Permission denied on dl.open() with ipython but not with python

Question

My initial goal is to open a dll file on Cygwin using ctypes. However I found some issues with it. I dug up to sys.dl which returns an unknown Permission denied only on IPython.

With python everything looks fine:

$ ls
my.dll
$ python
Python 2.7.8 (default, Jul 28 2014, 01:34:03)
[GCC 4.8.3] on cygwin
>>> import dl
>>> dl.open('my.dll')
<dl.dl object at 0xfffaa0c0>

With ipython I get the error:

$ ipython
Python 2.7.8 (default, Jul 28 2014, 01:34:03)   
In [1]: import dl   
In [2]: dl.open('my.dll')
---------------------------------------------------------------------------
error Traceback (most recent call last)
<ipython-input-2-c681630fa713> in <module>()
----> 1 dl.open('my.dll')

error: Permission denied

I investigated on this using strace. The output log for `IPython is huge, more than 4MB. Fortunately, I identified some weird things:

symlink.check(C:\Users\user\Home\projects\foo\my.dll, 0x28AB88) (0x4022)
   35 2705178 [main] python2.7 16924 path_conv::check: this->path(C:\Users\user\Home\projects\foo\my.dll), has_acls(1)
   37 2705215 [main] python2.7 16924 cwdstuff::get: posix /cygdrive/c/Users/user/Home/projects/foo
   32 2705247 [main] python2.7 16924 cwdstuff::get: (C:\Users\user\Home\projects\foo) = cwdstuff::get (0x8006ECF0, 32768, 0, 0), errno 11
--- Process 14376, exception c0000138 at 7726163E
 3286 2708533 [main] python2.7 16924 seterrno_from_win_error: /home/corinna/src/cygwin/cygwin-1.7.35/cygwin-1.7.35-1.i686/src/src/winsup/cygwin/dlfcn.cc:174 windows error 182
   42 2708575 [main] python2.7 16924 geterrno_from_win_error: unknown windows error 182, setting errno to 13
   36 2708611 [main] python2.7 16924 dlopen: ret 0x0

Who is /home/corinna? I have no corinna user in my installation, neither on my Windows. Corinna does not come from my installation. Is it some hard-coded stuff?

Now, here is what I get from strace for python:

symlink.check(C:\Users\user\Home\projects\foo\my.dll, 0x28B728) (0x4022)
   26 10440048 [main] python 12604 path_conv::check: this->path(C:\Users\user\Home\projects\foo\my.dll), has_acls(1)
   23 10440071 [main] python 12604 cwdstuff::get: posix /cygdrive/c/Users/user/Home/projects/foo
   25 10440096 [main] python 12604 cwdstuff::get: (C:\Users\user\Home\projects\foo) = cwdstuff::get (0x8006ECF0, 32768, 0, 0), errno 0
 3405 10443501 [main] python 12604 dlopen: ret 0x5B9C0000   

dlopen is returning 0x0 in IPython while it is returning 0x5B9C0000 for python. I notice that cwdstuff::get is raising an error before dlopen is called.

EDIT I sent a message to Cygwin's mailing list and the answer of Corinna regarding this issue is:

This is not Cygwin's fault, AFAICS. Cygwin never loads functions by ordinal. This is also a bit on the lean side as far as information is concerned. One can't see how the process calls dlopen, for instance. Corinna How to solve this issue?

My earlier tests using ctypes

Initially when I asked my question I was just playing with ctypes. I am working on Cygwin 32-bit and Windows 7. With IPython I got an OSError when I tried to load a dll using cdll.LoadLibrary.

Answer 1

Two ideas:

1) in the next cell, type %pdb, and then interactively "print self._name" to see what it is.

2) Use a full path to cdll.LoadLibrary("foo.dll") to see if that works.

Once you know what the issue is, then you can decide whose bug it is, and report it (could be a ctypes issue, but probably ipython)