ports/174689: lang/python27: 64-bit pointers returned by C library get reduced to 32-bit

[Marcus von Appen]

The following reply was made to PR ports/174689; it has been noted by GNATS.

From: Marcus von Appen <mva at FreeBSD.org>
To: rene at FreeBSD.org, bug-followup at FreeBSD.org
Cc: freebsd-python at FreeBSD.org
Subject: Re: ports/174689: lang/python27: 64-bit pointers returned by C
 library get reduced to 32-bit
Date: Tue, 25 Dec 2012 15:51:54 +0100

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 > When initializing libmpg123.so.0 (audio/mpg123) from Python with CDLL,
 > the 64-bit pointer value returned by mpg123_new(None, None) gets
 > reduced to 32 bits. The equivalent program in C does not have this
 > problem.
 
 > from ctypes import *
 >
 > mpg123 =3D CDLL('libmpg123.so') # audio/mpg123
 > print mpg123
 >
 > MPG123_OK =3D 0
 > if mpg123.mpg123_init() !=3D MPG123_OK:
 >     print "mpg123_init() failed"
 > else:
 >     mh =3D mpg123.mpg123_new(None, None)
 [...]
 
 I do not see that you provide any information to ctypes about how the
 function mpg123_new() should behave. By default it will assume to return
 a ctypes.c_int, which most likely will be a 4-byte value.
 
 >>> import ctypes
 >>> print ctypes.sizeof(ctypes.c_int)
 4
 
 Furthermore, the mpg123.h header declares the function as
 
    mpg123_handle *mpg123_new(const char* decoder, int *error);
 
 mpg123_handle is a struct typedef. Instead of using a 4-byte int, you
 might be better of with properly declaring the arguments
 (POINTER(c_char) and POINTER(c_int)) and  return
 value (c_void_p or a Structure stub) of the function within your ctypes
 code.
 
 =46rom what I can see on my test platform, it works properly according to
 the basic ctypes definition.
 
 Cheers
 Marcus
 
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