static void wait_for_inferior (inferior *inf);
+static void restart_threads (struct thread_info *event_thread,
+ inferior *inf = nullptr);
+
+static bool start_step_over (void);
+
/* Asynchronous signal handler registered as event loop source for
when we have pending events ready to be passed to the core. */
static struct async_event_handler *infrun_async_inferior_event_token;
inferior *parent_inf = current_inferior ();
inferior *child_inf = nullptr;
+ gdb_assert (parent_inf->thread_waiting_for_vfork_done == nullptr);
+
if (!follow_child)
{
/* Detach new forked process? */
child_inf->pending_detach = 0;
parent_inf->vfork_child = child_inf;
parent_inf->pending_detach = detach_fork;
- parent_inf->thread_waiting_for_vfork_done = nullptr;
}
else if (detach_fork)
{
parent = inferior_ptid;
child = tp->pending_follow.child_ptid ();
+ /* If handling a vfork, stop all the inferior's threads, they will be
+ restarted when the vfork shared region is complete. */
+ if (tp->pending_follow.kind () == TARGET_WAITKIND_VFORKED
+ && target_is_non_stop_p ())
+ stop_all_threads ("handling vfork", tp->inf);
+
process_stratum_target *parent_targ = tp->inf->process_target ();
/* Set up inferior(s) as specified by the caller, and tell the
target to do whatever is necessary to follow either parent
}
}
+/* Handle TARGET_WAITKIND_VFORK_DONE. */
+
+static void
+handle_vfork_done (thread_info *event_thread)
+{
+ /* We only care about this event if inferior::thread_waiting_for_vfork_done is
+ set, that is if we are waiting for a vfork child not under our control
+ (because we detached it) to exec or exit.
+
+ If an inferior has vforked and we are debugging the child, we don't use
+ the vfork-done event to get notified about the end of the shared address
+ space window. We rely instead on the child's exec or exit event, and the
+ inferior::vfork_{parent,child} fields are used instead. See
+ handle_vfork_child_exec_or_exit for that. */
+ if (event_thread->inf->thread_waiting_for_vfork_done == nullptr)
+ {
+ infrun_debug_printf ("not waiting for a vfork-done event");
+ return;
+ }
+
+ INFRUN_SCOPED_DEBUG_ENTER_EXIT;
+
+ /* We stopped all threads (other than the vforking thread) of the inferior in
+ follow_fork and kept them stopped until now. It should therefore not be
+ possible for another thread to have reported a vfork during that window.
+ If THREAD_WAITING_FOR_VFORK_DONE is set, it has to be the same thread whose
+ vfork-done we are handling right now. */
+ gdb_assert (event_thread->inf->thread_waiting_for_vfork_done == event_thread);
+
+ event_thread->inf->thread_waiting_for_vfork_done = nullptr;
+ event_thread->inf->pspace->breakpoints_not_allowed = 0;
+
+ /* On non-stop targets, we stopped all the inferior's threads in follow_fork,
+ resume them now. On all-stop targets, everything that needs to be resumed
+ will be when we resume the event thread. */
+ if (target_is_non_stop_p ())
+ {
+ /* restart_threads and start_step_over may change the current thread, make
+ sure we leave the event thread as the current thread. */
+ scoped_restore_current_thread restore_thread;
+
+ insert_breakpoints ();
+ restart_threads (event_thread, event_thread->inf);
+ start_step_over ();
+ }
+}
+
/* Enum strings for "set|show follow-exec-mode". */
static const char follow_exec_mode_new[] = "new";
continue;
}
+ if (tp->inf->thread_waiting_for_vfork_done != nullptr)
+ {
+ /* When we stop all threads, handling a vfork, any thread in the step
+ over chain remains there. A user could also try to continue a
+ thread stopped at a breakpoint while another thread is waiting for
+ a vfork-done event. In any case, we don't want to start a step
+ over right now. */
+ continue;
+ }
+
/* Remove thread from the THREADS_TO_STEP chain. If anything goes wrong
while we try to prepare the displaced step, we don't add it back to
the global step over chain. This is to avoid a thread staying in the
return a wildcard ptid. */
if (target_is_non_stop_p ())
return inferior_ptid;
- else
- return user_visible_resume_ptid (user_step);
+
+ /* The rest of the function assumes non-stop==off and
+ target-non-stop==off.
+
+ If a thread is waiting for a vfork-done event, it means breakpoints are out
+ for this inferior (well, program space in fact). We don't want to resume
+ any thread other than the one waiting for vfork done, otherwise these other
+ threads could miss breakpoints. So if a thread in the resumption set is
+ waiting for a vfork-done event, resume only that thread.
+
+ The resumption set width depends on whether schedule-multiple is on or off.
+
+ Note that if the target_resume interface was more flexible, we could be
+ smarter here when schedule-multiple is on. For example, imagine 3
+ inferiors with 2 threads each (1.1, 1.2, 2.1, 2.2, 3.1 and 3.2). Threads
+ 2.1 and 3.2 are both waiting for a vfork-done event. Then we could ask the
+ target(s) to resume:
+
+ - All threads of inferior 1
+ - Thread 2.1
+ - Thread 3.2
+
+ Since we don't have that flexibility (we can only pass one ptid), just
+ resume the first thread waiting for a vfork-done event we find (e.g. thread
+ 2.1). */
+ if (sched_multi)
+ {
+ for (inferior *inf : all_non_exited_inferiors ())
+ if (inf->thread_waiting_for_vfork_done != nullptr)
+ return inf->thread_waiting_for_vfork_done->ptid;
+ }
+ else if (current_inferior ()->thread_waiting_for_vfork_done != nullptr)
+ return current_inferior ()->thread_waiting_for_vfork_done->ptid;
+
+ return user_visible_resume_ptid (user_step);
}
/* Wrapper for target_resume, that handles infrun-specific
continue;
}
+ /* If a thread of that inferior is waiting for a vfork-done
+ (for a detached vfork child to exec or exit), breakpoints are
+ removed. We must not resume any thread of that inferior, other
+ than the one waiting for the vfork-done. */
+ if (tp->inf->thread_waiting_for_vfork_done != nullptr
+ && tp != tp->inf->thread_waiting_for_vfork_done)
+ {
+ infrun_debug_printf ("[%s] another thread of this inferior is "
+ "waiting for vfork-done",
+ tp->ptid.to_string ().c_str ());
+ continue;
+ }
+
infrun_debug_printf ("resuming %s",
tp->ptid.to_string ().c_str ());
error (_("Command aborted."));
}
}
- else if (!cur_thr->resumed () && !thread_is_in_step_over_chain (cur_thr))
+ else if (!cur_thr->resumed ()
+ && !thread_is_in_step_over_chain (cur_thr)
+ /* In non-stop, forbid resuming a thread if some other thread of
+ that inferior is waiting for a vfork-done event (this means
+ breakpoints are out for this inferior). */
+ && !(non_stop
+ && cur_thr->inf->thread_waiting_for_vfork_done != nullptr))
{
/* The thread wasn't started, and isn't queued, run it now. */
reset_ecs (ecs, cur_thr);
};
static bool handle_one (const wait_one_event &event);
-static void restart_threads (struct thread_info *event_thread,
- inferior *inf = nullptr);
/* Prepare and stabilize the inferior for detaching it. E.g.,
detaching while a thread is displaced stepping is a recipe for
context_switch (ecs);
- current_inferior ()->thread_waiting_for_vfork_done = nullptr;
- current_inferior ()->pspace->breakpoints_not_allowed = 0;
+ handle_vfork_done (ecs->event_thread);
+ gdb_assert (inferior_thread () == ecs->event_thread);
if (handle_stop_requested (ecs))
return;
--- /dev/null
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2022 Free Software Foundation, Inc.
+
+ 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 <assert.h>
+#include <pthread.h>
+#include <unistd.h>
+#include <sys/wait.h>
+
+static volatile int release_vfork = 0;
+static volatile int release_main = 0;
+
+static void *
+vforker (void *arg)
+{
+ while (!release_vfork)
+ usleep (1);
+
+ pid_t pid = vfork ();
+ if (pid == 0)
+ {
+ /* A vfork child is not supposed to mess with the state of the program,
+ but it is helpful for the purpose of this test. */
+ release_main = 1;
+ _exit(7);
+ }
+
+ int stat;
+ int ret = waitpid (pid, &stat, 0);
+ assert (ret == pid);
+ assert (WIFEXITED (stat));
+ assert (WEXITSTATUS (stat) == 7);
+
+ return NULL;
+}
+
+static void
+should_break_here (void)
+{}
+
+int
+main (void)
+{
+
+ pthread_t thread;
+ int ret = pthread_create (&thread, NULL, vforker, NULL);
+ assert (ret == 0);
+
+ /* We break here first, while the thread is stuck on `!release_fork`. */
+ release_vfork = 1;
+
+ /* We set a breakpoint on should_break_here.
+
+ We then set "release_fork" from the debugger and continue. The main
+ thread hangs on `!release_main` while the non-main thread vforks. During
+ the window of time where the two processes have a shared address space
+ (after vfork, before _exit), GDB removes the breakpoints from the address
+ space. During that window, only the vfork-ing thread (the non-main
+ thread) is frozen by the kernel. The main thread is free to execute. The
+ child process sets `release_main`, releasing the main thread. A buggy GDB
+ would let the main thread execute during that window, leading to the
+ breakpoint on should_break_here being missed. A fixed GDB does not resume
+ the threads of the vforking process other than the vforking thread. When
+ the vfork child exits, the fixed GDB resumes the main thread, after
+ breakpoints are reinserted, so the breakpoint is not missed. */
+
+ while (!release_main)
+ usleep (1);
+
+ should_break_here ();
+
+ pthread_join (thread, NULL);
+
+ return 6;
+}
--- /dev/null
+# Copyright 2022 Free Software Foundation, Inc.
+
+# 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/>.
+
+# Test that a multi-threaded program doing a vfork doesn't miss breakpoints.
+#
+# When a program vforks, its address space is shared with the parent. When we
+# detach a vfork child, we must keep breakpoints out of that shared address space
+# until the child either exits or execs, so that the child does not hit a
+# breakpoint while out of GDB's control. During that time, threads from
+# the parent must be held stopped, otherwise they could miss breakpoints.
+#
+# The thread that did the vfork is suspended by the kernel, so it's not a
+# concern. The other threads need to be manually stopped by GDB and resumed
+# once the vfork critical region is done.
+#
+# This test spawns one thread that calls vfork. Meanwhile, the main thread
+# crosses a breakpoint. A buggy GDB would let the main thread run while
+# breakpoints are removed, so the main thread would miss the breakpoint and run
+# until exit.
+
+standard_testfile
+
+if { [build_executable "failed to prepare" ${testfile} ${srcfile} {debug pthreads}] } {
+ return
+}
+
+set any "\[^\r\n\]*"
+
+# A bunch of util procedures to continue an inferior to an expected point.
+
+proc continue_to_parent_breakpoint {} {
+ gdb_test "continue" \
+ "hit Breakpoint .* should_break_here .*" \
+ "continue parent to breakpoint"
+}
+
+proc continue_to_parent_end {} {
+ gdb_test "continue" "Inferior 1.*exited with code 06.*" \
+ "continue parent to end"
+}
+
+# Run the test with the given GDB settings.
+
+proc do_test { target-non-stop non-stop follow-fork-mode detach-on-fork schedule-multiple } {
+ save_vars { ::GDBFLAGS } {
+ append ::GDBFLAGS " -ex \"maintenance set target-non-stop ${target-non-stop}\""
+ append ::GDBFLAGS " -ex \"set non-stop ${non-stop}\""
+ clean_restart ${::binfile}
+ }
+
+ gdb_test_no_output "set follow-fork-mode ${follow-fork-mode}"
+ gdb_test_no_output "set detach-on-fork ${detach-on-fork}"
+ gdb_test_no_output "set schedule-multiple ${schedule-multiple}"
+
+ # The message about thread 2 of inferior 1 exiting happens at a somewhat
+ # unpredictable moment, it's simpler to silence it than to try to match it.
+ gdb_test_no_output "set print thread-events off"
+
+ if { ![runto_main] } {
+ return
+ }
+
+ # The main thread is expected to hit this breakpoint.
+ gdb_test "break should_break_here" "Breakpoint $::decimal at .*"
+
+ continue_to_parent_breakpoint
+ continue_to_parent_end
+}
+
+# We only test with follow-fork-mode=parent and detach-on-fork=on at the
+# moment, but the loops below are written to make it easy to add other values
+# on these axes in the future.
+
+foreach_with_prefix target-non-stop {auto on off} {
+ foreach_with_prefix non-stop {off on} {
+ foreach_with_prefix follow-fork-mode {parent} {
+ foreach_with_prefix detach-on-fork {on} {
+ foreach_with_prefix schedule-multiple {off on} {
+ do_test ${target-non-stop} ${non-stop} ${follow-fork-mode} ${detach-on-fork} ${schedule-multiple}
+ }
+ }
+ }
+ }
+}
projects / binutils-gdb.git / commitdiff