Testcase for detaching while stepping over breakpointusers/palves/detach-step-over

This adds a testcase that exercises detaching while GDB is stepping
over a breakpoint, in all combinations of:

  - maint target non-stop off/on
  - set non-stop on/off
  - displaced stepping on/off

This exercises the bugs fixed in the previous 8 patches.

gdb/testsuite/ChangeLog:

	* gdb.threads/detach-step-over.c: New file.
	* gdb.threads/detach-step-over.exp: New file.

2 files changed, 402 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.threads/detach-step-over.c b/gdb/testsuite/gdb.threads/detach-step-over.c
new file mode 100644
index 0000000..13db9f6
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/detach-step-over.c
@@ -0,0 +1,112 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2021 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/>.  */
+
+#define _GNU_SOURCE
+#include <assert.h>
+#include <pthread.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+#include <signal.h>
+
+/* Number of threads we'll create.  */
+int n_threads = 10;
+
+int mypid;
+
+static void
+setup_done (void)
+{
+}
+
+/* Entry point for threads.  Loops forever.  */
+
+void *
+thread_func (void *arg)
+{
+  /* Avoid setting the breakpoint at an instruction that wouldn't
+     require a fixup phase, like a branch/jump.  In such a case, even
+     if GDB manages to detach the inferior with an incomplete
+     displaced step, GDB inferior may still not crash.  A breakpoint
+     at a line that increments a variable is good bet that we end up
+     setting a breakpoint at an instruction that will require a fixup
+     phase to move the PC from the scratch pad to the instruction
+     after the breakpoint.  */
+  volatile unsigned counter = 0;
+
+  while (1)
+    {
+      counter++; /* Set breakpoint here.  */
+      counter++;
+      counter++;
+    }
+
+  return NULL;
+}
+
+/* Allow for as much timeout as DejaGnu wants, plus a bit of
+   slack.  */
+#define SECONDS (TIMEOUT + 20)
+
+/* We'll exit after this many seconds.  */
+unsigned int seconds_left = SECONDS;
+
+/* GDB sets this whenever it's about to start a new detach/attach
+   sequence.  We react by resetting the seconds-left counter.  */
+volatile int again = 0;
+
+int
+main (int argc, char **argv)
+{
+  int i;
+
+  signal (SIGUSR1, SIG_IGN);
+
+  mypid = getpid ();
+  setup_done ();
+
+  if (argc > 1)
+    n_threads = atoi (argv[1]);
+
+  /* Spawn the test threads.  */
+  for (i = 0; i < n_threads; ++i)
+    {
+      pthread_t child;
+      int rc;
+
+      rc = pthread_create (&child, NULL, thread_func, NULL);
+      assert (rc == 0);
+    }
+
+  /* Exit after a while if GDB is gone/crashes.  But wait long enough
+     for one attach/detach sequence done by the .exp file.  */
+  while (--seconds_left > 0)
+    {
+      sleep (1);
+
+      if (again)
+	{
+	  /* GDB should be reattaching soon.  Restart the timer.  */
+	  again = 0;
+	  seconds_left = SECONDS;
+	}
+    }
+
+  printf ("timeout, exiting\n");
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.threads/detach-step-over.exp b/gdb/testsuite/gdb.threads/detach-step-over.exp
new file mode 100644
index 0000000..3298c5b
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/detach-step-over.exp
@@ -0,0 +1,290 @@
+# Copyright 2021 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 detaching from a process that is running and has threads
+# constantly hitting a breakpoint and stepping over it, in all
+# combinations of:
+#
+#  - maint target non-stop off/on
+#  - set non-stop on/off
+#  - displaced stepping on/off
+#
+# This stresses the edge cases of detaching while a displaced step or
+# an in-line step over are in progress.
+#
+# A fail mode is that the inferior process dies after being detached.
+# This can happen because e.g.:
+#
+# - GDB leaves a breakpoint installed behind, or
+#
+# - GDB leaves a thread running in the displaced step scratch buffer.
+#   With no debugger around to run the finish step, the thread runs
+#   off of the scratch buffer, with undefined results.
+#
+# To exercise this, the testcase reattaches to the process shortly
+# after detaching, ensuring the process is still alive and well.
+#
+# In addition, since GDB may pause threads of all processes for
+# stepping over a breakpoint, it needs to re-resume all threads if it
+# detaches from the process that was just stepping over the
+# breakpoint.  To ensure that, the testcase actually runs a second
+# process at the same time as the one that is used to test detaching.
+# After the first process is detached, the testcase sends a SIGUSR1 to
+# the second process.  If threads failed to be resumed, then the
+# SIGUSR1 is never reported to the user, resulting in timeout.  The
+# threads of this second process will also be constantly stepping over
+# a breakpoint, which has helped with exposing further corner case
+# bugs.
+
+if {![can_spawn_for_attach]} {
+    return 0
+}
+
+standard_testfile
+
+set bp_lineno [gdb_get_line_number "Set breakpoint here"]
+
+# The test proper.  See description above.
+proc test {condition_eval target_non_stop non_stop displaced} {
+    global binfile srcfile
+    global gdb_prompt
+    global decimal
+    global bp_lineno
+    global GDBFLAGS
+
+    # Number of threads started by the program.
+    set n_threads 10
+
+    save_vars { GDBFLAGS } {
+	append GDBFLAGS " -ex \"maint set target-non-stop $target_non_stop\""
+	append GDBFLAGS " -ex \"set non-stop $non_stop\""
+	append GDBFLAGS " -ex \"set displaced $displaced\""
+	append GDBFLAGS " -ex \"set schedule-multiple on\""
+	clean_restart $binfile
+    }
+
+    set test_spawn_id [spawn_wait_for_attach $binfile]
+    set testpid [spawn_id_get_pid $test_spawn_id]
+
+    set any "\[^\r\n\]*"
+
+    gdb_test "add-inferior" "Added inferior 2.*"
+    gdb_test "inferior 2" "Switching to .*"
+
+    gdb_load $binfile
+    if ![runto setup_done] then {
+	fail "can't run to setup_done"
+	kill_wait_spawned_process $test_spawn_id
+	return
+    }
+
+    gdb_test_no_output "set breakpoint condition-evaluation $condition_eval"
+
+    # Get the PID of the test process.
+    set pid_inf2 ""
+    gdb_test_multiple "p mypid" "get pid of inferior 2" {
+	-re " = ($decimal)\r\n$gdb_prompt $" {
+	    set pid_inf2 $expect_out(1,string)
+	    pass $gdb_test_name
+	}
+    }
+
+    set attempts 3
+    for {set attempt 1} { $attempt <= $attempts } { incr attempt } {
+	with_test_prefix "iter $attempt" {
+	    gdb_test "inferior 1" "Switching to .*"
+
+	    set attached 0
+	    set eperm 0
+	    set test "attach"
+	    gdb_test_multiple "attach $testpid" $test {
+		-re "new threads in iteration" {
+		    # Seen when "set debug libthread_db" is on.
+		    exp_continue
+		}
+		-re "is a zombie - the process has already terminated.*$gdb_prompt " {
+		    fail $gdb_test_name
+		}
+		-re "Unable to attach: .*$gdb_prompt " {
+		    fail $gdb_test_name
+		}
+		-re "Attaching to program.*process $testpid.*$gdb_prompt " {
+		    pass $test
+		    set attached 1
+		}
+	    }
+
+	    if {!$attached} {
+		kill_wait_spawned_process $test_spawn_id
+		return
+	    }
+
+	    if {$non_stop} {
+		# In non-stop, we will see one stop per thread after
+		# the prompt.
+		set stops 0
+		set tid_re "$::decimal\.$::decimal"
+		set test "seen all stops"
+		for {set thread 1} { $thread <= $n_threads } { incr thread } {
+		    if {[gdb_test_multiple "" $test {
+			-re "Thread ${tid_re} ${any} stopped" {
+			    incr stops
+			}
+		    }] != 0} {
+			break
+		    }
+		}
+
+		# This we haven't seen all stops, then the
+		# gdb_test_multiple in the loop above will have
+		# already issued a FAIL.
+		if {$stops != $n_threads} {
+		    kill_wait_spawned_process $test_spawn_id
+		    return
+		}
+		pass $test
+	    }
+
+	    # Set threads stepping over a breakpoint continuously.
+	    gdb_test "break $srcfile:$bp_lineno if 0" "Breakpoint.*" \
+		"break LOC if 0"
+
+	    if {$attempt < $attempts} {
+		# Kick the time out timer for another round.
+		gdb_test "print again = 1" " = 1" "reset timer in the inferior"
+		# Show the time we had left in the logs, in case
+		# something goes wrong.
+		gdb_test "print seconds_left" " = .*"
+	    }
+
+	    if {$non_stop} {
+		set cont_cmd "continue -a &"
+	    } else {
+		set cont_cmd "continue &"
+	    }
+
+	    set cont_cmd_re [string_to_regexp $cont_cmd]
+	    gdb_test_multiple $cont_cmd "" {
+		-re "^$cont_cmd_re\r\nContinuing\.\r\n$gdb_prompt " {
+		    pass $gdb_test_name
+		}
+	    }
+
+	    # Wait a bit, to give time for the threads to hit the
+	    # breakpoint.
+	    sleep 1
+
+	    set running_count 0
+	    set interrupted 0
+	    gdb_test_multiple "info threads" "all threads running" {
+		-re "\\(running\\)" {
+		    incr running_count
+		    exp_continue
+		}
+		-re "Cannot execute this command while the target is running.*$gdb_prompt $" {
+		    # Testing against a remote server that doesn't do
+		    # non-stop mode.  Explicitly interrupt.  This
+		    # doesn't test the same code paths in GDB, but
+		    # it's still something.
+		    set interrupted 1
+		    gdb_test_multiple "interrupt" "" {
+			-re "$gdb_prompt " {
+			    gdb_test_multiple "" $gdb_test_name {
+				-re "received signal SIGINT, Interrupt" {
+				    pass $gdb_test_name
+				}
+			    }
+			}
+		    }
+		}
+		-re "$gdb_prompt $" {
+		    gdb_assert {$running_count == ($n_threads + 1) * 2} $gdb_test_name
+		}
+	    }
+
+	    gdb_test "detach" "Detaching from.*"
+
+	    if {!$interrupted} {
+		# Now test whether inferior 2's thread were really left
+		# running.  Currently an inline step-over stops all
+		# threads of all processes.  If detach aborts such a step
+		# over, then threads of other inferiors should be
+		# re-resumed.  Test for that by sending a signal to
+		# inferior 2.
+		remote_exec target "kill -SIGUSR1 ${pid_inf2}"
+
+		gdb_test_multiple "" "stop with SIGUSR1" {
+		    -re "received signal SIGUSR1" {
+			pass $gdb_test_name
+		    }
+		}
+	    }
+
+	    delete_breakpoints
+	}
+    }
+    kill_wait_spawned_process $test_spawn_id
+}
+
+# The test program exits after a while, in case GDB crashes.  Make it
+# wait at least as long as we may wait before declaring a time out
+# failure.
+set options { "additional_flags=-DTIMEOUT=$timeout" debug pthreads }
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile $options] == -1} {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+# Probe support for "set breakpoint condition-evaluation target".
+# This setting influences who steps over the breakpoint, the (remote)
+# target (e.g. gdbserver) or gdb, thus exposing issues on either the
+# target or gdb.
+set supports_condition_eval_target 1
+set cmd "set breakpoint condition-evaluation target"
+gdb_test_multiple $cmd "probe condition-evaluation target support" {
+    -re "warning: Target does not support breakpoint condition evaluation.\r\nUsing host evaluation mode instead.\r\n$gdb_prompt $" {
+	# Target doesn't support breakpoint condition evaluation on
+	# its side.
+	set supports_condition_eval_target 0
+	pass $gdb_test_name
+    }
+    -re "^$cmd\r\n$gdb_prompt $" {
+	pass $gdb_test_name
+    }
+}
+
+foreach_with_prefix breakpoint-condition-evaluation {"host" "target"} {
+    if {!$supports_condition_eval_target && ${breakpoint-condition-evaluation} == "target"} {
+	continue
+    }
+
+    foreach_with_prefix target-non-stop {"off" "on"} {
+	foreach_with_prefix non-stop {"off" "on"} {
+	    if {${non-stop} && !${target-non-stop}} {
+		# "set non-stop" overrides "maint set
+		# target-non-stop", no use testing this combination.
+		continue
+	    }
+
+	    foreach_with_prefix displaced {"off" "auto"} {
+		test ${breakpoint-condition-evaluation} ${target-non-stop} ${non-stop} ${displaced}
+	    }
+	}
+    }
+}