darkkirb/old-cross-binutils
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity
old-cross-binutils/gdb/gdbserver/thread-db.c
Pedro Alves 2db9a4275c GNU/Linux: Stop using libthread_db/td_ta_thr_iter 
TL;DR - GDB can hang if something refreshes the thread list out of the
target while the target is running.  GDB hangs inside td_ta_thr_iter.
The fix is to not use that libthread_db function anymore.

Long version:

Running the testsuite against my all-stop-on-top-of-non-stop series is
still exposing latent non-stop bugs.

I was originally seeing this with the multi-create.exp test, back when
we were still using libthread_db thread event breakpoints.  The
all-stop-on-top-of-non-stop series forces a thread list refresh each
time GDB needs to start stepping over a breakpoint (to pause all
threads).  That test hits the thread event breakpoint often, resulting
in a bunch of step-over operations, thus a bunch of thread list
refreshes while some threads in the target are running.

The commit adds a real non-stop mode test that triggers the issue,
based on multi-create.exp, that does an explicit "info threads" when a
breakpoint is hit.  IOW, it does the same things the as-ns series was
doing when testing multi-create.exp.

The bug is a race, so it unfortunately takes several runs for the test
to trigger it.  In fact, even when setting the test running in a loop,
it sometimes takes several minutes for it to trigger for me.

The race is related to libthread_db's td_ta_thr_iter.  This is
libthread_db's entry point for walking the thread list of the
inferior.

Sometimes, when GDB refreshes the thread list from the target,
libthread_db's td_ta_thr_iter can somehow see glibc's thread list as a
cycle, and get stuck in an infinite loop.

The issue is that when a thread exits, its thread control structure in
glibc is moved from a "used" list to a "cache" list.  These lists are
simply circular linked lists where the "next/prev" pointers are
embedded in the thread control structure itself.  The "next" pointer
of the last element of the list points back to the list's sentinel
"head".  There's only one set of "next/prev" pointers for both lists;
thus a thread can only be in one of the lists at a time, not in both
simultaneously.

So when thread C exits, simplifying, the following happens.  A-C are
threads.  stack_used and stack_cache are the list's heads.

Before:

  stack_used -> A -> B -> C -> (&stack_used)
  stack_cache -> (&stack_cache)

After:

  stack_used -> A -> B -> (&stack_used)
  stack_cache -> C -> (&stack_cache)

td_ta_thr_iter starts by iterating at the list's head's next, and
iterates until it sees a thread whose next pointer points to the
list's head again.  Thus in the before case above, C's next points to
stack_used, indicating end of list.  In the same case, the stack_cache
list is empty.

For each thread being iterated, td_ta_thr_iter reads the whole thread
object out of the inferior.  This includes the thread's "next"
pointer.

In the scenario above, it may happen that td_ta_thr_iter is iterating
thread B and has already read B's thread structure just before thread
C exits and its control structure moves to the cached list.

Now, recall that td_ta_thr_iter is running in the context of GDB, and
there's no locking between GDB and the inferior.  From it's local copy
of B, td_ta_thr_iter believes that the next thread after B is thread
C, so it happilly continues iterating to C, a thread that has already
exited, and is now in the stack cache list.

After iterating C, td_ta_thr_iter finds the stack_cache head, which
because it is not stack_used, td_ta_thr_iter assumes it's just another
thread.  After this, unless the reverse race triggers, GDB gets stuck
in td_ta_thr_iter forever walking the stack_cache list, as no thread
in thatlist has a next pointer that points back to stack_used (the
terminating condition).

Before fully understanding the issue, I tried adding cycle detection
to GDB's td_ta_thr_iter callback.  However, td_ta_thr_iter skips
calling the callback in some cases, which means that it's possible
that the callback isn't called at all, making it impossible for GDB to
break the loop.  I did manage to get GDB stuck in that state more than
once.

Fortunately, we can avoid the issue altogether.  We don't really need
td_ta_thr_iter for live debugging nowadays, given PTRACE_EVENT_CLONE.
We already know how to map and lwp id to a thread id without iterating
(thread_from_lwp), so use that more.

gdb/ChangeLog:
2015-02-20  Pedro Alves  <palves@redhat.com>

	* linux-nat.c (linux_handle_extended_wait): Call
	thread_db_notice_clone whenever a new clone LWP is detected.
	(linux_stop_and_wait_all_lwps, linux_unstop_all_lwps): New
	functions.
	* linux-nat.h (thread_db_attach_lwp): Delete declaration.
	(thread_db_notice_clone, linux_stop_and_wait_all_lwps)
	(linux_unstop_all_lwps): Declare.
	* linux-thread-db.c (struct thread_get_info_inout): Delete.
	(thread_get_info_callback): Delete.
	(thread_from_lwp): Use td_thr_get_info and record_thread.
	(thread_db_attach_lwp): Delete.
	(thread_db_notice_clone): New function.
	(try_thread_db_load_1): If /proc is mounted and shows the
	process'es task list, walk over all LWPs and call thread_from_lwp
	instead of relying on td_ta_thr_iter.
	(attach_thread): Don't call check_thread_signals here.  Split the
	tail part of the function (which adds the thread to the core GDB
	thread list) to ...
	(record_thread): ... this function.  Call check_thread_signals
	here.
	(thread_db_wait): Don't call thread_db_find_new_threads_1.  Always
	call thread_from_lwp.
	(thread_db_update_thread_list): Rename to ...
	(thread_db_update_thread_list_org): ... this.
	(thread_db_update_thread_list): New function.
	(thread_db_find_thread_from_tid): Delete.
	(thread_db_get_ada_task_ptid): Simplify.
	* nat/linux-procfs.c: Include <sys/stat.h>.
	(linux_proc_task_list_dir_exists): New function.
	* nat/linux-procfs.h (linux_proc_task_list_dir_exists): Declare.

gdb/gdbserver/ChangeLog:
2015-02-20  Pedro Alves  <palves@redhat.com>

	* thread-db.c: Include "nat/linux-procfs.h".
	(thread_db_init): Skip listing new threads if the kernel supports
	PTRACE_EVENT_CLONE and /proc/PID/task/ is accessible.

gdb/testsuite/ChangeLog:
2015-02-20  Pedro Alves  <palves@redhat.com>

	* gdb.threads/multi-create-ns-info-thr.exp: New file.
2015-02-20 21:40:31 +00:00

1033 lines
28 KiB
C
Raw Blame History

/* Thread management interface, for the remote server for GDB.
Copyright (C) 2002-2015 Free Software Foundation, Inc.
Contributed by MontaVista Software.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#include "server.h"
#include "linux-low.h"
extern int debug_threads;
static int thread_db_use_events;
#include "gdb_proc_service.h"
#include "nat/gdb_thread_db.h"
#include "gdb_vecs.h"
#include "nat/linux-procfs.h"
#ifndef USE_LIBTHREAD_DB_DIRECTLY
#include <dlfcn.h>
#endif
#include <stdint.h>
#include <limits.h>
#include <ctype.h>
struct thread_db
{
/* Structure that identifies the child process for the
<proc_service.h> interface. */
struct ps_prochandle proc_handle;
/* Connection to the libthread_db library. */
td_thragent_t *thread_agent;
/* If this flag has been set, we've already asked GDB for all
symbols we might need; assume symbol cache misses are
failures. */
int all_symbols_looked_up;
#ifndef USE_LIBTHREAD_DB_DIRECTLY
/* Handle of the libthread_db from dlopen. */
void *handle;
#endif
/* Thread creation event breakpoint. The code at this location in
the child process will be called by the pthread library whenever
a new thread is created. By setting a special breakpoint at this
location, GDB can detect when a new thread is created. We obtain
this location via the td_ta_event_addr call. Note that if the
running kernel supports tracing clones, then we don't need to use
(and in fact don't use) this magic thread event breakpoint to
learn about threads. */
struct breakpoint *td_create_bp;
/* Addresses of libthread_db functions. */
td_err_e (*td_ta_new_p) (struct ps_prochandle * ps, td_thragent_t **ta);
td_err_e (*td_ta_event_getmsg_p) (const td_thragent_t *ta,
td_event_msg_t *msg);
td_err_e (*td_ta_set_event_p) (const td_thragent_t *ta,
td_thr_events_t *event);
td_err_e (*td_ta_event_addr_p) (const td_thragent_t *ta,
td_event_e event, td_notify_t *ptr);
td_err_e (*td_ta_map_lwp2thr_p) (const td_thragent_t *ta, lwpid_t lwpid,
td_thrhandle_t *th);
td_err_e (*td_thr_get_info_p) (const td_thrhandle_t *th,
td_thrinfo_t *infop);
td_err_e (*td_thr_event_enable_p) (const td_thrhandle_t *th, int event);
td_err_e (*td_ta_thr_iter_p) (const td_thragent_t *ta,
td_thr_iter_f *callback, void *cbdata_p,
td_thr_state_e state, int ti_pri,
sigset_t *ti_sigmask_p,
unsigned int ti_user_flags);
td_err_e (*td_thr_tls_get_addr_p) (const td_thrhandle_t *th,
psaddr_t map_address,
size_t offset, psaddr_t *address);
td_err_e (*td_thr_tlsbase_p) (const td_thrhandle_t *th,
unsigned long int modid,
psaddr_t *base);
const char ** (*td_symbol_list_p) (void);
};
static char *libthread_db_search_path;
static int find_one_thread (ptid_t);
static int find_new_threads_callback (const td_thrhandle_t *th_p, void *data);
static const char *
thread_db_err_str (td_err_e err)
{
static char buf[64];
switch (err)
{
case TD_OK:
return "generic 'call succeeded'";
case TD_ERR:
return "generic error";
case TD_NOTHR:
return "no thread to satisfy query";
case TD_NOSV:
return "no sync handle to satisfy query";
case TD_NOLWP:
return "no LWP to satisfy query";
case TD_BADPH:
return "invalid process handle";
case TD_BADTH:
return "invalid thread handle";
case TD_BADSH:
return "invalid synchronization handle";
case TD_BADTA:
return "invalid thread agent";
case TD_BADKEY:
return "invalid key";
case TD_NOMSG:
return "no event message for getmsg";
case TD_NOFPREGS:
return "FPU register set not available";
case TD_NOLIBTHREAD:
return "application not linked with libthread";
case TD_NOEVENT:
return "requested event is not supported";
case TD_NOCAPAB:
return "capability not available";
case TD_DBERR:
return "debugger service failed";
case TD_NOAPLIC:
return "operation not applicable to";
case TD_NOTSD:
return "no thread-specific data for this thread";
case TD_MALLOC:
return "malloc failed";
case TD_PARTIALREG:
return "only part of register set was written/read";
case TD_NOXREGS:
return "X register set not available for this thread";
#ifdef HAVE_TD_VERSION
case TD_VERSION:
return "version mismatch between libthread_db and libpthread";
#endif
default:
xsnprintf (buf, sizeof (buf), "unknown thread_db error '%d'", err);
return buf;
}
}
#if 0
static char *
thread_db_state_str (td_thr_state_e state)
{
static char buf[64];
switch (state)
{
case TD_THR_STOPPED:
return "stopped by debugger";
case TD_THR_RUN:
return "runnable";
case TD_THR_ACTIVE:
return "active";
case TD_THR_ZOMBIE:
return "zombie";
case TD_THR_SLEEP:
return "sleeping";
case TD_THR_STOPPED_ASLEEP:
return "stopped by debugger AND blocked";
default:
xsnprintf (buf, sizeof (buf), "unknown thread_db state %d", state);
return buf;
}
}
#endif
static int
thread_db_create_event (CORE_ADDR where)
{
td_event_msg_t msg;
td_err_e err;
struct lwp_info *lwp;
struct thread_db *thread_db = current_process ()->private->thread_db;
gdb_assert (thread_db->td_ta_event_getmsg_p != NULL);
if (debug_threads)
debug_printf ("Thread creation event.\n");
/* FIXME: This assumes we don't get another event.
In the LinuxThreads implementation, this is safe,
because all events come from the manager thread
(except for its own creation, of course). */
err = thread_db->td_ta_event_getmsg_p (thread_db->thread_agent, &msg);
if (err != TD_OK)
fprintf (stderr, "thread getmsg err: %s\n",
thread_db_err_str (err));
/* If we do not know about the main thread yet, this would be a good time to
find it. We need to do this to pick up the main thread before any newly
created threads. */
lwp = get_thread_lwp (current_thread);
if (lwp->thread_known == 0)
find_one_thread (current_thread->entry.id);
/* msg.event == TD_EVENT_CREATE */
find_new_threads_callback (msg.th_p, NULL);
return 0;
}
static int
thread_db_enable_reporting (void)
{
td_thr_events_t events;
td_notify_t notify;
td_err_e err;
struct thread_db *thread_db = current_process ()->private->thread_db;
if (thread_db->td_ta_set_event_p == NULL
|| thread_db->td_ta_event_addr_p == NULL
|| thread_db->td_ta_event_getmsg_p == NULL)
/* This libthread_db is missing required support. */
return 0;
/* Set the process wide mask saying which events we're interested in. */
td_event_emptyset (&events);
td_event_addset (&events, TD_CREATE);
err = thread_db->td_ta_set_event_p (thread_db->thread_agent, &events);
if (err != TD_OK)
{
warning ("Unable to set global thread event mask: %s",
thread_db_err_str (err));
return 0;
}
/* Get address for thread creation breakpoint. */
err = thread_db->td_ta_event_addr_p (thread_db->thread_agent, TD_CREATE,
&notify);
if (err != TD_OK)
{
warning ("Unable to get location for thread creation breakpoint: %s",
thread_db_err_str (err));
return 0;
}
thread_db->td_create_bp
= set_breakpoint_at ((CORE_ADDR) (unsigned long) notify.u.bptaddr,
thread_db_create_event);
return 1;
}
static int
find_one_thread (ptid_t ptid)
{
td_thrhandle_t th;
td_thrinfo_t ti;
td_err_e err;
struct thread_info *inferior;
struct lwp_info *lwp;
struct thread_db *thread_db = current_process ()->private->thread_db;
int lwpid = ptid_get_lwp (ptid);
inferior = (struct thread_info *) find_inferior_id (&all_threads, ptid);
lwp = get_thread_lwp (inferior);
if (lwp->thread_known)
return 1;
/* Get information about this thread. */
err = thread_db->td_ta_map_lwp2thr_p (thread_db->thread_agent, lwpid, &th);
if (err != TD_OK)
error ("Cannot get thread handle for LWP %d: %s",
lwpid, thread_db_err_str (err));
err = thread_db->td_thr_get_info_p (&th, &ti);
if (err != TD_OK)
error ("Cannot get thread info for LWP %d: %s",
lwpid, thread_db_err_str (err));
if (debug_threads)
debug_printf ("Found thread %ld (LWP %d)\n",
ti.ti_tid, ti.ti_lid);
if (lwpid != ti.ti_lid)
{
warning ("PID mismatch! Expected %ld, got %ld",
(long) lwpid, (long) ti.ti_lid);
return 0;
}
if (thread_db_use_events)
{
err = thread_db->td_thr_event_enable_p (&th, 1);
if (err != TD_OK)
error ("Cannot enable thread event reporting for %d: %s",
ti.ti_lid, thread_db_err_str (err));
}
/* If the new thread ID is zero, a final thread ID will be available
later. Do not enable thread debugging yet. */
if (ti.ti_tid == 0)
return 0;
lwp->thread_known = 1;
lwp->th = th;
return 1;
}
/* Attach a thread. Return true on success. */
static int
attach_thread (const td_thrhandle_t *th_p, td_thrinfo_t *ti_p)
{
struct process_info *proc = current_process ();
int pid = pid_of (proc);
ptid_t ptid = ptid_build (pid, ti_p->ti_lid, 0);
struct lwp_info *lwp;
int err;
if (debug_threads)
debug_printf ("Attaching to thread %ld (LWP %d)\n",
ti_p->ti_tid, ti_p->ti_lid);
err = linux_attach_lwp (ptid);
if (err != 0)
{
warning ("Could not attach to thread %ld (LWP %d): %s\n",
ti_p->ti_tid, ti_p->ti_lid,
linux_ptrace_attach_fail_reason_string (ptid, err));
return 0;
}
lwp = find_lwp_pid (ptid);
gdb_assert (lwp != NULL);
lwp->thread_known = 1;
lwp->th = *th_p;
if (thread_db_use_events)
{
td_err_e err;
struct thread_db *thread_db = proc->private->thread_db;
err = thread_db->td_thr_event_enable_p (th_p, 1);
if (err != TD_OK)
error ("Cannot enable thread event reporting for %d: %s",
ti_p->ti_lid, thread_db_err_str (err));
}
return 1;
}
/* Attach thread if we haven't seen it yet.
Increment *COUNTER if we have attached a new thread.
Return false on failure. */
static int
maybe_attach_thread (const td_thrhandle_t *th_p, td_thrinfo_t *ti_p,
int *counter)
{
struct lwp_info *lwp;
lwp = find_lwp_pid (pid_to_ptid (ti_p->ti_lid));
if (lwp != NULL)
return 1;
if (!attach_thread (th_p, ti_p))
return 0;
if (counter != NULL)
*counter += 1;
return 1;
}
static int
find_new_threads_callback (const td_thrhandle_t *th_p, void *data)
{
td_thrinfo_t ti;
td_err_e err;
struct thread_db *thread_db = current_process ()->private->thread_db;
err = thread_db->td_thr_get_info_p (th_p, &ti);
if (err != TD_OK)
error ("Cannot get thread info: %s", thread_db_err_str (err));
if (ti.ti_lid == -1)
{
/* A thread with kernel thread ID -1 is either a thread that
exited and was joined, or a thread that is being created but
hasn't started yet, and that is reusing the tcb/stack of a
thread that previously exited and was joined. (glibc marks
terminated and joined threads with kernel thread ID -1. See
glibc PR17707. */
if (debug_threads)
debug_printf ("thread_db: skipping exited and "
"joined thread (0x%lx)\n", ti.ti_tid);
return 0;
}
/* Check for zombies. */
if (ti.ti_state == TD_THR_UNKNOWN || ti.ti_state == TD_THR_ZOMBIE)
return 0;
if (!maybe_attach_thread (th_p, &ti, (int *) data))
{
/* Terminate iteration early: we might be looking at stale data in
the inferior. The thread_db_find_new_threads will retry. */
return 1;
}
return 0;
}
static void
thread_db_find_new_threads (void)
{
td_err_e err;
ptid_t ptid = current_ptid;
struct thread_db *thread_db = current_process ()->private->thread_db;
int loop, iteration;
/* This function is only called when we first initialize thread_db.
First locate the initial thread. If it is not ready for
debugging yet, then stop. */
if (find_one_thread (ptid) == 0)
return;
/* Require 4 successive iterations which do not find any new threads.
The 4 is a heuristic: there is an inherent race here, and I have
seen that 2 iterations in a row are not always sufficient to
"capture" all threads. */
for (loop = 0, iteration = 0; loop < 4; ++loop, ++iteration)
{
int new_thread_count = 0;
/* Iterate over all user-space threads to discover new threads. */
err = thread_db->td_ta_thr_iter_p (thread_db->thread_agent,
find_new_threads_callback,
&new_thread_count,
TD_THR_ANY_STATE,
TD_THR_LOWEST_PRIORITY,
TD_SIGNO_MASK, TD_THR_ANY_USER_FLAGS);
if (debug_threads)
debug_printf ("Found %d threads in iteration %d.\n",
new_thread_count, iteration);
if (new_thread_count != 0)
{
/* Found new threads. Restart iteration from beginning. */
loop = -1;
}
}
if (err != TD_OK)
error ("Cannot find new threads: %s", thread_db_err_str (err));
}
/* Cache all future symbols that thread_db might request. We can not
request symbols at arbitrary states in the remote protocol, only
when the client tells us that new symbols are available. So when
we load the thread library, make sure to check the entire list. */
static void
thread_db_look_up_symbols (void)
{
struct thread_db *thread_db = current_process ()->private->thread_db;
const char **sym_list;
CORE_ADDR unused;
for (sym_list = thread_db->td_symbol_list_p (); *sym_list; sym_list++)
look_up_one_symbol (*sym_list, &unused, 1);
/* We're not interested in any other libraries loaded after this
point, only in symbols in libpthread.so. */
thread_db->all_symbols_looked_up = 1;
}
int
thread_db_look_up_one_symbol (const char *name, CORE_ADDR *addrp)
{
struct thread_db *thread_db = current_process ()->private->thread_db;
int may_ask_gdb = !thread_db->all_symbols_looked_up;
/* If we've passed the call to thread_db_look_up_symbols, then
anything not in the cache must not exist; we're not interested
in any libraries loaded after that point, only in symbols in
libpthread.so. It might not be an appropriate time to look
up a symbol, e.g. while we're trying to fetch registers. */
return look_up_one_symbol (name, addrp, may_ask_gdb);
}
int
thread_db_get_tls_address (struct thread_info *thread, CORE_ADDR offset,
CORE_ADDR load_module, CORE_ADDR *address)
{
psaddr_t addr;
td_err_e err;
struct lwp_info *lwp;
struct thread_info *saved_thread;
struct process_info *proc;
struct thread_db *thread_db;
proc = get_thread_process (thread);
thread_db = proc->private->thread_db;
/* If the thread layer is not (yet) initialized, fail. */
if (thread_db == NULL || !thread_db->all_symbols_looked_up)
return TD_ERR;
/* If td_thr_tls_get_addr is missing rather do not expect td_thr_tlsbase
could work. */
if (thread_db->td_thr_tls_get_addr_p == NULL
|| (load_module == 0 && thread_db->td_thr_tlsbase_p == NULL))
return -1;
lwp = get_thread_lwp (thread);
if (!lwp->thread_known)
find_one_thread (thread->entry.id);
if (!lwp->thread_known)
return TD_NOTHR;
saved_thread = current_thread;
current_thread = thread;
if (load_module != 0)
{
/* Note the cast through uintptr_t: this interface only works if
a target address fits in a psaddr_t, which is a host pointer.
So a 32-bit debugger can not access 64-bit TLS through this. */
err = thread_db->td_thr_tls_get_addr_p (&lwp->th,
(psaddr_t) (uintptr_t) load_module,
offset, &addr);
}
else
{
/* This code path handles the case of -static -pthread executables:
https://sourceware.org/ml/libc-help/2014-03/msg00024.html
For older GNU libc r_debug.r_map is NULL. For GNU libc after
PR libc/16831 due to GDB PR threads/16954 LOAD_MODULE is also NULL.
The constant number 1 depends on GNU __libc_setup_tls
initialization of l_tls_modid to 1. */
err = thread_db->td_thr_tlsbase_p (&lwp->th, 1, &addr);
addr = (char *) addr + offset;
}
current_thread = saved_thread;
if (err == TD_OK)
{
*address = (CORE_ADDR) (uintptr_t) addr;
return 0;
}
else
return err;
}
#ifdef USE_LIBTHREAD_DB_DIRECTLY
static int
thread_db_load_search (void)
{
td_err_e err;
struct thread_db *tdb;
struct process_info *proc = current_process ();
gdb_assert (proc->private->thread_db == NULL);
tdb = xcalloc (1, sizeof (*tdb));
proc->private->thread_db = tdb;
tdb->td_ta_new_p = &td_ta_new;
/* Attempt to open a connection to the thread library. */
err = tdb->td_ta_new_p (&tdb->proc_handle, &tdb->thread_agent);
if (err != TD_OK)
{
if (debug_threads)
debug_printf ("td_ta_new(): %s\n", thread_db_err_str (err));
free (tdb);
proc->private->thread_db = NULL;
return 0;
}
tdb->td_ta_map_lwp2thr_p = &td_ta_map_lwp2thr;
tdb->td_thr_get_info_p = &td_thr_get_info;
tdb->td_ta_thr_iter_p = &td_ta_thr_iter;
tdb->td_symbol_list_p = &td_symbol_list;
/* This is required only when thread_db_use_events is on. */
tdb->td_thr_event_enable_p = &td_thr_event_enable;
/* These are not essential. */
tdb->td_ta_event_addr_p = &td_ta_event_addr;
tdb->td_ta_set_event_p = &td_ta_set_event;
tdb->td_ta_event_getmsg_p = &td_ta_event_getmsg;
tdb->td_thr_tls_get_addr_p = &td_thr_tls_get_addr;
tdb->td_thr_tlsbase_p = &td_thr_tlsbase;
return 1;
}
#else
static int
try_thread_db_load_1 (void *handle)
{
td_err_e err;
struct thread_db *tdb;
struct process_info *proc = current_process ();
gdb_assert (proc->private->thread_db == NULL);
tdb = xcalloc (1, sizeof (*tdb));
proc->private->thread_db = tdb;
tdb->handle = handle;
/* Initialize pointers to the dynamic library functions we will use.
Essential functions first. */
#define CHK(required, a) \
do \
{ \
if ((a) == NULL) \
{ \
if (debug_threads) \
debug_printf ("dlsym: %s\n", dlerror ()); \
if (required) \
{ \
free (tdb); \
proc->private->thread_db = NULL; \
return 0; \
} \
} \
} \
while (0)
CHK (1, tdb->td_ta_new_p = dlsym (handle, "td_ta_new"));
/* Attempt to open a connection to the thread library. */
err = tdb->td_ta_new_p (&tdb->proc_handle, &tdb->thread_agent);
if (err != TD_OK)
{
if (debug_threads)
debug_printf ("td_ta_new(): %s\n", thread_db_err_str (err));
free (tdb);
proc->private->thread_db = NULL;
return 0;
}
CHK (1, tdb->td_ta_map_lwp2thr_p = dlsym (handle, "td_ta_map_lwp2thr"));
CHK (1, tdb->td_thr_get_info_p = dlsym (handle, "td_thr_get_info"));
CHK (1, tdb->td_ta_thr_iter_p = dlsym (handle, "td_ta_thr_iter"));
CHK (1, tdb->td_symbol_list_p = dlsym (handle, "td_symbol_list"));
/* This is required only when thread_db_use_events is on. */
CHK (thread_db_use_events,
tdb->td_thr_event_enable_p = dlsym (handle, "td_thr_event_enable"));
/* These are not essential. */
CHK (0, tdb->td_ta_event_addr_p = dlsym (handle, "td_ta_event_addr"));
CHK (0, tdb->td_ta_set_event_p = dlsym (handle, "td_ta_set_event"));
CHK (0, tdb->td_ta_event_getmsg_p = dlsym (handle, "td_ta_event_getmsg"));
CHK (0, tdb->td_thr_tls_get_addr_p = dlsym (handle, "td_thr_tls_get_addr"));
CHK (0, tdb->td_thr_tlsbase_p = dlsym (handle, "td_thr_tlsbase"));
#undef CHK
return 1;
}
#ifdef HAVE_DLADDR
/* Lookup a library in which given symbol resides.
Note: this is looking in the GDBSERVER process, not in the inferior.
Returns library name, or NULL. */
static const char *
dladdr_to_soname (const void *addr)
{
Dl_info info;
if (dladdr (addr, &info) != 0)
return info.dli_fname;
return NULL;
}
#endif
static int
try_thread_db_load (const char *library)
{
void *handle;
if (debug_threads)
debug_printf ("Trying host libthread_db library: %s.\n",
library);
handle = dlopen (library, RTLD_NOW);
if (handle == NULL)
{
if (debug_threads)
debug_printf ("dlopen failed: %s.\n", dlerror ());
return 0;
}
#ifdef HAVE_DLADDR
if (debug_threads && strchr (library, '/') == NULL)
{
void *td_init;
td_init = dlsym (handle, "td_init");
if (td_init != NULL)
{
const char *const libpath = dladdr_to_soname (td_init);
if (libpath != NULL)
fprintf (stderr, "Host %s resolved to: %s.\n",
library, libpath);
}
}
#endif
if (try_thread_db_load_1 (handle))
return 1;
/* This library "refused" to work on current inferior. */
dlclose (handle);
return 0;
}
/* Handle $sdir in libthread-db-search-path.
Look for libthread_db in the system dirs, or wherever a plain
dlopen(file_without_path) will look.
The result is true for success. */
static int
try_thread_db_load_from_sdir (void)
{
return try_thread_db_load (LIBTHREAD_DB_SO);
}
/* Try to load libthread_db from directory DIR of length DIR_LEN.
The result is true for success. */
static int
try_thread_db_load_from_dir (const char *dir, size_t dir_len)
{
char path[PATH_MAX];
if (dir_len + 1 + strlen (LIBTHREAD_DB_SO) + 1 > sizeof (path))
{
char *cp = xmalloc (dir_len + 1);
memcpy (cp, dir, dir_len);
cp[dir_len] = '\0';
warning (_("libthread-db-search-path component too long,"
" ignored: %s."), cp);
free (cp);
return 0;
}
memcpy (path, dir, dir_len);
path[dir_len] = '/';
strcpy (path + dir_len + 1, LIBTHREAD_DB_SO);
return try_thread_db_load (path);
}
/* Search libthread_db_search_path for libthread_db which "agrees"
to work on current inferior.
The result is true for success. */
static int
thread_db_load_search (void)
{
VEC (char_ptr) *dir_vec;
char *this_dir;
int i, rc = 0;
if (libthread_db_search_path == NULL)
libthread_db_search_path = xstrdup (LIBTHREAD_DB_SEARCH_PATH);
dir_vec = dirnames_to_char_ptr_vec (libthread_db_search_path);
for (i = 0; VEC_iterate (char_ptr, dir_vec, i, this_dir); ++i)
{
const int pdir_len = sizeof ("$pdir") - 1;
size_t this_dir_len;
this_dir_len = strlen (this_dir);
if (strncmp (this_dir, "$pdir", pdir_len) == 0
&& (this_dir[pdir_len] == '\0'
|| this_dir[pdir_len] == '/'))
{
/* We don't maintain a list of loaded libraries so we don't know
where libpthread lives. We *could* fetch the info, but we don't
do that yet. Ignore it. */
}
else if (strcmp (this_dir, "$sdir") == 0)
{
if (try_thread_db_load_from_sdir ())
{
rc = 1;
break;
}
}
else
{
if (try_thread_db_load_from_dir (this_dir, this_dir_len))
{
rc = 1;
break;
}
}
}
free_char_ptr_vec (dir_vec);
if (debug_threads)
debug_printf ("thread_db_load_search returning %d\n", rc);
return rc;
}
#endif /* USE_LIBTHREAD_DB_DIRECTLY */
int
thread_db_init (int use_events)
{
struct process_info *proc = current_process ();
/* FIXME drow/2004-10-16: This is the "overall process ID", which
GNU/Linux calls tgid, "thread group ID". When we support
attaching to threads, the original thread may not be the correct
thread. We would have to get the process ID from /proc for NPTL.
For LinuxThreads we could do something similar: follow the chain
of parent processes until we find the highest one we're attached
to, and use its tgid.
This isn't the only place in gdbserver that assumes that the first
process in the list is the thread group leader. */
thread_db_use_events = use_events;
if (thread_db_load_search ())
{
if (use_events && thread_db_enable_reporting () == 0)
{
/* Keep trying; maybe event reporting will work later. */
thread_db_mourn (proc);
return 0;
}
/* It's best to avoid td_ta_thr_iter if possible. That walks
data structures in the inferior's address space that may be
corrupted, or, if the target is running, the list may change
while we walk it. In the latter case, it's possible that a
thread exits just at the exact time that causes GDBserver to
get stuck in an infinite loop. If the kernel supports clone
events, and /proc/PID/task/ exits, then we already know about
all threads in the process. When we need info out of
thread_db on a given thread (e.g., for TLS), we'll use
find_one_thread then. That uses thread_db entry points that
do not walk libpthread's thread list, so should be safe, as
well as more efficient. */
if (use_events
|| !linux_proc_task_list_dir_exists (pid_of (proc)))
thread_db_find_new_threads ();
thread_db_look_up_symbols ();
return 1;
}
return 0;
}
static int
any_thread_of (struct inferior_list_entry *entry, void *args)
{
int *pid_p = args;
if (ptid_get_pid (entry->id) == *pid_p)
return 1;
return 0;
}
static void
switch_to_process (struct process_info *proc)
{
int pid = pid_of (proc);
current_thread =
(struct thread_info *) find_inferior (&all_threads,
any_thread_of, &pid);
}
/* Disconnect from libthread_db and free resources. */
static void
disable_thread_event_reporting (struct process_info *proc)
{
struct thread_db *thread_db = proc->private->thread_db;
if (thread_db)
{
td_err_e (*td_ta_clear_event_p) (const td_thragent_t *ta,
td_thr_events_t *event);
#ifndef USE_LIBTHREAD_DB_DIRECTLY
td_ta_clear_event_p = dlsym (thread_db->handle, "td_ta_clear_event");
#else
td_ta_clear_event_p = &td_ta_clear_event;
#endif
if (td_ta_clear_event_p != NULL)
{
struct thread_info *saved_thread = current_thread;
td_thr_events_t events;
switch_to_process (proc);
/* Set the process wide mask saying we aren't interested
in any events anymore. */
td_event_fillset (&events);
(*td_ta_clear_event_p) (thread_db->thread_agent, &events);
current_thread = saved_thread;
}
}
}
static void
remove_thread_event_breakpoints (struct process_info *proc)
{
struct thread_db *thread_db = proc->private->thread_db;
if (thread_db->td_create_bp != NULL)
{
struct thread_info *saved_thread = current_thread;
switch_to_process (proc);
delete_breakpoint (thread_db->td_create_bp);
thread_db->td_create_bp = NULL;
current_thread = saved_thread;
}
}
void
thread_db_detach (struct process_info *proc)
{
struct thread_db *thread_db = proc->private->thread_db;
if (thread_db)
{
disable_thread_event_reporting (proc);
remove_thread_event_breakpoints (proc);
}
}
/* Disconnect from libthread_db and free resources. */
void
thread_db_mourn (struct process_info *proc)
{
struct thread_db *thread_db = proc->private->thread_db;
if (thread_db)
{
td_err_e (*td_ta_delete_p) (td_thragent_t *);
#ifndef USE_LIBTHREAD_DB_DIRECTLY
td_ta_delete_p = dlsym (thread_db->handle, "td_ta_delete");
#else
td_ta_delete_p = &td_ta_delete;
#endif
if (td_ta_delete_p != NULL)
(*td_ta_delete_p) (thread_db->thread_agent);
#ifndef USE_LIBTHREAD_DB_DIRECTLY
dlclose (thread_db->handle);
#endif /* USE_LIBTHREAD_DB_DIRECTLY */
free (thread_db);
proc->private->thread_db = NULL;
}
}
/* Handle "set libthread-db-search-path" monitor command and return 1.
For any other command, return 0. */
int
thread_db_handle_monitor_command (char *mon)
{
const char *cmd = "set libthread-db-search-path";
size_t cmd_len = strlen (cmd);
if (strncmp (mon, cmd, cmd_len) == 0
&& (mon[cmd_len] == '\0'
|| mon[cmd_len] == ' '))
{
const char *cp = mon + cmd_len;
if (libthread_db_search_path != NULL)
free (libthread_db_search_path);
/* Skip leading space (if any). */
while (isspace (*cp))
++cp;
if (*cp == '\0')
cp = LIBTHREAD_DB_SEARCH_PATH;
libthread_db_search_path = xstrdup (cp);
monitor_output ("libthread-db-search-path set to `");
monitor_output (libthread_db_search_path);
monitor_output ("'\n");
return 1;
}
/* Tell server.c to perform default processing. */
return 0;
}
Reference in a new issue View git blame Copy permalink