breakpoints/19546: Fix crash after updating breakpointsgdb-7.11-branchpoint

One of the last checks update_breakpoints_after_exec does while looping
over the list of breakpoints is check that the breakpoint has a valid
location spec. It uses event_location_empty_p to check if the location spec
is "empty", and if it is, the breakpoint is deleted.

momentary_breakpoint types rely on setting the breakpoint structure's
location spec to NULL, thereby causing an update to delete the breakpoint.
However, event_location_empty_p assumed that locations were never NULL.
As a result, GDB would crash dereferencing a NULL pointer whenever
update_breakpoints_after_exec would encounter a momentary_breakpoint.

This patch creates a new wrapper/helper function which tests that the given
breakpoint's location spec is non-NULL and if it is not "empty"
or "unspecified."

gdb/ChangeLog

	PR breakpoints/19546
	* breakpoint.c (breakpoint_event_location_empty_p): New function.
	(update_breakpoints_after_exec, bkpt_re_set): Use this new function
	instead of event_location_empty_p.

gdb/testsuite/ChangeLog

	PR breakpoints/19546
	* gdb.base/infcall-exec.c: New file.
	* gdb.base/infcall-exec2.c: New file.
	* gdb.base/infcall-exec.exp: New file.

1 files changed, 28 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.base/infcall-exec.c b/gdb/testsuite/gdb.base/infcall-exec.c
new file mode 100644
index 00000000000..6617934a491
--- /dev/null
+++ b/gdb/testsuite/gdb.base/infcall-exec.c
@@ -0,0 +1,28 @@
+/* This test program is part of GDB, the GNU debugger.
+
+   Copyright 2016 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 (int argc, char ** argv)
+{
+  const char *prog = "inf-exec2";
+
+  execlp (prog, prog, (char *) 0);
+
+  return 0;
+}