun state for the fork PTID.  */
 235
 236 static void
 237 fork_load_infrun_state (struct fork_info *fp)
 238 {
 239   extern void nullify_last_target_wait_ptid ();
 240   int i;
 241
 242   linux_nat_switch_fork (fp->ptid);
 243
 244   if (fp->savedregs && fp->clobber_regs)
 245     regcache_cpy (get_current_regcache (), fp->savedregs);
 246
 247   registers_changed ();
 248   reinit_frame_cache ();
 249
 250   stop_pc = regcache_read_pc (get_current_regcache ());
 251   nullify_last_target_wait_ptid ();
 252
 253   /* Now restore the file positions of open file descriptors.  */
 254   if (fp->filepos)
 255     {
 256       for (i = 0; i <= fp->maxfd; i++)
 257         if (fp->filepos[i] != (off_t) -1)
 258           call_lseek (i, fp->filepos[i], SEEK_SET);
 259       /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
 260          this is native-only.  If it ever has to be cross, we'll have
 261          to rethink this.  */
 262     }
 263 }
 264
 265 /* Save infrun state for the fork PTID.
 266    Exported for use by linux child_follow_fork.  */
 267
 268 static void
 269 fork_save_infrun_state (struct fork_info *fp, int clobber_regs)
 270 {
 271   char path[MAXPATHLEN];
 272   struct dirent *de;
 273   DIR *d;
 274
 275   if (fp->savedregs)
 276     regcache_xfree (fp->savedregs);
 277
 278   fp->savedregs = regcache_dup (get_current_regcache ());
 279   fp->clobber_regs = clobber_regs;
 280
 281   if (clobber_regs)
 282     {
 283       /* Now save the 'state' (file position) of all open file descriptors.
 284          Unfortunately fork does not take care of that for us...  */
 285       snprintf (path, MAXPATHLEN, "/proc/%ld/fd", (long) PIDGET (fp->ptid));
 286       if ((d = opendir (path)) != NULL)
 287         {
 288           long tmp;
 289
 290           fp->maxfd = 0;
 291           while ((de = readdir (d)) != NULL)
 292             {
 293               /* Count open file descriptors (actually find highest
 294                  numbered).  */
 295               tmp = strtol (&de->d_name[0], NULL, 10);
 296               if (fp->maxfd < tmp)
 297                 fp->maxfd = tmp;
 298             }
 299           /* Allocate array of file positions.  */
 300           fp->filepos = xrealloc (fp->filepos,
 301                                   (fp->maxfd + 1) * sizeof (*fp->filepos));
 302
 303           /* Initialize to -1 (invalid).  */
 304           for (tmp = 0; tmp <= fp->maxfd; tmp++)
 305             fp->filepos[tmp] = -1;
 306
 307           /* Now find actual file positions.  */
 308           rewinddir (d);
 309           while ((de = readdir (d)) != NULL)
 310             if (isdigit (de->d_name[0]))
 311               {
 312                 tmp = strtol (&de->d_name[0], NULL, 10);
 313                 fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
 314               }
 315           closedir (d);
 316         }
 317     }
 318 }
 319
 320 /* Kill 'em all, let God sort 'em out...  */
 321
 322 extern void
 323 linux_fork_killall (void)
 324 {
 325   /* Walk list and kill every pid.  No need to treat the
 326      current inferior_ptid as special (we do not return a
 327      status for it) -- however any process may be a child
 328      or a parent, so may get a SIGCHLD from a previously
 329      killed child.  Wait them all out.  */
 330   struct fork_info *fp;
 331   pid_t pid, ret;
 332   int status;
 333
 334   for (fp = fork_list; fp; fp = fp->next)
 335     {
 336       pid = PIDGET (fp->ptid);
 337       do {
 338         /* Use SIGKILL instead of PTRACE_KILL because the former works even
 339            if the thread is running, while the later doesn't.  */
 340         kill (pid, SIGKILL);
 341         ret = waitpid (pid, &status, 0);
 342         /* We might get a SIGCHLD instead of an exit status.  This is
 343          aggravated by the first kill above - a child has just
 344          died.  MVS comment cut-and-pasted from linux-nat.  */
 345       } while (ret == pid && WIFSTOPPED (status));
 346     }
 347   init_fork_list ();    /* Clear list, prepare to start fresh.  */
 348 }
 349
 350 /* The current inferior_ptid has exited, but there are other viable
 351    forks to debug.  Delete the exiting one and context-switch to the
 352    first available.  */
 353
 354 extern void
 355 linux_fork_mourn_inferior (void)
 356 {
 357   /* Wait just one more time to collect the inferior's exit status.
 358      Do not check whether this succeeds though, since we may be
 359      dealing with a process that we attached to.  Such a process will
 360      only report its exit status to its original parent.  */
 361   int status;
 362
 363   waitpid (ptid_get_pid (inferior_ptid), &status, 0);
 364
 365   /* OK, presumably inferior_ptid is the one who has exited.
 366      We need to delete that one from the fork_list, and switch
 367      to the next available fork.  */
 368   delete_fork (inferior_ptid);
 369
 370   /* There should still be a fork - if there's only one left,
 371      delete_fork won't remove it, because we haven't updated
 372      inferior_ptid yet.  */
 373   gdb_assert (fork_list);
 374
 375   fork_load_infrun_state (fork_list);
 376   printf_filtered (_("[Switching to %s]\n"),
 377                    target_pid_to_str (inferior_ptid));
 378
 379   /* If there's only one fork, switch back to non-fork mode.  */
 380   if (fork_list->next == NULL)
 381     delete_fork (inferior_ptid);
 382 }
 383
 384 /* The current inferior_ptid is being detached, but there are other
 385    viable forks to debug.  Detach and delete it and context-switch to
 386    the first available.  */
 387
 388 extern void
 389 linux_fork_detach (char *args, int from_tty)
 390 {
 391   /* OK, inferior_ptid is the one we are detaching from.  We need to
 392      delete it from the fork_list, and switch to the next available
 393      fork.  */
 394
 395   if (ptrace (PTRACE_DETACH, PIDGET (inferior_ptid), 0, 0))
 396     error (_("Unable to detach %s"), target_pid_to_str (inferior_ptid));
 397
 398   delete_fork (inferior_ptid);
 399
 400   /* There should still be a fork - if there's only one left,
 401      delete_fork won't remove it, because we haven't updated
 402      inferior_ptid yet.  */
 403   gdb_assert (fork_list);
 404
 405   fork_load_infrun_state (fork_list);
 406
 407   if (from_tty)
 408     printf_filtered (_("[Switching to %s]\n"),
 409                      target_pid_to_str (inferior_ptid));
 410
 411   /* If there's only one fork, switch back to non-fork mode.  */
 412   if (fork_list->next == NULL)
 413     delete_fork (inferior_ptid);
 414 }
 415
 416 /* Fork list <-> user interface.  */
 417
 418 static void
 419 delete_fork_command (char *args, int from_tty)
 420 {
 421   ptid_t ptid;
 422
 423   if (!args || !*args)
 424     error (_("Requires argument (checkpoint id to delete)"));
 425
 426   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 427   if (ptid_equal (ptid, minus_one_ptid))
 428     error (_("No such checkpoint id, %s"), args);
 429
 430   if (ptid_equal (ptid, inferior_ptid))
 431     error (_("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_fork_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 forks.  */
 468
 469 static void
 470 info_forks_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   /* Set/show restart-auto-finish: user-settable count.  Causes the
 660      first "restart" of a fork to do some number of "finish" commands
 661      before returning to user.
 662
 663      Useful because otherwise the virgin fork process will be stopped
 664      somewhere in the un-interesting fork system call.  */
 665
 666   /* Checkpoint command: create a fork of the inferior process
 667      and set it aside for later debugging.  */
 668
 669   add_com ("checkpoint", class_obscure, checkpoint_command, _("\
 670 Fork a duplicate process (experimental)."));
 671
 672   /* Restart command: restore the context of a specified checkpoint
 673      process.  */
 674
 675   add_com ("restart", class_obscure, restart_command, _("\
 676 restart <n>: restore program context from a checkpoint.\n\
 677 Argument 'n' is checkpoint ID, as displayed by 'info checkpoints'."));
 678
 679   /* Delete checkpoint command: kill the process and remove it from
 680      fork list.  */
 681
 682   add_cmd ("checkpoint", class_obscure, delete_fork_command, _("\
 683 Delete a checkpoint (experimental)."),
 684            &deletelist);
 685
 686   /* Detach checkpoint command: release the process to run independently,
 687      and remove it from the fork list.  */
 688
 689   add_cmd ("checkpoint", class_obscure, detach_fork_command, _("\
 690 Detach from a checkpoint (experimental)."),
 691            &detachlist);
 692
 693   /* Info checkpoints command: list all forks/checkpoints
 694      currently under gdb's control.  */
 695
 696   add_info ("checkpoints", info_forks_command,
 697             _("IDs of currently known checkpoints."));
 698 }