Fix a crash in jit.c

A user at Mozilla pointed out a crash in jit.c.  In his situation, an
inferior using the JIT API exec'd an executable that did not use it.
This caused an assertion failure when jit.c:free_objfile_data called
delete_breakpoint with NULL.

This patch fixes the problem in the obvious way.  New test case
included.

gdb/ChangeLog
2018-12-28  Tom Tromey  <tom@tromey.com>

	* jit.c (free_objfile_data): Only delete breakpoint if non-null.

gdb/testsuite/ChangeLog
2018-12-28  Tom Tromey  <tom@tromey.com>
	    Simon Marchi <simark@simark.ca>

	* gdb.base/jit-exec.exp: New file.
	* gdb.base/jit-exec.c: New file.
	* gdb.base/jit-execd.c: New file.

gdb/ChangeLog

@@ -1,3 +1,7 @@
+2018-12-28  Tom Tromey  <tom@tromey.com>
+
+	* jit.c (free_objfile_data): Only delete breakpoint if non-null.
+
 2018-12-28  Tom Tromey  <tom@tromey.com>
 
 	* NEWS: Mention terminal styling.

gdb/jit.c

@@ -1464,6 +1464,7 @@ free_objfile_data (struct objfile *objfile, void *data)
       if (ps_data != NULL && ps_data->objfile == objfile)
 	{
 	  ps_data->objfile = NULL;
+	  if (ps_data->jit_breakpoint != NULL)
 	    delete_breakpoint (ps_data->jit_breakpoint);
 	  ps_data->cached_code_address = 0;
 	}

gdb/testsuite/ChangeLog

@@ -1,3 +1,10 @@
+2018-12-28  Tom Tromey  <tom@tromey.com>
+	    Simon Marchi <simark@simark.ca>
+
+	* gdb.base/jit-exec.exp: New file.
+	* gdb.base/jit-exec.c: New file.
+	* gdb.base/jit-execd.c: New file.
+
 2018-12-28  Tom Tromey  <tom@tromey.com>
 
 	* gdb.base/style.exp: Update test to check for address styling.

gdb/testsuite/gdb.base/jit-exec.c

@@ -0,0 +1,28 @@
+/* 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/>.  */
+
+/* Simple standalone program using the JIT API.  */
+
+#include "jit-simple-jit.c"
+#include <unistd.h>
+
+int
+main (int argc, char **argv)
+{
+  execl (PROGRAM, PROGRAM, (char *) 0);
+  return 99;
+}

gdb/testsuite/gdb.base/jit-exec.exp

@@ -0,0 +1,52 @@
+# 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/>.
+
+# Regression test for a jit.c bug.  Previously it would crash if an
+# inferior that used the JIT API then exec'd a program that did not
+# use it.
+
+if { ![istarget "*-linux*"] } then {
+    return
+}
+
+standard_testfile jit-exec.c
+
+set testfile2 "jit-execd"
+set srcfile2 ${testfile2}.c
+set binfile2 [standard_output_file ${testfile2}]
+
+set compile_options [list debug additional_flags=-DPROGRAM=\"$binfile2\"]
+
+if {[gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" \
+	 executable $compile_options] != ""} {
+    untested "failed to compile"
+    return -1
+}
+
+if {[gdb_compile "${srcdir}/${subdir}/${srcfile2}" "${binfile2}" \
+	 executable $compile_options] != ""} {
+    untested "failed to compile"
+    return -1
+}
+
+clean_restart $binfile
+
+if {![runto_main]} {
+    fail "can't run to main"
+    return
+}
+
+delete_breakpoints
+gdb_test "continue" "Inferior .* exited normally.*"

gdb/testsuite/gdb.base/jit-execd.c

@@ -0,0 +1,22 @@
+/* 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/>.  */
+
+int
+main (int argc, char **argv)
+{
+  return 0;
+}