Add testcase for GDB hang fixed by previous commit

This adds a testcase for the previous commit.  The regression was
related to in-line step overs.  The reason we didn't see it on native
x86-64/s390 GNU/Linux testing is that native debugging uses displaced
stepping by default (because native debugging defaults to "maint set
target-non-stop on"), unlike remote debugging.

So in order to trigger the bug with native debugging as well, the
testcase disables displaced stepping explicitly.

Also, instead of using watchpoints to trigger the regression, the
testcase uses a breakpoint at address 0, which should be more
portable.

gdb/testsuite/ChangeLog:
2018-01-12  Pedro Alves  <palves@redhat.com>

	* gdb.base/continue-after-aborted-step-over.c: New.
	* gdb.base/continue-after-aborted-step-over.exp: New.

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2018-01-12  Pedro Alves  <palves@redhat.com>
+
+	* gdb.base/continue-after-aborted-step-over.c: New.
+	* gdb.base/continue-after-aborted-step-over.exp: New.
+
 2018-01-11  Simon Marchi  <simon.marchi@ericsson.com>
 
 	* lib/gdb.exp (gdb_compile): Ignore shlib= and shlib_load

gdb/testsuite/gdb.base/continue-after-aborted-step-over.c

@@ -0,0 +1,29 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2018 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/>.  */
+
+void
+function (void)
+{
+}
+
+int
+main ()
+{
+  function ();
+
+  return 0;
+}

gdb/testsuite/gdb.base/continue-after-aborted-step-over.exp

@@ -0,0 +1,87 @@
+# Copyright 2018 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 testcase is a regression test for a regression in the in-line
+# step-over machinery.  If a resumption that starts a step-over
+# failed, a following resumption would make GDB hang forever:
+#
+#  (gdb) b *0
+#  Breakpoint 2 at 0x0
+#  continue
+#  Continuing.
+#  Warning:
+#  Cannot insert breakpoint 2.
+#  Cannot access memory at address 0x0
+#
+#  Command aborted.
+#  delete breakpoints
+#  Delete all breakpoints? (y or n) y
+#  (gdb) b function
+#  Breakpoint 3 at 0x40048b: file test.c, line 33.
+#  continue
+#  Continuing.
+#  *GDB hangs forever*
+
+standard_testfile
+
+if {[build_executable "failed to prepare" $testfile $srcfile debug]} {
+    return -1
+}
+
+# DISPLACED indicates whether to use displaced-stepping.
+proc do_test {displaced} {
+    global gdb_prompt decimal
+    global srcfile binfile
+
+    clean_restart $binfile
+
+    gdb_test_no_output "set displaced-stepping $displaced"
+
+    if ![runto_main] {
+	fail "run to main"
+	return -1
+    }
+
+    # We rely on not being able to set a breakpoint at 0, as proxy for
+    # any kind of breakpoint insertion failure.  If we can examine
+    # what's at memory address 0, it is possible that we could also
+    # execute it.
+    if [is_address_zero_readable] {
+	untested "memory at address 0 is possibly executable"
+	return
+    }
+
+    # Set a breakpoint that fails to insert.
+    gdb_test "b *0" "Breakpoint $decimal at 0x0"
+
+    gdb_test "continue" \
+	"Command aborted\\." \
+	"continue aborts"
+
+    # Delete the "bad" breakpoint and try continuing again.
+    delete_breakpoints
+    gdb_test "b function" "Breakpoint $decimal .*$srcfile.*"
+
+    gdb_test "continue" \
+	"Breakpoint $decimal, function \\(\\) at .*$srcfile:.*" \
+	"continue to function"
+}
+
+# This testcase exercises a regression with the in-line step-over
+# machinery.  So make sure this runs with displaced stepping disabled,
+# and for good measure, also try with displaced stepping enabled.
+foreach_with_prefix displaced-stepping {"off" "on"} {
+    do_test ${displaced-stepping}
+}