From dff7f6c72d05d8a378dc346e6900ba7c4eba759f Mon Sep 17 00:00:00 2001 From: Andrew Burgess Date: Tue, 22 Apr 2025 21:31:02 +0100 Subject: gdb/python: stop using PyObject_IsInstance in py-disasm.c The PyObject_IsInstance function can return -1 for errors, 0 to indicate false, and 1 to indicate true. I noticed in python/py-disasm.c that we treat the result of PyObject_IsInstance as a bool. This means that if PyObject_IsInstance returns -1, then this will be treated as true. The consequence of this is that we will invoke undefined behaviour by treating the result from the _print_insn call as if it was a DisassemblerResult object, even though PyObject_IsInstance raised an error, and the result might not be of the required type. I could fix this by taking the -1 result into account, however, gdb.DisassemblerResult cannot be sub-classed, the type doesn't have the Py_TPFLAGS_BASETYPE flag. As such, we can switch to using PyObject_TypeCheck instead, which only return 0 or 1, with no error case. I have also taken the opportunity to improve the error message emitted if the result has the wrong type. Better error message make debugging issues easier. I've added a test which exposes the problem when using PyObject_IsInstance, and I've updated the existing test for the improved error message. Approved-By: Tom Tromey --- gdb/python/py-disasm.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) (limited to 'gdb/python') diff --git a/gdb/python/py-disasm.c b/gdb/python/py-disasm.c index 9ca8d22..17064dc 100644 --- a/gdb/python/py-disasm.c +++ b/gdb/python/py-disasm.c @@ -1311,12 +1311,13 @@ gdbpy_print_insn (struct gdbarch *gdbarch, CORE_ADDR memaddr, return {}; } - /* Check the result is a DisassemblerResult (or a sub-class). */ - if (!PyObject_IsInstance (result.get (), - (PyObject *) &disasm_result_object_type)) + /* Check the result is a DisassemblerResult. */ + if (!PyObject_TypeCheck (result.get (), &disasm_result_object_type)) { - PyErr_SetString (PyExc_TypeError, - _("Result is not a DisassemblerResult.")); + PyErr_Format + (PyExc_TypeError, + _("Result from Disassembler must be gdb.DisassemblerResult, not %s."), + Py_TYPE (result.get ())->tp_name); gdbpy_print_stack (); return std::optional (-1); } -- cgit v1.1