[review] gdb/infrun: stop all threads if there exists a non-stop target

Tankut Baris Aktemur (Code Review)
2020-02-05T11:54:43Z

Change URL: https://gnutoolchain-gerrit.osci.io/r/c/binutils-gdb/+/766
......................................................................

gdb/infrun: stop all threads if there exists a non-stop target

Stop all threads not only if the current target is non-stop, but also
if there exists a non-stop target.

The multi-target patch (5b6d1e4fa4f "Multi-target support") made the
following change to gdb/inf-child.c:

void
inf_child_target::maybe_unpush_target ()
{
- if (!inf_child_explicitly_opened && !have_inferiors ())
+ if (!inf_child_explicitly_opened)
unpush_target (this);
}

If we are in all-stop mode with multiple inferiors, and an exit event
is received from an inferior, target_mourn_inferior() gets to this
point and without the have_inferiors() check, the target is unpushed.
This leads to having exec_ops as the top target.

Here is a test scenario. Two executables, ./a.out returns
immediately; ./sleepy just sleeps.

$ gdb ./sleepy
(gdb) start
...
(gdb) add-inferior -exec ./a.out
...
(gdb) inferior 2
[Switching to inferior 2..
(gdb) start
...
(gdb) set schedule-multiple on
(gdb) set debug infrun 1
(gdb) continue

At this point, the exit event is received from ./a.out. Normally,
this would lead to stop_all_threads() to also stop ./sleepy, but this
doesn't happen, because target_is_non_stop_p() returns false. And it
returns false because the top target is no longer the process target;
it is the exec_ops.

This patch modifies 'stop_waiting' to call 'stop_all_threads' if there
exists a non-stop target, not just when the current top target is
non-stop.

Tested on X86_64 Linux.

gdb/ChangeLog:
2020-02-05 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>

* infrun.c (stop_all_threads): Update assertion, plus when
stopping threads, take into account that we might be trying
to stop an all-stop target.
(stop_waiting): Call 'stop_all_threads' if there exists a
non-stop target.

gdb/testsuite/ChangeLog:
2020-02-05 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>

* gdb.multi/stop-all-on-exit.c: New test.
* gdb.multi/stop-all-on-exit.exp: New file.

Change-Id: I6de26f990dc3b32ed526e60507e7bfe37fa1c6f1
---
M gdb/infrun.c
A gdb/testsuite/gdb.multi/stop-all-on-exit.c
A gdb/testsuite/gdb.multi/stop-all-on-exit.exp
3 files changed, 106 insertions(+), 4 deletions(-)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 3e846f8..fd72a74 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -4682,7 +4682,7 @@
int pass;
int iterations = 0;

- gdb_assert (target_is_non_stop_p ());
+ gdb_assert (exists_non_stop_target ());

if (debug_infrun)
fprintf_unfiltered (gdb_stdlog, "infrun: stop_all_threads\n");
@@ -4713,6 +4713,18 @@
to tell the target to stop. */
for (thread_info *t : all_non_exited_threads ())
{
+ /* For a single-target setting with an all-stop target,
+ we would not even arrive here. For a multi-target
+ setting, until GDB is able to handle a mixture of
+ all-stop and non-stop targets, simply skip all-stop
+ targets' threads. This should be fine due to the
+ protection of commit
+ 2f4fcf00399bc0ad5a4fed6b530128e8be4f40da */
+
+ switch_to_thread_no_regs (t);
+ if (!target_is_non_stop_p ())
+ continue;
+
if (t->executing)
{
/* If already stopping, don't request a stop again.
@@ -4724,7 +4736,6 @@
"infrun: %s executing, "
"need stop\n",
target_pid_to_str (t->ptid).c_str ());
- switch_to_thread_no_regs (t);
target_stop (t->ptid);
t->stop_requested = 1;
}
@@ -7837,9 +7848,9 @@
/* Let callers know we don't want to wait for the inferior anymore. */
ecs->wait_some_more = 0;

- /* If all-stop, but the target is always in non-stop mode, stop all
+ /* If all-stop, but there exists a non-stop target, stop all
threads now that we're presenting the stop to the user. */
- if (!non_stop && target_is_non_stop_p ())
+ if (!non_stop && exists_non_stop_target ())
stop_all_threads ();
}

diff --git a/gdb/testsuite/gdb.multi/stop-all-on-exit.c b/gdb/testsuite/gdb.multi/stop-all-on-exit.c
new file mode 100644
index 0000000..bca0c98
--- /dev/null
+++ b/gdb/testsuite/gdb.multi/stop-all-on-exit.c
@@ -0,0 +1,27 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2020 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 <unistd.h>
+
+static unsigned int duration = 1;
+
+int
+main ()
+{
+ sleep (duration);
+ return 0;
+}
diff --git a/gdb/testsuite/gdb.multi/stop-all-on-exit.exp b/gdb/testsuite/gdb.multi/stop-all-on-exit.exp
new file mode 100644
index 0000000..a0622ae
--- /dev/null
+++ b/gdb/testsuite/gdb.multi/stop-all-on-exit.exp
@@ -0,0 +1,64 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2020 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 in all-stop mode with multiple inferiors, GDB stops all
+# threads upon receiving an exit event from one of the inferiors.
+
+standard_testfile
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile]} {
+ return -1
+}
+
+if {![runto_main]} {
+ fail "starting inferior 1"
+ return -1
+}
+
+# This is a test specific for a native target, where we use the
+# "-exec" argument to "add-inferior" and we explicitly don't do
+# "maint set target-non-stop on".
+if {![gdb_is_target_native]} {
+ untested "the test is aimed at a native target"
+ return 0
+}
+
+# Add a second inferior that will sleep longer.
+gdb_test "add-inferior -exec $binfile" "Added inferior 2.*" \
+ "add the second inferior"
+gdb_test "inferior 2" ".*Switching to inferior 2.*"
+if {![runto_main]} {
+ fail "starting inferior 2"
+ return -1
+}
+gdb_test "print duration=10" "= 10"
+
+# Now continue both processes. We should get the exit event from the
+# first inferior.
+gdb_test_no_output "set schedule-multiple on"
+gdb_continue_to_end
+
+# GDB is expected to have stopped the other inferior. Switch to the
+# slow inferior's thread. It should not be running.
+gdb_test_multiple "thread 2.1" "check thread 2.1 is not running" {
+ -re ".*\\(running\\)\[\r\n\]+$gdb_prompt" {
+ fail $gdb_test_name
+ }
+ -re ".*$gdb_prompt" {
+ pass $gdb_test_name
+ }
+}

--
Gerrit-Project: binutils-gdb
Gerrit-Branch: master
Gerrit-Change-Id: I6de26f990dc3b32ed526e60507e7bfe37fa1c6f1
Gerrit-Change-Number: 766
Gerrit-PatchSet: 1
Gerrit-Owner: Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
Gerrit-MessageType: newchange