[PATCH v2 2/4] Add wrappers for some Python APIs

[Tom Tromey <tom@tromey.com>]

This adds some new functions that wrap Python APIs.  The wrapping
follows some proposed rules for Python safety in gdb:

* Functions returning a new reference return gdbpy_ref<>

* Errors are reported via exceptions, not special values

* Functions accepting a stolen reference take a gdbpy_ref<>&&
---
 gdb/python/py-wrappers.h     | 334 +++++++++++++++++++++++++++++++++++++++++++
 gdb/python/python-internal.h |   2 +
 2 files changed, 336 insertions(+)

diff --git a/gdb/python/py-wrappers.h b/gdb/python/py-wrappers.h
new file mode 100644
index 00000000000..78c1f8070cf
--- /dev/null
+++ b/gdb/python/py-wrappers.h
@@ -0,0 +1,334 @@
+/* Wrappers for some Python safety.
+
+   Copyright (C) 2026 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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/>.  */
+
+#ifndef GDB_PYTHON_PY_WRAPPERS_H
+#define GDB_PYTHON_PY_WRAPPERS_H
+
+#include "py-ref.h"
+
+/* Gdb implements its own wrappers for many Python APIs.  This is done
+   in an attempt to be more safe.
+
+   In particular, in gdb:
+
+   - APIs returning a new reference will return gdbpy_ref<>.  This
+   makes reference counting errors less likely.
+
+   - APIs will throw an exception rather than return a special value
+   (NULL or -1).  This makes error checking simpler.
+
+   - APIs requiring a stolen reference take a gdbpy_ref<>&&, to make
+   reference counting errors less likely.
+
+   This file holds the currently-defined wrappers.  If new APIs are
+   needed, the normal approach is to add a wrapper here.
+
+   APIs here are named after the underlying Python function, but using
+   lower case and an "_" at each word break.  */
+
+/* The type of exception thrown when the Python exception has been
+   set.  */
+struct gdb_python_exception
+{
+  gdb_python_exception ()
+  {
+    gdb_assert (PyErr_Occurred ());
+  }
+};
+
+template<typename T>
+gdbpy_ref<T>
+gdbpy_new ()
+{
+  gdbpy_ref<T> result (PyObject_New (T, T::corresponding_object_type));
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline gdbpy_ref<>
+gdbpy_bool_from_long (long value)
+{
+  /* This cannot fail.  */
+  return gdbpy_ref<> (PyBool_FromLong (value));
+}
+
+static inline char *
+gdbpy_bytes_as_string (gdbpy_borrowed_ref ref)
+{
+  char *result = PyBytes_AsString (ref);
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline void
+gdbpy_bytes_as_string_and_size (gdbpy_borrowed_ref ref,
+				char **buffer,
+				Py_ssize_t *length)
+{
+  if (PyBytes_AsStringAndSize (ref, buffer, length) == -1)
+    throw gdb_python_exception ();
+}
+
+static inline gdbpy_ref<>
+gdbpy_bytes_from_string (const char *str)
+{
+  gdb_assert (str != nullptr);
+  gdbpy_ref<> result (PyBytes_FromString (str));
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline gdbpy_ref<>
+gdbpy_bytes_from_string_and_size (const char *str, Py_ssize_t len)
+{
+  /* Python allows STR==nullptr but it leaves the object
+     uninitialized, and I think we should avoid this in gdb.  */
+  gdb_assert (str != nullptr);
+  gdbpy_ref<> result (PyBytes_FromStringAndSize (str, len));
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline Py_ssize_t
+gdbpy_bytes_size (gdbpy_borrowed_ref ref)
+{
+  Py_ssize_t result = PyBytes_Size (ref);
+  if (result == -1)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline gdbpy_ref<>
+gdbpy_new_list (Py_ssize_t len)
+{
+  gdbpy_ref<> result (PyList_New (len));
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline void
+gdbpy_list_append (gdbpy_borrowed_ref list, gdbpy_borrowed_ref val)
+{
+  if (PyList_Append (list, val) < 0)
+    throw gdb_python_exception ();
+}
+
+static inline gdbpy_ref<>
+gdbpy_new_dict ()
+{
+  gdbpy_ref<> result (PyDict_New ());
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline void
+gdbpy_dict_set_item_string (gdbpy_borrowed_ref dict,
+			    const char *key,
+			    gdbpy_borrowed_ref value)
+{
+  if (PyDict_SetItemString (dict, key, value) != 0)
+    throw gdb_python_exception ();
+}
+
+static inline void
+gdbpy_dict_del_item_string (gdbpy_borrowed_ref dict,
+			    const char *key)
+{
+  if (PyDict_DelItemString (dict, key) == -1)
+    throw gdb_python_exception ();
+}
+
+static inline gdbpy_borrowed_ref
+gdbpy_dict_get_item_with_error (gdbpy_borrowed_ref dict,
+				gdbpy_borrowed_ref key)
+{
+  PyObject *result = PyDict_GetItemWithError (dict, key);
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline gdbpy_ref<>
+gdbpy_dict_keys (gdbpy_borrowed_ref dict)
+{
+  gdbpy_ref<> result (PyDict_Keys (dict));
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline gdbpy_ref<>
+gdbpy_unicode_from_string (std::string_view str)
+{
+  gdbpy_ref<> result (PyUnicode_FromStringAndSize (str.data (), str.size ()));
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline gdbpy_ref<>
+gdbpy_unicode_from_format (const char *fmt, ...)
+{
+  va_list args;
+  va_start (args, fmt);
+  gdbpy_ref<> result (PyUnicode_FromFormatV (fmt, args));
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  va_end (args);
+  return result;
+}
+
+[[noreturn]] static inline void
+gdbpy_err_set_string (gdbpy_borrowed_ref type, const char *str)
+{
+  PyErr_SetString (type, str);
+  throw gdb_python_exception ();
+}
+
+/* This is a template because PyErr_FormatV was only added in Python
+   3.5.  */
+template<typename... Arg>
+[[noreturn]] void
+gdbpy_err_format (gdbpy_borrowed_ref type, const char *fmt, Arg... args)
+{
+  PyErr_Format (type, fmt, std::forward<Arg> (args)...);
+  throw gdb_python_exception ();
+}
+
+template<typename... Arg>
+void
+gdbpy_arg_parse_tuple_and_keywords (gdbpy_borrowed_ref args,
+				    gdbpy_opt_borrowed_ref kw,
+				    const char *fmt,
+				    const char **keywords,
+				    Arg... outputs)
+{
+  /* It would be cool if callers could use references to the
+     out-parameters and also if gdbpy_borrowed_ref could be used for
+     those.  That requires some hairy template metaprogramming
+     though.  */
+  if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, fmt, keywords,
+					std::forward<Arg> (outputs)...))
+    throw gdb_python_exception ();
+}
+
+static inline void
+gdbpy_arg_parse_tuple (gdbpy_borrowed_ref param, const char *format, ...)
+{
+  va_list args;
+  va_start (args, format);
+  if (!PyArg_VaParse (param, format, args))
+    throw gdb_python_exception ();
+  va_end (args);
+}
+
+static inline long
+gdbpy_long_as_long (gdbpy_borrowed_ref arg)
+{
+  long result = PyLong_AsLong (arg);
+  if (result == -1 && PyErr_Occurred ())
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline gdbpy_ref<>
+gdbpy_tuple_new (Py_ssize_t len)
+{
+  gdbpy_ref<> result (PyTuple_New (len));
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline gdbpy_borrowed_ref
+gdbpy_tuple_get_item (gdbpy_borrowed_ref tuple, Py_ssize_t pos)
+{
+  PyObject *result = PyTuple_GetItem (tuple, pos);
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline void
+gdbpy_tuple_set_item (gdbpy_borrowed_ref tuple, Py_ssize_t pos,
+		      gdbpy_ref<> &&item)
+{
+  if (PyTuple_SetItem (tuple, pos, item.release ()) == -1)
+    throw gdb_python_exception ();
+}
+
+static inline Py_ssize_t
+gdbpy_tuple_size (gdbpy_borrowed_ref tuple)
+{
+  Py_ssize_t result = PyTuple_Size (tuple);
+  if (result == -1)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline Py_ssize_t
+gdbpy_sequence_size (gdbpy_borrowed_ref seq)
+{
+  Py_ssize_t result = PySequence_Size (seq);
+  if (result == -1)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline gdbpy_ref<>
+gdbpy_sequence_get_item (gdbpy_borrowed_ref seq, Py_ssize_t i)
+{
+  gdbpy_ref<> result (PySequence_GetItem (seq, i));
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline void
+gdbpy_sequence_del_item (gdbpy_borrowed_ref seq, Py_ssize_t i)
+{
+  if (PySequence_DelItem (seq, i) == -1)
+    throw gdb_python_exception ();
+}
+
+static inline gdbpy_ref<>
+gdbpy_sequence_list (gdbpy_borrowed_ref seq)
+{
+  gdbpy_ref<> result (PySequence_List (seq));
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
+static inline gdbpy_ref<>
+gdbpy_sequence_concat (gdbpy_borrowed_ref first, gdbpy_borrowed_ref second)
+{
+  gdbpy_ref<> result (PySequence_Concat (first, second));
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
+#endif /* GDB_PYTHON_PY_WRAPPERS_H */
diff --git a/gdb/python/python-internal.h b/gdb/python/python-internal.h
index 693829e920d..6df0c62e2b3 100644
--- a/gdb/python/python-internal.h
+++ b/gdb/python/python-internal.h
@@ -1382,4 +1382,6 @@ py_notimplemented ()
 #undef Py_RETURN_FALSE
 #undef Py_RETURN_NOTIMPLEMENTED
 
+#include "py-wrappers.h"
+
 #endif /* GDB_PYTHON_PYTHON_INTERNAL_H */

-- 
2.49.0