Re: [cx-oracle-users] Segmentation fault in Python 3 - Cursor - chained exceptions

[Anthony T. <ant...@gm...>]

Thanks for the simple program to demonstrate the problem. :-) I have just
pushed a change to the source that resolves this issue. Apparently in
Python 3 the first time the exception is referenced it is not normalized
and so the error object I am creating is immediately accessible. The second
level of exception results in a normalized exception which means that it
can't be accessed in the same way. Fortunately the normalization can be
forced so that I can access the error object the same way each time. A
subtle and rare bug so I appreciate the pointer!

Anthony


On Tue, May 13, 2014 at 1:15 AM, Boris Dzuba <bor...@gm...> wrote:

> Hi all,
>
> The following test program gives a segmentation fault:
>
> C:\>python
> Python 3.3.3 (v3.3.3:c3896275c0f6, Nov 18 2013, 21:19:30) [MSC v.1600 64
> bit (AMD64)] on win32
> Type "help", "copyright", "credits" or "license" for more information.
> >>> import cx_Oracle
> >>> c=cx_Oracle.connect(<connect string>).cursor()
> >>> try:
> ...     c.execute("select")
> ... except:
> ...     try:
> ...             c.execute("select")
> ...     except:
> ...             pass
> ...
>
> C:\>
>
> Access Violation
> Faulting application name: python.exe
> Fault offset: 0x000000000000cacd
>
>
> Platform: 64bit, Win7, Oracle Client 11g (11.2.0.1.0), python 3.3.3,
> cx_Oracle 5.1.2
>
>
>
> At a guess, the problem is because in the function Cursor_SetErrorOffset()
> /Cursor.c/:
>
> static void Cursor_SetErrorOffset(
>     udt_Cursor *self)                   // cursor to get the error offset
> from
> {
>     PyObject *type, *value, *traceback;
>     udt_Error *error;
>
>     PyErr_Fetch(&type, &value, &traceback);
>     if (type == g_DatabaseErrorException) {
>         error = (udt_Error*) value;
>         OCIAttrGet(self->handle, OCI_HTYPE_STMT, &error->offset, 0,
>                 OCI_ATTR_PARSE_ERROR_OFFSET,
> self->environment->errorHandle);
>     }
>     PyErr_Restore(type, value, traceback);
> }
>
> OCIAttrGet() call attempts to write a value to the address
> /&error->offset/,
> therefore after the end of an allocated memory block of the borrowed
> pointer /PyObject *value/
>
> typedef struct {
>     PyObject_HEAD
>     sb4 code;
>     ub4 offset;
>     PyObject *message;
>     const char *context;
> } udt_Error;
>
>
> Commenting it out /* OCIAttrGet(self->handle, OCI_HTYPE_STMT,
> &error->offset, 0, OCI_ATTR_PARSE_ERROR_OFFSET,
> self->environment->errorHandle);*/
> fix this crash!
>
>
> Regards,
> Boris
>
>
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