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 /* Fork list data structure:  */
  45 struct fork_info
  46 {
  47   struct fork_info *next;
  48   ptid_t ptid;
  49   int num;                      /* Convenient handle (GDB fork id) */
  50   struct regcache *savedregs;   /* Convenient for info fork, saves
  51                                    having to actually switch contexts.  */
  52   int clobber_regs;             /* True if we should restore saved regs.  */
  53   off_t *filepos;               /* Set of open file descriptors' offsets.  */
  54   int maxfd;
  55 };
  56
  57 /* Fork list methods:  */
  58
  59 int
  60 forks_exist_p (void)
  61 {
  62   return (fork_list != NULL);
  63 }
  64
  65 /* Add a fork to the internal fork list.  */
  66
  67 struct fork_info *
  68 add_fork (pid_t pid)
  69 {
  70   struct fork_info *fp;
  71
  72   if (fork_list == NULL && pid != PIDGET (inferior_ptid))
  73     {
  74       /* Special case -- if this is the first fork in the list
  75          (the list is hitherto empty), and if this new fork is
  76          NOT the current inferior_ptid, then add inferior_ptid
  77          first, as a special zeroeth fork id.  */
  78       highest_fork_num = -1;
  79       add_fork (PIDGET (inferior_ptid));        /* safe recursion */
  80     }
  81
  82   fp = XZALLOC (struct fork_info);
  83   fp->ptid = ptid_build (pid, pid, 0);
  84   fp->num = ++highest_fork_num;
  85   fp->next = fork_list;
  86   fork_list = fp;
  87   return fp;
  88 }
  89
  90 static void
  91 free_fork (struct fork_info *fp)
  92 {
  93   /* Notes on step-resume breakpoints: since this is a concern for
  94      threads, let's convince ourselves that it's not a concern for
  95      forks.  There are two ways for a fork_info to be created.  First,
  96      by the checkpoint command, in which case we're at a gdb prompt
  97      and there can't be any step-resume breakpoint.  Second, by a fork
  98      in the user program, in which case we *may* have stepped into the
  99      fork call, but regardless of whether we follow the parent or the
 100      child, we will return to the same place and the step-resume
 101      breakpoint, if any, will take care of itself as usual.  And
 102      unlike threads, we do not save a private copy of the step-resume
 103      breakpoint -- so we're OK.  */
 104
 105   if (fp)
 106     {
 107       if (fp->savedregs)
 108         regcache_xfree (fp->savedregs);
 109       if (fp->filepos)
 110         xfree (fp->filepos);
 111       xfree (fp);
 112     }
 113 }
 114
 115 static void
 116 delete_fork (ptid_t ptid)
 117 {
 118   struct fork_info *fp, *fpprev;
 119
 120   fpprev = NULL;
 121
 122   for (fp = fork_list; fp; fpprev = fp, fp = fp->next)
 123     if (ptid_equal (fp->ptid, ptid))
 124       break;
 125
 126   if (!fp)
 127     return;
 128
 129   if (fpprev)
 130     fpprev->next = fp->next;
 131   else
 132     fork_list = fp->next;
 133
 134   free_fork (fp);
 135
 136   /* Special case: if there is now only one process in the list,
 137      and if it is (hopefully!) the current inferior_ptid, then
 138      remove it, leaving the list empty -- we're now down to the
 139      default case of debugging a single process.  */
 140   if (fork_list != NULL && fork_list->next == NULL &&
 141       ptid_equal (fork_list->ptid, inferior_ptid))
 142     {
 143       /* Last fork -- delete from list and handle as solo process
 144          (should be a safe recursion).  */
 145       delete_fork (inferior_ptid);
 146     }
 147 }
 148
 149 /* Find a fork_info by matching PTID.  */
 150 static struct fork_info *
 151 find_fork_ptid (ptid_t ptid)
 152 {
 153   struct fork_info *fp;
 154
 155   for (fp = fork_list; fp; fp = fp->next)
 156     if (ptid_equal (fp->ptid, ptid))
 157       return fp;
 158
 159   return NULL;
 160 }
 161
 162 /* Find a fork_info by matching ID.  */
 163 static struct fork_info *
 164 find_fork_id (int num)
 165 {
 166   struct fork_info *fp;
 167
 168   for (fp = fork_list; fp; fp = fp->next)
 169     if (fp->num == num)
 170       return fp;
 171
 172   return NULL;
 173 }
 174
 175 /* Find a fork_info by matching pid.  */
 176 extern struct fork_info *
 177 find_fork_pid (pid_t pid)
 178 {
 179   struct fork_info *fp;
 180
 181   for (fp = fork_list; fp; fp = fp->next)
 182     if (pid == ptid_get_pid (fp->ptid))
 183       return fp;
 184
 185   return NULL;
 186 }
 187
 188 static ptid_t
 189 fork_id_to_ptid (int num)
 190 {
 191   struct fork_info *fork = find_fork_id (num);
 192   if (fork)
 193     return fork->ptid;
 194   else
 195     return pid_to_ptid (-1);
 196 }
 197
 198 static void
 199 init_fork_list (void)
 200 {
 201   struct fork_info *fp, *fpnext;
 202
 203   if (!fork_list)
 204     return;
 205
 206   for (fp = fork_list; fp; fp = fpnext)
 207     {
 208       fpnext = fp->next;
 209       free_fork (fp);
 210     }
 211
 212   fork_list = NULL;
 213 }
 214
 215 /* Fork list <-> gdb interface.  */
 216
 217 /* Utility function for fork_load/fork_save.
 218    Calls lseek in the (current) inferior process.  */
 219
 220 static off_t
 221 call_lseek (int fd, off_t offset, int whence)
 222 {
 223   char exp[80];
 224
 225   snprintf (&exp[0], sizeof (exp), "lseek (%d, %ld, %d)",
 226             fd, (long) offset, whence);
 227   return (off_t) parse_and_eval_long (&exp[0]);
 228 }
 229
 230 /* Load infrun state for the fork PTID.  */
 231
 232 static void
 233 fork_load_infrun_state (struct fork_info *fp)
 234 {
 235   extern void nullify_last_target_wait_ptid ();
 236   int i;
 237
 238   linux_nat_switch_fork (fp->ptid);
 239
 240   if (fp->savedregs && fp->clobber_regs)
 241     regcache_cpy (get_current_regcache (), fp->savedregs);
 242
 243   registers_changed ();
 244   reinit_frame_cache ();
 245
 246   stop_pc = regcache_read_pc (get_current_regcache ());
 247   nullify_last_target_wait_ptid ();
 248
 249   /* Now restore the file positions of open file descriptors.  */
 250   if (fp->filepos)
 251     {
 252       for (i = 0; i <= fp->maxfd; i++)
 253         if (fp->filepos[i] != (off_t) -1)
 254           call_lseek (i, fp->filepos[i], SEEK_SET);
 255       /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
 256          this is native-only.  If it ever has to be cross, we'll have
 257          to rethink this.  */
 258     }
 259 }
 260
 261 /* Save infrun state for the fork PTID.
 262    Exported for use by linux child_follow_fork.  */
 263
 264 static void
 265 fork_save_infrun_state (struct fork_info *fp, int clobber_regs)
 266 {
 267   char path[MAXPATHLEN];
 268   struct dirent *de;
 269   DIR *d;
 270
 271   if (fp->savedregs)
 272     regcache_xfree (fp->savedregs);
 273
 274   fp->savedregs = regcache_dup (get_current_regcache ());
 275   fp->clobber_regs = clobber_regs;
 276
 277   if (clobber_regs)
 278     {
 279       /* Now save the 'state' (file position) of all open file descriptors.
 280          Unfortunately fork does not take care of that for us...  */
 281       snprintf (path, MAXPATHLEN, "/proc/%ld/fd", (long) PIDGET (fp->ptid));
 282       if ((d = opendir (path)) != NULL)
 283         {
 284           long tmp;
 285
 286           fp->maxfd = 0;
 287           while ((de = readdir (d)) != NULL)
 288             {
 289               /* Count open file descriptors (actually find highest
 290                  numbered).  */
 291               tmp = strtol (&de->d_name[0], NULL, 10);
 292               if (fp->maxfd < tmp)
 293                 fp->maxfd = tmp;
 294             }
 295           /* Allocate array of file positions.  */
 296           fp->filepos = xrealloc (fp->filepos,
 297                                   (fp->maxfd + 1) * sizeof (*fp->filepos));
 298
 299           /* Initialize to -1 (invalid).  */
 300           for (tmp = 0; tmp <= fp->maxfd; tmp++)
 301             fp->filepos[tmp] = -1;
 302
 303           /* Now find actual file positions.  */
 304           rewinddir (d);
 305           while ((de = readdir (d)) != NULL)
 306             if (isdigit (de->d_name[0]))
 307               {
 308                 tmp = strtol (&de->d_name[0], NULL, 10);
 309                 fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
 310               }
 311           closedir (d);
 312         }
 313     }
 314 }
 315
 316 /* Kill 'em all, let God sort 'em out...  */
 317
 318 void
 319 linux_fork_killall (void)
 320 {
 321   /* Walk list and kill every pid.  No need to treat the
 322      current inferior_ptid as special (we do not return a
 323      status for it) -- however any process may be a child
 324      or a parent, so may get a SIGCHLD from a previously
 325      killed child.  Wait them all out.  */
 326   struct fork_info *fp;
 327   pid_t pid, ret;
 328   int status;
 329
 330   for (fp = fork_list; fp; fp = fp->next)
 331     {
 332       pid = PIDGET (fp->ptid);
 333       do {
 334         /* Use SIGKILL instead of PTRACE_KILL because the former works even
 335            if the thread is running, while the later doesn't.  */
 336         kill (pid, SIGKILL);
 337         ret = waitpid (pid, &status, 0);
 338         /* We might get a SIGCHLD instead of an exit status.  This is
 339          aggravated by the first kill above - a child has just
 340          died.  MVS comment cut-and-pasted from linux-nat.  */
 341       } while (ret == pid && WIFSTOPPED (status));
 342     }
 343   init_fork_list ();    /* Clear list, prepare to start fresh.  */
 344 }
 345
 346 /* The current inferior_ptid has exited, but there are other viable
 347    forks to debug.  Delete the exiting one and context-switch to the
 348    first available.  */
 349
 350 void
 351 linux_fork_mourn_inferior (void)
 352 {
 353   /* Wait just one more time to collect the inferior's exit status.
 354      Do not check whether this succeeds though, since we may be
 355      dealing with a process that we attached to.  Such a process will
 356      only report its exit status to its original parent.  */
 357   int status;
 358
 359   waitpid (ptid_get_pid (inferior_ptid), &status, 0);
 360
 361   /* OK, presumably inferior_ptid is the one who has exited.
 362      We need to delete that one from the fork_list, and switch
 363      to the next available fork.  */
 364   delete_fork (inferior_ptid);
 365
 366   /* There should still be a fork - if there's only one left,
 367      delete_fork won't remove it, because we haven't updated
 368      inferior_ptid yet.  */
 369   gdb_assert (fork_list);
 370
 371   fork_load_infrun_state (fork_list);
 372   printf_filtered (_("[Switching to %s]\n"),
 373                    target_pid_to_str (inferior_ptid));
 374
 375   /* If there's only one fork, switch back to non-fork mode.  */
 376   if (fork_list->next == NULL)
 377     delete_fork (inferior_ptid);
 378 }
 379
 380 /* The current inferior_ptid is being detached, but there are other
 381    viable forks to debug.  Detach and delete it and context-switch to
 382    the first available.  */
 383
 384 void
 385 linux_fork_detach (char *args, int from_tty)
 386 {
 387   /* OK, inferior_ptid is the one we are detaching from.  We need to
 388      delete it from the fork_list, and switch to the next available
 389      fork.  */
 390
 391   if (ptrace (PTRACE_DETACH, PIDGET (inferior_ptid), 0, 0))
 392     error (_("Unable to detach %s"), target_pid_to_str (inferior_ptid));
 393
 394   delete_fork (inferior_ptid);
 395
 396   /* There should still be a fork - if there's only one left,
 397      delete_fork won't remove it, because we haven't updated
 398      inferior_ptid yet.  */
 399   gdb_assert (fork_list);
 400
 401   fork_load_infrun_state (fork_list);
 402
 403   if (from_tty)
 404     printf_filtered (_("[Switching to %s]\n"),
 405                      target_pid_to_str (inferior_ptid));
 406
 407   /* If there's only one fork, switch back to non-fork mode.  */
 408   if (fork_list->next == NULL)
 409     delete_fork (inferior_ptid);
 410 }
 411
 412 /* Fork list <-> user interface.  */
 413
 414 static void
 415 delete_checkpoint_command (char *args, int from_tty)
 416 {
 417   ptid_t ptid;
 418
 419   if (!args || !*args)
 420     error (_("Requires argument (checkpoint id to delete)"));
 421
 422   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 423   if (ptid_equal (ptid, minus_one_ptid))
 424     error (_("No such checkpoint id, %s"), args);
 425
 426   if (ptid_equal (ptid, inferior_ptid))
 427     error (_("\
 428 Please switch to another checkpoint before deleting the current one"));
 429
 430   if (ptrace (PTRACE_KILL, PIDGET (ptid), 0, 0))
 431     error (_("Unable to kill pid %s"), target_pid_to_str (ptid));
 432
 433   if (from_tty)
 434     printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid));
 435
 436   delete_fork (ptid);
 437 }
 438
 439 static void
 440 detach_checkpoint_command (char *args, int from_tty)
 441 {
 442   ptid_t ptid;
 443
 444   if (!args || !*args)
 445     error (_("Requires argument (checkpoint id to detach)"));
 446
 447   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 448   if (ptid_equal (ptid, minus_one_ptid))
 449     error (_("No such checkpoint id, %s"), args);
 450
 451   if (ptid_equal (ptid, inferior_ptid))
 452     error (_("\
 453 Please switch to another checkpoint before detaching the current one"));
 454
 455   if (ptrace (PTRACE_DETACH, PIDGET (ptid), 0, 0))
 456     error (_("Unable to detach %s"), target_pid_to_str (ptid));
 457
 458   if (from_tty)
 459     printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid));
 460
 461   delete_fork (ptid);
 462 }
 463
 464 /* Print information about currently known checkpoints.  */
 465
 466 static void
 467 info_checkpoints_command (char *arg, int from_tty)
 468 {
 469   struct gdbarch *gdbarch = get_current_arch ();
 470   struct frame_info *cur_frame;
 471   struct symtab_and_line sal;
 472   struct symtab *cur_symtab;
 473   struct fork_info *fp;
 474   int cur_line;
 475   ULONGEST pc;
 476   int requested = -1;
 477   struct fork_info *printed = NULL;
 478
 479   if (arg && *arg)
 480     requested = (int) parse_and_eval_long (arg);
 481
 482   for (fp = fork_list; fp; fp = fp->next)
 483     {
 484       if (requested > 0 && fp->num != requested)
 485         continue;
 486
 487       printed = fp;
 488       if (ptid_equal (fp->ptid, inferior_ptid))
 489         {
 490           printf_filtered ("* ");
 491           pc = regcache_read_pc (get_current_regcache ());
 492         }
 493       else
 494         {
 495           printf_filtered ("  ");
 496           pc = regcache_read_pc (fp->savedregs);
 497         }
 498       printf_filtered ("%d %s", fp->num, target_pid_to_str (fp->ptid));
 499       if (fp->num == 0)
 500         printf_filtered (_(" (main process)"));
 501       printf_filtered (_(" at "));
 502       fputs_filtered (paddress (gdbarch, pc), gdb_stdout);
 503
 504       sal = find_pc_line (pc, 0);
 505       if (sal.symtab)
 506         {
 507           char *tmp = strrchr (sal.symtab->filename, '/');
 508
 509           if (tmp)
 510             printf_filtered (_(", file %s"), tmp + 1);
 511           else
 512             printf_filtered (_(", file %s"), sal.symtab->filename);
 513         }
 514       if (sal.line)
 515         printf_filtered (_(", line %d"), sal.line);
 516       if (!sal.symtab && !sal.line)
 517         {
 518           struct minimal_symbol *msym;
 519
 520           msym = lookup_minimal_symbol_by_pc (pc);
 521           if (msym)
 522             printf_filtered (", <%s>", SYMBOL_LINKAGE_NAME (msym));
 523         }
 524
 525       putchar_filtered ('\n');
 526     }
 527   if (printed == NULL)
 528     {
 529       if (requested > 0)
 530         printf_filtered (_("No checkpoint number %d.\n"), requested);
 531       else
 532         printf_filtered (_("No checkpoints.\n"));
 533     }
 534 }
 535
 536 /* The PID of the process we're checkpointing.  */
 537 static int checkpointing_pid = 0;
 538
 539 int
 540 linux_fork_checkpointing_p (int pid)
 541 {
 542   return (checkpointing_pid == pid);
 543 }
 544
 545 static void
 546 checkpoint_command (char *args, int from_tty)
 547 {
 548   struct objfile *fork_objf;
 549   struct gdbarch *gdbarch;
 550   struct target_waitstatus last_target_waitstatus;
 551   ptid_t last_target_ptid;
 552   struct value *fork_fn = NULL, *ret;
 553   struct fork_info *fp;
 554   pid_t retpid;
 555   struct cleanup *old_chain;
 556   long i;
 557
 558   /* Make the inferior fork, record its (and gdb's) state.  */
 559
 560   if (lookup_minimal_symbol ("fork", NULL, NULL) != NULL)
 561     fork_fn = find_function_in_inferior ("fork", &fork_objf);
 562   if (!fork_fn)
 563     if (lookup_minimal_symbol ("_fork", NULL, NULL) != NULL)
 564       fork_fn = find_function_in_inferior ("fork", &fork_objf);
 565   if (!fork_fn)
 566     error (_("checkpoint: can't find fork function in inferior."));
 567
 568   gdbarch = get_objfile_arch (fork_objf);
 569   ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 570
 571   /* Tell linux-nat.c that we're checkpointing this inferior.  */
 572   old_chain = make_cleanup_restore_integer (&checkpointing_pid);
 573   checkpointing_pid = PIDGET (inferior_ptid);
 574
 575   ret = call_function_by_hand (fork_fn, 0, &ret);
 576   do_cleanups (old_chain);
 577   if (!ret)     /* Probably can't happen.  */
 578     error (_("checkpoint: call_function_by_hand returned null."));
 579
 580   retpid = value_as_long (ret);
 581   get_last_target_status (&last_target_ptid, &last_target_waitstatus);
 582   if (from_tty)
 583     {
 584       int parent_pid;
 585
 586       printf_filtered (_("checkpoint: fork returned pid %ld.\n"),
 587                        (long) retpid);
 588       if (info_verbose)
 589         {
 590           parent_pid = ptid_get_lwp (last_target_ptid);
 591           if (parent_pid == 0)
 592             parent_pid = ptid_get_pid (last_target_ptid);
 593           printf_filtered (_("   gdb says parent = %ld.\n"),
 594                            (long) parent_pid);
 595         }
 596     }
 597
 598   fp = find_fork_pid (retpid);
 599   if (!fp)
 600     error (_("Failed to find new fork"));
 601   fork_save_infrun_state (fp, 1);
 602 }
 603
 604 static void
 605 linux_fork_context (struct fork_info *newfp, int from_tty)
 606 {
 607   /* Now we attempt to switch processes.  */
 608   struct fork_info *oldfp;
 609   ptid_t ptid;
 610   int id, i;
 611
 612   gdb_assert (newfp != NULL);
 613
 614   oldfp = find_fork_ptid (inferior_ptid);
 615   gdb_assert (oldfp != NULL);
 616
 617   fork_save_infrun_state (oldfp, 1);
 618   remove_breakpoints ();
 619   fork_load_infrun_state (newfp);
 620   insert_breakpoints ();
 621
 622   printf_filtered (_("Switching to %s\n"),
 623                    target_pid_to_str (inferior_ptid));
 624
 625   print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC);
 626 }
 627
 628 /* Switch inferior process (checkpoint) context, by checkpoint id.  */
 629 static void
 630 restart_command (char *args, int from_tty)
 631 {
 632   struct fork_info *fp;
 633
 634   if (!args || !*args)
 635     error (_("Requires argument (checkpoint id to restart)"));
 636
 637   if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
 638     error (_("Not found: checkpoint id %s"), args);
 639
 640   linux_fork_context (fp, from_tty);
 641 }
 642
 643 void
 644 _initialize_linux_fork (void)
 645 {
 646   init_fork_list ();
 647
 648   /* Checkpoint command: create a fork of the inferior process
 649      and set it aside for later debugging.  */
 650
 651   add_com ("checkpoint", class_obscure, checkpoint_command, _("\
 652 Fork a duplicate process (experimental)."));
 653
 654   /* Restart command: restore the context of a specified checkpoint
 655      process.  */
 656
 657   add_com ("restart", class_obscure, restart_command, _("\
 658 restart <n>: restore program context from a checkpoint.\n\
 659 Argument 'n' is checkpoint ID, as displayed by 'info checkpoints'."));
 660
 661   /* Delete checkpoint command: kill the process and remove it from
 662      the fork list.  */
 663
 664   add_cmd ("checkpoint", class_obscure, delete_checkpoint_command, _("\
 665 Delete a checkpoint (experimental)."),
 666            &deletelist);
 667
 668   /* Detach checkpoint command: release the process to run independently,
 669      and remove it from the fork list.  */
 670
 671   add_cmd ("checkpoint", class_obscure, detach_checkpoint_command, _("\
 672 Detach from a checkpoint (experimental)."),
 673            &detachlist);
 674
 675   /* Info checkpoints command: list all forks/checkpoints
 676      currently under gdb's control.  */
 677
 678   add_info ("checkpoints", info_checkpoints_command,
 679             _("IDs of currently known checkpoints."));
 680 }