ctypes not working (Fwd: [pypy-dev] 2.6.1 and freebsd-9)

[David Naylor]

Hi list,

Please see the correspondence below from the pypy team about some failing 
tests.  Specifically, why is test.py producing None whereas test.c is 
producing the desired results?  

Regards

----------  Forwarded Message  ----------

Subject: Re: [pypy-dev] 2.6.1 and freebsd-9
Date: Monday, 24 August 2015, 23:07:20
From: David Naylor <naylor.b.david at gmail.com>
To: pypy-dev at python.org
CC: Matti Picus <matti.picus at gmail.com>

On Saturday, 22 August 2015 21:25:44 Matti Picus wrote:
> I would like to add the freebsd-9-x86-64 binary tgz to our released
> downloads. We still have a number of failing tests showing up on
> http://buildbot.pypy.org/summary?category=freebsd64
> among them many
> DLOpenError: "opening 'libm.so' with ctypes.CDLL() works, but not with
> c_dlopen()??"
> and the more worrying SIGSEGV in
> http://buildbot.pypy.org/summary/longrepr?testname=unmodified&builder=pypy-c
> -jit-freebsd-9-x86-64&build=655&mod=lib-python.2.7.test.test_io
> 
> Could someone proficient in freebsd suggest what is going on?

Hi Matti,

I am able to reproduce this on FreeBSD 10.2:
# cat > test.py << __EOF
from ctypes import *

libc = CDLL("libc.so.7")
dlopen = libc["dlopen"]

# see <dlfnc.h>: void    *dlopen(const char *, int);
dlopen.argtypes = [c_char_p, c_int]
dlopen.restype = c_void_p

print dlopen(c_char_p("libm.so"), c_int(0))
__EOF
# python test.py
None

However, contract this with the C equivalent:
# cat > test.c << __EOF
#include <dlfcn.h>
#include <stdio.h>

int main(int argc, char** argv)
{
    printf("%p\n", dlopen("libm.so", RTLD_LOCAL));
}
__EOF
# cc -o test test.c
# ./test
0x800620800

<snip/>
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