how to debug

[lion6230i]

Hi ,

I porting vlc library to mips platform and use vlc.py to test.
But have some error.

python vlc.py

Usage: vlc.py [options] <movie_filename>
Once launched, type ? for help.

Build date: Fri Oct 7 12:04:48 2016 (0x0)
Error: no function 'libvlc_get_version'

Could any one suggest me how to debug?
I have confirm libvlc.so have libvlc_get_version function.

[oaubert]

Hi

You should first try the basic loading of the vlc lib from a python
interpreter:

import ctypes
from ctypes.util import find_library
p = find_library('vlc')
dll = ctypes.CDLL(p)
dll.libvlc_get_version()

and see if it works.

Olivier

On Mon, 2016-11-21 at 01:25 -0800, lion6230i wrote:

Hi ,
I porting vlc library to mips platform and use vlc.py to test.
But have some error.
python vlc.py
Usage: vlc.py [options] <movie_filename>
Once launched, type ? for help.
Build date: Fri Oct 7 12:04:48 2016 (0x0)
Error: no function 'libvlc_get_version'
Could any one suggest me how to debug?
I have confirm libvlc.so have libvlc_get_version function.
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[lion6230i]

Hi Olivier,
Thanks for your reply.
I try the command step by step ,

python

Python 2.7.6 (default, Nov 16 2016, 11:18:53)
[GCC 4.7.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.

import ctypes
from ctypes.util import find_library
p = find_library('vlc')
dll = ctypes.CDLL(p)
dll.libvlc_get_version()
Traceback (most recent call last):
File "", line 1, in
File "/media/python_nfs/lib/python2.7/ctypes/init.py", line 378, in getattr
func = self.getitem(name)
File "/media/python_nfs/lib/python2.7/ctypes/init.py", line 383, in getitem
func = self._FuncPtr((name_or_ordinal, self))
AttributeError: Unable to resolve symbol

Is it mean python can't find my libvlc.so ?
I have set LD_LIBRARY_PATH before I run python.

[oaubert]

python seems to find libvlc.so (else it would fail at the ctypes.CDLL
line). Maybe your symbol names are mangled in the lib ? You should
check with 
readelf -Ws /path/to/libvlc.so
or
objdump -TC /path/to/libvlc.so

If the symbol information is correct, then maybe it has to do with the
arch. You should then investigate ctypes on mips, by for instance
building a minimal lib with a unique symbol.

Olivier

On Mon, 2016-11-21 at 02:23 -0800, lion6230i wrote:

Hi Olivier,
Thanks for your reply.
I try the command step by step ,
python
Python 2.7.6 (default, Nov 16 2016, 11:18:53)
[GCC 4.7.3] on linux2
Type "help", "copyright", "credits" or "license" for more
information.
import ctypes
from ctypes.util import find_library
p = find_library('vlc')
dll = ctypes.CDLL(p)
dll.libvlc_get_version()
Traceback (most recent call last):
File "", line 1, in 
File "/media/python_nfs/lib/python2.7/ctypes/init.py", line 378, in
getattr
func = self.getitem(name)
File "/media/python_nfs/lib/python2.7/ctypes/init.py", line 383, in
getitem
func = self._FuncPtr((name_or_ordinal, self))
AttributeError: Unable to resolve symbol
Is it mean python can't find my libvlc.so ?
I have set LD_LIBRARY_PATH before I run python.
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[lion6230i]

Hi Olivier,

I dump symbol information in library , it's correct.

[root@localhost lib]# objdump -TC libvlc.so|grep vlc_get_version
00005954 g DF .text 00000018 Base libvlc_get_version

Then I try the command in below:

python

Python 2.7.6 (default, Nov 16 2016, 11:18:53)
[GCC 4.7.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.

from ctypes import *
cdll.LoadLibrary("libc.so.0")
<CDLL 'libc.so.0', handle 43d838 at 2b396410>
libc = CDLL("libc.so.0")
libc.printf
<_FuncPtr object at 0x2b38b260>
libc.printf("lion debug")
lion debug10

Does it mean ctypes work fine on mips?

[oaubert]

So it seems ctypes is working on mips, and you have the correct symbol
in libvlc. Maybe the ctypes.util.find_library does not find the
appropriate library, could you check the output?

Olivier
On Mon, 2016-11-21 at 17:33 -0800, lion6230i wrote:

Hi Olivier,
I dump symbol information in library , it's correct.
[root@localhost lib]# objdump -TC libvlc.so|grep vlc_get_version
00005954 g DF .text 00000018 Base libvlc_get_version
Then I try the command in below:
python
Python 2.7.6 (default, Nov 16 2016, 11:18:53)
[GCC 4.7.3] on linux2
Type "help", "copyright", "credits" or "license" for more
information.
from ctypes import *
cdll.LoadLibrary("libc.so.0")
<CDLL 'libc.so.0', handle 43d838 at 2b396410>
libc = CDLL("libc.so.0")
libc.printf
<_FuncPtr object at 0x2b38b260>
libc.printf("lion debug")
lion debug10
Does it mean ctypes work fine on mips?
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[lion6230i]

Hi Olivier,

You are right. The problem case by find_library.
I modify vlc.py skip find_library step , load libvlc.so directly.
Then test it , it's works fine.

python vlc.py

lion debug 1
Usage: vlc.py [options] <movie_filename>
Once launched, type ? for help.

Build date: Fri Oct 7 12:04:48 2016 (0x0)
LibVLC version: 2.2.4 Weatherwax (0x2020400)
LibVLC compiler: gcc version 4.7.3 (Buildroot 2013.08-00907-ga7254e1)

I think , it's may cause by my platform do not have ldconfig.
Somebody said find_library will use ldconfig to look up where library can load.
Anyway thanks for your support.