Re: [PATCH v1] gdb/python: fix memory leak in gdb_py_tp_name

[Matthieu Longo <matthieu.longo@arm.com>]

On 26/05/2026 17:35, Tom Tromey wrote:
>>>>>> "Matthieu" == Matthieu Longo <matthieu.longo@arm.com> writes:
> 
> Matthieu> The proposed approach consists in changing gdb_py_tp_name() to return a
> Matthieu> std::string
> 
> That seems fine.
> 
> Matthieu> A unfortunate side effect of this fix is that every call sites where the
> Matthieu> tp_name is printed, must now use `.c_str()' because PyErr_Format()
> Matthieu> and its siblings cannot handle std::string.
> 
> Yeah, that's unfortunate but normal.
> 
> Matthieu>  /* Return the type's fully qualified name from a PyTypeObject.  */
> Matthieu> -const char *
> Matthieu> +std::string
> Matthieu>  gdb_py_tp_name (PyTypeObject *py_type) noexcept
> Matthieu>  {
> Matthieu>  #if PY_VERSION_HEX >= 0x030d0000
> Matthieu>    /* Note: PyType_GetFullyQualifiedName() was added in version 3.13, and is
> Matthieu>       part of the stable ABI since version 3.13.  */
> Matthieu> -  PyObject *fully_qualified_name = PyType_GetFullyQualifiedName (py_type);
> Matthieu> +  gdbpy_ref<> fully_qualified_name (PyType_GetFullyQualifiedName (py_type));
> Matthieu>    if (fully_qualified_name == nullptr)
> Matthieu>      return nullptr;
> 
> First, returning nullptr here seems really weird.  I think this should
> cause a crash?  In C++23 this constructor is even deleted.
> 
> Second, if PyType_GetFullyQualifiedName fails, this will violate the
> invariants gdb normally uses for error handling.
> 
> Matthieu> -  return PyUnicode_AsUTF8AndSize (fully_qualified_name, nullptr);
> Matthieu> +  return PyUnicode_AsUTF8AndSize (fully_qualified_name.get (), nullptr);
>   
> I think this can also fail.
> 
> Matthieu> +  gdbpy_ref<> qualname (PyType_GetQualName (py_type));
> Matthieu>    if (qualname == nullptr)
> Matthieu>      return nullptr;
>   
> Matthieu> -  return PyUnicode_AsUTF8AndSize (qualname, nullptr);
> Matthieu> +  return PyUnicode_AsUTF8AndSize (qualname.get (), nullptr);
>   
> Similar stuff in these spots.
> 
> Tom

Sorry, I completely missed those issues while I was changing the code in others places.
I should definitely have spotted them if it was not my thoughtlessness in those last days.

Here below is the diff of gdb_py_tp_name() with fixes for all the issues you previously mentioned.
Thanks for your patience with me, Tom.

Matthieu

--- a/gdb/python/py-obj-type.c
+++ b/gdb/python/py-obj-type.c
@@ -21,17 +21,23 @@
  #include "py-obj-type.h"

  /* Return the type's fully qualified name from a PyTypeObject.  */
-const char *
+std::string
  gdb_py_tp_name (PyTypeObject *py_type) noexcept
  {
+  auto pyobj_to_str = [](PyObject *name) -> std::string
+  {
+    const char *s = PyUnicode_AsUTF8AndSize (name, nullptr);
+    return (s == nullptr) ? "" : s;
+  };
+
  #if PY_VERSION_HEX >= 0x030d0000
    /* Note: PyType_GetFullyQualifiedName() was added in version 3.13, and is
       part of the stable ABI since version 3.13.  */
-  PyObject *fully_qualified_name = PyType_GetFullyQualifiedName (py_type);
+  gdbpy_ref<> fully_qualified_name (PyType_GetFullyQualifiedName (py_type));
    if (fully_qualified_name == nullptr)
-    return nullptr;
+    return {};

-  return PyUnicode_AsUTF8AndSize (fully_qualified_name, nullptr);
+  return pyobj_to_str (fully_qualified_name.get ());

  #else /* PY_VERSION_HEX < 0x030d0000 && ! defined (Py_LIMITED_API)  */
    /* For non-heap types, the fully qualified name corresponds to tp_name.  */
@@ -44,11 +50,11 @@ gdb_py_tp_name (PyTypeObject *py_type) noexcept

  # if PY_VERSION_HEX >= 0x030b0000
    /* Note: PyType_GetQualName() was added in version 3.11.  */
-  PyObject *qualname = PyType_GetQualName (py_type);
+  gdbpy_ref<> qualname (PyType_GetQualName (py_type));
    if (qualname == nullptr)
-    return nullptr;
+    return {};

-  return PyUnicode_AsUTF8AndSize (qualname, nullptr);
+  return pyobj_to_str (qualname.get ());

  # else
    /* In the absence of PyType_GetQualName(), fallback on using PyHeapTypeObject
@@ -58,15 +64,15 @@ gdb_py_tp_name (PyTypeObject *py_type) noexcept
       when the minimum supported Python version is increased above 3.10.  */
    PyHeapTypeObject *ht = (PyHeapTypeObject *) py_type;
    if (ht->ht_qualname == nullptr)
-    return nullptr;
+    return {};

-  return PyUnicode_AsUTF8AndSize (ht->ht_qualname, nullptr);
+  return pyobj_to_str (ht->ht_qualname);
  # endif
  #endif
  }