Question

I have built a linux shared object which I inject into a 3rd party program to intercept some dynamic function calls using LD_PRELOAD.

The 3rd party program uses a SO “libabc.so” located at some path. My injected SO uses another SO, also called “libabc.so” located at another path (essentially identical but slight code differences).

My problem is now, that calls to a function “def” which appear in both libabc.so are always resolved by the first. (Presumably because it is loaded first?!) How can I get them to be resolved with the second libabc.so?

Many thanks!

Answer 1

Unless something changed since I used to do this, you will need to dlopen() the library you want to pass calls on to and call the function manually, something like;

handle = dlopen("/path/to/libabc.so", RTLD_LAZY);
otherDef = dlsym(handle, "def");
orderDef(parameter);

There is a complete example how to do this very thing at LinuxJournal.