gdb/linux-fork.c

   1 /* GNU/Linux native-dependent code for debugging multiple forks.
   2
   3    Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010
   4    Free Software Foundation, Inc.
   5
   6    This file is part of GDB.
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  20
  21 #include "defs.h"
  22 #include "arch-utils.h"
  23 #include "inferior.h"
  24 #include "regcache.h"
  25 #include "gdbcmd.h"
  26 #include "infcall.h"
  27 #include "objfiles.h"
  28 #include "gdb_assert.h"
  29 #include "gdb_string.h"
  30 #include "linux-fork.h"
  31 #include "linux-nat.h"
  32
  33 #include <sys/ptrace.h>
  34 #include "gdb_wait.h"
  35 #include <sys/param.h>
  36 #include "gdb_dirent.h"
  37 #include <ctype.h>
  38
  39 struct fork_info *fork_list;
  40 static int highest_fork_num;
  41
  42 /* Prevent warning from -Wmissing-prototypes.  */
  43 extern void _initialize_linux_fork (void);
  44
  45 /* Fork list data structure:  */
  46 struct fork_info
  47 {
  48   struct fork_info *next;
  49   ptid_t ptid;
  50   int num;                      /* Convenient handle (GDB fork id) */
  51   struct regcache *savedregs;   /* Convenient for info fork, saves
  52                                    having to actually switch contexts.  */
  53   int clobber_regs;             /* True if we should restore saved regs.  */
  54   off_t *filepos;               /* Set of open file descriptors' offsets.  */
  55   int maxfd;
  56 };
  57
  58 /* Fork list methods:  */
  59
  60 int
  61 forks_exist_p (void)
  62 {
  63   return (fork_list != NULL);
  64 }
  65
  66 /* Add a fork to the internal fork list.  */
  67
  68 struct fork_info *
  69 add_fork (pid_t pid)
  70 {
  71   struct fork_info *fp;
  72
  73   if (fork_list == NULL && pid != PIDGET (inferior_ptid))
  74     {
  75       /* Special case -- if this is the first fork in the list
  76          (the list is hitherto empty), and if this new fork is
  77          NOT the current inferior_ptid, then add inferior_ptid
  78          first, as a special zeroeth fork id.  */
  79       highest_fork_num = -1;
  80       add_fork (PIDGET (inferior_ptid));        /* safe recursion */
  81     }
  82
  83   fp = XZALLOC (struct fork_info);
  84   fp->ptid = ptid_build (pid, pid, 0);
  85   fp->num = ++highest_fork_num;
  86   fp->next = fork_list;
  87   fork_list = fp;
  88   return fp;
  89 }
  90
  91 static void
  92 free_fork (struct fork_info *fp)
  93 {
  94   /* Notes on step-resume breakpoints: since this is a concern for
  95      threads, let's convince ourselves that it's not a concern for
  96      forks.  There are two ways for a fork_info to be created.  First,
  97      by the checkpoint command, in which case we're at a gdb prompt
  98      and there can't be any step-resume breakpoint.  Second, by a fork
  99      in the user program, in which case we *may* have stepped into the
 100      fork call, but regardless of whether we follow the parent or the
 101      child, we will return to the same place and the step-resume
 102      breakpoint, if any, will take care of itself as usual.  And
 103      unlike threads, we do not save a private copy of the step-resume
 104      breakpoint -- so we're OK.  */
 105
 106   if (fp)
 107     {
 108       if (fp->savedregs)
 109         regcache_xfree (fp->savedregs);
 110       if (fp->filepos)
 111         xfree (fp->filepos);
 112       xfree (fp);
 113     }
 114 }
 115
 116 static void
 117 delete_fork (ptid_t ptid)
 118 {
 119   struct fork_info *fp, *fpprev;
 120
 121   fpprev = NULL;
 122
 123   for (fp = fork_list; fp; fpprev = fp, fp = fp->next)
 124     if (ptid_equal (fp->ptid, ptid))
 125       break;
 126
 127   if (!fp)
 128     return;
 129
 130   if (fpprev)
 131     fpprev->next = fp->next;
 132   else
 133     fork_list = fp->next;
 134
 135   free_fork (fp);
 136
 137   /* Special case: if there is now only one process in the list,
 138      and if it is (hopefully!) the current inferior_ptid, then
 139      remove it, leaving the list empty -- we're now down to the
 140      default case of debugging a single process.  */
 141   if (fork_list != NULL && fork_list->next == NULL &&
 142       ptid_equal (fork_list->ptid, inferior_ptid))
 143     {
 144       /* Last fork -- delete from list and handle as solo process
 145          (should be a safe recursion).  */
 146       delete_fork (inferior_ptid);
 147     }
 148 }
 149
 150 /* Find a fork_info by matching PTID.  */
 151 static struct fork_info *
 152 find_fork_ptid (ptid_t ptid)
 153 {
 154   struct fork_info *fp;
 155
 156   for (fp = fork_list; fp; fp = fp->next)
 157     if (ptid_equal (fp->ptid, ptid))
 158       return fp;
 159
 160   return NULL;
 161 }
 162
 163 /* Find a fork_info by matching ID.  */
 164 static struct fork_info *
 165 find_fork_id (int num)
 166 {
 167   struct fork_info *fp;
 168
 169   for (fp = fork_list; fp; fp = fp->next)
 170     if (fp->num == num)
 171       return fp;
 172
 173   return NULL;
 174 }
 175
 176 /* Find a fork_info by matching pid.  */
 177 extern struct fork_info *
 178 find_fork_pid (pid_t pid)
 179 {
 180   struct fork_info *fp;
 181
 182   for (fp = fork_list; fp; fp = fp->next)
 183     if (pid == ptid_get_pid (fp->ptid))
 184       return fp;
 185
 186   return NULL;
 187 }
 188
 189 static ptid_t
 190 fork_id_to_ptid (int num)
 191 {
 192   struct fork_info *fork = find_fork_id (num);
 193   if (fork)
 194     return fork->ptid;
 195   else
 196     return pid_to_ptid (-1);
 197 }
 198
 199 static void
 200 init_fork_list (void)
 201 {
 202   struct fork_info *fp, *fpnext;
 203
 204   if (!fork_list)
 205     return;
 206
 207   for (fp = fork_list; fp; fp = fpnext)
 208     {
 209       fpnext = fp->next;
 210       free_fork (fp);
 211     }
 212
 213   fork_list = NULL;
 214 }
 215
 216 /* Fork list <-> gdb interface.  */
 217
 218 /* Utility function for fork_load/fork_save.
 219    Calls lseek in the (current) inferior process.  */
 220
 221 static off_t
 222 call_lseek (int fd, off_t offset, int whence)
 223 {
 224   char exp[80];
 225
 226   snprintf (&exp[0], sizeof (exp), "lseek (%d, %ld, %d)",
 227             fd, (long) offset, whence);
 228   return (off_t) parse_and_eval_long (&exp[0]);
 229 }
 230
 231 /* Load infrun state for the fork PTID.  */
 232
 233 static void
 234 fork_load_infrun_state (struct fork_info *fp)
 235 {
 236   extern void nullify_last_target_wait_ptid ();
 237   int i;
 238
 239   linux_nat_switch_fork (fp->ptid);
 240
 241   if (fp->savedregs && fp->clobber_regs)
 242     regcache_cpy (get_current_regcache (), fp->savedregs);
 243
 244   registers_changed ();
 245   reinit_frame_cache ();
 246
 247   stop_pc = regcache_read_pc (get_current_regcache ());
 248   nullify_last_target_wait_ptid ();
 249
 250   /* Now restore the file positions of open file descriptors.  */
 251   if (fp->filepos)
 252     {
 253       for (i = 0; i <= fp->maxfd; i++)
 254         if (fp->filepos[i] != (off_t) -1)
 255           call_lseek (i, fp->filepos[i], SEEK_SET);
 256       /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
 257          this is native-only.  If it ever has to be cross, we'll have
 258          to rethink this.  */
 259     }
 260 }
 261
 262 /* Save infrun state for the fork PTID.
 263    Exported for use by linux child_follow_fork.  */
 264
 265 static void
 266 fork_save_infrun_state (struct fork_info *fp, int clobber_regs)
 267 {
 268   char path[MAXPATHLEN];
 269   struct dirent *de;
 270   DIR *d;
 271
 272   if (fp->savedregs)
 273     regcache_xfree (fp->savedregs);
 274
 275   fp->savedregs = regcache_dup (get_current_regcache ());
 276   fp->clobber_regs = clobber_regs;
 277
 278   if (clobber_regs)
 279     {
 280       /* Now save the 'state' (file position) of all open file descriptors.
 281          Unfortunately fork does not take care of that for us...  */
 282       snprintf (path, MAXPATHLEN, "/proc/%ld/fd", (long) PIDGET (fp->ptid));
 283       if ((d = opendir (path)) != NULL)
 284         {
 285           long tmp;
 286
 287           fp->maxfd = 0;
 288           while ((de = readdir (d)) != NULL)
 289             {
 290               /* Count open file descriptors (actually find highest
 291                  numbered).  */
 292               tmp = strtol (&de->d_name[0], NULL, 10);
 293               if (fp->maxfd < tmp)
 294                 fp->maxfd = tmp;
 295             }
 296           /* Allocate array of file positions.  */
 297           fp->filepos = xrealloc (fp->filepos,
 298                                   (fp->maxfd + 1) * sizeof (*fp->filepos));
 299
 300           /* Initialize to -1 (invalid).  */
 301           for (tmp = 0; tmp <= fp->maxfd; tmp++)
 302             fp->filepos[tmp] = -1;
 303
 304           /* Now find actual file positions.  */
 305           rewinddir (d);
 306           while ((de = readdir (d)) != NULL)
 307             if (isdigit (de->d_name[0]))
 308               {
 309                 tmp = strtol (&de->d_name[0], NULL, 10);
 310                 fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
 311               }
 312           closedir (d);
 313         }
 314     }
 315 }
 316
 317 /* Kill 'em all, let God sort 'em out...  */
 318
 319 void
 320 linux_fork_killall (void)
 321 {
 322   /* Walk list and kill every pid.  No need to treat the
 323      current inferior_ptid as special (we do not return a
 324      status for it) -- however any process may be a child
 325      or a parent, so may get a SIGCHLD from a previously
 326      killed child.  Wait them all out.  */
 327   struct fork_info *fp;
 328   pid_t pid, ret;
 329   int status;
 330
 331   for (fp = fork_list; fp; fp = fp->next)
 332     {
 333       pid = PIDGET (fp->ptid);
 334       do {
 335         /* Use SIGKILL instead of PTRACE_KILL because the former works even
 336            if the thread is running, while the later doesn't.  */
 337         kill (pid, SIGKILL);
 338         ret = waitpid (pid, &status, 0);
 339         /* We might get a SIGCHLD instead of an exit status.  This is
 340          aggravated by the first kill above - a child has just
 341          died.  MVS comment cut-and-pasted from linux-nat.  */
 342       } while (ret == pid && WIFSTOPPED (status));
 343     }
 344   init_fork_list ();    /* Clear list, prepare to start fresh.  */
 345 }
 346
 347 /* The current inferior_ptid has exited, but there are other viable
 348    forks to debug.  Delete the exiting one and context-switch to the
 349    first available.  */
 350
 351 void
 352 linux_fork_mourn_inferior (void)
 353 {
 354   /* Wait just one more time to collect the inferior's exit status.
 355      Do not check whether this succeeds though, since we may be
 356      dealing with a process that we attached to.  Such a process will
 357      only report its exit status to its original parent.  */
 358   int status;
 359
 360   waitpid (ptid_get_pid (inferior_ptid), &status, 0);
 361
 362   /* OK, presumably inferior_ptid is the one who has exited.
 363      We need to delete that one from the fork_list, and switch
 364      to the next available fork.  */
 365   delete_fork (inferior_ptid);
 366
 367   /* There should still be a fork - if there's only one left,
 368      delete_fork won't remove it, because we haven't updated
 369      inferior_ptid yet.  */
 370   gdb_assert (fork_list);
 371
 372   fork_load_infrun_state (fork_list);
 373   printf_filtered (_("[Switching to %s]\n"),
 374                    target_pid_to_str (inferior_ptid));
 375
 376   /* If there's only one fork, switch back to non-fork mode.  */
 377   if (fork_list->next == NULL)
 378     delete_fork (inferior_ptid);
 379 }
 380
 381 /* The current inferior_ptid is being detached, but there are other
 382    viable forks to debug.  Detach and delete it and context-switch to
 383    the first available.  */
 384
 385 void
 386 linux_fork_detach (char *args, int from_tty)
 387 {
 388   /* OK, inferior_ptid is the one we are detaching from.  We need to
 389      delete it from the fork_list, and switch to the next available
 390      fork.  */
 391
 392   if (ptrace (PTRACE_DETACH, PIDGET (inferior_ptid), 0, 0))
 393     error (_("Unable to detach %s"), target_pid_to_str (inferior_ptid));
 394
 395   delete_fork (inferior_ptid);
 396
 397   /* There should still be a fork - if there's only one left,
 398      delete_fork won't remove it, because we haven't updated
 399      inferior_ptid yet.  */
 400   gdb_assert (fork_list);
 401
 402   fork_load_infrun_state (fork_list);
 403
 404   if (from_tty)
 405     printf_filtered (_("[Switching to %s]\n"),
 406                      target_pid_to_str (inferior_ptid));
 407
 408   /* If there's only one fork, switch back to non-fork mode.  */
 409   if (fork_list->next == NULL)
 410     delete_fork (inferior_ptid);
 411 }
 412
 413 /* Fork list <-> user interface.  */
 414
 415 static void
 416 delete_checkpoint_command (char *args, int from_tty)
 417 {
 418   ptid_t ptid;
 419
 420   if (!args || !*args)
 421     error (_("Requires argument (checkpoint id to delete)"));
 422
 423   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 424   if (ptid_equal (ptid, minus_one_ptid))
 425     error (_("No such checkpoint id, %s"), args);
 426
 427   if (ptid_equal (ptid, inferior_ptid))
 428     error (_("\
 429 Please switch to another checkpoint before deleting the current one"));
 430
 431   if (ptrace (PTRACE_KILL, PIDGET (ptid), 0, 0))
 432     error (_("Unable to kill pid %s"), target_pid_to_str (ptid));
 433
 434   if (from_tty)
 435     printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid));
 436
 437   delete_fork (ptid);
 438 }
 439
 440 static void
 441 detach_checkpoint_command (char *args, int from_tty)
 442 {
 443   ptid_t ptid;
 444
 445   if (!args || !*args)
 446     error (_("Requires argument (checkpoint id to detach)"));
 447
 448   ptid = fork_id_to_ptid (parse_and_eval_long (args));
 449   if (ptid_equal (ptid, minus_one_ptid))
 450     error (_("No such checkpoint id, %s"), args);
 451
 452   if (ptid_equal (ptid, inferior_ptid))
 453     error (_("\
 454 Please switch to another checkpoint before detaching the current one"));
 455
 456   if (ptrace (PTRACE_DETACH, PIDGET (ptid), 0, 0))
 457     error (_("Unable to detach %s"), target_pid_to_str (ptid));
 458
 459   if (from_tty)
 460     printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid));
 461
 462   delete_fork (ptid);
 463 }
 464
 465 /* Print information about currently known checkpoints.  */
 466
 467 static void
 468 info_checkpoints_command (char *arg, int from_tty)
 469 {
 470   struct gdbarch *gdbarch = get_current_arch ();
 471   struct frame_info *cur_frame;
 472   struct symtab_and_line sal;
 473   struct symtab *cur_symtab;
 474   struct fork_info *fp;
 475   int cur_line;
 476   ULONGEST pc;
 477   int requested = -1;
 478   struct fork_info *printed = NULL;
 479
 480   if (arg && *arg)
 481     requested = (int) parse_and_eval_long (arg);
 482
 483   for (fp = fork_list; fp; fp = fp->next)
 484     {
 485       if (requested > 0 && fp->num != requested)
 486         continue;
 487
 488       printed = fp;
 489       if (ptid_equal (fp->ptid, inferior_ptid))
 490         {
 491           printf_filtered ("* ");
 492           pc = regcache_read_pc (get_current_regcache ());
 493         }
 494       else
 495         {
 496           printf_filtered ("  ");
 497           pc = regcache_read_pc (fp->savedregs);
 498         }
 499       printf_filtered ("%d %s", fp->num, target_pid_to_str (fp->ptid));
 500       if (fp->num == 0)
 501         printf_filtered (_(" (main process)"));
 502       printf_filtered (_(" at "));
 503       fputs_filtered (paddress (gdbarch, pc), gdb_stdout);
 504
 505       sal = find_pc_line (pc, 0);
 506       if (sal.symtab)
 507         {
 508           char *tmp = strrchr (sal.symtab->filename, '/');
 509
 510           if (tmp)
 511             printf_filtered (_(", file %s"), tmp + 1);
 512           else
 513             printf_filtered (_(", file %s"), sal.symtab->filename);
 514         }
 515       if (sal.line)
 516         printf_filtered (_(", line %d"), sal.line);
 517       if (!sal.symtab && !sal.line)
 518         {
 519           struct minimal_symbol *msym;
 520
 521           msym = lookup_minimal_symbol_by_pc (pc);
 522           if (msym)
 523             printf_filtered (", <%s>", SYMBOL_LINKAGE_NAME (msym));
 524         }
 525
 526       putchar_filtered ('\n');
 527     }
 528   if (printed == NULL)
 529     {
 530       if (requested > 0)
 531         printf_filtered (_("No checkpoint number %d.\n"), requested);
 532       else
 533         printf_filtered (_("No checkpoints.\n"));
 534     }
 535 }
 536
 537 /* The PID of the process we're checkpointing.  */
 538 static int checkpointing_pid = 0;
 539
 540 int
 541 linux_fork_checkpointing_p (int pid)
 542 {
 543   return (checkpointing_pid == pid);
 544 }
 545
 546 static void
 547 checkpoint_command (char *args, int from_tty)
 548 {
 549   struct objfile *fork_objf;
 550   struct gdbarch *gdbarch;
 551   struct target_waitstatus last_target_waitstatus;
 552   ptid_t last_target_ptid;
 553   struct value *fork_fn = NULL, *ret;
 554   struct fork_info *fp;
 555   pid_t retpid;
 556   struct cleanup *old_chain;
 557   long i;
 558
 559   /* Make the inferior fork, record its (and gdb's) state.  */
 560
 561   if (lookup_minimal_symbol ("fork", NULL, NULL) != NULL)
 562     fork_fn = find_function_in_inferior ("fork", &fork_objf);
 563   if (!fork_fn)
 564     if (lookup_minimal_symbol ("_fork", NULL, NULL) != NULL)
 565       fork_fn = find_function_in_inferior ("fork", &fork_objf);
 566   if (!fork_fn)
 567     error (_("checkpoint: can't find fork function in inferior."));
 568
 569   gdbarch = get_objfile_arch (fork_objf);
 570   ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
 571
 572   /* Tell linux-nat.c that we're checkpointing this inferior.  */
 573   old_chain = make_cleanup_restore_integer (&checkpointing_pid);
 574   checkpointing_pid = PIDGET (inferior_ptid);
 575
 576   ret = call_function_by_hand (fork_fn, 0, &ret);
 577   do_cleanups (old_chain);
 578   if (!ret)     /* Probably can't happen.  */
 579     error (_("checkpoint: call_function_by_hand returned null."));
 580
 581   retpid = value_as_long (ret);
 582   get_last_target_status (&last_target_ptid, &last_target_waitstatus);
 583   if (from_tty)
 584     {
 585       int parent_pid;
 586
 587       printf_filtered (_("checkpoint: fork returned pid %ld.\n"),
 588                        (long) retpid);
 589       if (info_verbose)
 590         {
 591           parent_pid = ptid_get_lwp (last_target_ptid);
 592           if (parent_pid == 0)
 593             parent_pid = ptid_get_pid (last_target_ptid);
 594           printf_filtered (_("   gdb says parent = %ld.\n"),
 595                            (long) parent_pid);
 596         }
 597     }
 598
 599   fp = find_fork_pid (retpid);
 600   if (!fp)
 601     error (_("Failed to find new fork"));
 602   fork_save_infrun_state (fp, 1);
 603 }
 604
 605 static void
 606 linux_fork_context (struct fork_info *newfp, int from_tty)
 607 {
 608   /* Now we attempt to switch processes.  */
 609   struct fork_info *oldfp;
 610   ptid_t ptid;
 611   int id, i;
 612
 613   gdb_assert (newfp != NULL);
 614
 615   oldfp = find_fork_ptid (inferior_ptid);
 616   gdb_assert (oldfp != NULL);
 617
 618   fork_save_infrun_state (oldfp, 1);
 619   remove_breakpoints ();
 620   fork_load_infrun_state (newfp);
 621   insert_breakpoints ();
 622
 623   printf_filtered (_("Switching to %s\n"),
 624                    target_pid_to_str (inferior_ptid));
 625
 626   print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC);
 627 }
 628
 629 /* Switch inferior process (checkpoint) context, by checkpoint id.  */
 630 static void
 631 restart_command (char *args, int from_tty)
 632 {
 633   struct fork_info *fp;
 634
 635   if (!args || !*args)
 636     error (_("Requires argument (checkpoint id to restart)"));
 637
 638   if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
 639     error (_("Not found: checkpoint id %s"), args);
 640
 641   linux_fork_context (fp, from_tty);
 642 }
 643
 644 void
 645 _initialize_linux_fork (void)
 646 {
 647   init_fork_list ();
 648
 649   /* Checkpoint command: create a fork of the inferior process
 650      and set it aside for later debugging.  */
 651
 652   add_com ("checkpoint", class_obscure, checkpoint_command, _("\
 653 Fork a duplicate process (experimental)."));
 654
 655   /* Restart command: restore the context of a specified checkpoint
 656      process.  */
 657
 658   add_com ("restart", class_obscure, restart_command, _("\
 659 restart <n>: restore program context from a checkpoint.\n\
 660 Argument 'n' is checkpoint ID, as displayed by 'info checkpoints'."));
 661
 662   /* Delete checkpoint command: kill the process and remove it from
 663      the fork list.  */
 664
 665   add_cmd ("checkpoint", class_obscure, delete_checkpoint_command, _("\
 666 Delete a checkpoint (experimental)."),
 667            &deletelist);
 668
 669   /* Detach checkpoint command: release the process to run independently,
 670      and remove it from the fork list.  */
 671
 672   add_cmd ("checkpoint", class_obscure, detach_checkpoint_command, _("\
 673 Detach from a checkpoint (experimental)."),
 674            &detachlist);
 675
 676   /* Info checkpoints command: list all forks/checkpoints
 677      currently under gdb's control.  */
 678
 679   add_info ("checkpoints", info_checkpoints_command,
 680             _("IDs of currently known checkpoints."));
 681 }