Always emit =thread-exited notifications, even if silent

[Note: the testcased added by this commit depends on
https://sourceware.org/pipermail/gdb-patches/2022-June/190259.html,
otherwise GDB just crashes when detaching the core]

Currently, in MI, =thread-created are always emitted, like:

 =thread-group-started,id="i1",pid="195680"
 =thread-created,id="1",group-id="i1"
 ...

but on teardown, if the target uses exit_inferior_silent, then you'll
only see the inferior exit notification (thread-group-exited), no
notification for threads.

The core target is one of the few targets that use
exit_inferior_silent.  Here's an example session:

 -target-select core $corefile
 =thread-group-started,id="i1",pid="195680"
 =thread-created,id="1",group-id="i1"
 ...
 ^connected,frame=....
 (gdb)
 -target-detach
 =thread-group-exited,id="i1"
 ^done
 (gdb)

This imbalance of emitting =thread-created but then not =thread-exited
seems off to me.  (And, it complicates changes I want to do to
centralize emitting thread exit notifications for the CLI, which is
why I'm looking at this.)

And then, since most other targets use exit_inferior instead of
exit_inferior_silent, MI is already emitting =thread-exited
notifications when tearing down an inferior, for most targets.

This commit makes MI always emit the =thread-exited notifications,
even for exit_inferior_silent.

Afterwards, when debugging a core, MI outputs:

 (gdb)
 -target-detach
 =thread-exited,id="1",group-id="i1"    << new line
 =thread-group-exited,id="i1"
 ^done
 (gdb)

Surprisingly, there's no MI testcase debugging a core file.  This
commit adds the first.

Change-Id: I5100501a46f07b6bbad3e04d120c2562a51c93a4

3 files changed, 96 insertions, 3 deletions

diff --git a/gdb/mi/mi-interp.c b/gdb/mi/mi-interp.c
index 8d6e033..937a3d9 100644
--- a/gdb/mi/mi-interp.c
+++ b/gdb/mi/mi-interp.c
@@ -358,9 +358,6 @@ mi_new_thread (struct thread_info *t)
 static void
 mi_thread_exit (struct thread_info *t, int silent)
 {
-  if (silent)
-    return;
-
   SWITCH_THRU_ALL_UIS ()
     {
       struct mi_interp *mi = as_mi_interp (top_level_interpreter ());
diff --git a/gdb/testsuite/gdb.mi/mi-corefile.c b/gdb/testsuite/gdb.mi/mi-corefile.c
new file mode 100644
index 0000000..58e6f35
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/mi-corefile.c
@@ -0,0 +1,27 @@
+/* Copyright 2022 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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/>.  */
+
+/* Simple little program that just generates a core dump.  */
+
+#include <stdlib.h>
+
+int
+main (int argc, char **argv)
+{
+  abort ();
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.mi/mi-corefile.exp b/gdb/testsuite/gdb.mi/mi-corefile.exp
new file mode 100644
index 0000000..d8ca6b3
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/mi-corefile.exp
@@ -0,0 +1,69 @@
+# 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 loading and unloading a core file.
+
+load_lib mi-support.exp
+set MIFLAGS "-i=mi"
+
+if ![isnative] then {
+    return
+}
+
+standard_testfile
+
+if {[build_executable $testfile.exp $testfile $srcfile debug] == -1} {
+    untested "failed to compile"
+    return -1
+}
+
+set corefile [core_find $binfile {}]
+if {$corefile == ""} {
+    return 0
+}
+
+if [mi_gdb_start] {
+    return
+}
+
+# Test loading and unloading a core file.
+
+proc test_core_file {} {
+    mi_delete_breakpoints
+    mi_gdb_reinitialize_dir $::srcdir/$::subdir
+    mi_gdb_load ${::binfile}
+
+    # This also tests that MI emits paired =thread-created and
+    # =thread-exited notifications when loading and unloading the
+    # core.  At some point, GDB emitted =thread-created notifications,
+    # but not =thread-exited notifications.
+
+    mi_gdb_test \
+	"-target-select core $::corefile" \
+	[multi_line \
+	     "=thread-group-started,id=\"i1\",.*" \
+	     "=thread-created,id=\"1\",group-id=\"i1\"" \
+	     ".*\\^connected,frame=.*"] \
+	"-target-select core \$corefile"
+
+    mi_gdb_test \
+	"-target-detach" \
+	[multi_line \
+	     "=thread-exited,id=\"1\",group-id=\"i1\"" \
+	     "=thread-group-exited,id=\"i1\"" \
+	     ".*\\^done"]
+}
+
+test_core_file