[PATCH] breakpoints/19546: Fix crash after updating breakpoints

[Keith Seitz <keiths at redhat dot com>]

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/inf-exec.c: New file.
	* gdb.base/inf-exec2.c: New file.
	* gdb.base/inf-exec.exp: New file.

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index c059861..f99a7ab 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -3764,6 +3764,14 @@ create_exception_master_breakpoint (void)
     }
 }
 
+/* Does B have a location spec?  */
+
+static int
+breakpoint_event_location_empty_p (const struct breakpoint *b)
+{
+  return b->location != NULL && event_location_empty_p (b->location);
+}
+
 void
 update_breakpoints_after_exec (void)
 {
@@ -3878,7 +3886,7 @@ update_breakpoints_after_exec (void)
     /* Without a symbolic address, we have little hope of the
        pre-exec() address meaning the same thing in the post-exec()
        a.out.  */
-    if (event_location_empty_p (b->location))
+    if (breakpoint_event_location_empty_p (b))
       {
 	delete_breakpoint (b);
 	continue;
@@ -13063,7 +13071,7 @@ static void
 bkpt_re_set (struct breakpoint *b)
 {
   /* FIXME: is this still reachable?  */
-  if (event_location_empty_p (b->location))
+  if (breakpoint_event_location_empty_p (b))
     {
       /* Anything without a location can't be re-set.  */
       delete_breakpoint (b);
diff --git a/gdb/testsuite/gdb.base/inf-exec.c b/gdb/testsuite/gdb.base/inf-exec.c
new file mode 100644
index 0000000..6617934
--- /dev/null
+++ b/gdb/testsuite/gdb.base/inf-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;
+}
diff --git a/gdb/testsuite/gdb.base/inf-exec.exp b/gdb/testsuite/gdb.base/inf-exec.exp
new file mode 100644
index 0000000..79cb413
--- /dev/null
+++ b/gdb/testsuite/gdb.base/inf-exec.exp
@@ -0,0 +1,49 @@
+# 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/>.
+
+# Test an inferior function call which execs a new program.
+# This is a test for breakpoints/19546.
+
+standard_testfile inf-exec.c
+
+set testfile2 "inf-exec2"
+set srcfile2 "${testfile2}.c"
+set binfile2 [standard_output_file $testfile2]
+
+# Build the two executables for the test.
+if {[gdb_compile $srcdir/$subdir/$srcfile $binfile executable debug] != ""} {
+    untested "could not build $binfile"
+    return -1
+}
+if {[gdb_compile $srcdir/$subdir/$srcfile2 $binfile2 executable debug] != ""} {
+    untested "could not build $binfile2"
+    return -1
+}
+
+gdb_exit
+clean_restart $binfile
+
+if {![runto_main]} {
+    untested "could not run to main"
+    return -1
+}
+
+set expected_result "process \[0-9\]+ is executing new program: $binfile2"
+append expected_result "\[\r\n\]+"
+append expected_result "Breakpoint 1, main.*at .*/$srcfile2:\[0-9\]+"
+append expected_result ".*"
+
+gdb_test "call execlp \(\"$binfile2\", \"$binfile2\", \(char \*\)0\)" \
+    $expected_result "call execlp"
diff --git a/gdb/testsuite/gdb.base/inf-exec2.c b/gdb/testsuite/gdb.base/inf-exec2.c
new file mode 100644
index 0000000..bb2a008
--- /dev/null
+++ b/gdb/testsuite/gdb.base/inf-exec2.c
@@ -0,0 +1,22 @@
+/* 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/>.  */
+
+int
+main (int argc, char ** argv)
+{
+  return 0;
+}
-- 
2.1.0