[gdb/testsuite] Add gdb.opt/break-on-_exit.exp

Add a test-case to excercise the problem scenario reported in PR28527 and
fixed in commit a50bdb99afe "[gdb/tdep, rs6000] Don't skip system call in
skip_prologue":
- set a breakpoint on _exit, and
- verify that it triggers.

Note that this is not a regression test for that commit.  Since the actual
code in _exit may vary across os instances, we cannot guarantee that the
problem will always trigger with this test-case.

Rather, this test-case is a version of the original test-case
(gdb.threads/process-dies-while-detaching.exp) that is minimal while still
reproducing the problem reported in PR28527, in that same setting.

The benefit of this test-case is that it exercise real-life code and may
expose similar problems in other settings.  Also, it provides a much easier
test-case to investigate in case a similar problem occurs.

Tested on x86_64-linux and ppc64le-linux.

1 files changed, 26 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.opt/break-on-_exit.c b/gdb/testsuite/gdb.opt/break-on-_exit.c
new file mode 100644
index 0000000..d8da661
--- /dev/null
+++ b/gdb/testsuite/gdb.opt/break-on-_exit.c
@@ -0,0 +1,26 @@
+/* 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/>.  */
+
+#include <unistd.h>
+
+int
+main (void)
+{
+  _exit (0);
+
+  return 0;
+}