libsqlite3.so loading on Python

Question

I want to replace libsqlite3 with the special version for Python. I have a special version of libsqlite3.so.0 /path/to/libsqlite3.so.0 and configured LD_LIBRARY_PATH. However, python's internal will not load it.

I checked and noticed the following:

import sqlite3 loads python's original /usr/lib/python2.7/sqlite/__init__.py and dbapi2.py.
dbapi2.py imports _sqlite, and this indicates /usr/lib/python2.7//lib-dynload/_sqlite3.so.
_sqlite3.so always loads /usr/lib/i386-linux-gnu/libsqlite3.so.0, in spite of setting LD_LIBRARY_PATH.
If I copy libpthread.so.0 to /path/to/libpthread.so.0, _sqlite3.so loads it. So, /path/to/libpthread.so.0 is loaded but /path/to/libsqlite3.so.0 is not loaded.

I want to know how to load /path/to/libsqlite3.so.0, a special version, without replacing /usr/lib/i386-linux-gnu/libsqlite3.so.0 (only with non-privileged permission).

tito · Accepted Answer · 2012-02-16 16:48:16Z

6

You might try to force loading of the lib with:

LD_PRELOAD=/path/to/libsqlite3.so.0 python ...

The library will be loaded in memory when python will be executed. So normally when _sqlite3 module will be imported, it will not load libsqlite3.so.0, and use the version already preloaded in memory.

Edit

The LD_LIBRARY_PATH doesn't work in that case cause libsqlite3.so.0 is loaded by _sqlite.so module, loaded by dlopen() within Python. In that case, the manpage of dlopen() said that the order is:

(ELF only) If the executable file for the calling program contains a DT_RPATH tag, and does not contain a DT_RUNPATH tag, then the directories listed in the DT_RPATH tag are searched.
If, at the time that the program was started, the environment variable LD_LIBRARY_PATH was defined to contain a colon-separated list of directories, then these are searched. (As a security measure this variable is ignored for set-user-ID and set-group-ID programs.)
...

So if an DT_RPATH is set on the binary, it will be taken prior to your LD_LIBRARY_PATH.

edited Feb 16, 2012 at 16:48

answered Feb 16, 2012 at 16:34

tito

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4 Comments

Tomoya Kabe Over a year ago

Thanks, it works but do I have to use LD_PRELOAD? Setting LD_LIBRARY_PATH will work to replace libpthread.so.0 but not to replace libsqlite3.so.0. I'm bothered by this fact. What is the difference between two libraries?

tito Over a year ago

libpthread.so.0 is loaded by python itself (check ldd /usr/bin/python2.7) while libsqlite3.so.0 is loaded by _sqlite.so, loaded itself by dlopen() in Python. I don't know why LD_LIBRARY_PATH doesn't work in that case. Maybe cause of rpath in _sqlite.so ?

tito Over a year ago

That's cause of the rpath, check the manpage of dlopen(), the priority order is explained: 1. rpath, 2. LD_LIBRARY_PATH, 3. runpath, ...

Tomoya Kabe Over a year ago

I succeeded to load my original one with only setting LD_LIBRARY_PATH, by copying _sqlite3.so to /path/to and chrpath --delete /path/to/_sqlite3.so to remove rpath information from it. So many thanks to you!

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