[PATCH] gdb/python: Fix segfault when iterating over empty linetable

[Toby Lloyd Davies <tlloyddavies@undo.io>]

symtab-> linetable () is set to null in
buildsym_compunit::end_symtab_with_blockvector () if the symtab has no
linetable. Attempting to iterate over this linetable using the Python
API caused GDB to segfault.
---
 gdb/python/py-linetable.c                     |  3 +-
 gdb/testsuite/gdb.python/py-linetable-empty.c | 23 ++++++
 .../gdb.python/py-linetable-empty.exp         | 72 +++++++++++++++++++
 3 files changed, 97 insertions(+), 1 deletion(-)
 create mode 100644 gdb/testsuite/gdb.python/py-linetable-empty.c
 create mode 100644 gdb/testsuite/gdb.python/py-linetable-empty.exp

diff --git a/gdb/python/py-linetable.c b/gdb/python/py-linetable.c
index 3b173712270..cd49b796f62 100644
--- a/gdb/python/py-linetable.c
+++ b/gdb/python/py-linetable.c
@@ -397,7 +397,8 @@ ltpy_iternext (PyObject *self)
 
   LTPY_REQUIRE_VALID (iter_obj->source, symtab);
 
-  if (iter_obj->current_index >= symtab->linetable ()->nitems)
+  if (symtab->linetable () == nullptr
+      || iter_obj->current_index >= symtab->linetable ()->nitems)
     {
       PyErr_SetNone (PyExc_StopIteration);
       return NULL;
diff --git a/gdb/testsuite/gdb.python/py-linetable-empty.c b/gdb/testsuite/gdb.python/py-linetable-empty.c
new file mode 100644
index 00000000000..85e5588589d
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-linetable-empty.c
@@ -0,0 +1,23 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2024 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()
+{
+  asm ("main_label: .globl main_label");
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.python/py-linetable-empty.exp b/gdb/testsuite/gdb.python/py-linetable-empty.exp
new file mode 100644
index 00000000000..4e6138cdb99
--- /dev/null
+++ b/gdb/testsuite/gdb.python/py-linetable-empty.exp
@@ -0,0 +1,72 @@
+# Copyright (C) 2024 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 accessing an empty linetable in Python.
+
+load_lib dwarf.exp
+load_lib gdb-python.exp
+
+require dwarf2_support allow_python_tests
+
+standard_testfile .c -dw.S
+
+set asm_file [standard_output_file ${srcfile2}]
+Dwarf::assemble $asm_file {
+
+    cu {} {
+	compile_unit {
+	    {language @DW_LANG_C}
+	    {name py-linetable-empty.c}
+	} {
+	    subprogram {
+			{MACRO_AT_func {main}}
+	    }
+	}
+    }
+}
+
+if { [prepare_for_testing "failed to prepare" ${testfile} \
+	  [list $srcfile $asm_file] {nodebug}] } {
+    return -1
+}
+
+if ![runto_main] {
+	return -1
+}
+
+gdb_test "python print(gdb.selected_frame().function().symtab.fullname())" \
+	"py-linetable-empty.c" "Test main has symtab"
+
+# Get the linetable for main's symbol table. This is empty as we didn't include
+# a linetable in the debug info.
+gdb_py_test_silent_cmd "python lt = gdb.selected_frame().function().symtab.linetable()" \
+    "get linetable" 0
+
+gdb_test "python print(lt.is_valid())" "True" \
+	"Test linetable is valid"
+
+gdb_test "python print(lt.line(1))" "None" \
+	"Test line() returns None"
+
+gdb_test "python print(lt.has_line(1))" \
+	".*RuntimeError: Linetable information not found in symbol table.*" \
+	"Test has_line() throws exception"
+
+gdb_test "python print(lt.source_lines())" \
+	".*RuntimeError: Linetable information not found in symbol table.*" \
+	"Test source_lines() throws exception"
+
+gdb_test "python print(list(lt))" "\\\[\\\]" \
+	"Test iterating over linetable"
-- 
2.34.1