1 /* libthread_db assisted debugging support, generic parts.
3 Copyright (C) 1999-2017 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/>. */
22 #include "gdb_proc_service.h"
23 #include "nat/gdb_thread_db.h"
28 #include "gdbthread.h"
36 #include "solib-svr4.h"
39 #include "linux-nat.h"
40 #include "nat/linux-procfs.h"
41 #include "nat/linux-ptrace.h"
42 #include "nat/linux-osdata.h"
43 #include "auto-load.h"
44 #include "cli/cli-utils.h"
47 #include "nat/linux-namespaces.h"
50 /* GNU/Linux libthread_db support.
52 libthread_db is a library, provided along with libpthread.so, which
53 exposes the internals of the thread library to a debugger. It
54 allows GDB to find existing threads, new threads as they are
55 created, thread IDs (usually, the result of pthread_self), and
56 thread-local variables.
58 The libthread_db interface originates on Solaris, where it is both
59 more powerful and more complicated. This implementation only works
60 for NPTL, the glibc threading library. It assumes that each thread
61 is permanently assigned to a single light-weight process (LWP). At
62 some point it also supported the older LinuxThreads library, but it
65 libthread_db-specific information is stored in the "private" field
66 of struct thread_info. When the field is NULL we do not yet have
67 information about the new thread; this could be temporary (created,
68 but the thread library's data structures do not reflect it yet)
69 or permanent (created using clone instead of pthread_create).
71 Process IDs managed by linux-thread-db.c match those used by
72 linux-nat.c: a common PID for all processes, an LWP ID for each
73 thread, and no TID. We save the TID in private. Keeping it out
74 of the ptid_t prevents thread IDs changing when libpthread is
75 loaded or unloaded. */
77 static char *libthread_db_search_path;
79 /* Set to non-zero if thread_db auto-loading is enabled
80 by the "set auto-load libthread-db" command. */
81 static int auto_load_thread_db = 1;
83 /* "show" command for the auto_load_thread_db configuration variable. */
86 show_auto_load_thread_db (struct ui_file *file, int from_tty,
87 struct cmd_list_element *c, const char *value)
89 fprintf_filtered (file, _("Auto-loading of inferior specific libthread_db "
95 set_libthread_db_search_path (const char *ignored, int from_tty,
96 struct cmd_list_element *c)
98 if (*libthread_db_search_path == '\0')
100 xfree (libthread_db_search_path);
101 libthread_db_search_path = xstrdup (LIBTHREAD_DB_SEARCH_PATH);
105 /* If non-zero, print details of libthread_db processing. */
107 static unsigned int libthread_db_debug;
110 show_libthread_db_debug (struct ui_file *file, int from_tty,
111 struct cmd_list_element *c, const char *value)
113 fprintf_filtered (file, _("libthread-db debugging is %s.\n"), value);
116 /* If we're running on GNU/Linux, we must explicitly attach to any new
119 /* This module's target vector. */
120 static struct target_ops thread_db_ops;
122 /* Non-zero if we have determined the signals used by the threads
124 static int thread_signals;
125 static sigset_t thread_stop_set;
126 static sigset_t thread_print_set;
128 struct thread_db_info
130 struct thread_db_info *next;
132 /* Process id this object refers to. */
135 /* Handle from dlopen for libthread_db.so. */
138 /* Absolute pathname from gdb_realpath to disk file used for dlopen-ing
139 HANDLE. It may be NULL for system library. */
142 /* Structure that identifies the child process for the
143 <proc_service.h> interface. */
144 struct ps_prochandle proc_handle;
146 /* Connection to the libthread_db library. */
147 td_thragent_t *thread_agent;
149 /* True if we need to apply the workaround for glibc/BZ5983. When
150 we catch a PTRACE_O_TRACEFORK, and go query the child's thread
151 list, nptl_db returns the parent's threads in addition to the new
152 (single) child thread. If this flag is set, we do extra work to
153 be able to ignore such stale entries. */
154 int need_stale_parent_threads_check;
156 /* Pointers to the libthread_db functions. */
158 td_init_ftype *td_init_p;
159 td_ta_new_ftype *td_ta_new_p;
160 td_ta_map_lwp2thr_ftype *td_ta_map_lwp2thr_p;
161 td_ta_thr_iter_ftype *td_ta_thr_iter_p;
162 td_thr_get_info_ftype *td_thr_get_info_p;
163 td_thr_tls_get_addr_ftype *td_thr_tls_get_addr_p;
164 td_thr_tlsbase_ftype *td_thr_tlsbase_p;
167 /* List of known processes using thread_db, and the required
169 struct thread_db_info *thread_db_list;
171 static void thread_db_find_new_threads_1 (ptid_t ptid);
172 static void thread_db_find_new_threads_2 (ptid_t ptid, int until_no_new);
174 static void check_thread_signals (void);
176 static struct thread_info *record_thread
177 (struct thread_db_info *info, struct thread_info *tp,
178 ptid_t ptid, const td_thrhandle_t *th_p, const td_thrinfo_t *ti_p);
180 /* Add the current inferior to the list of processes using libpthread.
181 Return a pointer to the newly allocated object that was added to
182 THREAD_DB_LIST. HANDLE is the handle returned by dlopen'ing
185 static struct thread_db_info *
186 add_thread_db_info (void *handle)
188 struct thread_db_info *info = XCNEW (struct thread_db_info);
190 info->pid = ptid_get_pid (inferior_ptid);
191 info->handle = handle;
193 /* The workaround works by reading from /proc/pid/status, so it is
194 disabled for core files. */
195 if (target_has_execution)
196 info->need_stale_parent_threads_check = 1;
198 info->next = thread_db_list;
199 thread_db_list = info;
204 /* Return the thread_db_info object representing the bookkeeping
205 related to process PID, if any; NULL otherwise. */
207 static struct thread_db_info *
208 get_thread_db_info (int pid)
210 struct thread_db_info *info;
212 for (info = thread_db_list; info; info = info->next)
213 if (pid == info->pid)
219 /* When PID has exited or has been detached, we no longer want to keep
220 track of it as using libpthread. Call this function to discard
221 thread_db related info related to PID. Note that this closes
222 LIBTHREAD_DB_SO's dlopen'ed handle. */
225 delete_thread_db_info (int pid)
227 struct thread_db_info *info, *info_prev;
231 for (info = thread_db_list; info; info_prev = info, info = info->next)
232 if (pid == info->pid)
238 if (info->handle != NULL)
239 dlclose (info->handle);
241 xfree (info->filename);
244 info_prev->next = info->next;
246 thread_db_list = info->next;
251 /* Use "struct private_thread_info" to cache thread state. This is
252 a substantial optimization. */
254 struct thread_db_thread_info : public private_thread_info
256 /* Flag set when we see a TD_DEATH event for this thread. */
259 /* Cached thread state. */
260 td_thrhandle_t th {};
264 static thread_db_thread_info *
265 get_thread_db_thread_info (thread_info *thread)
267 return static_cast<thread_db_thread_info *> (thread->priv.get ());
271 thread_db_err_str (td_err_e err)
278 return "generic 'call succeeded'";
280 return "generic error";
282 return "no thread to satisfy query";
284 return "no sync handle to satisfy query";
286 return "no LWP to satisfy query";
288 return "invalid process handle";
290 return "invalid thread handle";
292 return "invalid synchronization handle";
294 return "invalid thread agent";
296 return "invalid key";
298 return "no event message for getmsg";
300 return "FPU register set not available";
302 return "application not linked with libthread";
304 return "requested event is not supported";
306 return "capability not available";
308 return "debugger service failed";
310 return "operation not applicable to";
312 return "no thread-specific data for this thread";
314 return "malloc failed";
316 return "only part of register set was written/read";
318 return "X register set not available for this thread";
319 #ifdef THREAD_DB_HAS_TD_NOTALLOC
321 return "thread has not yet allocated TLS for given module";
323 #ifdef THREAD_DB_HAS_TD_VERSION
325 return "versions of libpthread and libthread_db do not match";
327 #ifdef THREAD_DB_HAS_TD_NOTLS
329 return "there is no TLS segment in the given module";
332 snprintf (buf, sizeof (buf), "unknown thread_db error '%d'", err);
337 /* Fetch the user-level thread id of PTID. */
339 static struct thread_info *
340 thread_from_lwp (ptid_t ptid)
345 struct thread_db_info *info;
346 struct thread_info *tp;
348 /* Just in case td_ta_map_lwp2thr doesn't initialize it completely. */
351 /* This ptid comes from linux-nat.c, which should always fill in the
353 gdb_assert (ptid_get_lwp (ptid) != 0);
355 info = get_thread_db_info (ptid_get_pid (ptid));
357 /* Access an lwp we know is stopped. */
358 info->proc_handle.ptid = ptid;
359 err = info->td_ta_map_lwp2thr_p (info->thread_agent, ptid_get_lwp (ptid),
362 error (_("Cannot find user-level thread for LWP %ld: %s"),
363 ptid_get_lwp (ptid), thread_db_err_str (err));
365 err = info->td_thr_get_info_p (&th, &ti);
367 error (_("thread_get_info_callback: cannot get thread info: %s"),
368 thread_db_err_str (err));
370 /* Fill the cache. */
371 tp = find_thread_ptid (ptid);
372 return record_thread (info, tp, ptid, &th, &ti);
376 /* See linux-nat.h. */
379 thread_db_notice_clone (ptid_t parent, ptid_t child)
381 struct thread_db_info *info;
383 info = get_thread_db_info (ptid_get_pid (child));
388 thread_from_lwp (child);
390 /* If we do not know about the main thread yet, this would be a good
392 thread_from_lwp (parent);
397 verbose_dlsym (void *handle, const char *name)
399 void *sym = dlsym (handle, name);
401 warning (_("Symbol \"%s\" not found in libthread_db: %s"),
406 /* Verify inferior's '\0'-terminated symbol VER_SYMBOL starts with "%d.%d" and
407 return 1 if this version is lower (and not equal) to
408 VER_MAJOR_MIN.VER_MINOR_MIN. Return 0 in all other cases. */
411 inferior_has_bug (const char *ver_symbol, int ver_major_min, int ver_minor_min)
413 struct bound_minimal_symbol version_msym;
414 CORE_ADDR version_addr;
416 int err, got, retval = 0;
418 version_msym = lookup_minimal_symbol (ver_symbol, NULL, NULL);
419 if (version_msym.minsym == NULL)
422 version_addr = BMSYMBOL_VALUE_ADDRESS (version_msym);
423 got = target_read_string (version_addr, &version, 32, &err);
424 if (err == 0 && memchr (version, 0, got) == &version[got -1])
428 retval = (sscanf (version, "%d.%d", &major, &minor) == 2
429 && (major < ver_major_min
430 || (major == ver_major_min && minor < ver_minor_min)));
437 /* Similar as thread_db_find_new_threads_1, but try to silently ignore errors
440 Return 1 if the caller should abort libthread_db initialization. Return 0
444 thread_db_find_new_threads_silently (ptid_t ptid)
449 thread_db_find_new_threads_2 (ptid, 1);
452 CATCH (except, RETURN_MASK_ERROR)
454 if (libthread_db_debug)
455 exception_fprintf (gdb_stdlog, except,
456 "Warning: thread_db_find_new_threads_silently: ");
458 /* There is a bug fixed between nptl 2.6.1 and 2.7 by
459 commit 7d9d8bd18906fdd17364f372b160d7ab896ce909
460 where calls to td_thr_get_info fail with TD_ERR for statically linked
461 executables if td_thr_get_info is called before glibc has initialized
464 If the nptl bug is NOT present in the inferior and still thread_db
465 reports an error return 1. It means the inferior has corrupted thread
466 list and GDB should fall back only to LWPs.
468 If the nptl bug is present in the inferior return 0 to silently ignore
469 such errors, and let gdb enumerate threads again later. In such case
470 GDB cannot properly display LWPs if the inferior thread list is
471 corrupted. For core files it does not apply, no 'later enumeration'
474 if (!target_has_execution || !inferior_has_bug ("nptl_version", 2, 7))
476 exception_fprintf (gdb_stderr, except,
477 _("Warning: couldn't activate thread debugging "
478 "using libthread_db: "));
487 /* Lookup a library in which given symbol resides.
488 Note: this is looking in GDB process, not in the inferior.
489 Returns library name, or NULL. */
492 dladdr_to_soname (const void *addr)
496 if (dladdr (addr, &info) != 0)
497 return info.dli_fname;
501 /* Attempt to initialize dlopen()ed libthread_db, described by INFO.
503 Failure could happen if libthread_db does not have symbols we expect,
504 or when it refuses to work with the current inferior (e.g. due to
505 version mismatch between libthread_db and libpthread). */
508 try_thread_db_load_1 (struct thread_db_info *info)
512 /* Initialize pointers to the dynamic library functions we will use.
513 Essential functions first. */
515 #define TDB_VERBOSE_DLSYM(info, func) \
516 info->func ## _p = (func ## _ftype *) verbose_dlsym (info->handle, #func)
518 #define TDB_DLSYM(info, func) \
519 info->func ## _p = (func ## _ftype *) dlsym (info->handle, #func)
528 CHK (TDB_VERBOSE_DLSYM (info, td_init));
530 err = info->td_init_p ();
533 warning (_("Cannot initialize libthread_db: %s"),
534 thread_db_err_str (err));
538 CHK (TDB_VERBOSE_DLSYM (info, td_ta_new));
540 /* Initialize the structure that identifies the child process. */
541 info->proc_handle.ptid = inferior_ptid;
543 /* Now attempt to open a connection to the thread library. */
544 err = info->td_ta_new_p (&info->proc_handle, &info->thread_agent);
547 if (libthread_db_debug)
548 fprintf_unfiltered (gdb_stdlog, _("td_ta_new failed: %s\n"),
549 thread_db_err_str (err));
554 #ifdef THREAD_DB_HAS_TD_VERSION
557 /* The errors above are not unexpected and silently ignored:
558 they just mean we haven't found correct version of
562 warning (_("td_ta_new failed: %s"), thread_db_err_str (err));
567 /* These are essential. */
568 CHK (TDB_VERBOSE_DLSYM (info, td_ta_map_lwp2thr));
569 CHK (TDB_VERBOSE_DLSYM (info, td_thr_get_info));
571 /* These are not essential. */
572 TDB_DLSYM (info, td_thr_tls_get_addr);
573 TDB_DLSYM (info, td_thr_tlsbase);
575 /* It's best to avoid td_ta_thr_iter if possible. That walks data
576 structures in the inferior's address space that may be corrupted,
577 or, if the target is running, may change while we walk them. If
578 there's execution (and /proc is mounted), then we're already
579 attached to all LWPs. Use thread_from_lwp, which uses
580 td_ta_map_lwp2thr instead, which does not walk the thread list.
582 td_ta_map_lwp2thr uses ps_get_thread_area, but we can't use that
583 currently on core targets, as it uses ptrace directly. */
584 if (target_has_execution
585 && linux_proc_task_list_dir_exists (ptid_get_pid (inferior_ptid)))
586 info->td_ta_thr_iter_p = NULL;
588 CHK (TDB_VERBOSE_DLSYM (info, td_ta_thr_iter));
590 #undef TDB_VERBOSE_DLSYM
594 if (info->td_ta_thr_iter_p == NULL)
597 int pid = ptid_get_pid (inferior_ptid);
599 linux_stop_and_wait_all_lwps ();
602 if (ptid_get_pid (lp->ptid) == pid)
603 thread_from_lwp (lp->ptid);
605 linux_unstop_all_lwps ();
607 else if (thread_db_find_new_threads_silently (inferior_ptid) != 0)
609 /* Even if libthread_db initializes, if the thread list is
610 corrupted, we'd not manage to list any threads. Better reject this
611 thread_db, and fall back to at least listing LWPs. */
615 printf_unfiltered (_("[Thread debugging using libthread_db enabled]\n"));
617 if (*libthread_db_search_path || libthread_db_debug)
619 struct ui_file *file;
622 library = dladdr_to_soname ((const void *) *info->td_ta_new_p);
624 library = LIBTHREAD_DB_SO;
626 /* If we'd print this to gdb_stdout when debug output is
627 disabled, still print it to gdb_stdout if debug output is
628 enabled. User visible output should not depend on debug
630 file = *libthread_db_search_path != '\0' ? gdb_stdout : gdb_stdlog;
631 fprintf_unfiltered (file, _("Using host libthread_db library \"%s\".\n"),
635 /* The thread library was detected. Activate the thread_db target
636 if this is the first process using it. */
637 if (thread_db_list->next == NULL)
638 push_target (&thread_db_ops);
643 /* Attempt to use LIBRARY as libthread_db. LIBRARY could be absolute,
644 relative, or just LIBTHREAD_DB. */
647 try_thread_db_load (const char *library, int check_auto_load_safe)
650 struct thread_db_info *info;
652 if (libthread_db_debug)
653 fprintf_unfiltered (gdb_stdlog,
654 _("Trying host libthread_db library: %s.\n"),
657 if (check_auto_load_safe)
659 if (access (library, R_OK) != 0)
661 /* Do not print warnings by file_is_auto_load_safe if the library does
662 not exist at this place. */
663 if (libthread_db_debug)
664 fprintf_unfiltered (gdb_stdlog, _("open failed: %s.\n"),
665 safe_strerror (errno));
669 if (!file_is_auto_load_safe (library, _("auto-load: Loading libthread-db "
670 "library \"%s\" from explicit "
676 handle = dlopen (library, RTLD_NOW);
679 if (libthread_db_debug)
680 fprintf_unfiltered (gdb_stdlog, _("dlopen failed: %s.\n"), dlerror ());
684 if (libthread_db_debug && strchr (library, '/') == NULL)
688 td_init = dlsym (handle, "td_init");
691 const char *const libpath = dladdr_to_soname (td_init);
694 fprintf_unfiltered (gdb_stdlog, _("Host %s resolved to: %s.\n"),
699 info = add_thread_db_info (handle);
701 /* Do not save system library name, that one is always trusted. */
702 if (strchr (library, '/') != NULL)
703 info->filename = gdb_realpath (library).release ();
705 if (try_thread_db_load_1 (info))
708 /* This library "refused" to work on current inferior. */
709 delete_thread_db_info (ptid_get_pid (inferior_ptid));
713 /* Subroutine of try_thread_db_load_from_pdir to simplify it.
714 Try loading libthread_db in directory(OBJ)/SUBDIR.
715 SUBDIR may be NULL. It may also be something like "../lib64".
716 The result is true for success. */
719 try_thread_db_load_from_pdir_1 (struct objfile *obj, const char *subdir)
721 struct cleanup *cleanup;
724 const char *obj_name = objfile_name (obj);
727 if (obj_name[0] != '/')
729 warning (_("Expected absolute pathname for libpthread in the"
730 " inferior, but got %s."), obj_name);
734 alloc_len = (strlen (obj_name)
735 + (subdir ? strlen (subdir) + 1 : 0)
736 + 1 + strlen (LIBTHREAD_DB_SO) + 1);
737 path = (char *) xmalloc (alloc_len);
738 cleanup = make_cleanup (xfree, path);
740 strcpy (path, obj_name);
741 cp = strrchr (path, '/');
742 /* This should at minimum hit the first character. */
743 gdb_assert (cp != NULL);
750 strcat (cp, LIBTHREAD_DB_SO);
752 result = try_thread_db_load (path, 1);
754 do_cleanups (cleanup);
758 /* Handle $pdir in libthread-db-search-path.
759 Look for libthread_db in directory(libpthread)/SUBDIR.
760 SUBDIR may be NULL. It may also be something like "../lib64".
761 The result is true for success. */
764 try_thread_db_load_from_pdir (const char *subdir)
768 if (!auto_load_thread_db)
772 if (libpthread_name_p (objfile_name (obj)))
774 if (try_thread_db_load_from_pdir_1 (obj, subdir))
777 /* We may have found the separate-debug-info version of
778 libpthread, and it may live in a directory without a matching
780 if (obj->separate_debug_objfile_backlink != NULL)
781 return try_thread_db_load_from_pdir_1 (obj->separate_debug_objfile_backlink,
790 /* Handle $sdir in libthread-db-search-path.
791 Look for libthread_db in the system dirs, or wherever a plain
792 dlopen(file_without_path) will look.
793 The result is true for success. */
796 try_thread_db_load_from_sdir (void)
798 return try_thread_db_load (LIBTHREAD_DB_SO, 0);
801 /* Try to load libthread_db from directory DIR of length DIR_LEN.
802 The result is true for success. */
805 try_thread_db_load_from_dir (const char *dir, size_t dir_len)
807 struct cleanup *cleanup;
811 if (!auto_load_thread_db)
814 path = (char *) xmalloc (dir_len + 1 + strlen (LIBTHREAD_DB_SO) + 1);
815 cleanup = make_cleanup (xfree, path);
817 memcpy (path, dir, dir_len);
819 strcpy (path + dir_len + 1, LIBTHREAD_DB_SO);
821 result = try_thread_db_load (path, 1);
823 do_cleanups (cleanup);
827 /* Search libthread_db_search_path for libthread_db which "agrees"
828 to work on current inferior.
829 The result is true for success. */
832 thread_db_load_search (void)
834 VEC (char_ptr) *dir_vec;
835 struct cleanup *cleanups;
839 dir_vec = dirnames_to_char_ptr_vec (libthread_db_search_path);
840 cleanups = make_cleanup_free_char_ptr_vec (dir_vec);
842 for (i = 0; VEC_iterate (char_ptr, dir_vec, i, this_dir); ++i)
844 const int pdir_len = sizeof ("$pdir") - 1;
847 this_dir_len = strlen (this_dir);
849 if (strncmp (this_dir, "$pdir", pdir_len) == 0
850 && (this_dir[pdir_len] == '\0'
851 || this_dir[pdir_len] == '/'))
854 struct cleanup *free_subdir_cleanup
855 = make_cleanup (null_cleanup, NULL);
857 if (this_dir[pdir_len] == '/')
859 subdir = (char *) xmalloc (strlen (this_dir));
860 make_cleanup (xfree, subdir);
861 strcpy (subdir, this_dir + pdir_len + 1);
863 rc = try_thread_db_load_from_pdir (subdir);
864 do_cleanups (free_subdir_cleanup);
868 else if (strcmp (this_dir, "$sdir") == 0)
870 if (try_thread_db_load_from_sdir ())
878 if (try_thread_db_load_from_dir (this_dir, this_dir_len))
886 do_cleanups (cleanups);
887 if (libthread_db_debug)
888 fprintf_unfiltered (gdb_stdlog,
889 _("thread_db_load_search returning %d\n"), rc);
893 /* Return non-zero if the inferior has a libpthread. */
896 has_libpthread (void)
901 if (libpthread_name_p (objfile_name (obj)))
907 /* Attempt to load and initialize libthread_db.
908 Return 1 on success. */
911 thread_db_load (void)
913 struct thread_db_info *info;
915 info = get_thread_db_info (ptid_get_pid (inferior_ptid));
920 /* Don't attempt to use thread_db on executables not running
922 if (!target_has_registers)
925 /* Don't attempt to use thread_db for remote targets. */
926 if (!(target_can_run (¤t_target) || core_bfd))
929 if (thread_db_load_search ())
932 /* We couldn't find a libthread_db.
933 If the inferior has a libpthread warn the user. */
934 if (has_libpthread ())
936 warning (_("Unable to find libthread_db matching inferior's thread"
937 " library, thread debugging will not be available."));
941 /* Either this executable isn't using libpthread at all, or it is
942 statically linked. Since we can't easily distinguish these two cases,
943 no warning is issued. */
948 check_thread_signals (void)
955 lin_thread_get_thread_signals (&mask);
956 sigemptyset (&thread_stop_set);
957 sigemptyset (&thread_print_set);
959 for (i = 1; i < NSIG; i++)
961 if (sigismember (&mask, i))
963 if (signal_stop_update (gdb_signal_from_host (i), 0))
964 sigaddset (&thread_stop_set, i);
965 if (signal_print_update (gdb_signal_from_host (i), 0))
966 sigaddset (&thread_print_set, i);
973 /* Check whether thread_db is usable. This function is called when
974 an inferior is created (or otherwise acquired, e.g. attached to)
975 and when new shared libraries are loaded into a running process. */
978 check_for_thread_db (void)
980 /* Do nothing if we couldn't load libthread_db.so.1. */
981 if (!thread_db_load ())
985 /* This function is called via the new_objfile observer. */
988 thread_db_new_objfile (struct objfile *objfile)
990 /* This observer must always be called with inferior_ptid set
994 /* libpthread with separate debug info has its debug info file already
995 loaded (and notified without successful thread_db initialization)
996 the time observer_notify_new_objfile is called for the library itself.
997 Static executables have their separate debug info loaded already
998 before the inferior has started. */
999 && objfile->separate_debug_objfile_backlink == NULL
1000 /* Only check for thread_db if we loaded libpthread,
1001 or if this is the main symbol file.
1002 We need to check OBJF_MAINLINE to handle the case of debugging
1003 a statically linked executable AND the symbol file is specified AFTER
1004 the exec file is loaded (e.g., gdb -c core ; file foo).
1005 For dynamically linked executables, libpthread can be near the end
1006 of the list of shared libraries to load, and in an app of several
1007 thousand shared libraries, this can otherwise be painful. */
1008 && ((objfile->flags & OBJF_MAINLINE) != 0
1009 || libpthread_name_p (objfile_name (objfile))))
1010 check_for_thread_db ();
1014 check_pid_namespace_match (void)
1016 /* Check is only relevant for local targets targets. */
1017 if (target_can_run (¤t_target))
1019 /* If the child is in a different PID namespace, its idea of its
1020 PID will differ from our idea of its PID. When we scan the
1021 child's thread list, we'll mistakenly think it has no threads
1022 since the thread PID fields won't match the PID we give to
1024 if (!linux_ns_same (ptid_get_pid (inferior_ptid), LINUX_NS_PID))
1026 warning (_ ("Target and debugger are in different PID "
1027 "namespaces; thread lists and other data are "
1028 "likely unreliable. "
1029 "Connect to gdbserver inside the container."));
1034 /* This function is called via the inferior_created observer.
1035 This handles the case of debugging statically linked executables. */
1038 thread_db_inferior_created (struct target_ops *target, int from_tty)
1040 check_pid_namespace_match ();
1041 check_for_thread_db ();
1044 /* Update the thread's state (what's displayed in "info threads"),
1045 from libthread_db thread state information. */
1048 update_thread_state (thread_db_thread_info *priv,
1049 const td_thrinfo_t *ti_p)
1051 priv->dying = (ti_p->ti_state == TD_THR_UNKNOWN
1052 || ti_p->ti_state == TD_THR_ZOMBIE);
1055 /* Record a new thread in GDB's thread list. Creates the thread's
1056 private info. If TP is NULL or TP is marked as having exited,
1057 creates a new thread. Otherwise, uses TP. */
1059 static struct thread_info *
1060 record_thread (struct thread_db_info *info,
1061 struct thread_info *tp,
1062 ptid_t ptid, const td_thrhandle_t *th_p,
1063 const td_thrinfo_t *ti_p)
1065 /* A thread ID of zero may mean the thread library has not
1066 initialized yet. Leave private == NULL until the thread library
1068 if (ti_p->ti_tid == 0)
1071 /* Construct the thread's private data. */
1072 thread_db_thread_info *priv = new thread_db_thread_info;
1075 priv->tid = ti_p->ti_tid;
1076 update_thread_state (priv, ti_p);
1078 /* Add the thread to GDB's thread list. If we already know about a
1079 thread with this PTID, but it's marked exited, then the kernel
1080 reused the tid of an old thread. */
1081 if (tp == NULL || tp->state == THREAD_EXITED)
1082 tp = add_thread_with_info (ptid, priv);
1084 tp->priv.reset (priv);
1086 if (target_has_execution)
1087 check_thread_signals ();
1093 thread_db_detach (struct target_ops *ops, const char *args, int from_tty)
1095 struct target_ops *target_beneath = find_target_beneath (ops);
1096 struct thread_db_info *info;
1098 info = get_thread_db_info (ptid_get_pid (inferior_ptid));
1101 delete_thread_db_info (ptid_get_pid (inferior_ptid));
1103 target_beneath->to_detach (target_beneath, args, from_tty);
1105 /* NOTE: From this point on, inferior_ptid is null_ptid. */
1107 /* If there are no more processes using libpthread, detach the
1108 thread_db target ops. */
1109 if (!thread_db_list)
1110 unpush_target (&thread_db_ops);
1114 thread_db_wait (struct target_ops *ops,
1115 ptid_t ptid, struct target_waitstatus *ourstatus,
1118 struct thread_db_info *info;
1119 struct target_ops *beneath = find_target_beneath (ops);
1121 ptid = beneath->to_wait (beneath, ptid, ourstatus, options);
1123 switch (ourstatus->kind)
1125 case TARGET_WAITKIND_IGNORE:
1126 case TARGET_WAITKIND_EXITED:
1127 case TARGET_WAITKIND_THREAD_EXITED:
1128 case TARGET_WAITKIND_SIGNALLED:
1132 info = get_thread_db_info (ptid_get_pid (ptid));
1134 /* If this process isn't using thread_db, we're done. */
1138 if (ourstatus->kind == TARGET_WAITKIND_EXECD)
1140 /* New image, it may or may not end up using thread_db. Assume
1141 not unless we find otherwise. */
1142 delete_thread_db_info (ptid_get_pid (ptid));
1143 if (!thread_db_list)
1144 unpush_target (&thread_db_ops);
1149 /* Fill in the thread's user-level thread id and status. */
1150 thread_from_lwp (ptid);
1156 thread_db_mourn_inferior (struct target_ops *ops)
1158 struct target_ops *target_beneath = find_target_beneath (ops);
1160 delete_thread_db_info (ptid_get_pid (inferior_ptid));
1162 target_beneath->to_mourn_inferior (target_beneath);
1164 /* Detach thread_db target ops. */
1165 if (!thread_db_list)
1166 unpush_target (ops);
1169 struct callback_data
1171 struct thread_db_info *info;
1176 find_new_threads_callback (const td_thrhandle_t *th_p, void *data)
1181 struct thread_info *tp;
1182 struct callback_data *cb_data = (struct callback_data *) data;
1183 struct thread_db_info *info = cb_data->info;
1185 err = info->td_thr_get_info_p (th_p, &ti);
1187 error (_("find_new_threads_callback: cannot get thread info: %s"),
1188 thread_db_err_str (err));
1190 if (ti.ti_lid == -1)
1192 /* A thread with kernel thread ID -1 is either a thread that
1193 exited and was joined, or a thread that is being created but
1194 hasn't started yet, and that is reusing the tcb/stack of a
1195 thread that previously exited and was joined. (glibc marks
1196 terminated and joined threads with kernel thread ID -1. See
1198 if (libthread_db_debug)
1199 fprintf_unfiltered (gdb_stdlog,
1200 "thread_db: skipping exited and "
1201 "joined thread (0x%lx)\n",
1202 (unsigned long) ti.ti_tid);
1208 /* A thread ID of zero means that this is the main thread, but
1209 glibc has not yet initialized thread-local storage and the
1210 pthread library. We do not know what the thread's TID will
1213 /* In that case, we're not stopped in a fork syscall and don't
1214 need this glibc bug workaround. */
1215 info->need_stale_parent_threads_check = 0;
1220 /* Ignore stale parent threads, caused by glibc/BZ5983. This is a
1221 bit expensive, as it needs to open /proc/pid/status, so try to
1222 avoid doing the work if we know we don't have to. */
1223 if (info->need_stale_parent_threads_check)
1225 int tgid = linux_proc_get_tgid (ti.ti_lid);
1227 if (tgid != -1 && tgid != info->pid)
1231 ptid = ptid_build (info->pid, ti.ti_lid, 0);
1232 tp = find_thread_ptid (ptid);
1233 if (tp == NULL || tp->priv == NULL)
1234 record_thread (info, tp, ptid, th_p, &ti);
1239 /* Helper for thread_db_find_new_threads_2.
1240 Returns number of new threads found. */
1243 find_new_threads_once (struct thread_db_info *info, int iteration,
1246 struct callback_data data;
1247 td_err_e err = TD_ERR;
1250 data.new_threads = 0;
1252 /* See comment in thread_db_update_thread_list. */
1253 gdb_assert (info->td_ta_thr_iter_p != NULL);
1257 /* Iterate over all user-space threads to discover new threads. */
1258 err = info->td_ta_thr_iter_p (info->thread_agent,
1259 find_new_threads_callback,
1262 TD_THR_LOWEST_PRIORITY,
1264 TD_THR_ANY_USER_FLAGS);
1266 CATCH (except, RETURN_MASK_ERROR)
1268 if (libthread_db_debug)
1270 exception_fprintf (gdb_stdlog, except,
1271 "Warning: find_new_threads_once: ");
1276 if (libthread_db_debug)
1278 fprintf_unfiltered (gdb_stdlog,
1279 _("Found %d new threads in iteration %d.\n"),
1280 data.new_threads, iteration);
1286 return data.new_threads;
1289 /* Search for new threads, accessing memory through stopped thread
1290 PTID. If UNTIL_NO_NEW is true, repeat searching until several
1291 searches in a row do not discover any new threads. */
1294 thread_db_find_new_threads_2 (ptid_t ptid, int until_no_new)
1296 td_err_e err = TD_OK;
1297 struct thread_db_info *info;
1300 info = get_thread_db_info (ptid_get_pid (ptid));
1302 /* Access an lwp we know is stopped. */
1303 info->proc_handle.ptid = ptid;
1307 /* Require 4 successive iterations which do not find any new threads.
1308 The 4 is a heuristic: there is an inherent race here, and I have
1309 seen that 2 iterations in a row are not always sufficient to
1310 "capture" all threads. */
1311 for (i = 0, loop = 0; loop < 4 && err == TD_OK; ++i, ++loop)
1312 if (find_new_threads_once (info, i, &err) != 0)
1314 /* Found some new threads. Restart the loop from beginning. */
1319 find_new_threads_once (info, 0, &err);
1322 error (_("Cannot find new threads: %s"), thread_db_err_str (err));
1326 thread_db_find_new_threads_1 (ptid_t ptid)
1328 thread_db_find_new_threads_2 (ptid, 0);
1331 /* Implement the to_update_thread_list target method for this
1335 thread_db_update_thread_list (struct target_ops *ops)
1337 struct thread_db_info *info;
1338 struct inferior *inf;
1344 struct thread_info *thread;
1349 info = get_thread_db_info (inf->pid);
1353 thread = any_live_thread_of_process (inf->pid);
1354 if (thread == NULL || thread->executing)
1357 /* It's best to avoid td_ta_thr_iter if possible. That walks
1358 data structures in the inferior's address space that may be
1359 corrupted, or, if the target is running, the list may change
1360 while we walk it. In the latter case, it's possible that a
1361 thread exits just at the exact time that causes GDB to get
1362 stuck in an infinite loop. To avoid pausing all threads
1363 whenever the core wants to refresh the thread list, we
1364 instead use thread_from_lwp immediately when we see an LWP
1365 stop. That uses thread_db entry points that do not walk
1366 libpthread's thread list, so should be safe, as well as more
1368 if (target_has_execution_1 (thread->ptid))
1371 thread_db_find_new_threads_1 (thread->ptid);
1374 /* Give the beneath target a chance to do extra processing. */
1375 ops->beneath->to_update_thread_list (ops->beneath);
1379 thread_db_pid_to_str (struct target_ops *ops, ptid_t ptid)
1381 struct thread_info *thread_info = find_thread_ptid (ptid);
1382 struct target_ops *beneath;
1384 if (thread_info != NULL && thread_info->priv != NULL)
1386 static char buf[64];
1387 thread_db_thread_info *priv = get_thread_db_thread_info (thread_info);
1389 snprintf (buf, sizeof (buf), "Thread 0x%lx (LWP %ld)",
1390 (unsigned long) priv->tid, ptid_get_lwp (ptid));
1395 beneath = find_target_beneath (ops);
1396 return beneath->to_pid_to_str (beneath, ptid);
1399 /* Return a string describing the state of the thread specified by
1403 thread_db_extra_thread_info (struct target_ops *self,
1404 struct thread_info *info)
1406 if (info->priv == NULL)
1409 thread_db_thread_info *priv = get_thread_db_thread_info (info);
1417 /* Return pointer to the thread_info struct which corresponds to
1418 THREAD_HANDLE (having length HANDLE_LEN). */
1420 static struct thread_info *
1421 thread_db_thread_handle_to_thread_info (struct target_ops *ops,
1422 const gdb_byte *thread_handle,
1424 struct inferior *inf)
1426 struct thread_info *tp;
1427 thread_t handle_tid;
1429 /* Thread handle sizes must match in order to proceed. We don't use an
1430 assert here because the resulting internal error will cause GDB to
1431 exit. This isn't necessarily an internal error due to the possibility
1432 of garbage being passed as the thread handle via the python interface. */
1433 if (handle_len != sizeof (handle_tid))
1434 error (_("Thread handle size mismatch: %d vs %zu (from libthread_db)"),
1435 handle_len, sizeof (handle_tid));
1437 handle_tid = * (const thread_t *) thread_handle;
1439 ALL_NON_EXITED_THREADS (tp)
1441 thread_db_thread_info *priv = get_thread_db_thread_info (tp);
1443 if (tp->inf == inf && priv != NULL && handle_tid == priv->tid)
1450 /* Get the address of the thread local variable in load module LM which
1451 is stored at OFFSET within the thread local storage for thread PTID. */
1454 thread_db_get_thread_local_address (struct target_ops *ops,
1459 struct thread_info *thread_info;
1460 struct target_ops *beneath;
1462 /* Find the matching thread. */
1463 thread_info = find_thread_ptid (ptid);
1465 /* We may not have discovered the thread yet. */
1466 if (thread_info != NULL && thread_info->priv == NULL)
1467 thread_info = thread_from_lwp (ptid);
1469 if (thread_info != NULL && thread_info->priv != NULL)
1473 thread_db_info *info = get_thread_db_info (ptid_get_pid (ptid));
1474 thread_db_thread_info *priv = get_thread_db_thread_info (thread_info);
1476 /* Finally, get the address of the variable. */
1479 /* glibc doesn't provide the needed interface. */
1480 if (!info->td_thr_tls_get_addr_p)
1481 throw_error (TLS_NO_LIBRARY_SUPPORT_ERROR,
1482 _("No TLS library support"));
1484 /* Note the cast through uintptr_t: this interface only works if
1485 a target address fits in a psaddr_t, which is a host pointer.
1486 So a 32-bit debugger can not access 64-bit TLS through this. */
1487 err = info->td_thr_tls_get_addr_p (&priv->th,
1488 (psaddr_t)(uintptr_t) lm,
1493 /* If glibc doesn't provide the needed interface throw an error
1494 that LM is zero - normally cases it should not be. */
1495 if (!info->td_thr_tlsbase_p)
1496 throw_error (TLS_LOAD_MODULE_NOT_FOUND_ERROR,
1497 _("TLS load module not found"));
1499 /* This code path handles the case of -static -pthread executables:
1500 https://sourceware.org/ml/libc-help/2014-03/msg00024.html
1501 For older GNU libc r_debug.r_map is NULL. For GNU libc after
1502 PR libc/16831 due to GDB PR threads/16954 LOAD_MODULE is also NULL.
1503 The constant number 1 depends on GNU __libc_setup_tls
1504 initialization of l_tls_modid to 1. */
1505 err = info->td_thr_tlsbase_p (&priv->th, 1, &address);
1506 address = (char *) address + offset;
1509 #ifdef THREAD_DB_HAS_TD_NOTALLOC
1510 /* The memory hasn't been allocated, yet. */
1511 if (err == TD_NOTALLOC)
1512 /* Now, if libthread_db provided the initialization image's
1513 address, we *could* try to build a non-lvalue value from
1514 the initialization image. */
1515 throw_error (TLS_NOT_ALLOCATED_YET_ERROR,
1516 _("TLS not allocated yet"));
1519 /* Something else went wrong. */
1521 throw_error (TLS_GENERIC_ERROR,
1522 (("%s")), thread_db_err_str (err));
1524 /* Cast assuming host == target. Joy. */
1525 /* Do proper sign extension for the target. */
1526 gdb_assert (exec_bfd);
1527 return (bfd_get_sign_extend_vma (exec_bfd) > 0
1528 ? (CORE_ADDR) (intptr_t) address
1529 : (CORE_ADDR) (uintptr_t) address);
1532 beneath = find_target_beneath (ops);
1533 return beneath->to_get_thread_local_address (beneath, ptid, lm, offset);
1536 /* Implement the to_get_ada_task_ptid target method for this target. */
1539 thread_db_get_ada_task_ptid (struct target_ops *self, long lwp, long thread)
1541 /* NPTL uses a 1:1 model, so the LWP id suffices. */
1542 return ptid_build (ptid_get_pid (inferior_ptid), lwp, 0);
1546 thread_db_resume (struct target_ops *ops,
1547 ptid_t ptid, int step, enum gdb_signal signo)
1549 struct target_ops *beneath = find_target_beneath (ops);
1550 struct thread_db_info *info;
1552 if (ptid_equal (ptid, minus_one_ptid))
1553 info = get_thread_db_info (ptid_get_pid (inferior_ptid));
1555 info = get_thread_db_info (ptid_get_pid (ptid));
1557 /* This workaround is only needed for child fork lwps stopped in a
1558 PTRACE_O_TRACEFORK event. When the inferior is resumed, the
1559 workaround can be disabled. */
1561 info->need_stale_parent_threads_check = 0;
1563 beneath->to_resume (beneath, ptid, step, signo);
1566 /* qsort helper function for info_auto_load_libthread_db, sort the
1567 thread_db_info pointers primarily by their FILENAME and secondarily by their
1568 PID, both in ascending order. */
1571 info_auto_load_libthread_db_compare (const void *ap, const void *bp)
1573 struct thread_db_info *a = *(struct thread_db_info **) ap;
1574 struct thread_db_info *b = *(struct thread_db_info **) bp;
1577 retval = strcmp (a->filename, b->filename);
1581 return (a->pid > b->pid) - (a->pid - b->pid);
1584 /* Implement 'info auto-load libthread-db'. */
1587 info_auto_load_libthread_db (const char *args, int from_tty)
1589 struct ui_out *uiout = current_uiout;
1590 const char *cs = args ? args : "";
1591 struct thread_db_info *info, **array;
1592 unsigned info_count, unique_filenames;
1593 size_t max_filename_len, max_pids_len, pids_len;
1594 struct cleanup *back_to;
1598 cs = skip_spaces (cs);
1600 error (_("'info auto-load libthread-db' does not accept any parameters"));
1603 for (info = thread_db_list; info; info = info->next)
1604 if (info->filename != NULL)
1607 array = XNEWVEC (struct thread_db_info *, info_count);
1608 back_to = make_cleanup (xfree, array);
1611 for (info = thread_db_list; info; info = info->next)
1612 if (info->filename != NULL)
1613 array[info_count++] = info;
1615 /* Sort ARRAY by filenames and PIDs. */
1617 qsort (array, info_count, sizeof (*array),
1618 info_auto_load_libthread_db_compare);
1620 /* Calculate the number of unique filenames (rows) and the maximum string
1621 length of PIDs list for the unique filenames (columns). */
1623 unique_filenames = 0;
1624 max_filename_len = 0;
1627 for (i = 0; i < info_count; i++)
1629 int pid = array[i]->pid;
1630 size_t this_pid_len;
1632 for (this_pid_len = 0; pid != 0; pid /= 10)
1635 if (i == 0 || strcmp (array[i - 1]->filename, array[i]->filename) != 0)
1638 max_filename_len = std::max (max_filename_len,
1639 strlen (array[i]->filename));
1643 pids_len -= strlen (", ");
1644 max_pids_len = std::max (max_pids_len, pids_len);
1648 pids_len += this_pid_len + strlen (", ");
1652 pids_len -= strlen (", ");
1653 max_pids_len = std::max (max_pids_len, pids_len);
1656 /* Table header shifted right by preceding "libthread-db: " would not match
1658 if (info_count > 0 && args == auto_load_info_scripts_pattern_nl)
1662 ui_out_emit_table table_emitter (uiout, 2, unique_filenames,
1663 "LinuxThreadDbTable");
1665 uiout->table_header (max_filename_len, ui_left, "filename", "Filename");
1666 uiout->table_header (pids_len, ui_left, "PIDs", "Pids");
1667 uiout->table_body ();
1669 pids = (char *) xmalloc (max_pids_len + 1);
1670 make_cleanup (xfree, pids);
1672 /* Note I is incremented inside the cycle, not at its end. */
1673 for (i = 0; i < info_count;)
1675 ui_out_emit_tuple tuple_emitter (uiout, NULL);
1679 uiout->field_string ("filename", info->filename);
1682 while (i < info_count && strcmp (info->filename,
1683 array[i]->filename) == 0)
1685 if (pids_end != pids)
1690 pids_end += xsnprintf (pids_end,
1691 &pids[max_pids_len + 1] - pids_end,
1692 "%u", array[i]->pid);
1693 gdb_assert (pids_end < &pids[max_pids_len + 1]);
1699 uiout->field_string ("pids", pids);
1705 do_cleanups (back_to);
1707 if (info_count == 0)
1708 uiout->message (_("No auto-loaded libthread-db.\n"));
1712 init_thread_db_ops (void)
1714 thread_db_ops.to_shortname = "multi-thread";
1715 thread_db_ops.to_longname = "multi-threaded child process.";
1716 thread_db_ops.to_doc = "Threads and pthreads support.";
1717 thread_db_ops.to_detach = thread_db_detach;
1718 thread_db_ops.to_wait = thread_db_wait;
1719 thread_db_ops.to_resume = thread_db_resume;
1720 thread_db_ops.to_mourn_inferior = thread_db_mourn_inferior;
1721 thread_db_ops.to_update_thread_list = thread_db_update_thread_list;
1722 thread_db_ops.to_pid_to_str = thread_db_pid_to_str;
1723 thread_db_ops.to_stratum = thread_stratum;
1724 thread_db_ops.to_has_thread_control = tc_schedlock;
1725 thread_db_ops.to_get_thread_local_address
1726 = thread_db_get_thread_local_address;
1727 thread_db_ops.to_extra_thread_info = thread_db_extra_thread_info;
1728 thread_db_ops.to_get_ada_task_ptid = thread_db_get_ada_task_ptid;
1729 thread_db_ops.to_thread_handle_to_thread_info = thread_db_thread_handle_to_thread_info;
1730 thread_db_ops.to_magic = OPS_MAGIC;
1732 complete_target_initialization (&thread_db_ops);
1736 _initialize_thread_db (void)
1738 init_thread_db_ops ();
1740 /* Defer loading of libthread_db.so until inferior is running.
1741 This allows gdb to load correct libthread_db for a given
1742 executable -- there could be multiple versions of glibc,
1743 and until there is a running inferior, we can't tell which
1744 libthread_db is the correct one to load. */
1746 libthread_db_search_path = xstrdup (LIBTHREAD_DB_SEARCH_PATH);
1748 add_setshow_optional_filename_cmd ("libthread-db-search-path",
1750 &libthread_db_search_path, _("\
1751 Set search path for libthread_db."), _("\
1752 Show the current search path or libthread_db."), _("\
1753 This path is used to search for libthread_db to be loaded into \
1755 Its value is a colon (':') separate list of directories to search.\n\
1756 Setting the search path to an empty list resets it to its default value."),
1757 set_libthread_db_search_path,
1759 &setlist, &showlist);
1761 add_setshow_zuinteger_cmd ("libthread-db", class_maintenance,
1762 &libthread_db_debug, _("\
1763 Set libthread-db debugging."), _("\
1764 Show libthread-db debugging."), _("\
1765 When non-zero, libthread-db debugging is enabled."),
1767 show_libthread_db_debug,
1768 &setdebuglist, &showdebuglist);
1770 add_setshow_boolean_cmd ("libthread-db", class_support,
1771 &auto_load_thread_db, _("\
1772 Enable or disable auto-loading of inferior specific libthread_db."), _("\
1773 Show whether auto-loading inferior specific libthread_db is enabled."), _("\
1774 If enabled, libthread_db will be searched in 'set libthread-db-search-path'\n\
1775 locations to load libthread_db compatible with the inferior.\n\
1776 Standard system libthread_db still gets loaded even with this option off.\n\
1777 This options has security implications for untrusted inferiors."),
1778 NULL, show_auto_load_thread_db,
1779 auto_load_set_cmdlist_get (),
1780 auto_load_show_cmdlist_get ());
1782 add_cmd ("libthread-db", class_info, info_auto_load_libthread_db,
1783 _("Print the list of loaded inferior specific libthread_db.\n\
1784 Usage: info auto-load libthread-db"),
1785 auto_load_info_cmdlist_get ());
1787 /* Add ourselves to objfile event chain. */
1788 observer_attach_new_objfile (thread_db_new_objfile);
1790 /* Add ourselves to inferior_created event chain.
1791 This is needed to handle debugging statically linked programs where
1792 the new_objfile observer won't get called for libpthread. */
1793 observer_attach_inferior_created (thread_db_inferior_created);