Forcing dlopen to look at LD_LIBRARY_PATH again

wiredj · 09-23-2004, 02:14 PM

I've run into a situation where I'm developing a plugin for another application, and I need to load up some shared libraries. The problem is one of the shared libraries is commonly not in the user's LD_LIBRARY_PATH. So, I want this plugin to be plug-and-play, and I want to update LD_LIBRARY_PATH (for my app only) if it fails to load the first time. I am successfully setting LD_LIBRARY_PATH, but when I call dlopen again, it fails to find the library. If I give it the full path to the library name, it fails when it tries to find other libraries that are in the folder.

Does anyone know how to make dlopen look at the environment variables again? I've searched high and low and haven't found out

Thanks in advance,
Jon

rjlee · 09-24-2004, 06:49 PM

If your program is a normal ELF executable, then you can (apparantly) set the DT_RUNPATH tag to a list of directories to search for the library. How you do this I do not know.

Personally, I would suggest that you use setenv() to append the additional directories to the LD_LIBRARY_PATH variable, like this:

Code:

char * path = getenv("LD_LIBRARY_PATH");
char buffer[strlen(path)+100];
sprintf(buffer,"%s:%s",path,"/other/path/here");
setenv("LD_LIBRARY_PATH",buffer,1);

Note that you should also test if path is NULL before calling strlen (to avoid a segmentation fault if LD_LIBRARY_PATH is not defined).

Edit: This will only affect your app (and any child processes your app spawns); you should do this before calling dlopen().

wiredj · 09-24-2004, 06:55 PM

Thanks for the info. I'll look into the DT_RUNPATH, see if I can find info about that.

I am actually doing the other part -- appending to LD_LIBRARY_PATH. The problem is that I'm developing a plugin for a regular app. The plugin is "weak-linking" the other libraries because although the library provides some functionality that is better than mine, I have some functionality I can fall back on.

So, the problem with modifying the library path is that the program has already used dlopen to open my shared library

Sticky situation, I guess :P

Thanks again for your reply,
Jon