gdb: disable commit resumed in target_kill

New in this version:

 - Better comment in target_kill
 - Uncomment line in test to avoid hanging when exiting, when testing on
   native-extended-gdbserver

PR 28275 shows that doing a sequence of:

 - Run inferior in background (run &)
 - kill that inferior
 - Run again

We get into this assertion:

    /home/smarchi/src/binutils-gdb/gdb/target.c:2590: internal-error: target_wait: Assertion `!proc_target->commit_resumed_state' failed.

    #0  internal_error_loc (file=0x5606b344e740 "/home/smarchi/src/binutils-gdb/gdb/target.c", line=2590, fmt=0x5606b344d6a0 "%s: Assertion `%s' failed.") at /home/smarchi/src/binutils-gdb/gdbsupport/errors.cc:54
    #1  0x00005606b6296475 in target_wait (ptid=..., status=0x7fffb9390630, options=...) at /home/smarchi/src/binutils-gdb/gdb/target.c:2590
    #2  0x00005606b5767a98 in startup_inferior (proc_target=0x5606bfccb2a0 <the_amd64_linux_nat_target>, pid=3884857, ntraps=1, last_waitstatus=0x0, last_ptid=0x0) at /home/smarchi/src/binutils-gdb/gdb/nat/fork-inferior.c:482
    #3  0x00005606b4e6c9c5 in gdb_startup_inferior (pid=3884857, num_traps=1) at /home/smarchi/src/binutils-gdb/gdb/fork-child.c:132
    #4  0x00005606b50f14a5 in inf_ptrace_target::create_inferior (this=0x5606bfccb2a0 <the_amd64_linux_nat_target>, exec_file=0x604000039f50 "/home/smarchi/build/binutils-gdb/gdb/test", allargs="", env=0x61500000a580, from_tty=1)
        at /home/smarchi/src/binutils-gdb/gdb/inf-ptrace.c:105
    #5  0x00005606b53b6d23 in linux_nat_target::create_inferior (this=0x5606bfccb2a0 <the_amd64_linux_nat_target>, exec_file=0x604000039f50 "/home/smarchi/build/binutils-gdb/gdb/test", allargs="", env=0x61500000a580, from_tty=1)
        at /home/smarchi/src/binutils-gdb/gdb/linux-nat.c:978
    #6  0x00005606b512b79b in run_command_1 (args=0x0, from_tty=1, run_how=RUN_NORMAL) at /home/smarchi/src/binutils-gdb/gdb/infcmd.c:468
    #7  0x00005606b512c236 in run_command (args=0x0, from_tty=1) at /home/smarchi/src/binutils-gdb/gdb/infcmd.c:526

When running the kill command, commit_resumed_state for the
process_stratum_target (linux-nat, here) is true.  After the kill, when
there are no more threads, commit_resumed_state is still true, as
nothing touches this flag during the kill operation.  During the
subsequent run command, run_command_1 does:

    scoped_disable_commit_resumed disable_commit_resumed ("running");

We would think that this would clear the commit_resumed_state flag of
our native target, but that's not the case, because
scoped_disable_commit_resumed iterates on non-exited inferiors in order
to find active process targets.  And after the kill, the inferior is
exited, and the native target was unpushed from it anyway.  So
scoped_disable_commit_resumed doesn't touch the commit_resumed_state
flag of the native target, it stays true.  When reaching target_wait, in
startup_inferior (to consume the initial expect stop events while the
inferior is starting up and working its way through the shell),
commit_resumed_state is true, breaking the contract saying that
commit_resumed_state is always false when calling the targets' wait
method.

(note: to be correct, I think that startup_inferior should toggle
commit_resumed between the target_wait and target_resume calls, but I'll
ignore that for now)

I can see multiple ways to fix this.  In the end, we need
commit_resumed_state to be cleared by the time we get to that
target_wait.  It could be done at the end of the kill command, or at the
beginning of the run command.

To keep things in a coherent state, I'd like to make it so that after
the kill command, when the target is left with no threads, its
commit_resumed_state flag is left to false.  This way, we can keep
working with the assumption that a target with no threads (and therefore
no running threads) has commit_resumed_state == false.

Do this by adding a scoped_disable_commit_resumed in target_kill.  It
clears the target's commit_resumed_state on entry, and leaves it false
if the target does not have any resumed thread on exit.  That means,
even if the target has another inferior with stopped threads,
commit_resumed_state will be left to false, which makes sense.

Add a test that tries to cover various combinations of actions done
while an inferior is running (and therefore while commit_resumed_state
is true on the process target).

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28275
Change-Id: I8e6fe6dc1f475055921520e58cab68024039a1e9
Approved-By: Andrew Burgess <aburgess@redhat.com>

3 files changed, 164 insertions, 0 deletions

diff --git a/gdb/target.c b/gdb/target.c
index 0c86b57..0eae530 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -908,6 +908,15 @@ add_deprecated_target_alias (const target_info &tinfo, const char *alias)
 void
 target_kill (void)
 {
+
+  /* If the commit_resume_state of the to-be-killed-inferior's process stratum
+     is true, and this inferior is the last live inferior with resumed threads
+     of that target, then we want to leave commit_resume_state to false, as the
+     target won't have any resumed threads anymore.  We achieve this with
+     this scoped_disable_commit_resumed.  On construction, it will set the flag
+     to false.  On destruction, it will only set it to true if there are resumed
+     threads left.  */
+  scoped_disable_commit_resumed disable ("killing");
   current_inferior ()->top_target ()->kill ();
 }
 
diff --git a/gdb/testsuite/gdb.base/run-control-while-bg-execution.c b/gdb/testsuite/gdb.base/run-control-while-bg-execution.c
new file mode 100644
index 0000000..8092fad
--- /dev/null
+++ b/gdb/testsuite/gdb.base/run-control-while-bg-execution.c
@@ -0,0 +1,33 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2020-2022 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 <unistd.h>
+
+static pid_t mypid = -1;
+
+static void
+after_getpid (void)
+{
+}
+
+int
+main (void)
+{
+  mypid = getpid ();
+  after_getpid ();
+  sleep (30);
+}
diff --git a/gdb/testsuite/gdb.base/run-control-while-bg-execution.exp b/gdb/testsuite/gdb.base/run-control-while-bg-execution.exp
new file mode 100644
index 0000000..5b4834f
--- /dev/null
+++ b/gdb/testsuite/gdb.base/run-control-while-bg-execution.exp
@@ -0,0 +1,122 @@
+# 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/>.
+
+# This test aims at testing various operations after getting rid of an inferior
+# that was running in background, or while we have an inferior running in
+# background.  The original intent was to expose cases where the commit-resumed
+# state of the process stratum target was not reset properly after killing an
+# inferior running in background, which would be a problem when trying to run
+# again.  The test was expanded to test various combinations of
+# run-control-related actions done with an inferior running in background.
+
+if {[use_gdb_stub]} {
+    unsupported "test requires running"
+    return
+}
+
+standard_testfile
+
+if {[build_executable "failed to prepare" $testfile $srcfile]} {
+    return
+}
+
+# Run one variation of the test:
+#
+# 1. Start an inferior in the background with "run &"
+# 2. Do action 1
+# 3. Do action 2
+#
+# Action 1 indicates what to do with the inferior running in background:
+#
+#  - kill: kill it
+#  - detach: detach it
+#  - add: add a new inferior and switch to it, leave the inferior running in
+#    background alone
+#  - none: do nothing, leave the inferior running in background alone
+#
+# Action 2 indicates what to do after that:
+#
+#  - start: use the start command
+#  - run: use the run command
+#  - attach: start a process outside of GDB and attach it
+proc do_test { action1 action2 } {
+    save_vars { ::GDBFLAGS } {
+	append ::GDBFLAGS " -ex \"maintenance set target-non-stop on\""
+	clean_restart $::binfile
+    }
+
+    # Ensure we are at least after the getpid call, should we need it.
+    if { ![runto "after_getpid"] } {
+	return
+    }
+
+    # Some commands below ask for confirmation.  Turn that off for simplicity.
+    gdb_test "set confirm off"
+    gdb_test_multiple "continue &" "" {
+	-re ".*\r\n$::gdb_prompt " {
+	    pass $gdb_test_name
+	}
+    }
+
+    if { $action1 == "kill" } {
+	gdb_test "kill" "Inferior 1 .* killed.*"
+    } elseif { $action1 == "detach" } {
+	set child_pid [get_integer_valueof "mypid" -1]
+	if { $child_pid == -1 } {
+	    fail "failed to extract child pid"
+	    return
+	}
+
+	gdb_test "detach" "Inferior 1 .* detached.*" "detach from first instance"
+
+	# Kill the detached process, to avoid hanging when exiting GDBserver,
+	# when testing with the native-extended-gdbserver board.
+	remote_exec target "kill $child_pid"
+    } elseif { $action1 == "add" } {
+	gdb_test "add-inferior -exec $::binfile" \
+	    "Added inferior 2 on connection 1.*" "add-inferior"
+	gdb_test "inferior 2" "Switching to inferior 2 .*"
+    } elseif { $action1 == "none" } {
+
+    } else {
+	error "invalid action 1"
+    }
+
+    if { $action2 == "start" } {
+	gdb_test "start" "Temporary breakpoint $::decimal\(?:\.$::decimal\)?, main .*"
+    } elseif { $action2 == "run" } {
+	gdb_test "break main" "Breakpoint $::decimal at $::hex.*"
+	gdb_test "run" "Breakpoint $::decimal\(?:\.$::decimal\)?, main .*"
+    } elseif { $action2 == "attach" } {
+	set test_spawn_id [spawn_wait_for_attach $::binfile]
+	set test_pid [spawn_id_get_pid $test_spawn_id]
+
+	if { [gdb_attach $test_pid] } {
+	    gdb_test "detach" "Inferior $::decimal .* detached.*" \
+		"detach from second instance"
+	}
+
+	# Detach and kill this inferior so we don't leave it around.
+	kill_wait_spawned_process $test_spawn_id
+    } else {
+	error "invalid action 2"
+    }
+}
+
+foreach_with_prefix action1 { kill detach add none } {
+    foreach_with_prefix action2 { start run attach } {
+	do_test $action1 $action2
+    }
+}