Re: [ctypes-users] Win32 access violation in cdll call to _xpcom. cif->abi is FFI_SYSV?

[Brad C. <bk...@mu...>]

I am tracking this down using the VC debugger (on Win2k) with 0.9.1 and I note two odd 
things.

First, I'm calling into pyxpcom.pyd. 

It exports a function declared like this in pyXPCOM.h:

inline PYXPCOM_EXPORT PRBool IIDFromPyObject(PyObject *ob, nsIID *pRet) {
    return Py_nsIID::IIDFromPyObject(ob, pRet);
}

My python script looks like this:

        xpcom_dll = CDLL('_xpcom.pyd')
        IIDFromPyObject = xpcom_dll.IIDFromPyObject
        IIDFromPyObject.argtypes = [PyObject, c_void_p]
        IIDFromPyObject.restype = int
        # convert mozilla type to an iid
        browser_IID = "@mozilla.org/embedding/browser/nsWebBrowser;1"
        # get pointer to it
        IID_Type = c_char * 128
        IID = IID_Type()
        raw_input("enter for crash")
        res = IIDFromPyObject(browser_IID, byref(IID))

I've traced this throgh CFuncPtr_Call, into _CallProc

I note in _call_function_pointer:

flags & FUNCFLAG_PYTHONAPI  == 0

Somehow I need to set this flag from Python so that the GIL is not released. How do I do 
that?

And then, in ffi_call cif->abi == FFI_SYSV

Shouldn't cif->abi be FFI_STDCALL ?

And then it crashes somewhere in Python because ffi_call has gone somewhere it shouldn't.


I must have missed something obvious in the docs. 

should

        xpcom_dll = CDLL('_xpcom.pyd')

be

        xpcom_dll = WINDLL('_xpcom.pyd')

ah ah aha .. light bulb goes off.

Ok, so I created this class:


class WINPYDLL(CDLL):
    class _StdcallFuncPtr(_CFuncPtr):
        _flags_ = _FUNCFLAG_STDCALL | _FUNCFLAG_PYTHONAPI
        _restype_ = c_int # default, can be overridden in instances
        
    def __getattr__(self, name):
        if name[:2] == '__' and name[-2:] == '__':
            raise AttributeError, name
        func = self._StdcallFuncPtr(name, self)
        setattr(self, name, func)
        return func

then did this:

        xpcom_dll = WINPYDLL('_xpcom.pyd')


Now when I call 

        res = IIDFromPyObject(browser_IID, byref(IID))


I get this:

Traceback (most recent call last):
  File "O:\Python\mozcontrol\mozaxwindow.py", line 226, in __init__
    aBrowser.get_aBrowser()
  File "O:\Python\mozcontrol\mozaxwindow.py", line 155, in get_aBrowser
    res = IIDFromPyObject(browser_IID, byref(IID))
ValueError: Procedure probably called with too many arguments (8 bytes in excess
)

8 bytes, that's two pointers worth. So, someone left them on the stack I guess. That means 
that it should be .. CDECL ? but won't that get me back into FFI_SYSV again?



-- 
Brad Clements,                bk...@mu...   (315)268-1000
http://www.murkworks.com                          (315)268-9812 Fax
http://www.wecanstopspam.org/                   AOL-IM: BKClements