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Teach GDBserver's Linux backend about no unwaited-for children (TARGET_WAITKIND_NO_RESUMED).

Browse source 
GDBserver currently hangs forever in waitpid if the leader thread
exits before other threads, or if all resumed threads exit - e.g.,
next over a thread exit with sched-locking on.  This is exposed by
leader-exit.exp.  leader-exit.exp is part of a series of tests for a
set of related problems.  See
<http://www.sourceware.org/ml/gdb-patches/2011-10/msg00704.html>:

 "
 To recap, on the Linux kernel, ptrace/waitpid don't allow reaping the
 leader thread until all other threads in the group are reaped.  When
 the leader exits, it goes zombie, but waitpid will not return an exit
 status until the other threads are gone.  This is presently exercised
 by the gdb.threads/leader-exit.exp test.  The fix for that test, in
 linux-nat.c:wait_lwp, handles the case where we see the leader gone
 when we're stopping all threads to report an event to some other
 thread to the core.

 (...)

 The latter bit about not blocking if there no resumed threads in the
 process also applies to some other thread exiting, not just the main
 thread.  E.g., this test starts a thread, and runs to a breakpoint in
 that thread:

 ...
 (gdb) c
 Continuing.
 [New Thread 0x7ffff75a4700 (LWP 23397)]
 [Switching to Thread 0x7ffff75a4700 (LWP 23397)]

 Breakpoint 2, thread_a (arg=0x0) at ../../../src/gdb/testsuite/gdb.threads/no-unwaited-for-left.c:28
 28        return 0; /* break-here */
 (gdb) info threads
 * 2 Thread 0x7ffff75a4700 (LWP 23397)  thread_a (arg=0x0) at ../../../src/gdb/testsuite/gdb.threads/no-unwaited-for-left.c:28
   1 Thread 0x7ffff7fcb720 (LWP 23391)  0x00007ffff7bc606d in pthread_join (threadid=140737343276800, thread_return=0x0) at pthread_join.c:89

 The thread will exit as soon as we resume it.  But if we only resume
 that thread, leaving the rest of the threads stopped:

 (gdb) set scheduler-locking on
 (gdb) c
 Continuing.
 ^C^C^C^C^C^C^C^C
 "

This patch fixes the issues by implementing TARGET_WAITKIND_NO_RESUMED
on GDBserver, similarly to what the patch above did for native
Linux GDB.

gdb.threads/leader-exit.exp now passes.

gdb.threads/no-unwaited-for-left.exp now at least errors out instead
of hanging:

 continue
 Continuing.
 warning: Remote failure reply: E.No unwaited-for children left.

 [Thread 15454] #1 stopped.
 0x00000034cf408e60 in pthread_join (threadid=140737353922368, thread_return=0x0) at pthread_join.c:93
 93          lll_wait_tid (pd->tid);
 (gdb) FAIL: gdb.threads/no-unwaited-for-left.exp: continue stops when the main thread exits

The gdb.threads/non-ldr-exc-*.exp tests are skipped because GDBserver
unfortunately doesn't support fork/exec yet, but I'm confident this
fixes the related issues.

I'm leaving modeling TARGET_WAITKIND_NO_RESUMED in the RSP for a
separate pass.

(BTW, in case of error in response to a vCont, it would be better for
GDB to query the target for the current thread, or re-select one,
instead of assuming current inferior_ptid is still the selected
thread.)

This implementation is a little different from GDB's, because I'm
avoiding bringing in more of this broken use of waitpid(PID) into
GDBserver.  Specifically, this avoids waitpid(PID) when stopping all
threads.  There's really no need for wait_for_sigstop to wait for each
LWP in turn.  Instead, with some refactoring, we make it reuse
linux_wait_for_event.

gdb/gdbserver/
2014-02-27  Pedro Alves  <palves@redhat.com>

	PR 12702
	* inferiors.h (A_I_NEXT, ALL_INFERIORS_TYPE, ALL_PROCESSES): New
	macros.
	* linux-low.c (delete_lwp, handle_extended_wait): Add debug
	output.
	(last_thread_of_process_p): Take a PID argument instead of a
	thread pointer.
	(linux_wait_for_lwp): Delete.
	(num_lwps, check_zombie_leaders, not_stopped_callback): New
	functions.
	(linux_low_filter_event): New function, party factored out from
	linux_wait_for_event.
	(linux_wait_for_event): Rename to ...
	(linux_wait_for_event_filtered): ... this.  Add new filter ptid
	argument.  Partly rewrite.  Always use waitpid(-1, WNOHANG) and
	sigsuspend.  Check for zombie leaders.
	(linux_wait_for_event): Reimplement as wrapper around
	linux_wait_for_event_filtered.
	(linux_wait_1): Handle TARGET_WAITKIND_NO_RESUMED.  Assume that if
	a normal or signal exit is seen, it's the whole process exiting.
	(wait_for_sigstop): No longer a for_each_inferior callback.
	Rewrite on top of linux_wait_for_event_filtered.
	(stop_all_lwps): Call wait_for_sigstop directly.
	* server.c (resume, handle_target_event): Handle
	TARGET_WAITKIND_NO_RESUMED.
This commit is contained in:
Pedro Alves 2014-02-27 14:30:08 +00:00
parent d632a0971c
commit fa96cb382c
4 changed files with 586 additions and 370 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

28
gdb/gdbserver/ChangeLog
View file

@ -1,3 +1,31 @@
2014-02-27 Pedro Alves <palves@redhat.com>
PR 12702
* inferiors.h (A_I_NEXT, ALL_INFERIORS_TYPE, ALL_PROCESSES): New
macros.
* linux-low.c (delete_lwp, handle_extended_wait): Add debug
output.
(last_thread_of_process_p): Take a PID argument instead of a
thread pointer.
(linux_wait_for_lwp): Delete.
(num_lwps, check_zombie_leaders, not_stopped_callback): New
functions.
(linux_low_filter_event): New function, party factored out from
linux_wait_for_event.
(linux_wait_for_event): Rename to ...
(linux_wait_for_event_filtered): ... this. Add new filter ptid
argument. Partly rewrite. Always use waitpid(-1, WNOHANG) and
sigsuspend. Check for zombie leaders.
(linux_wait_for_event): Reimplement as wrapper around
linux_wait_for_event_filtered.
(linux_wait_1): Handle TARGET_WAITKIND_NO_RESUMED. Assume that if
a normal or signal exit is seen, it's the whole process exiting.
(wait_for_sigstop): No longer a for_each_inferior callback.
Rewrite on top of linux_wait_for_event_filtered.
(stop_all_lwps): Call wait_for_sigstop directly.
* server.c (resume, handle_target_event): Handle
TARGET_WAITKIND_NO_RESUMED.
2014-02-26 Joel Brobecker <brobecker@adacore.com>
* win32-low.c (psapi_get_dll_name,

22
gdb/gdbserver/inferiors.h
View file

@ -99,6 +99,28 @@ void clear_inferior_list (struct inferior_list *list);
int one_inferior_p (struct inferior_list *list);
/* Helper for ALL_INFERIORS_TYPE. Gets the next element starting at
CUR, if CUR is not NULL. */
#define A_I_NEXT(type, list, cur) \
((cur) != NULL \
? (type *) ((struct inferior_list_entry *) cur)->next \
: NULL)
/* Iterate over all inferiors of type TYPE in LIST, open loop
style. */
#define ALL_INFERIORS_TYPE(type, list, cur, tmp) \
for ((cur) = (type *) (list)->head, (tmp) = A_I_NEXT (type, list, cur); \
(cur) != NULL; \
(cur) = (tmp), (tmp) = A_I_NEXT (type, list, cur))
/* Iterate over all inferiors in LIST, open loop style. */
#define ALL_INFERIORS(list, cur, tmp) \
ALL_INFERIORS_TYPE (struct inferior_list_entry, list, cur, tmp)
/* Iterate over all processes, open loop style. */
#define ALL_PROCESSES(cur, tmp) \
ALL_INFERIORS_TYPE (struct process_info, &all_processes, cur, tmp)
extern struct thread_info *current_inferior;
void remove_inferior (struct inferior_list *list,
struct inferior_list_entry *entry);

826
gdb/gdbserver/linux-low.c
View file

@ -214,6 +214,8 @@ static void linux_resume_one_lwp (struct lwp_info *lwp,
static void linux_resume (struct thread_resume *resume_info, size_t n);
static void stop_all_lwps (int suspend, struct lwp_info *except);
static void unstop_all_lwps (int unsuspend, struct lwp_info *except);
static int linux_wait_for_event_filtered (ptid_t wait_ptid, ptid_t filter_ptid,
int *wstat, int options);
static int linux_wait_for_event (ptid_t ptid, int *wstat, int options);
static struct lwp_info *add_lwp (ptid_t ptid);
static int linux_stopped_by_watchpoint (void);
@ -276,7 +278,7 @@ static int linux_event_pipe[2] = { -1, -1 };
#define target_is_async_p() (linux_event_pipe[0] != -1)
static void send_sigstop (struct lwp_info *lwp);
static void wait_for_sigstop (struct inferior_list_entry *entry);
static void wait_for_sigstop (void);
/* Return non-zero if HEADER is a 64-bit ELF file. */
@ -335,7 +337,12 @@ linux_pid_exe_is_elf_64_file (int pid, unsigned int *machine)
static void
delete_lwp (struct lwp_info *lwp)
{
remove_thread (get_lwp_thread (lwp));
struct thread_info *thr = get_lwp_thread (lwp);
if (debug_threads)
debug_printf ("deleting %ld\n", lwpid_of (thr));
remove_thread (thr);
free (lwp->arch_private);
free (lwp);
}
@ -396,6 +403,11 @@ handle_extended_wait (struct lwp_info *event_child, int wstat)
warning ("wait returned unexpected status 0x%x", status);
}
if (debug_threads)
debug_printf ("HEW: Got clone event "
"from LWP %ld, new child is LWP %ld\n",
lwpid_of (event_thr), new_pid);
ptid = ptid_build (pid_of (event_thr), new_pid, 0);
new_lwp = add_lwp (ptid);
@ -847,10 +859,8 @@ second_thread_of_pid_p (struct inferior_list_entry *entry, void *args)
}
static int
last_thread_of_process_p (struct thread_info *thread)
last_thread_of_process_p (int pid)
{
ptid_t ptid = thread->entry.id;
int pid = ptid_get_pid (ptid);
struct counter counter = { pid , 0 };
return (find_inferior (&all_threads,
@ -1252,152 +1262,107 @@ find_lwp_pid (ptid_t ptid)
return get_thread_lwp ((struct thread_info *) thread);
}
static struct lwp_info *
linux_wait_for_lwp (ptid_t ptid, int *wstatp, int options)
/* Return the number of known LWPs in the tgid given by PID. */
static int
num_lwps (int pid)
{
int ret;
int to_wait_for = -1;
struct lwp_info *child;
struct thread_info *thread;
struct inferior_list_entry *inf, *tmp;
int count = 0;
ALL_INFERIORS (&all_threads, inf, tmp)
{
if (ptid_get_pid (inf->id) == pid)
count++;
}
return count;
}
/* Detect zombie thread group leaders, and "exit" them. We can't reap
their exits until all other threads in the group have exited. */
static void
check_zombie_leaders (void)
{
struct process_info *proc, *tmp;
ALL_PROCESSES (proc, tmp)
{
pid_t leader_pid = pid_of (proc);
struct lwp_info *leader_lp;
leader_lp = find_lwp_pid (pid_to_ptid (leader_pid));
if (debug_threads)
debug_printf ("linux_wait_for_lwp: %s\n", target_pid_to_str (ptid));
debug_printf ("leader_pid=%d, leader_lp!=NULL=%d, "
"num_lwps=%d, zombie=%d\n",
leader_pid, leader_lp!= NULL, num_lwps (leader_pid),
linux_proc_pid_is_zombie (leader_pid));
if (ptid_equal (ptid, minus_one_ptid))
to_wait_for = -1; /* any child */
else
to_wait_for = ptid_get_lwp (ptid); /* this lwp only */
options |= __WALL;
retry:
ret = my_waitpid (to_wait_for, wstatp, options);
if (ret == 0 || (ret == -1 && errno == ECHILD && (options & WNOHANG)))
return NULL;
else if (ret == -1)
perror_with_name ("waitpid");
if (debug_threads
&& (!WIFSTOPPED (*wstatp)
|| (WSTOPSIG (*wstatp) != 32
&& WSTOPSIG (*wstatp) != 33)))
debug_printf ("Got an event from %d (%x)\n", ret, *wstatp);
child = find_lwp_pid (pid_to_ptid (ret));
if (child != NULL)
thread = get_lwp_thread (child);
else
thread = NULL;
/* If we didn't find a process, one of two things presumably happened:
- A process we started and then detached from has exited. Ignore it.
- A process we are controlling has forked and the new child's stop
was reported to us by the kernel. Save its PID. */
if (child == NULL && WIFSTOPPED (*wstatp))
if (leader_lp != NULL
/* Check if there are other threads in the group, as we may
have raced with the inferior simply exiting. */
&& !last_thread_of_process_p (leader_pid)
&& linux_proc_pid_is_zombie (leader_pid))
{
add_to_pid_list (&stopped_pids, ret, *wstatp);
goto retry;
}
else if (child == NULL)
goto retry;
/* A leader zombie can mean one of two things:
child->stopped = 1;
- It exited, and there's an exit status pending
available, or only the leader exited (not the whole
program). In the latter case, we can't waitpid the
leader's exit status until all other threads are gone.
child->last_status = *wstatp;
- There are 3 or more threads in the group, and a thread
other than the leader exec'd. On an exec, the Linux
kernel destroys all other threads (except the execing
one) in the thread group, and resets the execing thread's
tid to the tgid. No exit notification is sent for the
execing thread -- from the ptracer's perspective, it
appears as though the execing thread just vanishes.
Until we reap all other threads except the leader and the
execing thread, the leader will be zombie, and the
execing thread will be in `D (disc sleep)'. As soon as
all other threads are reaped, the execing thread changes
it's tid to the tgid, and the previous (zombie) leader
vanishes, giving place to the "new" leader. We could try
distinguishing the exit and exec cases, by waiting once
more, and seeing if something comes out, but it doesn't
sound useful. The previous leader _does_ go away, and
we'll re-add the new one once we see the exec event
(which is just the same as what would happen if the
previous leader did exit voluntarily before some other
thread execs). */
if (WIFSTOPPED (*wstatp))
{
struct process_info *proc;
if (debug_threads)
fprintf (stderr,
"CZL: Thread group leader %d zombie "
"(it exited, or another thread execd).\n",
leader_pid);
/* Architecture-specific setup after inferior is running. This
needs to happen after we have attached to the inferior and it
is stopped for the first time, but before we access any
inferior registers. */
proc = find_process_pid (pid_of (thread));
if (proc->private->new_inferior)
{
struct thread_info *saved_inferior;
saved_inferior = current_inferior;
current_inferior = thread;
the_low_target.arch_setup ();
current_inferior = saved_inferior;
proc->private->new_inferior = 0;
delete_lwp (leader_lp);
}
}
}
/* Fetch the possibly triggered data watchpoint info and store it in
CHILD.
/* Callback for `find_inferior'. Returns the first LWP that is not
stopped. ARG is a PTID filter. */
On some archs, like x86, that use debug registers to set
watchpoints, it's possible that the way to know which watched
address trapped, is to check the register that is used to select
which address to watch. Problem is, between setting the
watchpoint and reading back which data address trapped, the user
may change the set of watchpoints, and, as a consequence, GDB
changes the debug registers in the inferior. To avoid reading
back a stale stopped-data-address when that happens, we cache in
LP the fact that a watchpoint trapped, and the corresponding data
address, as soon as we see CHILD stop with a SIGTRAP. If GDB
changes the debug registers meanwhile, we have the cached data we
can rely on. */
static int
not_stopped_callback (struct inferior_list_entry *entry, void *arg)
{
struct thread_info *thr = (struct thread_info *) entry;
struct lwp_info *lwp;
ptid_t filter = *(ptid_t *) arg;
if (WIFSTOPPED (*wstatp) && WSTOPSIG (*wstatp) == SIGTRAP)
{
if (the_low_target.stopped_by_watchpoint == NULL)
{
child->stopped_by_watchpoint = 0;
}
else
{
struct thread_info *saved_inferior;
if (!ptid_match (ptid_of (thr), filter))
return 0;
saved_inferior = current_inferior;
current_inferior = get_lwp_thread (child);
lwp = get_thread_lwp (thr);
if (!lwp->stopped)
return 1;
child->stopped_by_watchpoint
= the_low_target.stopped_by_watchpoint ();
if (child->stopped_by_watchpoint)
{
if (the_low_target.stopped_data_address != NULL)
child->stopped_data_address
= the_low_target.stopped_data_address ();
else
child->stopped_data_address = 0;
}
current_inferior = saved_inferior;
}
}
/* Store the STOP_PC, with adjustment applied. This depends on the
architecture being defined already (so that CHILD has a valid
regcache), and on LAST_STATUS being set (to check for SIGTRAP or
not). */
if (WIFSTOPPED (*wstatp))
child->stop_pc = get_stop_pc (child);
if (debug_threads
&& WIFSTOPPED (*wstatp)
&& the_low_target.get_pc != NULL)
{
struct thread_info *saved_inferior = current_inferior;
struct regcache *regcache;
CORE_ADDR pc;
current_inferior = get_lwp_thread (child);
regcache = get_thread_regcache (current_inferior, 1);
pc = (*the_low_target.get_pc) (regcache);
debug_printf ("linux_wait_for_lwp: pc is 0x%lx\n", (long) pc);
current_inferior = saved_inferior;
}
return child;
return 0;
}
/* This function should only be called if the LWP got a SIGTRAP.
@ -1749,23 +1714,259 @@ cancel_breakpoint (struct lwp_info *lwp)
return 0;
}
/* Do low-level handling of the event, and check if we should go on
and pass it to caller code. Return the affected lwp if we are, or
NULL otherwise. */
static struct lwp_info *
linux_low_filter_event (ptid_t filter_ptid, int lwpid, int wstat)
{
struct lwp_info *child;
struct thread_info *thread;
child = find_lwp_pid (pid_to_ptid (lwpid));
/* If we didn't find a process, one of two things presumably happened:
- A process we started and then detached from has exited. Ignore it.
- A process we are controlling has forked and the new child's stop
was reported to us by the kernel. Save its PID. */
if (child == NULL && WIFSTOPPED (wstat))
{
add_to_pid_list (&stopped_pids, lwpid, wstat);
return NULL;
}
else if (child == NULL)
return NULL;
thread = get_lwp_thread (child);
child->stopped = 1;
child->last_status = wstat;
if (WIFSTOPPED (wstat))
{
struct process_info *proc;
/* Architecture-specific setup after inferior is running. This
needs to happen after we have attached to the inferior and it
is stopped for the first time, but before we access any
inferior registers. */
proc = find_process_pid (pid_of (thread));
if (proc->private->new_inferior)
{
struct thread_info *saved_inferior;
saved_inferior = current_inferior;
current_inferior = thread;
the_low_target.arch_setup ();
current_inferior = saved_inferior;
proc->private->new_inferior = 0;
}
}
/* Store the STOP_PC, with adjustment applied. This depends on the
architecture being defined already (so that CHILD has a valid
regcache), and on LAST_STATUS being set (to check for SIGTRAP or
not). */
if (WIFSTOPPED (wstat))
{
if (debug_threads
&& the_low_target.get_pc != NULL)
{
struct thread_info *saved_inferior;
struct regcache *regcache;
CORE_ADDR pc;
saved_inferior = current_inferior;
current_inferior = thread;
regcache = get_thread_regcache (current_inferior, 1);
pc = (*the_low_target.get_pc) (regcache);
debug_printf ("linux_low_filter_event: pc is 0x%lx\n", (long) pc);
current_inferior = saved_inferior;
}
child->stop_pc = get_stop_pc (child);
}
/* Fetch the possibly triggered data watchpoint info and store it in
CHILD.
On some archs, like x86, that use debug registers to set
watchpoints, it's possible that the way to know which watched
address trapped, is to check the register that is used to select
which address to watch. Problem is, between setting the
watchpoint and reading back which data address trapped, the user
may change the set of watchpoints, and, as a consequence, GDB
changes the debug registers in the inferior. To avoid reading
back a stale stopped-data-address when that happens, we cache in
LP the fact that a watchpoint trapped, and the corresponding data
address, as soon as we see CHILD stop with a SIGTRAP. If GDB
changes the debug registers meanwhile, we have the cached data we
can rely on. */
if (WIFSTOPPED (wstat) && WSTOPSIG (wstat) == SIGTRAP)
{
if (the_low_target.stopped_by_watchpoint == NULL)
{
child->stopped_by_watchpoint = 0;
}
else
{
struct thread_info *saved_inferior;
saved_inferior = current_inferior;
current_inferior = thread;
child->stopped_by_watchpoint
= the_low_target.stopped_by_watchpoint ();
if (child->stopped_by_watchpoint)
{
if (the_low_target.stopped_data_address != NULL)
child->stopped_data_address
= the_low_target.stopped_data_address ();
else
child->stopped_data_address = 0;
}
current_inferior = saved_inferior;
}
}
if (WIFSTOPPED (wstat) && child->must_set_ptrace_flags)
{
linux_enable_event_reporting (lwpid);
child->must_set_ptrace_flags = 0;
}
if (WIFSTOPPED (wstat) && WSTOPSIG (wstat) == SIGTRAP
&& wstat >> 16 != 0)
{
handle_extended_wait (child, wstat);
return NULL;
}
if (WIFSTOPPED (wstat) && WSTOPSIG (wstat) == SIGSTOP
&& child->stop_expected)
{
if (debug_threads)
debug_printf ("Expected stop.\n");
child->stop_expected = 0;
if (thread->last_resume_kind == resume_stop)
{
/* We want to report the stop to the core. Treat the
SIGSTOP as a normal event. */
}
else if (stopping_threads != NOT_STOPPING_THREADS)
{
/* Stopping threads. We don't want this SIGSTOP to end up
pending in the FILTER_PTID handling below. */
return NULL;
}
else
{
/* Filter out the event. */
linux_resume_one_lwp (child, child->stepping, 0, NULL);
return NULL;
}
}
/* Check if the thread has exited. */
if ((WIFEXITED (wstat) || WIFSIGNALED (wstat))
&& num_lwps (pid_of (thread)) > 1)
{
if (debug_threads)
debug_printf ("LLW: %d exited.\n", lwpid);
/* If there is at least one more LWP, then the exit signal
was not the end of the debugged application and should be
ignored. */
delete_lwp (child);
return NULL;
}
if (!ptid_match (ptid_of (thread), filter_ptid))
{
if (debug_threads)
debug_printf ("LWP %d got an event %06x, leaving pending.\n",
lwpid, wstat);
if (WIFSTOPPED (wstat))
{
child->status_pending_p = 1;
child->status_pending = wstat;
if (WSTOPSIG (wstat) != SIGSTOP)
{
/* Cancel breakpoint hits. The breakpoint may be
removed before we fetch events from this process to
report to the core. It is best not to assume the
moribund breakpoints heuristic always handles these
cases --- it could be too many events go through to
the core before this one is handled. All-stop always
cancels breakpoint hits in all threads. */
if (non_stop
&& WSTOPSIG (wstat) == SIGTRAP
&& cancel_breakpoint (child))
{
/* Throw away the SIGTRAP. */
child->status_pending_p = 0;
if (debug_threads)
debug_printf ("LLW: LWP %d hit a breakpoint while"
" waiting for another process;"
" cancelled it\n", lwpid);
}
}
}
else if (WIFEXITED (wstat) || WIFSIGNALED (wstat))
{
if (debug_threads)
debug_printf ("LLWE: process %d exited while fetching "
"event from another LWP\n", lwpid);
/* This was the last lwp in the process. Since events are
serialized to GDB core, and we can't report this one
right now, but GDB core and the other target layers will
want to be notified about the exit code/signal, leave the
status pending for the next time we're able to report
it. */
mark_lwp_dead (child, wstat);
}
return NULL;
}
return child;
}
/* When the event-loop is doing a step-over, this points at the thread
being stepped. */
ptid_t step_over_bkpt;
/* Wait for an event from child PID. If PID is -1, wait for any
child. Store the stop status through the status pointer WSTAT.
OPTIONS is passed to the waitpid call. Return 0 if no child stop
event was found and OPTIONS contains WNOHANG. Return the PID of
the stopped child and update current_inferior otherwise. */
/* Wait for an event from child(ren) WAIT_PTID, and return any that
match FILTER_PTID (leaving others pending). The PTIDs can be:
minus_one_ptid, to specify any child; a pid PTID, specifying all
lwps of a thread group; or a PTID representing a single lwp. Store
the stop status through the status pointer WSTAT. OPTIONS is
passed to the waitpid call. Return 0 if no event was found and
OPTIONS contains WNOHANG. Return -1 if no unwaited-for children
was found. Return the PID of the stopped child otherwise. */
static int
linux_wait_for_event (ptid_t ptid, int *wstat, int options)
linux_wait_for_event_filtered (ptid_t wait_ptid, ptid_t filter_ptid,
int *wstatp, int options)
{
struct thread_info *event_thread;
struct lwp_info *event_child, *requested_child;
ptid_t wait_ptid;
sigset_t block_mask, prev_mask;
retry:
/* N.B. event_thread points to the thread_info struct that contains
event_child. Keep them in sync. */
event_thread = NULL;
@ -1774,18 +1975,18 @@ linux_wait_for_event (ptid_t ptid, int *wstat, int options)
/* Check for a lwp with a pending status. */
if (ptid_equal (ptid, minus_one_ptid) || ptid_is_pid (ptid))
if (ptid_equal (filter_ptid, minus_one_ptid) || ptid_is_pid (filter_ptid))
{
event_thread = (struct thread_info *)
find_inferior (&all_threads, status_pending_p_callback, &ptid);
find_inferior (&all_threads, status_pending_p_callback, &filter_ptid);
if (event_thread != NULL)
event_child = get_thread_lwp (event_thread);
if (debug_threads && event_thread)
debug_printf ("Got a pending child %ld\n", lwpid_of (event_thread));
}
else
else if (!ptid_equal (filter_ptid, null_ptid))
{
requested_child = find_lwp_pid (ptid);
requested_child = find_lwp_pid (filter_ptid);
if (stopping_threads == NOT_STOPPING_THREADS
&& requested_child->status_pending_p
@ -1814,146 +2015,142 @@ linux_wait_for_event (ptid_t ptid, int *wstat, int options)
if (debug_threads)
debug_printf ("Got an event from pending child %ld (%04x)\n",
lwpid_of (event_thread), event_child->status_pending);
*wstat = event_child->status_pending;
*wstatp = event_child->status_pending;
event_child->status_pending_p = 0;
event_child->status_pending = 0;
current_inferior = event_thread;
return lwpid_of (event_thread);
}
if (ptid_is_pid (ptid))
/* But if we don't find a pending event, we'll have to wait.
We only enter this loop if no process has a pending wait status.
Thus any action taken in response to a wait status inside this
loop is responding as soon as we detect the status, not after any
pending events. */
/* Make sure SIGCHLD is blocked until the sigsuspend below. Block
all signals while here. */
sigfillset (&block_mask);
sigprocmask (SIG_BLOCK, &block_mask, &prev_mask);
while (event_child == NULL)
{
/* A request to wait for a specific tgid. This is not possible
with waitpid, so instead, we wait for any child, and leave
children we're not interested in right now with a pending
status to report later. */
wait_ptid = minus_one_ptid;
pid_t ret = 0;
/* Always use -1 and WNOHANG, due to couple of a kernel/ptrace
quirks:
- If the thread group leader exits while other threads in the
thread group still exist, waitpid(TGID, ...) hangs. That
waitpid won't return an exit status until the other threads
in the group are reaped.
- When a non-leader thread execs, that thread just vanishes
without reporting an exit (so we'd hang if we waited for it
explicitly in that case). The exec event is reported to
the TGID pid (although we don't currently enable exec
events). */
errno = 0;
ret = my_waitpid (-1, wstatp, options | WNOHANG);
if (debug_threads)
debug_printf ("LWFE: waitpid(-1, ...) returned %d, %s\n",
ret, errno ? strerror (errno) : "ERRNO-OK");
if (ret > 0)
{
if (debug_threads)
{
debug_printf ("LLW: waitpid %ld received %s\n",
(long) ret, status_to_str (*wstatp));
}
else
wait_ptid = ptid;
/* We only enter this loop if no process has a pending wait status. Thus
any action taken in response to a wait status inside this loop is
responding as soon as we detect the status, not after any pending
events. */
while (1)
event_child = linux_low_filter_event (filter_ptid,
ret, *wstatp);
if (event_child != NULL)
{
event_child = linux_wait_for_lwp (wait_ptid, wstat, options);
/* We got an event to report to the core. */
event_thread = get_lwp_thread (event_child);
break;
}
if ((options & WNOHANG) && event_child == NULL)
/* Retry until nothing comes out of waitpid. A single
SIGCHLD can indicate more than one child stopped. */
continue;
}
/* Check for zombie thread group leaders. Those can't be reaped
until all other threads in the thread group are. */
check_zombie_leaders ();
/* If there are no resumed children left in the set of LWPs we
want to wait for, bail. We can't just block in
waitpid/sigsuspend, because lwps might have been left stopped
in trace-stop state, and we'd be stuck forever waiting for
their status to change (which would only happen if we resumed
them). Even if WNOHANG is set, this return code is preferred
over 0 (below), as it is more detailed. */
if ((find_inferior (&all_threads,
not_stopped_callback,
&wait_ptid) == NULL))
{
if (debug_threads)
debug_printf ("LLW: exit (no unwaited-for LWP)\n");
sigprocmask (SIG_SETMASK, &prev_mask, NULL);
return -1;
}
/* No interesting event to report to the caller. */
if ((options & WNOHANG))
{
if (debug_threads)
debug_printf ("WNOHANG set, no event found\n");
sigprocmask (SIG_SETMASK, &prev_mask, NULL);
return 0;
}
if (event_child == NULL)
error ("event from unknown child");
/* Block until we get an event reported with SIGCHLD. */
if (debug_threads)
debug_printf ("sigsuspend'ing\n");
event_thread = get_lwp_thread (event_child);
if (ptid_is_pid (ptid)
&& ptid_get_pid (ptid) != ptid_get_pid (ptid_of (event_thread)))
{
if (! WIFSTOPPED (*wstat))
mark_lwp_dead (event_child, *wstat);
else
{
event_child->status_pending_p = 1;
event_child->status_pending = *wstat;
}
continue;
sigsuspend (&prev_mask);
sigprocmask (SIG_SETMASK, &prev_mask, NULL);
goto retry;
}
sigprocmask (SIG_SETMASK, &prev_mask, NULL);
current_inferior = event_thread;
/* Check for thread exit. */
if (! WIFSTOPPED (*wstat))
if (! WIFSTOPPED (*wstatp))
{
if (debug_threads)
debug_printf ("LWP %ld exiting\n", lwpid_of (event_thread));
gdb_assert (last_thread_of_process_p (pid_of (event_thread)));
/* If the last thread is exiting, just return. */
if (last_thread_of_process_p (current_inferior))
{
if (debug_threads)
debug_printf ("LWP %ld is last lwp of process\n",
lwpid_of (event_thread));
debug_printf ("LWP %d is the last lwp of process. "
"Process %ld exiting.\n",
pid_of (event_thread), lwpid_of (event_thread));
return lwpid_of (event_thread);
}
if (!non_stop)
{
current_inferior = get_first_thread ();
if (debug_threads)
debug_printf ("Current inferior is now %ld\n",
lwpid_of (current_inferior));
}
else
{
current_inferior = NULL;
if (debug_threads)
debug_printf ("Current inferior is now <NULL>\n");
}
/* If we were waiting for this particular child to do something...
well, it did something. */
if (requested_child != NULL)
{
int lwpid = lwpid_of (event_thread);
/* Cancel the step-over operation --- the thread that
started it is gone. */
if (finish_step_over (event_child))
unstop_all_lwps (1, event_child);
delete_lwp (event_child);
return lwpid;
}
delete_lwp (event_child);
/* Wait for a more interesting event. */
continue;
}
if (event_child->must_set_ptrace_flags)
{
linux_enable_event_reporting (lwpid_of (event_thread));
event_child->must_set_ptrace_flags = 0;
}
if (WIFSTOPPED (*wstat) && WSTOPSIG (*wstat) == SIGTRAP
&& *wstat >> 16 != 0)
{
handle_extended_wait (event_child, *wstat);
continue;
}
if (WIFSTOPPED (*wstat)
&& WSTOPSIG (*wstat) == SIGSTOP
&& event_child->stop_expected)
{
int should_stop;
if (debug_threads)
debug_printf ("Expected stop.\n");
event_child->stop_expected = 0;
should_stop = (current_inferior->last_resume_kind == resume_stop
|| stopping_threads != NOT_STOPPING_THREADS);
if (!should_stop)
{
linux_resume_one_lwp (event_child,
event_child->stepping, 0, NULL);
continue;
}
}
return lwpid_of (event_thread);
}
}
/* NOTREACHED */
return 0;
/* Wait for an event from child(ren) PTID. PTIDs can be:
minus_one_ptid, to specify any child; a pid PTID, specifying all
lwps of a thread group; or a PTID representing a single lwp. Store
the stop status through the status pointer WSTAT. OPTIONS is
passed to the waitpid call. Return 0 if no event was found and
OPTIONS contains WNOHANG. Return -1 if no unwaited-for children
was found. Return the PID of the stopped child otherwise. */
static int
linux_wait_for_event (ptid_t ptid, int *wstatp, int options)
{
return linux_wait_for_event_filtered (ptid, ptid, wstatp, options);
}
/* Count the LWP's that have had events. */
@ -2322,32 +2519,37 @@ retry:
pid = linux_wait_for_event (step_over_bkpt, &w, options & ~WNOHANG);
}
if (pid == 0) /* only if TARGET_WNOHANG */
if (pid == 0)
{
gdb_assert (target_options & TARGET_WNOHANG);
if (debug_threads)
{
debug_printf ("linux_wait_1 ret = null_ptid, "
"TARGET_WAITKIND_IGNORE\n");
debug_exit ();
}
ourstatus->kind = TARGET_WAITKIND_IGNORE;
return null_ptid;
}
else if (pid == -1)
{
if (debug_threads)
{
debug_printf ("linux_wait_1 ret = null_ptid\n");
debug_printf ("linux_wait_1 ret = null_ptid, "
"TARGET_WAITKIND_NO_RESUMED\n");
debug_exit ();
}
ourstatus->kind = TARGET_WAITKIND_NO_RESUMED;
return null_ptid;
}
event_child = get_thread_lwp (current_inferior);
/* If we are waiting for a particular child, and it exited,
linux_wait_for_event will return its exit status. Similarly if
the last child exited. If this is not the last child, however,
do not report it as exited until there is a 'thread exited' response
available in the remote protocol. Instead, just wait for another event.
This should be safe, because if the thread crashed we will already
have reported the termination signal to GDB; that should stop any
in-progress stepping operations, etc.
Report the exit status of the last thread to exit. This matches
LinuxThreads' behavior. */
if (last_thread_of_process_p (current_inferior))
{
/* linux_wait_for_event only returns an exit status for the last
child of a process. Report it. */
if (WIFEXITED (w) || WIFSIGNALED (w))
{
if (WIFEXITED (w))
@ -2381,12 +2583,6 @@ retry:
return ptid_of (current_inferior);
}
}
else
{
if (!WIFSTOPPED (w))
goto retry;
}
/* If this event was not handled before, and is not a SIGTRAP, we
report it. SIGILL and SIGSEGV are also treated as traps in case
@ -2929,24 +3125,15 @@ mark_lwp_dead (struct lwp_info *lwp, int wstat)
lwp->stop_expected = 0;
}
static void
wait_for_sigstop (struct inferior_list_entry *entry)
{
struct thread_info *thread = (struct thread_info *) entry;
struct lwp_info *lwp = get_thread_lwp (thread);
struct thread_info *saved_inferior;
int wstat;
ptid_t saved_tid;
ptid_t ptid;
int pid;
/* Wait for all children to stop for the SIGSTOPs we just queued. */
if (lwp->stopped)
{
if (debug_threads)
debug_printf ("wait_for_sigstop: LWP %ld already stopped\n",
lwpid_of (thread));
return;
}
static void
wait_for_sigstop (void)
{
struct thread_info *saved_inferior;
ptid_t saved_tid;
int wstat;
int ret;
saved_inferior = current_inferior;
if (saved_inferior != NULL)
@ -2954,50 +3141,15 @@ wait_for_sigstop (struct inferior_list_entry *entry)
else
saved_tid = null_ptid; /* avoid bogus unused warning */
ptid = thread->entry.id;
if (debug_threads)
debug_printf ("wait_for_sigstop: pulling one event\n");
debug_printf ("wait_for_sigstop: pulling events\n");
pid = linux_wait_for_event (ptid, &wstat, __WALL);
/* If we stopped with a non-SIGSTOP signal, save it for later
and record the pending SIGSTOP. If the process exited, just
return. */
if (WIFSTOPPED (wstat))
{
if (debug_threads)
debug_printf ("LWP %ld stopped with signal %d\n",
lwpid_of (thread), WSTOPSIG (wstat));
if (WSTOPSIG (wstat) != SIGSTOP)
{
if (debug_threads)
debug_printf ("LWP %ld stopped with non-sigstop status %06x\n",
lwpid_of (thread), wstat);
lwp->status_pending_p = 1;
lwp->status_pending = wstat;
}
}
else
{
if (debug_threads)
debug_printf ("Process %d exited while stopping LWPs\n", pid);
lwp = find_lwp_pid (pid_to_ptid (pid));
if (lwp)
{
/* Leave this status pending for the next time we're able to
report it. In the mean time, we'll report this lwp as
dead to GDB, so GDB doesn't try to read registers and
memory from it. This can only happen if this was the
last thread of the process; otherwise, PID is removed
from the thread tables before linux_wait_for_event
returns. */
mark_lwp_dead (lwp, wstat);
}
}
/* Passing NULL_PTID as filter indicates we want all events to be
left pending. Eventually this returns when there are no
unwaited-for children left. */
ret = linux_wait_for_event_filtered (minus_one_ptid, null_ptid,
&wstat, __WALL);
gdb_assert (ret == -1);
if (saved_inferior == NULL || linux_thread_alive (saved_tid))
current_inferior = saved_inferior;
@ -3124,7 +3276,7 @@ stop_all_lwps (int suspend, struct lwp_info *except)
find_inferior (&all_threads, suspend_and_send_sigstop_callback, except);
else
find_inferior (&all_threads, send_sigstop_callback, except);
for_each_inferior (&all_threads, wait_for_sigstop);
wait_for_sigstop ();
stopping_threads = NOT_STOPPING_THREADS;
if (debug_threads)

18
gdb/gdbserver/server.c
View file

@ -2367,8 +2367,18 @@ resume (struct thread_resume *actions, size_t num_actions)
{
last_ptid = mywait (minus_one_ptid, &last_status, 0, 1);
if (last_status.kind == TARGET_WAITKIND_NO_RESUMED)
{
/* No proper RSP support for this yet. At least return
error. */
sprintf (own_buf, "E.No unwaited-for children left.");
disable_async_io ();
return;
}
if (last_status.kind != TARGET_WAITKIND_EXITED
&& last_status.kind != TARGET_WAITKIND_SIGNALLED)
&& last_status.kind != TARGET_WAITKIND_SIGNALLED
&& last_status.kind != TARGET_WAITKIND_NO_RESUMED)
current_inferior->last_status = last_status;
/* From the client's perspective, all-stop mode always stops all
@ -3897,7 +3907,11 @@ handle_target_event (int err, gdb_client_data client_data)
last_ptid = mywait (minus_one_ptid, &last_status,
TARGET_WNOHANG, 1);
if (last_status.kind != TARGET_WAITKIND_IGNORE)
if (last_status.kind == TARGET_WAITKIND_NO_RESUMED)
{
/* No RSP support for this yet. */
}
else if (last_status.kind != TARGET_WAITKIND_IGNORE)
{
int pid = ptid_get_pid (last_ptid);
struct process_info *process = find_process_pid (pid);