[PATCH] Allow conversion of 128-bit integers to Python

[Tom Tromey <tom@tromey.com>]

Currently, trying to convert a 128-bit integer from a gdb.Value to a
Python integer will fail.  This is surprising because Python uses
bigints internally.

The bug here is that valpy_long uses value_as_long, which fails for
anything wider than LONGEST.  This patch fixes the problem by using
the recommended Python API.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33366
---
 gdb/python/py-value.c                 | 41 +++++++++++++++++++++++----
 gdb/testsuite/gdb.python/py-value.exp | 12 ++++++++
 2 files changed, 47 insertions(+), 6 deletions(-)

diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
index 833ce26d5a3..973785b5e4a 100644
--- a/gdb/python/py-value.c
+++ b/gdb/python/py-value.c
@@ -1866,7 +1866,7 @@ valpy_long (PyObject *self)
 {
   struct value *value = ((value_object *) self)->value;
   struct type *type = value->type ();
-  LONGEST l = 0;
+  PyObject *result;
 
   try
     {
@@ -1882,17 +1882,46 @@ valpy_long (PyObject *self)
 	  && type->code () != TYPE_CODE_PTR)
 	error (_("Cannot convert value to long."));
 
-      l = value_as_long (value);
+      gdb::array_view<const gdb_byte> contents = value->contents ();
+#if PY_VERSION_HEX >= 0x030d0000
+      int flags = (type_byte_order (type) == BFD_ENDIAN_BIG
+		   ? Py_ASNATIVEBYTES_BIG_ENDIAN
+		   : Py_ASNATIVEBYTES_LITTLE_ENDIAN);
+      if (type->is_unsigned ())
+	flags |= Py_ASNATIVEBYTES_UNSIGNED_BUFFER;
+      result = PyLong_FromNativeBytes (contents.data (), contents.size (),
+				       flags);
+#else
+      /* We need this roundabout approach because int.from_bytes
+	 requires "signed" to be a keyword arg.  */
+      gdbpy_ref<> args
+	(Py_BuildValue ("(y#s)", contents.data (),
+			(Py_ssize_t) contents.size (),
+			(type_byte_order (type) == BFD_ENDIAN_BIG
+			 ? "big" : "little")));
+      if (args == nullptr)
+	return nullptr;
+
+      gdbpy_ref<> kwargs (Py_BuildValue ("{sO}", "signed",
+					 type->is_unsigned ()
+					 ? Py_False : Py_True));
+      if (kwargs == nullptr)
+	return nullptr;
+
+      gdbpy_ref<> callable (PyObject_GetAttrString ((PyObject *) &PyLong_Type,
+						    "from_bytes"));
+      if (callable == nullptr)
+	return nullptr;
+
+      result = PyObject_Call (callable.get (), args.get (), kwargs.get ());
+#endif
     }
   catch (const gdb_exception &except)
     {
       return gdbpy_handle_gdb_exception (nullptr, except);
     }
 
-  if (type->is_unsigned ())
-    return gdb_py_object_from_ulongest (l).release ();
-  else
-    return gdb_py_object_from_longest (l).release ();
+  return result;
 }
 
 /* Implements conversion to float.  */
diff --git a/gdb/testsuite/gdb.python/py-value.exp b/gdb/testsuite/gdb.python/py-value.exp
index ab49f2deb92..089bf7563bf 100644
--- a/gdb/testsuite/gdb.python/py-value.exp
+++ b/gdb/testsuite/gdb.python/py-value.exp
@@ -844,3 +844,15 @@ if {[allow_cplus_tests]} {
 	test_subscript_regression "${binfile}-cxx" "c++"
     }
 }
+
+if {[allow_rust_tests]} {
+    gdb_test "set lang rust"
+
+    set cst 0x80000000000000000000000000000000
+    gdb_test "python print(int(gdb.parse_and_eval('${cst}u128')))" \
+	"170141183460469231731687303715884105728" \
+	"convert 128 bit unsigned constant to python int"
+    gdb_test "python print(int(gdb.parse_and_eval('${cst}i128')))" \
+	"-170141183460469231731687303715884105728" \
+	"convert 128 bit signed constant to python int"
+}
-- 
2.49.0