Question

I would like to trace calls to some 3rd party library which are made from another 3rd party library.

Example: I want to trace calls to library A. My application statically links library B, which in turn is statically linked to library A. So basically what I have is libAB.a

In case of dynamic linking I could write library A2 with wrappers for functions which I want to trace of library A and use LD_PRELOAD=A2.so. Then, my wrappers will be called instead, and I will see the trace.
In my case I cannot use dynamic linking.

Is it possible to achieve the same using static linking?

In ideal case I would like to link my application with libAB.a and trace library libA2.a and get the trace.

Thanks,
Robusta

Answer 1

Okay, I found it 🙂

man ld

       --wrap symbol
       Use a wrapper function for symbol.  Any undefined reference to symbol will be resolved to "__wrap_symbol".  Any undefined ref‐
       erence to "__real_symbol" will be resolved to symbol.

       This  can  be  used to provide a wrapper for a system function.  The wrapper function should be called "__wrap_symbol".  If it
       wishes to call the system function, it should call "__real_symbol".

       Here is a trivial example:

               void *
               __wrap_malloc (size_t c)
               {
                 printf ("malloc called with %zu\n", c);
                 return __real_malloc (c);
               }

       If you link other code with this file using --wrap malloc, then all calls to "malloc" will call the  function  "__wrap_malloc"
       instead.  The call to "__real_malloc" in "__wrap_malloc" will call the real "malloc" function.