1 /* GNU/Linux native-dependent code for debugging multiple forks.
3 Copyright (C) 2005-2019 Free Software Foundation, Inc.
5 This file is part of GDB.
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.
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.
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/>. */
21 #include "arch-utils.h"
28 #include "linux-fork.h"
29 #include "linux-nat.h"
30 #include "gdbthread.h"
33 #include "nat/gdb_ptrace.h"
34 #include "common/gdb_wait.h"
40 /* Fork list data structure: */
43 explicit fork_info (pid_t pid)
50 /* Notes on step-resume breakpoints: since this is a concern for
51 threads, let's convince ourselves that it's not a concern for
52 forks. There are two ways for a fork_info to be created.
53 First, by the checkpoint command, in which case we're at a gdb
54 prompt and there can't be any step-resume breakpoint. Second,
55 by a fork in the user program, in which case we *may* have
56 stepped into the fork call, but regardless of whether we follow
57 the parent or the child, we will return to the same place and
58 the step-resume breakpoint, if any, will take care of itself as
59 usual. And unlike threads, we do not save a private copy of
60 the step-resume breakpoint -- so we're OK. */
68 ptid_t ptid = null_ptid;
69 ptid_t parent_ptid = null_ptid;
71 /* Convenient handle (GDB fork id). */
74 /* Convenient for info fork, saves having to actually switch
76 readonly_detached_regcache *savedregs = nullptr;
80 /* Set of open file descriptors' offsets. */
81 off_t *filepos = nullptr;
86 static std::list<fork_info> fork_list;
87 static int highest_fork_num;
89 /* Fork list methods: */
94 return !fork_list.empty ();
97 /* Return the last fork in the list. */
99 static struct fork_info *
100 find_last_fork (void)
102 if (fork_list.empty ())
105 return &fork_list.back ();
108 /* Return true iff there's one fork in the list. */
113 return (!fork_list.empty ()
114 && &fork_list.front () == &fork_list.back ());
117 /* Add a new fork to the internal fork list. */
122 fork_list.emplace_back (pid);
125 highest_fork_num = 0;
127 fork_info *fp = &fork_list.back ();
128 fp->num = ++highest_fork_num;
132 delete_fork (ptid_t ptid)
134 linux_target->low_forget_process (ptid.pid ());
136 for (auto it = fork_list.begin (); it != fork_list.end (); ++it)
137 if (it->ptid == ptid)
139 fork_list.erase (it);
141 /* Special case: if there is now only one process in the list,
142 and if it is (hopefully!) the current inferior_ptid, then
143 remove it, leaving the list empty -- we're now down to the
144 default case of debugging a single process. */
145 if (one_fork_p () && fork_list.front ().ptid == inferior_ptid)
147 /* Last fork -- delete from list and handle as solo
148 process (should be a safe recursion). */
149 delete_fork (inferior_ptid);
155 /* Find a fork_info by matching PTID. */
156 static struct fork_info *
157 find_fork_ptid (ptid_t ptid)
159 for (fork_info &fi : fork_list)
166 /* Find a fork_info by matching ID. */
167 static struct fork_info *
168 find_fork_id (int num)
170 for (fork_info &fi : fork_list)
177 /* Find a fork_info by matching pid. */
178 extern struct fork_info *
179 find_fork_pid (pid_t pid)
181 for (fork_info &fi : fork_list)
182 if (pid == fi.ptid.pid ())
189 fork_id_to_ptid (int num)
191 struct fork_info *fork = find_fork_id (num);
198 /* Fork list <-> gdb interface. */
200 /* Utility function for fork_load/fork_save.
201 Calls lseek in the (current) inferior process. */
204 call_lseek (int fd, off_t offset, int whence)
208 snprintf (&exp[0], sizeof (exp), "(long) lseek (%d, %ld, %d)",
209 fd, (long) offset, whence);
210 return (off_t) parse_and_eval_long (&exp[0]);
213 /* Load infrun state for the fork PTID. */
216 fork_load_infrun_state (struct fork_info *fp)
218 extern void nullify_last_target_wait_ptid ();
221 linux_nat_switch_fork (fp->ptid);
224 get_current_regcache ()->restore (fp->savedregs);
226 registers_changed ();
227 reinit_frame_cache ();
229 inferior_thread ()->suspend.stop_pc
230 = regcache_read_pc (get_current_regcache ());
231 nullify_last_target_wait_ptid ();
233 /* Now restore the file positions of open file descriptors. */
236 for (i = 0; i <= fp->maxfd; i++)
237 if (fp->filepos[i] != (off_t) -1)
238 call_lseek (i, fp->filepos[i], SEEK_SET);
239 /* NOTE: I can get away with using SEEK_SET and SEEK_CUR because
240 this is native-only. If it ever has to be cross, we'll have
245 /* Save infrun state for the fork FP. */
248 fork_save_infrun_state (struct fork_info *fp)
255 delete fp->savedregs;
257 fp->savedregs = new readonly_detached_regcache (*get_current_regcache ());
258 fp->pc = regcache_read_pc (get_current_regcache ());
260 /* Now save the 'state' (file position) of all open file descriptors.
261 Unfortunately fork does not take care of that for us... */
262 snprintf (path, PATH_MAX, "/proc/%ld/fd", (long) fp->ptid.pid ());
263 if ((d = opendir (path)) != NULL)
268 while ((de = readdir (d)) != NULL)
270 /* Count open file descriptors (actually find highest
272 tmp = strtol (&de->d_name[0], NULL, 10);
276 /* Allocate array of file positions. */
277 fp->filepos = XRESIZEVEC (off_t, fp->filepos, fp->maxfd + 1);
279 /* Initialize to -1 (invalid). */
280 for (tmp = 0; tmp <= fp->maxfd; tmp++)
281 fp->filepos[tmp] = -1;
283 /* Now find actual file positions. */
285 while ((de = readdir (d)) != NULL)
286 if (isdigit (de->d_name[0]))
288 tmp = strtol (&de->d_name[0], NULL, 10);
289 fp->filepos[tmp] = call_lseek (tmp, 0, SEEK_CUR);
295 /* Kill 'em all, let God sort 'em out... */
298 linux_fork_killall (void)
300 /* Walk list and kill every pid. No need to treat the
301 current inferior_ptid as special (we do not return a
302 status for it) -- however any process may be a child
303 or a parent, so may get a SIGCHLD from a previously
304 killed child. Wait them all out. */
306 for (fork_info &fi : fork_list)
308 pid_t pid = fi.ptid.pid ();
312 /* Use SIGKILL instead of PTRACE_KILL because the former works even
313 if the thread is running, while the later doesn't. */
315 ret = waitpid (pid, &status, 0);
316 /* We might get a SIGCHLD instead of an exit status. This is
317 aggravated by the first kill above - a child has just
318 died. MVS comment cut-and-pasted from linux-nat. */
319 } while (ret == pid && WIFSTOPPED (status));
322 /* Clear list, prepare to start fresh. */
326 /* The current inferior_ptid has exited, but there are other viable
327 forks to debug. Delete the exiting one and context-switch to the
331 linux_fork_mourn_inferior (void)
333 struct fork_info *last;
336 /* Wait just one more time to collect the inferior's exit status.
337 Do not check whether this succeeds though, since we may be
338 dealing with a process that we attached to. Such a process will
339 only report its exit status to its original parent. */
340 waitpid (inferior_ptid.pid (), &status, 0);
342 /* OK, presumably inferior_ptid is the one who has exited.
343 We need to delete that one from the fork_list, and switch
344 to the next available fork. */
345 delete_fork (inferior_ptid);
347 /* There should still be a fork - if there's only one left,
348 delete_fork won't remove it, because we haven't updated
349 inferior_ptid yet. */
350 gdb_assert (!fork_list.empty ());
352 last = find_last_fork ();
353 fork_load_infrun_state (last);
354 printf_filtered (_("[Switching to %s]\n"),
355 target_pid_to_str (inferior_ptid));
357 /* If there's only one fork, switch back to non-fork mode. */
359 delete_fork (inferior_ptid);
362 /* The current inferior_ptid is being detached, but there are other
363 viable forks to debug. Detach and delete it and context-switch to
364 the first available. */
367 linux_fork_detach (int from_tty)
369 /* OK, inferior_ptid is the one we are detaching from. We need to
370 delete it from the fork_list, and switch to the next available
373 if (ptrace (PTRACE_DETACH, inferior_ptid.pid (), 0, 0))
374 error (_("Unable to detach %s"), target_pid_to_str (inferior_ptid));
376 delete_fork (inferior_ptid);
378 /* There should still be a fork - if there's only one left,
379 delete_fork won't remove it, because we haven't updated
380 inferior_ptid yet. */
381 gdb_assert (!fork_list.empty ());
383 fork_load_infrun_state (&fork_list.front ());
386 printf_filtered (_("[Switching to %s]\n"),
387 target_pid_to_str (inferior_ptid));
389 /* If there's only one fork, switch back to non-fork mode. */
391 delete_fork (inferior_ptid);
394 /* Temporarily switch to the infrun state stored on the fork_info
395 identified by a given ptid_t. When this object goes out of scope,
396 restore the currently selected infrun state. */
398 class scoped_switch_fork_info
401 /* Switch to the infrun state held on the fork_info identified by
402 PPTID. If PPTID is the current inferior then no switch is done. */
403 explicit scoped_switch_fork_info (ptid_t pptid)
406 if (pptid != inferior_ptid)
408 struct fork_info *newfp = nullptr;
410 /* Switch to pptid. */
411 m_oldfp = find_fork_ptid (inferior_ptid);
412 gdb_assert (m_oldfp != nullptr);
413 newfp = find_fork_ptid (pptid);
414 gdb_assert (newfp != nullptr);
415 fork_save_infrun_state (m_oldfp);
416 remove_breakpoints ();
417 fork_load_infrun_state (newfp);
418 insert_breakpoints ();
422 /* Restore the previously selected infrun state. If the constructor
423 didn't need to switch states, then nothing is done here either. */
424 ~scoped_switch_fork_info ()
426 if (m_oldfp != nullptr)
428 /* Switch back to inferior_ptid. */
431 remove_breakpoints ();
432 fork_load_infrun_state (m_oldfp);
433 insert_breakpoints ();
435 CATCH (ex, RETURN_MASK_ALL)
437 warning (_("Couldn't restore checkpoint state in %s: %s"),
438 target_pid_to_str (m_oldfp->ptid), ex.message);
444 DISABLE_COPY_AND_ASSIGN (scoped_switch_fork_info);
447 /* The fork_info for the previously selected infrun state, or nullptr if
448 we were already in the desired state, and nothing needs to be
450 struct fork_info *m_oldfp;
454 inferior_call_waitpid (ptid_t pptid, int pid)
456 struct objfile *waitpid_objf;
457 struct value *waitpid_fn = NULL;
460 scoped_switch_fork_info switch_fork_info (pptid);
462 /* Get the waitpid_fn. */
463 if (lookup_minimal_symbol ("waitpid", NULL, NULL).minsym != NULL)
464 waitpid_fn = find_function_in_inferior ("waitpid", &waitpid_objf);
466 && lookup_minimal_symbol ("_waitpid", NULL, NULL).minsym != NULL)
467 waitpid_fn = find_function_in_inferior ("_waitpid", &waitpid_objf);
468 if (waitpid_fn != nullptr)
470 struct gdbarch *gdbarch = get_current_arch ();
471 struct value *argv[3], *retv;
474 argv[0] = value_from_longest (builtin_type (gdbarch)->builtin_int, pid);
475 argv[1] = value_from_pointer (builtin_type (gdbarch)->builtin_data_ptr, 0);
476 argv[2] = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
478 retv = call_function_by_hand (waitpid_fn, NULL, argv);
480 if (value_as_long (retv) >= 0)
487 /* Fork list <-> user interface. */
490 delete_checkpoint_command (const char *args, int from_tty)
493 struct fork_info *fi;
496 error (_("Requires argument (checkpoint id to delete)"));
498 ptid = fork_id_to_ptid (parse_and_eval_long (args));
499 if (ptid == minus_one_ptid)
500 error (_("No such checkpoint id, %s"), args);
502 if (ptid == inferior_ptid)
504 Please switch to another checkpoint before deleting the current one"));
506 if (ptrace (PTRACE_KILL, ptid.pid (), 0, 0))
507 error (_("Unable to kill pid %s"), target_pid_to_str (ptid));
509 fi = find_fork_ptid (ptid);
511 pptid = fi->parent_ptid;
514 printf_filtered (_("Killed %s\n"), target_pid_to_str (ptid));
518 /* If fi->parent_ptid is not a part of lwp but it's a part of checkpoint
519 list, waitpid the ptid.
520 If fi->parent_ptid is a part of lwp and it is stopped, waitpid the
522 thread_info *parent = find_thread_ptid (pptid);
523 if ((parent == NULL && find_fork_ptid (pptid))
524 || (parent != NULL && parent->state == THREAD_STOPPED))
526 if (inferior_call_waitpid (pptid, ptid.pid ()))
527 warning (_("Unable to wait pid %s"), target_pid_to_str (ptid));
532 detach_checkpoint_command (const char *args, int from_tty)
537 error (_("Requires argument (checkpoint id to detach)"));
539 ptid = fork_id_to_ptid (parse_and_eval_long (args));
540 if (ptid == minus_one_ptid)
541 error (_("No such checkpoint id, %s"), args);
543 if (ptid == inferior_ptid)
545 Please switch to another checkpoint before detaching the current one"));
547 if (ptrace (PTRACE_DETACH, ptid.pid (), 0, 0))
548 error (_("Unable to detach %s"), target_pid_to_str (ptid));
551 printf_filtered (_("Detached %s\n"), target_pid_to_str (ptid));
556 /* Print information about currently known checkpoints. */
559 info_checkpoints_command (const char *arg, int from_tty)
561 struct gdbarch *gdbarch = get_current_arch ();
563 const fork_info *printed = NULL;
566 requested = (int) parse_and_eval_long (arg);
568 for (const fork_info &fi : fork_list)
570 if (requested > 0 && fi.num != requested)
574 if (fi.ptid == inferior_ptid)
575 printf_filtered ("* ");
577 printf_filtered (" ");
580 printf_filtered ("%d %s", fi.num, target_pid_to_str (fi.ptid));
582 printf_filtered (_(" (main process)"));
583 printf_filtered (_(" at "));
584 fputs_filtered (paddress (gdbarch, pc), gdb_stdout);
586 symtab_and_line sal = find_pc_line (pc, 0);
588 printf_filtered (_(", file %s"),
589 symtab_to_filename_for_display (sal.symtab));
591 printf_filtered (_(", line %d"), sal.line);
592 if (!sal.symtab && !sal.line)
594 struct bound_minimal_symbol msym;
596 msym = lookup_minimal_symbol_by_pc (pc);
598 printf_filtered (", <%s>", MSYMBOL_LINKAGE_NAME (msym.minsym));
601 putchar_filtered ('\n');
606 printf_filtered (_("No checkpoint number %d.\n"), requested);
608 printf_filtered (_("No checkpoints.\n"));
612 /* The PID of the process we're checkpointing. */
613 static int checkpointing_pid = 0;
616 linux_fork_checkpointing_p (int pid)
618 return (checkpointing_pid == pid);
621 /* Return true if the current inferior is multi-threaded. */
624 inf_has_multiple_threads ()
628 /* Return true as soon as we see the second thread of the current
630 for (thread_info *tp ATTRIBUTE_UNUSED : current_inferior ()->threads ())
638 checkpoint_command (const char *args, int from_tty)
640 struct objfile *fork_objf;
641 struct gdbarch *gdbarch;
642 struct target_waitstatus last_target_waitstatus;
643 ptid_t last_target_ptid;
644 struct value *fork_fn = NULL, *ret;
645 struct fork_info *fp;
648 if (!target_has_execution)
649 error (_("The program is not being run."));
651 /* Ensure that the inferior is not multithreaded. */
652 update_thread_list ();
653 if (inf_has_multiple_threads ())
654 error (_("checkpoint: can't checkpoint multiple threads."));
656 /* Make the inferior fork, record its (and gdb's) state. */
658 if (lookup_minimal_symbol ("fork", NULL, NULL).minsym != NULL)
659 fork_fn = find_function_in_inferior ("fork", &fork_objf);
661 if (lookup_minimal_symbol ("_fork", NULL, NULL).minsym != NULL)
662 fork_fn = find_function_in_inferior ("fork", &fork_objf);
664 error (_("checkpoint: can't find fork function in inferior."));
666 gdbarch = get_objfile_arch (fork_objf);
667 ret = value_from_longest (builtin_type (gdbarch)->builtin_int, 0);
669 /* Tell linux-nat.c that we're checkpointing this inferior. */
671 scoped_restore save_pid
672 = make_scoped_restore (&checkpointing_pid, inferior_ptid.pid ());
674 ret = call_function_by_hand (fork_fn, NULL, {});
677 if (!ret) /* Probably can't happen. */
678 error (_("checkpoint: call_function_by_hand returned null."));
680 retpid = value_as_long (ret);
681 get_last_target_status (&last_target_ptid, &last_target_waitstatus);
683 fp = find_fork_pid (retpid);
689 printf_filtered (_("checkpoint %d: fork returned pid %ld.\n"),
690 fp != NULL ? fp->num : -1, (long) retpid);
693 parent_pid = last_target_ptid.lwp ();
695 parent_pid = last_target_ptid.pid ();
696 printf_filtered (_(" gdb says parent = %ld.\n"),
702 error (_("Failed to find new fork"));
706 /* Special case -- if this is the first fork in the list (the
707 list was hitherto empty), then add inferior_ptid first, as a
708 special zeroeth fork id. */
709 fork_list.emplace_front (inferior_ptid.pid ());
712 fork_save_infrun_state (fp);
713 fp->parent_ptid = last_target_ptid;
717 linux_fork_context (struct fork_info *newfp, int from_tty)
719 /* Now we attempt to switch processes. */
720 struct fork_info *oldfp;
722 gdb_assert (newfp != NULL);
724 oldfp = find_fork_ptid (inferior_ptid);
725 gdb_assert (oldfp != NULL);
727 fork_save_infrun_state (oldfp);
728 remove_breakpoints ();
729 fork_load_infrun_state (newfp);
730 insert_breakpoints ();
732 printf_filtered (_("Switching to %s\n"),
733 target_pid_to_str (inferior_ptid));
735 print_stack_frame (get_selected_frame (NULL), 1, SRC_AND_LOC, 1);
738 /* Switch inferior process (checkpoint) context, by checkpoint id. */
740 restart_command (const char *args, int from_tty)
742 struct fork_info *fp;
745 error (_("Requires argument (checkpoint id to restart)"));
747 if ((fp = find_fork_id (parse_and_eval_long (args))) == NULL)
748 error (_("Not found: checkpoint id %s"), args);
750 linux_fork_context (fp, from_tty);
754 _initialize_linux_fork (void)
756 /* Checkpoint command: create a fork of the inferior process
757 and set it aside for later debugging. */
759 add_com ("checkpoint", class_obscure, checkpoint_command, _("\
760 Fork a duplicate process (experimental)."));
762 /* Restart command: restore the context of a specified checkpoint
765 add_com ("restart", class_obscure, restart_command, _("\
766 restart N: restore program context from a checkpoint.\n\
767 Argument N is checkpoint ID, as displayed by 'info checkpoints'."));
769 /* Delete checkpoint command: kill the process and remove it from
772 add_cmd ("checkpoint", class_obscure, delete_checkpoint_command, _("\
773 Delete a checkpoint (experimental)."),
776 /* Detach checkpoint command: release the process to run independently,
777 and remove it from the fork list. */
779 add_cmd ("checkpoint", class_obscure, detach_checkpoint_command, _("\
780 Detach from a checkpoint (experimental)."),
783 /* Info checkpoints command: list all forks/checkpoints
784 currently under gdb's control. */
786 add_info ("checkpoints", info_checkpoints_command,
787 _("IDs of currently known checkpoints."));